Infrared linear array detectors frequently experience vertical, low-frequency, and periodic stripe noise during imaging, stemming from electro-mechanical interference. Unlike conventional periodic disturbances, this interference showcases long periodicities and is uniquely columnar in orientation. Its presence, especially within the low-frequency domain, renders conventional filtering techniques ineffective and, at times, detrimental to image quality. Addressing this challenge, we introduce Fourier-Assisted Correlative Denoising (FACD), a correlation-centric denoising approach tailored for such unique interference patterns. This mechanism begins with the capture of a pure background image, inclusive of periodic noise, during the non-uniform correction phase of the infrared detector. Leveraging the noise’s frequency domain attributes, we extract a one-dimensional single-cycle noise signal. The infrared image is subsequently segmented into parts, and using the detected noise periodicity, the one-dimensional signals for each segment are computed. By leveraging the correlation between these signals and the benchmark one-dimensional noise pattern, we ascertain the noise profile within each segment. This profile is then employed for spatial domain denoising across the entire image frame. Empirical assessments confirm that the FACD outperforms contemporary denoising techniques by augmenting the peak signal-to-noise ratio by approximately 2.5 dB, underscoring its superior robustness. Furthermore, in light of its specificity to this noise model, FACD rapidly denoises high-resolution real infrared linear array scans, thus meeting the stringent real-time and resolution imperatives of advanced infrared linear array scanning apparatuses. As advancements continue in large-scale focal plane arrays and infrared linear array detector techniques ,2, the 3Stripe noise, originating from detector inconsistencies, frequently demonstrates a directional preference, manifesting horizontally or vertically. This noise distribution does not adhere to a consistent pattern and typically corresponds to the detector’s photosensitive element’s response to illumination. Addressing the challenges posed by image stripes due to detector non-uniformity, Li Fangzhou et al.  proposedInfrared linear array detectors, when employed in 360-degree rotational scanning, require instantaneous imaging due to their rapid acquisition rates. A single pass can produce tens of thousands of image columns. This imaging modality introduces a peculiar kind of periodic stripe noise attributable to electromagnetic interference. Unlike noises from other devices, this noise showcases a protracted period and a lower frequency, aligning conspicuously with the direct current (DC) component within the frequency domain.Notably, deploying denoising methodologies as suggested by Hamd M H et al.  and YadaConsidering the abovementioned challenges, this paper proposes an infrared linear array image denoising algorithm based on signal correlation. The foundational framework of the denoising algorithm hinges on a correlation-centric approach. Specifically, our proposed algorithm, FACD (Fourier-Assisted Correlative Denoising), operates by leveraging the intrinsic frequency domain attributes of periodic noise. At its core, FACD begins by capturing a background image saturated with the said noise. It then delves into the frequency spectrum to extract a one-dimensional, single-cycle noise signal. By segmenting the infrared image and matching the detected noise periodicity, the algorithm harnesses the correlation between these segmented signals and the established one-dimensional noise pattern. This correlation-driven methodology enables FACD to precisely ascertain the noise profile within each segment of the image, facilitating effective spatial domain denoising. The primary advantage of the FACD approach lies in its precision and specificity to target the unique interference patterns presented by electromechanical interferences in infrared linear array detectors. Experimental results show this algorithm proficiently eliminates periodic noise in high-resolution 360-degree rotational scanning images, satisfying the real-time imperatives of infrared linear array detectors.Periodic noise is a prevalent noise type in images, typically emanating from interference during image capture or subsequent transmission. Traditionally, this noise is typified by its high frequency, manifesting as luminous sectors within the image’s two-dimensional Fourier transform domain, as delineated in This paper concentrates on a distinct type of noise, divergent from traditional periodic disturbances. Infrared linear array detectors capture the images under scrutiny during their comprehensive 360-degree rotational scanning. Electromechanical disturbances during this procedure introduce noise with a lower frequency. In the spatial domain of the image, this noise manifests as subtle, gradually varying stripes. Conversely, within the image’s two-dimensional Fourier transform domain, it is observed as luminous sectors proximate to the DC component. The noise image of the infrared detector obtained through blackbody is shown in Upon juxtaposing the frequency domain images of periodic noise depicted in As illustrated in Normally, infrared detectors need to be calibrated to ensure consistent response from the detection unit before each use. In this study, the non-uniformity correction deployed for the infrared detector is based on the single-point method. Given that the infrared images acquired during this correction phase primarily reflect the pure background, they remain relatively insulated from external scene perturbations. Such images exhibit a pronounced presence of periodic noise. Therefore, the algorithm employs the Fourier transform to analyze the images obtained during non-uniformity correction, aiming to discern the noise periodicity attributable to electromechanical interference. In this example, upon examination of the periodic noise within the pure background imagery, it was ascertained that the noise periodicity for the selected infrared detector approximates 850 columns. Furthermore, recognizing the high resolution inherent to infrared linear array scanning images and the need for multiple noise periods in Fourier transform calculations, this section crops the line scanning images, adjusting their resolution to 1024 × 4096.Since the periodic noise of infrared linear array images primarily shows in the column direction, the clipped image is first converted into a one-dimensional signal in the column direction, as shown by the following formula:In the next step, Fourier transform is applied to In this formula, In this context, the function Since the number of columns of the cropped image In addition, other noises that are present in the collected signal can also influence the estimated value Initially, the median value, ‘In this context, Within this framework, In this discussion, The periodic noise in the infrared columnar image caused by electromechanical interference is a type of additive noise, and its image signal model is shown in Equation (10).In this context, Based on the analysis of the linear array detector’s periodic noise in Let R indicates its rows. From the sequence In this context, To address the infrared image affected by periodic noise, it is segmented into individual blocks. Each block has a column size matching the noise cycle The subsequent phase involves computing the one-dimensional sequence in the column direction for each subdivided block, as represented by the following equation:In this equation:Use Formula (14) to calculate the offset Sort all the During the non-uniformity correction process of the infrared camera, collect the cyclical noise image under a pure background;Implementing the Fourier Transform-centric periodic solution algorithm, as introduced in Employing Formula (13) and the ascertained noise period Step 1: Single-Cycle Noise Sequence Extraction Step 2: Image Data Partition and ProcessingAs illustrated in Begin by subdividing the procured images into specific blocks, as illustrated in Step 3: Cross-Correlation Function and Offset DeterminationFor each one-dimensional image sequence Step 4: Sequence Ordering and Offset RefinementAfter the previous steps, the offset series Step 5: Image DenoisingCollaboratively, with the sequence The preceding section articulated that the Fourier-Assisted Correlative Denoising (FACD) mechanism requires an image characterized by periodic noise against a pure background. We conducted a comprehensive experiment to assess the applicability and robustness of the proposed mechanism in real-world scenarios. For the empirical study, the experiment was designed to meticulously record and analyze the fluctuations in noise periodicity and amplitude over successive time intervals following the initial power-up of the detector without undergoing any rebooting processes.We employed a 1024-pixel long-wave infrared linear array detector, which boasts a specialized shutter mechanism. This shutter is purposefully activated when a non-uniformity correction command is initiated, facilitating the precise non-uniformity correction procedure. The images obtained at this critical juncture form the foundation of our data source. By applying histogram statistical methods, we discerned the columnar distribution associated with the noise periodicity within the current image framework. Data were harvested across varied operational intervals, culminating in four distinct datasets. Each of these sets encapsulated an average of 55 noise cycles. The resultant histograms are illustrated in the subsequent figure. Within this graphical representation, the x-axis demarcates the column count corresponding to the noise periodicity, while the y-axis quantifies the cycle counts spanning diverse noise periods.For a deeper insight into noise amplitude fluctuations, we compiled and analyzed data from 220 noise periods across the four intervals. Drawing from these observations, the infrared linear array detector for the experiment, once powered up, maintains consistent noise characteristics in terms of period and amplitude. This consistency underscores the effectiveness of the FACD algorithm. Initialized with a single-period noise signal extracted at power-up, the FACD algorithm can consistently denoise images without needing recalibration during extended operation periods.As depicted in Conversely, when one opts for larger block widths, the number of blocks extracted from an infrared linear array image of the exact dimensions is reduced. The calculation time for the column-direction signal increases. Given that the correlation between the image scene and periodic noise is relatively weak, the influence of the image scene on the correlation algorithm is considerably reduced when the block’s width is larger.In this subsection, we conduct an experiment utilizing 20 infrared line-scanning images, each with a resolution of 1024 × 4096. A pure background periodic noise image of identical resolution is acquired through a blackbody. We create a simulated infrared image with noise by superimposing this periodic noise image onto the clean infrared line-scanning image. Using the algorithm described in In the context of image acquisition with infrared linear array detectors, the content of the captured scenes significantly influences the denoising effectiveness of the algorithm presented in this paper. For images that primarily feature background elements, the fluctuations in the one-dimensional signal, as elaborated in To systematically replicate the interplay of scene content on the denoising efficiency of the algorithm, this section incorporates a one-dimensional signal characterized by a Gaussian distribution centered at zero and exhibiting diverse variances. This signal is superimposed onto the one-dimensional signal permeated with periodic noise, computed per the methodology above. The underlying logic remains lucid: an augmentation in the variance of the Gaussian distribution signifies increased scene complexity, as illustratively presented