Several polymers like ethylene glycol exhibit non-Newtonian rheological behavior. Ethylene glycol is a world-widely used engine coolant and therefore, investigation of thermal enhancement by dispersing mono and hybrid nanoparticles in ethylene glycol is worthful. Since ethylene glycol has shear rate-dependent viscosity and it obeys the power-law rheological model. Therefore, based on these facts, the power-law rheological model with thermophysical properties is augmented with basic law of heat transfer in fluid for the modeling of the considered physical situation.  The power-law fluid model is used here in this study because it best describes the rheological behavior of ethylene glycol7 as the objective of this study is to discuss the thermal performance of ethylene glycol. In reference7, it is claimed that the rheological behavior of ethylene glycol is characterized by a constitutive equation called the power law model. Therefore, the power law constitutive model is selected for the present study. Further, ethylene glycol is electrically conducting and remarkable Lorentz force arises due to the movement of ethylene glycol when it is subjected to the magnetic field. Moreover, ethylene glycol is used as a car engine coolant because it has anti-freezing and anti-boiling properties that encounter heat transfer. This is the main reason for studying heat transfer enhancement in ethylene glycol.Natural and industrial fluids show deviation from Newton's law of viscosity because their viscosity does not show linear relation with the rate of deformation. Such fluids are called non-Newtonian fluids. Non-Newtonian fluids are further classified into many classes. Shear rate-dependent non-Newtonian fluids are a well-known class of non-Newtonian fluids. Fluids of shear rate-dependent viscosity are further classified into power-law fluid7. Although this rheological model has been used in several studies but here, we discuss only those which related to the present investigation. For example, Nawaz et al.8 discussed two-dimensional heat transfer enhancement in the power-law fluid by considering hybrid nanofluid. Cheng9 discussed simultaneous transport of heat and mass in power-law fluid subjected to mass and thermal stratification over a vertical wavy surface. Khan et al.10 performed theoretical analysis for heat and mass transfer in power-law fluid over a surface subjected to convective boundary conditions. Sarafan et al.11 examined heat and mass transfer in power-law fluid in a microchannel immersed in a porous medium. Pal and Chatterjee12 analyzed Soret and Dufour effects on heat and mass transfer in power fluid over a vertical surface subjected to Buoyancy force considering variable thermal conductivity. El-Kabeir et al.13 discussed the impact of stagnation point flow on heat and mass transfer in power-law fluid over moveable walls with the consideration of combined effects of Soret and Dufour and chemical reaction. However, it is very important to mention that studies13 described above have not considered ethylene glycol as a power-law fluid. This arises an anomaly with recently published work7 proving ethylene glycol as a power-law rheological fluid. In view of this published fact, the present study considered the enhancement of heat transfer in ethylene glycol.The reason for the selection of the power-law model for the rheology of ethylene glycol is because of recent work by Minako et al.14 studied the combined impact of thermal radiation, buoyancy force, and nanoparticles on heat transfer in the fluid under Brownian motion. Dogonchi et al.15 discussed the impact of viscous dissipation and dispersion of nanoparticles on heat transfer in fluid with copper nanoparticles filled in a permeable enclosure. Sheikholeslami et al.16 used a numerical method to discuss the role of nanoparticles on heat transfer in an electrically conducting fluid subjected to the magnetic field and viscous dissipation. Sheikholeslami and Sadoughi17 analyzed heat transfer in fluid filled in a cavity with pores. They considered nanoparticles in the fluid and discussed the influence of nanoparticles on heat transfer in MHD fluid using the mesoscopic method. Qureshi et al.18 used the finite element method to analyze the impact of nanoparticles on heat transfer in the fluid passing through a porous medium. Nawaz et al.19 discussed the Soret and Dufour effects on simultaneous transport of mass heat transfer in MHD flow of viscous fluid over a radially moving surface. Hayat et al.20 studied heat transfer in micropolar fluid in the presence of homogeneous-heterogeneous chemical reactions. They considered the above-mentioned effects in fluids over a curved surface.Heat transfer has its importance as it occurs in many natural and man-made processes. Heat exchangers, thermal and cooling systems, energy storage, solar systems, MHD generators, food processing processes, etc. are well-known processes where heat transfer is an integral part. The studies related to heat transfer are numerous. However, here, we describe the investigations which are mostly related to the present work. For example, Dogonchi and Ganji20 and the references therein are restricted to the classical Fourier law of heat conduction which does not measure heat conduction in shear rate dependent fluid (like power-law fluid) accurately because classical law of heat conduction does not give a prediction of thermal relaxation time. This limitation was fixed by Cattaneo21 and Christov22 and the modified law of Fourier is called generalized Fourier law or Cattaneo-Christov heat flux model. This generalized law has been used in various studies. However, no study on thermal enhancement in ethylene glycol treating as the power-law fluid has been discussed so far.It is also observed that the studies23 discussed the role of suspension of nanoparticles on an enhancement in partially ionized fluid during mass transport of species. Qureshi et al.18 studied the role of suspension of nanoparticles on heat transfer in magnetohydrodynamic flow exposed to the magnetic field of constant intensity in the presence of mass transfer and chemical reaction. Ellahi et al.24 examined the role of nanoparticles on heat transfer in blood moving under the peristaltic mechanism in a couple of stress-fluid. Sheikholeslami et al.25 visualized the impact of dispersion of nanoparticles on heat transfer in MHD fluid moving in a porous medium. Sandeep and Kumar26 considered suspension of nanoparticles in fluid flow subjected to the simultaneous transport of heat and mass. Qi et al.27 modeled heat transfer in the fluid under the influence of suspension of nanoparticles and solved the problems using the Lattice Boltzmann approach to visualize thermal enhancement in the fluid. Gheynani et al.28 examined the effect of the size of nanoparticles on heat transfer in non-Newtonian fluid flow. They considered carboxymethyl cellulose as a base fluid. Archana et al.29 modeled heat transfer enhancement in yield stress exhibiting fluid (Casson fluid) under the effects of the suspension of nanoparticles and time dependent magnetic field. They solved the problems numerically and investigated the role of various factors on heat transfer in the fluid. They recommended the use of nanoparticles in the working fluid for the improvement in the efficiency of thermal systems.The efficiency of the process related to heat transfer can be enhanced by using a working fluid with higher thermal conductivity. The thermal conductivity of the working fluid can be enhanced by the dispersion of nanoparticles on the fluid. This dispersion of nanoparticles is possible now as synthesis and dispersion of such nanoparticles in a base fluid can be made due to the advancement in technology. Having this fact in mind, researchers have analyzed the role of nanoparticles on thermal enhancement. For example, Nawaz et al.30 discussed the impact of simultaneous dispersion of copper and aluminum oxide on heat transfer and mass transport in the fluid passing through a porous medium. Ghadikol et al.31 considered the dispersion of 32 and Ramesh33 performed numerical simulations related to the enhancement of heat transfer in the fluid. Hossein et al.34 noted the optimized heat transfer in fluid containing hybrid nanoparticles. Sreedevi et al.35 and Alharbi et al.36 recommended the dispersion of hybrid nanoparticles for the optimized enhancement in thermal transport in the fluid. Several authors have studied the impact of hybrid nanoparticles 7, not per recent development in the field. To fill this gap, authors have considered dispersion of As far as thermal enhancement of heat transfer is concerned, the dispersion of hybrid nanoparticles (nanoparticles of more than one kind) is recommended as the dispersion of hybrid nanoparticles results in an optimized enhancement in heat transfer. The recent works on hybrid nanofluids are described here. For example, Ahmad et al.37 considered the role of hybrid nanoparticles on the enhancement of heat transfer in the MHD flow of fluid over a rotating disk exposed to the magnetic field. They solved related models numerically and noted from simulations that an optimized enhancement of heat transfer in a fluid is possible by the dispersion of hybrid nano-sized particles of higher thermal conductivity. Kumar et al.38 considered the simultaneous effects of hybrid nanoparticles and thermal radiations on the heat transfer enhancement in the fluid. They obtained coupled models and solved them numerically to investigate the phenomenon. They noted maximized heat transfer due to the dispersion of hybrid nanoparticles in the fluid. They concluded that working fluid with hybrid nanoparticles is a better coolant and an optimized transport of heat is possible. Reddy et al.39 used novel heat flux theory to model heat transfer enhancement in the fluid and examined the role of hybrid nanoparticles on heat transfer subjected to the thermal relaxation time characteristics. Kumar et al.40 numerically discussed the impact of hybrid nanoparticles on thermal enhancement in the radiative fluid occupying space in a moving frame of reference. They also analyzed the impact of the spherical shapes of nanoparticles on the heat transport in the fluid. Bai et al.41 analyzed the combined effects of stagnation point flow and thermal relaxation time on heat transfer in the Oldroyd-B fluid. Similar studies related to Cattaneo-Christov can be seen in the references43.Reddy et al.Authors through a literature survey knew that no study on three-dimensional heat transfer enhancement in power-law fluid (ethylene glycol) due to the simultaneous dispersion of 21 and Christov22 which for heat transfer in incompressible flow is given byPower-law rheological models are capable of exhibiting shear rate-dependent viscosity. Several industrial products during the thermal process behave as shear rate-dependent fluid. Modern research has revealed that fluid with shear rate-dependent viscosity, does not obey the classical law of heat conduction. Therefore, we model transfer in the power-law fluid using the non-classical law of heat conduction. This non-Fourier law of heat conduction was proposed by Cattaneo44Thus, governing laws and power-law constitutive models are simultaneously used for the development of the problem. The power-law constitutive equation is given by43Let