Biomaterials are materials that are used in contact with biological systems. Biocompatibility and applicability of surface modification with current uses of metallic, polymeric and ceramic biomaterials allow alteration of properties to enhance performance in a biological environment while retaining bulk properties of the desired device.
Surface modification involves the fundamentals of physicochemical interactions between the biomaterial and the physiological environment at the molecular, cellular and tissue levels (reduce bacterial adhesion, promote cell adhesion). Currently, there are various methods of characterization and surface modification of biomaterials and useful applications of fundamental concepts in several biomedical solutions.
Function
The function of surface modification is to change the physical and chemical properties of surfaces to improve the functionality of the original material. Protein surface modification of various types biomaterials (ceramics, polymers, metals, composites) is performed to ultimately increase biocompatibility of the material and interact as a bioactive material for specific applications. In various biomedical applications of developing implantable medical devices (such as pacemakers and stents), surface properties/interactions of proteins with a specific material must be evaluated with regards to biocompatibility as it plays a major role in determining a biological response. For instance, surface hydrophobicity or hydrophilicity of a material can be altered. Engineering biocompatibility between the physiological environment and the surface material allows new medical products, materials and surgical procedures with additional biofunctionality.
Surface modification can be done through various methods, which can be classified through three main groups: physical (physical adsorption, Langmuir blodgett film), chemical (oxidation by strong acids, ozone treatment, chemisorption, and flame treatment) and radiation (glow discharge, corona discharge, photo activation (UV), laser, ion beam, plasma immersion ion implantation, electron beam lithography, and γ-irradiation).
Biocompatibility
In a biomedical perspective, biocompatibility is the ability of a material to perform with an appropriate host response in a specific application. It is described to be non-toxic, no induced adverse reactions such as chronic inflammatory response with unusual tissue formation, and designed to function properly for a reasonable lifetime. It is a requirement of biomaterials in which the surface modified material will cause no harm to the host, and the material itself will not harmed by the host. Although most synthetic biomaterials have the physical properties that meet or even exceed those of natural tissue, they often result in an unfavorable physiological reaction such as thrombosis formation, inflammation and infection.
Biointegration is the ultimate goal in for example orthopedic implants that bones establish a mechanically solid interface with complete fusion between the artificial implanted material and bone tissues under good biocompatibility conditions. Modifying the surface of a material can improve its biocompatibility, and can be done without changing its bulk properties. The properties of the uppermost molecular layers are critical in biomaterials since the surface layers are in physicochemical contact with the biological environment.
Furthermore, although some of the biomaterials have good biocompatibility, it may possess poor mechanical or physical properties such as wear resistance, anti-corrosion, or wettability or lubricity. In these cases, surface modification is utilized to deposit a layer of coating or mixing with substrate to form a composite layer.
Cell adhesion
As proteins are made up of different sequences of amino acids, proteins can have various functions as its structural shape driven by a number of molecular bonds can change. Amino acids exhibit different characteristics such as being polar, non-polar, positively or negatively charged which is determined by having different side chains. Thus, attachment of molecules with different protein for example, those containing Arginine-Glycine-Aspartate (RGD) sequences are expected to modify the surface of tissue scaffolds and result in improvement of cell adhesion when placed into its physiological environment. Additional modifications of the surface could be through attachment of functional groups of 2D or 3D patterns on the surface so that cell alignment is guided and new tissue formation is improved.