2. Abstract 3D scanners have revolutionised how podiatrists capture foot morphology in order to design custom orthoses (insoles). While various 3D scanning technologies are used in clinical practice, they vary greatly in cost and ease of use and many of these are not specifically designed for podiatry applications. There is limited literature comparing accuracy between scanners, and many approaches require prolonged scan times during which the patient must remain still. Multicamera photogrammetry offers a promising solution by enabling high-quality, rapid 3D scanning which other devices cannot provide. This study compared the accuracy and clinical utility of four 3D scanners. One was a high accuracy reference scanner (Artec Spider) which was used as a gold standard. Two further scanners which are commonly used in the clinic were also investigated (Apple iPad 6 with Structure Sensor attachment ‘iPad’, and Envisic VeriScan Podiatric Scanner ‘laser’) and these were directly compared with a novel prototype multicamera photogrammetry 3D scanner. The left feet of 20 healthy volunteers were scanned using each of the four devices and scans were evaluated for accuracy, completeness, and acquisition and processing times. All scanners produced clinically acceptable scans, with the novel photogrammetry scanner demonstrating superior accuracy. Scan times varied significantly between scanners, with the photogrammetry device capturing scans much faster. All scanners had acceptable levels of completeness, though the iPad and photogrammetry outperformed the laser scanner. These results provide a valuable tool for clinics seeking guidance on scanner selection and highlight the benefits of instantaneous photogrammetry scanning to improve workflow efficiency and accessibility.

Scaffold-guided bone regeneration is poised to revolutionize the management of critical-sized bone defects. However, translation into clinical practice has been hampered by the focus on bioresorbable scaffolds where the rate of degradation needs to match the rate of bone formation and metal plates are required to overcome their mechanical limitations. Metal plates are problematic because they cause stress shielding and X-ray perturbation, increasing the likelihood of hardware failure and interfering with post-operative radiotherapy and imaging. Segmental defects of the mandible are challenging due to high tensile and shear stresses encountered during mastication, with the ovine mandible especially vexing because of the high repetitive loads. Here we show long-term reconstruction of ovine segmental mandibulectomy defects using a permanent, patient-matched, numerically optimized, 3D-printed, thermally toughened, plasma-treated, and laser-sintered polyetherketone gyroid scaffold housing a resorbable ceramic lattice infused with a stem cell laden hydrogel serving as an osteoinductive reservoir of calcium. The durable clinical performance observed indicates a translatable alternative to traditional reconstruction using bone grafts with metal plate fixation.

Osseointegration is a crucial property of biomaterials used for bone defect repair. While titanium is the gold standard in craniofacial surgeries, various polymeric biomaterials are being explored as alternatives. However, polymeric materials can be bioinert, hindering integration with surrounding tissues. In this investigation, plasma ion immersion implantation (PIII)-treated polyether ether ketone (PEEK) and polyether ketone (PEK) implants were assessed in a sheep maxilla and mandible model. Defects were filled with PIII-treated PEEK and PEK implants, produced through fused filament fabrication (FFF) and selective laser sintering (SLS), respectively. Positive controls were grade 23 titanium implants via selective laser melting, while untreated PEEK implants served as negative controls. Surface analyses using scanning electron microscopy and atomic force microscopy revealed favorable properties. Osseointegration was qualitatively and quantitatively assessed at 8-, 10-, and 12-weeks post-implantation, showing significantly improved outcomes for both PIII-treated PEEK and PEK implants compared to untreated controls. The study suggests PIII treatment enhances FFF-printed PEEK's osseointegration, and PIII-treated SLS-printed PEK achieves comparable osseointegration to 3D printed titanium. These findings underscore surface modification strategies' potential for polymeric biomaterials, offering insights into developing alternative implant materials for craniofacial surgeries, with enhanced biocompatibility and osseointegration capabilities for improved clinical outcomes.