us consider a two-dimensionally moving stretchable surface having a constant temperature mentclass2pt{minimAfter implementation of the nonslip mechanism, one can get the boundary conditions which are written below44The velocity and temperature variables via symmetry analysis are expressed asAbove relations for velocity and temperature field help to transform Eqs. –7) in t in t7) i36 byThe quantities involved in the above equations are expressedThe dimensionless parameters are 44Stresses (in dimensionless forms) in The heat transfer rate can be determined throughThe numerical values for thermos-physical properties of base fluid and nanoparticles used in the simulations are tabulated in Table i.Derivation of integral residual statements in their weak forms.ii.Here, in this investigation, the weak forms are approximated using the Galerkin procedure.iii.The derivation of stiffness elements and their use in the assembly process. The nonlinear system is obtained via the assembly process.iv.The nonlinear equations are linearized and obtained linearized system is solved iteratively.v.Computations are performed to ensure the results to be grid-independent. The grid-independent analysis is done through numerous numerical experiments and outcomes are listed in Table The finite element method (FEM) is the most suitable method for the solution of CFD problems. The convergence associated with FEM can be achieved easily. Further convergence rate of solutions obtained by FEM is faster than other methods like finite volume method, finite difference method, spectral method, etc. The working principle for FEM can consist of the following important steps.Equations  and 11)11) are aUsing the above approximations in the weak formulation of weighted residuals, the stiffness, and the boundary elements are given byAssembly procedure we get the system of nonlinear algebraic equations of the formStiffness matrix It is important to note that the stiffness matrix Domain The computational domain is Error The error in the simulated results is calculated usingThe numerical values for density specific heats, thermal conductivities, and electrical conductivities for solid particles entclass1pt{minimaIt is very important to mention that no experimental study related to the present work is available. Moreover, a theoretical study on the three-dimensional flow of power-law fluid with the numerical data as a special case of present work is not available in the literature. Therefore, it is not possible to provide validation of our results. However, the results found by two different methods are compared and their comparison is presented in Table Rheological models, models of hybrid nanoparticles, and fundamental dimensionless equations are solved numerically using FEM. After, ensuring convergence, grid independence, and validation of results, numerical experiments for the behaviors of related parameters on field variables are done. The simulations are visualized and recorded in graphical and numerical data. Following is the discussion.The parameter entclass1pt{minimaentclass1pt{minimaThe behaviors of parameters The above discussion has revealed that if ethylene glycol with hybrid nanostructures has been used as engine coolant, its cooling performance is much better than pure ethylene glycol or ethylene with The behavior of tangential stresses and heat flux are examined for sampling values of The comparative analysis between thermal efficiencies of The heat generation may affect the cooling performance by It is recommended to use ethylene glycol with hybrid nanostructures as an engine coolant, its cooling performance is much better than pure ethylene glycol or ethylene with In many boundaries layer flow passing over the surface like the surface of aircraft, automobile vehicles, etc. Lorentz force for the case when ethylene glycol does not exhibit Ohmic dissipation. However, in the case of Ohmic dissipated fluid, Lorentz force in controlling the thermal boundary layer is less effective. This is another limitation of the working fluid.Non-Fourier heat transfer is slower than Fourier transfer due to thermal memory effects based on thermal relaxation time. Thus, thermal changes tend to be restored due to the thermal relaxation phenomenon.The power-law fluid with nanoparticles (It is found that thermal relaxation time for power-law fluid with Magnetic field is responsible for inducing Lorentz force which is responsible for creating shear stresses on the surface. Thus tangential stresses are increased by increasing the magnetic field intensity.Heat flux decreases when the heat generative parameter is increased.There is a significant difference between heat fluxes for Governing laws in terms of differential equations associated with a thermal enhancement in ethylene glycol due to the dispersion of In literature, ethylene glycol has not been proved or disproved to be heat generating. If it is heat generating then obviously its thermal performance will be compromised. Contrary to this if ethylene glycol is not a heated generative then it is a stable coolant and its thermal performance will be optimized. The present era is a time of new and innovative technologies. Thus manufacturing of non-heat generating fluid will be possible in coming days.


Alphaviruses are positive-sense RNA arboviruses that are capable of causing severe disease in otherwise healthy individuals. There are many aspects of viral infection that determine pathogenesis and major efforts regarding the identification and characterization of virulence determinants have largely focused on the roles of the nonstructural and structural proteins. Nonetheless, the viral RNAs of the alphaviruses themselves play important roles in regard to virulence and pathogenesis. In particular, many sequences and secondary structures within the viral RNAs play an important part in the development of disease and may be considered important determinants of virulence. In this review article, we summarize the known RNA-based virulence traits and host:RNA interactions that influence alphaviral pathogenesis for each of the viral RNA species produced during infection. Overall, the viral RNAs produced during infection are important contributors to alphaviral pathogenesis and more research is needed to fully understand how each RNA species impacts the host response to infection as well as the development of disease. Alphaviruses are single-stranded, positive-sense RNA viruses that are naturally transmitted between a mosquito vector and a vertebrate host. Epizootic spillover events result in the infection of humans and horses, potentially resulting in severe disease. Alphaviruses are largely classified as either arthritogenic or encephalitic based on the symptoms of infection. Arthritogenic alphaviral infection causes disease varying from mild to severe multi-joint arthritis and can persist for several months to years past the acute phase of infection . This inThe primary purpose of this review is to summarize what is known about how the viral RNAs (vRNAs) produced during alphaviral infection influence pathogenesis . While mAlphaviruses produce primarily three RNA species during viral replication: the genome, which encodes the nonstructural proteins; the minus-strand RNA, which serves as the template for viral replication and transcription; and the subgenome, which encodes the structural proteins . The speFrom a compositional perspective, there are two features of the alphaviral RNAs that arise in a non-templated fashion during replication/transcription. These two features are the 5′ cap structure and the 3′ poly(A) tail. Despite being non-templated, these RNA features arise from the specific activities of the alphaviral replication complex; with the addition of the 5′ cap being due to the concerted activities of nsP1 and nsP2, and the addition of the poly(A) tail is due to nsP4. While, to date, there have been no reported virulence determinants associated with the 3′ poly(A) tail, the 5′ cap structure, in contrast, has been associated with virulence at several levels.The alphaviral cap structure is different from host cap moieties, creating a major means by which the host is able to distinguish between self and viral RNAs. More specifically, eukaryotes incorporate a Type-1 cap that is 2′O methylated . CytosolNonetheless, the alphaviral capping machinery is not absolutely efficient. Recent work from our lab has demonstrated that a significant proportion of the genomic RNAs produced during alphaviral infection lack a 5′ cap structure . In lieuWhile the direct mechanistic impact of the noncapped genomic RNAs remains a topic of ongoing assessment, altering the ratio of capped/noncapped genomic vRNA produced during infection is known to have significant impacts on alphaviral pathogenesis. More specifically, increasing the proportion of capped genomic RNA produced during SINV infection of 4-week old C57BL/6 mice resulted in almost complete ablation of morbidity and mortality as well as significantly reduced levels of inflammatory cytokine transcripts compared to wild type SINV infection . ImportaDue to the genetic arrangement of the alphaviruses, the genomic and subgenomic viral RNAs possess shared and nonshared untranslated regions. Specifically, the 5′ untranslated regions (UTRs) of the genomic and subgenomic RNAs are different from one another due to the utilization of an internal initiation site on the minus strand template RNA for subgenomic RNA synthesis, whereas synthesis of the genomic RNA begins at the 3′ terminus of the template minus-strand RNA . In contThe alphaviral 5′ UTR varies in both length and sequence among the different alphaviruses and is typically between 27 and 85 nucleotides long . AlthougNonetheless, the 5′UTR of the alphavirus genomic RNA does have structural elements which are directly involved in virulence, and the importance of these features has been demonstrated in multiple alphaviruses through point mutations of specific residues. Specifically, mutation of nucleotide 3 in VEEV has been shown to result in avirulence in immunocompetent mice but does not affect pathogenesis in IFNAR-/- mice ,24,25. SSimilar to the alphaviral genomic RNA, the 5′ UTR of the subgenomic RNA and its adjacent coding region also has a functional role in alphaviral pathogenesis through the presence of cis-acting features. However, unlike the genomic RNA, the 5′ features of the subgenomic RNA focus largely on the regulation or enhancement of translational activity. The most notable feature is the Downstream LooP (DLP), which is a stable stem-loop structure present in the subgenome located approximately 27–31nt downstream of the initiation codon of the capsid protein  32]. Th. Th32]. Like the 5′ UTRs, the canonical 3′ UTRs of the alphaviruses vary greatly in both sequence and length, being anywhere from ~80 to over 700 nucleotides long depending on the species ,39. In aA notable element of the alphaviral 3′ UTR is the presence of Repeated Sequence Elements (RSEs) which form stem-loop structures. Although the composition, number, and length of the RSEs vary among the alphavirus genus as a whole, the RSEs of alphaviruses in the same clade retain a large degree of similarity . In CHIKA second readily identifiable element of the alphaviral 3′UTR is the U-Rich Element (URE), which is typically found immediately 