Bioactive coatings for direct skeletal attachment applications for lower limb prostheses

To tackle the current drawbacks with metallic implants used in direct skeletal attachment, novel bioactive glasses are considered as implant coatings in order to reduce bacterial infections and promote bone cell growth. Silica-based and borate-based glasses, with increasing amounts of titanium dioxide at the expense of either silica (for the silica-based glasses) or borate (for the borate-based glasses), respectively, were synthesized and characterized to determine the parameters that define a glass capable of inhibiting bacterial growth, stimulating cell proliferation and offering mechanical stability when enameled into a surgical alloy. The effect of substituting the glass backbone with titanium dioxide, in both glass series, is also investigated with respect to its effect on both biocompatibility and mechanical properties of the resultant glass/implant constructs. Borate-based glasses exhibited greater processing windows compared to the silica-based glasses, making them more desirable for coating applications. They also exhibited superior performance in terms of their in vitro bioactivity and biocompatibility, over their silica-based counterparts, due to their higher solubility and greater ability to inhibit S. epidermidis and E. coli bacteria. Specifically, glass BRT0 (control borate-based glass, with no titanium incorporated) exhibited an inhibition zone against S. epidermidis of 17.5 mm and a mass loss of 40% after 30 days, with BRT3 (borate-based glass, with 15 mol% titanium incorporated) exhibiting an inhibition zone against S. epidermidis of 7.6 mm and a mass loss of 34% after 30 days. Furthermore, borate-based glasses with greater titanium dioxide contents exhibited superior mechanical properties (e.g. bulk hardness, and critical strain energy release rates), which could be attributed to their more closely matched coefficients of thermal expansion with the titanium alloy substrate, Ti6Al4V, to which they were adhered. The critical strain energy release rates in mode I for the silica-based coating/substrate system ranged from 6.2 J/m2 (for SRT0, control silica-based glass with no titanium) to 12.08 J/m2 (for SRT3), whereas for the borate-based systems they ranged from 10.86 J/m2 (for BRT0) to 18.5 J/m2 (for BRT3), with the increase for the borate-based glasses being attributed to the presence of compressive residual stresses in the coating after application.

Bioactive coatings for direct skeletal attachment applications for lower limb prostheses

To tackle the current drawbacks with metallic implants used in direct skeletal attachment, novel bioactive glasses are considered as implant coatings in order to reduce bacterial infections and promote bone cell growth. Silica-based and borate-based glasses, with increasing amounts of titanium dioxide at the expense of either silica (for the silica-based glasses) or borate (for the borate-based glasses), respectively, were synthesized and characterized to determine the parameters that define a glass capable of inhibiting bacterial growth, stimulating cell proliferation and offering mechanical stability when enameled into a surgical alloy. The effect of substituting the glass backbone with titanium dioxide, in both glass series, is also investigated with respect to its effect on both biocompatibility and mechanical properties of the resultant glass/implant constructs. Borate-based glasses exhibited greater processing windows compared to the silica-based glasses, making them more desirable for coating applications. They also exhibited superior performance in terms of their in vitro bioactivity and biocompatibility, over their silica-based counterparts, due to their higher solubility and greater ability to inhibit S. epidermidis and E. coli bacteria. Specifically, glass BRT0 (control borate-based glass, with no titanium incorporated) exhibited an inhibition zone against S. epidermidis of 17.5 mm and a mass loss of 40% after 30 days, with BRT3 (borate-based glass, with 15 mol% titanium incorporated) exhibiting an inhibition zone against S. epidermidis of 7.6 mm and a mass loss of 34% after 30 days. Furthermore, borate-based glasses with greater titanium dioxide contents exhibited superior mechanical properties (e.g. bulk hardness, and critical strain energy release rates), which could be attributed to their more closely matched coefficients of thermal expansion with the titanium alloy substrate, Ti6Al4V, to which they were adhered. The critical strain energy release rates in mode I for the silica-based coating/substrate system ranged from 6.2 J/m2 (for SRT0, control silica-based glass with no titanium) to 12.08 J/m2 (for SRT3), whereas for the borate-based systems they ranged from 10.86 J/m2 (for BRT0) to 18.5 J/m2 (for BRT3), with the increase for the borate-based glasses being attributed to the presence of compressive residual stresses in the coating after application.

Effects of Crimped Fiber Paths on Mixed Mode Delamination Behaviors in Woven Fabric Composites

This research investigated the fracture toughness and crack propagation behaviors of woven fabric reinforced polymer (WFRP) composite laminates subjected to single and mixed mode loadings using numerical models. The objectives were to characterize the fracture behaviors and toughness properties at the fiber/matrix interfaces and to identify mechanisms that can be exploited for increasing delamination resistance. The mode-I and mode-II strain energy release rates GI and GII, the effective critical strain energy release rate, Gc_eff, (also known as the mixed mode fracture toughness) and crack growth stabilities were determined as functions of crimped fiber paths using meso-scale, 2D multi-continuum finite element models. Three variations of a plain-woven fabric architecture were considered; each having different crimped fiber paths. The presence of mixed-mode strain energy release rates at the meso-scale due to the curvilinear fiber paths was shown to influence the interlaminar fracture toughness and was explored for pure single-mode and mixed-mode global loadings. It was concluded that woven fabric composites provided a Fracture Toughness Conversion Mechanism (FTCM) and their toughness properties were dependent upon and varied with positon along the crimped fiber paths. The FTCM was identified as an advanced tailoring mechanism that can be further utilized to improve toughness and damage tolerance thresholds especially when the mode-II fracture toughness GIIc is greater than the mode-I fracture toughness GIc.

Delamination Resistance Of Laminate Made With VBO MTM46/HTS Prepreg

A laminate made with the Vacuum Bag Only (VBO) prepregs can be cured out of autoclave. Because of low curing pressure such a process can result in deterioration of laminate mechanical properties. They can be significantly lower than those displayed by the autoclave cured ones. The resistance against delamination can be among the most affected. Since this property is a week point of all the laminates it was of particular interest. Delamination resistance of unidirectional laminate made from VBO MTM46/HTS(12K) prepreg was in the scope of the presented research and the critical values of the Strain Energy Release Rates and the Paris-type equations corresponding to Mode I, Mode II and Mixed-Mode I/II static and cyclic loadings, respectively, were determined.