title: Nanoindentation analysis of αtricalcium phosphate-poly(lactide-co-glycolide) nanocomposite degradation.
abstract: The internal mechanical property characteristics as functions of position and degradation time of PLGA(50:50)-αTCP nanocomposites of varying ceramic-polymer ratios degraded in an aqueous medium have been assessed using depth-sensing nanoindentation. The addition of nanoparticulate αTCP increases the elastic modulus of undegraded specimens from 3.72 ± 0.12 GPa for pure PLGA(50:50) samples to 7.23 ± 0.16 GPa recorded for undegraded 40 wt.% TCP nanocomposites. Additionally αTCP incorporation decreases the viscoelastic loss tangent from 0.189 ± 0.040 measured for pure undegraded PLGA(50:50) to an average of 0.091 ± 0.006 for undegraded ceramic-polymer composites. No variation in viscosity for the composites with ceramic loading was evidenced. The stiffening effect of αTCP addition closely conforms to the lower Hashin-Shtrikman bounds demonstrating that an evenly dispersed nano-filler is the least amenable ceramic configuration to enhance the mechanical properties of PLGA-αTCP nanocomposites. The mechanical property evolution for all composite types in an aqueous degradation medium is dominated by material hydration which effects reduced material stiffness and increased specimen viscosity generating a core-periphery mechanical property distribution in terms of elastic modulus and viscoelastic phase angle. The mechanical property core-periphery structure correlates strongly with the core-periphery density structure characterized using X-ray microtomography. Hydrated regions exhibit significant reductions in elastic modulus and viscosity increases which are typical of elastomers.
authors: Cambridge Centre for Medical Materials, Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK. Electronic address: cebaz577@gmail.com.
authors: C E
authors: CE
authors: Barrett
authors: Cambridge Centre for Medical Materials, Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK.
authors: R E
authors: RE
authors: Cameron
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry*; D055119:Elastic Modulus; D019344:Lactic Acid / Q000737:chemistry*; D053761:Nanocomposites / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D014783:Viscosity
chemical_list: D002130:Calcium Phosphates; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; C018392:tricalcium phosphate
keywords: Calcium phosphate; Mechanical properties; Nanocomposite; Nanoindentation; Poly(lactic-co-glycolic) acid