Bone Fixation Devices Research Articles

Determining critical Zn/Ca atomic ratio and its role in mechanical and corrosion properties of biodegradable Mg-Ca-Zn-Mn alloys

Mg-Ca-Zn-Mn alloys are promising for applications in biodegradable bone fixation devices. The Zn/Ca atomic ratio in the compositions of these alloys is important to their corrosion and mechanical properties. This paper investigated the Zn/Ca ratio using a phase-focused approach based on CALPHAD (CALculation of PHAse Diagrams) modeling and experimental validation. Six Mg-0.5Ca-xZn-0.5Mn (all wt.%) alloys were cast with x = 0.96, 1.15, 1.47, 1.69, 1.94, and 3.81 so that the Zn/Ca atomic ratio spanned from 1.18 to 4.66. The microstructure is studied in the as-cast, solution-treated, and as-rolled conditions. A critical ratio was determined to be 2.77, above which Mg2Ca phase can be suppressed in as-cast microstructure. In the solution-treated condition, a Zn/Ca ratio of less than 2.0 was required to dissolve the Ca2Mg6Zn3 phase. Alloys below 2.0 Zn/Ca were found to have yield strength of 300 MPa and a corrosion rate of 0.25 to 0.3 mg/cm2/day as measured by both weight loss and hydrogen evolution. In alloys above 2.0 Zn/Ca, the yield strength decreased to 280 MPa and the corrosion rate measured by weight-loss increased to 0.5 mg/cm2/day. Above the critical ratio, the yield strength was the highest at 347 MPa but a corrosion rate of 0.4 mg/cm2/day. The Zn/Ca region with the best combination of corrosion resistance and mechanical properties is between 1.18 and 1.8 (in rolled sheet condition), which provides important guidance for biomedical Mg-Ca-Zn alloy design and optimization.

Surface aspects of novel Bio-HEAs MAO-treated in a Ca-, P-, and Mg-rich electrolyte

This study evaluated the effect of alloying elements, applied voltage, and bioactive species (Ca, P, and Mg) enrichment during the micro-arc oxidation (MAO) treatment of novel high entropy alloys (HEAs) targeted for biomedical applications. The non-equiatomic TiZrNbTaMo (TaMo), TiZrNbTaMn (TaMn), and TiZrNbFeMo (FeMo) samples were submitted to MAO treatment at distinct voltages (100, 200, and 300 V), then their chemical, phase, and morphological aspects were evaluated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM and TEM). Finally, the preliminary physicochemical behavior regarding contact angle and surface energy in distilled water at room temperature was evaluated. The results indicated that the alloying elements played a global role in the bulk’s phase composition, possessing distinct proportions of BCC and HCP phases. The MAO-treated surfaces depicted different mechanisms of anodic oxide growth and dielectric breakdown, forming the typical porous surface at distinct applied voltages. The bioactive species (Ca, P, and Mg) were gradually enriched in the oxide layer, composed of distinct nano-crystalline and amorphous layers that are typical of MAO-treated surfaces. As a result, roughness, contact angle and surface energy values of the MAO-treated samples were affected by the applied voltage and the bulk’s chemical composition, indicating potential for use in the biomedical field, especially as long-term implants and bone fixation devices.

In vitro calibration and in vivo validation of phenomenological corrosion models for resorbable magnesium-based orthopaedic implants

