Abstract:The objective of this study was to characterize strength (IFSS) of C/PLLA and CaP/PLLA microcomposites and evaluate the performance of various fiber-matrix comwas 33.9 and 12.6 MPa, respectively. Upon in vitro hydrolysis, posite systems by studying the mechanical, thermal, and C/PLLA retained 49% of IFSS after 15 days and CaP/PLLA physical properties of the fiber and matrix components, and retained 46% of IFSS after 6 h. Using a fiber fragmentation by studying the fiber-matrix interface adhesion strength usmethod, the initial IFSS of C/PLLA, CaP/PLLA, and chitin/ ing both microbond and fragmentation methods. The com-PLLA was 22.2, 15.6, and 28.3 MPa, respectively. The perforposites studied were poly(L-lactic acid) (PLLA) matrix reinmance of carbon fibers and C/PLLA composites was superior forced with continuous fibers of either nonabsorbable AS4to the other fibers and fiber/PLLA systems, but the carbon carbon (C), absorbable calcium phosphate (CaP), poly(glyfiber was nonabsorbable. CaP had the most suitable modulus colic acid) (PGA), or chitin. Carbon and CaP single fibers of the absorbable fibers for fixing cortical bone fractures, had high Young's moduli and failed in a brittle manner. PGA but its rapid deterioration of mechanical properties and and chitin single fibers had relatively lower Young's moduli loss of IFSS limits its use. PGA and chitin fibers had suitable and relatively higher ductility. Upon in vitro hydrolysis, CaP mechanical properties and their retention for fixing canfibers retained 17% of their tensile strength and 39% of their cellous bone fractures, but likely had insufficient stiffness Young's modulus after 12 h, PGA fibers retained 10% of their for applications such as bone plates for fixing cortical bone tensile strength and 52% of their Young's modulus after 16 fractures. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, days, and chitin fibers retained 87% of their tensile strength 36, [469][470][471][472][473][474][475][476][477] 1997. and 130% of their Young's modulus after 25 days. PLLA films had much lower strength and Young's moduli, but much higher ductility relative to the single fibers. Using the

In this study, a new visual characterization method was developed using laser scanning confocal microscopy (LSCM) to study morphologic properties, particularly at the fiber-matrix interface, by optical sectioning of bioabsorbable single-fiber composites. The interface gap width (IGW) between the fiber and matrix, and the changes in IGW after in vitro hydrolysis, named the gap rate (R g ), were measured from images obtained using the LSCM. Higher values for IGW and R g showed faster degradation of the fiber-matrix interface. These parameters were used to investigate the effects of strain, wicking, different reinforcing fibers, and ␥-irradiation on the fiber-matrix interface morphology. The component materials used were nonbioabsorbable AS4 carbon (C) fibers, bioabsorbable calcium phosphate (CaP), poly(glycolic acid) (PGA), and chitin fibers, and bioabsorbable poly(L-lactic acid) (PLLA) matrix. The application of strain on CaP/PLLA composites increased the IGW up to about 15%, after which there was no change up to 25%. The R g for CaP/PLLA composites with the fiber ends exposed in vitro (permitting wicking) was greater than for CaP/PLLA with the fiber ends embedded completely within the matrix (preventing wicking). Open-end C/PLLA composites had the slowest rate of interface degradation in vitro, followed by chitin/PLLA, PGA/PLLA, and CaP/PLLA. The exposure of closed-end CaP/PLLA composites to 4 Mrad of ␥-irradiation, in air at room temperature or in vacuum at 77K, accelerated the rate of interface degradation in vitro. In conclusion, an effective new visual characterization method was developed using LSCM, and it was used to show that (a) moderate strain could accelerate the degradation of the interface, (b) fiber-matrix interface wicking could accelerate the rate of degradation of the interface, (c) the rate of interface degradation depends on the type of fiber used, and (d) ␥-irradiation could accelerate the rate of interface degradation. Furthermore, the results of LSCM analysis of different reinforcing fibers with a PLLA matrix agree with measurements of interfacial shear strength (IFSS) and single-fiber tensile strength reported in Part I of this study.