5′ of the 3′CSE sequence. While not strictly conserved across the genus, this element was found to interact with the host HuR protein. thereby promoting viral RNA stability via preventing transcript-specific deadenylation ,47. AlphIn addition to the viral cis-features of the alphavirus 3′UTRs, there are instances whereby aspects of the host RNA regulatory pathways influence alphaviral pathogenesis. These include host derived MicroRNAs (miRNA) which are short host RNAs that regulate protein translation in a transcript specific manner. These regulatory RNAs can have both pro-viral and antiviral functions and can influence viral replication directly by targeting viral RNA or indirectly by targeting host mRNAs to alter the cellular environment. In situations where the miRNA directly interacts with viral RNA, viral replication is either restricted due to miRNA inhibition of viral genomic translation or enhanced due to the miRNA increasing the stability of the viral RNA ,50,51.The most well-described miRNA known to impact alphaviral pathogenesis is miR-142-3p. This hematopoietic-specific miRNA has been shown to bind to the 3′UTR of both EEEV and WEEV and restrict viral replication in myeloid-lineage cells  49,52].,52.49,52While most miRNA:vRNA interactions occur in the 5′ and 3′ UTRs, an interaction site in the structural open reading frame (ORF) of SINV and CHIKV has been recently described. Specifically, the interaction of the neuronal-specific miR-124 with the E1 region of SINV and CHIKV has been shown to positively regulate viral replication  54]. Al. Al54]. The nonstructural and structural open reading frames comprise the vast majority of the genomic and subgenomic RNAs and the sequences of these regions are much less varied between the different alphaviruses, especially in comparison with the 5′ and 3′ UTRs. Relatively little is known about how the RNA structures, modifications, and RNA:Protein interactions that occur in these portions of the viral RNA contribute to pathogenesis outside of influencing the nonstructural and structural proteins they encode. Furthermore, whether there are differences between the structural open reading frames of the genome and subgenome that influence pathogenesis in different ways is also largely unknown. In spite of all that is unknown, there are a number of studies that illustrate several aspects of the viral genome and subgenome that are known to be important determinants for alphaviral pathogenesis.In studies assessing the usage of dinucleotide motifs and codon pairs in viruses relative to their hosts, it was found that many arboviruses utilize codon pairs which are overrepresented in their vertebrate hosts as opposed to the invertebrate vector . AlphaviZAP suppression of alphaviral replication is important for host type-I IFN mediated antiviral defense, as suckling mice deficient in ZAP are unable to adequately control SINV replication and have increased mortality . In miceA key feature of many alphaviruses is the presence of an Opal stop codon in between the nsP3 and nsP4 coding regions. Several studies have identified the Opal stop codon as a virulence determinant, but the overall impact of the Opal stop codon is, interestingly, highly dependent on the particular alphavirus species. Mutation of the Opal stop codon in CHIKV results in reduced pathogenicity, as mice infected with a virus where the Opal codon has been replaced with arginine experienced decreased footpad swelling and reduced inflammation in the joints . In contIn addition to the Opal stop codon, there is a proximal stem-loop structure that promotes read-through by the ribosome. Several studies have shown that the presence and stability of this stem-loop structure influences the expresion of nsP4, but the overall impact of this secondary structure motif on alphaviral pathogenesis is unclear as direct studies involving animal models have not been pursued ,70. RegaDue to their nature as single-stranded RNA viruses, the alphaviral RNAs are capable of folding into a diverse array of secondary structures during the viral lifecycle. Indeed, recent studies have shown the presence of extensive RNA secondary structures throughout the viral genome . HoweverIn addition to the generalized structured nature of the alphaviral genome and the likely implications of such, there are several key secondary structures with specific identified roles during infection. These include the Packaging Signal (PS) located in the nonstructural ORF, and the aforementioned DLP element, and the 6K/TF Frameshift structures located in the structural ORF.The primary role of the PS is to select the genomic RNA for encapsidation during viral infection. The precise location of the packaging signal varies across the members of the genus, with the majority of the alphaviruses having a packaging signal in nsP1, and SFV and RRV having their packaging signal in the coding region of the nsP2 protein ,75. The The second known structural element in the structural ORF of the subgenomic RNA that contributes to pathogenicity is the stem-loop which causes a frameshift during the translation of the 6K protein resulting in the production of the transframe (TF) protein  76]. Th. Th76]. While numerous viral and host protein interactions with the alphaviral RNA have been described, the best-characterized interactions are those that impact viral translation or vRNA synthesis. Interfering with the interactions would certainly affect alphaviral pathogenesis, as efficient translation and synthesis of the alphaviral RNA are vital for viral replication as well as for impairing the host immune response. However, because these interactions only seem to indirectly affect alphaviral pathogenesis because they deal with important aspects of the viral life cycle, they are beyond the scope of this review and will not be discussed in detail.In addition to the two major positive-sense RNAs produced during alphaviral infection, there are several other RNA species with known and/or unknown functions that are produced at non-trivial amounts during infection. These include the negative-sense minus-strand RNA, the cryptic RNA II positive-sense RNA species, and defective viral RNAs. In this section, the known functions and contributions of each of these “other” viral RNA species are described.Functionally, the minus-strand RNA serves as the template for the synthesis of all other positive-sense viral RNAs. It is a primary product of the viral replication cycle and is synthesized by the earliest forms of the alphaviral replication complex. Indeed, the maturation of the alphaviral nonstructural polyprotein rapidly diminishes the synthesis of the minus-strand RNA in favor of the two positive-sense RNA species.Even though the function of the minus-strand RNA is believed to be well understood, the role of the minus-strand RNA in pathogenesis is less clearly defined. What few RNA structures and protein:RNA interactions have been described for the minus-strand RNA are in the context of viral replication and transcription. While disruption of features that promote efficient production of the viral genome and subgenome would have obvious impacts on the development of disease. As the mechanistic effects of these mutations involve fundamentally altering viral replication, they are beyond the scope of this review. Thus, the full extent of the RNA secondary structures present in the minus-strand RNA as well as any connected protein:RNA interactions and how they impact alphaviral pathogenesis has not yet been characterized. One aspect of the minus-strand RNA important to viral pathogenesis is that it can activate the various innate immune sensors which target non-self RNAs, such as RIG-I and MDA-5. To avoid being detected by these sensors, alphaviruses sequester the minus-strand RNA into replication spherules formed from host membranes . HoweverThe fourth viral RNA species that is generated during alphaviral infection is the positive-sense RNA species RNA II. RNA II consists of the first ~7.6kb of the genome and ends at the subgenomic promoter  81]. RN. RN81]. Defective viral genomes (DVGs) consist of viral RNAs which have large deletions that render them unable to initiate infection. During viral replication, truncation, recombination, and/or rearrangement events of the viral genome can result in the production of DVGs. Alone, DVGs are unable to replicate as they lack a full complement of replication machinery and structural proteins. However, in the presence of the wild-type virus, the DVGs can be replicated and packaged into viral particles. During alphaviral infection, DVGs are typically produced during high MOI serial passaging studies and were found to repress viral replication ,86. In pGiven the capacity for DVGs to restrict viral replication in tissue culture, there is the potential that DVG production could affect alphaviral pathogenesis in animal models as well. In SFV, mice inoculated intranasally with tissue culture-derived DVGs were protected from lethal infection, presumably because the DVGs interfered with viral dissemination and replication in the brain . HoweverAlthough the addition or excess production of DVGs during alphaviral infection is largely antiviral, the DVGs naturally produced over the course of infection may have different effects on viral pathogenesis. While the role DVGs play in the development of disease has not yet been shown for alphaviruses, it has been characterized for other RNA viruses. In the Sendai virus, DVGs have been shown to be immunostimulatory, as viral strains that produce higher levels of DVGs induce a greater IFN response than strains producing relatively few DVGs. In mice infected with the Sendai virus, DVGs produced by the virus have been found to be responsible for inducing the production of type-I IFN and triggering the host immune response . In tissAs summarized above, the alphaviral RNAs directly contribute to virulence and pathogenesis to a significant extent. These contributions are in addition to the obvious linkage between viral replication/RNA synthetic fitness and pathogenesis, and typically involve multiple aspects of the host/pathogen interface. The mechanisms by which the viral RNAs contribute to virulence are both direct, as in acting to directly evade or resist aspects of the host innate immune response, and indirect via the modulation of the production of viral proteins during infection. The alphaviral RNA virulence determinants are often, but not always, associated with secondary structures and may be found throughout the entire length of the viral RNA. Furthermore, virulence determinants that lack defined secondary structures often act as interaction sites for host and viral RNA-binding proteins. In these instances, the virulence determinant is directly linked to the primary sequences of the viral RNAs themselves.Overall, the critical contributions of the alphaviral RNAs to pathogenesis have been established, but much work remains to identify the full extent to which the alphaviral RNAs are intertwined with pathogenesis and the precise mechanisms by which the viral RNA influence disease. While the knowledge compiled above represents the current state of understanding in this regard, it also highlights the presence of significant critical gaps in the understanding of the role of viral RNAs in pathogenesis.


