BACKGROUND:Implant orientation has been linked to postoperative outcomes and is frequently assessed on radiographs. However, the projection of the three-dimensional joint and implant structure to a two-dimensional radiograph complicates its assessment. The main objective of this study was to demonstrate a novel method for evaluating radiographic stem version, in a manner robust to multiaxial rotations, particularly AP tilt and flexion. METHODS:Radiographic features where synthesised using a computational stem geometry and radiographic simulation, building in clinical error sources. Features trained a Gaussian process regression predictor of radiographic stem version. The impact of AP tilt on the accuracy of the Weber technique was then evaluated and the feasibility of AP tilt assessment from the same radiograph investigated. FINDINGS:Radiographic stem version prediction accuracy was evaluated on in vitro radiographs with R2 rising from 0.85 (P < 0.01) using the Weber technique to 0.98 (P < 0.01) using the trained model. Similar results were observed in a larger in silico dataset with R2 rising from 0.89 (P < 0.01) to 0.98 (P < 0.01). Tilt was shown to reduce the accuracy of the Weber technique. Projectional symmetry was then demonstrated about the femoral implant with AP tilt, elucidating ambiguity when assessing tilt on an AP radiograph. INTERPRETATION:The novel feature-based method is a reliable measure of radiographic stem version that is robust to variation on multiaxial orientation, allowing assessment of changing rotation in series of postoperative radiographs. However, a controlled radiograph is required to ensure this mirrors implanted stem version.

Crystal structure and morphology dictate the mechanical, thermal, and degradation properties of poly l-lactide (PLLA), the structural polymer of the first clinically approved bioresorbable vascular scaffolds (BVS). New experimental methods are developed to reveal the underlying mechanisms governing structure formation during the crimping step of the BVS manufacturing process. Our research specifically examines the "U-bends" - the region where the curvature is highest and stress is maximised during crimping, which can potentially lead to failure of the device with dramatic consequences on patient life. A custom-made crimping rig operated at a synchrotron beamline enabled collection of wide- and small-angle X-ray scattering (WAXS/SAXS) to probe local variations of the polymer morphology as a function of position in the crest of multiple U-bends with 5 μm resolution in situ after crimping and expansion. Additionally, polarised light microscopy (PLM) images of these deformed U-bends revealed areas with varying stress distribution developed during crimping and expansion. These variations were dependant on the initial biaxial stretching processing step. The integrated X-ray scattering-microscopy approach offered a comprehensive work-flow for uncovering the intricate relationship between processing conditions and the corresponding spatially-resolved semicrystalline morphology of a BVS. STATEMENT OF SIGNIFICANCE: This research introduces a new method for gaining critical insights into the structural changes that occur during the manufacturing process of bioresorbable vascular scaffolds (BVS). The crimping and expansion of poly l-lactide (PLLA) - the structural material of BVS - are sequential manufacturing steps characterised by highly non-linear deformations at temperature conditions that remain unexplored. By utilising synchrotron X-ray scattering techniques alongside polarised light microscopy, we have developed new experimental methods to uncover the mechanisms governing structure formation during processing. This innovative approach not only deepens our understanding of the relationship between processing conditions and polymer morphology but also establishes the foundation for real-time observation methods during crimping and expansion. By improving the design and performance of BVS, this study has the potential to advance cardiovascular treatments and improve patient safety, making it highly relevant and impactful to both scientific research and clinical applications.

