The rapidly evolving discipline of biological and biomedical engineering requires adaptive instructional approaches that teach students to target and solve multi-pronged and ill-structured problems at the cutting edge of scientific research. Here we present a modular approach to designing a lab-based course in the emerging field of biofabrication and biological design, leading to a final capstone design project that requires students to formulate and test a hypothesis using the scientific method.Students were assessed on a range of metrics designed to evaluate the format of the course, the efficacy of the format for teaching new topics and concepts, and the depth of the contribution this course made to students training for biological engineering careers. The evaluation showed that the problem-based format of the course was well suited to teaching students how to use the scientific method to investigate and uncover the fundamental biological design rules that govern the field of biofabrication.We show that this approach is an efficient and effective method of translating emergent scientific principles from the lab bench to the classroom and training the next generation of biological and biomedical engineers for careers as researchers and industry practicians.The online version of this article (doi:10.1186/s13036-016-0032-5) contains supplementary material, which is available to authorized users. Training engineers to solve ill-structured real-world problems, including the unanticipated complications and conflicting constraints such problems entail, has long been a challenge to engineering educators. The traditional lecture-based approach of teaching a set curriculum, which focuses on solving well-structured problems, does not yield a skill set that is readily transferrable to engineering practice . This fiLab- and project-based approaches have successful records of teaching core engineering principles in interdisciplinary fields , 6. ThisThis study employed four teams of two students each, all senior undergraduates in the bioengineering program at the University of Illinois at Urbana-Champaign (UIUC) and enrolled in “BioE 306: Biofabrication Lab”. Since proficiency in aseptic mammalian cell culture technique is a pre-requisite to the labs in this course, enrollment was limited to students who had previously completed a cell culture lab course required of sophomores in the bioengineering program. Enrolled students were also required to complete online safety training as required by the Division of Research Safety (IBC-3923) and undergo a practical laboratory test on aseptic cell culture technique during the first week of class.The course (BioE 306: Biofabrication) was structured as a series of four labs, each addressing a distinct aspect of biofabrication and tissue engineering, leading up to the final capstone project that required students to draw on skills learned in the prior labs , computer-aided design (CAD) project (10 %), team laboratory reports  and a final presentation on the capstone design project (30 %) to course instructors, fellow students, and professors and graduate student researchers in related fields.U tests with p values signified in figure captions. This study was approved by the Institutional Review Board (Reference #12224). All students in the course signed consent forms before participating in this study.Students were assessed on the metrics listed in Table The quantitative survey metrics assessed over the course of the class all increased from the mid- to end-course time points, indicating an overall positive trend in the students’ course experience , and 40 % of students cited lab reports as the aspect of the course that helped them learn most efficiently (the other 60 % cited lab work).The capstone project was intentionally designed to be open-ended, requiring that students form a hypothesis and devise a robust experiment to test that hypothesis using the techniques taught in previous labs. Specifically, students were asked to design and build a biological machine to achieve a functional behavior relevant to an application in biomedical engineering. The student teams, which were self-assigned, reported no conflicts over the course of the semester. Indeed, two of the teams coalesced to form a larger team for the capstone project, in order to test more sample sets and generate more data. Some students attempted to make the walking bio-bots developed in Lab 4 walk at greater speeds by incorporating flexible 3D printed hinges into the bio-bot skeletons. Other students designed an entirely new 3D printed skeleton, mimicking the natural architecture of the esophagus in the human body, to create a muscle-powered peristaltic pump that could potentially be used as an implant for applications in regenerative medicine. Another group of students incorporated skills taught in other bioengineering undergraduate classes, such as genetic engineering of cells and bioinstrumentation, to incorporate new functionalities into the biological machines they had learned to fabricate. The student projects thus displayed broad diversity in terms of target application, while still maintaining a core focus in biofabrication. This served as additional validation that the capstone design project provided students with the unique opportunity to freely pursue empirical inquiry in the field of biomedical engineering and understand the underlying design rules and principles of “building with biology”.Students were actively engaged in the final project throughout the semester, and presented their ideas for the capstone to instructors prior to the scheduled start of the final lab. The layered roles of the primary instructor with expertise in teaching fundamental biological concepts, the guest lecturer specializing in the topic area of biofabrication and biological machines, and the teaching assistant well versed in the experimental techniques, provided students with different types and levels of individual mentorship and attention, which has been shown to generate positive learning outcomes .By the end of the semester, 100 % of the students in the class indicated that the course fulfilled their expectations, that they enjoyed the course experience, and that they would recommend the course to other students. Additionally, all the student presented their capstone design projects to professors and graduate students in the department working in relevant research fields, and 50 % of the students in the class signed up to continue working on their final projects the following semester under the guidance of the guest lecturer and course instructor. As ethics training is an especially important component of biomedical engineering education , 20, allThe rapidly evolving field of biomedical engineering requires adaptive teaching approaches that teach students how to target and solve multi-pronged and ill-structured problems at the cutting edge of scientific research. This is especially important in interdisciplinary fields such as biomedical engineering, as they are subject to many types of conflicting constraints, and require problem-solvers that are well versed in a variety of relevant topics while maintaining depth of expertise in specific focus disciplines. One such discipline that is widely applicable across the field of biomedical engineering, as well as the adjacent fields of mechanical, materials science, and chemical engineering, is that of biofabrication – using modern manufacturing technologies (such as 3D printing) to design and build with biological materials. This course provided students with a foundation in the core design rules and principles of “building with biology”, coupled with specific tools and techniques that were broadly applicable to engineering living tissue for a variety of applications.The lab-based format of this course, building towards the cumulative yet open-ended final capstone design project, proved to be an effective method of translating the latest biomedical research from the lab bench to the classroom. Incorporating in-class discussion of lab results as preparation for writing lab reports, motivated by mid-course student survey feedback, was shown to enhance student learning outcomes. This format of four relatively well-structured labs leading to a final open-ended project is modular and can readily be adapted to other interdisciplinary courses. In future iterations of the course, we plan to extend the length of time allotted for the final independent project, allowing student teams to truly experience the iterative and adaptive nature of scientific study design. Furthermore, we plan to evaluate the next cohort of students in this course alongside students in more traditional lab classes in the field of biological research. We believe this future study will provide more evidence that the skills-building and independent thinking encouraged by the format of this course directly resulted in improved learning outcomes.We have shown that a lab-focused structure and layered roles of individual student mentorship can be an efficient and effective method of teaching students to employ the scientific method for designing and executing robust experiments. We anticipate that nurturing these skillsets in undergraduate education will generate engineers who are well prepared for future careers in interdisciplinary fields.


