BMEE04.1: Biomaterials - Polymer/Organic Coatings - no. BMEE04.1

Abstract

Many biomaterials currently in clinical use were originally developed for engineering applications and surface modification is thus needed for their biomedical applications. The biomaterials specifically designed and developed for certain medical application(s) may require another set of surface characteristics that are suitable for the material to be used in another clinical environment; or surface modification is required for enhancing the clinical performance of the biomaterial in its targeted application(s). What our body 'sees' and deals with when an implant is placed in our body is the surface of the implant. Therefore, surface properties of materials or biomaterials are of paramount importance, which can determine the success or failure of a material for its intended biomedical applications. Different types of biomaterials – metals, polymers, ceramics and composites – are now used in various biomedical applications. As these substrates are drastically different from each other, different coatings and surface modification techniques are used for implantable metals, biopolymers, bioceramics and iomedical composites (porous composite scaffolds in particular in recent years). And coatings themselves can be polymeric, metallic, ceramic or even composite in nature. Polymer coatings are very attractive for the surface modification of biomaterials because they provide great versatility in chemical groups on the surface for controlling the cell-biomaterial interactions. They are relatively easy to form/produce, using simple techniques such as dip-coating or solvent casting. Coatings can also be made via chemical grafting of molecules onto the biomaterial surface. Techniques/structures such as self-assembled monolayers (SAMs) and layer-by-layer (LBL) assembly are extensively investigated in the biomedical field due to their distinctive advantages. For example, PEGylated SAMs are formed for controlling the surface interaction of biomaterials with proteins, and drugs are incorporated in LBL-formed polymer coatings for their controlled release in vivo. In the area of metal implants, NiTi shape memory alloys (SMAs) becomes a focus of research because they possess unique properties of shape memory and superelasticity. However, metals are bioinert and NiTi SMAs cause concerns over their long-term biocompatibility due to toxic ion release. Investigations have been performed to use the plasma immersion ion implantation and deposition technique to modify the NiTi SMA surface, yielding encouraging mechanical and biological results. For tissue regeneration, tissue engineering scaffolds play a crucial role but scaffold alone is not sufficient for regenerating functional body tissues. Growth factors are needed for prompting specific cell behaviors and functions. Additive manufacturing technologies such as selective laser sintering (SLS) may not be able to produce growth factor-incorporated scaffolds directly, but SLS-formed polymer scaffolds can be surface modified for incorporating growth factors for their controlled release later. One example is SLS-formed PHBV scaffolds with the surface modification of heparin onto which rhBMP-2 is incorporated. These advanced scaffolds have exhibited enhanced ability for bone tissue regeneration in vivo. This lecture will (1) briefly review clinical requirements (mainly surface requirements) for biomedical materials, (2) give an overview of coatings and surface modification techniques for different types of substrates, and (3) present and discuss the performance of some surface-modified biomaterials and indicate future trends.