Retention of mechanical properties and cytocompatibility of a phosphate-based glass fiber/polylactic acid composite

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.

Effect of varying the Mg with Ca content in highly porous phosphate-based glass microspheres

This paper reports on the role of phosphate-based glass (PBG) microspheres and their physicochemical properties including in vitro biological response to human mesenchymal stem cells (hMSCs). Solid and porous microspheres were prepared via a flame spheroidisation process. The Mg content in the PBG formulations explored was reduced from 24 to 2 mol% with a subsequent increase in Ca content. A small quantity of TiO₂ (1 mol%) was added to the lower Mg-content glass (2 mol%) to avoid crystallisation. Morphological and physical characterisation of porous microspheres revealed interconnected porosity (up to 76 ± 5 %), average external pore sizes of 55 ± 5 μm with surface areas ranging from 0.38 to 0.43 m² g^-1. Degradation and ion release studies conducted compared the solid (non-porous) and porous microspheres and revealed 1.5 to 2.5 times higher degradation rate for porous microspheres. Also, in vitro bioactivity studies using simulated body fluid (SBF) revealed Ca/P ratios for porous microspheres of all three glass formulations were between 0.75 and 0.92 which were within the range suggested for precipitated amorphous calcium phosphate. Direct cell seeding and indirect cell culture studies (via incubation with microsphere degradation products) revealed hMSCs were able to grow and undergo osteogenic differentiation in vitro, confirming cytocompatibility of the formulations tested. However, the higher Mg content (24 mol%) porous microsphere showed the most potent osteogenic response and is therefore considered as a promising candidate for bone repair applications.

Additive-Manufactured Gyroid Scaffolds of Magnesium Oxide, Phosphate Glass Fiber and Polylactic Acid Composite for Bone Tissue Engineering

Composites of biodegradable phosphate glass fiber and polylactic acid (PGF/PLA) show potential for bone tissue engineering scaffolds, due to their ability to release Ca, P, and Mg during degradation, thus promoting the bone repair. Nevertheless, glass degradation tends to acidify the surrounding aqueous environment, which may adversely affect the viability and bone-forming activities of osteoblasts. In this work, MgO was investigated as a neutralizing agent. Porous network-phase gyroid scaffolds were additive-manufactured using four different materials: PLA, MgO/PLA, PGF/PLA, and (MgO + PGF)/PLA. The addition of PGF enhanced compressive properties of scaffolds, and the resultant scaffolds were comparably strong and stiff with human trabecular bone. While the degradation of PGF/PLA composite induced considerable acidity in degradation media and intensified the degradation of PGF in return, the degradation media of (MgO + PGF)/PLA maintained a neutral pH close to a physiological environment. The experiment results indicated the possible mechanism of MgO as the neutralizing agent: the local acidity was buffered as the MgO reacted with the acidic degradation products thereby inhibiting the degradation of PGF from being intensified in an acidic environment. The (MgO + PGF)/PLA composite scaffold appears to be a candidate for bone tissue engineering.

The Influence of Sub-Zero Conditions on the Mechanical Properties of Polylactide-Based Composites

Polylactide-based composites filled with waste fillers due to their sustainability are a subject of many current papers, in which their structural, mechanical, and thermal properties are evaluated. However, few studies focus on their behavior in low temperatures. In this paper, dynamic and quasi-static mechanical properties of polylactide-based composites filled with 10 wt% of linseed cake (a by-product of mechanical oil extraction from linseed) were evaluated at room temperature and at -40 °C by means of dynamic mechanical analysis (DMA), Charpy's impact strength test and uniaxial tensile test. It was found that the effect of plasticization provided by the oil contained in the filler at room temperature is significantly reduced in sub-zero conditions due to solidification of the oil around -18 °C, as it was shown by differential scanning calorimetry (DSC) and DMA, but the overall mechanical performance of the polylactide-based composites was sufficient to enable their use in low-temperature applications.

Recent advances and future perspectives of sol–gel derived porous bioactive glasses: a review

Sol–gel derived bioactive glasses have been extensively explored as a promising and highly porous scaffold materials for bone tissue regeneration applications owing to their exceptional osteoconductivity, osteostimulation and degradation rates.

Ga and Ce ion-doped phosphate glass fibres with antibacterial properties and their composite for wound healing applications

Novel gallium/cerium-doped phosphate glass fibres (PGF) were successfully manufactured by the melt-quenching and melt-spinning process. The amorphous character of the materials produced was confirmed using X-ray powder diffraction (XRD), and the elemental composition was investigated with X-ray fluorescence confirming the presence of 2 mol% of Ga₂O₃ or CeO₂. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of Q¹ and Q² structural phosphate species. Mechanical properties of the PGFs revealed tensile strength values of 428 ± 94 MPa and 379 ± 80 MPa, with elastic modulus values of 45 ± 4 GPa and 54 ± 9 GPa for Ce-PGF (diameter 25 μm) and Ga-PGF (diameter 18 μm), respectively. The influence of both dopants on the glass degradation properties was evaluated by tests in deionised water, which revealed a decreased dissolution rate for gallium-doped PGF in comparison to cerium-doped PGF. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) measurements were used to explore ion release in cell culture medium, while ICP-mass spectrometry (ICP-MS) was used to measure ion release in deionised water. These techniques showed controlled release of therapeutic and antibacterial ions from the PGF. Antibacterial properties of Ce-PGF and Ga-PGF, based on turbidity measurements, were confirmed against Gram-positive bacteria. Moreover, Ce-doped phosphate glass fibres did not disturb the proliferation of human epidermal keratinocyte (HaCaT) cells or the mobility of mice embryonic fibroblasts (MEF). Applying an in vitro scratch assay showed full wound closure after 24 h of indirect incubation with Ga-PGF. Due to their superior processability as compared with Ga-PGFs, a fully degradable mesh based on Ce-PGF was designed and found to achieve high water uptake (up to 800%), suggesting its suitability for wound healing applications.