Static fatigue behavior is the main failure mode of optical fibers applied in sensors. In this paper, a computational framework based on continuum damage mechanics (CDM) is presented to calculate the crack propagation process and failure time of optical fibers subjected to static bending and tensile loads. For this purpose, the static fatigue crack propagation in the glass core of the optical fiber is studied. Combining a finite element method (FEM), we use the continuum damage mechanics for the glass core to calculate the crack propagation path and corresponding failure time. In addition, three factors including bending radius, tensile force and optical fiber diameter are investigated to find their impacts on the crack propagation process and failure time of the optical fiber under concerned situations. Finally, experiments are conducted and the results verify the correctness of the simulation calculation. It is believed that the proposed method could give a straightforward description of the crack propagation path in the inner glass core. Additionally, the predicted crack propagation time of the optical fiber with different factors can provide effective suggestions for improving the long-term usage of optical fibers. Optical fibers are widely investigated and applied in both telecommunication and sensor industries due to their prominent properties. On account of high capacity and low transmission loss, optical fibers are mostly used in long-haul communication systems. Additionally, they are also widely applied in sensors ,2,3, conStatistical method based on the failure data.Mechanical method based on the crack growth model.The common mechanical failure mode for optical fibers is the slow crack propagation at the initial stage and unsteady fast fracture. This can be determined as the static fatigue. The static fatigue-induced damage process mainly is related to the following three factors. Firstly, according to our observation shown in The statistical method needs enough failure data to support the life prediction modelling of the optical fiber. For example, Annovazzi-Ledi et al.  carried Currently, several empirical and mechanism-based models have been proposed for the life prediction of optical fiber. Under the static load, the fiber usually fractures from the surface of the inner glass core . Hence, In order to model the actual fracture behavior of glass with initial defects, the framework of continuum damage mechanics (CDM) has been thoroughly researched. CDM characterizes the effect of micro defects on the macro-scale properties of materials. The initial concept of CDM was introduced by Kachanov , then deThe remainder is organized as follows: Based on the behavior of glass at room temperature ,27, the E is the elasticity modulus. In Equation (3), D is the accumulated damage, the damage rate K, n and s are material parameters, and A and n.The total strain rate of glass Kachanov  and LemaKachanov . Assume s fibers . Under tThe crack-opening mode is assumed to be dominated by the normal tensile principle stress component above a certain damage threshold . TherefoUnder the static loading condition,  results , which m damaged .The material and damage variables are isotropic.The initial state In addition, the following assumptions are considered:D is calculated under the averaged stress for each element. By using the element death technique [D is accumulated such that D = 1, and the dead elements do not contribute to the stiffness anymore.The damage variable echnique , elementIn this work, the finite element model is generated in ANSYS Workbench to obtain the mechanics parameters, including strain and stress, that will be used in the calculation of damage of interested elements. Here, we use the three-dimensional optical fiber winding model in hydrophone  with a cThe optical fiber is composed of several layers. The doped glass with a higher refractive index is used to transfer the optical signal. The cladding layer is doped glass with a lower refractive index, to make sure that light is restricted to the core. The mechanical properties of core and cladding glasses are quite similar, and these two parts could be simplified as the glass core with 125 μm diameter. The glass core is coated with two protecting polymer layers whose diameters are 187 μm and 245 μm. The Young’s modulus of the inner coating is 3.5 MPa, and that of the outer coating is 6.24 GPa. The other geometry parameters as well as the material properties of the optical fiber in the simulation are listed in .l = 73 μm, a = 60 μm. On the basis of the experimental results, the optical fiber under bending circumstances fractures from the surface of the glass core. Once the glass core is broken, the light transmission of the optical fiber is stopped. Thus, the crack propagation in the glass core is focused. A penny-shaped crack is introduced on the optical fiber surface as shown in Tensile forces are applied to the distal end section of the optical fiber, and the spool rotates around its axis for 45 degrees, leading the optical fiber to unwind on the spool surface. The stress on the cross section of the middle part is obtained to simulate the bending deformation of a part of optical fiber.iE is the Young’s modulus of the ith component layer, id and ir are respectively the diameter and radius of the ith layer in the optical fiber , and R is the bending radius.Transverse loads are applied, including tensile forces and bending moments, which are defined asct is the crack propagation time and i at the jth step.Based on the definition and revolution law of the damage variable, the maximum principal stress of each element is directly obtained after one calculation cycle from the finite element model. The calculation procedure of the damage values and the crack propagation times is proposed in ith element is shown in i is omitted). The black solid curve represents the actual damage-increasing track under the changing stress, while the yellow dotted line is the virtual damage-increasing track under jth stress along with time. It can be observed from jD to j+1D is parallel to part of the yellow dotted line. Since the damage development trend is only related to the current stress level and accumulated damage jD, the rate of damage change of the actual track from jD to jD+1 shown by the black solid line should be exactly the same as that of the virtual path shown by the yellow dotted line. This means that in the same time interval Moreover, the computational procedure of accumulated damage for jD to jD+1 at the step j, the time-of-damage variable from jD to 1, noted as jD+1 after calculation cycle j through the yellow curve based on Equation (6). The total crack propagation time is the summary of the entire time steps. The fully damaged elements are killed in the finite element model and the crack profile is modified accordingly for the next cycle.To calculate the increased damage from The calculating process iterates until the glass core is completely fractured, as in the process shown in R = 15 mm is already fractured; the crack under R = 17 mm is quite deep and presents an elliptical shape . The SEM images provide the information of crack geometry and initiations of the fiber fracture.SEM images of fractured cross sections under different bending radii are illustrated in R = 17 mm. This is mainly due to the weak bonding strength between the coating and the glass core, and its effect should be further studied.Cracks initiate from the preset defects in the coating and gradually propagate until they cause a complete fracture. There are two phases of the fracture process, which can be observed in the SEM images. The first stable propagation phase results in a smooth penny-shaped crack, and the second unstable crack extension phase is reflected on the radial cracks on the fractured cross section. The boundaries of the two phases are pointed out with arrows. It can be seen that the average depth of cracks is 32 μm with an acceptable disparity. Despite the normal fracture features, peeling of the coating layer can be observed while Specimens tested under different tensile forces are also observed with SEM examinations, and the fracture morphologies are shown in To verify the proposed method, the crack propagation time versus bending radius for both the simulation and experiment are presented in In addition, Therefore, for the twining of optical fiber in a hydrophone, lower tensile force and greater bending radius would increase the crack propagation time of optical fiber remarkably. For the circumstance where bended optical fibers are composed as the key part of the sensor, longer lifetime could be obtained by improving the structure to decrease the stress on the glass core.(1)From the simulation results, the change of the crack-front shape in the propagation process is consistent with the observed image in the actual test, which indicates that the traces of the crack fronts present a fan-like pattern path.(2)The crack propagation process can be divided into two stages. Firstly, the crack-initiation stage lasts from the starting point to the moment that nearly 30 elements are killed, and the crack growth rates are relatively low, since a long time is taken for the material to be damaged in the first place. Then, once entering the early crack-extension stage, the crack growth rates increase rapidly as elements are killed faster until the failure criteria are met.(3)Under different bending radii, the simulated crack propagation time values show that there is an obvious inversely proportional relationship between the crack propagation time and bending radius. The reason is that a smaller bending radius causes a higher bending load on the optical fiber, and it increases the damage-accumulating speed. Additionally, compared with the test data, the simulation results have the same variation tendency and similar magnitude changes in the range of acceptable errors.(4)Based on the simulation results, greater tensile forces can easily cause elements on the crack flank to take on higher damage values and be killed, leading to the appearance of wider cracks. The phenomenon basically conforms to the test results. In addition, the simulated crack propagation times are close to the extrapolated values from fitting the curve of the experimental results.(5)The geometry size of optical fibers manufactured can seriously affect the optical fibers’ crack propagation times through the finite element analysis. Through deeply investigating simulation results, the maximum stress on the glass core decreases first and then increases along with the diameter of the glass core, which can explain the non-linear relationship between the crack propagation time and glass core diameter. Thus, there is an optimum diameter for the glass core that takes on the lowest stress, which could give an optimization policy in the size design of optical fibers to improve their usage time under static loads.Optical fibers are widely investigated and applied in both telecommunication and sensor industries due to their prominent properties. For satisfying the long-term usage requirement of optical fibers under critical operating conditions, it is essential to make an accurate failure-time prediction for optical fibers in sensors. In this paper, an approach based on continuum damage mechanics is presented for calculating the crack propagation process and failure time of the optical fiber under static bending and tensile loads. The finite element model of the optical fiber subsection is built with a pre-existing crack defect introduced in post-processing. The maximum principal stress is used to calculate the damage variables for each element based on the time-varying damage revolution mechanism. The crack propagates by killing damaged elements in the finite element model until the fracture threshold is reached. Finally, the test data validate the results from the three-dimensional simulation under different bending and tensile loads well. It is believed that the proposed method could give an intuitionistic process of optical fiber crack propagation and provide effective improvement countermeasures for long-term usage of optical fibers. The main conclusions are summarized below:


For the surgical treatment of Hirschsprung’s disease, several surgical techniques are used to resect the distal aganglionic colon. Two frequently used techniques are the Duhamel procedure and the transanal endorectal pull-through procedure. During the ‘8th Pediatric Colorectal Course’ in Nijmegen, November 2015, a workshop was organized to share experiences of both techniques by several experts in the field and to discuss (long term) outcomes. Specifically, the objective of the meeting was to discuss the main controversies in relation to the technical execution of both procedures in order to make an initial assessment of the limitations of available evidence for clinical decision-making and to formulate a set of preliminary recommendations for current clinical care and future research. Hirschsprung’s disease (HD) is a congenital condition that is caused by the absence of ganglion cells in the submucosal and myenteric plexuses of the distal intestine , 2. The The TERPT procedure, first developed by De La Torre and Langer, was a Soave-like transanal submucosal dissection with an endorectal pull-through, leaving an aganglionic rectal muscular cuff , 7. ThisWhen the Duhamel procedure is performed, the distal part of the aganglionic colon (rectum) remains in situ. After the resection, the ganglionic colon is placed in the avascular retrorectal plane and stapled or sutured side-to-side to the native aganglionic rectum , 10. ThiIn recent years some centres of paediatric surgery have transitioned from performing the Duhamel procedure to performing the TERPT procedure in almost all cases , 13, butDuring the 8th Pediatric Colorectal Course and Workshops, in Nijmegen, the Netherlands, in November 2015, a ‘Surgical techniques & outcomes in Hirschsprung disease’ workshop was organized that focused on this topic. The aim of the meeting was to: (1) discuss the main controversies related to the technical execution of the TERPT and Duhamel procedures and (2) to formulate a set of preliminary recommendations for current clinical care and future research.Experiences with both techniques differed greatly between the expert panel and participants in the workshop. It was agreed, however, by both the experts and the participants that the currently available evidence, particularly with regard to long-term outcomes, appears to be insufficient to significantly impact clinical decision. The consultants’ personal experience with a certain technique seems to have the strongest influence on the choice of treatment on each centre. In addition, there was a general consensus amongst experts that only highly skilled experienced surgeons could successfully perform the procedures, particularly the Duhamel procedure. It was agreed that a minimum of 20 cases was required to reach the plateau of the learning curve for each of the procedures, and generally training was not begun until fellow status was reached. Positive experiences with the Duhamel procedure that were shared by all experts were the limited anal stretching necessary for this procedure and the good visibility during the whole process. Also, the minimally invasive nature of the TERPT procedure and the good cosmesis were points of agreement.In addition to these points of consensus, several controversial aspects of the surgical technique were discussed in the workshop; (1) the modus operandi for identifying the transitional zone by means of surgical biopsy, (2) the type of muscular cuff that is created in the TERPT technique and (3) the (native) pouch and/or spur left after removal of the aganglionic bowel using the Duhamel technique.Before the actual process of removing the aganglionic bowel can be initiated, the transition zone between ganglionic bowel tissue and non-functioning aganglionic bowel needs to be determined. The gold standard for the diagnosis of HD is a biopsy , 19, forDuring surgery (open or laparoscopy), a seromuscular or a transmural full-thickness biopsy can be taken. A punch biopsy that samples seromuscular bowel tissue only is regarded as a simple, safe, fast and inexpensive method, although this type of biopsy may be more difficult for the pathologist to interpret , 23, 24.The experts’ view on the preferred modus operandi for acquiring the biopsy during a TERPT or Duhamel procedure was the first point discussed during the workshop. The seromuscular biopsy was preferred by some experts since in their experience it had the advantage of a lower risk of spillage of bowel contents in the abdominal cavity and minimized the risk of perforation postoperatively. Several textbooks and published papers also mention seromuscular biopsies for diagnostics during laparoscopy , and theA full-thickness biopsy on the other hand allows the pathologist to review all the layers of the bowel. Another method that can be used (particularly in open Duhamel procedures) is that of a circumferential doughnut biopsy taken intraoperatively. This allows the pathologist to review a sample in all quadrants rather than just the antimesenteric border, when a single-point biopsy is taken. This will certainly give the least errors. The potential benefit of a full-thickness biopsy or doughnut is that it will significantly decrease the number of patients with a transitional zone pull-through. Many of these patients require redo surgery although the exact numbers are not available . The potThe experts also disagreed about the timing of the biopsy. TERPT is mostly initiated with a perineal dissection, and a biopsy is generally taken when a change in circumference or calibre of the colon is observed. However, several experts favoured a preliminary biopsy by means of laparoscopy or through an umbilical incision, before initiating the perineal dissection. The advantage of taking a preliminary biopsy is that it provides more certainty about the location of the transitional zone, which may be particularly important as this location may differ from the radiological findings , 28. ConThe original TERPT procedure described by De La Torre  and in aAnother point of discussion was the length of the cuff in the original De La Torre and Langer technique. The original descriptions of TERPT by Soave include a submucosal dissection above the peritoneal reflection to prevent injury to pelvic structures . HoweverOne of the major issues that were discussed by the participants was the length of the rectal cuff. A complete rectal cuff  may constrict the pull-through bowel because of its obvious aganglionic nature, even when it is incised at the end of the procedure. It has also been described in the literature that a long seromuscular cuff should be avoided as it can lead to obstruction, constipation, constriction and enterocolitis , 34 and In the Duhamel procedure, a pouch is made with aganglionic tissue on the ventral side and ganglionic tissue on the dorsal side, whereas in the TERPT procedure almost all aganglionic tissues are removed and an end-to-end anastomosis is made 1 cm above the dentate line , 10. It Four long-term complications were considered essential by experts in patients with HD: obstructive symptoms , enterocolitis, incontinence and soiling. The experiences with these complications differed greatly amongst experts. The skill level of the surgeon was deemed of great importance for the success of the procedure and outcomes during long-term follow-up. There is only limited data available on long-term functional results after Duhamel or TERPT procedures. Systematic reviews by several groups report on research that explores outcomes of the Duhamel and TERPT techniques and predominantly include small, observational studies with limited follow-up length and heterogeneous patient samples , 39, 40.Bias in the reporting of outcomes may exist, since in the studies it is often operating surgeon who monitors long-term outcome . InteresAlthough the evolution of surgical techniques in the treatment of HD has provided tremendous improvement in patient outcomes, there are certain aspects of treatment that could be improved. As regards the Duhamel versus TERPT technique, evidence is insufficient to recommend one technique over the other and the surgeon’s experience is the key factor determining the choice of procedure. Perhaps these techniques could be applied more efficiently in certain subgroups, which have to be determined. This expert workshop led to the recommendation for a systematic review on the technical execution of the Duhamel and TERPT procedures.The experience of the main surgeon is likely to have a major effect on long-term outcomes. As there currently is no evidence to suggest one technique has significant superiority over another, the technique, the surgeon is most experienced with, is recommended.Duhamel or TERPT may be the best for specific subgroups of patients, but this needs further research and evidence. The TERPT technique may be preferable in straightforward cases, with a more distal localization of aganglionosis, and the Duhamel technique is favourable when treating patients with long-segment disease affecting the proximal colon.Laparoscopy is preferred over open techniques to assist in a Duhamel and/or transanal pull-through procedure.A preliminary biopsy (preferably full thickness) and laparoscopic intraabdominal mobilization of the proximal colon should be considered to reduce stress on the anal sphincter (TERPT) and permit proper localization of the transitional zone.There is a need for objective and clear definitions of both the surgical techniques and the primary long-term outcomes (bowel function) preferably including quality of life.Summary of the main consensus points and recommendations:


A fracture of root canal instruments, with a fractured piece protruding beyond the apex, is a troublesome incident during an endodontic treatment. Locating and retrieving them represents a challenge to maxillofacial surgeons because it is difficult to access due to the proximity between the foreign body and vital structures. Although safe and accurate for surgery, radiographs and electromagnetic devices do not provide a precise three-dimensional position. In contrast, computer-aided navigation provides a correlation between preoperatively collected data and intraoperatively encountered anatomy.However, using a navigation system for mandible treatment is difficult as the mobile nature of the mandible complicates its synchronization with the preoperative imaging data during surgery.This report describes a case of a dental instrument breakage in the mandible during an endodontic treatment for a restorative dental procedure in a 65-year-old Japanese woman. The broken dental instrument was removed using a minimally invasive approach with a surgical navigation system and an interocclusal splint for a stable, identically repeatable positioning of the mandible. Using the three-dimensional position of the navigation probe, a location that best approximated the most anterior extent of the fragment was selected. A minimally invasive vestibular incision was made at this location, a subperiosteal reflection was performed, and the foreign body location was confirmed using a careful navigation system. The instrument was carefully visualized and extruded from the apical to the tooth crown side and was then removed using mosquito forceps through the medullary cavity of the crown side of the tooth. Follow-up was uneventful; her clinical course was good.The use of a surgical navigation system together with an interocclusal splint enabled the retrieval of a broken dental instrument in a safe and minimally invasive manner without damaging the surrounding vital structures. Root canal is one of the most basic dental treatments and is fundamentally dependent on root canal preparation. The treatment comprises the cleaning and shaping of canals. A fracture of root canal instruments is one of the most troublesome incidents during an endodontic treatment. The prevalence of broken instruments ranges from 0.5 to 5% –4. If thFor a safe and accurate surgery, the intraoperative use of radiographs and electromagnetic devices may be helpful for removing foreign objects but do not provide a precise three-dimensional position , 10. In Here, we report a case of an efficient, minimally invasive retrieval of a broken dental instrument using an intraoperative three-dimensional navigation system and a custom-made interocclusal splint for the reproducibility of the mandibular position.A 65-year-old Japanese woman was referred by her local dentist to our hospital for retrieval of a fragment of Peeso reamer that had broken during a root canal enlargement and that was embedded in the canal of her right mandibular first premolar, extending beyond the apex (tooth number 44). As it was not possible to remove the mandibular foreign body from the root canal at the referral dentist, she was admitted to get it removed using a surgical approach. During the intraoral clinical examination, there was an access cavity filled with a temporary filling material and the tooth was sensitive to pressure. There was tenderness in the apical portion of the tooth. A panoramic radiograph obtained at the initial visit after the patient referral revealed a well-defined fractured instrument lying in the mandible beyond the apical foramen of her right mandibular premolar tooth. Moreover, computed tomography (CT) images revealed that the fractured segment was located within the mandibular bone Fig. . A diagnSurgical intervention was required to find the apical root cutting-edge lesion and the broken dental instrument through a small bony window and to remove it from the oral cavity by pushing up in order to reliably preserve the tooth for restorative treatment. Therefore, we decided to use three-dimensional navigation-guided surgery for its minimally invasive nature and high surgical accuracy. As it is difficult to synchronize with the preoperative imaging data during surgery due to the mobile nature of the mandible, we used a customized interocclusal splint for repeatable mandibular positioning while enabling surgical access. As part of the CT imaging preparation for navigation, a customized interocclusal splint was fabricated by pressing acrylic resin into a dental mold at the first visit. First, the created bimaxillary upper and lower jaw splints were adhered using resin at a stable position of the mandible, that is, the position in which the mandible is slightly opened from the central occlusion. A maxillofacial CT was obtained using the customized interocclusal splint to maintain the mandible in a repeatable position, which would be vital for the accuracy required for retrieving the small foreign body Fig. .Fig. 2InThe imaging data were obtained in a Digital Imaging and Communication in Medicine format and transferred to a Medtronic StealthStation S7 workstation with Synergy Fusion Cranial 2.2.6 software . Our patient was taken into the operating room where her customized interocclusal splint was reinserted. A Patient Tracker EM was affixed to her forehead to act as a reference array to track the navigation probe. To perform patient-to-CT data registration, the instrumentation navigation probe was used to trace the reference array, soft tissue landmarks of the face, and hard tissue points  Fig. . After dUsing the three-dimensional location of the navigation probe with respect to the broken instrument fragment, a location was selected that best approximated the most anterior extent of the fragment in conjunction with the navigation probe Fig. . An apprEndodontic files, burs, and occasionally, other dental instruments tend to break off during surgical procedures because of defective manufacturing, stress, fatigue, rust, or poor handling . The diaIn this case, an intraoperative navigation system was used to locate the broken dental fragment and aid in its removal. Navigation was initially developed for stereotactic interventions in neurosurgery but has been recently introduced to other specialties. The use of navigation systems to retrieve foreign bodies during craniomaxillofacial surgery has been previously reported , 17.Image-guided systems can improve preoperative planning and provide high-degree intraoperative accuracy and precision. However, the navigational accuracy is limited by the system used, the method of obtaining the imaging data, and syncing the imaging data with the patient’s actual position during the procedure. Some limitations of the currently available image-guided systems should be considered because most were originally developed for neurosurgical purposes . TherefoFurthermore, there are currently three possible solutions for the application of navigation in the mandible. The first approach is to mount a dynamic reference frame to the mandible that enables continuous tracking of the mandibular movement and its position during the surgery . This meIn the present case, a navigation system for the mandibular lesion was further beneficial in determining the accurate location of the object and provided us, the oral-maxillofacial surgeons, with intraoperative guidance for the safe and reliable use of an individual occlusion splint. This splint, which could be easily made from a simple impression, used each tooth of the maxilla and mandible as a fixed source. Therefore, it is possible to reproduce the mandibular position for various mandibular movements. This method also has the advantages of improving surgical and oromandibular anatomical accuracy, manifesting precise individual dental root positions, minimizing surgical invasiveness, and reducing operation time using an easily constructed splint.The use of a surgical navigation system together with an interocclusal splint enabled the retrieval of a broken dental instrument in a safe and minimally invasive manner without damaging nearby vital structures.


In Zimbabwe, a recent increase in the volume of research on recurrent non-specific low back pain (NSLBP) has revealed that adolescents are commonly affected. This is alarming to health professionals and parents and calls for serious primary preventative strategies to be developed and implemented forthwith. Early identification initiatives should be prioritised in order to curtail the condition and its progression. In an attempt to be proactive in minimising the prevalence of recurrent NSLBP, this study was conducted to evaluate the content validity and test-retest reliability of a survey questionnaire with the aim of proffering a valid and reliable questionnaire which can be used in non-clinical settings to identify adolescents with recurrent NSLBP in Harare, Zimbabwe and determine the possible factors associated with the condition.The study was conducted in two parts. The first part assessed content validity of the questionnaire using four experts derived from academia and clinical practice. The second part evaluated the reliability of the questionnaire among 125 high school-children aged between 13 and 19 years in a test-retest study.k=0.94), sports participation (k=0.97), and lifetime prevalence (k=0.89).Twenty-six (26) out of thirty questions in the questionnaire had an Item Content Validity index of 1.00, demonstrating complete agreement among content experts. Overall, the Scale Content Validity Index for the questionnaire was 0.97. Item completion for the reliability study was satisfactory. The questionnaire items had kappa values ranging from 0.17 (slight agreement) to 1 (perfect agreement). High levels of reliability were found for the questions on school bag use  questionnaire. These results are comparable to findings of other studies evaluating the psychometric properties of LBP questionnaires. Cognisant of the limitations of the study, the results of this study suggest that the LBP questionnaire could be used in local studies investigating LBP among adolescents although questions enquiring on functional limitations and sciatica may need further consideration.The online version of this article (doi:10.1186/s40945-017-0031-y) contains supplementary material, which is available to authorized users. Low back pain (LBP) is a highly prevalent health problem worldwide . In the The consequences of recurrent NSLBP in adolescents are well documented in the literature. Unabated, the condition negatively affect the health-related quality of life (HRQoL) leading to school absenteeism and functional limitations –21. In aAdditionally, adolescent recurrent NSLBP has been linked to disc degenerative