PurposeRecent developments in additive manufacturing have made possible the fabrication of custom clinical devices like wheelchair cushions that are tuneable, comfortable, and capable of achieving pressure offloading to reduce the risk of pressure injuries developing. However, no published research has demonstrated that 3D printed cushions have equivalent performance to their traditionally manufactured counterparts, which is a requisite first step towards this vision. To address this gap, this paper compares a variable stiffness 3D printed thermoplastic polyurethane gyroid wheelchair cushion with a conventional multilayered foam cushion.Materials and MethodsThe cushion was designed and printed in four sections, enabling the use of consumer grade 3D printers. The 3D printed cushion was designed with varying stiffness regions to offload pressure. Twenty-one healthy adult subjects (11 men, 10 women, age range 19-48 years, mean weight 76 kg) sat on both cushions in a blind study. Participants completed a comfort survey and cushion temperature was measured using infrared thermography. Pressure mapping data was collected for three additional subjects to compare peak contact pressure and pressure distribution across cushions.ResultsThe 3D printed and foam cushions performed equally in terms of comfort, pressure, and temperature. Notably, participants were unable to identify a difference in them when seated. Contact pressure measurements were similar across both cushion types. The 3D printed cushion was significantly cheaper and able to be customised to a specific patient at little additional cost.ConclusionsIt was concluded that 3D printed cushion can match the performance of an existing standard of care cushion. This provides the foundation for future development of personalised 3D printed cushions offering significant advances in affordability, comfort, and pressure reduction, for wheelchair users.

Big mechanically-active culture systems (BigMACS) are promising to stimulate, control, and pattern cell and tissue behaviours with less soluble factor requirements. However, it remains challenging to predict if and how distributed mechanical forces impact single-cell behaviours to pattern tissue. In this study, we introduce a tissue-scale finite element analysis framework able to correlate sub-cellular quantitative histology with centimetre-scale biomechanics. Our framework is relevant to diverse BigMACS, including media perfusion, tensile-stress, magnetic, and pneumatic tissue culture platforms. We apply our framework to understand how the design and operation of a multi-axial soft robotic bioreactor can spatially control mesenchymal stem cell (MSC) proliferation, orientation, differentiation to smooth muscle, and extracellular vascular matrix deposition. We find MSC proliferation and matrix deposition to positively correlate with mechanical stimulation but cannot be locally patterned by soft robot mechanical stimulation within a centimetre scale tissue. In contrast, local stress distribution was able to locally pattern MSC orientation and differentiation to smooth muscle phenotypes, where MSCs aligned perpendicular to principal stress direction and expressed increased α-SMA with increasing 3D Von Mises Stresses from 0 to 15 kPa. Altogether, our new biomechanical-histological simulation framework is a promising technique to derive the future mechanical design equations to control cell behaviours and engineer patterned tissue.

Congenital microtia manifests abnormalities in the external ear leading to potential adverse impacts on psychosocial health and hearing impairment. Three-dimensional (3D) technologies have demonstrated potential applications for personalised prosthesis fabrication; however, the large hardware costs limit their routine clinical use. Frugal 3D scan-model-print pipelines can disrupt traditional processes and increase accessibility. In this study, we aimed to further validate 3D photogrammetry using 3 different smartphone models. Both ears of 10 participants were scanned with 4 devices: Samsung Galaxy S8, Samsung Galaxy S9, Apple® iPhone 8S, and Artec Spider 3D scanner. Scan, processing times, accuracy, completeness, and repeatability of the smartphone models were analysed with no significant difference across all tested models (Accuracy: 1.1 ± 0.3 mm, Completeness: 81 ± 10%). This demonstrates a flexibility in capture device selection for smartphone photogrammetry, with the potential to broaden the translation of this frugal 3D scanning approach to personalised prosthesis production.