IntroductionThe incidences of fragility fractures, often because of osteoporosis, are increasing. Research has moved towards bioresorbable scaffolds that provide temporary mechanical stability and promote osteogenesis. This research aims to fabricate a 3D printed composite Poly (l-lactic-co-glycolic acid)-strontium doped tricalcium phosphate (PLGA-SrTCP) scaffold and evaluate in an in vitro co culture study containing osteoporotic donor cells.MethodPLGA, PLGA TCP, and PLGA SrTCP scaffolds were produced using Fused Filament Fabrication (FFF). A four-group 35-day cell culture study was carried out using human bone marrow derived mesenchymal stem cells (hMSCs) from osteoporotic and control donors (monoculture) and hMSCs & human monocytes (hMCs) (Co culture). Outcome measures were biochemical assays, PCR, and cell imaging. Cells were cultured on scaffolds that had been pre-degraded for six weeks at 47°C prior to drying and gamma sterilisation.Result3D printed scaffolds were successfully produced by FFF. All groups in the study supported cell attachment onto the scaffolds, producing extracellular matrices as well as evidence of osteoclast cell structures. Osteoporotic cells increased CTSK activity and CAII activity and decreased ALP activity compared to controls. In control cultures, the addition of bTCP and bTCP/Sr to the PLGA reduced TRAP5b, CAII and ALP activity compared to PLGA alone. The addition of Sr did not show any differences between donors.ConclusionThis study details suitability of 3D printed polymer scaffolds for use in bone tissue applications. Both composite and pure polymer scaffolds promote osteogenesis in vitro. The introduction of ceramic filler and ion doping does not beneficially effect osteogenic potential and can reduce its ability compared to pure polymer. This study suggests the behaviour of control and osteoporotic cells are different and that osteoporotic cells are more prone to bone resorption. Therefore, it is important to design bone scaffolds that are specific to the patient as well as to the region of fracture.

Bioresorbable poly-L-lactide (PLLA) stents have the potential to fully dissolve after treating injured arteries, leaving nothing behind. However, the manufacturing process for bioresorbable stents (BRS) needs further refinement to eventually replace current permanent stents. This study investigates the effect of radial and biaxial expansion procedures on the microstructure and mechanical properties of PLLA expanded tubes using microfocus wide -angle X-ray scattering (WAXS) and multi-directional tensile tests. A complex microstructure with an orientation gradient across the thickness of the tube wall was observed and linked to the strain history experienced during processing. Correlations between the stretch ratios applied and the mechanical properties of the PLLA tubes were also noted and discussed in relation to stent application.

Layer-by-layer (LbL) assembly is a powerful technique for fabricating nanocomposite thin-film coatings with a diverse range of constituents, properties, and functionalities. Templated deposition of these coatings has enabled the translation of mechanical properties from the microscale of thin-films to the macro-scale of nanocompositecoated porous materials and has been used to tailor the elastic modulus and porosity of coated open-cell foams for potential applications including lightweight structures and engineered tissue scaffolds. However, the presence of moisture in these application environments is expected to affect the physico-mechanical behavior of the nanocomposite coating. In this work, open-cell foams coated with nanocomposites consisting of poly(ethyleneimine), poly(acrylic acid), and Na+-montmorillonite were characterised under high relative humidity and upon complete submersion in water. The nanocomposite coating imparted a substantial increase in compressive elastic modulus when tested under ambient conditions, from 0.08 +/- 0.00 MPa to 4.90 +/- 0.46 MPa, but had little to no mechanical effect when hydrated, and upon drying the mechanical properties of coated foams recovered to pre-hydrated levels. Chemical crosslinking of amine groups within the polymers resulted in the retention of significant compressive elastic modulus of 2.91 +/- 0.49 MPa when hydrated. Initial trials showed that uncrosslinked coated foams exhibit a hydration induced shape memory effect that could be used to enable the actuation or expansion of a previously passive open-cell foam.

A novel method aimed at evaluating the active drag profile during front-crawl swimming is proposed. Fourteen full trials were conducted with each trial using a stationary load cell set-up and a commercial resistance trainer to record the tension force in a rope, caused by an athlete swimming. Seven different stroke cycles in each experiment were identified for resampling time dependent data into position dependent data. Active drag was then calculated by subtracting resistance trainer force data away from the stationary load cell force data. Mean active drag values across the stroke cycle were calculated for comparison with existing methods, with mean active drag values calculated between 76 and 140 N depending on the trial. Comparing results with established active drag methods, such as the Velocity Perturbation Method (VPM), shows agreement in the magnitude of the mean active drag forces. Repeatability was investigated using one athlete, repeating the load cell set-up experiment, indicating results collected could range by 88 N depending on stroke cycle position. Variation in results is likely due to inconsistencies in swimmer technique and power output, although further investigation is required. The method outlined is proposed as a representation of the active drag profile over a full stroke cycle.