In vertebrates, the skeletal muscles of the body and their associated stem cells originate from muscle progenitor cells, during development. The specification of the muscles of the trunk, head and limbs, relies on the activity of distinct genetic hierarchies. The major regulators of trunk and limb muscle specification are the paired-homeobox transcription factors PAX3 and PAX7. Distinct gene regulatory networks drive the formation of the different muscles of the head. Despite the redeployment of diverse upstream regulators of muscle progenitor differentiation, the commitment towards the myogenic fate requires the expression of the early myogenic regulatory factors MYF5, MRF4, MYOD and the late differentiation marker MYOG. The expression of these genes is activated by muscle progenitors throughout development, in several waves of myogenic differentiation, constituting the embryonic, fetal and postnatal phases of muscle growth. In order to achieve myogenic cell commitment while maintaining an undifferentiated pool of muscle progenitors, several signaling pathways regulate the switch between proliferation and differentiation of myoblasts. The identification of the gene regulatory networks operating during myogenesis is crucial for the development of in vitro protocols to differentiate pluripotent stem cells into myoblasts required for regenerative medicine. Skeletal muscles constitute the most abundant tissue in the vertebrate body. The voluntary contraction of the muscles requires electrical stimuli provided by motoneurons to the fibers. Then, the mechanical forces generated by muscle fiber contraction are transmitted to the bones (or connective tissues) by the tendons. The contractibility of the fibers relies on the structural organization of the actin and myosin proteins that constitute the sarcomeres.In tetrapods, skeletal muscles from the trunk and limbs derive from the somites, while head muscles originate from the cranial and prechordal mesoderm. During development, paraxial mesoderm in the trunk undergoes segmentation, forming the somites, which are transient mesodermal structures that subsequently mature into distinct layers, the dermomyotome, the myotome, the syndetome and the sclerotome Fig. A Buckin. DorsallPax3-deficient embryos, trunk muscle formation is impaired, cells of the hypaxial domain of the dermomyotome undergo cell death and consequently limb muscles and other muscles of migratory origin are absent  and Myf5-mutants . Regarding MRFs compensation, combined ablations usually lead to severe skeletal muscle development impairment  are deleted  to activate the expression of the Myogenic Regulatory Factors (MRF) in muscle progenitors. The MRFs are a family of basic-Helix-Loop-Helix (bHLH) transcription factors that recognize the E-box consensus motif CANNTG in DNA. In order to bind DNA, MRF proteins need to heterodimerize with the ubiquitous bHLH E-proteins , activating its expression in these cells  has been identified as a PAX3 interacting protein that is required for myogenic specification  family  or to the phorbol ester TPA, leads to inhibition of fetal myoblast differentiation, while embryonic myoblasts are not affected  that lacks the dystrophin protein. When engrafted, these cells are capable of generating healthy fibers that express dystrophin and replenish the satellite cells which once again adopt a position under the basal lamina , combined with cell sorting to enrich for paraxial mesoderm , efficiently produces a myogenic progenitor population Table  Darabi . SimilarMYOD1 messenger RNA combined with interferon inhibitors efficiently directed hiPSC (human induced pluripotent stem cells) differentiation into myoblasts  study identified the surface markers FGFR4 and CDH13 as being expressed in myogenic progenitors. Furthermore, cells purified with each one of these markers were able to generate Dystrophin-positive fibers when transplanted into an immunodeficient mouse model for DMD (Nalbandian et al., Although the use of transgene-free cultures to differentiate stem cells into the myogenic lineage has advantages regarding a putative future use for cell therapy, the significant degree of contamination by other cell types may require cell sorting to isolate pure myogenic populations. By using a One common drawback of most iPSC-differentiation protocols is the inability to produce mature cell types in vitro. This is also the case for myogenic differentiation protocols that do not yield fully differentiated myotubes in vitro and prevents a deeper analysis of the late myogenic differentiation phases. In fact, the myotubes present in these cultures usually have an embryonic or early fetal phenotype and lack the capacity to mature into late fetal or adult myofibers. Transcriptomic analysis of human PSC-derived myogenic progenitors and human fetal myoblasts highlighted differences in the expression of signaling pathways components between these two populations (Hicks et al., The optimization of protocols to differentiate human PSCs into myoblasts for use in therapeutic approaches also relies on the understanding of the molecular networks operating during human myogenesis that may differ from those of the mouse. Therefore, the development of databases and resources to increase the knowledge of human myogenesis is of major importance. Recently, a scRNA-seq experiment performed in embryonic, fetal and postnatal human skeletal muscles allowed the mapping of myogenic differentiation trajectories of human myoblasts (Xi et al., The development of skeletal muscle progenitors is tightly regulated and relies on the hierarchical expression of genes that coordinate their specification and commitment. The role of the PAX genes as well as that of the MRF transcription factors regulating myogenesis is well established. In addition, several genome-wide analyses for PAX3 and PAX7 binding sites have been performed, revealing many potential PAX3/PAX7 target genes. However, only recently has the muscle field started to appreciate the role of these factors as tissue-specific chromatin remodeling factors that rely on interactions with ubiquitous chromatin architecture regulators. Furthermore, the identification of upstream regulators of PAX3 and PAX7 as well as their regulatory regions remains to be done. The answers to these questions could lead to the understanding of how these genes act and regulate downstream targets by inter-playing with chromatin remodelers and also how they are regulated in different developmental contexts.


The analyses of amplification and melting curves have been shown to provide valuable information on the quality of the individual reactions in quantitative PCR (qPCR) experiments and to result in more reliable and reproducible quantitative results.q per reaction. The melting curve analysis encompasses smoothing of the observed fluorescence data, normalization to remove product-independent fluorescence loss, peak calling and assessment of the correct peak by comparing its melting temperature with the known melting temperature of the intended amplification product.The main steps in the amplification curve analysis are (1) a unique baseline subtraction, not using the ground phase cycles, (2) PCR efficiency determination from the exponential phase of the individual reactions, (3) setting a common quantification threshold and (4) calculation of the efficiency-corrected target quantity with the common threshold, efficiency per assay and CThe LinRegPCR web application provides visualization and analysis of a single qPCR run. The user interface displays the analysis results on the amplification curve analysis and melting curve analysis in tables and graphs in which deviant reactions are highlighted. The annotated results in the tables can be exported for calculation of gene-expression ratios, fold-change between experimental conditions and further statistical analysis. Web-based LinRegPCR addresses two types of users, wet-lab scientists analyzing the amplification and melting curves of their own qPCR experiments and bioinformaticians creating pipelines for analysis of series of qPCR experiments by splitting its functionality into a stand-alone back-end RDML  Python library and several companion applications for data visualization, analysis and interactive access. The use of the RDML data standard enables machine independent storage and exchange of qPCR data and the RDML-Tools assist with the import of qPCR data from the files exported by the qPCR instrument.https://www.gear-genomics.com/rdml-tools/) is platform independent and much faster than the original Windows-based versions of the LinRegPCR program. Moreover, web-based LinRegPCR includes a novel statistical outlier detection and the combination of amplification and melting curve analyses allows direct validation of the amplification product and reporting of reactions that amplify artefacts.The combined implementation of these analyses in the newly developed web-based LinRegPCR (The online version contains supplementary material available at 10.1186/s12859-021-04306-1. When the DNA becomes single stranded, the bound fluorochrome is released and the observed fluorescence drops  [m to the Tm of the positive control, or the previously determined Tm of the correct product, enables discrimination between the correct amplification product and artifacts. When a saturating DNA-binding dye, e.g. LCGreen, is used, the fluorescence associated with the peak of the correct product can be used to remove artifact bias [Most qPCR systems can perform a melting protocol after the amplification protocol. The melting protocol involves gradual heating of the reaction volume while continuously monitoring the fluorescence. Heating will cause the double-stranded DNA to denature when its melting temperature  . Compariact bias .m and other peak characteristics, like peak height, width and area. None of the systems attaches consequences of this analysis with respect to the reported quantitative data resulting from the amplification curve analysis. In the web-based LinRegPCR an unbiased transparent melting peak analysis procedure is included that is free of user involvement with respect to peak finding and identification [0) of the target.A complete melting curve analysis involves data processing, peak finding, identification of the melting peaks, measurement of the fluorescence associated with each peak and calculation of the contribution of the peak of the correct product to the total fluorescence. However, most, if not all, companies do not disclose how they perform analysis of melting curve data. Without going into an extensive review, we illustrate three examples. The Biorad CFX system has the user set a threshold to determine the minimum height of the melting peaks to be reported. The Roche Lightcycler system uses an undisclosed method to restrict the number of peaks reported to the number requested by the user. The ABI Prism system has the user set a temperature window in which the melting peak of the correct amplification product is expected and then evaluates the validity of the reaction by determining whether the peak area ratio of peaks inside and outside this window is above a user defined value. In all cases the systems report the Tfication . The useLinRegPCR has been available for qPCR data analysis since 2003 , with a The first, and critical, step in the analysis is the accurate estimation of the baseline fluorescence per reaction. Both LinRegPCR versions determine this baseline in an iterative approach. Initially, the baseline is set to a level that is too high. Then the data points in the exponential phase are split into two parts and the slopes of the straight lines through the subsets are compared. The baseline estimate is step-wise lowered until the slope of the upper halve becomes steeper than the slope of the lower halve, indicating that the baseline estimate has become too low. The baseline estimate is then increased by one step and the step is halved. The procedure is iterated until the slopes differ less than 0.0001; at a PCR efficiency of 1.8, this criterion translates into an efficiency difference of 0.0004 . This baThe second step of the analysis is to determine the efficiency value from the slope of the line fitted to a subset of data points in the linear exponential phase of each individual reaction . An initThe LinRegPCR web-application implements two strategies to determine, and optionally exclude, reactions with an individual PCR efficiency that deviates strongly from the mean efficiency per assay. In the Windows version of LinRegPCR the user has the option to use all PCR efficiencies or to exclude PCR efficiencies outside a user-defined range (default setting ± 0.05) around the median efficiency per assay. However, this simple approach tends to exclude too many reactions in wide normal distributions. To avoid this unwanted behaviour, a novel statistical outlier detection, based on the distribution skewness and the Grubbs’s test, is implemented in this new version of LinRegPCR. Because this optional outlier exclusion changes the distribution of the efficiencies of the included reactions, the W-o-L setting and mean efficiency calculation are iterated until no new outliers occur. Reactions