Despite the growing significance of generating highly porous, high-precision 3D printed scaffolds using melt electrowriting (MEW), the absence of easy-to-use and robust design and g-code generation tools hinders its effectiveness and widespread adoption. This article introduces a versatile scaffold design workflow for MEW fabrication, drawing on learnings in scaffold design and fabrication optimization from pioneers in the field and unifies innovative approaches into one user-friendly platform. The application contains a library of validated flat and tubular patterns, as well as incorporating automated solutions to common challenges such as scaffold dimension fitting and toolpath corrections previously reported in the literature and historically challenging to deploy into new g-codes. Available to users via GitHub, this application readily generates a g-code that compensates for MEW fiber lag across diverse geometries on a variety of flat and cylindrical collectors. The application's capabilities are demonstrated through proof-of-concept prints, including layer-shifting strategies, and their effects on scaffold mechanical properties. By integrating design flexibility, layer-shifting strategies, and advanced visualization, this application streamlines the MEW scaffold design process, offering a valuable tool for researchers and promises to both advance the field and enable greater access to tools required to produce high-quality, reproducible scaffolds. This study presents a versatile scaffold design software for melt electrowriting (MEW) fabrication. Consolidating a broad library of scaffold design patterns and fabrication correction tools presented in the MEW literature, this software enables rapid design iterations and automatic g-code generation. Using this software, researchers can incorporate best practice scaffold fabrication features to improve print accuracy, and reproducibility, and accelerate MEW innovation. image

This study demonstrates a new approach to manufacturing biomimetic auricular surgical implants using melt electrowriting (MEW) technology to fabricate microfiber high-density polyethylene (HDPE) scaffolds. An emerging filament-driven printhead and MEW printer, termed the "MEWron", is used to enable precise control over the material extrusion process and fiber formation. By predicting the optimal extrusion conditions, continuous and uninterrupted fiber production is achieved, enabling further optimization of filament-driven MEW fibers with a diameter of 60.5 +/- 2.6 mu m. As a case study, an application of microfiber HDPE fabrication is selected that comprised the design and fabrication of personalized auricular (ear) surgical implants, specifically tailored to match the unique morphology of individual patients. Patient-specific implant models matched to the natural shape and structure of the human ear are successfully fabricated. Furthermore, the manufactured implants exhibit excellent mechanical properties, offering a 13-fold increase in tensile stiffness compared to MEW PCL scaffolds. Overall, this research demonstrates the feasibility and potential of MEW-based HDPE implants as a promising alternative to traditional auricular reconstruction methods, offering an alternative avenue for improved patient outcomes and enhanced aesthetic results. Using melt electrowriting (MEW) technology, biomimetic auricular surgical implants are fabricated using high density polyethylene. Precise control over material extrusion and fiber formation is achieved using a filament-driven printhead. Patient-specific auricular implants with excellent mechanical properties are successfully fabricated, demonstrating the potential of MEW-based HDPE implants as an alternative for improved auricular reconstruction and enhanced aesthetics.image

Cardiovascular disease (CVD) is the leading cause of mortality worldwide and its incidence is rising due to an aging population. The development and progression of CVD is directly linked to adverse vascular hemodynamics and biomechanics, whose in-vivo measurement remains challenging but can be simulated numerically and experimentally. The ability to evaluate these parameters in patient-specific CVD cases is crucial to better predict future disease progression, risk of adverse events, and treatment efficacy. While significant progress has been made toward patient-specific hemodynamic simulations, blood vessels are often assumed to be rigid, which does not consider the compliant mechanical properties of vessels whose malfunction is implicated in disease. In an effort to simulate the biomechanics of flexible vessels, fluid-structure interaction (FSI) simulations have emerged as promising tools for the characterization of hemodynamics within patient-specific cardiovascular anatomies. Since FSI simulations combine the blood's fluid domain with the arterial structural domain, they pose novel challenges for their experimental validation. This paper reviews the scientific work related to FSI simulations for patient-specific arterial geometries and the current standard of FSI model validation including the use of compliant arterial phantoms, which offer novel potential for the experimental validation of FSI results.