Computed-Tomography scans represent the gold standard for accuracy when preoperatively templating and postoperatively assessing the hip. However, planar radiographs are used as standard, sacrificing accuracy. In this work, a method is proposed to more accurately assess femoral offset and neck-shaft angle from two planar radiographs (frontal and lateral), allowing more reliable templating of a modular stem. A second method is proposed to accurately assess postoperative stem version from planar frontal radiographs.

In situ synchrotron X-ray scattering was used to reveal the transient microstructure of poly(L-lactide) (PLLA)/tungsten disulfide inorganic nanotubes (WS2NTs) nanocomposites. This microstructure is formed during the blow molding process (“tube expansion”) of an extruded polymer tube, an important step in the manufacturing of PLLA-based bioresorbable vascular scaffolds (BVS). A fundamental understanding of how such a microstructure develops during processing is relevant to two unmet needs in PLLA-based BVS: increasing strength to enable thinner devices and improving radiopacity to enable imaging during implantation. Here, we focus on how the flow generated during tube expansion affects the orientation of the WS2NTs and the formation of polymer crystals by comparing neat PLLA and nanocomposite tubes under different expansion conditions. Surprisingly, the WS2NTs remain oriented along the extrusion direction despite significant strain in the transverse direction while the PLLA crystals (c-axis) form along the circumferential direction of the tube. Although WS2NTs promote the nucleation of PLLA crystals in nanocomposite tubes, crystallization proceeds with largely the same orientation as in neat PLLA tubes. We suggest that the reason for the unusual independence of the orientations of the nanotubes and polymer crystals stems from the favorable interaction between PLLA and WS2NTs. This favorable interaction leads WS2NTs to disperse well in PLLA and strongly orient along the axis of the PLLA tube during extrusion. As a consequence, the nanotubes are aligned orthogonally to the circumferential stretching direction, which appears to decouple the orientations of PLLA crystals and WS2NTs.

Polymer crystallization, particularly near the glass transition, exhibits strong nonlinearities and prolonged metastability that enable fabrication of devices with complex hierarchal structure from nm to mm. A fascinating example arises in the production of bioresorbable scaffolds (BRS) from poly(L-lactide) (PLLA), in which a sequence of processes (extrusion, stretch-blow molding and crimping) create diverse semicrystalline morphologies, side-by-side within a span of a hundred microns ( Figure 1) . To discover how these structures form, we need to examine transient structure under conditions that mimic manufacturing processes. An apparatus that enables scattering measurements during the stretch- blow molding step, called “tube expansion” imposes a nearly constant-width elongation as it converts an extruded “preform” into an “expanded tube”. To increase the range of accessible properties of PLLA -based BRS, we use this apparatus to examine inorganic nanotubes as potential reinforcing agents that also enhance radiopacity, relevant to clinical applications. Understanding how their microstructure develops during processing is relevant to increasing strength to enable thinner devices and improving radiopacity to enable imaging during implantation. Consistent with the premise of this MS, in-situ X-ray scattering reveals unanticipated phenomena in the transient microstructure of PLLA/WS 2 NTs nanocomposites during “tube expansion” ( Figure 2 ). Surprisingly, the WS 2 NT orientation hardly changes from that produced during extrusion of the preform ( z -dir., defined Fig. 1A), despite significant strain in the transverse direction (at inner diameter, 500% strain in  -dir. ). Although WS 2 NTs promote PLLA nucleation, the NTs do not modify the orientation of crystallization (c-axis along  , just as observed in tube expansion of neat PLLA). The striking independence of the orientations of the NT and polymer crystals stems may arise from the favorable interaction between PLLA and WS 2 NTs: facile and stable dispersion of WS 2 NTs in PLLA enables strong NT orientation in shear (extrusion); NT that are orthogonal to the stretching direction do not reorient; remaining orthogonal to decouples WS 2 NT orientation from that of PLLA crystals. Future directions include evaluating cross-reinforcement of the mutually orthogonal NT and PLLA crystals. Based on the surprising effects we have found, further discoveries likely lie ahead in the effects of WS 2 NT on morphology development during crimping.