changes in the spine , 19. In With longitudinal epidemiological evidence linking adolescent recurrent NSLBP to chronic debilitating LBP in adulthood, this further raise a lot of questions on the most effective prevention strategies to curtail the transitioning , 12, 21.In Zimbabwe, the problem of LBP among adolescents is a recent or emerging epidemiological phenomenon. This evidenced by a sudden increase in the number of published studies investigating recurrent NSLBP in adolescents since 2014. Evidence from cross-sectional studies conducted so far have highlighted the existence, magnitude and the factors associated with recurrent NSLBP among Zimbabwean adolescents in high schools , 22–24. This study was conducted, therefore, to document the evidence of content validity and reproducibility of a LBP survey questionnaire developed to identify adolescents with recurrent NSLBP and identify the factors associated with the condition. The specific objectives of this study were to determine the Item Content Validity Index (I-CVI) of each question in the questionnaire and henceforth calculate the average Scale Content Validity Index (S-CVI/Ave) for the questionnaire. Secondarily, the study sought to determine the kappa coefficient (k) for each ordinal item in the questionnaire and the Intraclass Correlation Coefficient (ICCs) for each question eliciting continuous responses as a measure of test-retest reliability.Broadly, this study was conducted in two parts. The first part was conducted to establish the content validity of the developed questionnaire from a cross-sectional sample of experienced experts. As reported in the literature, content validity assesses whether an instrument adequately or exhaustively contains all the items necessary to represent the concept being measured . SubsequParticipants for the content validation study were experts recruited from various medical departments at the University of Zimbabwe, College of Health Sciences (UZCHS) and government-owned tertiary health-care institutions in Harare, Zimbabwe. The UZCHS is the only institution that offers training to all health care professionals in the country. There are three state tertiary health care institutions serving as referral centres in Harare namely, Parirenyatwa Group of Hospital, Harare Central Hospital and Chitungwiza Central Hospital.1 category (17 schools) and S2 (38 schools), only three schools (One from S1 and Two from S2) were randomly selected, based on a strategy that considered ratio of schools in each category. At the time of data collection, there were 3 246 registered full-time school-children enrolled at these three selected high schools. However, with the high school education system in Zimbabwe made up of two levels, Ordinary level education (Form 1 to 4) and Advanced level education (Form 5 & 6), two independent forms were randomly selected from each of the three selected schools. This gave a total of six different classes with a total of 180 students all eligible for participation in the study.Participants for the reliability study were high school learners recruited from government-administered high schools in Harare, Zimbabwe. Of the 55 government high schools in Harare, which are divided into SParticipation was based on students’ expression of willingness to participate evidenced by signing of the assent form. In addition, only students with parental/legal guardian permissions through signing of the informed consent form were recruited. To further select appropriate students, the exclusion criteria previously used in other related cross-sectional studies investigating LBP problems among adolescents in the local setting was adopted. Students with parental reports on the Adolescent Medical Health Questionnaire of spinal, neurological, orthopaedic conditions and any previous report of trauma to the back, hip and knees were excluded , 22. ParThe LBP Questionnaire was developed in English language mainly to determine the prevalence of recurrent NSLBP and investigate the factors associated with the condition among a cross-sectional sample of high school Zimbabwean adolescents. The choice of a questionnaire as a survey instrument was based on the reported fact that pain is a subjective experience and 85-90% of school-children can reliably report their pain experience , 28. AltThe questionnaire developed contained four sections with a total of 30 questions . Section C had questions on physical activity . Section D asked about lifetime and recent (in the past week) smoking status of the adolescents. These pre-selected factors were included in the questionnaire on the basis that they had been reported in previous studies as significant factors associated with LBP among adolescents , 37–42.After obtaining institutional approvals from the Ministry of Primary and Secondary Education (C/426/3) and Harare Provincial Educational Office (G/42/1), ethical approval was sought and obtained from the Joint Research Ethics Committee for the University of Zimbabwe College of Health Sciences and Parirenyatwa Group of Hospitals (JREC/254/15) and the Medical Research Council of Zimbabwe (MRCZ/B/961). Further approvals to access the schools were obtained from the respective headmasters of the three participating schools. Content experts had to submit a signed informed consent form indicating willingness to participate.Pre-testing of the English LBP Questionnaire was conducted at one of the selected schools after obtaining ethical and institutional approvals. Twenty (20) randomly selected Form Three (3) students (mean age=15.5±2.6 years) volunteered to participate in the preliminary study. The students were deliberately omitted in the main study data collection. The primary objectives of the pre-test study were to assess the comprehensibility of the questionnaire and evaluate the feasibility concerns for the main study data collection. The maximum amount of time needed to complete the questionnaires by all the participants was used as a measure of comprehensibility.The procedure for the pre-test involved giving information letters explaining the purpose and the nature of the pre-test study to the respondents first. The researcher (TNC) augmented the information by clear oral explanations. Thereafter, the questionnaires were self-administered in the presence of the class teacher. While completing the questionnaires, respondents were strongly encouraged to ask the researcher questions when clarification was necessary. At the end, respondents were requested to comment whether they understood each question in the questionnaire and the response options provided. Any question, response option, word or phrase that was misunderstood by at least one of the respondents was modified or reworded by the researcher until it was deemed satisfactory by the respective respondent(s).On average, the respondents took 40±6 minutes to complete the questionnaire which was more than the anticipated 10±5 minutes. This was attributable to a number of reasons. The participants seemed elated to be participating in the study resulting in unceasing deliberations and stifled laughs amongst themselves whilst answering the questionnaire. This was particularly noticed on questions enquiring about LBP status, smoking status and sports participation. This was despite several attempts by the researcher and the class teacher encouraging independency in completing the questionnaires. Another significant reason noted for the lengthened time of completing the questionnaires was the frequent interruptions made by the respondents seeking clarification from the researcher. This happened on a number of questions such as the question on pain intensity for recurrent NSLBP, sciatica, and functional limitations, type of sports or exercise and smoking status.The research team had to ensure that respondents were organised in sitting arrangements that does not allow for copying or deliberate discussions of their responses.It was important for the research team to have a class teacher present during data collection to ensure that respondents conduct themselves cordially and professionally;It was important for the research team to communicate with the school authorities prior to their data collection visit either by telephone or a physical visit to the school to arrange for time and place for data collection, class of students eligible for the main study and possibly negotiate for local assistance from the class teachers for the data collection;It was important to translate the English questionnaire into a local language and for the main study data collection to allow the respondents to choose a questionnaire in a language they prefer for ease of understanding.Overall, there were no changes suggested by the respondents on the nature of the questions in the questionnaire and there were also no changes in the total number of question items following the pre-testing. However, there were lessons drawn from the pre-test study which informed the design of the main study data collection procedure worth mentioning:Content validation of the instrument was conducted after the pre-test study between December 2015 and March 2016. Although literature is controversial on the ideal number of content experts needed in a validation study, invitational letters were sent to seven independent content experts soliciting their participation. The content experts were nominated on the basis of either experience in epidemiological and/or musculoskeletal research as evidenced by the number of publications in that field or significant clinical work experience in LBP management whether in medicine, orthopaedic surgery, neurology and rehabilitation from the three large health-care facilities.1 = not relevant, 2 = somewhat relevant, 3 = quite relevant, 4 = highly relevant.The content experts were given one week to respond to our request to participate in the study. Those that indicated willingness to participate were thereafter furnished through email with an informed consent form attached to an information cover letter, the English version of survey questionnaire, a brief demographic questionnaire and the evaluation criteria form. The information cover letter explained the purpose of the study, the reasons for the selecting the content expert, a description of the questionnaire and an explanation on the content evaluation procedure. Each expert was asked to assess the relevance of each question in the instrument. This meant that experts had to assess whether all the items in the LBP Questionnaire refer to relevant aspects of the construct of recurrent NSLBP being measured. In addition, experts had to assess whether all the items were relevant for the target population and the intended purpose of the questionnaire. To judge relevance of each question, a 4-point scale based on a criteria propounded by Davis was used . The expThe experts were specifically requested