Creep, recovery, and stress relaxation behavior of nanostructured bioactive calcium phosphate glass-POSS/polymer composites for bone implants studied under simulated physiological conditions

The creep and recovery and the stress relaxation behaviors of poly(butylene adipate-co-terephthalate) (PBAT) and polyhydroxyalkanoates (PHA) binary blends incorporating 30 wt % of a mixture of trisilanolisobutyl polyhedral oligomeric silsesquioxanes (POSS) and calcium phosphate glass (CaP-g) were investigated under simulated physiological and human body temperature conditions. The synergistic effect of PHA and CaP-g/POSS filler remarkably improved the creep behavior of the PBAT matrix and decreased its residual strain, consequently enhancing its elastic recovery. A considerable increase of the relaxation modulus of the hybrid materials was also observed upon incorporation of PHA and CaP-g/POSS. The relaxation modulus of the neat PBAT sample increased from ~60 MPa to ~1600 MPa after addition of 30 wt % CaP-g/POSS and 70 wt % PHA. However, after exposure of the composites to the simulated human body conditions for 14 days, a drop of dynamic mechanical properties of the studied material systems was observed along with formation of a desirable calcium phosphate phase on the material surface. The long-term (i.e., up to 7 × 10⁵  s) viscoelastic behavior of the studied materials was successfully predicted using the time-temperature superposition principle and the obtained creep strain and the relaxation modulus master curves were satisfactorily fitted to the Findley power law equation and the generalized Maxwell model, respectively. This study demonstrates a facile method for tailoring CaP-g/POSS bioactive glasses composition for bone-like apatite formation on biopolymer surfaces. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2419-2432, 2019.

Flame-Spheroidized Phosphate-Based Glass Particles with Improved Characteristics for Applications in Mesenchymal Stem Cell Culture Therapy and Tissue Engineering

The chemical formulation of phosphate-based glasses (PBGs) can be tailored to fit particular end applications such as bone tissue engineering. While most reports to date have evaluated the effect of PBG chemical formulation on bone cells, this study specifically explored the manufacturing process, the changes in physical and chemical properties of PBG particles after flame spheroidization, and subsequent effects on human mesenchymal stem cells (hMSCs), a prime cell type for regenerative medicine applications. Flame spheroidization involves feeding irregular PBG particles (microparticles, MP) into a hot flame, causing them to melt and mold into solid spherical PBG particles (microspheres, MS). The laser diffraction analysis showed an increase in the volume-weighted mean diameter of particles from 48 to 139 μm after spheroidization and also revealed changes in the chemical composition of smaller MS (< 45 μm in size), whereas MS in other size ranges did not show significantly different chemical composition compared to MP. Additionally, some air bubbles were entrapped inside particles during spheroidization, causing a 2% drop in relative density of MS. However, the packing density of MS was 30% higher than that of MP. Culture of hMSCs on the particles showed significant improvement in cell spreading on MS compared to that on MP and nearly 2 times higher cell metabolic activity after 7 days of culture, suggesting that MS provided a more favorable support and geometry for hMSC attachment and growth for tissue engineering.

Characterisation of CorGlaes(®) Pure 107 fibres for biomedical applications

A degradable ultraphosphate (55 mol % P2O5) quinternary phosphate glass composition has been characterised in terms of its chemical, mechanical and degradation properties both as a bulk material and after drawing into fibres. This glass formulation displayed a large processing window simplifying fibre drawing. The fibres displayed stiffness and strength of 65.5 ± 20.8 GPa and 426±143 MPa. While amorphous discs of the glass displayed a linear dissolution rate of 0.004 mg cm(-2) h(-1) at 37 °C, in a static solution with a reduction in media pH. Once drawn into fibres, the dissolution process dropped the pH to <2 in distilled water, phosphate buffer saline and corrected-simulated body fluid, displaying an autocatalytic effect with >90 % mass loss in 4 days, about seven times faster than anticipated for this solution rate. Only cell culture media was able to buffer the pH taking over a week for full fibre dissolution, however, still four times faster dissolution rate than as a bulk material. However, at early times the development of a HCA layer was seen indicating potential bioactivity. Thus, although initial analysis indicated potential orthopaedic implant applications, autocatalysis leads to accelerating degradation in vitro.