Background: In total hip arthroplasty the surgeon aims to restore the biomechanics of the joint. Femoral height has the greatest influence on restoring limb length and contributes equally to the restoration of femoral head centre. On X-ray, the level of femoral neck resection is most often referenced off the upper border of lesser trochanter. Less frequently, femoral head centre is referenced from the tip of the greater trochanter. The error in measurement of femoral height resulting from unknown femoral rotation is crucially important and can result in inappropriate surgical planning for implant selection and placement. It is unknown which reference produces lower error. Methods: A sample of femoral shapes was generated using a femoral statistical shape model. These were placed in a range of orientations in terms of external rotation and flexion, at intervals of 10 degrees. Simulated X-rays were then produced and the distances from the tip of either greater or lesser trochanter to femoral head centre were measured. Findings: Although using greater trochanter as a reference demonstrated greater errors at the extremes, both techniques resulted in errors of 7-8 mm with 20 degrees of both femoral external rotation and flexion. Interpretation: Moderate degrees of femoral external rotation combined with flexion can result in unsatisfactory errors when templating limb length. There should be greater focus and an agreed definition for femoral height. There is a clinical need for a method with a lower error in determining true femoral height and the level of neck resection.

Introduction Up to 20-30% of women over the age of 20 may suffer from pelvic floor disorders and up to 50% of women over the age of 501. Furthermore, injuries to the pelvic floor muscles as a result of childbirth can lead to varying types of incontinence, pelvic organ prolapse (POP), and avulsions2 3. Better understanding of the mechanical properties of the muscles is thus required to improve risk assessment for child birth induced injury. As pelvic floor muscle is anisotropic and can be subjected to large multiaxial deformations during childbirth, mechanical characterisation requires multi-axial testing. Pelvic floor tissue sample sizes are typically small (<20mm) and expected forces are low (<15N). Modern commercially available machines are big and expensive, designed to apply large load to structural materials. The aim of this project is to develop a displacement-controlled multiaxial stretching device for characterising viscoelastic properties of female pelvic floor tissue.

Binder jetting additive manufacturing (AM) is a promising process to print hydroxyapatite (HA) powder into bone tissue implants. However, one challenge remaining is the poor reactivity between HA powder with standard water-based ink. This study investigated different water-soluble adhesives to increase the 3D printability of HA powder. Maltodextrin and polyvinyl alcohol (PVOH) with low and high molecular weight (MW) were blended with HA from 10 to 30 wt%. Powder characterisation and evaluation of the compressive properties and geometrical accuracy of the 3D printed scaffolds were performed to identify the optimal adhesive powder. This study adopted an image registration technique to quantify the geometrical accuracy of the final 3D printed scaffold in a more comprehensive and representative way than conventionally dimensional measurement. With these approaches, a highly promising binder jetting formulation has been developed via mixing HA powder with 30 wt% PVOH (high MW). Samples manufactured from this formulation successfully achieved a geometrical accuracy greater than 85% and an excellent green compressive strength of 5.63 +/- 0.27 MPa, which was 500% higher than the commercial binder jetting powder. This is the first study to demonstrate a high level of printability when using a formulation containing >= 70 wt% HA powder and a water-based binder in the binder jetting AM process. Using the optimal powder composition developed in this study could potentially improve the structural, mechanical, and biological performances of HA-based 3D scaffolds manufactured using the binder jetting AM process for bone tissue engineering applications.