considered to be efficiency outliers are reported in the result file Fig. C.q value and to calculate the efficiency-corrected target quantity (N0) per reaction. These steps require a quantification threshold to be set  that are efficiency-corrected and can thus be freely compared between assays and runs [0 values as q), the PCR efficiency per assay (Etar) and the Cq value per reaction [q values, the reported target quantities per reaction are the same for the two versions of LinRegPCR [see Additional file The use of a common threshold for all assays does not remove the bias inherent to the fact that Cependent . Therefoand runs . The Linreaction . After amentclass2pt{minimm) of the associated DNA fragment(s) , is then compared to the given melting temperature of the correct product, to assess whether the melting peak represents the correct product . In RDML, the user has to label each reaction in the run as positive or negative control, or as unknown reaction. This information allows web-based LinRegPCR to provide intelligent error reporting. While processing the amplification data per reaction, the program does a number of quality checks which may lead to warnings and errors reported per reaction  and bioinformaticians creating pipelines to analyze thousands of such experiments with minimal user involvement. Therefore, the functionality of this web-based application is split into a back-end RDML-Python library for the actual calculations and several companion web applications that visualize the data and provide an interactive access.To enable machine independent storage and exchange of qPCR data, the RDML format entered the qPCR field in 2009 , 25. Thihttps://github.com/RDML-consortium/rdmlpython) builds the back-end which handles RDML files and performs all amplification and melting curve processing, analyses and calculations. An additional file shows the class design of the Python library [see Additional file https://numpy.org) for the acceleration of array calculations, the SciPy package (https://www.scipy.org) for advanced statistical calculations and the lxml package (https://lxml.de) for the handling of XML files using the C libraries libxml2 and libxslt. A core functionality of the RDML-Python library can open, read and write RDML files and handle the dependencies within the RDML format. The amplification curve and melting curve analysis parts of the RDML-Python based LinRegPCR are implemented as callable functions linRegPCR and meltCurveAnalysis within this library. Results of calculations are written back into the RDML file and, if there are no equivalent elements in the RDML format, displayed as spreadsheet tables. The RDML-Python library can be easily integrated into Python programs and bioinformatics pipelines. It also offers a limited command line interface which can be used to analyze amplification and melting curves in batch programs.The stand-alone RDML-Python library (https://www.gear-genomics.com/rdml-tools/). The front-end applications are designed for the interactive usage on a molecular biology laboratory floor. The RDML-Tools follow the classic client–server architecture with a web app as front-end calling a dedicated Python server which is performing the calculations using the RDML-Python library. In principle, the web app collects the input files and user input, and sends this information to the server. The server checks the parameters and translates the user requests into calls for the RDML-Python library. Once the calculations are complete, the server sends the results back to the web app which displays the results and allows the user to explore them.The RDML-Tools are hosted on GEAR, a web server for molecular biology applications  and are explained below.The RDML-Tools Help is available on the RDML-Tools page and provides an introduction to the RDML-Tools and gives detailed information on the parameters of the tools and their optimal usage.XML files are bound to a predefined usage of elements by schema files. RDML-Validate validates RDML files against the RDML schema of the correct version. The tool will show a report including the used RDML version. If errors are encountered, a hint to the conflicting rule is given. RDML-Edit (see below) can then be used to correct the error.https://www.gear-genomics.com/rdml-tools/tableshaper.html) fills the gap by loading the exported spreadsheets and converting them step by step into the format that can be imported into RDML-Edit for further editing and annotation. If the export format of the qPCR machine is already known, a file with the correct parameters can be selected from a dropdown menu. Otherwise, these parameters must be found by iteratively walking through the tabs of RDML-TableShaper. Once completed, the import parameters can be saved for future use. An additional file shows an example of the TableShaper interface [see Additional file Not all qPCR machines export RDML files and, therefore, many users are left with plain spreadsheet exports that cannot be directly imported into RDML-Edit (see below). RDML-TableShaper , the other view shows the fluorescence data as a graph. The user can choose between amplification and melting curves, customize the used colors, for example to discriminate between wells with different targets or different tissue samples and switch between logarithmic and linear scaling of the fluorescence axis. An additional file shows an example of the RunView interface [see Additional file RDML-Edit shows all information up to the single run. Once a single run is selected in RDML-Edit, it is visualized in RDML-RunView in two ways. One view shows the plate lay-out with information about the sample, target and Cq values using the LinRegPCR algorithm. The results are displayed in a spreadsheet table and deviant reactions are highlighted. If a row is double-clicked, the amplification curve of the corresponding reaction is highlighted in the RunView tab complemented with the window of linearity, and the values of the quantification threshold and Cq. The Melting Curve Analysis tab shows the results from the melting curve analysis. Screenshots of the amplification curve analysis and melting curve analysis interfaces are shown in additional files [see Additional file RDML-LinRegPCR facilitates visualization and analysis of amplification and melting curve data of a single qPCR run. The user interface is similar to RDML-RunView and is used to display the contents of the RDML file or the analysis results on the Amplification Curve Analysis and Melting Curve Analysis tabs. The Amplification Curve Analysis tab allows to (re)calculate Cq value to a low-quality reaction. Although the outcome of such reactions could be of relevance in clinical diagnostics, they should not be used for quantitative purposes, because low quality is often associated with a very low PCR efficiency [Most qPCR machine software does not extract all relevant information that is present in the amplification curves. Because reaching the quantification threshold is often enough to consider a reaction to be positive, this also results in the assignment of a Cficiency . The ampficiency .q value of individual reactions, the LinRegPCR web-application uses the mean PCR efficiency per assay. In doing so, the reported Cq value is not affected by residual random baseline noise. Although LinRegPCR thus reports Cq values called from a common quantification threshold per run, which would allow direct comparison of Cq values, it is not recommended to do so. Because of the dependency of Cq on the PCR efficiency, conclusions drawn from ΔCq values can be severely biased [For calling the Cy biased , 3, 5. Oq value and PCR efficiency of the individual reaction in the output, the user can manually calculate the starting concentration of individual reactions using the reported values.By default, LinRegPCR calculates the target quantity per reaction using the PCR efficiency per assay. This efficiency per assay is calculated as the mean of the PCR efficiencies observed for the individual reactions per assay. The reporting of the PCR efficiency for individual reactions in the output table not only serves as a quality criterion but this PCR efficiency value can also be used to calculate the starting concentration of the individual reaction. The latter option is often indicated in case of clinical point-of-care analysis, where sample purification can be less optimal, or even absent, and the PCR efficiency can be affected by sample contaminations. In those cases, the variation in the PCR efficiencies between samples does not allow calculation of a reliable and meaningful PCR efficiency per assay . BecauseAlthough many researchers are not aware of the existence of the melting curve analysis, this analysis should be considered an essential step in qPCR analysis, especially when DNA-binding dyes are used to monitor the PCR. The melting curve analysis allows the identification of artefacts besides the intended target, which is easy, quick, cheap and more sensitive than size separation on agarose gels , 17. TheThis new version of LinRegPCR includes a user-independent analysis of the melting curve data and reports all observed melting peaks. The program identifies the peak of the intended amplification target using the melting temperature given in the RDML input. To this end, the user has to determine this melting temperature from a pilot study with positive control samples. In a validated PCR assay, such a positive control should show amplification of only one product. The melting curve analysis primarily serves to determine whether the correct product, artefacts or both are amplified in unknown samples. Customarily, reactions that amplify artefacts are excluded from further analysis. However, we recently showed that the results of the amplification curve analysis can be corrected by determining the contribution of the correct peak to the total fluorescence . This meq or N0 with the melting curve results requires that the observed fluorescence comes from a saturating dye [When to use the LinRegPCR program? The amplification curve analysis in LinRegPCR can be used for analysis of qPCR data resulting from all amplification monitoring modalities . Meltingting dye .0) per reaction, calculated with the quantification threshold per run, PCR efficiency per assay and Cq value per reaction. These target quantities represent the gene expression per reaction, and can be used to calculate the gene-expression ratio between target and reference genes  and the fold-difference between experimental conditions (fold = ratioexperiment/ratiocontrol). After analysis of the amplification curves the annotated results (efficiency per assay and Cq per reaction) are stored in the RDML file. These analysis results can be further analysed with specialised programs like qBase [How to use results of this program? The main result of the analysis of qPCR data with LinRegPCR is the target quantity (Nke qBase  or exporhttps://github.com/RDML-consortium/rdmlpython) or as 'rdmlpython' package using pip3. During implementation of the different functions of this web-based LinRegPCR some changes were also made in the Windows version LinRegPCR. These changes did not affect the target quantities reported by the Windows version. Although the different quantification thresholds result in different Cq values, upon release of the web-based LinRegPCR, the reported target quantities (N0) of both program versions are identical [see Additional file q values are based on a common threshold, we do not recommend direct comparison of these Cq values without taking the PCR efficiency into account [As described, all tools involved in this Python-based version of LinRegPCR are open source and the tools are free to use. The implementation of the algorithms is transparent and can be extended by the users’ requirements. The RDML-Python library is available under MIT license as source distribution : Platform independentProgramming language: Python, Java ScriptOther requirements: numpy, scipy, lxml, flaskLicense: GPL-3.0 (RDML-Tools), MIT (RDML-Python library)Any restrictions to use by non-academics: noneAdditional file 1. Excel file comparing the output of the new Python with the original Windows LinRegPCR version. Also illustrating the escence axis.Additional file 2. Screenshot of the LinRegPCR web interface showing the amplification curve analysis RunView tab.Additional file 3. Screenshot of the LinRegPCR web interface showing the LinRegPCR tab with results of the amplificationcurve analysis.Additional file 4. Screenshot of the MeltCurveAnalysis web interface showing the melting curve analysis RunViewtab.Additional file 5. Screenshot of the MeltCurveAnalysis web interface showing the MeltCurveAnalysis tab withresults of the melting curve analysis.Additional file 6. This file contains example amplification and melting curve data in RDML format.Additional file 7. Overview of the classes defined in the RDML-Python library..Additional file 8. Screenshot of the TableShaper web interface showing an example conversion form spreadsheettot RDML format.Additional file 9. Screenshot of the RunView web interface showing the plate-layout with reaction annotation andraw fluorescence data on a logarithmic fluorescence scale.