The field of melt electrowriting (MEW) has seen significant progress, bringing innovative advancements to the fabrication of biomaterial scaffolds, and creating new possibilities for applications in tissue engineering and beyond. Multidisciplinary collaboration across materials science, computational modeling, AI, bioprinting, microfluidics, and dynamic culture systems offers promising new opportunities to gain deeper insights into complex biological systems. As the focus shifts towards personalized medicine and reduced reliance on animal models, the multidisciplinary approach becomes indispensable. This review provides a concise overview of current strategies and innovations in controlling and optimizing cellular responses to MEW scaffolds, highlighting the potential of scaffold material, MEW architecture, and computational modeling tools to accelerate the development of efficient biomimetic systems. Innovations in material science and the incorporation of biologics into MEW scaffolds have shown great potential in adding biomimetic complexity to engineered biological systems. These techniques pave the way for exciting possibilities for tissue modeling and regeneration, personalized drug screening, and cell therapies.

End-to-side anastomoses are commonly utilised in peripheral arterial bypass surgery and are plagued by high rates of re-stenosis as a result of non-physiological blood flow impacting arterial and graft structures. Computational simulations can examine how patient-specific surgical decisions in bypass graft placement and material selection affect blood flow and future risk of graft restenosis. Despite graft geometry and compliance being key predictors of restenosis, current simulations do not consider the interaction of flowing blood with compliant vessel, graft, and suture structures. Utilising fluid-structure interaction simulations, this study examines the impact of surgical technique, such as anastomosis angle, graft material, and suture material, on blood flow and fluid-structure forces in patient-specific asymptomatic arterial tree versus side-to-end peripheral grafts for symptomatic atherosclerotic disease. To render these complex simulations numerically feasible, our pipeline uses regional suture mechanics and a pre-stress pipeline previously validated in small-scale idealised models. Our simulations found that higher anastomosis angles generate larger regions of slow and recirculating blood, characterised by non-physiologically low shear stress and high oscillatory shear index. The use of compliant graft materials reduces regions of non-physiologically high shear stress only when used in combination with compliant suture materials. Altogether, our fluid-structure interaction simulation provides patient-specific platforms for vascular surgery decisions concerning graft geometry and material. ### Competing Interest Statement DFF consults to the local Ansys distributors which gives him access to Ansys technical staff as needed. The remaining authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The femoropopliteal artery (FPA) is a long, flexible vessel that travels down the anteromedial compartment of the thigh as the femoral artery and then behind the kneecap as the popliteal artery. This artery undergoes various degrees of flexion, extension, and torsion during normal walking movements. The FPA is also the most susceptible peripheral artery to atherosclerosis and is where peripheral artery disease manifests in 80% of cases. The connection between peripheral artery location, its mechanical flexion, and its physiological or pathological biochemistry has been investigated for decades; however, histochemical methods remain poorly leveraged in their ability to spatially correlate normal or abnormal extracellular matrix and cells with regions of mechanical flexion. This study generates new histological image processing pipelines to quantitate tissue composition across high-resolution FPA regions-of-interest or low-resolution whole-section cross-sections in relation to their anatomical locations and flexions during normal movement. Comparing healthy ovine femoral, popliteal, and cranial-tibial artery sections as a pilot, substantial arterial contortion was observed in the distal popliteal and cranial tibial regions of the FPA which correlated with increased vascular smooth muscle cells and decreased elastin content. These methods aim to aid in the quantitative characterization of the spatial distribution of extracellular matrix and cells in large heterogeneous tissue sections such as the FPA. RESEARCH HIGHLIGHTS: Large-format histology preserves artery architecture. Elastin and smooth muscle content is correlated with distance from heart and contortion during flexion. Cell and protein analyses are sensitive to sectioning plane and image magnification.