to provide recommendations (for revision or deletion) for each question which they would have scored low (1 or 2). For the questions in need of revision, the experts had to comment on the clarity (how clearly the question was worded) and were requested to provide a possible option of ensuring the relevance of the question. The experts were given a maximum period of two weeks to validate the questionnaire and return through email or in person to the researcher (TNC). Reminders would be sent through emails and short messaging service (SMS) after every three days to maximize the response rate. At the end of the validation, responses from the experts were analysed by one of the researchers (MC).After the LBP Questionnaire was content-validated and necessary changes effected as suggested by the content experts, the questionnaire was translated into Shona, a local language spoken in Harare, Zimbabwe. The procedure for the translation process was informally guided by the suggestions from a study by Sousa et al. . Two quaThe test-retest reliability study was conducted after the content validation and translation of the English questionnaire into Shona. Initially, parental documents  were sent to parents/guardians of eligible children. The school-children were given seven days to return the documents to their school teacher with the written informed consent forms signed and the Adolescent Medical Health Questionnaire completed. The Adolescent Medical Health Questionnaire was used to establish the medical history of the participating children as reported by parents. The questionnaire was adopted from previous studies and it provided the basis for excluding school-children not fulfilling the inclusion criteria , 23, 24.After obtaining parental permissions, the researcher (TNC) visited the three participating schools consecutively for data collection. The questionnaires were self-administered in classrooms to eligible students in the presence of the class teacher. Standardised oral instructions were given to participants to supplement the information regarding the study provided on information letters. Participants had the option of either choosing the English or the translated Shona questionnaire. Participants were free to ask questions for clarification purposes when necessary. The students sat approximately 50cm apart from each other and were strictly instructed not to discuss their responses with one another. During the initial test, the participants were not told that they will be re-tested after seven days.After the seven days, the questionnaires were self-administered again to the participating school-children, present at school and in class, using the same procedures described for the test study and completing the same language version of the questionnaire as previous. The time interval of seven days was chosen to reduce the possibility of participants remembering their initial responses, the so-called “carry-over” effect and to lessen the possibility of the LBP changing between the tests . It is aContent experts had to rate the relevance of each question/item in the questionnaire on a scale of 1 to 4. One proportion agreement method, the Content Validity Index (CVI), was used to estimate quantitatively the content validity , 47. Spet-test independent by groups was used to compare the mean age of onset for LBP as well as the mean intensity of recurrent NSLBP by gender. The significance level was fixed at p<0.05. Item completion was evaluated and percentage agreement calculated for each question as the number of agreement scores divided by the total number of scores between studies . Figure Age data of participants was normally distributed  to 1 (perfect agreement). Almost perfect to perfect agreements were found for the items that evaluated school bag use (k=1), sports participation (k=0.97), lifetime prevalence (k=0.89), smoking status (k=0.84) and perceptions of school bag weight (k=0.81). The screening question for recurrent NSLBP showed substantial agreement (k=0.78) so as questions related to the frequency and duration of recurrent NSLBP episodes. The questionnaire items adopted from Hanover Functional Ability Questionnaire evaluating functional consequences had low kappa values ranging from 0.17 (slight) to 0.43 (moderate). However, the question eliciting information on the health-seeking behaviour of school-children with recurrent NSLBP had substantial agreement (k=0.73). The question on school absenteeism achieved moderate reliability (k=0.45). Intraclass correlation coefficients (ICCs) for questions eliciting continuous responses showed variable reliability values for the questions on age of onset for LBP (ICC=0.87), pain intensity for recurrent non-specific (ICC=0.97) and point prevalence pain (ICC=0.62)  were consistent between the two tests. Table According to experts, the questionnaire showed excellent content validity. This indicates that the questionnaire contain relevant questions that could be used to identify adolescents with recurrent NSLBP and possibly determine the factors associated with the condition. These results should be interpreted with the understanding that the questionnaire was evaluated by four out of the possible seven experts. Although the seven experts would have made the sample representative of the intended professionals in academia and clinical practice, only four timeously responded to the call to participate in the study. The reasons for the lack of participation could not be established but it is largely possible that the experts could have been extremely busy considering the time the content validation study was conducted in December 2015 to March 2016, a period which marks end of the year and the beginning of second final semester at the UZCHS. In anticipation for this, invited experts were given seven days to respond to our request to participate with several reminders being sent through emails. Future studies in our context wanting to include health professionals in academia and clinical practice as content experts may need to ensure that the experts are given sufficient amount of time, probably more than a week, for them to respond to the call to participate and fervently employ other avenues of communication besides emails.To our knowledge, studies evaluating the content validity of LBP adolescent questionnaires rarely report their procedures and findings. This makes comparisons of findings difficult. Chiwah et al.  and AdegAlthough certain questions may require some modifications prior to use, test-retest reliability results showed that the present study LBP questionnaire could be used for the investigation of recurrent NSLBP and factors associated among high school-children in Harare, Zimbabwe. Against the background of high prevalence of recurrent NSLBP affecting adolescents in Harare, Zimbabwe, this study may be of epidemiological and clinical importance in that it presents a reliable instrument that could be used in non-clinical settings and in future studies to identify adolescents with LBP and the possible factors associated with the condition. Although there are few published articles in the literature specifically conducted to evaluate the test-retest reliability of developed LBP questionnaires for adolescents, results of the present study are comparable to findings of other studies , 30, 45.k=0.82) and absenteeism from work (k=0.76). Although this study was carried in the adult population and the interval period for the test- retest study was 12 months, results on lifetime prevalence confirm that questions eliciting such information are usually reproducible. However, for the present study, the question on school absenteeism which can be equated to the question on work absenteeism from Walsh and Coggon [In the present study, high levels of reliability were found for the items that evaluated school bag use, sports participation, lifetime prevalence, smoking status and perceptions of school bag weight. These results suggest that these questions could be appropriate for the investigation of LBP complaints and associated factors in adolescent studies. Comparatively, in a study testing the reproducibility of histories of LBP obtained by self-administered questionnaire from 225 men and women, Walsh and Coggon  reportedd Coggon  showed mk=0.71-1.00). In comparison, perceived characteristics of recurrent NSLBP for the present study showed similar reliability with questions on frequency and duration of episodes yielding kappa statistic of 0.71 and 0.65, respectively. In addition, the ICC for the pain intensity question was high with a small standard error of measurement. However, in agreement with findings of Walsh and Coggon [k=0.20). A pilot study conducted by Chiwaridzo and Naidoo [k=0.32). It is possible that concept of sciatica as pain radiating to the lower extremities from the lower back may be difficult to comprehend for adolescents and adults as evidenced by the low reproducibility values. Therefore, it suffices to suggest for careful consideration to be exercised when information related to sciatica is elicited from participants, especially adolescents, in epidemiological studies.Bejia et al.  found hid Coggon , the scrd Naidoo  validatiAlthough the relevance of questions eliciting information on functional consequences secondary to recurrent NSLBP in epidemiological research is undoubtable, the present study found low kappa coefficients for the questions adopted from the Hanover Functional Ability questionnaire enquiring on functional limitations. These results compare with other reports in the literature which reported information on disabilities for everyday activities associated with LBP . The preThe results of this study should be interpreted with caution cognisant of a number of limitations. The sample of four content experts who agreed to participate in the validation study was not representative of the intended professionals. In addition, the fact that the experts were tasked to comment only on the relevance of each question as index of validity poses some concerns on the comprehensiveness of the validation of each question. This criterion was recommended by Davies  and was In terms of the relevance of the questions, the survey questionnaire was found to have excellent content validity by content experts. The questionnaire showed slight to perfect test-retest reliability among high school adolescents. These results calls for further studies assessing the content validity of the questionnaire with increased number of experts representing all the professionals and evaluating several other fundamental parameters of content validation such as clarity, simplicity and ambiguity. In addition, questions which achieved slight reliability such as questions on sciatica and functional limitations should be modified or considered carefully before being used in future studies on adolescent LBP.