Metallic bioresorbable orthopaedic implants based on magnesium, iron and zinc-based alloys that provide rigid internal fixation without foreign-body complications associated with permanent implants have great potential as next-generation orthopaedic devices. Magnesium (Mg) based alloys exhibit excellent biocompatibility. However, the mechanical performance of such implants for orthopaedic applications is contingent on limiting the rate of corrosion in vivo throughout the bone healing process. Additionally, the surgical procedure for the implantation of internal bone fixation devices may impart plastic deformation to the device, potentially altering the corrosion rate of the device. The primary objective of this study was to develop a computer-based model for predicting the in vivo corrosion behaviour of implants manufactured from a Mg-1Zn-0.25Ca ternary alloy (ZX10). The proposed corrosion model was calibrated with an extensive range of mechanical and in vitro corrosion testing. Finally, the model was validated by comparing the in vivo corrosion performance of the implants during preliminary animal testing with the corrosion performance predicted by the model. The proposed model accurately predicts the in vitro corrosion rate, while overestimating the in vivo corrosion rate of ZX10 implants. Overall, the model provides a “first-line of design” for the development of new bioresorbable Mg-based orthopaedic devices. Statement of significanceBiodegradable metallic orthopaedic implant devices have emerged as a potential alternative to permanent implants, although successful adoption is contingent on achieving an acceptable degradation profile. A reliable computational method for accurately estimating the rate of biodegradation in vivo would greatly accelerate the development of resorbable orthopaedic implants by highlighting the potential risk of premature implant failure at an early stage of the device development. Phenomenological corrosion modelling approach is a promising computational tool for predicting the biodegradation of implants. However, the validity of the models for predicting the in vivo biodegradation of Mg alloys is yet to be determined. Present study investigates the validity of the phenomenological modelling approach for simulating the biodegradation of resorbable metallic orthopaedic implants by using a porcine model that targets craniofacial applications.

Optimizing Biomedical Facilities Performance with Dombeya Fiber-Paper Particle Hybrid Reinforced Epoxy Composites

Since the last two decades, the use of natural fiber reinforced polymer composites has garnered significant application considerations over the synthetic fiber reinforced composites due to their numerous advantages and unique properties. Likewise, epoxy resin has attracted the interest of many researchers for composite synthesis, basically because of its chemical stability, thermal and mechanical characteristics. Hence, the primary aim of this study was to investigate the influence of dombeya fiber and paper particulate on the physical and mechanical properties of dombeya fiber and paper particulate-reinforced polymer composites for structural applications. Dombeya fiber and paper particles are renewable and biodegradable materials, thereby making them environmentally friendly materials to replace synthetic materials. Hand lay-up technique was utilized to fabricate the hybrid-reinforced biocomposites after which they were subjected to mechanical, wear, density, and moisture absorption properties. The surface morphology of the fractured surface was also analyzed to investigate its microstructural features. It was discovered from the results that hybrid biocomposites demonstrated improved properties over the unreinforced composite, with composites from 9-wt% dombeya fiber-paper particles reinforced biocomposite exhibiting the most suitable properties with commensurate density with the unreinforced epoxy matrix. These obtained characteristics support the material as a suitable material for biomedical apparatus application such as orthopedic implants, surgical instruments, and bone fixation devices.

Influence of silver nanoparticles addition on antibacterial properties of PEO coatings formed on magnesium

Magnesium is a biodegradable material and thus could be a choice for bone fixation devices and implants with a specific purpose. This study aims to enhance the anti-corrosive, biocompatible, and antibacterial properties on magnesium-based materials through ceramic coatings formation. To achieve this the silicate-based electrolyte was used to create of Plasma Electrolytic Oxidation (PEO) coatings. During investigation the bioactive surfaces were presented by highly developed morphology with pore size from 0.008 ± 0.01 to 0.098 ± 0.14 μm2. The thickness of the coatings reached 7 μm, which provides better corrosive behaviour. The silver nanoparticles (AgNPs) added during plasma electrolytic oxidation (PEO) into a silicate electrolytic bath allowed for achieving enhanced bioactive properties of coating. It increased hydrophilicity from 118° to 62° and showed no cytotoxic effects, which made the coatings promising for further biomedical investigations. Moreover, incorporation of AgNPs into the PEO coating led to release of silver during immersion test, which enhanced antibacterial properties of the surfaces.