in In To verify the influence of the one-dimensional Gaussian noise on the denoising efficacy of the presented algorithm, an experimental setup, encapsulated within this section, leveraged 20 frames of immaculate real infrared linear array rotational scanning images, each boasting a resolution of 1024 × 4096. By overlaying these images with the pure background periodic noise sourced from the blackbody, we achieved 20 frames of infrared linear array images replete with periodic noise and identical resolution parameters. As the denoising mechanism of our algorithm took course, diverse variances of Gaussian noise sequences were added to the one-dimensional signal extracted from the periodic noise-laden linear array images. In the results presented in To substantiate the denoising efficacy of the presented algorithm, we undertook simulation experiments utilizing noise-free infrared images. We sourced 50 infrared frames from the CAMEL dataset  and incoWe then applied two periodic noise removal algorithms, Two-Circle Filter  and LocaThe enhanced NL-means algorithm  operatedlization  and Wavelization  algorithAs discerned from Despite calibrating the filter radius r to a value of 2, the intrinsic operations of the denoising algorithm might have inadvertently perturbed the DC component within the frequency domain, consequently altering the global mean value of the image frame. Such a phenomenon correlates with the visually diminished luminosity observed in images processed using the Two-Circle algorithm, as depicted in To validate the effectiveness of the proposed algorithm in the context of authentic high-resolution infrared linear array images, this section employs two real infrared linear array scanned images with dimensions of 1024 × 4096 containing periodic noise for the denoising experiment, along with one pure background noise image obtained during the equipment’s non-uniformity correction process. For the Wavelet Gradient-Equalization algorithm  and the In Furthermore, in the real infrared linear array-scanned images, the noise period is approximately 850 columns, much higher than that in the simulated images. Consequently, the change in pixel values between adjacent image columns is even more gradual. Such slow variation exacerbates the inadequacy of the improved NL-means algorithm , WaveletGiven the fast imaging capabilities and high resolution provided by infrared linear array detectors, it is imperative for associated algorithms to maintain optimal real-time performance. In this section, we assess the denoising time for each algorithm, utilizing authentic infrared linear array images (resolution 1024 × 4096) afflicted with periodic noise. The specifics of these algorithms remain consistent with As the image resolution escalates, there is an evident proportional increase in the runtime across all algorithms. This increment is particularly pronounced in methods like the improved NL-means, which exhibit a substantial time surge even with modest increments in resolution. However, a compelling observation is the minimal runtime escalation of our proposed FACD method, which manifests only slight increments even when the image resolution multiplies. This indicates the scalability and robustness of our approach, making it particularly adept for applications that might necessitate varied image resolutions. Furthermore, when juxtaposed with other algorithms, the FACD’s time increment remains negligible, reinforcing its prowess in ensuring consistent and rapid denoising irrespective of resolution expansions.Our algorithm emerges as a potent tool within infrared linear array imaging systems. According to the characteristics of this system, it first needs to close the baffle to perform the non-uniformity correction every time it powers up. Collect a frame of the image as the pure background image at this moment. Subsequent analysis yields noise periodicity and amplitude. The baffle is then reopened, and leveraging our algorithm’s methodology, the noise’s correlation with authentic images is ascertained, facilitating spatial domain denoising. After completing the above steps, the image denoising process is simply arithmetic operations on every pixel after receiving a column image. This streamlined approach ensures brevity in execution, addressing long-standing challenges posed by periodic noise due to electromechanical disturbances within infrared linear array imaging systems.Within the confines of the experiments outlined in the preceding section, our proposed algorithm exhibited marked proficiency in attenuating low-frequency noise, while simultaneously upholding commendable real-time operational efficiency. When one broaches the subject of high-resolution, real-time image processing systems, it becomes pivotal to note that the periodicity of columns in infrared linear array detectors might shrink to approximately 30 microseconds. Such systems predominantly find utility in the domains of target extraction and recognition. Given the prodigious generation rate, surpassing 30,000 image columns every second, resorting to a full-frame buffering approach for image elaboration would entail a substantial memory overhead, jeopardizing the real-time assurance. Conventionally, systems of this ilk adopt a staggered processing paradigm, buffering at intervals of 128 or 256 columns. In other words, with every caching instance, the system extracts targets within the image to achieve real-time target output. Thus, the advantages of column-by-column noise reduction are evident. Our algorithm can be deployed during the embedded image preprocessing phase. After performing rapid noise reduction on each column, the image is passed to the next stage. The resultant computational footprint is minimal, both in terms of resource consumption and parameter storage overhead. Such efficiency earmarks ample computational latitude for downstream algorithms, rendering our method an ideal fit for embedded systems that are relatively resource-constrained. However, our algorithm requires a preliminary step—namely, collecting pure noise images against a blackbody or a baffle. It may not resonate well with imaging systems without a baffle or a blackbody. Although one could obtain relatively clean background images by tilting the detector toward the sky, this method has limitations . Future endeavors could contemplate refining this preliminary step, striving for simultaneous acquisition of periodic noise frequencies while not compromising the real-time operation. While there is potential to dovetail neural network frameworks into our model, a salient point of contention remains. As underscored earlier, extant deep convolutional neural networks (CNNs) tailored for noisy image mitigation predominantly fixate on entire frame denoising. Their deployment complexities, especially when juxtaposed with real-time processing demands, stand as impediments. Additionally, the conspicuous absence of high-resolution training datasets further hinders the optimization and effectiveness of such neural networks.This research offers a novel solution to the prevalent challenge of low-frequency periodic signal noise induced by electromechanical interferences in infrared linear array detectors. We introduced an efficient denoising algorithm grounded in signal correlation principles, focusing on extracting and utilizing noise signals from pure backgrounds to achieve comprehensive denoising. The robustness and efficiency of our approach were validated through extensive simulations and real imagery tests, demonstrating notable enhancements in PSNR and superior denoising capabilities compared to existing methods. Notably, our algorithm maintained high performance even under substantial perturbations and noise variations, evidencing its adaptability to different noise conditions. Furthermore, the algorithm exhibited remarkable real-time efficiency in processing high-resolution images, showcasing its practical applicability and readiness for deployment in the embedded image preprocessing phase, ensuring minimal computational footprint and resource consumption. However, it is crucial to note that our algorithm necessitates a preliminary step of collecting pure noise images, which may pose limitations in certain working environments or system configurations. Future endeavors could focus on refining this preliminary step and exploring the integration of neural network frameworks, addressing the deployment complexities associated with real-time processing and the lack of high-resolution training datasets.


Climate change is a pressing global issue that demands immediate attention due to its far-reaching implications not just for the environment but also human well-being. As the Earth's climate continues to warm, extreme weather events, rising sea levels, and habitat destruction threaten ecosystems and livelihoods. The significance of climate change lies in its potential to disrupt the delicate balance of life on our planet. People play a crucial role in addressing this crisis by making informed environmental decisions  influence their support for policy measures, focusing on the five emotions of guilt, anger, hope, fear, and sadness. Recognizing the global scope and complexity of climate concerns, Böhm et al. use Appraisal Theory to examine cross-cultural differences in emotional reactions to climate change and climate related actions. Zhang et al. also bring an international scope studying how adolescents' happiness may influence their willingness to protect the environment using data from eight countries. Our penultimate article, Geiger et al. use meta-analysis to investigate the effectiveness of hope in promoting sustainable decisions.This Research Topic of Böhm et al.) and age . Investigating whether emotions differ in intensity and directionality depending on the type of environmental concern  and the geographic, cultural, or socio-economic context in which individuals are situated can provide valuable insights for tailoring communication and policy approaches.Future research on the role of individuals' emotions in environmental decision-making should further explore how emotional responses vary across different environmental issues and contexts beyond culture . Ultimately, these investigations can empower policymakers, educators, and activists to effectively harness emotions as a force for positive environmental change. Indeed, recognizing emotions not toward climate change itself but toward communication  will further expand how emotions play a role in sustainable decision-making. Policy-makers can design incentives and rewards that trigger positive emotions for adopting eco-friendly behaviors, reinforcing the link between personal well-being and environmental responsibility. Finally, new methods such as meta-analyses  can better assess the effectiveness of strategies and interventions beyond traditional psychological methods of surveys and experiments.Understanding the nuanced emotional landscape surrounding diverse environmental challenges can inform targeted interventions that resonate with individuals' emotional realities, fostering more profound connections to nature and driving meaningful pro-environmental actions. Additionally, research could delve into the interplay between emotions and cognitive processes in online environments as communication these days are largely done using social media , or guilt, pride and even sympathy  policy makers can highlight success stories and the transformative potential of sustainable practices, inspiring individuals to take action. By tapping into the emotional dimensions of decision-making, policy makers can foster a sense of shared responsibility and collective action, empowering individuals to become agents of positive environmental change.Indeed, policy-makers can strategically leverage people's emotions to promote environmentally friendly choices and decisions by employing targeted communication and policy interventions, as EC: Writing—original draft, Writing—review and editing. KH: Writing—original draft, Writing—review and editing. FS: Writing—original draft, Writing—review and editing.


