Mechanical properties and in vivo performance of load-bearing fiber-reinforced composite intramedullary nails with improved torsional strength

Load-bearing composite fracture-fixation devices with tailored fibre placement for toy-breed dogs

Fibre reinforced composites are attractive materials for hard tissue reconstructions, due to the high strength and low flexural modulus. However, lack of contourability in the operation theatre inhibits their clinical applications. The study presents a novel in situ contourable composite implant system for load-bearing conditions. The implant system consists of a thin bioresorbable shell with several cavities, much like bubble-wrap. The central cavity contains a semi-flexible glass fibre preform prepared using Tailored Fibre Placement method. The preform is either pre-impregnated with a light curable resin, or the resin is injected into the cavity during the surgical procedure, followed by light curing. The semi-flexible glass fibre preforms were also examined as separate devices, "miniplates". Two types of miniplates were scrutinized, a simplified pilot design and a spatially refined, "optimized" design. The optimized miniplates were implemented as biostable and bioresorbable versions. The feasibility of the in situ contourable composite implant system was demonstrated. The potential of Tailored Fibre Placement for the semi-flexible glass fibre preforms and miniplates was confirmed in a series of biomechanical tests. However, structural optimization is required. Antebrachial fractures in toy-breeds of dogs are exemplar veterinary applications of the devices; further applications in veterinary and human patients are foreseen.

Structural composite based on 3D printing polylactic acid/carbon fiber laminates (PLA/CFRC) as an alternative material for femoral stem prosthesis

In recent years, surgical procedures for hip prostheses have increased. These implants are manufactured with materials with high stiffness compared to the bone, causing bone loss or aseptic loosening. This research proposes an alternative structural composite consisting of 3D-printing polylactic acid layers and carbon fiber laminates (PLA/CFRC) with potential application in prosthetic implants. Fourier-transform infrared spectroscopy (FTIR) achieved to characterize starting materials and structural composites revealed secondary chemical interactions between the carbonyl group of PLA with the hydroxyl group of epoxy resin from CFRC. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results show both components (PLA and CFRC) influence the structural composite's thermal behavior, observed in the temperatures of degradation, glass transition, and melting. Furthermore, the composite reached cell viability above 80%, a tensile modulus of 19.29 ± 0.48 GPa and tensile strength of 238.91 ± 25.95 MPa, with mechanical properties very similar to the bone. The results of this study demonstrated that the proposed PLA/CFRC composite can be used as candidate base material for the manufacturing of a hip femoral stem prostheses.

Biomechanical comparison of locking and non-locking patient-specific mandibular reconstruction plate using finite element analysis

Patient-specific mandibular reconstruction plate (PSMRP), as one of the patient-specific implants (PSIs), offers a host of benefits to mandibular reconstruction. Due to the limitation of fabricating screw hole threads in the PSMRP, 3D printed PSMRP is applied to the non-locking system directly in the mandibular reconstruction with bone graft regardless of the locking system. Since the conventional manual-bending reconstruction plate (CMBRP) provides better fixation in the locking system, it needs to be validated whether the locking PSMRP performs better than the non-locking PSMRP in the patient-specific mandibular reconstruction. Thereupon, the purpose of this study was to compare the biomechanical behavior between the locking and non-locking PSMRP. Finite element analysis (FEA) was used to conduct the biomechanical comparison between the locking PSMRP and non-locking PSMRP by simulating the momentary incisal clenching through static structural analysis. Mandible was reconstructed through the virtual surgical planning, and subsequently a 3D model of mandibular reconstruction assembly, including reconstructed mandible, PSMRP, and fixation screws, was generated and meshed for the following FEA simulations. In the form of equivalent von Mises stress, equivalent elastic strain, and total deformation, the locking PSMRP demonstrated its higher strengths of preferable safety, desirable flexibility, and anticipated stability compared with the non-locking PSMRP, indicated by much lower maximum stress, lower maximum strain and equivalent displacement. Locking PSMRP/screw system provides a better fixation effect to the patient-specific mandibular reconstruction than the non-locking one as a result of its productive fixation nature. FEA plays a paramount role in pre-validating the design of PSMRP through the biomechanical behavior evaluation in static structural analysis.

