Tissue engineered microsphere-based matrices for bone repair: design and evaluation

The need for synthetic alternatives to conventional bone grafts is due to t he limitations of current grafting materials. Our approach has been to desi gn polymer-based graft substitutes using microsphere technology. The gel mi crosphere matrix and the sintered microsphere matrix were designed using th e random packing of poly(lactide-co-glycolide) microspheres to create a thr ee-dimensional porous structure, The evaluation of these methods dealt with analysis of effects of matrix co mposition and processing. Matrices were evaluated structurally by scanning electron microscopy and porosimetry, and biomechanically by compression tes ting. The evaluation revealed the high modulus Of the gel microsphere matri x and the versatility of the sintered microsphere matrix. The gel microsphe re matrix incorporated hydroxyapatite particles and had a Young's modulus o f 1651 MPa, but structural analysis through SEM revealed a pore system less optimal for bone in-growth. The sintered microsphere matrices were fabrica ted without hydroxyapatite particles by thermally fusing polymeric microsph eres into a three-dimensional array, possessing interconnectivity and a mod ulus range of 241 (+/- 82) 349 (+/- 89) MPa. The sintered microsphere matri x demonstrated a connected pore system and mechanical properties in the mid -range of cancellous bone. Porosimetry data indicated that matrix pore diam eter varied directly with microsphere diameter, while pore volume was indep endent of microsphere diameter in the range of diameters examined. The micr osphere-based matrices show promise as polymeric substitutes for bone repai r. (C) 2001 Elsevier Science Ltd. All rights reserved.