The present review places emphasis on a comprehensive survey of experimental techniques to probe the structural and morphological features at the nanoscale range in thin magnetic films, incorporating those available at in-house laboratories as well as those at state-of-the-art synchrotron radiation facilities. This elucidating the range of available techniques, and the information they can yield represents a step for advancing the understanding of and for unlocking new possibilities in the design and optimization of thin magnetic films across a wide range of applications. Magnetic thin and ultrathin films are materials with a thickness of the order of a few nanometers or less, down to the atomic monolayers, exhibiting unique magnetic properties with respect to their bulk form mainly originating from their reduced dimensionality and interface phenomena ,2,3. TheThe initial drive behind the exploration of magnetic thin films was their potential to enhance data storage capacity, particularly for high and ultra-high densities. By manipulating the magnetization of these films, information can be encoded and retrieved in the form of magnetic bits. In this context, perpendicular magnetic anisotropy (PMA) has been identified for offering the smallest bit size and the highest storage capacity. Consequently, magnetic thin films have been developed as the active layer for data storage in magnetic recording media and magnetic memories . In receAs film thicknesses are reduced to nano and sub-nano scale dimensions, interfacial effects profoundly influence the intrinsic magnetic properties due to broken symmetry and altered electronic structure at boundaries ,50,51,52Various physical vapor deposition techniques are employed for thin-film growth, including molecular beam epitaxy (MBE), chemical vapor deposition (CVD), pulsed laser deposition (PLD), magnetron sputtering, electrodeposition (electroplating), atomic layer deposition, spin coating and sol gel synthesis ,56,57,58Considering all the above, quantitative morphological, structural and coordination chemistry analysis is thus imperative to reliably relate magnetic properties with the underlying structural landscape. The scope of this review is based on the state-of-the-art techniques available to date for the study of magnetic thin films, both in the laboratory (abbreviated as Lab. in the text below) and at large research facilities, such as synchrotron light sources (abbreviated as Sync. in the text below). Characterization techniques can be grouped into three main classes according to the information that can be obtained: morphological characterization techniques, scattering-based techniques, and spectroscopic-based techniques. Morphological information is generally derived from imaging tools such as microscopy-based techniques. Scattering techniques involving diffraction, small-angle scattering and reflectivity are generally based on X-ray or neutron radiations, they provide information about crystallographic phases, layer thickness, interface roughness and atomic structure in the film. Spectroscopic studies look at the response of the system as a function of energy and, depending on the probe used—electron, photon, neutron—provide chemically selective details of local composition, coordination chemistry, electronic structure and magnetization state. We will discuss the main techniques with specific examples below. This will enable the reader to navigate through a wide range of possibilities and identify specific combinations of techniques that are appropriate for their interests.Microscopy imaging techniques are critical for the morphological characterization of thin films because they provide nanoscale structural and compositional information that impacts properties. Techniques discussed below reveal grain size, grain boundaries, surface roughness and interfaces, and defects at high resolution. When coupled with spectroscopy, microscopy may provide compositional mapping and magnetic information. This multiscale morphological information is key to elucidating structure–property relationships in thin films.Transmission electron microscopy (TEM) is a powerful materials characterization technique that utilizes a high-energy electron beam transmitted through a thin specimen see . The intIn addition to conventional TEM, there are several specific applications of TEM-based techniques that can be suitably exploited for studying thin magnetic films and their interfaces. Scanning TEM (STEM) is like conventional TEM, but it scans a focused electron beam to reconstruct images. STEM can utilize different modes like bright field, dark field and high-angle annular dark field (HAADF) imaging to provide contrast based on composition, thickness, diffraction, etc. ,62. EnerIt is an essential characterization tool for understanding the structural and morphological properties of magnetic thin films. SEM utilizes a focused beam of electrons to image the sample surface see , providiFor magnetic thin films, key aspects studied via SEM include grain size, grain boundaries, film continuity and surface roughness. Grain size impacts magnetic properties like coercivity and anisotropy. Smaller grains lead to more grain boundaries, which act as pinning sites for domain wall motion, increasing coercivity. Anisotropy depends on crystal symmetry, so larger grains with fewer defects promote magnetocrystalline anisotropy. Film continuity is critical for properties like giant magnetoresistance in multilayers. Surface roughness affects domain structure and impacts magnetic behavior. SEM can also directly image magnetic domain patterns in the film when combined with electron backscatter diffraction (EBSD). The recent reviews on SEM analysis have been listed in Mass spectrometry is an analytical technique that uses a mass spectrometer to separate ions by their mass-to-charge ratio. It is a powerful yet (micro-)destructive tool that provides information about a given sample from both its surface ) and bulk (with a sensitivity of part per billion (ppb)) in comparison to EDS, AES (Auger electron spectroscopy) and XPS . It prov1 nm. The depth resolution is, however, higher thanks to Fabry–Perot-type interferometers that allows for a thickness resolution in thin films down to the atomic scale. The main limitations of SPLEEM are that it requires crystalline materials with a strong preferred crystal orientation that can produce a specular beam along the optical axis of the microscope to achieve a suitable resolution.For Low-Energy Electron Microscopy (LEEM), surfaces are imaged with the elastically backscattering of coherent low-energy electron beams that produce a high reflected electron intensity ,138. SPLSPLEEM has been used to address aspects of magnetic domain and domain wall structure in thin magnetic films and surface-supported nanostructures ,142,143,Photoemission Electron Microscopy (PEEM) is a powerful imaging technique. It combines photoelectron spectroscopies with microscopic techniques and is specifically useful to study thin magnetic films and interfaces ,153,154.Atomic force microscopy (AFM) has become an indispensable tool for the characterization and development of thin-film materials and devices, allowing for the wide probing of several surfaces and interfaces properties with nanoscale resolution. In AFM, a sharp tip on the end of a flexible cantilever scans across the sample surface while deflections of the cantilever are measured . These dThe main use of AFM is for surface topography. It can provide high-resolution images of thin films, revealing their surface roughness, grain boundaries and other surface features. By analyzing the height profile obtained from AFM images, the film thickness can be determined with nanometer-level precision. This is particularly useful for monitoring the growth or deposition process of thin films. By analyzing the force field, AFM can map the nanomechanical properties of thin films, such as their elastic modulus, adhesion and hardness. By exploiting different modes of AFM, such as force spectroscopy or nanoindentation, the local mechanical response of the film can be measured. This information is crucial for understanding the film’s behavior under different conditions and for optimizing its performance.1 nm scale resolution. Magnetic exchange force microscopy (MExFM) directly provides 2D maps describing the variation of magnetic exchange coupling strength. In this technique, a non-magnetic tip is used, and the interaction between the probe and the sample arises from the magnetic exchange coupling between the probe and the magnetic sample. The spin-polarized scanning tunneling microscopy (SP-STM) uses a magnetic tip to probe magnetic states with atomic resolution. It can directly observe nanoscale spin textures at surfaces and interfaces. Furthermore, 2D magnetic imaging can be performed while simultaneously applying electric or magnetic fields to reveal dynamic switching behavior. High-resolution AFM techniques can directly observe domain wall structure, pinning, and motion at surfaces and buried layers.Advanced AFM modes provide specific applications addressed to study magnetic nanostructures, giving a wealth of information critical for understanding the magnetic behavior of these thin films and interfaces. Magnetic force microscopy (MFM) is a specialized AFM mode that detects long-range magnetic forces between a magnetic tip and the sample surface. This method allows for the imaging of magnetic domain structures down to some 10To conclude the section of imaging methods, Scattering-based techniques rely on the interference of waves (radiation or particles) scattered from the sample. We focus here on X-ray-scattering techniques because neutron techniques require dedicated large-scale facilities, and electron diffraction is mainly focused on surface analysis due to the specific surface sensitivity of the electron probes. Although we notice that neutron-based techniques can be considered thanks to the specific sensitivity of neutrons to magnetic momentum, electron diffraction is routinely available at TEM facilities on suitably prepared thin-section samples.q) methods are used to provide crystallographic information in terms of unit cell symmetry and structure (average atomic positions in the unit cell). XRD is a well-known, laboratory available, non-destructive technique used primarily for the phase identification of crystal structures in bulk materials. Analysis of the diffractograms provides quantitative details such as particle size, strain, the degree of ordering, texturing and superstructures. Low-angle (or low q) methods are used to probe longer periodicities such as multilayers and superstructures. The role of X-ray diffraction in the characterization of thin epitaxial films, multilayers and superlattices have been reviewed in various studies . T. T112]. Resonant Inelastic X-ray Scattering (RIXS) has emerged as a suitable and powerful chemically selective technique for studying the electronic structure of materials. RIXS is a photon -in and a photon-out process in which the energy of incident X-rays is tuned to a specific atomic absorption edge in the sample  to resonantly excite core electrons into unoccupied states, which then undergoes a radiative decay to the final state . RevealiX-ray scattering and diffraction techniques provide critical insights into crystal structure, lattice spacing, epitaxial relations and texture in magnetic thin films. Small-angle X-ray scattering reveals magnetic domain sizes and correlations. Synchrotron-based X-ray spectroscopy elucidates element-specific magnetic properties with higher resolution. Advanced electron microscopy methods enable the direct imaging of magnetic domains, grains, defects and interfaces. Spectroscopy techniques help to analyze chemical composition and oxidation states at surfaces and interfaces. Neutron reflectometry provides depth-resolved magnetic structure profiling. Thus, by correlating macroscopic magnetic measurements with microscopic and spectroscopic characterization, fundamental structure–property relationships can be established in thin-film systems. Big data analytics and machine learning can accelerate knowledge discovery from multidimensional characterization datasets. Advanced simulations could guide interpretations. Overall, the continued development of operando techniques and multi-modal datasets would be helpful in providing deeper insight into magnetism in thin films.