The Effect of Niobium Addition on Properties of Titanium-Based Alloy Fabricated via Mechanical Alloying

The aim of this study was to investigate the effect of niobium addition on phase formation, densification, microhardness and compressive properties of Ti-Nb alloys that possess suitable characteristics as bone fixation device. The mixture of Ti and Nb powders was mechanically alloyed (MA) in a planetary mill for two hours. The effect of Nb addition to Ti was investigated by x-ray diffraction (XRD) analysis. In addition, density, microhardness and compressive behavior of the sintered alloy were also determined by the principle of Archimedes, Vickers microhardness test and compression test, respectively. The results suggested that Nb addition has changed the phase from α-Ti to β-Ti. As the Nb addition was increased from 0 wt.% to 40 wt.%, it is observed that the density of alloy increased from 4.17 g/cm3 to 5.24 g/cm3. The microhardness and compressive modulus were 306.92 HV and 57.06 GPa for Ti-0Nb (wt.%), while the mechanical properties of the alloy dropped to 218.23 HV and 25.88 GPa when the Nb addition was up to 40 wt.%. This trend is similar to the compression strength, which the compression strength for Ti-0Nb (3221 MPa) decreased to 2123 MPa as Nb was incorporated into Ti up to 40 wt.%. It is found that Ti-40Nb possess close resemblance to the Young’s modulus of human cortical bone which lies in the range of 7-30 GPa and exhibit suitable characteristics as bone fixation device.

Strontium-Substituted Nanohydroxyapatite-Incorporated Poly(lactic acid) Composites for Orthopedic Applications: Bioactive, Machinable, and High-Strength Properties.

Traditional metal-alloy bone fixation devices provide structural support for bone repair but have limitations in actively promoting bone healing and often require additional surgeries for implant removal. In this study, we focused on addressing these challenges by fabricating biodegradable composites using poly(lactic acid) (PLA) and strontium-substituted nanohydroxyapatite (SrHAP) via melt compounding and injection molding. Various percentages of SrHAP (5, 10, 20, and 30% w/w) were incorporated into the PLA matrix. We systematically investigated the structural, morphological, thermal, mechanical, rheological, and dynamic mechanical properties of the prepared composites. Notably, the tensile modulus, a critical parameter for orthopedic implants, significantly improved from 2.77 GPa in pristine PLA to 3.73 GPa in the composite containing 10% w/w SrHAP. The incorporation of SrHAP (10% w/w) into the PLA matrix led to an increased storage modulus, indicating a uniform dispersion of SrHAP within the PLA and good compatibility between the polymer and nanoparticles. Moreover, we successfully fabricated screws using PLA composites with 10% (w/w) SrHAP, demonstrating their formability at room temperature and radiopacity when observed under X-ray microtomography (micro-CT). Furthermore, the water contact angle decreased from 93 ± 2° for pristine PLA to 75 ± 3° for the composite containing SrHAP, indicating better surface wettability. To assess the biological behavior of the composites, we conducted in vitro cell-material tests, which confirmed their osteoconductive and osteoinductive properties. These findings highlight the potential of our developed PLA/SrHAP10 (10% w/w) composites as machinable implant materials for orthopedic applications. In conclusion, our study presents the fabrication and comprehensive characterization of biodegradable composites comprising PLA and strontium-substituted nanohydroxyapatite (SrHAP). These composites exhibit improved mechanical properties, formability, and radiopacity while also demonstrating desirable biological behavior. Our results suggest that these PLA/SrHAP10 composites hold promise as machinable implant materials for orthopedic applications.

Surface analysis of (Ti,Mg)N coated bone fixation devices following the rabbit femur surgery.

Magnesium (Mg) enhances the bone regeneration, mineralization and attachment at the tissue/biomaterial interface. In this study, the effect of Mg on mineralization/osseointegration was determined using (Ti,Mg)N thin film coated Ti6Al4V based plates and screws in vivo. TiN and (Ti,Mg)N coated Ti6Al4V plates and screws were prepared using arc-PVD technique and used to fix rabbit femur fractures for 6 weeks. Then, mineralization/osseointegration was assessed by surface analysis including cell attachment, mineralization, and hydroxyapatite deposition on concave and convex sides of the plates along with the attachment between the screw and the bone. According to Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses; cell attachment and mineralization were higher on the concave sides of the plates from both groups in comparison to the convex sides. However, mineralization was significantly higher on Mg-containing ones. The mean gray value indicating mineralized area after von Kossa staining was found as 0.48 ±0.01 and 0.41 ±0.04 on Mg containing and free ones respectively. Similarly, Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) analyses showed that hydroxyapatite growth was abundant on the Mg-containing and concave sides of the plates. Enhanced mineralization and strong attachment to bone were also detected in EDS and SEM analyses of Mg-containing screws. These findings indicated that (Ti,Mg)N coatings can be used to increase attachment at the implant tissue interface due to accelerated mineralization, cell attachment, and hydroxyapatite growth.