In vitro degradation of biodegradable polylactic acid/magnesium composites: Relevance of Mg particle shape

Absorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone in the implantation site. In this work, biodegradable composites formed by a polylactic acid matrix reinforced with 10%wt. magnesium microparticles were processed and their in vitro degradation investigated during 28 days. A joint analysis of the amount of H2 released, the changes in pH in buffered (PBS) and non-buffered media (distilled water), the variations in mass, microstructure and the mechanical performance of the specimens was developed. The main aim was to elucidate the relevance of Mg particles shape on tailoring the degradation kinetics of these novel composites. The results show that the shape of the Mg reinforcing particles plays a crucial role in the degradation rate of PLA/Mg composites, with spherical particles promoting a lower degradation rate than irregular particles. This fact is only partially due to the smaller surface area to volume ratio of the spherical particles. Irregular particles promote a faster formation of cracks and, therefore, an increasingly faster degradation of the polymeric matrix. In every case, the amount of H2 released by the composites was well below that released by monolithic Mg. The pH of PBS during degradation remained always within 7.2 and 7.4. PLA/Mg reinforced with spherical particles retains more than 90% of its mechanical properties after 7 days of immersion and more than 60% after 28 days.

STATEMENT OF SIGNIFICANCE

The increasing demand for temporary orthopaedic implants is the driving force to seek new strategies to decrease costs and simultaneously improve patients comfort as well as simplify surgical procedures. Resorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone. We are presenting for the first time results of the degradation kinetics of a new material based on polylactic acid reinforced with 10%wt. Mg microparticles. This work analyzes the relevance of Mg particle shape (irregular and spherical) on tailoring the degradation behaviour of these composites. Conclusions withdrawn from this study help to customize bioabsorbable materials in order to meet the requirements for a specific application and patient.

In-situ polymerisation of fully bioresorbable polycaprolactone/phosphate glass fibre composites: In vitro degradation and mechanical properties

Fully bioresorbable composites have been investigated in order to replace metal implant plates used for hard tissue repair. Retention of the composite mechanical properties within a physiological environment has been shown to be significantly affected due to loss of the integrity of the fibre/matrix interface. This study investigated phosphate based glass fibre (PGF) reinforced polycaprolactone (PCL) composites with 20%, 35% and 50% fibre volume fractions (Vf) manufactured via an in-situ polymerisation (ISP) process and a conventional laminate stacking (LS) followed by compression moulding. Reinforcing efficiency between the LS and ISP manufacturing process was compared, and the ISP composites revealed significant improvements in mechanical properties when compared to LS composites. The degradation profiles and mechanical properties were monitored in phosphate buffered saline (PBS) at 37°C for 28 days. ISP composites revealed significantly less media uptake and mass loss (p<0.001) throughout the degradation period. The initial flexural properties of ISP composites were substantially higher (p<0.0001) than those of the LS composites, which showed that the ISP manufacturing process provided a significantly enhanced reinforcement effect than the LS process. During the degradation study, statistically higher flexural property retention profiles were also seen for the ISP composites compared to LS composites. SEM micrographs of fracture surfaces for the LS composites revealed dry fibre bundles and poor fibre dispersion with polymer rich zones, which indicated poor interfacial bonding, distribution and adhesion. In contrast, evenly distributed fibres without dry fibre bundles or polymer rich zones, were clearly observed for the ISP composite samples, which showed that a superior fibre/matrix interface was achieved with highly improved adhesion.

Cytocompatibility, mechanical and dissolution properties of high strength boron and iron oxide phosphate glass fibre reinforced bioresorbable composites

In this study, Polylactic acid (PLA)/phosphate glass fibres (PGF) composites were prepared by compression moulding. Fibres produced from phosphate based glasses P2O5-CaO-MgO-Na2O (P45B0), P2O5-CaO-MgO-Na2O-B2O3 (P45B5), P2O5-CaO-MgO-Na2O-Fe2O3 (P45Fe3) and P2O5-CaO-MgO-Na2O-B2O3-Fe2O3 (P45B5Fe3) were used to reinforce the bioresorbable polymer PLA. Fibre mechanical properties and degradation rate were investigated, along with the mechanical properties, degradation and cytocompatibility of the composites. Retention of the mechanical properties of the composites was evaluated during degradation in PBS at 37°C for four weeks. The fibre volume fraction in the composite varied from 19 to 23%. The flexural strength values (ranging from 131 to 184MPa) and modulus values (ranging from 9.95 to 12.29GPa) obtained for the composites matched those of cortical bone. The highest flexural strength (184MPa) and modulus (12.29GPa) were observed for the P45B5Fe3 composite. After 28 days of immersion in PBS at 37°C, ~35% of the strength profile was maintained for P45B0 and P45B5 composites, while for P45Fe3 and P45B5Fe3 composites ~40% of the initial strength was maintained. However, the overall wet mass change of P45Fe3 and P45B5Fe3 remained significantly lower than that of the P45B0 and P45B5 composites. The pH profile also revealed that the P45B0 and P45B5 composites degraded quicker, correlating well with the degradation profile. From SEM analysis, it could be seen that after 28 days of degradation, the fibres in the fractured surface of P45B5Fe3 composites remain fairly intact as compared to the other formulations. The in vitro cell culture studies using MG63 cell lines revealed both P45Fe3 and P45B5Fe3 composites maintained and showed higher cell viability as compared to the P45B0 and P45B5 composites. This was attributed to the slower degradation rate of the fibres in P45Fe3 and P45B5Fe3 composites as compared with the fibres in P45B0 and P45B5 composites.