Significant progress in the diagnosis and treatment of cardiovascular disease (CVD) has been made in the past decade, yet it remains a leading cause of morbidity and mortality globally, claiming an estimated 17.9 million deaths per year. Although encompassing any condition that affects the circulatory system, including thrombotic blockage, stenosis, aneurysms, blood clots and arteriosclerosis , the most prevalent underlying hallmark of CVD is atherosclerosis; the plaque-associated arterial thickening. Further, distinct CVD conditions have overlapping dysregulated molecular and cellular characteristics which underlie their development and progression, suggesting some common aetiology. The identification of heritable genetic mutations associated with the development of atherosclerotic vascular disease (AVD), in particular resulting from Genome Wide Association Studies (GWAS) studies has significantly improved the ability to identify individuals at risk. However, it is increasingly recognised that environmentally-acquired, epigenetic changes are key factors associated with atherosclerosis development. Increasing evidence suggests that these epigenetic changes, most notably DNA methylation and the misexpression of non-coding, microRNAs (miRNAs) are potentially both predictive and causal in AVD development. This, together with their reversible nature, makes them both useful biomarkers for disease and attractive therapeutic targets potentially to reverse AVD progression. We consider here the association of aberrant DNA methylation and dysregulated miRNA expression with the aetiology and progression of atherosclerosis, and the potential development of novel cell-based strategies to target these epigenetic changes therapeutically. Epigenetics is the study of mechanisms that regulate mitotically stable patterns of gene expression and hence cellular phenotype without altering the genomic sequence of the cell. The field has converged upon the locus-specific regulation of chromatin structure and accessibility by DNA methylation, the covalent and non-covalent modification of histones together with non-coding RNA-based mechanisms . Epigenetrans-acting factors and hence is a critical regulator of transcriptional gene expression  in the context of CpG dinucleotides and is controlled by enzymatic systems which add or remove methyl groups, termed writers and erasers. CpG dinucleotides are distributed unevenly across the genome, and regions rich in CpG dinucleotides are known as CpG islands. Characteristically, CpG islands have a GC content >50% and are at least 200 bp in size. They contain around 7% of total CpG dinucleotides present in the human genome and are commonly found within promoter regions such that 60% of human gene promoter sites contain CpG islands methylation has commonly been observed, associated with downregulation of key proteins that are essential in regulating the inflammatory response or those that are involved in the modulation of lipid pathways  , togetheDnmt3a and Tet2  within the atherosclerotic plaque arise from the clonal expansion of a few select cells within the medial arterial wall and although not conclusively proven, much evidence suggests that this is also the case in the human pathology . This rain vitro and in animal models in vivo  cells and CD34+ve HSPCs, strongly suggesting the existence of a common precursor cell , embryonic stem cells or induced pluripotent stem cells (iPSCs) as a vector, all of which have associated advantages and drawbacks [reviewed in -associated protein (CRISPR/Cas9) system is now widely implemented towards the goal of correcting specific mutations to treat a wide range of diseases . Many exiewed in ]. iPSCs iewed in . There iiewed in .Tet2 and Dnmt3a mutations within haematopoietic cells this may not present as an issue. However, as suggested above, mutations within these genes will also possibly be found to associate with EC and/or VSMC pathology. In this context, it is promising that ECs derived from EPCs in vitro can occupy the perivascular space when introduced into immuno-suppressed mice and anastomose with the host vasculature  marks. By fusing “dead” Cas9 to the catalytic domains of epigenetic writers and erasers, epigenetic changes can be introduced at specific sites, guided by CRISPR guide-RNAs (gRNAs) . Both siApproximately 99% of the human genome does not encode proteins . AlthougPerhaps unexpectedly, miRNAs have been found to be relatively stable and can readily be detected in body fluids including blood, urine and saliva. This is now believed to be predominantly due to their encapsulation within microvesicles and particularly exosomes . These aO-methyl (2′-OMe), phosphorothioate, 2′-O-methyoxyethyl (2′-MOE), 2′-fluoro (2′-F) and N,N–diethyl–4-- phenylamine (ZEN) modifications and locked nucleic acid (LNA) technologies. These are all aimed at increasing the stability and reducing the immune recognition of oligonucleotides while maintaining their binding affinity and specificity and functional efficacy .in vitro before injecting them either into the circulation or directly into the target site  and the efficiency with which they can cross cellular membranes . In thisget site . As requin vivo has also been demonstrated. Thus exosomes isolated from nicotine-treated macrophages induced VSMC proliferation and migration via the miR-21-3p-dependent targeting of PTEN in vitro, while in vivo they promoted the generation of atherosclerotic lesions in mice  somatic mutations within the epigenetic modifying enzymes, The misexpression of specific miRNA(s), when shown to be causal in atherosclerosis development, also represents a promising therapeutic target to treat the disease. Genetically-programmed cell-based therapies involving the generation of exosomes loaded with specific small RNA cargo are therefore also being developed. Further, the clinical use of  exosomes expressing therapeutically-beneficial miRNAs, isolated from stem cell populations offers great promise.Both the above approaches have significant inherent challenges to overcome and will rely on a fuller understanding of the methylation/miRNA changes involved, their causal relationship with the disease, and the involvement of specific cell-types in atherosclerosis pathology. This will be necessary both to inform the epigenetic changes to target and the choice of stem cell to engineer.


Antimicrobial resistance (AMR) was a leading cause of death globally in 2019. Sadly, COVID-19 has exacerbated AMR, nonetheless, the process of developing new antibiotics remains very challenging. This urgently requires the adoption of alternative approaches to treat multi-drug-resistant bacterial infections. This editorial introduces the ‘Bacteriophages against multi-drug resistant bacteria’ collection launched at BMC Infectious Diseases which highlights progress towards using bacteriophages to tackle AMR. The World Health Organization (WHO) has indicated that the global new antibiotic discovery pipeline is inadequate to address the mounting threat of antimicrobial resistance (AMR)  which isSince 2018, research demonstrating the application of bacteriophages against MDR bacterial infections has been steadily increasing. This has been matched by the global bacteriophage market that is projected to reach a value of USD 1,441.3 million by 2028 , therefoEnterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species are the leading cause of most MDR hospital-acquired infections  throughout the world causing life-threatening infections amongst the critically ill and immunocompromised patients. The development of novel MDR alternative treatment approaches such as the application of phage therapy has mainly targeted these pathogens. This is partly because besides causing serious nosocomial infections, ESKAPE organisms utilize a diverse array of antibiotic resistance and virulence mechanisms with the potential to disseminate them to other clinically important bacteria. Both MDR Klebsiella pneumoniae and Acinetobacter baumannii have been listed on the WHO’s most critical group of pathogens for prioritization regarding R & D of new antibiotics or other alternative therapies. These bacteria have become resistant to a large number of commonly used antibiotics, including third-generation cephalosporins and carbapenems. The latter reduces both the available treatment options and survival rates of the patients.A group of bacterial pathogens abbreviated as ESKAPE standing for; Acinetobacter baumannii, a common opportunistic nosocomial pathogen that is responsible for MDR infections [K. pneumoniae [K. pneumoniae is a member of the family Enterobacteriaceae and most often found associated with infections in healthcare settings and infections may be endogenous such as pneumonia, bloodstream infections, meningitis, and urinary tract infections. Compassionate use of bacteriophages for severe persistent infections during the first 5 years of the Israeli Phage Therapy Center showed that their number of registered requests was growing annually with MDR bacteria accounting for 38% of all phage requests [Some of the selected recent phage therapy reports, for example, have isolated a lytic phage against extensively drug-resistant fections  includineumoniae . K. pneuGlobally in 2021, at least 137 phage targets were listed from 135 academic and commercial phage facilities and 92 organizations such as phage banks, and biotechnology companies . The antAs a Guest Editor of this Collection titled, “Bacteriophages against multi-drug resistant bacteria”, I am honored to invite infectious diseases experts to contribute high-quality original research articles on advances made in the use of bacteriophages as a treatment for multi-drug and pan-drug resistant bacteria. This may include efficacy data generated through clinical trials or even compassionate phage therapy. Furthermore, manuscripts may also include work that explores the mechanisms of phage-bacteria interactions, the impact of phage therapy on the natural microflora composition of the human body, the development and optimization of phage therapy protocols, and findings from applications of phage therapy in tissues, humans, and animals among others. I am motivated to believe that this collection will greatly contribute to an in-depth understanding of this well-timed promising field and facilitate further innovation to guide the scale-up of phage therapy.