A comparative study of 3D printing and heat-compressing methods for manufacturing the thermoplastic composite bone fixation plate: Design, characterization, and in vitro biomechanical experimentation

Metallic bone fixations, due to their high rigidity, can cause long-term complications. To alleviate metallic biomaterials' drawbacks, in this research new Glass Fiber/Polypropylene (GF/PP) composite internal fixations were developed, and an investigation of their mechanical behavior was performed through in vitro biomechanical experiments. Short randomly oriented, long unidirectional prepreg, and long unidirectional fiber yarn were considered as reinforcements, and the effects on their mechanical properties of different manufacturing processes, that is, 3D printing and heat-compressing, were investigated. The constructed fixation plates were tested in the transversely fractured diaphysis of bovine tibia under axial compression loading. The overall stiffness and the Von Mises strain field of the fixation plates were obtained within stable and unstable fracture conditions. The samples were loaded until failure to determine their failure loads, strains, and mechanisms. Based on the results, the GF/PP composite fixation plates can provide adequate interfragmentary movement to amplify bone ossification, so they can provide proper support for bone healing. Moreover, their potential for stress shielding reduction and their load-bearing capacity suggest their merits in replacing traditional metallic plates.

Bioactive Glass Fiber-Reinforced Plastic Composites Prompt a Crystallographic Lophelia Atoll-Like Skeletal Microarchitecture Actuating Periosteal Cambium

The touchstone for bone replacing or anchoring trauma implants, besides resorption, includes functional ankylosis at a fixation point and replacement by viable functional neo-bone tissues. These parameters redefined the concept of "resorbability" as "bioresorbability." Interference screws are the most commonly used resorbable anchoring implants for anterior cruciate ligament (ACL) reconstruction (surgery). Over the years, the bioresorbable screw fixation armamentarium has amplified countless choices, but instability and postimplantation complications have raised concerns about its reliability and efficacy. Owing to this interest, in this work, bioactive glass fiber-reinforced plastic (BGFP) composites with (BGFPnb5) and without (BGFP5) niobicoxide composing multiplexed network modifiers are reported as bioresorbable bone-anchoring substitutes. These synergistically designed composites have a fabricated structure of continuous, unidirectional BG fibers reinforced in an epoxy resin matrix using "melt-drawing and microfabrication" technology. The BGFP microarchitecture is comprised of multiplexed oxide components that influence bioactive response in a distinctive lophelia atoll-like apatite formation. Furthermore, it assists in the proliferation, adherence, and migration of bone marrow-derived mesenchymal stem cells. It also exhibits superior physicochemical characteristics such as surface roughness, hydrophilic exposure, distinctive flexural strength, and bioresorption. Thus, it induces restorative bone osseointegration and osteoconduction and actuates periosteum function. In addition, the BGFP influences the reduction of DH5-α Escherichia coli in suspension culture, demonstrating potential antibacterial efficacy. In conclusion, the BGFP composite therapeutic efficacy demonstrates distinctive material characteristics aiding in bone regeneration and restoration that could serve as a pioneer in orthopedic regenerative medicine.

A Polymer for Application as a Matrix Phase in a Concept of In Situ Curable Bioresorbable Bioactive Load-Bearing Continuous Fiber Reinforced Composite Fracture Fixation Plates

The use of bioresorbable fracture fixation plates made of aliphatic polyesters have good potential due to good biocompatibility, reduced risk of stress-shielding, and eliminated need for plate removal. However, polyesters are ductile, and their handling properties are limited. We suggested an alternative, PLAMA (PolyLActide functionalized with diMethAcrylate), for the use as the matrix phase for the novel concept of the in situ curable bioresorbable load-bearing composite plate to reduce the limitations of conventional polyesters. The purpose was to obtain a preliminary understanding of the chemical and physical properties and the biological safety of PLAMA from the prospective of the novel concept. Modifications with different molecular masses (PLAMA-500 and PLAMA-1000) were synthesized. The efficiency of curing was assessed by the degree of convergence (DC). The mechanical properties were obtained by tensile test and thermomechanical analysis. The bioresorbability was investigated by immersion in simulated body fluid. The biocompatibility was studied in cell morphology and viability tests. PLAMA-500 showed better DC and mechanical properties, and slower bioresorbability than PLAMA-1000. Both did not prevent proliferation and normal morphological development of cells. We concluded that PLAMA-500 has potential for the use as the matrix material for bioresorbable load-bearing composite fracture fixation plates.