Biological and technical systems operate in a rich multimodal environment. Due to the diversity of incoming sensory streams a system perceives and the variety of motor capabilities a system exhibits there is no single representation and no singular unambiguous interpretation of such a complex scene. In this work we propose a novel sensory processing architecture, inspired by the distributed macro-architecture of the mammalian cortex. The underlying computation is performed by a network of computational maps, each representing a different sensory quantity. All the different sensory streams enter the system through multiple parallel channels. The system autonomously associates and combines them into a coherent representation, given incoming observations. These processes are adaptive and involve learning. The proposed framework introduces mechanisms for self-creation and learning of the functional relations between the computational maps, encoding sensorimotor streams, directly from the data. Its intrinsic scalability, parallelisation, and automatic adaptation to unforeseen sensory perturbations make our approach a promising candidate for robust multisensory fusion in robotic systems. We demonstrate this by applying our model to a 3D motion estimation on a quadrotor. A fundamental task of a nervous system is to increase the chance of survival of an organism by guiding its actions through the environment, seeking advantageous states, and avoiding dangers. In order to select and execute the most favourable action, either for decision-making  or sensoSensorimotor processing is inherently influenced by the real-world constraints and structure. Sensory streams contain certain statistical dependencies determined by the structure of the world, which impose constraints on a system’s sensorimotor affordances . This liToday’s technical systems, in particular mobile robots, have limited capabilities to generalize their sensorimotor capabilities to new tasks. Typically, the system designer is responsible for defining the system’s structure and describe its sensorimotor dynamics. Although providing good solutions for particular scenarios, traditional system design approaches are bound to parametrization routines characterised by a high use of computational resources and processing time. Moreover, task-dependent parameter configurations and prior assumptions limit flexibility.Tackling the challenging problem of learning underlying correlations from data, our approach comes as an alternative to already developed methods. Various methods, ranging from neural circuitry implementations to statistical correlation analysis, have been developed to extract correlational structure in sensory data.Related work in  used a cIn order to frame our work within state-of-the-art using similar data analysis tools we briefly introduce work carried on sensor fusion using entropy and information theory, e.g., condition monitoring, predictive control. Introducing an extension for Dempster-Schafer evidence theory, the study proposed in  intorducLessons from neuroscience taught us that learning mechanisms allow a system to generalize over multiple tasks. Perceptual learning is the way developing organisms discover invariants of features, states, and layout of the environment in new contexts . PerceptThe question is how to engineer a model that has a structure capable of representing the relation between inputs or between inputs and outputs? One approach is to exploit regularities in correlated sensorimotor streams in order to associate relevant cues that disambiguate the system’s state. Is it advantageous to design a system capable to learn its own structure by autonomously extracting correlations in its sensorimotor space? In this work we tackle these questions and show that, once sensory associations are learned, generalization can be conceived as an adaptation of the internal model to the learned structure.In order to frame our work in the already introduced context, we address the problem of robust self-motion perception. We explore how this task can be performed efficiently through learning sensorimotor correlations. Not only are there many types and combinations of motion, but there are various factors governing the perception of self-motion and orientation, an important one being the functional representation between sensory physics and the nervous system . AdherinAfter briefly describing the investigation context in the Introduction section, we introduce the generic neural processing model in the Methods section. We focus on the basic functionality for correlation extraction, self-synthesis, and the specific tools used in our real-world instantiation. Our preliminary results, along with an in-depth analysis, are introduced in the Results sections. The core observations in the Results section are further extended in the Discussion session where we also introduce alternative approaches and evaluate their applicability in real-world scenarios. Providing a thorough analysis and comparison, this section emphasizes the novelty and the main contributions of our work. Finally, the Conclusions section revamps the core principles and motivation behind our work and provides an outlook on possible extensions and improvements.The core contribution of this work is a novel processing and representation paradigm capable of extracting underlying correlations in incoming sensory streams and integrating their contributions into a coherent percept. In this work we employ a processing principle known to be ubiquitous in the mammalian cortex, namely distributed processing with only local processing and storage. Obeying local dynamics of mutual interaction, the multitude of sensorimotor streams, encoded as processing maps, converge to global consensus. Aiming at obtaining a globally consistent representation, each map tries to minimize the disagreement among connected representations. Globally, this process learns an internal model based on underlying physical properties of cross-sensory interactions via continuous belief update given sensory observations.In order to validate our framework and its hypotheses, we extend the basic model in  towards In order to give an intuition on the inner workings of the aforementioned mechanisms, we start with a simple bimodal scenario, depicted in k, the network follows the processing stages depicted in i-th neuron in the p-th input SOM, with the preferred value The input Self-Organizing Maps (SOMs) are responsible for extracting the statistics of the incoming data and encoding sensory samples in a distributed activity pattern, as shown in p-th population, kThe winner neuron of the During self-organisation, at the input level, competition for highest activation is followed by cooperation in representing the input space =This corresponds to the adaptation stage in The learned tuning curve shapes for 5 representative neurons in the input SOMs  are depicted in Using this mechanism, the network optimally allocates resources : a higher amount to areas in the input space which need a finer representation; and a lower amount for those areas that don’t. This feature emerging from the model is consistent with recent work on optimal sensory encoding in neural populations . This cli,j-units in the population, that allows wrap-up and a uniform distribution of the activity at the boundaries.The second component of our model is the Hebbian linkage, more precisely a covariance learning rule akin to the one introduced in : a fullyThe effective correlation pattern encoded in the In order to test the proposed model, we apply it for a quadrotor 3D egomotion estimation, as depicted in x-axis and gravity  to extract the pitch contribution of the acceleration, and we combine magnetic field intensities on the x and y axes to extract the yaw contribution of the magnetometer.This shall serve as an example to introduce the system structure learning mechanism, namely the process that infers a plausible network structure for multisensory fusion. Envisioning a system capable of self-deployment, our work proposes an autonomous method to learn a system’s structure from sensory associations. Prior to learning multisensory fusion rules, the system must decide which sensors can be associated for coherent estimates of each motion component, using only available on-board sensors. The basic idea is to determine which regularities in the different sensory streams are informative and enforce the connections between correlated sensors to provide a relevant rule for fusion. As the system follows a developmental process (offline), one can only evaluate the system’s real-time capabilities after learning. The sensors used in our instantiation are the 3-dimensional integrated gyroscope readings, 3-dimensional net accelerations, and 3-dimensional magnetic field intensities, as shown in Physical systems are continuously and dynamically coupled to their environment. This coupling offers the system the capability to explicitly structure its sensory input and generate statistical regularities in it . Such reIn our approach we address the problem of recovering the structure of a network from available sensory data in its most general form, namely time-series streams of sensory data. No assumptions about the underlying structure of the sensory data are made and no prior knowledge about the system is taken into account. Furthermore, interactions between the various sensory streams are deduced from the statistical features of the data using information theoretic tools. This approach extends the generality of our framework for learning sensory correlations used for multisensory fusion.X and Y to denote random sensory variables consisting of the set of possible samples In the simplest bimodal scenario, we assume Intuitively, mutual information is high if both sensory quantities have high variance  and are highly correlated  . In our Using this basic formulation of information theoretic metrics, we developed our network inference algorithm which is synthetically depicted in Initially, uni-dimensional, multi-dimensional  entropies, τ in the sensory data time-series:τ is 0, as the sensors are sampled at the same time although, due to physics, they have different reaction time induced by the motion of the robot. It is easy to see that high values of mutual information between variables determine a smaller distance value as shown in Y . Hence, a link between Y is predicted if and only if the entropy reduction T.The distance metric used for constructing the distance matrix is the Entropy Metric Construction (EMC) ,26. An ie-series:dEMCEquation , exceedsIn order to obtain reliable estimates of joint entropies of the many sensory variables, the large amount of data observations  provides an advantage. Furthermore, exploiting the rich input space, the proposed algorithm is able to exploit the intrinsic statistical regularities of the sensory data to generate a plausible network configuration. The raw sensory data fed to the system is sampled at 200 Hz. For each degree of freedom there is decoupled data from each sensor axis paired for each degree of freedom , the network learns the relation between the roll and pitch angle estimates from gyroscope data and rotational acceleration components . Similarly, the yaw angle is extracted by learning the relation between the yaw angle estimate from integrated gyroscope