Physiologic postoperative presepsin kinetics following primary cementless total hip arthroplasty: A prospective observational study.

Presepsin is an emerging biomarker in the diagnosis of sepsis. In the field of orthopaedics, it could be useful in diagnosing and managing periprosthetic joint infections. To define the normal postoperative presepsin plasmatic curve, in patients undergoing primary cementless total hip arthroplasty (THA). Patients undergoing primary cementless THA at our Institute were recruited. Inclusion criteria were: Primary osteoarthritis of the hip; urinary catheter time of permanence < 24 h; peripheral venous cannulation time of permanence < 24 h; no postoperative homologous blood transfusion administration and hospital stay ≤ 8 d. Exclusion criteria were: The presence of other articular prosthetic replacement or bone fixation devices; chronic inflammatory diseases; chronic kidney diseases; history of recurrent infections or malignant neoplasms; previous surgery in the preceding 12 mo; diabetes mellitus; immunosuppressive drug or corticosteroid assumption. All the patients received the same antibiotic prophylaxis. All the THA were performed by the same surgical and anaesthesia team; total operative time was defined as the time taken from skin incision to completion of skin closure. At enrollment, anthropometric data, smocking status, osteoarthritis stage according to Kellgren and Lawrence, Harris Hip Score, drugs assumption and comorbidities were recorded. All the patients underwent serial blood tests, including complete blood count, presepsin (PS) and C-reactive protein 24 h before arthroplasty and at 24, 48, 72 and 96 h postoperatively and at 3, 6 and 12-mo follow-up. A total of 96 patients (51 female; 45 male; mean age = 65.74 ± 5.58) were recruited. The mean PS values were: 137.54 pg/mL at baseline, 192.08 pg/mL at 24 h post-op; 254.85 pg/mL at 48 h post-op; 259 pg/mL at 72 h post-op; 248.6 pg/mL at 96-h post-op; 140.52 pg/mL at 3-mo follow-up; 135.55 pg/mL at 6-mo follow-up and 130.11 pg/mL at 12-mo follow-up. In two patients (2.08%) a soft-tissue infection was observed; in these patients, higher levels (> 350 pg/mL) were recorded at 3-mo follow-up. The dosage of plasmatic PS concentration is highly recommended in patients undergoing THA before surgery to exclude the presence of an unknown infection. The PS plasmatic concentration should be also assessed at 72 h post-operatively, evaluate the maximum postoperative PS value, and at 96 h post-operatively when a decrease of presepsin should be found. The lack of a presepsin decrease at 96 h post-operatively could be a predictive factor of infection.

Machinable diopside-lanthanum phosphate composite ceramics for fabricating load bearing bone implants

Bioceramic-based composites are extensively being used in orthopedics for decades due to their excellent biocompatibility and osteoconductivity. However, the inherent brittleness and high hardness of ceramics heavily impact their machinability, thus restricting their use as bone fixation devices. In this study, Mg-doped calcium silicate ceramic diopside (DI) has been employed as a ceramic matrix material owing to its superior mechanical properties in comparison to hydroxyapatite. To impart machinability in the diopside, rare earth lanthanum phosphate (LP) was introduced as a reinforcement. The indigenously synthesized and 800 °C calcined DI and LP powders were employed for composite fabrication by varying LP content (0–50% w/w). The composites were sintered at different temperatures (1000 °C, and 1200 °C) and sintering conditions (single sintered, and double sintered), and the 1200 °C double sintered (ds) composites were optimized due to their highest densification and mechanical properties. Among the optimized composites, ds-DI-LP (50:50, DL50) displayed the highest compressive strength (140 ± 5.21 MPa) compared to DL5 (121.16 ± 14.82 MPa) and DL10 (122.78 ± 28.74 MPa) composites. It was observed that the weak and layered LP interface in between the DI phase promoted machinability in the composites. Apart from being machinable, these ceramic composites were found to be bioactive, resulting in the formation of an apatite layer when immersed in simulated body fluid. Further, the optimized ceramic composites were found to be biocompatible and osteoconductive in nature on their functional assessment using primary rat calvarial osteoblast cells. Based on the results obtained, the ds-DL10 composites displayed considerable bioactivity and the highest ALP activity compared to ds-DL5 (p ≤ 0.01) and ds-DL50 (p ≤ 0.05) composites.