Biomechanical Response under Stress-Controlled Tension-Tension Fatigue of a Novel Carbon Fiber/Epoxy Intramedullary Nail for Femur Fractures

Metallic intramedullary nails are the "gold standard" implant for repairing femur shaft fractures. However, their rigidity may eliminate axial micromotion at the fracture (causing delayed healing) and they may carry too much load relative to the femur (causing "stress shielding"). Consequently, some researchers have proposed fiber-reinforced composite nails, but only one evaluated cyclic fatigue performance. Therefore, this study assessed the cyclic fatigue response of a carbon fiber/epoxy nail with a novel ply stacking sequence of [0₂/-45/45₂/-45/0/-45/45₂/-45₂/45₂/-45/90₂] previously developed by the present authors. Nails were cyclically loaded in tension-tension at 5 Hz with a stress ratio of R=0.1 from 30% - 85% of the material's ultimate tensile strength (UTS). Thermographic stress analysis, rather than conventional fatigue testing, was used to obtain high cycle fatigue strength (HCFS), below which the nail can be cyclically loaded indefinitely without damage. Also, the mechanical test machine's built-in load cell and an extensometer were used to create stress-strain curves, from which the change in static E^O and dynamic E* moduli were obtained. Results showed that HCFS was 70.3% of UTS (or about 283 MPa), while E^O and E* remained at 42 GPa without any dRegradation during testing. The current nail shows potential for clinical use.

Scattering of therapeutic radiation in the presence of craniofacial bone reconstruction materials

Purpose

Radiation scattering from bone reconstruction materials can cause problems from prolonged healing to osteoradionecrosis. Glass fiber reinforced composite (FRC) has been introduced for bone reconstruction in craniofacial surgery but the effects during radiotherapy have not been previously studied. The purpose of this study was to compare the attenuation and back scatter caused by different reconstruction materials during radiotherapy, especially FRC with bioactive glass (BG) and titanium.

Methods

The effect of five different bone reconstruction materials on the surrounding tissue during radiotherapy was measured. The materials tested were titanium, glass FRC with and without BG, polyether ether ketone (PEEK) and bone. The samples were irradiated with 6 MV and 10 MV photon beams. Measurements of backscattering and dose changes behind the sample were made with radiochromic film and diamond detector dosimetry.

Results

An 18% dose enhancement was measured with a radiochromic film on the entrance side of irradiation for titanium with 6 MV energy while PEEK and FRC caused an enhancement of 10% and 4%, respectively. FRC‐BG did not cause any measurable enhancement. The change in dose immediately behind the sample was also greatest with titanium (15% reduction) compared with the other materials (0–1% enhancement). The trend is similar with diamond detector measurements, titanium caused a dose enhancement of up to 4% with a 1 mm sample and a reduction of 8.5% with 6 MV energy whereas FRC, FRC‐BG, PEEK or bone only caused a maximum dose reduction of 2.2%.

Conclusions

Glass fiber reinforced composite causes less interaction with radiation than titanium during radiotherapy and could provide a better healing environment after bone reconstruction.

Biostable glass fibre-reinforced dimethacrylate-based composites as potential candidates for fracture fixation plates in toy-breed dogs: Mechanical testing and finite element analysis

In toy-breed dogs (bodyweight <5 kg), the fractures of the radius and ulna are particularly common and can be caused by minimal trauma. While fracture fixation using metallic plates is a feasible treatment modality, the excessive stiffness of these devices produces the underloading of the bone which may result in the adverse bone remodelling and complications in the healing of the fracture. In this study, we investigated bisphenol A glycidylmethacrylate -based glass fibre reinforced composites as potential alternatives to metals in the devices intended for the fracture fixation of the distal radius in toy-breed dogs. Four composites with different glass fibre reinforcements were prepared as rectangular specimens and as fracture fixation plates. These were mechanically tested in three-point and four-point bending. There were two controls: polyether etherketone reinforced with short carbon fibres (specimens and plates) and commercially available stainless-steel plates. Finite element simulations were used for the assessment of the behaviour of the plates. For the control stainless steel plate, the bending strength was 1.358 N*m, superior to that of any of the composite plates. The composite plate with the matrix reinforced with continuous unidirectional glass fibres had the bending strength of 1.081 N*m, which is sufficient in this clinical context. For the plates made of polyether etherketone reinforced with carbon fibres, the strength was 0.280 N*m. Similar conclusions on the biomechanical behaviour of the plates could be made solely based on the results of the finite element simulations, provided the geometries and the material properties are well defined.