data  and aligned magnetic field components from the magnetic sensor . The learned sensory associations are not arbitrary, but rather represent the dynamics of the system and are consistent with recently developed modelling and attitude control approaches for quadrotors ,28.To make use of the learned relations, we decode the Hebbian connectivity matrix using a relatively simple optimisation method . After lBy tackling a challenging multisensory fusion scenario for 3D motion estimation, we designed a system capable to extract associations between sensory cues from on-board sensory data without any prior assumptions. The system structure emerges from the underlying regularities in the sensory streams. Once relevant associations are extracted cross-sensory relations are learned. The learned relations constitute the rules to integrate the available on-board sensory quantities. These rules impose constraints on the possible values a sensory cue can take by updating the representations toward a coherent state.The inferred relations provide a plausible description of cross-sensory interactions and provide prediction capabilities and improved individual sensory estimates for each motion component. This capability is a fundamental strength of the system as it provides a robust way to infer the underlying internal model, while preserving a stable cross-sensory integration mechanism. This behaviour is visible in a sample scenario depicted in In order to validate the extracted relations, we use the aforementioned mechanism to extract the roll, pitch, and yaw estimates for the quadrotor scenario. x and z axis to an absolute pitch angle estimate. The learned cross-sensory relations, encoded in the Hebbian matrix, provide the intrinsic constraints between the sensors. After learning, in order to compute individual contributions of the sensors for each degree of freedom , we feed one side of the network with samples from one sensory modality ; we project the corresponding activity pattern through the learned Hebbian matrix to compute the cross-modal activation; and finally, we decode the expected value for the associated sensory modality . This process is performed for each of the associated sensory modalities in the network. The integrated and improved individual estimates are shown in We observe that the learned relations resemble the nonlinear functions used in typical modelling approaches, although irregularities in the cross-sensory relations are preserved. More precisely, the agreement with the previous control approaches refers to the capability of the proposed system to extract the nonlinear transformations among sensory quantities, for example the transformation  from a ratio among accelerations on For roll estimation a the netFor pitch estimation the network extracts the nonlinear dependency between the accelerometer data and the gyroscope data. Although both cues follow the trend of change in angle, as shown in t = 5 s. Investigating during many test flights, we noticed that the current change generated when starting the rotors introduced a significant modification in magnetic field distribution, subsequently reflected in the magnetometer readings. In the current setup, the inferred network is not able to explicitly compensate for the offset, as one can see in Finally, for yaw estimation the network uses the gyroscope absolute angle and the magnetometer contribution, based on magnetic field readings on the x and y axes. Interestingly, despite the fact that the yaw estimate of the magnetometer follows the trend, as visible in Following the processing pipeline introduced by our approach, the system fuses the associated sensory cues for each degree of freedom using the learned relations and provides better estimates than the individual sensory cues, as shown in Our results show that the model is able to extract the underlying data statistics without any prior information such that the sensory data distribution was learned directly from the input data. Moreover, following the statistics of the data, the network allocates more neurons to represent areas in the sensory space with a higher density such that the cross-sensory relations are sharpened. As one can see there is no need for any specific parameter tuning routine to handle different kinds of input data for different scenarios.The generic processing elements  ensure that the network first learns the structure of the data in an unsupervised manner, and then uses this representation to sharpen its correlational structure. Moreover, given the learned relations, the network is able to infer missing quantities in case of sensor failures. As the relation is encoded as a synaptic weight, after learning, it is enough to provide samples from one sensor, encode them in the SOM, and project the activity pattern through the Hebbian matrix. The resulting activity pattern can be subsequently decoded to provide the missing real-world sensory value.The proposed learning scheme extends our previous work, in which given various sensory inputs and simple relations defining inter-sensory dependencies, the model infers a precise estimate of the perceived motion. Now, by alleviating the need to explicitly encode sensory relations in the network, we propose a model providing flexible and robust multisensory fusion, without prior modelling assumptions, and using only the intrinsic sensory correlation pattern.The present work introduces a novel framework for learning underlying correlations in sensorimotor streams. As our preliminary results show, this approach has attractive features, highly relevant in today’s challenging and dynamic scenarios robotic systems operate in. Through self-creation, the system alleviates the need to manually perform tedious and constrained system identification and parametrization routines. Moreover, learning processes allow the system to extract the intimate  relations among correlated sensory cues.After learning sensory relations from incoming sensory streams, the system supports judicious integration of the perceived quantities into a coherent percept that is more precise than individual sensory contributions, shown in Furthermore, these constraints act upon acquired observations, such that individual estimates are “pulled” towards the correct and stable solution manifold, one which ensures consensus in the network and a precise fused estimate, as shown in In order to emphasize the core contribution and significance of our model, we summarize the most important common features of other models (briefly introduced in the Introduction) following the same aspects we addressed when describing our model’s features.One initial aspect is the design and functionality. Either using distributed representations, as in ,5, or coA second aspect is the amount of prior information set by the designer in the system. It is typical that, depending on the instantiation, a new set of parameters is needed, making the models less flexible. Although less intuitive, the pure mathematical approaches like  need lesA third aspect, relevant to the analysis, is the stability and robustness of the obtained representation. The inferred representation can be encoded in a weight matrix, as shown in ,5, allowThe capability to handle noisy data, is another important aspect influencing applicability in real-world scenarios. Using either computational mechanisms for de-noising, as those employed in ,5, the iAnother relevant feature is the capability to infer  missing quantities once the relation is learned. The capability is available when using either the learned co-activation weight matrix, as done in ,5, or thAlthough not explicitly treated in the presented models, decoding the extracted representations is not trivial. Using a tiled mapping of the input values along the neural representations the model proposed in  decoded Given the complex and multimodal scenarios in which robotic systems operate, with noisy and partially obstructed environment features, the capability to precisely and rapidly extract estimates of egomotion critically influences the set of possible actions. With extensive sensing capabilities, today’s robotic systems face a different problem, namely how to advantageously use correlated sensory streams for building an internal model of their motion and environment, which can subsequently improve their perception. Although inherently noisy and uncertain, available sensory streams contain regularities imposed by the motion of the robot through the environment.In the challenge to understand how a robotic system can exploit these underlying regularities and correlations, we developed a framework capable of tackling three key topics related to the fundamental understanding of sensorimotor learning: what has to be learned, how is it learned, and how knowledge developed during learning can be represented and used in closing the loop. In order to respond to the first topic, namely what has to be learned, we developed a mechanism which uses generic information metrics, like entropy, to analyse the intimate structure of the incoming sensory streams, identify regularities, and use them to build a network of sensory variables corresponding to each of the available sensors. After a structure is created, the system uses simple, well understood, and cheap computations to learn the intrinsic relations among sensors along with their statistics. Finally, in order to use the knowledge about sensory correlations acquired during learning, the system implements the extracted relations as constraints to fuse the available sensory streams so as to obtain a globally more precise state estimate.Going away from traditional approaches, our perspective resides on four core principles also known to explain development processes in biological systems. Given the wide range of available sensory streams, the system learns sensory associations from the data and builds a network of associations. This network enforces relevant rules for multisensory fusion. Exploiting underlying regularities in the data, the system uses a distributed representation and simple computations, like competition and cooperation to learn the underlying correlations. Finally, the development process of the system is autonomous and it is not mediated by a teacher or error/reinforcement signal.Amenable to support analysis and versatile modelling, these principles enable the system to capture the full complexity of real-world motion estimation and we expect that the learning model will generalize to new tasks.This initial exploratory phase allowed us to investigate the flexibility and robustness of neurally inspired computation mechanisms for representation, learning, and processing of sensorimotor streams. In the next steps, we aim at closing the loop after learning the sensory feedback, and further explore re-learning and adaptation for new scenarios. Moreover, focusing on having a real-time capable system after deployment , we are interested in investigating parallel implementations. This is a natural extension to exploit inherent distributed representations and computation in our system, especially on parallel embedded hardware platforms. Finally, due to knowledge about network structure and the simple dynamics, the system can be easily extended to accommodate an arbitrary number of sensory modalities and diverse representations for improved perception.