Investigating the compression and fretting wear behaviour of FDM printed PLA samples for bone fixation

ABSTRACT The metallic plate is used for bone fixation in biomedical applications, which causes health risks to the patient by leaching ion elements due to the formation of micro-motion between the plate and screw. Currently, the polylactic acid is favoured for replacing metal alloys in temporary implants due to the biodegradable property. However, polylactic acid has low mechanical properties compared to metal alloys and is not preferred as a fixation device. Therefore, the polylactic acid was printed using FDM technique under both horizontal and vertical orientations to improve the mechanical properties. After printing, the samples were post-heat treated at 60℃ for 24 h (B1) and 70℃ for 12 h (B2). Later, compression and fretting wear tests were performed for the printed and post-heat-treated samples to estimate the compression strength and fretting wear. The results indicated that the post-heat-treated horizontal sample B2 obtained a higher compression yield strength of 80.15 ± 3.53 MPa compared to printed and post-treated sample B1. This value lies within the range of bone fixation device. Moreover, a low coefficient of friction (1.34 ± 0.23) was obtained for sample B2 due to the improvement of yield strength. The worn morphology showed that the formation of cracks and spalling was more for the printed and B1 sample compared to the B2

Surgically-induced deformation in biodegradable orthopaedic implant devices

The biocompatibility and mechanical performance of biodegradable metals (e.g. magnesium, iron, and zinc-based alloys) in orthopaedic-targeted applications are contingent on limiting the rate of corrosion in vivo throughout the bone healing. Concurrently, the surgical procedure for the implantation of internal bone fixation devices may impart plastic deformation to the device, potentially altering the corrosion rate of the device. However, the potential effect of the surgical implantation procedure on the mechanochemical performance of metallic degradable orthopaedic devices in vivo remains largely unresolved. The objective of the present study is to develop a robust technique that permits the quantification of the strain introduced due to surgical implantation of degradable orthopaedic devices. Specifically, a novel combined experimental-modelling approach based on 3D laser scanning in situ and the finite element method is utilised to quantify the plastic strain introduced to a bone fixation plate following surgical implantation in a cadaveric porcine model where the plate is based on a ternary magnesium-zinc-calcium alloy (ZX10). The magnitude of plastic strains determined by the above approach for the Mg craniofacial miniplate confirms that the surgical procedure itself has the potential to enhance the corrosion rate of the Mg alloy in an accelerated and potentially localised manner. Statement of SignificanceBiodegradable metallic orthopaedic implant devices have emerged as a potential alternative to permanent implants, although successful adoption is contingent on achieving an acceptable degradation profile. Plastic strain that is introduced to the device during surgical implantation may influence the resulting degradation behaviour of the implant. In the present work, 3D laser scanning is combined with computer simulation to estimate the level and distribution of surgically-induced plastic strain in a magnesium alloy (ZX10). Subsequently, clinically-relevant pre-strain is shown to influence the rate of corrosion of ZX10 in vitro, indicating the value of such an approach in the design of biodegradable metallic devices under multiaxial loading.