Extracellular vesicles (EVs) are nanoscale extracellular particles that have received widespread scientific attention for carrying a variety of biomolecules such as nucleic acids and proteins and participating in the process of intercellular information exchange, making them become a research hotspot due to their potential diagnostic value. Breast cancer is the leading cause of cancer-related death in women, approximately 90% of patient deaths are due to metastasis complications. Brain metastasis is an important cause of mortality in breast cancer patients, about 10–15% of breast cancer patients will develop brain metastasis. Therefore, early prevention of brain metastasis and the development of new treatments are crucial. Small EVs have been discovered to be involved in the entire process of breast cancer brain metastasis (BCBM), playing an important role in driving organ-specific metastasis, forming pre-metastatic niches, disrupting the blood-brain barrier, and promoting metastatic tumor cell proliferation. We summarize the mechanisms of small EVs in the aforementioned pathological processes at the cellular and molecular levels, and anticipate their potential applications in the treatment of breast cancer brain metastasis, with the hope of providing new ideas for the precise treatment of breast cancer brain metastasis. Cancer (IARC), the number of new breast cancer cases worldwide has reached 2.26 million in 2020, surpassing lung cancer as the world’s most common cancer. Breast cancer is the leading cause of death in females among malignant tumors  with the plasma membrane . HoweverThe International Society for Extracellular Vesicles (ISEV) has defined the term “extracellular vesicles (EVs)“ and defined EVs subtypes based on the physical characteristics of EVs, replacing “exosomes” and “microvesicles” to enable the early realization of the value of EVs as biomarkers or therapeutic applications. The term extracellular vesicle refers to natural particles released from the cell and delimited by a lipid bilayer and cannot self-replicate. Guidelines set by the ISEV2018 differentiate EVs subtypes based on physical characteristics such as EV size , density, and biochemical composition  . TetraspThis review will concentrate on small EVs and references dealing with “exosomes” will fall into this category as suggested by the ISEV. EVs can be produced and released by almost all cell types and are widely found in body fluids such as blood, saliva, and urine . Small EThe organ-preference patterns of tumor metastasis have been the greatest puzzle since Stephen Paget proposed the “seed and soil” hypothesis in 1889 . For instance, lung cancer, breast cancer, and melanoma are the most frequent metastasize to the brain . Recent For instance, In addition to the aforementioned studies, MicroRNAs (miRNAs) found in small EVs, in addition to proteins, have been shown to play an important role in the formation of pre-metastatic niches. The Warburg effect is known to be widespread in tumor cells with low adenosine-triphosphate (ATP) production efficiency . To meetThe blood-brain barrier (BBB) is a highly complex and dynamic central nervous system structure, mainly composed of brain microvascular endothelial cells (BMECs), pericytes, basement membranes, and astrocytes  Figure . BMECs aCancer cells secrete humoral factors during this event, causing BBB destruction and tumor cell extravasation , migration (lamellar pseudopods), and invasion (invasive pseudopods) . The majvia various pathways, including non-specific and receptor-mediated pathways (via endocytosis transport. via a specific Cdc42-dependent clathrin-independent carrier/GPI-AP-enriched compartment (CLIC/GEEC) endocytic pathway, downregulating the target gene TIMP-2, a matrix metalloproteinase inhibitor. This causes changes in the brain microenvironment, leading to the formation of an ecological niche favorable to tumor cell growth. These studies discover small EVs -driven mechanisms of transport across the BBB in breast cancer brain metastasis, which can be used to develop effective drug delivery methods and early intervention for breast cancer brain metastasis.Cells can internalize small EVs pathways . While mSuccessful extravasation of metastatic cells to distant metastatic sites often results in a dynamic cross-talk with the metastatic site microenvironment, altering resident cell gene expression patterns to facilitate their proliferation in a microenvironment significantly different from the primary organ . Small Ein vitro non-invasive blood sampling, liquid biopsy obtains circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), small EVs, and other tumor tissues shed in circulating blood, the information of which provides a strong basis for early diagnosis, disease assessment, efficacy follow-up, and prognosis prediction of tumor patients   . Using aetc.) , demonstetc.) . So this. Furthermore, these molecules may aid in small EVs-mediated drug delivery , which limits their effectiveness in treating patients with brain cancer (Chemotherapeutic medications are unable to efficiently enter the brain due to the BBB’s low permeability and the presence of numerous drug-resistance proteins (BCRP, P-gp, n cancer . Small En cancer . Small En cancer . Due to n cancer . Engineen cancer . New diaAs carriers of intercellular information exchange, small EVs have shown great promise in preliminary basic laboratory studies for clinical tumor diagnosis and treatment. However, there are some challenges in applying small EVs to clinical applications. The controversy between exosomes and extracellular vesicles has been described in detail in the previous section. In addition to this, the yield of natural small EVs is generally low and difficult to scale up. This creates some difficulties for research and clinical applications. It is unclear whether the resulting engineered small EVs can be used for clinical disease treatment due to their small size, complex components, low yield of isolation and purification, and difficulty in controlling the engineering modification technology.The most appealing aspect of small EVs in tumor metastasis research is their ability of organotropism and the formation of pre-metastatic ecological niches, and in the future, they hold promise as biomarkers for predicting the occurrence of brain metastasis in patients and for early intervention in such patients to prevent brain metastasis. However, the potential use of small EVs as a disease diagnostic marker is dependent on technological advances in small EVs-based drug delivery systems, and large-scale industrial production of small EVs for clinical therapeutic use faces significant challenges. The precise mechanism of small EVs uptake by target cells, which is critical to the use of small EVs as a drug delivery tool, has yet to be described.Small EVs’ ability to direct tumor organ propensity and mediate the formation of pre-metastatic ecological niches have provided researchers with new avenues to investigate the mechanisms of breast cancer brain metastasis. Currently, most research has concentrated on pre-metastatic ecological niches and BBB disruption, with only a few laboratories investigating the specific mechanisms by which small EVs promote the proliferation of metastatic tumor cells in the brain microenvironment. The prevention of brain metastasis is the focus of research; however, for the fraction of patients who have already had brain metastasis at the time of breast cancer diagnosis, effective therapeutic approaches are urgently needed. Thus, research on the mechanisms of dynamics and mutual cross-talk between tumor cells and metastatic niches is critical. If applicable, it would be greatly appreciated if relevant studies in this area could be increased. Fortunately, while studying the pathogenesis of breast cancer brain metastasis, some researchers are looking into new ways to treat brain metastases .In conclusion, investigating tumor cell mechanisms at the gene and protein levels during tumor development is a massive long-term project, but further investigation of the limited information contained in small EVs, as a key pathway of tumor cell information transfer, will undoubtedly provide strong guidance on tumor treatment strategies in the coming years. The ultimate goal is to prevent breast cancer patients without brain metastasis and even other types of tumors from developing, as well as to prolong the overall survival of patients with brain metastasis, and achieve long-term survival with tumors.