Biodegradable Materials for Bone Repair and Tissue Engineering Applications

This review discusses and summarizes the recent developments and advances in the use of biodegradable materials for bone repair purposes. The choice between using degradable and non-degradable devices for orthopedic and maxillofacial applications must be carefully weighed. Traditional biodegradable devices for osteosynthesis have been successful in low or mild load bearing applications. However, continuing research and recent developments in the field of material science has resulted in development of biomaterials with improved strength and mechanical properties. For this purpose, biodegradable materials, including polymers, ceramics and magnesium alloys have attracted much attention for osteologic repair and applications. The next generation of biodegradable materials would benefit from recent knowledge gained regarding cell material interactions, with better control of interfacing between the material and the surrounding bone tissue. The next generations of biodegradable materials for bone repair and regeneration applications require better control of interfacing between the material and the surrounding bone tissue. Also, the mechanical properties and degradation/resorption profiles of these materials require further improvement to broaden their use and achieve better clinical results.

Bioactive glasses—structure and properties

Bioactive glasses were the first synthetic materials to show bonding to bone, and they are successfully used for bone regeneration. They can degrade in the body at a rate matching that of bone formation, and through a combination of apatite crystallization on their surface and ion release they stimulate bone cell proliferation, which results in the formation of new bone. Despite their excellent properties and although they have been in clinical use for nearly thirty years, their current range of clinical applications is still small. Latest research focuses on developing new compositions to address clinical needs, including glasses for treating osteoporosis, with antibacterial properties, or for the sintering of scaffolds with improved mechanical stability. This Review discusses how the glass structure controls the properties, and shows how a structure-based design may pave the way towards new bioactive glass implants for bone regeneration.

Mechanical, degradation and cytocompatibility properties of magnesium coated phosphate glass fibre reinforced polycaprolactone composites

Retention of mechanical properties of phosphate glass fibre reinforced degradable polyesters such as polycaprolactone and polylactic acid in aqueous media has been shown to be strongly influenced by the integrity of the fibre/polymer interface. A previous study utilising ‘single fibre’ fragmentation tests found that coating with magnesium improved the fibre and matrix interfacial shear strength. Therefore, the aim of this study was to investigate the effects of a magnesium coating on the manufacture and characterisation of a random chopped fibre reinforced polycaprolactone composite. Short chopped strand non-woven phosphate glass fibre mats were sputter coated with degradable magnesium to manufacture phosphate glass fibre/polycaprolactone composites. The degradation behaviour (water uptake, mass loss and pH change of the media) of these polycaprolactone composites as well as of pure polycaprolactone was investigated in phosphate buffered saline. The Mg coated fibre reinforced composites revealed less water uptake and mass loss during degradation compared to the non-coated composites. The cations released were also explored and a lower ion release profile for all three cations investigated (namely Na+, Mg2+ and Ca2+) was seen for the Mg coated composite samples. An increase of 17% in tensile strength and 47% in tensile modulus was obtained for the Mg coated composite samples. Both flexural and tensile properties were investigated and a higher retention of mechanical properties was obtained for the Mg coated fibre reinforced composite samples up to 10 days immersion in PBS. Cytocompatibility study showed both composite samples (coated and non-coated) had good cytocompatibility with human osteosarcoma cell line.

Effect of boron oxide addition on fibre drawing, mechanical properties and dissolution behaviour of phosphate-based glass fibres with fixed 40, 45 and 50 mol% P2O5

Previous studies investigating manufacture of phosphate-based glass fibres from glasses fixed with P2O5 content less than 50 mol% showed that continuous manufacture without breakage was very difficult. In this study, nine phosphate-based glass formulations from the system P2O5-CaO-Na2O-MgO-B2O3 were prepared with P2O5 contents fixed at 40, 45 and 50 mol%, where Na2O was replaced by 5 and 10 mol% B2O3 and MgO and CaO were fixed to 24 and 16 mol%, respectively. The effect of B2O3 addition on the fibre drawing, fibre mechanical properties and dissolution behaviour was investigated. It was found that addition of 5 and 10 mol% B2O3 enabled successful drawing of continuous fibres from glasses with phosphate (P2O5) contents fixed at 40, 45 and 50 mol%. The mechanical properties of the fibres were found to significantly increase with increasing B2O3 content. The highest tensile strength (1200 ± 130 MPa) was recorded for 45P2O5-16CaO-5Na2O-24MgO-10B2O3 glass fibres. The fibres were annealed, and a comparison of the mechanical properties and mode of degradation of annealed and non-annealed fibres were investigated. A decrease in tensile strength and an increase in tensile modulus were observed for the annealed fibres. An assessment of the change in mechanical properties of both the annealed and non-annealed fibres was performed in phosphate-buffered saline (PBS) at 37℃ for 28 and 60 days, respectively. Initial loss of mechanical properties due to annealing was found to be recovered with degradation. The B2O3-containing glass fibres were found to degrade at a much slower rate as compared to the non-B2O3-containing fibres. Both annealed and non-annealed fibres exhibited a peeling effect of the fibre's outer layer during degradation.

Magnesium coated bioresorbable phosphate glass fibres: investigation of the interface between fibre and polyester matrices

Bioresorbable phosphate glass fibre reinforced polyester composites have been investigated as replacement for some traditional metallic orthopaedic implants, such as bone fracture fixation plates. However, composites tested revealed loss of the interfacial integrity after immersion within aqueous media which resulted in rapid loss of mechanical properties. Physical modification of fibres to change fibre surface morphology has been shown to be an effective method to improve fibre and matrix adhesion in composites. In this study, biodegradable magnesium which would gradually degrade to Mg(2+) in the human body was deposited via magnetron sputtering onto bioresorbable phosphate glass fibres to obtain roughened fibre surfaces. Fibre surface morphology after coating was observed using scanning electron microscope (SEM). The roughness profile and crystalline texture of the coatings were determined via atomic force microscope (AFM) and X-ray diffraction (XRD) analysis, respectively. The roughness of the coatings was seen to increase from 40 ± 1 nm to 80 ± 1 nm. The mechanical properties (tensile strength and modulus) of fibre with coatings decreased with increased magnesium coating thickness.

