Modeling of polymer / ceramic composites via molecular dynamics simulations

Abstract

Polymer-calcium phosphate (CaP) composites arise as alternatives to biological bone substitutes and are widely used as biomaterials. Among various CaP ceramics, hydroxyapatite (HAp), β-tricalcium phosphate (β-TCP) and their mixtures known as biphasic calcium phosphates (BCP) are the most important bioceramics due to their superior features as bioactivity, biocompatibility, and stability in physiological environ ment. In the current thesis, polymer-CaP ceramics, including HAp, β-TCP, and BCP, are comparatively studied via MD simulations. In the first part, binding mechanism of (poly)lactic acid (PLA)-HAp and (poly)ethylene (PE)-HAp systems is examined using MD simulations with different number of monomers (10 ≤ N ≤ 400) on HAp surfaces at two different thicknesses. HAp models with thicker bulk region consistently yielded positive global binding energy values. Change in binding energy and the occupied area by polymer (occA) show exponential recovery relationships as a function of N. Binding energy values in PLA-HAp systems converge to higher values compared to PE-HAp complexes while occA values stabilize at lower values in PLA-HAp complexes. Bulk re gion of HAp is found to be a major constituent of the total binding energy, followed by polymer-surface interactions for both systems. Concentration profiles revealed that O= units are mainly responsible for the PLA-HAp interaction, intensifying until N ≈ 200, in agreement with surface-polymer interaction and Ca-O coordination number profiles. In PE-HAp systems, interface concentration constantly increases with respect to N, parallel to surface-polymer interaction profiles. In the second part of the thesis, interac tion of PLA with biphasic calcium phosphate and its building blocks, HAp and β-TCP is studied in an introductory manner. The initial results are promising, yielding bind ing energy ranked as β-TCP>BCP>HAp, complemented by concentration profiles, in which O= units are again found to be responsible for the interfacial adhesion.