Preparation and properties of oriented microcellular Poly(l-lactic acid) foaming material

Poly(l-lactic acid) (PLLA) displays simultaneous repair and regeneration properties. Therefore, it is vital for developing bone repair materials while improving their mechanical strength, and biocompatibility is essential for guaranteeing its application. In this manuscript, using solid hot drawing (SHD) technology to fabricate an oriented shish-kebab like structure, furthermore, the interface-oriented grain boundary controlled the nucleation site and cell morphology during low temperature supercritical carbon dioxide (SC-CO2) foaming process, resulted in an oriented microcellular structure which was similar to load-bearing bone. The tensile strength, elastic modulus, and elongation at break of the oriented microcellular PLLA were 98.4 MPa, 3.3 GPa, and 16.4%, respectively. Furthermore, the biomimetic structure improved osteoblast cells (MC3T3) attachment, proliferation, and propagation. These findings may pave the way for designing novel biomaterials for bone fixation or tissue engineering devices.

An experimentally validated failure model for bioresorbable composites subject to flexural loading

The focus of this paper is to investigate the deformation and failure response of a new class of bioresorbable composites subject to flexural loading. The composite consists of a biocompatible polylactic acid (PLA) matrix reinforced by long, continuous, bioresorbable silk fibers, which shows great promise for making load-bearing bone fixation devices. Three-point bend tests were carried out to characterize the material's flexural behavior. Experimental results show that the composite fails due to delamination, which is evident from images processed using the Digital Image Correlation (DIC) technique. To predict crack propagation in the composite, an enhanced fracture energy-based Smeared Crack Approach (SCA) was developed and implemented in a Finite Element Analysis (FEA) framework. The new SCA model incorporates orthogonal cracks that allow for complete energy dissipation under mode-I and mode-II failure types, with the approach being validated through benchmark studies of Double-Cantilever Beam (DCB) and End-Notched Flexure (ENF) simulations. The new fracture model, coupled with a micromechanics-based elastic model, successfully predicts the deformation and progressive damage response of the bioresorbable composite subjected to three-point bending. Effects of the strength and toughness of the binding polymer on the resulting composite response were investigated, providing crucial information for the design of new bioresorbable composites with target properties.

Effect of Draw Ratio in Tensile Drawing on Mechanical Properties of Tricalcium Phosphate/Poly(lactic acid) Composites

Tricalcium phosphate/poly(lactic acid) (TCP/PLA) composite is attracted the attention as a material of bone fixation device because it doesn’t require removal by reoperation after healing bone fracture. However, mechanical properties of TCP/PLA composite were low. In this study, effect of draw ratio (DR) on mechanical properties of drawn TCP/PLA composite was investigated to improve the mechanical properties. Orientation function of drawn TCP/PLA composite was investigated to clarify mechanism of changing mechanical properties by drawing. As a result, tensile strength was improved with draw ratio up to DR 2.5. Tensile strengths of drawn TCP/PLA composite up to DR 2.5 were higher than that of PLA. Elastic modulus was improved with draw ratio up to 2.0. Orientation function of α form crystal was improved with draw ratio up to 2.0. From these results, it was suggested that increase mechanical properties of drawn TCP/PLA composite due to orientation of α form crystals.

Effect of Extrusion Ratio on Mechanical Properties of TCP/PLA Bone Fixation Screw Molded by Extrusion Die Forging

Metal bone fixation devices are used in the treatment of bone fractures. However, metallic materials cause inflammation in the body. In this study, we focused on bioabsorbable composite material of poly(lactic acid) (PLA) and tricalcium phosphate (TCP). However, the mechanical properties of TCP/PLA composites are lower than those of metal materials. In order to improve the mechanical properties of TCP/PLA bone fixation screws, molecular orientation by extrusion die forging was focused under various extrusion ratios (ER) and TCP contents. The orientation of molecular chains depends on the forging conditions. The purpus of this study is investigation effect of forging condition on mechanical properties of TCP/PLA scres. Then, screws were formed by extrusion die forging at ER 1.3, 4 and 8, and shear strengthe of the screws was measured. As a result, the shear strength increased with ER, and the maximum shear strength was observed at ER 4.