Cytocompatibility assessment of chemical surface treatments for phosphate glass to improve adhesion between glass and polyester

Fully resorbable phosphate glass fiber reinforced polymer composites have shown real potential for replacing some of the existing metallic bone fracture fixation devices. However, some of these composites have not provided suitable mechanical strength profiles over the required healing period for bone. Typically, it has been seen that these composites can lose up to 50% or more of their strength within the first week of degradation. Functionalizing the glass surface to promote polymer adhesion or to introduce hydrophobicity at the glass surface could potentially introduce control over the mechanical properties of the composite and their retention. In this study eight chemical agents namely, Glycerol 2-phosphate disodium salt; 3-phosphonopropionic acid; 3-aminopropyltriethoxy silane; etidronic acid; hexamethylene diisocyanate; sorbitol/sodium ended PLA oligomers and amino phosphonic acid, were selected to functionalise the bulk phosphate glass surface. Selected chemical agents had one functional group (-OH or O C N) to react with the glass and another functionality (either -OH, NH2, or Na) to react with the polymer matrix and/or produce hydrophobicity at the fiber surface. Bulk phosphate glass surface-treated with the above agents were assessed for the cytotoxicity of degradation products cell-material interaction in short- and long-term direct cytocompatibility studies. Results obtained from these cytocompatibility studies (using human osteosarcoma (MG63) and primary human osteoblast cell lines) revealed no cytotoxicity from the degradation products and a response comparable to controls in terms of cell functions (attachment, viability, metabolic activity, proliferation, and differentiation) and morphology.

Dissolution behavior of high strength bioresorbable glass fibers manufactured by continuous fiber drawing

This article describes the dissolution behavior of three silica-based resorbable glasses manufactured by an industrial-type continuous fiber drawing process yielding fibers with tensile strength of 1800-2300MPa. The results of a long-term in vitro degradation testing of the manufactured high strength bioresorbable glass fibers are presented. The degradation was performed by exposing the glass fibers to SBF and TRIS for 26 weeks at physiological conditions at 37°C. All fibers showed continuous resorption throughout the study and two of the fibers revealed bioactivity by forming a calcium phosphate (CaP) layer in SBF.

Bioresorbable composite screws manufactured via forging process: pull-out, shear, flexural and degradation characteristics

Bioresorbable screws have the potential to overcome some of the complications associated with metallic screws currently in use. Removal of metallic screws after bone has healed is a serious issue which can lead to refracture due to the presence of screw holes. Poly lactic acid (PLA), fully 40 mol% P(2)O(5) containing phosphate unidirectional (P40UD) and a mixture of UD and short chopped strand random fibre mats (P40 70%UD/30%RM) composite screws were prepared via forging composite bars. Water uptake and mass loss for the composite screws manufactured increased significantly to ∼1.25% (P=0.0002) and ∼1.1% (P<0.0001), respectively, after 42 days of immersion in PBS at 37 °C. The initial maximum flexural load for P40 UD/RM and P40 UD composite screws was ∼60% (P=0.0047) and ∼100% (P=0.0037) higher than for the PLA screws (∼190 N), whilst the shear load was slightly higher in comparison to PLA (∼2.2 kN). The initial pull-out strengths for the P40 UD/RM and PLA screws were similar whereas that for P40 UD screws was ∼75% higher (P=0.022). Mechanical properties for the composite screws decreased initially after 3 days of immersion and this reduction was ascribed to the degradation of the fibre/matrix interface. After 3 days interval the mechanical properties (flexural, shear and pull-out) maintained their integrity for the duration of the study (at 42 days). This property retention was attributed to the chemical durability of the fibres used and stability of the matrix properties during the degradation process. It was also deemed necessary to enhance the fibre/matrix interface via use of a coupling agent in order to maintain the initial mechanical properties acquired for the required period of time. Lastly, it is also suggested that the degrading reinforcement fibres may have the potential to buffer any acidic products released from the PLA matrix.

Cytocompatibility and Mechanical Properties of Short Phosphate Glass Fibre Reinforced Polylactic Acid (PLA) Composites: Effect of Coupling Agent Mediated Interface

In this study three chemical agents Amino-propyl-triethoxy-silane (APS), sorbitol ended PLA oligomer (SPLA) and Hexamethylene diisocyanate (HDI) were identified to be used as coupling agents to react with the phosphate glass fibre (PGF) reinforcement and the polylactic acid (PLA) polymer matrix of the composite. Composites were prepared with short chopped strand fibres (l = 20 mm, ϕ = 20 µm) in a random arrangement within PLA matrix. Improved, initial composite flexural strength (~20 MPa) was observed for APS treated fibres, which was suggested to be due to enhanced bonding between the fibres and polymer matrix. Both APS and HDI treated fibres were suggested to be covalently linked with the PLA matrix. The hydrophobicity induced by these coupling agents (HDI, APS) helped to resist hydrolysis of the interface and thus retained their mechanical properties for an extended period of time as compared to non-treated control. Approximately 70% of initial strength and 65% of initial modulus was retained by HDI treated fibre composites in contrast to the control, where only ~50% of strength and modulus was retained after 28 days of immersion in PBS at 37 °C. All coupling agent treated and control composites demonstrated good cytocompatibility which was comparable to the tissue culture polystyrene (TCP) control, supporting the use of these materials as coupling agent’s within medical implant devices.