Microwave-assisted synthesis and in vitro osteogenic analysis of novel bioactive glass fibers for biomedical and dental applications

Glass fiber-based materials have gained interest for use in biomedical and dental applications. The aim of this study was to make E-glass fiber bioactive by a novel method using the microwave irradiation technique. Industrial E-glass fibers were used after surface activation with the hydrolysis method. The ratio of calcium and phosphorous precursors was set at 1.67. After maintaining the pH of the calcium solution, E-glass fibers in two ratios, i.e. 30% (nHA/E30) and 50% (nHA/E50) wt/wt, were added. The phosphorous precursor was added later and the solution was irradiated in a microwave to obtain nano-hydroxyapatite (nHA) particles on E-glass fibers. The structural, physical and in vitro biocompatibility analyses of the resulting materials were conducted. The expression of osteopontin (OPN) and collagen (Col) type 1 was measured by reverse transcription polymerase chain reaction (RT-PCR) and comparison was made between all the groups. Fourier transform infrared spectroscopy and x-ray diffraction showed characteristic peaks of nHA, and a change in the peak intensities was observed with an increase in the concentration of E-glass fibers. Scanning electron microscopic (SEM) images confirmed the homogenous adhesion of nHA spherical particles all over the fibers. Cell viability with mesenchymal stem cells showed growth, proliferation, and adhesion. All the materials were able to upregulate the expression of the OPN and Col, where gene expression was highest in nHA followed by nHA/E30 and nHA/E50. The bioactive glass fibers were synthesized in the shortest time and showed osteogenic properties. These materials have the potential for use in bone tissue engineering, dental prosthesis, and tooth restoration.

Mechanical properties and cytotoxicity of hierarchical carbon fiber-reinforced poly (ether-ether-ketone) composites used as implant materials

Weak mechanical properties affect the application of PEEK as an implant. Carbon fiber (CFR) reinforcement provides an excellent solution to improve the mechanical strength of PEEK and to provide perfect matching of elastic modulus between CFR-PEEK composites and human bone. To investigate the effect of carbon fiber content on the mechanical, thermal properties and cytotoxicity of CFR reinforced PEEK composites, a series of CFR-PEEK composites with different carbon fiber content (25 wt%, 30 wt%, 35 wt%, 40 wt%) was prepared in this work. Thermal decomposition behavior and melting temperature were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. Subsequently, mechanical properties including bending strength, compressive strength, impact strength and hardness were tested respectively. Afterwards, the fracture morphology of the bending test samples was observed by scanning electron microscopy (SEM). In addition, murine fibroblast L929 cells were adopted for cytotoxicity test by CCK-8 assay in vitro, and the morphology of cells was observed by inverted fluorescence microscope simultaneously, cell compatibility of CFR-PEEK composites was tested.

Flexural and torsional properties of a glass fiber-reinforced composite diaphyseal bone model with multidirectional fiber orientation

Although widely used, metallic implants have certain drawbacks in reconstructive bone surgery. Their high stiffness in respect to cortical bone can lead to complications which include periprosthetic fractures and aseptic loosening. In contrast to metallic alloys, fiber-reinforced composites (FRC) composed of a thermoset polymer matrix reinforced with continuous E-glass fibers have elastic properties matching those of bone. We investigated the mechanical properties of straight FRC tubes and FRC bone models representing the diaphysis of rabbit femur prepared from glass fiber/bisphenol A glycidyl methacrylate (BisGMA) - triethylene glycol dimethacrylate (TEGDMA) composite in three-point bending and torsion. Three groups of straight FRC tubes with different fiber orientations were mechanically tested to determine the best design for the FRC bone model. Tube 1 consisted most axially oriented unidirectional fiber roving and fewest bidirectional fiber sleevings. Fiber composition of tube 3 was the opposite. Tube 2 had moderate composition of both fiber types. Tube 2 resisted highest stresses in the mechanical tests and its fiber composition was selected for the FRC bone model. FRC bone model specimens were then prepared and the mechanical properties were compared with those of cadaver rabbit femora. In three-point bending, FRC bone models resisted 39-54% higher maximum load than rabbit femora with similar flexural stiffness. In torsion, FRC bone models resisted 31% higher maximum torque (p < 0.001) and were 38% more rigid (p = 0.001) than rabbit femora. Glass fiber-reinforced composites have good biocompatibility and from a biomechanical perspective, they could be used even in reconstruction of segmental diaphyseal defects. Development of an implant applicable for clinical use requires further studies.