Heterobilharzia americana, the most westerly report of this endemic North American schistosome, and the first from Utah. Raccoon scats collected near the pond were positive for H. americana eggs, and snails living near the pond's water line identified as Galba humilis shed H. americana cercariae, the first indication of natural infections in this widespread North American snail species. The susceptibility of G. humilis to H. americana was confirmed experimentally. Our studies support the existence of two variants of H. americana and emphasize the need for further investigations of lymnaeids and their compatibility with H. americana, to better define the future potential for its spread. Capture of a new species of intermediate host vector snail and construction of man-made habitats suitable for this snail have created the potential for a much more widespread animal health problem, especially for dogs and horses. H. americana will prove difficult to control because of the role of raccoons in maintaining transmission and the amphibious habits of the snail hosts of this pathogenic schistosome.Parasites with complex life cycles engaging multiple host species living among different environments well-exemplify the value of a cross-cutting One Health approach to understanding fundamental concerns like disease emergence or spread. Here we provide new information regarding a pathogenic schistosome trematode parasite of both wild and domestic mammals that has recently expanded its known range from mesic/wet environments of the southeastern United States to the arid southwest. In 2018, 12 dogs living near a man-made pond in Moab, Utah, were found positive for   •Heterobilharzia americana expands its known range.The pathogenic canine schistosome •Galba humilis.First evidence of new snail vector, •Galba humilis is widely distributed in North America, enabling further spread.•Raccoons are also important hosts and their increasing abundance also favors spread. The content for this paper is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.This work was supported by the core laboratory support provided by The None.


Coherence, purpose and significance were defined as the three facets of the presence of meaning in life . This study investigated the age differences in the three facets of meaning in life between younger and older adults. We recruited 241 younger adults  and 114 older adults  from Hong Kong to fill out a one-hour online survey. We adapted the Multidimensional Existential Meaning Scale, which measured sense of coherence, purpose, significance. In specific, the adapted version measured significance in two sub facets: the naturalistic significance (important to other people) and cosmic significance (impact lasts beyond lifetime and space). The results showed that older adults had higher sense of coherence , higher sense of cosmic significance  but lower sense of purpose than younger adults . There were no significant differences in naturalistic significance between the two age groups . Within both age groups, participants had the highest score in purpose, followed by coherence and naturalistic significance. They had the lowest score in cosmic significance. This study illustrated that younger and older adults have different absolute levels of meaning facets but are similar in the relative levels of meaning facets. Further studies can investigate how changes in absolute levels of meaning facet and preservation of the relative levels may affect well-being across age.


When performing pancreaticoduodenectomy with resection of the confluence of the superior mesenteric vein and portal vein, division of the splenic vein may cause sinistral portal hypertension resulting in gastrointestinal bleeding, splenic congestion, and hypersplenism. To prevent these adverse events, it is important to intentionally decompress the splenic vein. This report is of a 68-year-old woman with stage IA carcinoma of the head of the pancreas who survived for more than six years following tumor resection and pancreaticoduodenectomy and distal splenorenal shunt. A 68-year-old woman was diagnosed with carcinoma of the head of the pancreas that involved the confluence of the superior mesenteric vein, portal vein, and splenic vein. No unresectable cancer sites or distant metastases were detected. Pancreaticoduodenectomy with resection of the confluence of the superior mesenteric vein and portal vein was performed. The superior mesenteric vein and portal vein were anastomosed in the end-to-end fashion, and the remnant splenic vein was anastomosed to the superior aspect of the left renal vein in the end-to-side fashion. At 22 months after the initial surgery, the patient underwent partial lung resection for a metachronous lung metastasis. For 6 years after the initial surgery, the venous reconstructions have maintained their patency without any obstruction of splenic venous flow, and the patient has remained in good health without further metastases or recurrences. This case has shown the importance of early diagnosis of carcinoma of the head of the pancreas, as appropriate and timely surgical management can result in good outcome. This patient responded well and remains alive six years following pancreaticoduodenectomy and preservation of the spleen with the use of a distal splenorenal shunt. Pancreas cancer is the fourth leading cause of cancer-related death in developed countries , and thePancreatic cancer located in the pancreatic head and/or uncus easily invades the superior mesenteric vein and/or portal vein –11. AlthW. Dean Warren (1924-1989) was a pioneer in surgery for portal hypertension , and he Division and ligation of the splenic vein during pancreaticoduodenectomy is often associated with the development of sinistral portal hypertension, which results in gastrointestinal bleeding, splenic congestion, and hypersplenism over the long term , 13. TheThis report describes a 68-year-old woman with stage IA carcinoma of the head of the pancreas who survived for more than six years following tumor resection and pancreaticoduodenectomy with the use of a distal splenorenal shunt to preserve the spleen.A 68-year-old woman was referred to our hospital for the investigation of elevated serum levels of amylase and lipase. Enhanced computed tomography (CT) detected a hypovascular mass (18 mm diameter) in the pancreatic head Figures . The maien bloc resection of the confluence of these veins was performed, with simultaneous venous reconstructions  was graphically detected in the right lung. The patient underwent partial lung resection for a right lung tumor that was pathologically diagnosed as a lung metastasis originated from the pancreatic cancer , although graphical and surgical curability were obtained. Chemotherapy with S-1 was resumed for 1 year after the lung resection. The patient has been in good health, with no other oncologic metastases detected during the 6 years since the initial surgery.μL and 235,000/μL, respectively. The estimated splenic volumes before surgery and at 5 years and 6 months after the initial surgery were 38 mL and 35 mL, respectively.Dynamic CT and upper esophagogastric endoscopy performed 5 years and 6 months after the initial surgery revealed that all venous reconstructions had maintained good patency , and theIntentional decompression of the splenic vein after division of this vein is still controversial –20, and Although venous reconstruction of the superior mesenteric vein and portal vein during pancreaticoduodenectomy for pancreatic cancer is widely accepted, intentional decompression of the splenic vein in case when division of the splenic vein is needed is still controversial –20. It hAs pancreatic cancer generally has a very poor prognosis –6, many A native vein may be the optimal candidate as a drainage route of the splenic vein. The inferior mesenteric vein is useful as a drainage route from the splenic vein , 34, 35,Most surgeons currently believe that the splenic venous flow must be reconstructed in cases where the splenic vein is divided –20. AlthWarren was a pioneer in surgery for portal hypertension and variceal bleeding and originally published the distal splenorenal shunt in 1967 as an operative procedure for bleeding esophageal varices . Warren To our knowledge, there are only few reported cases of splenic venous reconstruction via a distal splenorenal shunt , 37–39. In conclusion, this case has shown the importance of early diagnosis of carcinoma of the head of the pancreas, as appropriate and timely surgical management can result in good outcome. This patient responded well and remains alive six years following pancreaticoduodenectomy and preservation of the spleen with the use of a distal splenorenal shunt.