Ear prostheses are commonly used for restoring aesthetics to those suffering missing or malformed external ears. Traditional fabrication of these prostheses is labour intensive and requires expert skill from a prosthetist. Advanced manufacturing including 3D scanning, modelling and 3D printing has the potential to improve this process, although more work is required before it is ready for routine clinical use. In this paper, we introduce a parametric modelling technique capable of producing high quality 3D models of the human ear from low-fidelity, frugal, patient scans; significantly reducing time, complexity and cost. Our ear model can be tuned to fit the frugal low-fidelity 3D scan through; (a) manual tuning, or (b) our automated particle filter approach. This potentially enables low-cost smartphone photogrammetry-based 3D scanning for high quality personalised 3D printed ear prosthesis. In comparison to standard photogrammetry, our parametric model improves completeness, from (81 ± 5)% to (87 ± 4)%, with only a modest reduction in accuracy, with root mean square error (RMSE) increasing from (1.0 ± 0.2) mm to (1.5 ± 0.2) mm (relative to metrology rated reference 3D scans, n = 14). Despite this reduction in the RMS accuracy, our parametric model improves the overall quality, realism, and smoothness. Our automated particle filter method differs only modestly compared to manual adjustments. Overall, our parametric ear model can significantly improve quality, smoothness and completeness of 3D models produced from 30-photograph photogrammetry. This enables frugal high-quality 3D ear models to be produced for use in the advanced manufacturing of ear prostheses.

This study demonstrates how either a heated flat or cylindrical collector enables defect-free melt electrowriting (MEW) of complex geometries from high melting temperature polymers. The open-source "MEWron" printer uses nylon-12 filament and combined with a heated flat or cylindrical collector, produces well-defined fibers with diameters ranging from 33±4 µm to 95±3 µm. We optimize processing parameters for stable jet formation and minimal defects based on thermal modeling for hardware design. We achieve the balance of processing temperature and collector temperature to achieve auxetic patterns, while showing that annealing nylon-12 tubes significantly alters their mechanical properties. The samples exhibit varied pore sizes and wall thicknesses influenced by jet dynamics and fiber bridging. Tensile testing shows nylon-12 tubes are notably stronger than PCL ones and while annealing has limited impact on tensile strength, yield, and elastic modulus, it dramatically reduces elongation. The equipment described and material used broadens MEW applications for high melting point polymers and highlights the importance of cooling dynamics for reproducible samples.

Vascular compliance is considered both a cause and a consequence of cardiovascular disease and a significant factor in the mid- and long-term patency of vascular grafts. However, the biomechanical effects of localised changes in compliance cannot be satisfactorily studied with the available medical imaging technologies or surgical simulation materials. To address this unmet need, we developed a coupled silico-vitro platform which allows for the validation of numerical fluid-structure interaction results as a numerical model and physical prototype. This numerical one-way and two-way fluid-structure interaction study is based on a three-dimensional computer model of an idealised femoral artery which is validated against patient measurements derived from the literature. The numerical results are then compared with experimental values collected from compliant arterial phantoms via direct pressurisation and ring tensile testing. Phantoms within a compliance range of 1.4-68.0%/ 100 mmHg were fabricated via additive manufacturing and silicone casting, then mechanically characterised via ring tensile testing and optical analysis under direct pressurisation with moderately statistically significant differences in measured compliance ranging between 10 and 20% for the two methods. One-way fluid-structure interaction coupling underestimated arterial wall compliance by up to 14.7% compared with two-way coupled models. Overall, SolarisTM (Smooth-On) matched the compliance range of the numerical and in vivo patient models most closely out of the tested silicone materials. Our approach is promising for vascular applications where mechanical compliance is especially important, such as the study of diseases which commonly affect arterial wall stiffness, such as atherosclerosis, and the model-based design, surgical training, and optimisation of vascular prostheses.

