Modeling of polymer/ceramic composites via molecular dynamics simulations

Polymer-calcium phosphate (CaP) ceramics arise as alternatives to biological bone substitutes and metal implants, and are widely used as biomaterials. Among various CaP ceramics, hydroxyapatite (HAp), β-tricalcium phosphate (β-TCP) and their mixtures known as biphasic tricalcium phosphate (BCP) are the most important bioceramics due to their superior features such as bioactivity, biocompatibility, and good stability in physiological environment. In the current thesis, polymer-calcium phosphate 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 region 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 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, interaction 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 binding 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.