Material characterisation and cytocompatibility assessment of quinternary phosphate glasses

Six phosphate glass formulations (in the system P(2)O(5)-CaO-MgO-Na(2)O-Fe(2)O(3)) were produced with fixed magnesium and calcium content at 24 and 16 mol%, respectively. P(2)O(5) and Fe(2)O(3) were varied between 40-50 and 0-4 mol% respectively, with the balance being Na(2)O. EDX analyses confirmed the final composition of the glasses investigated to within a 1-2 % error margin. Thermal analyses showed a linear increase in T(g) with increasing Fe(2)O(3) and P(2)O(5) contents, with Fe(2)O(3) showing a greater effect than P(2)O(5). This was proposed to be due to the formation of Fe-O-P bonds and an increase in the cross-link density of the glass network enhancing the durability of the glass. The glasses that were investigated revealed a decrease in degradation rate with increasing Fe(2)O(3) and P(2)O(5) contents and again the effect of Fe(2)O(3) was greater. All the above characteristics correlated well with structural changes measured by IR and XPS analyses. Cytocompatibility studies showed good cellular (MG63) response to the glasses up to 168 h in terms of cell viability, proliferation and differentiation. Statistical analysis revealed that all the formulations with the exception of P50Fe4 gave a comparable response to the control (TCP), which suggested that after a threshold level of glass durability is achieved the degradation rate has no or minimal effect on biocompatibility. However, it was seen that the glass chemistry can also affect cellular response, since increasing the P(2)O(5) content promoted phenotypic expression that was not related to degradation rate but to the degradation products. This was supported using an elution assay.

Bioresorbable screws reinforced with phosphate glass fibre: manufacturing and mechanical property characterisation

Use of bioresorbable screws could eliminate disadvantages associated with metals such as removal operations, corrosion, MRI interference and stress shielding. Mechanical properties of bioresorbable polymers alone are insufficient for load bearing applications application as screws. Thus, reinforcement is necessary to try and match or surpass the mechanical properties of cortical bone. Phosphate based glass fibres were used to reinforce polylactic acid (PLA) in order to produce unidirectionally aligned (UD) and unidirectionally plus randomly distributed (UD/RM) composite screws (P40 UD and P40 UD/RM). The maximum flexural and push-out properties for the composite screws (P40 UD and P40 UD/RM) increased by almost 100% in comparison with the PLA screws. While the pull-out strength and stiffness of the headless composite screws were ∼80% (strength) and ∼130% (stiffness) higher than for PLA, those with heads exhibited properties lower than those for PLA alone as a result of failure at the heads. An increase in the maximum shear load and stiffness for the composite screws (∼30% and ∼40%) in comparison to the PLA screws was also seen. Maximum torque for the PLA screws was ∼1000 mN m, while that for the composite screws were slightly lower. The SEM micrographs for P40 UD and P40 UD/RM screws revealed small gaps around the fibres, which were suggested to be due to buckling of the UD fibres during the manufacturing process.

Finite element modelling of the flexural performance of resorbable phosphate glass fibre reinforced PLA composite bone plates

A finite element method is presented to predict the flexural properties of resorbable phosphate glass fibre reinforced PLA composite bone plates. A novel method for meshing discontinuous fibre architectures is presented, which removes many of the limitations imposed by conventional finite element approaches. The model is used to understand the effects of increasing the span-to-thickness ratio for different fibre architectures used for PBG/PLA composites. A span-to-thickness ratio of 16:1 is found to be appropriate for materials with randomly orientated fibres, which agrees well with the test standard. However, for highly aligned materials the model indicates that a span-to-thickness ratio of 80:1 is required, in order to minimise the effects of shear deflection. The model is validated against flexural stiffness data from the literature for a range of polymers, fibres and fibre volume fractions. Generally there is less than 10% error between the FE predictions and experimental values. The model is subsequently used to perform a parametric study to understand what material developments are required to match the properties of PGF/PLA composites to cortical bone. It is concluded that alignment of the fibre is necessary to exceed the 20 GPa target, since the current manufacturing methods limit the fibre length to ∼10 mm, which consequently restricts the flexural modulus to ∼19 GPa (at 50% volume fraction).

Investigating the use of coupling agents to improve the interfacial properties between a resorbable phosphate glass and polylactic acid matrix

Eight different chemicals were investigated as potential candidate coupling agents for phosphate glass fibre reinforced polylactic acid composites. Evidence of reaction of the coupling agents with phosphate glass and their effect on surface wettability and glass degradation were studied along with their principle role of improving the interface between glass reinforcement and polymer matrix. It was found that, with an optimal amount of coupling agent on the surface of the glass/polymer, interfacial shear strength improved by a factor of 5. Evidence of covalent bonding between agent and glass was found for three of the coupling agents investigated, namely: 3-aminopropyltriethoxysilane; etidronic acid and hexamethylene diisocyanate. These three coupling agents also improved the interfacial shear strength and increased the hydrophobicity of the glass surface. It is expected that this would provide an improvement in the macroscopic properties of full-scale composites fabricated from the same materials which may also help to retain these properties for the desired length of time by retarding the breakdown of the fibre/matrix interface within these composites.