The management of bone defects is complicated by the presence of clinical conditions, such as critical-sized defects created by high-energy trauma, tumour resection, infection, and skeletal abnormalities, whereby the bone regeneration capacity is compromised. A bone scaffold is a three-dimensional structure matrix serving as a template to be implanted into the defects to promote vascularisation, growth factor recruitment, osteogenesis, osteoconduction, and mechanical support. This review aims to summarise the types and applications of natural and synthetic scaffolds currently adopted in bone tissue engineering. The merits and caveats of natural and synthetic scaffolds will be discussed. A naturally derived bone scaffold offers a microenvironment closer to in vivo conditions after decellularisation and demineralisation, exhibiting excellent bioactivity, biocompatibility, and osteogenic properties. Meanwhile, an artificially produced bone scaffold allows for scalability and consistency with minimal risk of disease transmission. The combination of different materials to form scaffolds, along with bone cell seeding, biochemical cue incorporation, and bioactive molecule functionalisation, can provide additional or improved scaffold properties, allowing for a faster bone repair rate in bone injuries. This is the direction for future research in the field of bone growth and repair. Healthy bone undergoes the proper coupling of bone resorption with osteoclasts and bone formation with osteoblasts to achieve physiological bone remodelling and systemic mineral homeostasis . It alsoA bone scaffold serves as a temporary platform that provides structural support, facilitates bone repair, and guides bone growth in bone defects . To inveDesigning a scaffold which facilitates the structural and functional restoration of the bone remains a critical challenge. Scaffolds are usually derived from living organisms or from synthetic origins. A natural scaffold has similar extracellular matrix characteristics to the bone, superior biocompatibility and bioactivity; however, the variability, batch-to-batch inconsistency, and ethical concerns raised by using animal-derived scaffolds make them less desirable. On the other hand, a synthetic scaffold enables the modification, consistency, reproducibility, availability, and selection of low-cost materials. Previous reviews have provided detailed descriptions of the characterisation of natural and synthetic polymer-based nanocomposites, as well as scaffold design and fabrication ,7. The cScaffolds originating from animals  and humans have been used by researchers to examine their effects on bone regeneration .The trabecular region of animal and human bone can be used to develop bone scaffolds. However, bones derived from one host induce an immune response after implantation in another host . For insSeveral groups of investigators have developed decellularised bovine bone scaffolds using a combination of different decellularization methods. Shahabipour et al. obtained cancellous bone scaffolds (5 mm diameter × 2 mm height) from the epiphyseal of the bovine femur, which was subjected to immersion in hot water for lipid removal and freeze–thaw cycles for cell lysis. After that, chemical treatment ensued using sodium dodecyl sulphate with gentle agitation. The complete removal of cells with similar structural properties to native bones were noted after the decellularisation process. Histological analysis and scanning electron microscopy showed increased cell growth, adhesion, and integration on the decellularised bone scaffold after seeding with rat bone marrow mesenchymal stem cells . Bianco Bone demineralisation is another strategy used along with bone decellularisation to improve the preparation of bone scaffolds from natural sources. It is a process of removing fat residues, impurities, and inorganic minerals while leaving the collagen matrix and bone morphogenetic proteins in the bone . DeminerA study by Shi et al. demonstrated that the demineralised bone matrix derived from bovine bone had good degradation activity as well as providing a suitable microenvironment for cell attachment and bone mineralisation after 14 days of incubation with human umbilical cord mesenchymal stem cells . RecentlSepia officinalis. The hydrothermal transformation approach converts the calcium carbonate in cuttlefish bone into calcium phosphate (hydroxyapatite). The scaffold was tested with mouse osteoblast-like cells (MC3T3-E1) for the expression of osteogenic markers. The level of alkaline phosphatase (ALP) was increased at an early stage of cell differentiation and the expression of osteocalcin (OCN) was elevated at the later stage of osteogenesis. These results reiterated that the hydroxyapatite porous scaffolds derived from cuttlefish bone support the expression of bone-related proteins involved in osteoblast cell proliferation and bone calcification [Apart from bovine bone, cuttlefish is a marine vertebrate and the bone of cuttlefish can be used to develop bone scaffold. Cuttlefish bone consists of calcium carbonate mimicking the chemical, crystallographic structures, and morphology of the mineral phase of natural bone . Cuttleffication .Oreochromis mossambicus). The scaffold was characterised by its mechanical behaviours and biological properties. The findings showed that the fabricated scaffold exhibited higher tensile and compressive strength compared to the native bones from humans, cattle, swines and horses. An in vitro experiment culturing human osteoblast cells (MG63) on the fish scales-derived hydroxyapatite scaffold found similar cell viability to the control hydroxyapatite without fish scales. The scaffold was tested in vivo by implanting the test materials into the bone defect created at the cortex region of the rabbit’s left femur. The microscopic view of the bone defect region showed good bio-affinity and osteoconductivity, evidenced by the infiltration of cells into the materials and the presence of new cell lining [Fish scales are biowaste materials that can be processed into hydroxyapatite powder. A scaffold made from fish scales mimics the crystallographic structure, phase, composition, and morphology of native bone . A naturl lining .Cockle shells are biowaste products from consumed cockles or molluscs, such as mussels or scallops. Cockle shells consist of the pure aragonite form of calcium carbonate polymorph that can be replaced by bones, making it suitable to be used as bone scaffolds . A study®-processed human bone. It is a bone graft generated through an alkaline treatment for delipidisation, an osmotic treatment to break down the cell wall, an oxidative treatment to remove the immunogenic structures of viruses, solvent dehydration to preserve the natural tissue matrix, and a γ-irradiation procedure to sterilise the graft. Cells seeded onto the Tutoplast®-processed human bone showed good cell adhesion and higher osteoblastic gene expression after a week. The subcutaneous grafting of biomaterial containing hBMSCs in 7-week-old severe combined immunodeficient (SCID) mice resulted in bone neoformation as early as two weeks after implantation [A study by Mebarki et al. investigated the characteristics of hBMSCs when cultured onto Tutoplastantation .Researchers have attempted to combine several natural materials to establish new bone scaffolds. Collagen is the most abundant protein in the human body and a main component of the connective tissues, including tendons, ligaments, and bones. It appears as an ideal material for bone repair mainly attributable to its compatibility, degradability, strong plasticity, and low immunogenicity. The combination of collagen with other bioactive materials is often preferable because pure collagen lacks geometrical properties due to its low biomechanical strength and exerts insufficient osteogenic activity to stimulate bone formation , hence lRecently, a biomimetic composite scaffold was developed using an eggshell membrane as a template with the addition of tricalcium phosphate from bovine bone ash, gelatin, and chitosan . GelatinIn summary, natural scaffolds originating from animals support cell growth, attachment, proliferation, and functionality. However, the shortcomings of the previous investigations and the use of bone scaffolds from animals need to be acknowledged. Firstly, a static culturing environment is often used on animal bone scaffolds. The lack of sufficient oxygen and nutrient supply and the accumulation of metabolic waste products limit cell growth and form irregular cell density within the scaffold. This problem can be solved by developing a bioreactor system which provides a dynamic environment for cell-loaded scaffold culture . SecondlBone scaffolds from plant tissue serve as an alternative to scaffolds obtained from animals and humans, overcoming the issues of immunogenicity and ethical concerns about the use of animal- and human-derived bone scaffolds.Various three-dimensional cellulose constructs of plants  with various sizes and shapes have been decellularised and tested for their ability to serve as scaffolds to enhance osteoblast growth and proliferation . Among tPlant materials used for scaffold establishment can be obtained conveniently in a mass as they are abundantly grown in various topographies on earth. Similar to animal-derived scaffolds, plant-derived scaffolds have been proven to have bone regeneration properties. However, their mechanical properties may be considerably lower than those of natural bone tissue. Plant scaffolds could be applied clinically as bone filler in non-load-bearing sites. In addition, their combination with other inorganic biocomposites (such as hydroxyapaptite) could be considered to enhance their mechanical strength. The properties of natural scaffolds in bone tissue engineering have been summarised in Calcium phosphate cement is a bioactive grafting material typically used in orthopaedic applications for bone regeneration due to its similarity to natural bone mineral composition. It exists in the form of a powder and sets as hydroxyapatite upon the addition of a liquid phase. Calcium phosphate cement and hydroxyapatite exhibit great biocompatibility, osteoconductivity, resorbability, self-setting ability, injectability, and mouldability. It can act as a controlled drug carrier . Many st® nude mice resulted in increases in total bone formation, mature bone formation, and neovascularisation [Chen et al. studied the efficacy of β-TCP scaffold co-cultured with human bone marrow stem cells and periosteal-derived stem cells in athymic mice. The insertion of a scaffold with co-cultured cells into the subcutaneous dorsal surface of CD-1risation . A studyrisation .Leventis et al. created a circular bicortical critical-size cranial defect in male New Zealand white rabbits, which was grafted with a synthetic scaffold containing β-TCP and calcium sulphate. Six weeks after implantation, the grafted material was observed to have incorporated with the bone and showed no inflammatory responses. Histological results showed no decrease in the osteoblast number (Ob.N), osteoblast perimeter (Ob.Pm), or fibrous connective tissue area (Fb.Ar), but showed a decrease in the graft volume/tissue volume (Gr.V/TV) and graft area (Gr.Ar), and marginal increases in BV/TV, osteoid volume/tissue volume (OV/TV), bone area (B.Ar), osteoid area (O.Ar), osteoid perimeter (O.Pm), osteoclast number (Oc.N), and