In vitro studies of degradation and bioactivity of aliphatic polyesther composites

IN VITRO STUDIES OF DEGRADATION AND BIOACTIVITY OF ALIPHATIC POLYESTER COMPOSITES by Georgia Chouzouri In spite of numerous publications on the potential use of combinations of aliphatic polyester composites containing bioactivity fillers for bone regeneration, little information exists on the combined in vitro mechanisms involving simultaneously diffusion for polymer degradation and bioactivity through nucleation and growth of apatite in simulated body fluid (BF) solution. The objective of this study is to contribute to the understanding of the fundamentals in designing nonporous, solid materials for bone regeneration, from experimental data along with their engineering interpretation. Bioactivity, in terms of apatite growth, was assessed through several experimental methods such as scanning electron microscopy (SEAM), energy dispersive X-ray analysis (EDX), X-ray-diffraction (CORD) and changes in ion concentration. In the case of the six neat fillers evaluated, the filler shape, form and chemical structure showed significant differences in bioactivity response. Bioglass and calcium silicate fillers showed faster nucleation and growth rates in the screening experiments. Aomposites at 30 % by weight filler were prepared by solution and/or melt mixing. Polycaprolactone (PAL) composites containing five different fillers were evaluated. Solution processed PCL/calcium silicate (AS) samples showed faster bioactivity, as determined by apatite growth, compared to melt mixed samples. The onset time for bioactivity was different for all PAIL composites. The limited bioactivity in the PAL composites over longer periods of time could be attributed to the PAL hydrophobicity leading to a slow polymer degradation rate, and also to the lack of BF replenishment. For both polylactic acid (PLA) composites containing AS and biomass significant growth was observed after one week and in the case of AS was still evident after four weeks immersion. However, at prolonged time periods no further bioactive was observed, although ion release results indicated a faster release rate that would eventually lead to a faster polymer degradation and possibly continuing bioactivity. The presence of silicate fillers enhanced the hydrolytic degradation rate of both PAIL and PLA as shown from kinetic data calculations based on molecular weight measurements. Unfilled PLAN samples showed significant embattlement after two weeks immersion, whereas for the AS filled system more significant changes could be observed in the compressive strength and modulus after the same time period. Experimental data were also fitted into an equation proposed to calculate erosion number; in the case of unfilled PLAN predictions were found to agree with literature results suggesting bulk erosion. By assuming impermeable, randomly dispersed mass flakes, water transport in a composite system, prior to significant polymer degradation could be modeled. However, modeling of transport in the case of the composite consisting of a degrading polymer and a reactive decaying filler was challenging, particularly in the case of directional bioactivity reinforcements, due to the occurrence of simultaneous time dependent diffusion phenomena that altered the integrity of the sample. IN VITRO STUDIES OF DEGRADATION AND BIOACTIVITY OF ALIPHATIC POLYESTER COMPOSITES by Georgia Chouzouri A Dissertation Submitted to the Faculty of New Jersey Institute of Technology In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemical Engineering Otto H. York Department of Chemical Engineering May 2007 Copyright © 2007 by Georgia Chouzouri ALL RIGHTS RESERVED APPROVAL PAGE IN VITRO STUDIES OF DEGRADATION AND BIOACTWITY OF ALIPHATIC POLYESTER COMPOSITES Georgia Chouzouri Dr. Marino Xanthos, Dissertation Advisor Date Professor, Otto H. York Department of Chemical Engineering, NJIT Dr. Treena Liviττgstοn Arinzeh, Committee Member Date Associate Professor, Biomedical Engineering, NJIT Dr. Michael Jaffe, • ' ittee Member Date Research Profess • , ' iomedical Engineering, NJIT Dr. ÍJaυrent Simon, Cómmittee Member l Date Assistant Professor, Otto H. York Department of Chemical Engineering, NJIT Dr. Jing Wu, Committee Member Date Assistant Professor, Otto H. York Department of Chemical Engineering, NJIT