Effect of Si and Fe doping on calcium phosphate glass fibre reinforced polycaprolactone bone analogous composites

Reinforcing biodegradable polymers with phosphate-based glass fibres (PGF) is of interest for bone repair and regeneration. In addition to increasing the mechanical properties, PGF can also release bioinorganics, as they are water soluble, a property that may be controllably translated into a fully degradable composite. Herein, the effect of Si and Fe on the solubility of calcium-containing phosphate-based glasses (PG) in the system (50P(2)O(5)-40CaO-(10-x)SiO(2)-xFe(2)O(3), where x=0, 5 and 10 mol.%) were investigated. On replacing SiO(2) with Fe(2)O(3), there was an increase in the glass transition temperature and density of the PG, suggesting greater crosslinking of the phosphate chains. This significantly reduced the dissolution rates of degradation and ion release. Two PG formulations, 50P(2)O(5)-40CaO-10Fe(2)O(3) (Fe10) and 50P(2)O(5)-40CaO-5Fe(2)O(3)-5SiO(2) (Fe5Si5), were melt drawn into fibres and randomly incorporated into polycaprolactone (PCL). Initially, the flexural strength and modulus significantly increased with PGF incorporation. In deionized water, PCL-Fe(5)Si(5) displayed a significantly greater weight loss and ion release compared with PCL-Fe10. In simulated body fluid, brushite was formed only on the surface of PCL-Fe(5)Si(5). Dynamic mechanical analysis in phosphate buffered saline (PBS) at 37°C revealed that the PCL-Fe10 storage modulus (E') was unchanged up to day 7, whereas the onset of PCL-Fe(5)Si(5)E' decrease occurred at day 4. At longer-term ageing in PBS, PCL-Fe(5)Si(5) flexural strength and modulus decreased significantly. MC3T3-E1 preosteoblasts seeded onto PCL-PGF grew up to day 7 in culture. PGF can be used to control the properties of biodegradable composites for potential application as bone fracture fixation devices.

Influence of screw holes and gamma sterilization on properties of phosphate glass fiber-reinforced composite bone plates

Polymers prepared from polylactic acid (PLA) have found a multitude of uses as medical devices. For a material that degrades, the main advantage is that an implant would not necessitate a second surgical event for removal. In this study, fibers produced from a quaternary phosphate-based glass (PBG) in the system 50P2O5-40CaO-5Na2O-5Fe2O3 were used to reinforce PLA polymer. The purpose of this study was to assess the effect of screw holes in a range of PBG-reinforced PLA composites with varying fiber layup and volume fraction. The flexural properties obtained showed that the strength and modulus values increased with increasing fiber volume fraction; from 96 MPa to 320 MPa for strength and between 4 GPa and 24 GPa for modulus. Furthermore, utilizing a larger number of thinner unidirectional (UD) fiber prepreg layers provided a significant increase in mechanical properties, which was attributed to enhanced wet out and thus better fiber dispersion during production. The effect of gamma sterilization via flexural tests showed no statistically significant difference between the sterilized and nonsterilized samples, with the exception of the modulus values for samples with screw holes. Degradation profiles revealed that samples with screw holes degraded faster than those without screw holes due to an increased surface area for the plates with screw holes in PBS up to 30 days. Scanning electron microscope (SEM) analysis revealed fiber pullout before and after degradation. Compared with various fiber impregnation samples, with 25% volume fraction, 8 thinner unidirectional prepreg stacked samples had the shortest fiber pull-out lengths in comparison to the other samples investigated.

Effect of phosphate-based glass fibre surface properties on thermally produced poly(lactic acid) matrix composites

Incorporation of soluble bioactive glass fibres into biodegradable polymers is an interesting approach for bone repair and regeneration. However, the glass composition and its surface properties significantly affect the nature of the fibre-matrix interface and composite properties. Herein, the effect of Si and Fe on the surface properties of calcium containing phosphate based glasses (PGs) in the system (50P(2)O(5)-40CaO-(10-x)SiO(2)-xFe(2)O(3), where x = 0, 5 and 10 mol.%) were investigated. Contact angle measurements revealed a higher surface energy, and surface polarity as well as increased hydrophilicity for Si doped PG which may account for the presence of surface hydroxyl groups. Two PG formulations, 50P(2)O(5)-40CaO-10Fe(2)O(3) (Fe10) and 50P(2)O(5)-40CaO-5Fe(2)O(3)-5SiO(2) (Fe5Si5), were melt drawn into fibres and randomly incorporated into poly(lactic acid) (PLA) produced by melt processing. The ageing in deionised water (DW), mechanical property changes in phosphate buffered saline (PBS) and cytocompatibility properties of these composites were investigated. In contrast to Fe10 and as a consequence of the higher surface energy and polarity of Fe5Si5, its incorporation into PLA led to increased inorganic/organic interaction indicated by a reduction in the carbonyl group of the matrix. PLA chain scission was confirmed by a greater reduction in its molecular weight in PLA-Fe5Si5 composites. In DW, the dissolution rate of PLA-Fe5Si5 was significantly higher than that of PLA-Fe10. Dissolution of the glass fibres resulted in the formation of channels within the matrix. Initial flexural strength was significantly increased through PGF incorporation. After PBS ageing, the reduction in mechanical properties was greater for PLA-Fe5Si5 compared to PLA-Fe10. MC3T3-E1 preosteoblasts seeded onto PG discs, PLA and PLA-PGF composites were evaluated for up to 7 days indicating that the materials were generally cytocompatible. In addition, cell alignment along the PGF orientation was observed showing cell preference towards PGF.