Drug delivery using oral route is the most popular, convenient, safest and least expensive approach. It includes oral transmucosal delivery of bioactive compounds as the mucosal cavity offers an intriguing approach for systemic drug distribution. Owing to the dense vascular architecture and high blood flow, oral mucosal layers are easily permeable and can be an ideal site for drug administration. Recently, the transmucosal route is being investigated for other therapeutic candidates such as vaccines for their efficient delivery. Vaccines have the potential to trigger immune reactions and can act as both prophylactic and therapeutic conduit to a variety of diseases. Administration of vaccines using transmucosal route offers multiple advantages, the most important one being the needle-free (non-invasive) delivery. Development of needle-free devices are the most recent and pioneering breakthrough in the delivery of drugs and vaccines, enabling patients to avoid needles, reducing anxiety, pain and fear as well as improving compliance. Oral, nasal and aerosol vaccination is a novel immunization approach that utilizes a nanocarrier to administer the vaccine. Nanocarriers improve the bioavailability and serve as adjuvants to elicit a stronger immune response, resulting in increased effectiveness of vaccination. Drugs and vaccines with lower penetration abilities can also be delivered transmucosally while maintaining their biological function. The development of micro/nanocarriers for transmucosal delivery of macromolecules, vaccines and other substances is currently drawing much attention and a number of studies were performed recently. This comprehensive review is aimed to summarize the most recent investigations on needle-free and non-invasive approaches for the delivery of vaccines using oral transmucosal route, their strengths and associated challenges. The oral transmucosal vaccine delivery by nanocarriers is the most upcoming advancement in efficient vaccine delivery and this review would help further research and trials in this field. The world has a long history of global disease outbreaks such as severe acute respiratory syndrome-coronavirus (SARS-CoV) in 2003, Influenza A virus subtype H1N1 causing swine flu in 2009–2010, Middle East respiratory syndrome (MERS) in 2012, and the very recent coronavirus disease-19 (COVID-19). The COVID-19 is caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) and has been declared as a potential threat and pandemic by the World Health Organization (WHO). Exploring treatment regimens, effective therapeutic agents and vaccines for complete eradication of the virus are one of the priorities of the scientific fraternity, including all healthcare providers . SeveralNeedle-free, as the name indicates, aims to deliver the dose of a vaccine dose at high velocity into the dermal and subcutaneous layers without penetration by a needle. This method can be considered the newest method for vaccine delivery and holds maximum benefits in terms of waste management as generated needle waste is reduced and the potential risk of accidental needling after injection is eliminated. Needle-free vaccines for multiple and monodoses are currently being explored by researchers across the globe . This swThe advantages of needle-free drug delivery systems include the elimination of broken needles, needle sticks, and needle disposal, reduction of pain and stress, consistent drug or vaccine delivery, and reduced drug or vaccine volume. The disadvantages include high startup costs, infrastructure demand, and requirements for training and maintenance . CurrentThis review article is aimed to raise awareness of needle-free vaccine delivery systems as one of the approaches for the treatment and prevention of various diseases especially in cases, where mass vaccination is required. The needle-free vaccines can be administered using the transmucosal route and extensive efforts have been made in the last few years in developing the mucoadhesive delivery systems that could deliver the drugs and antigens in appropriate concentrations. In this article, we emphasized on the oral transmucosal and intranasal route of drug/vaccine administration and various advancements made in the field are reviewed. Transmucosal delivery using nanocarriers and the approaches for the delivery of COVID-19 vaccines are also covered.The mucoadhesive drug/vaccine delivery systems are needed owing to various advantages associated with them. Some of the benefits of using transmucosal systems include increased drug absorption due to abundant blood supply as well as good blood flow rate in the mucosal sites resulting in increased therapeutic efficacy. Other advantages include prevention of first pass metabolism resulting in increased drug bioavailability, prevention of drug degradation due to acidic environment of the gastrointestinal tract (GIT), ease of drug/vaccine administration, targeted and localized administration of the dosage form at a specific site, and provision of intimate contact between dosage form and the absorptive mucosa resulting in high drug flux at the absorbing tissue . MucoadhThe general mechanism of mucoadhesion includes two steps; the contact stage (between mucoadhesive polymer and the mucus membrane) and the consolidation stage  as shown in Apart from painless drug administration, the transmucosal route offers many advantages and showed potential and flexibility in various clinical studies . Owing tDespite all these important aspects about the oral route of drug administration, oral vaccine delivery is still not a very successful approach for presenting antigens to the body, and the reason lies in the human body physiology. The inactivating enzymes and acidic environment of the gastrointestinal tract will quickly degrade antigens before they are presented to the M-cells of Peyer’s patches . TherefoPoliovirus, Vibrio cholerae, Salmonella typhii and Rotavirus as well as the nasal vaccine against the Influenza virus  are made up of Peyer’s patches, which serve as important inductive sites for both humoral and cell-mediated immunity. Secretory immunoglobulin A (sIgA) antibodies are produced by GALT . The mucNasal nanovaccines administered through the intranasal route are optimal for mass vaccination in pandemics and are convenient for the stimulation of mucosal and systemic immune responses . Nasal dThe problems associated with oral, parenteral and rectal routes of drug administrations prompted exploration of the intranasal delivery of various drugs. The incorporation of mucoadhesive polymers and absorption promoters facilitate the transport of colloidal formulations and enhance their transport across nasal mucosal barriers. Various vaccines can be delivered through the intranasal route effectively, particularly vaccines for the brain . Other ain vitro and in vivo approaches and a few of them are summarized in in vivo experiment  etc.  etc. .in vitro evaluation was performed using flow cytometry which helped in the detection, identification and cell count measurement of antigens. In another study, liposome-based vaccine was developed using PspA antigens against the S. pneumoniae infection, which was characterized in vitro using cell culture method and in vivo using ELISA for the detection of PspA-specific antibodies  techniques and X-ray examinations and immunological tests were performed as part of in vivo studies , electron microscopy and AFM techniques were used to characterize chimeric nanoparticles-based vaccine prepared against the T cell leukemia virus, whereas the in vivo methods included determination of specific antibodies and cytokine responses  as antigen and Quil-A as adjuvant was prepared and characterized using chniques . The preesponses .in vivo evaluation was performed on nursery piglets which showed that the immunization was safe and effective. Particle size, zeta potential and cellular uptake experiments using in vitro techniques were performed on the APCs , delivery system  and antigen . The alternative routes of administration through the oral cavity, such as buccal or sublingual, have gained advantages in systemic and mucosal immunity. Oral mucosal vaccines are easy to prepare and safer than parenteral vaccines . MucosalExtensive efforts have been made to develop effective vaccine antigen delivery systems that increase uptake by local antigen-presenting cells (APCs), resulting in protective mucosal immunological responses. Effective mucosal adjuvants and efficient delivery systems are vital for the successful mucosal vaccine delivery . Non-invAlthough, only few transmucosal vaccines made it to the market till now, however, current technological advancements and improved understanding of the concepts of mucosal immune responses have increased the optimistic approach on the future of transmucosal vaccines. Some of the marketed oral and intranasal transmucosal vaccines along with their manufacturers are presented in In order to provide maximum vaccine effects at the mucosal site for a prolonged duration, it is desirable for the mucosal vaccine to remain adhered with the mucosal membrane. Thus, the vaccine delivery through the mucosal route  requires the use of mucoadhesive polymers such as Chitosan, Cellulose, Eudragit and Hybrid polymers for the production of the mucoadhesive systems. These mucoadhesive polymeric particles for mucosal vaccine delivery pose numerous advantages such as protection of antigens from degradation, controlled release of the loaded vaccine, prolonged residence time of the antigen at the target site and rapid induction of mucosal and systemic immune responses .The use of adjuvants in the delivery of vaccine is critical as they boost the immune responses when used in conjunction with specific antigens and increase the effectiveness of vaccines. Additionally, adjuvants are non-specific immunopotentiators and they are able to alter the nature of immune responses. The choice of adjuvants in the development of vaccine depends on several factors including the type of disease, route of vaccination, nature of antigen and the type of immune response. The use of incorrect adjuvant might result in a reduction in the vaccine efficiency. Till date, only a few adjuvants are approved for human vaccines which include alum , heat-laRecently, ovalbumin was used as an antigen in the development of microneedles where OVA-coated microneedles were prepared with and without cholera toxin (CT) as adjuvant along with disks without tips . These dHowever, the use of microneedles is associated with issues such as higher cost, slower antigen delivery and inability to generate mucosal immunity which is important especially in case of immunity against pathogens. To overcome these problems, a novel non-invasive buccal mucosa immunization strategy called “MucoJet” was developed recently, which is a three-dimensional microelectromechanical system-based vaccine/drug delivery technology . MucoJetStaphylococcal enterotoxin-B were successfully used to immunize mice subcutaneously. These microspheres showed 500-folds increase in the circulating anti-toxin response. The strength of adjuvant activity was shown to be dependent upon the size of microspheres and should not be more than 10 microns in diameter and requiring that the antigen is present within the particles , University of Cambridge also developed a PharmaJet needleless vaccine called DIOS-CoVax2 that can be delivered through patient’s skin using a single jet of air and does not cause pain . The strCOVI-VAC, a vaccine developed by Codagenix, also provided good protection against the current COVID-19 virus. It can be administered intranasally and does not require the use of a syringe or needle. It is a single-dose live-attenuated vaccine that can be given directly to the nasal mucosa where the coronavirus infection starts . COVI-VANeisseria meningitidis or at least two of serogroups A, C, W135 and Y of N. meningitidis. The carrier protein should be conjugated to the capsular saccharides and conjugated oligosaccharides were more preferred. Another invention in 2008 revealed the development of an intranasal vaccine using chitosan as an adjuvant having a molecular weight ranging from 10 kD to 500 kD and antigen consisting of inactivated, disrupted, or live attenuated viruses (Several patents have been granted on the development of oral transmucosal and intranasal vaccines which were both related to the process of development of vaccine as well as the final product. Several researchers used chitosan as an adjuvant to develop the vaccine for influenza virus intended for mucosal administration and in one such attempt, a pharmaceutical product was developed comprising of a dispensing device in order to deliver the vaccine intranasally. It was claimed that mucosal delivery of influenza vaccine was found to be significantly enhanced upon addition of chitosan as an adjuvant . The eff viruses . Chitosa viruses . ChitosaAnother approach to encapsulate the antigens using nanocarriers was made when oral alginate microsphere vaccines with a size of less than 5 nm were successfully developed for oral mucosal administration . The vacin vivo (Helicobacter pylori, Clostridium difficile and Listeria infections (Dry powder vaccine containing antigens along with microcrystalline cellulose having diameter in the range of 10–100 microns were prepared for the prevention of influenza virus infection and to be given through intranasal route . The spein vivo . In anotin vivo . Fluorinfections . A fast fections . The devfections .In continuation with the development of nanocarrier-based mucosal vaccines, a nanoemulsion-based vaccine was invented which was both safe and effective against a wide variety of pathogens that have been exposed to the atmosphere . The samVaccination through transmucosal route is a needle-free and therefore medical waste-free strategy providing immunity in both mucosal and systemic compartments against a range of pathogenic bacteria and viruses. The mucosa is enriched with both lymphatic and vascular drainage and the pre-systemic elimination and first-pass metabolism can be avoided. A retentive device can easily be incorporated into the mucosal area and is well suited for patients of all age groups. Vaccine delivery through the mucosal route can further be improved using nanotechnology and by employing physical methods such as sonophoresis and iontophoresis. As the details of all mucosal sites are available, specific mucosal site for a particular situation can easily be selected. Needle-free vaccines are being explored extensively nowadays as they have the potential to increase the efficiencies, are adaptable to every operation, and can be altered in order to optimize their production. Various methods which can produce longer-lasting medications and therefore reducing the number of injections are also being investigated. However, safe and effective substances that enhance the buccal permeation and absorption are vital for the development of buccal drug delivery systems. Currently, commercially available formulations are mostly limited to tablets and films, while the buccal and sublingual routes offer great prospects and several formulation approaches are being investigated for this purpose. Previous studies reported that the nanoscale drug delivery devices hold significant potential in both clinical and industrial applications. Nanocarrier-based technologies are also being utilized to deliver antigens in an efficient, targeted, and controlled manner that is not achievable with traditional approaches. Polymeric nanoparticles, liposomes, virosomes, niosomes, and nanoemulsions are among the nano-sized delivery vehicles used in these technologies. Although, various types of nanocarrier-based formulations are being assessed for the mucosal administration of nonliving vaccines; most of them are still in the preclinical development phase and none has entered clinical trials. The vaccine delivery systems are gaining much popularity these days owing to their benefits in being patient-friendly, minimizing the need of booster doses and giving long-term treatment in modest doses.


