Bioresorbable Composite Research Articles

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.

High performance resorbable composites for load-bearing bone fixation devices.

Bone fractures are some of the most common injuries annually, and many require a fixation device to help properly heal. The present study focuses on developing a bioresorbable composite that has high strength and stiffness for bone fixation applications. To achieve this, a design of experiments was performed, testing the effect of long fiber reinforcement type, matrix type, matrix amount, and particle reinforcement amount on the flexural properties of the composite. Based on these results, the ideal resorbable long fiber reinforcement, particle reinforcement, and matrix material are degummed silk fibroin, hydroxyapatite, and polylactic acid, respectively. Through further optimizations of the particle reinforcement phase a flexural modulus and strength of 13.7 GPa and 437 MPa, respectively, was achieved. Both values are among the highest found in literature, with the strength far exceeding the requirement for a fixation device and the highest for such a bioresorbable composite material, showing great promise for use as a bioresorbable fixation device.

Enzyme-catalyzed degradation behavior of l-lactide/trimethylene carbonate/glycolide terpolymers and their composites with poly(l-lactide-co-glycolide) fibers

Abstract A series of high molar mass terpolymers is synthesized by ring-opening polymerization of l -lactide (LLA), 1, 3-trimethylene carbonate (TMC) and glycolide (GA). A totally bioresorbable composite is obtained by reinforcing a terpolymer matrix with plasma treated poly ( l -lactide- co -glycolide) (PLGA) short fibers. Solution cast films of the various materials are allowed to degrade at 37 °C at pH 8.5 Tris buffer using proteinase K, in comparison with a PLLA-TMC copolymer and a PLLA homopolymer. Degradation is monitored by using various analytical techniques such as gravimetry, DSC, GPC, 1 H NMR and SEM. The results show that the enzymatic degradation rate of PLLA-TMC-GA terpolymers with predominant LLA component is affected by both the average LLA block length ( l LLA ) and crystallinity. A shorter average LLA block length results in lower crystallinity, which will lead to faster degradation. However, too short average LLA block length ( i.e. l LLA ≤4.0) can retard the degradation process. The composition of the copolymers remains unchanged during degradation. In contrast, the molar mass decreases due to hydrolytic chain cleavage in the bulk. Similarly, thermal property changes are observed with increase of the melting temperature and melting enthalpy in most cases. SEM observation strongly supports a surface erosion mechanism. The composite PLTG95/5/5C exhibits lower mass loss rate as compared to neat PLTG95/5/5 due to the presence of PLGA fibers which are non-degradable by proteinase K. On the other hand, the composite shows much faster molar mass loss rate than PLTG95/5/5 because the rapid hydrolytic degradation of PLGA fibers speeds up the degradation of the matrix by internal autocatalysis.

Preparation and Properties of Bioactive Composite Based on Bioactive Glass and Poly-L-Lactide

Bioactive and bioresorbable composite was fabricated based on poly-L-lactide (PLLA) and bioactive glass (average particle size: 4.24 µm) by the combination of solvent evaporation technique and hot pressing. Bioactive glass granules are distributed homogeneously in the composite. With the increasing of the amount of bioactive glass, the bending strength and shearing strength of composite decrease while the bending modulus increases. PLLA/bioactive glass composites present a typical morphology of brittle failure with a smooth fracture surface. The biocompatibility test shows that the bioactive glass existing in the composite facilitates both adhesion and proliferation of rat fibroblast on the PLLA/bioactive glass composite film.

Bioactivity of bioresorbable composite based on bioactive glass and poly-L-lactide

Bioactive and bioresorbable composite was fabricated by a solvent evaporation technique using poly-L-lactide(PLLA) and bioactive glass (average particle size: 6.8 μm). Bioactive glass granules are homogeneously distributed in the composite with microcrack structure. The formation of hydroxyapatite(HA) on the composite in simulated body fluid(SBF) was analyzed by scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and Raman spectra. Rod-like HA crystals deposit on the surface of PLLA/bioactive glass composite after soaking for 3 d. Both rod-like crystals and HA layer form on the surface for 14 d in SBF. The high bioactivity of PLLA/bioactive glass composite indicates the potential of materials for integration with bone.

Nanocrystalline hydroxyapatite and calcium sulphate as biodegradable composite carrier material for local delivery of antibiotics in bone infections

The use of polymethylmetacrylate beads for local delivery of antibiotics requires a second surgical procedure for their removal and resorbable calcium sulphate exhibits cytotoxic effects. In this work, a bioresorbable composite of calcium sulphate and nanoparticulate hydroxyapatite (PerOssal®) was studied regarding its antibiotic release properties and biocompatibility.Material characteristics of plain PerOssal® and pure calcium sulphate pellets were studied using scanning and electron microscopy and X-ray methods. Pellets were soaked with gentamicin and vancomycin, respectively. Release properties of both antibiotics from both materials were investigated over 10 days. Quantitative and qualitative cytotoxic assays were performed for biocompatibility testing.Specific surface was 106m2/g for PerOssal® and 2.2m2/g for pure calcium sulphate. Almost complete elution of gentamicin was found for both carrier materials (94.7% for PerOssal® vs. 95.8% for calcium sulphate) within 10 days, whereas vancomycin release was higher for PerOssal® (96.3% vs. 74.8%). PerOssal® showed higher initial and lower release after approximately 5 days compared to calcium sulphate. No significant in vitro cytotoxic differences were found between PerOssal® and nontoxic cell culture medium. Calcium sulphate showed cytotoxic effects in two out of four tests. PerOssal® exhibits excellent properties regarding resorption, biocompatibility, and antibiotic release.