mineralisation. The biphasic scaffolds composed of β-TCP and calcium sulphate showed excellent biocompatibility, osteoconductivity, and biodegradability .The clinical application of calcium phosphate cement and hydroxyapatite has also been reported. An earlier study carried out by Mattson et al. indicated that the augmentation of calcium phosphate cement improved the stability of fractures by lowering fracture movement and rotation in patients with unstable trochanteric fractures (aged 66–95 years old) . RecentlThe major limitations of calcium phosphate cement and hydroxyapatite include low mechanical performance, poor washout resistance, and lack of osteogenic activities. The incorporation of other materials into calcium phosphate cement and hydroxyapatite has been proven to overcome these shortcomings and/or enhance the original features of the biomaterials ,42. NairIn addition, Shi et al. established a three-dimensional scaffold consisting of dopamine-modified alginate and quaternised chitosan-templated hydroxyapatite. The scaffold was created to enhance the biomechanical strength of the scaffold. The bone-repairing properties of the scaffold were studied in both in vitro and in vivo studies. The dopamine-modified alginate and quaternised chitosan-templated hydroxyapatite was shown to support cell adhesion and the growth of human chondrocytes and fibroblasts. Using an in vivo model of New Zealand white rabbits with femoral bone defects, the implanted scaffold promoted new bone formation and accelerated defect healing .A recent study by Dulany et al. evaluated the in vitro and in vivo behaviours of β-TCP added with poly and cerium oxide nanoparticles using primary human osteoblasts and a healthy rat model. Findings from the in vitro study indicated promising cell attachment, low cytotoxicity, increased cell proliferation, and mineralisation of osteoblast cells on nanocomposite scaffolds under normal and oxidative stress conditions. The nanocomposite scaffolds were also implanted subcutaneously into the eight-week-old Sprague–Dawley rats. It was found that the nanocomposite scaffolds exhibited biocompatible properties, evidenced by the presence of cell infiltration throughout the scaffolds and a minimal immune response of the surrounding tissues. In addition, scaffold degradation occurred after 30 days from implantation. The postulated underlying mechanism for bone tissue generation was mediation through the free radical scavenging property, facilitating the reduction of oxidative stress .In conclusion, calcium phosphate cement and hydroxyapatite are commonly used by researchers in scaffold compositions as they provide great biocompatibility to the cells cultured on them. In addition, calcium phosphate cement and hydroxyapatite scaffold were rarely rejected by the animal or human hosts in observations of the union of graft materials with the host bone. Reinforcement utilising biological or synthetic materials also helps in improving the shortcomings and increasing the effectiveness of calcium phosphate cement and hydroxyapatite. The use of calcium phosphate cement and hydroxyapatite scaffold in vivo, in vitro, and in humans is summarised in Bioglasses, or bioactive glasses, are highly reactive silicone-based glass-ceramic biomaterials that contain calcium and phosphorus. They release ions and form a carbonated hydroxyapatite layer when immersed in biological fluids, promoting protein adsorption for bone formation and implant–bone integration . The bio® in polyvinyl alcohol as the porogen. The findings of the in vitro study indicated that bioglass was a good graft material for bone regeneration. There was no cytotoxicity, but increased cell proliferation was reported in the mono- and co-cultures seeded onto the bioglass-derived porous scaffolds. The scaffolds also showed an excellent interconnected porous structure, allowing for excellent cell penetration from the outer to the inner layer of the scaffolds when observed with a scanning electron microscope. The proliferation response of the human osteoblast cells seeded on the bioglass was found to be better than for hydroxyapatite [2), sodium oxide (Na2O), potassium oxide (K2O), magnesium oxide (MgO), calcium oxide (CaO), and phosphorus pentoxide (P2O5). Their novel biomaterial scaffold was implanted into a non-critical-sized tibial defect of male Wistar rats to investigate the in vivo tissue response. The novel scaffold showed complete degradation over time, a lack of inflammatory response, new bone formation, an increased Runt-related transcription factor 2 (Runx-2) expression, and a higher maximal load [An earlier study by Deb and colleagues used bioglass as a graft material in both the mono- and co-culture of primary human osteoblasts and human umbilical vein endothelial cells (HUVECs). The scaffold was fabricated using powdered 45S5 Bio-glassyapatite . Gabbai-mal load . Anothermal load .Given that the bioglass did not achieve comparable bone healing properties to the autografts , researcAn in vivo study carried out by Li et al. assessed the effect of baghdadite scaffold unmodified, or modified with polycaprolactone coating containing bioactive glass nanoparticles, on bone regeneration in a sheep model with bone defects. A critical-sized segmented bone defect was created at the right tibia of Merino wethers, and the scaffolds were implanted. The defect site was then subjected to radiographic, biomechanical, micro-computed tomography, and histological assessments after 26 weeks. Both the unmodified and modified baghdadite scaffolds showed similar outcomes for interconnected porosity, bone remodelling, new bone formation within the area of defect, good integration, bone infiltration, and new bone ingrowth. A biomechanical analysis showed no difference in torsional stiffness and ultimate torsional strength between the animals inserted with the unmodified or modified baghdadite scaffolds .In summary, the documented evidence indicates that bioglass is a potential biomaterial for bone tissue regeneration, with an efficacy higher than hydroxyapatite but lower than autologous bone. Bioglass contains alkali metals that provide an optimum alkaline environment which promote osteoblast proliferation and inhibit osteoclast production, thus suggesting it as a biomaterial superior to hydroxyapatite, which is slightly acidic. The clinical uses of bioglass have been extensively implemented in the field of dental and maxillofacial applications , with leChitosan mimics the glycosaminoglycans of the extracellular matrix which facilitate cellular adhesion. Pure chitosan has weak mechanical strength due to its linear structure in nature. Hence, it is a limiting factor in its use for the purpose of bone tissue engineering . The preThe combination of commercially purchased chitosan and hydroxyapatite increased the compression strength of the scaffolds as compared to the pure chitosan scaffolds. Seeding with MC3T3-E1 cells resulted in good cell attachment, proliferation, and differentiation on the exterior surface and within the pores of the chitosan–hydroxyapatite scaffold . SimilarWith the continuous advancement of technology, the use of nanoparticles has been a valuable and promising material due to their nanoscale size, high surface area, excellent biocompatibility, and easy functionalisation which fulfils the requirements of bone tissue engineering. Silica serves as a material involved in the early stages of bone calcification by allowing the crystallisation of apatite crystals, cell adhesion, and the formation of collagen. Its nano-sized particles provide a larger surface area which enables interaction with the surrounding bone tissues, hence improving the bioactivity of the composite scaffold . The chi4)-layered double hydroxide . Both nanofillers have opposite surface charges facilitating sustained drug delivery in the chitosan matrix. An in vitro study using mouse embryonic fibroblast (NIH 3T3) cells demonstrated great biocompatibility, mechanical strength, and no cytotoxicity. The rats subjected to femoral bone defects which were filled with the test scaffold showed greater bone healing, denser bone morphology, and higher osteoblast numbers as compared to the rats implanted with pure chitosan scaffolds, with no observable adverse effect on the liver or kidneys [Nanohybrid technology using several types of nanofillers , has also been adopted to improve the mechanical properties of chitosan. Mahanta et al. fabricated a nanohybrid chitosan scaffold using nanoclay  and magnesium aluminium phosphate oxide  have been used to enhance gelatin-derived scaffolds. Kwon et al. utilised bioglass to improve the mechanical strength of methacrylated gelatin. The incorporation of these biomaterials showed promising results in bone regeneration in vivo and in vitro. The seeding of human tonsil-derived mesenchymal stem cells on bioglass-incorporated methacrylated gelatin demonstrated a non-cytotoxic cellular response and an increased bone-related gene expression of OCN, COL1, and Runx-2. Staining with Alizarin Red showed an increase in calcium content when the cells were cultured on methacrylated gelatin incorporated with bioglass. In female BALB/c mice, the bioglass embedded in methacrylated gelatin was implanted into the cranial defect. The micro-computed tomography results showed a linear increase in BV/TV with an increasing concentration of bioglass. Haematoxylin and eosin, as well as Masson’s trichome staining, indicated the enhancement in bone tissue regeneration at the defect site . The stuAnada et al. synthesised hydrogel constructs, consisting of spheroids of HUVECs representing the bone marrow space, and gelatin methacrylate and octacalcium phosphate representing the cortical bone, via three-dimensional bioprinting technology. Octacalcium phosphate is a calcium phosphate that can be transformed into hydroxyapatite under physiological conditions, suggesting its role as a precursor for bones and teeth. The hydrogel constructs reinforced with octacalcium phosphate successfully induced osteogenesis and angiogenesis, evidenced by the increased proliferation of mouse multipotent mesenchymal C3H10T1/2 cells, ALP activity, and sprout formation . Apart fA chitosan-based hydrogel was developed and reinforced using metal organic frameworks  and modified with catechol to promote blood supply, osteogenic differentiation, bone reconstruction, and support the polymer framework of the bone graft. The properties of the synthesised hydrogel were characterised in vitro using rat bone marrow mesenchymal stem cells and in vivo using Sprague–Dawley rats with a cranial defect. The osteogenic and angiogenic activities of the rat bone marrow mesenchymal stem cells were enhanced. In animals, micro-CT analysis identified new bone formation with a thicker structure and increased BV/TV. Histological staining showed completely healed bones with mineralisation of collagen fibres, new blood vessels, and fewer inflammatory cells .In brief, hydrogel exhibits superior biocompatibility, biodegradability, osteogenic capability, injectability, and drug delivery to enable optimum bone repair with minimal invasive procedures during bone graft substitution and implantation. However, hydrogel obtained solely from natural sources might be insufficient to provide greater mechanical strength, thus its application could be limited to bone regeneration purposes at non-load bearing sites. The incorporation