A magnetoelastic bone fixation device for controlled mechanical stimulation at femoral fractures in rodents

Studies have shown that mechanical stimulations can provide anabolic bone formation and counteract conditions such as osteoporosis in intact bones, as well as promote healing of bone fractures. However, many of these studies are based on external mechanical loading platforms or bulky wearable force loading systems, which are inconvenient and impractical in clinical settings especially for the treatment of bone injuries. To overcome this limitation, a bone fixation device was developed to provide localized mechanical strains across a bone fracture site. The fixation device, designed for a rodent’s femoral fracture (critical-size segmental defect), is consisted of a magnetoelastic (ME) actuator that changes its physical dimension when exposed to magnetic fields. The strain produced by the ME actuator is transferred to the bone fixation device, which acts directly on the bone-implant interface to produce a highly focused and localized mechanical loading. The actuation generated by the fixation device was evaluated, and results show the device was able to provide up to 150 με at 30 Hz. Mechanical characterization of the fixation device showed its off-axis compressive stiffness was higher than 160 N mm−1, which was comparable to existing fixation devices used for the same rodent’s femoral fracture model. Furthermore, the fixation device was implanted in rodent subjects for 8 weeks to validate its safety and biocompatibility in vivo. Results indicate the device is biocompatible, showing no adverse impact on bone regeneration.

Strategies for Enhancing Polyester-Based Materials for Bone Fixation Applications.

Polyester-based materials are established options, regarding the manufacturing of bone fixation devices and devices in routine clinical use. This paper reviews the approaches researchers have taken to develop these materials to improve their mechanical and biological performances. Polymer blending, copolymerisation, and the use of particulates and fibre bioceramic materials to make composite materials and surface modifications have all been studied. Polymer blending, copolymerisation, and particulate composite approaches have been adopted commercially, with the primary focus on influencing the in vivo degradation rate. There are emerging opportunities in novel polymer blends and nanoscale particulate systems, to tune bulk properties, and, in terms of surface functionalisation, to optimise the initial interaction of devices with the implanted environment, offering the potential to improve the clinical performances of fracture fixation devices.

A novel design of printable tunable stiffness metamaterial for bone healing

A tunable stiffness bone rod was designed, optimized, and 3D printed to address the shortcomings of existing bone fixation devices, such as stress shielding and bone nonunion in the healing of fractured bones. Current bone plates/rods have constant and high stiffness. High initial stiffness prevents the micromotion of newly formed bone and results in poor bone healing. Our novel design framework provides surgeons with a ready-for-3D-printing, patient-specific design, optimized to have the desired force-displacement response with a stopping mechanism for preventing further deformation under higher-than-normal loads, such as falling. The computational framework is a design optimization based on the multi-objective genetic algorithm (GA) optimization with the FE simulation to quantify the objectives: tuning the varied stiffness while minimizing the maximum von Mises stress of the model to avoid plastic and permanent deformation of the bone rod. The computational framework for optimum design of tunable stiffness metamaterial presented in this paper is not specific for a tibia bone rod, and it can be used for any application where bilinear stiffness is desirable.

Rheological characterization, compression, and injection molding of hydroxyapatite-silk fibroin composites

Traditional bone fixation devices made from inert metal alloys provide structural strength for bone repair but are limited in their ability to actively promote bone healing. Although several naturally derived bioactive materials have been developed to promote ossification in bone defects, it is difficult to translate small-scale benchtop fabrication of these materials to high-output manufacturing. Standard industrial molding processes, such as injection and compression molding, have typically been limited to use with synthetic polymers since most biopolymers cannot withstand the harsh processing conditions involved in these techniques. Here we demonstrate injection and compression molding of a bioceramic composite comprised of hydroxyapatite (HA) and silk fibroin (SF) from Bombyx mori silkworm cocoons. Both the molding behavior of the HA-SF slurry and final scaffold mechanics can be controlled by modulating SF protein molecular weight, SF content, and powder-to-liquid ratio. HA-SF composites with up to 20 weight percent SF were successfully molded into stable three-dimensional structures using high pressure molding techniques. The unique durability of silk fibroin enables application of common molding techniques to fabricate composite silk-ceramic scaffolds. This work demonstrates the potential to move bone tissue engineering one step closer to large-scale manufacturing of natural protein-based resorbable bone grafts and fixation devices.