Biofunctionalization

Much effort is invested in the novel design and synthesis of biomaterials for the fabrication of biomedical applications as implants or nanoparticles with appropriate functionality, mechanical properties and durability. Depending on the application, requirements might differ considerably, ranging from high mechanical stress resistance to high transparency. These functions are generally governed by the bulk composition of the biomaterial. The biological response is in contrast largely controlled by the surface chemistry and structure. The rationale for surface modification of polymers is therefore straightforward: retaining the key physical properties of a biomaterial while modifying only the outermost surface to influence the biointeraction. Commonly observed interactions of any material with a biological system or system containing biomolecules cover adsorption or adhesion processes of proteins and bacteria or platelets as well as phagocytosis and fibrous encapsulation. Effective surface modification of biomaterials should mediate these interactions, for example, with the purpose of improved tissue-interface related-biocompatibility, that is especially important for modern implant design, which aim to improve implant integration while avoiding chronic inflammation and foreign body reactions, and thus loss of the intended implant function. Within the current issue, Hartmann and Krastev [1] outline specific strategies using polyelectrolyte multilayers to modulate these interactions between biomaterial surfaces and biological systems. Biofunctionalization is one particular form of surface modification involving the immobilization of biomolecules as proteins, peptides and polysaccharides or bioactive drugs with the same purpose. Various immobilization methods are available while the chosen strategy/design significantly defines the biological activity of the functionalized biomaterial. In this context, Spatz et al. [2] discuss the impact of spacer integration between biomaterial surface and the integrin-recognition motif cyclic RGD on the formation of integrin-based cellular adhesion. Furthermore, the immobilization strategy defines the short-term or long-term localization of the biomolecule on the biomaterials surface, which is explored using the example of the immobilization of the potent angiogenic vascular endothelial growth factor (VEGF) in order to improve the hemocompatibility and endothelialization of biodegradable polymer surfaces [3]. One more important field is the biofunctionalization of nanostructured materials and nanoparticles with possible biomedical application for imaging and quantifying of target molecules such as proteins in assays, cells and tissues. In this context, Walter et al. [4] give general insights into the principles and factors controlling the binding affinity of aptamers, as promising alternative binders that can substitute antibodies in various applications immobilized to nanostructured materials. The short review by Salehi [5] additionally summarizes current designs of different biofunctionalized nanoparticles as surface-enhanced Raman scattering substrates and highlights the improvement of particularly simple and gentle conjugation methods. One recently evolving field for surface functionalization can be found in dentistry. One focus in particular is the enhancement of the bioactivity of polyetheretherketone (PEEK) that presents a promising polymeric alternative to metal implant components. A review of PEEK modification reactions are collocated with general information on polymer-based drug delivery systems as well as the biofunctionalization of polymers and with a discussion of their applicability for PEEK in the article by Harting et al. [6]. Freifrau von Maltzahn et al. [7] in contrast highlights the evaluation of the antibacterial effect of a drug releasing poly(3-hydroxybutyrate) [P(3HB)] implant coating in comparison to pure titanium on Aggregatibacter actinomycetemcomitans as a model periodontopathogen to prevent biofilm formation on dental implant surfaces. A further modification possibility is the alteration of surface roughness of dental implant surfaces. Grohmann et al. [8] report results on in vitro and in vivo experiments of rough yttria-stabilized tetragonal zirconia polycrystal materials revealing a cytocompatibility and a bone-implant contact that is very comparable to titanium as a reference material. The editors are aware that this issue can only highlight some of the multiple aspects in biofunctionalization. We hope that our selection of the articles included will stimulate your work towards innovative applications and you will enjoy this issue!