INTRODUCTION::Acetabular cup orientation during total hip arthroplasty (THA) remains a challenge. This is influenced by patient positioning during surgery and the method used to orientate the acetabular cup. The aim of this study was to assess current UK practice for patient positioning and cup orientation, particularly with respect to patient supports and techniques used to achieve target version and inclination.METHODS::A literature review and pilot study were initially conducted to develop the questionnaire, which was completed by British Hip Society members ( n = 183). As the majority of THA surgical procedures within the UK are performed with the patient in lateral decubitus, orthopaedic surgeons who operated with the patient in the supine position were excluded ( n = 18); a further 6% were incomplete and also excluded ( n = 11).RESULTS::Of those who operated in lateral decubitus, 76.6% ( n = 118/154) used the posterior approach. Only 31% ( n = 47/154) considered their supports to be completely rigid. More than 35% ( n = 55/154) were unhappy with the supports that they presently use. The most common methods for controlling operative inclination and version were a mechanical alignment guide (MAG; n = 78/154; 50.6%) and the transverse acetabular ligament (TAL; n = 82/154; 53.2%); 31.2% (48/154) used a freehand technique to control operative inclination.CONCLUSION::Limited studies have been conducted whereby patient supports have been analysed and key design principles outlined. With 35.7% of the orthopaedic surgeons surveyed having issues with their current supports, a greater awareness of essential characteristics for patient supports is required.

Orthopaedic surgeons often experience a mismatch between perceived intra-operative and radiographic acetabular cup orientation. This research aimed to assess the impact of pelvic orientation and surgical positioning technique on operative and radiographic cup orientation. Radiographic orientations for two surgical approaches were computationally simulated: a mechanical alignment guide and a transverse acetabular ligament approach, both in combination with different pelvic orientations. Positional errors were defined as the difference between the target radiographic orientation and that achieved. The transverse acetabular ligament method demonstrated smaller positional errors for radiographic version; 4.0° ± 2.9° as compared to 9.4° ± 7.3° for the mechanical alignment guide method. However, both methods resulted in similar errors in radiographic inclination. Multiple regression analysis showed that intraoperative pelvic rotation about the anterior-posterior axis was a strong predictor for these errors (BTAL = -0.893, BMAG = -0.951, p < 0.01). Application of the transverse acetabular ligament method can reduce errors in radiographic version. However, if the orthopaedic surgeon is referencing off the theatre floor to control inclination when operating in lateral decubitus, this is only reliable if the pelvic sagittal plane is horizontal. There is currently no readily available method for ensuring that this is the case during total hip replacement surgery.

A poly(L-lactic acid) stent is exposed to a variety of processing techniques, temperatures and environmental conditions during its lifecycle, from the manufacturing process, to crimping through to deployment within the body. The effect of the biaxial stretching procedure and the effects of temperature and extension rate (post-processing) on the mechanical response of poly(L-lactic acid) are hereby investigated, and a constitutive model calibrated against experimental data is proposed. Dumb-bell specimens were punched from biaxially stretched sheets subjected to different processing histories, and tested under uniaxial tension at various temperatures (20, 37 and 55 °C) and extension rates (1, 5 and 10 mm/min). A Design of Experiments methodology was employed to identify the parameters that had the most significant effect on the mechanical response of the polymer. Results show that the elastic modulus and yield strength of the stretched sheets are strongly dependent on the aspect ratio of the biaxial deformation, along with the temperature during uniaxial deformation (post-processing). In contrast, these mechanical properties were not heavily dependent on extension rate (post-processing). A transversely isotropic, elastic-plastic constitutive model for finite element implementation is proposed, with the intention that it may be used as a design tool for developing high stiffness, thin-strut polymeric stents that contend with the performance of their metallic counterparts.

Coronary stents for treating atherosclerosis are traditionally manufactured from metallic alloys. However, metal stents permanently reside in the body and may trigger undesirable immunological responses. Bioresorbable polymer stents can provide a temporary scaffold that resorbs once the artery heals but are mechanically inferior, requiring thicker struts for equivalent radial support, which may increase thrombosis risk. This study addresses the challenge of designing mechanically effective but sufficiently thin poly(L-lactic acid) stents through a computational approach that optimises material properties and stent geometry. Forty parametric stent designs were generated: cross-sectional area (post-dilation), foreshortening, stent-to-artery ratio and radial collapse pressure were evaluated computationally using finite element analysis. Response surface methodology was used to identify performance trade-offs by formulating relationships between design parameters and response variables. Multi-objective optimisation was used to identify suitable stent designs from approximated Pareto fronts and an optimal design is proposed that offers comparable performance to designs in clinical practice. In summary, a computational framework has been developed that has potential application in the design of high stiffness, thin strut polymeric stents.

