NOVEL AMINO ACID MODIFIED NANOCLAYS IN TISSUE ENGINEERING SCAFFLDS FOR IMPROVED MECHANICAL RESPONSES

摘要

Design of scaffolds with optimal bioactivity, biocompatibility, biodegradability, porosity, and mechanical response are the important issues in tissue engineering. Human cells respond to surface chemistry and mechanics of the synthetic materials they grow on (scaffolds). In addition mechanics of cells is indicative of their growth, proliferation and adhesion on scaffolds. Earlier, in our prior work on polymer clay nanocomposites (PCNs), we have developed a unified theory on the mechanisms of mechanical property enhancement in these composites with addition of nanoscale clay particulates. This theory is based on an 'altered phase model' which is developed through extensive experimental and multiscale modeling (molecular dynamics to 3D finite element modeling) efforts. Here, we incorporate the results of the theory into design of new nanoclay based biopolymer hydroxyapatite nanocomposites for bone tissue engineering applications. Montmorillonite (MMT) clay was modified using unnatural amino acids as potentially new biocompatible modifiers. The specific choice of amino acids is based on both the antibacterial activity reported in literature and also our previous studies on role of chain length, functional groups etc of modifiers in influencing mechanical behavior in PCNs. Biocompatibility studies using cell culture experiments as well as mechanical behavior is evaluated for the biomedical PCNs. Also evaluated are the changes to molecular structure through FTIR spectroscopy. The increase in dooi spacing of modified clay compared to pure clay obtained from XRD experiments confirms successful intercalation of modifier. From cell culture experiments, osteoblast cells were found to grow and proliferate over the substrates. Here, we describe the use of novel modeling (through steered molecular dynamics) and experimental techniques (nanomechanical) to evaluate the role of engineered interfaces on mechanical response in the nanocomposite systems. Nodule formation indicative of osteogenic behavior, with hierarchical structure, mechanics and chemistry mimicking bone is presented. Overall, in this work, we demonstrate the use of evaluating nanoscale mechanics in nanocomposites for design of biomaterials for bone tissue engineering. In addition results of mechanical behavior of cell-scaffold structures as cells grow, proliferate and differentiate as scaffolds degrade is presented over the time scale of degradation of scaffold.