Heterogeneous modeling based prosthesis design with porosity and material variation

The work proposes the development of heterogeneous bio-implants with the aim to minimize stress shielding effect and enhance bone ingrowth. Stress shielding in the implant can be minimized by reducing the overall stiffness of the implant, which is achieved here by varying the material based on stress distribution across the prosthesis. To increase overall stability of the implant by simultaneous enhancing osseointegration and reducing stress shielding, the work proposes the design of heterogeneous prosthesis with graded porosity and material having radial, axial and mixed (simultaneous radial and axial) variations. Static analysis for material variation models and consolidation analysis for graded porosity and material variation models are performed. After comparisons of results among different models, radial variation model was observed to deliver the results.

Biodegradable intramedullary nails reinforced with carbon and alginate fibers: In vitro and in vivo biocompatibility

BACKGROUND

Commonly, intramedullary nails are made of nondegradable materials, and hence they need to be removed once the bone fracture is healed. We propose a novel composite material consisting of poly-L-lactide matrix modified with carbon and alginate fibers to be used for biodegradable intramedullary fixation. The aim of this study was to make in vitro and in vivo biocompatibility assessments.

METHODS

In the in vitro conditions, biocompatibility of biomaterials was compared using normal human osteoblasts. After 3 and 7 days, cytotoxicity, viability and proliferation tests were performed, as well as cell morphology and adhesion observations. In the in vivo experiments, Californian rabbits (approx. 9 months old) were used. The composite nails and controls (Kirschner wires) were used for fixation of distal femoral osteotomy. The evaluation was made on the basis of clinical observations, radiographs taken after 2, 4, 6 and 8 weeks post implantation, and macroscopic and histological observations.

RESULTS

Cell tests indicated that both modifiers had a positive influence on cell viability. Biodegradable composite nails led to bony union when used for fixation of distal diaphysis osteotomy in rabbits. Histological analysis showed that the initial focal necrosis should be fully compensated for by the osteoblast proliferation and trabeculae formation.

CONCLUSIONS

Both in vitro and in vivo tests confirmed biocompatibility and potential applicability of novel biodegradable intramedullary nails modified with long carbon and alginate fibers for osteosynthesis of bone epiphysis.

Bioactive glass surface for fiber reinforced composite implants via surface etching by Excimer laser

Biostable fiber-reinforced composites (FRC) prepared from bisphenol-A-glycidyldimethacrylate (BisGMA)-based thermosets reinforced with E-glass fibers are promising alternatives to metallic implants due to the excellent fatigue resistance and the mechanical properties matching those of bone. Bioactive glass (BG) granules can be incorporated within the polymer matrix to improve the osteointegration of the FRC implants. However, the creation of a viable surface layer using BG granules is technically challenging. In this study, we investigated the potential of Excimer laser ablation to achieve the selective removal of the matrix to expose the surface of BG granules. A UV-vis spectroscopic study was carried out to investigate the differences in the penetration of light in the thermoset matrix and BG. Thereafter, optimal Excimer laser ablation parameters were established. The formation of a calcium phosphate (CaP) layer on the surface of the laser-ablated specimens was verified in simulated body fluid (SBF). In addition, the proliferation of MG63 cells on the surfaces of the laser-ablated specimens was investigated. For the laser-ablated specimens, the pattern of proliferation of MG63 cells was comparable to that in the positive control group (Ti6Al4V). We concluded that Excimer laser ablation has potential for the creation of a bioactive surface on FRC-implants.