of other synthetic materials has been proposed to strengthen the mechanical properties of hydrogel-derived scaffolds. A summary of the use of hydrogel as bone scaffolds in vivo and in vitro is presented in PMMA is a synthetic resin produced from the polymerization of methyl methacrylate. It is clinically applicable in the orthopaedic field, attributable to its stable mechanical properties and surgical operability. Some disadvantages of PMMA include: (a) a high exothermic reaction causes thermal necrosis to the surrounding bone tissues; (b) it is bioinert and its poor biocompatibility inhibits cell adherence, bone formation, and causes loosening of the implantation; (c) high stiffness may increase the risk of adjacent fractures after surgery ,76; and Calcium phosphate is an osteoconductive material that allows the release of calcium and phosphorus leading to the improvement of cement-to-bone bonding. The degradation of calcium phosphate subsequently induces porosities in the PMMA scaffold, thus stimulating secondary bone ingrowth. Lye et al. introduced a composite scaffold comprising β-TCP and PMMA into a rabbit model of a bilateral mandibular defect. Histological analysis indicated good scaffolding and defect bridging, no inflammation, extensive resorption of β-TCP, and the presence of intervening fibrous tissue after 15 weeks from implantation . Fang etMetallic nanoparticles, such as magnesium oxide (MgO), possess excellent mechanical properties and durability. MgO nanoparticles release magnesium ions to activate alkaline phosphatase, enhance bone tissue formation, regulate cell functions , as well as preventing adverse reactions by the rapid degradation of magnesium. Li et al. incorporated MgO into a PMMA scaffold and tested its osteogenic capabilities on a calvarial critical bone defect in a rat model. The micro-CT and histomorphometry analysis demonstrated new bone formation and increased BMD in the animals. The better biocompatibility of the mouse embryo osteoblast precursor cells, increased formation of calcium nodules, and higher osteogenic gene expression were noted after seeding on the composite nano-metallic-polymer scaffold .Platelet gel is formed by the activation of platelet-rich plasma via the addition of calcium chloride and/or thrombin. Platelet-rich plasma possesses the excellent characteristics of osteoconductivity and osteoinductivity due to its high content of growth factors which are essential for bone regeneration. A previous study demonstrated that the implantation of a PMMA scaffold added with platelet gel into a rat model of a forearm radii defect resulted in less inflammation, complete degradation of the grafting material, and increased bone formation and densities of the cartilaginous osseous tissues 8 weeks post-injury. The bone healing potential was comparable between the PMMA-platelet gel scaffold and an autograft . LinoleiOverall, PMMA as a single filler material for bone defects lacks biocompatibility, osteoconductivity, osteoinductivity, and osteogenic properties. In addition, the high stiffness of plain PMMA may contribute to an increased fracture risk, particularly of the adjacent osteoporotic bone. Hence, the addition of a bioactive component ensures better functionality of PMMA. A summary of the use of PMMA as bone scaffolds in vivo and in vitro is presented in The most extensively investigated synthetic biodegradable polymers for bone tissue engineering include poly(glycolic acid) (PGA), poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA), and polycaprolactone (PCL). They are linear polymers of lactic acid, glycolic acid, and/or ester synthesised through polymerisation processes.PGA has high crystallinity with a controlled degradation rate whereby the mechanical strength decreases after two to four weeks from implantation . In an iPLA has excellent mechanical and thermal properties. A study by Wang et al. designed pure PLA scaffolds with and without the addition of nano-hydroxyapatite. Both scaffolds were biocompatible and not toxic to rabbit bone marrow mesenchymal stem cells. The formation of calcium nodules and the expression of osteogenic bone markers were also detected in cells cultured on pure PLA and composite scaffolds, with a higher level in the composite scaffolds as compared to the pure PLA scaffold. An in vivo study demonstrated good osteointegration and biocompatibility of the scaffold, with no inflammation and no tissue necrosis after implantation of pure PLA and composite scaffolds in male New Zealand white rabbits with a femoral defect. The composite scaffold showed a higher rate of new bone growth and BV/TV than the pure PLA scaffold .PLGA is a co-polymer of lactic acid and glycolic acid. The ratio between lactic acid and glycolic acid can be adjusted to control the degradation time of PLGA. Double-layered PLGA scaffolds with different pore sizes in different layers were prepared by several groups of researchers to mimic natural cartilage and subchondral bone. Their in vivo bone-repairing ability was examined in osteochondral tissue. A study by Duan et al. demonstrated that PLGA scaffolds with 100–200 μm pores in the chondral layer and 300–450 μm pores in the osseous layer exhibited the best results in stimulating the regeneration of articular cartilage and subchondral bone in a rabbit model of osteochondral defects after 12 weeks. The seeding of bone marrow mesenchymal stem cells further enhanced the osteogenic properties of the bilayer scaffolds ,89. AnotReinforcement of the PLGA scaffold has been conducted by researchers. Oizumi et al. introduced octacalcium phosphate into the PLGA scaffold and its osteoinductivity was examined in rats with a femoral defect. The results showed the formation of new trabecular bone as early as 4 weeks and the bone defect was almost completely bridged 8 weeks after the octacalcium phosphate/PLGA scaffold implantation, and its bone repair ability was superior when compared to PLGA alone. The results from micro-computed tomography supported the histological findings, indicating higher BV/TV, Tb.Th, and lower Tb.Sp eight weeks post-implantation. Accumulation of tartrate-resistant acid phosphatase-positive osteoclast-like cells was observed at week 4, whereas osteocalcin-positive osteoblastic cells appeared at week 8, reiterating the biodegradation of the implanted scaffold followed by new bone formation at the defect site .Chen et al. incorporated icaritin and tricalcium phosphate into the PLGA scaffold. Icaritin serves as an exogenous growth factor, whereas tricalcium phosphate balances the pH during the degradation of PLGA to reduce inflammation. The composite scaffold resulted in the formation of mineralised bones and blood vessels when implanted in an ulnar-bone-defect rabbit model . In anotPCL is a biodegradable polyester with thermal stability, elasticity, flexibility, permeability to small drug molecules, and biocompatibility, but a slow degradation rate when compared to other synthetic biodegradable polymers. With these features, it has been suggested that PCL could be more appropriate as a long-term implant or used in combination with other polymer biomaterials . Yao et In general, synthetic biodegradable polymers offer several advantages. First, the degradation products  can be safely metabolised and excreted through physiological metabolic cycles. Second, they have a high tensile and elastic modulus, but their strength decreases with the gradual degradation of the implant time. This dynamic characteristic provides good mechanical properties to support the bone defect site. Third, the polymers can be incorporated with various bioactive factors to facilitate bone regeneration . The exc®-processed human bone as compared to hydroxyapatite/β-TCP scaffold, due to the open pore structure and interconnectivity of the Tutoplast®-processed human bone. A higher receptor activator of the nuclear factor-kappa B ligand (RANKL) expression was noted when hBMSCs were loaded on the hydroxyapatite/β-TCP scaffold relative to the Tutoplast®-processed human bone. In vivo, the frequency of bone formation was higher in mice implanted with the natural Tutoplast®-processed human bone as compared to those implanted with the synthetic hydroxyapatite/β-TCP scaffold [The naturally derived scaffolds better mimic the native architecture of a bone than synthetic scaffolds in allowing and supporting cellular growth . Mebarkiscaffold . Althougscaffold . DeminerSynthetic scaffolds offer several advantages over natural scaffolds. Firstly, the chemical composition is controllable to ensure excellent mechanical strength. For instance, the combination of hydroxyapatite with silica mixture provides a greater mechanical strength that supports tensile stress and manages to bear loads . SecondlLimitations to the current evidence need to be addressed. Limited studies have been conducted to compare the potential use of natural and synthetic scaffolds under the same experimental setting. Moreover, although the osteogenic properties of natural and synthetic scaffolds have been proven, their vascularisation capacity should not be neglected. More comprehensive research is warranted to improve vascularisation by allowing cells to form microvasculatures in the scaffold prior to implantation. Several considerations in developing bone scaffolds for bone tissue engineering need to be acknowledged. The biocompatibility of a bone scaffold refers to the ability of the material to function in a living organism with no risk of immunological rejection and inflammatory response. This remains the indispensable feature an ideal material for application in bone tissue engineering must fulfil. Synthesising an engineered bone that mimics an in vivo situation requires the optimisation of the porosity–strength relationship. Adequate mechanical strength is needed from the time of implantation until the bone remodelling process is complete. Meanwhile, an ideal porosity with a large surface area is essential for osteointegration between the scaffold and host tissues. Another aspect that limits the clinical application of bone scaffolds is the healing process, which could vary depending on the patient’s condition. A commercially viable bone scaffold should be cost-effective and able to be scaled up into batch production with good manufacturing practices and a long shelf availability to be translated into a clinical application. However, the bone repair process is rapid in young and healthy individuals, but slows down in individuals who are elderly and who have medical conditions. Hence, a tailor-made bone graft is a way forward which could lead to a higher cost of fabrication.Both natural and synthetic scaffolds have their unique advantages and disadvantages, whereby the former is ideal for its bioactivity and biocompatibility, whereas the latter enables better control of mechanics, geometry, porosity, and degradation rate. The current advancements in bone tissue engineering should focus on the development of bone substitutes with a combination of the three main aspects, including scaffold, cells, and osteoconductive stimuli, to better mimic the physiological condition of endogenous bone. The combination of natural and synthetic materials could be a better choice given the merits of the intrinsic biocompatibility of natural scaffolds and the physicochemical properties of synthetic materials in the fabrication of biocomposites in bone tissue engineering.