This study aimed to assess the effect of flexion and external rotation on measurement of femoral offset (FO), greater trochanter to femoral head centre (GT-FHC) distance, and neck shaft angle (NSA)...

Variation in hip joint contact forces directly influences the performance of total hip replacements (THRs). Measurement and calculation of contact forces in THR patients has been limited by small sample sizes, wide variation in patient and surgical factors, and short-term follow-up. This study hypothesised that, at long-term follow-up, unilateral THR patients have similar calculated hip contact forces compared to controls walking at similar (self-selected) speeds and, in contrast, THR patients walking at slower (self-selected) speeds have reduced hip contact forces. It was further hypothesised that there is no difference in calculated hip contact forces between operated and non-operated limbs at long-term follow-up for both faster and slower patients. Gait analysis data for THR patients walking at faster (walking speed: 1.29 ± 0.12 m/s; n = 11) and slower (walking speed: 0.72 ± 0.09 m/s; n = 11) speeds were used. Healthy subjects constituted the control group (walking speed: 1.36 ± 0.12 m/s; n = 10). Hip contact forces were calculated using static optimisation. There was no significant difference (p > 0.31) in hip contact forces between faster and control groups. Conversely, force was reduced at heel strike by 19% (p = 0.002), toe-off by 31% (p < 0.001) and increased at mid-stance by 15% (p = 0.02) for the slower group compared to controls. There were no differences between operated and non-operated limbs for the slower group or the faster group, suggesting good biomechanical recovery at long-term follow-up. Loading, at different walking speeds, presented here can improve the relevance of preclinical testing methods.

Fixed flexion and external rotation contractures are common in patients with hip osteoarthritis and in particular before total hip replacement (THR). We aimed to answer the following question: how does combined flexion and external rotation of the femur influence the radiographic assessment of 1) femoral offset (FO) 2) neck-shaft angle (NSA) and 3) distance (parallel to the femoral axis) from greater trochanter to femoral head centre (GT-FHC)? Combined flexion and external rotation impact the accuracy of two-dimensional (2D) proximal femur measurements. Three-dimensional (3D) CT segmentations of the right femur from 30 male and 42 female subjects were acquired and used to build a statistical shape model. A cohort (n = 100; M:F = 50:50) of shapes was generated using the model. Each 3D femur was subjected to external rotation (0°–50°) followed by flexion (0°–50°) in 10° increments. Simulated radiographs of each femur in these orientations were produced. Measurements of FO, NSA and GT-FHC were automatically taken on the 2D images. Combined rotations influenced the measurement of FO (p < 0.05), NSA (p < 0.001) and GT-FHC (p < 0.001). Femoral offset was affected predominantly by external rotation (19.8 ± 2.6 mm [12.2 to 26.1 mm] underestimated at 50°); added flexion in combined rotations only slightly impacted measurement error (20.7 ± 3.1 mm [13.2 to 28.8 mm] underestimated at 50° combined). Neck-shaft angle was reduced with flexion when external rotation was low (9.5 ± 2.1° [4.4 to 14.2°] underestimated at 0° external and 50° flexion) and increased with flexion when external rotation was high (24.4 ± 3.9° [15.7 to 31.9°] overestimated at 50° external and 50° flexion). Femoral head centre was above GT by 17.0 ± 3.4 mm [3.9 to 22.1 mm] at 50° external and 50 °flexion. In contrast, in neutral rotation, FHC was 12.2 ± 3.4 mm [3.9 to 22.1 mm] below GT. This investigation adds to current understanding of the effect of femoral orientation on preoperative planning measurements through the study of combined rotations (as opposed to single-axis). Planning measurements are shown to be significantly affected by flexion, external rotation, and their interaction. IV Biomechanical study.