Composites for bone repair: phosphate glass fibre reinforced PLA with varying fibre architecture

Internal fixation for bone fractures with rigid metallic plates, screws and pins is a proven operative technique. However, refracture's have been observed after rigid internal fixation with metal plates and plate fixation has been known to cause localised osteopenia under and near the plate. In the present study, resorbable composites comprising a PLA matrix reinforced with iron doped phosphate glass fibres were investigated. Non-woven random mat laminates of approximately 30% and 45% fibre volume fraction (V(f)) were produced, along with unidirectional and 0°-90° samples of approximately 20% V(f). The non-woven composite laminates achieved maximum values of 10 GPa modulus and 120 MPa strength. The 0-90º samples showed unexpectedly low strengths close to matrix value (~50 MPa) although with a modulus of 7 GPa. The UD specimens exhibited values of 130 MPa and 11.5 GPa for strength and modulus respectively. All the modulus values observed were close to that expected from the rule of mixtures. Samples immersed in deionised water at 37°C revealed rapid mechanical property loss, more so for the UD and 0-90º samples. It was suggested that continuous fibres wicked the degradation media into the composite plates which sped up the deterioration of the fibre-matrix interface. The effect was less pronounced in the non-woven random mat laminates due to the discontinuous arrangement of fibres within the composite, making it less prone to wicking. Random mat composites revealed a higher mass loss than the UD and 0°-90° specimens, it was suggested this was due to the higher fibre volume fractions of these composites and SEM studies revealed voidage around the fibres by day 3. Studies of pH of the degradation media showed similar profiles for all the composites investigated. An initial decrease in pH was attributed to the release of phosphate ions into solution followed by a gradual return back to neutral.

In vitro degradation, flexural, compressive and shear properties of fully bioresorbable composite rods

Several studies have investigated self-reinforced polylactic acid (SR-PLA) and polyglycolic acid (SR-PGA) rods which could be used as intramedullary (IM) fixation devices to align and stabilise bone fractures. This study investigated totally bioresorbable composite rods manufactured via compression moulding at ~100 °C using phosphate glass fibres (of composition 50P(2)O(5)-40CaO-5Na(2)O-5Fe(2)O(3) in mol%) to reinforce PLA with an approximate fibre volume fraction (v(f)) of 30%. Different fibre architectures (random and unidirectional) were investigated and pure PLA rods were used as control samples. The degradation profiles and retention of mechanical properties were investigated and PBS was selected as the degradation medium. Unidirectional (P50 UD) composite rods had 50% higher initial flexural strength as compared to PLA and 60% higher in comparison to the random mat (P50 RM) composite rods. Similar initial profiles for flexural modulus were also seen comparing the P50 UD and P50 RM rods. Higher shear strength properties were seen for P50 UD in comparison to P50 RM and PLA rods. However, shear stiffness values decreased rapidly (after a week) whereas the PLA remained approximately constant. For the compressive strength studies, P50 RM and PLA rods remained approximately constant, whilst for the P50 UD rods a significantly higher initial value was obtained, which decreased rapidly after 3 days immersion in PBS. However, the mechanical properties decreased after immersion in PBS as a result of the plasticisation effect of water within the composite and degradation of the fibres. The fibres within the random and unidirectional composite rods (P50 RM and P50 UD) degraded leaving behind microtubes as seen from the SEM micrographs (after 28 days degradation) which in turn created a porous structure within the rods. This was the main reason attributed for the increase seen in mass loss and water uptake for the composite rods (~17% and ~16%, respectively).

Investigation of Crystallinity, Molecular Weight Change, and Mechanical Properties of PLA/PBG Bioresorbable Composites as Bone Fracture Fixation Plates

In this study, bioresorbable phosphate-based glass (PBG) fibers were used to reinforce poly(lactic acid) (PLA). PLA/PBG random mat (RM) and unidirectional (UD) composites were prepared via laminate stacking and compression molding with fiber volume fractions between 14% and 18%, respectively. The percentage of water uptake and mass change for UD composites were higher than the RM composites and unreinforced PLA. The crystallinity of the unreinforced PLA and composites increased during the first few weeks and then a plateau was seen. XRD analysis detected a crystalline peak at 16.6° in the unreinforced PLA sample after 42 days of immersion in phosphate buffer solution (PBS) at 37°C. The initial flexural strength of RM and UD composites was ∼106 and ∼115 MPa, whilst the modulus was ∼6.7 and ∼9 GPa, respectively. After 95 days immersion in PBS at 37°C, the strength decreased to 48 and 52 MPa, respectively as a result of fiber–matrix interface degradation. There was no significant change in flexural modulus for the UD composites, whilst the RM composites saw a decrease of ∼45%. The molecular weight of PLA alone, RM, and UD composites decreased linearly with time during degradation due to chain scission of the matrix. Short fiber pull-out was seen from SEM micrographs for both RM and UD composites.