Three-dimensional printing (3DP), also known as additive manufacturing (AM), has rapidly evolved over the past few decades. Researchers around the globe have been putting their efforts into AM processes improvement and materials development. One of the most widely used extrusion-based technology under AM processes is Fused Deposition Modeling (FDM), also known as Fused Filament Fabrication (FFF). Numerical simulation tools are being employed to predict the FFF process complexities and material behavior. These tools allow exploring candidate materials for their potential use in the FFF process and process improvements. The prime objective of this study is to provide a comprehensive review of state-of-the-art scientific achievements in numerical simulations of the FFF process for polymers and their composites. The first section presents an in-depth discussion of the FFF process’s physical phenomena and highlights the multi-level complexity. The subsequent section discusses the research efforts, specifically on numerical simulation techniques reported in the literature for simulation of the FFF process. Finally, conclusions are drawn based on the reviewed literature, and future research directions are identified. Three-dimensional printing, also known as additive manufacturing (AM), has rapidly evolved over the past few decades ,2. AM prFused Deposition Modeling (FDM), also known as Fused Filament Fabrication (FFF), one of the most widely used AM processes, was proposed and developed by Scott Crump at Stratasys . In the Researchers around the globe have been putting their efforts into AM processes improvement and novel materials over the past few decades ,14. The The prime objective of this study is to provide a comprehensive review of the state-of-the-art scientific achievements in numerical simulations of the FFF process for polymers and their composites. The first section presents an in-depth discussion of the FFF process’s physical phenomena and highlights the multi-level complexity. The subsequent section discusses the research efforts, specifically on numerical simulation methods reported in the literature for simulation of the FFF process. Finally, conclusions are drawn based on the reviewed literature, and future research directions are identified.This section presents the physical phenomena involved in the FFF process. An in-depth understanding of this phenomenon is essential to improve the process and 3D printed part quality. The overall FFF process can be divided into three phases; material flow through the nozzle and deposition on the print bed or already deposited material (extrusion), interaction of deposited beads to make a bond (fusion), and the cooling process (solidification), as elaborated in The first process involves material flow through the nozzle body, nozzle orifice, and deposition . This phIn the second phase, the deposited material reheats or re-melts the already deposited material beads . The bonLastly, the deposited material begins to solidify as it cools down. The cooling process during and post-printing is governed by convective and radiative heat losses on external surfaces of the beads and conductive heat transfer at beads contact points and printing bed. If the material is deposited at a higher speed, i.e., a large amount of material is deposited in a shorter time, it will not allow the pre-laid layer to cool down sufficiently before depositing the next layer . It willThere has been an increasing interest in modeling and simulation of the FFF process since the commercial availability of 3D printers. The past and ongoing research related to computational modeling of the FFF process can be broken down into two domains. In the first domain, thermal variations and fluid flow behavior of the material in the heating zone are modeled. Overall melt flow behavior of the material inside the printer extruder depends upon the heat capacities of the nozzle and liquefier and the thermal properties of the material. Secondly, when the material is extruded through the nozzle, sudden pressure change causes swelling following the deposition. This stage is of great interest as material flow outside the nozzle, bead shape, bonding of beads, and residual stresses are governed by these factors. Following, we present the computational works related to the FFF of polymers and polymer composites, also reported in The first study on modeling and characterization of material flow inside the liquefier and nozzle in the FFF process was conducted by Bellini . The matAlthough the first study in this area considered ceramic materials, it laid the foundation for the numerical analysis of 3D printed polymers. Ramanath et al.  numericaResearchers have also considered ABS material for numerical studies. ABS material can is widely regarded for the synthesis of polymer composites . This maIn another study, Bellini et al.  studied Other than PCL and ABS, Polylactic acid (PLA) is also a widely explored polymer in materials science due to its sustainability and biodegradability . PLA is ®, COMSOL®, and Moldflow®, is reported in the literature. Mostafa et al. [Numerical studies on fused filament fabrication of fiber-reinforced materials are limited. Fiber orientation during the FFF process and mechanical properties are strongly affected by nozzle shape, fiber concentration, material flow rate, and pressure difference. The use of computational modeling software, such as ANSYSa et al.  investiga et al.  studied Fiber orientation in short or continuous fiber-reinforced composites is critical to achieving desired mechanical, thermal, or electrical properties in 3D printed materials. Several experimental studies provided insight into fiber orientation and fiber flow behavior within the nozzle and deposition of extruded beads ,64,65,66Heller et al.  studied In addition to the numerical simulations of fiber-reinforced material flow within the nozzle, several studies have reported the fiber orientation within the deposited beads. Bertevas et al.  were theThe solidification behavior of material governs the bonding between deposited beads, polymer crystallization, and ultimately the mechanical properties of the 3D printed part. When two adjacent beads are deposited, they contact and form necking at the interface  Figure . The resZhou et al.  considerXia et al.  recentlyThe above equation was solved analytically with defined boundary conditions to obtain the following solution for temperature variations during the cooling process:Subsequently, sintering experiments were performed to investigate the dynamics involved in the bond formation of extruded filaments. The developed model also considered the effect of different printing parameters. It was suggested that better control of the cooling process could assist in controlling the mechanical properties of FFF parts. Further investigation was conducted in another study , where aR corresponds to the radius of curvature, L represents the section length of the part, n presents the number of deposited layers, The strength and dimensional stability of 3D printed parts are affected by induced residual stresses and warpage. Wang et al.  developea et al.  3D printAn analytical model was also derived for both the elastic and plastic behavior of multiple-layer deformations based on the experimental observations. Layer thickness significantly affected the residual stresses, warpage, and surface characteristics.Xinhua et al.  developeWatanable , using aFitzharris et al.  extendedZhang and Chou  presenteCattenone et al.  developeTalagani et al.  exploredFiber Orientation: The fiber orientation in deposited beads depends upon the material flow through the nozzle and deposition process. Most of the literature reports the use of Newtonian isotropic fluid properties; however, these materials should be modeled under anisotropic viscous flow conditions. Current modeling software cannot solve fourth or higher-order orientation tensors and cannot consider anisotropic flow characteristics (which is the case with fiber-reinforced composites). Therefore, there is a need for better numerical simulation tools to consider realistic fiber orientation during material flow.Beads Deposition: Several heat transfer models have been reported in the literature to predict the cooling process of the deposited beads. However, due to the anisotropy involved in the 3DP process, interlayer conduction phenomena need to be considered as thermal conductivities of deposited beads change with the fiber orientation.Interface and Bonding: Bonding between the subsequent layers is highly correlated with the interface; therefore, the presence of fibers on the bead surface can affect this process. In addition, the necking phenomenon is derived by the gradients of surface tension is also influenced by the bead surface morphology. Finally, the material behavior  will reflect its viscosity, which ultimately affects the bonding process; therefore, it must be accounted for accurate process modeling.Integrated Simulation Models: The FFF process is a complex multi-stage process as described in this paper. However, most reported computational work either focused on the material flow inside the liquefier or material behavior after deposition and is not as mature as the experimental literature. Therefore, there is a need for integrated studies considering all these phases of the FFF process .Model Validation: The validation of numerical and analytical models is vital through experimental studies. Limited studies compared the numerical simulation results with experimental work, which is essential for validating and broader application of these models.Materials Portfolio: Materials portfolio for the FFF process is rapidly growing. However, few materials (such as PLA and ABS) are considered for numerical and analytical modeling of process or material behavior. The researchers should focus on implementing existing models to a broader range of materials or develop models for materials not yet considered in the literature.Polymer Composites: Two-phase materials (composites) are also barely considered for the numerical modeling of material or the FFF process. The most reported models address linear amorphous polymers. Different polymers exhibit different characteristics, such as bare PLA and ABS act as amorphous materials; however, PBT, PA12, and PEEK exhibit a semi-crystalline nature [e nature ,85,86. Me nature . The effThe fused filament fabrication process has been under continuous development since the commercial availability of this technology. Several studies reported experimental analysis and virtual modeling of different phases involved in the process. The numerical modeling of material flow inside/outside the printing head and behavior after deposition with promising outcomes have been reported. Based on the extensive literature review performed on numerical simulation techniques, the following research challenges and gaps are identified:This study provides a comprehensive review of state-of-the-art scientific achievements in numerical simulations for the FFF process of polymers and their composites. The first section presents an in-depth discussion on the physical phenomena involved in the FFF process and highlights the multi-level complexity. The subsequent section discusses the research efforts, specifically on numerical simulation techniques reported in the literature for the FFF process.The future of 3DP processes, specifically the FFF process, is promising due to research and development interest. However, several challenges are still faced. The focused research on the gaps mentioned above could further improve the process and material design.Currently, the FFF process is being explored extensively; however, the numerical simulation approaches are still empirically calibrated. This work has identified several issues persisting the wide use of numerical simulation techniques for its development. Addressing these research challenges will enable a more realistic and reliable prediction of the FFF process.