BACKGROUND:Non-removable knee-high devices are the gold-standard offloading treatments to heal plantar diabetic foot ulcers (DFUs). These devices are underused in practice for a variety of reasons. Recommending these devices for all patients, regardless of their circumstances and preferences influencing their ability to tolerate the devices, does not seem a fruitful approach.PURPOSE:The aim of this article is to explore the potential implications of a more personalized approach to offloading DFUs and suggest avenues for future research and development.METHODS:Non-removable knee-high devices effectively heal plantar DFUs by reducing plantar pressure and shear at the DFU, reducing weight-bearing activity and enforcing high adherence. We propose that future offloading devices should be developed that aim to optimize these mechanisms according to each individual's needs. We suggest three different approaches may be developed to achieve such personalized offloading treatment. First, we suggest modular devices, where different mechanical features (rocker-bottom sole, knee-high cast walls/struts, etc.) can be added or removed from the device to accommodate different patients' needs and the evolving needs of the patient throughout the treatment period. Second, advanced manufacturing techniques and novel materials could be used to personalize the design of their devices, thereby improving common hindrances to their use, such as devices being heavy, bulky, and hot. Third, sensors could be used to provide real-time feedback to patients and clinicians on plantar pressures, shear, weight-bearing activity, and adherence.CONCLUSIONS:By the use of these approaches, we could provide patients with personalized devices to optimize plantar tissue stress, thereby improving clinical outcomes.

Melt electrowriting (MEW) is an additive manufacturing technique characterized by its ability to fabricate micronscale fibers from molten polymers into highly controlled 3D microfiber scaffolds. This emerging technique is gaining traction in tissue engineering and biofabrication research, however limitations in the ability to develop advanced coding to program MEW printers to fabricate scaffolds with complex fiber architectures has inhibited the development of structures with tunable and biomimetic mechanical properties. This study reports a series of non-straight scaffold architectures with combinations of independently controlled X & Y fiber spacing, corrections for MEW jet lag , and characterizations of their influences on scaffold mechanics. Polycaprolactone scaffolds with an elastic modulus ranging from 0.3 to 7.3 MPa were fabricated utilizing scaffolds manufactured from 5 layers of 55 μm fibers. The inclusion of scaffold design corrections in the gcode to compensate for decreasing deposition accuracy with increasing layer height enabled us to correct for discontinuous stress-strain mechanics and improved scaffold fabrication reproducibility. This study provides a comparison between a series of highly reproducible MEW scaffold architectures with non-straight fibers compared to the common crosshatch design to inform the development of more biomimetic scaffolds applicable to a variety of clinical applications. It further illustrates the significant effect toolpath correction has on reducing poor stress-strain mechanics, therefore improving the control, reproducibility, and biomimetic capacity of the MEW technique.

AbstractVascular compliance is considered both a cause and a consequence of cardiovascular disease and a significant factor in the mid- and long-term patency of vascular grafts. However, the biomechanical effects of localised changes in compliance, such as during plaque development or after bypass grafting and stenting, cannot be satisfactorily studied with the available medical imaging technologies or surgical simulation materials. To address this unmet need, we developed a coupledsilico-vitroplatform which allows for the validation of numerical fluid-structure interaction (FSI) results as a numerical model and physical prototype. This numerical one-way and two-way FSI study is based on a three-dimensional computer model of an idealised femoral artery which is validated against patient measurements derived from the literature. The numerical results are then compared with experimental values collected from compliant arterial phantoms. Phantoms within a compliance range of 1.4 - 68.0%/100mmHg were fabricatedviaadditive manufacturing and silicone casting, then mechanically characterisedviaring tensile testing and optical analysis under direct pressurisation with differences in measured compliance ranging between 10 - 20% for the two methods. One-way FSI coupling underestimated arterial wall compliance by up to 14.71% compared to two-way FSI modelling. Overall, Smooth-On Solaris matched the compliance range of the numerical andin vivopatient models most closely out of the tested silicone materials. Our approach is promising for vascular applications where mechanical compliance is especially important, such as the study of diseases which commonly affect arterial wall stiffness, such as atherosclerosis, and the model-based design, surgical training, and optimisation of vascular prostheses.