Effects of particle size and porosity on in vivo remodeling of settable allograft bone/polymer composites

Abstract

Established clinical approaches to treat bone voids include the implantation of autograft or allograft bone, ceramics, and other bone void fillers (BVFs). Composites prepared from lysine-derived polyurethanes and allograft bone can be injected as a reactive liquid and set to yield BVFs with mechanical strength comparable to trabecular bone. In this study, we investigated the effects of porosity, allograft particle size, and matrix mineralization on remodeling of injectable and settable allograft/polymer composites in a rabbit femoral condyle plug defect model. Both low viscosity (LV) and high viscosity (HV) grafts incorporating small (<105 μm) particles only partially healed at 12 weeks, and the addition of 10% demineralized bone matrix did not enhance healing. In contrast, composite grafts with large (105 – 500 μm) allograft particles healed at 12 weeks post-implantation, as evidenced by radial μCT and histomorphometric analysis. This study highlights particle size and surface connectivity as influential parameters regulating the remodeling of composite bone scaffolds.

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“…The primary outcome was bone volume/total volume measured by lCT in the middle region of the defect. An a priori power analysis indicated that a sample size of four would detect a 7.5% difference in bone volume/total volume between groups assuming a mean and SD of 30% and 5%, respectively in the middle region of interest of the graft (2.5 mm from the center-line) [13,37]. This is with a power of 80% and an alpha level of 0.05 using a two-tailed t-test of two independent samples.…”

“…Osteoclast precursor cells were prepared from spleens of four adult C57 WT mice by the Ficoll (Lymphocyte Separation Medium; MP Biomedicals, Solon, OH, USA) gradient method [6] and plated separately at a density of 2. [13,14,37]. An advantage of low-viscosity grafts compared with calcium phosphate cements or allograft is its ability to support diffusion-controlled sustained release of biologics [20,41].…”

“…Lowviscosity components were gamma-irradiated (25-40 kGy) by Sterigenics International Inc (Westerville, OH, USA), mixed, and injected in the defects. Wounds were closed after cure (15 minutes after implantation) as described previously [14,37]. The primary outcome was bone volume/total volume measured by lCT in the middle region of the defect.…”

“…The three inner regions incorporated the composites, whereas the outer region included the host bone interface. Ossified tissue was segmented using a threshold of 340 mg hydroxyapatite per cm À3 to include new bone and ceramic as reported previously [13,37]. Bone volume fraction (bone volume/total volume), trabecular separation, trabecular number, and trabecular thickness were measured for each annular region and plotted versus the mean radial distance from the core of the defect (R m ) [13,37].…”

“…Ossified tissue was segmented using a threshold of 340 mg hydroxyapatite per cm À3 to include new bone and ceramic as reported previously [13,37]. Bone volume fraction (bone volume/total volume), trabecular separation, trabecular number, and trabecular thickness were measured for each annular region and plotted versus the mean radial distance from the core of the defect (R m ) [13,37]. These morphometric parameters were chosen to quantitatively assess the remodeling of trabecular bone architecture in three dimensions assuming a fixed-structure model [5].…”