Hierarchical Self-Assembly of Microgel-Modified Biomaterials Surfaces
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Hierarchical Self-Assembly of Microgel-Modified Biomaterials Surfaces Yong Wu, Jing Liang, Qichen Wang, and Matthew Libera Department of Chemical Engineering and Materials Science Stevens Institute of Technology, Hoboken, NJ, 07030 ABSTRACT Microgels are hydrogel particles with micron and sub-micron diameters. They have been developed, studied, and exploited for a broad range of applications because of their unique combination of size, soft mechanical properties, and controllable network properties. We have been using microgels to modulate the properties of surfaces to differentially control their interactions with tissue cells and bacteria. The long-term goal is to create biomaterials that promote healing while simultaneously inhibiting infection. Because poly(ethylene glycol) [PEG] is used in a number of FDA-approved products and has well-known antifouling properties, we work primarily with PEG-based microgels. We render these anionic either by copolymerization with monomeric acids or by blending with polyacids. Both methods produce pH-dependent negative charge. Surfaces, both planar 2-D surfaces as well as topographically complex 3-D surfaces, can be modified using a hierarchy of non-line-of-sight electrostatic deposition processes that create biomaterials surfaces whose cell adhesiveness is modulated by a submonolayer of microgels. Average inter-microgel spacings of 1-2 microns exploit natural differences between staphylococcal bacteria and tissue cells, which open the opportunity to differentially control surface interactions with them based on length-scale effects. After deposition, the microgels can be loaded with a variety of small-molecule, cationic antimicrobials. The details of loading depend on the relative sizes of the antimicrobials and the microgel network structure as well as on the amount and spatial distribution of electrostatic charge within both the microgel and on the antimicrobial. The exposed surface between microgels can be further modified by the adsorption of adhesion-promoting proteins such as fibronectin via electrostatic interaction. This approach combines a rich interplay of microgel structure and chemistry as a key component in a simple and translatable approach to modulate the surface properties of next-generation biomaterials. INTRODUCTION Biomaterials-associated infection occurs when bacteria colonize the surface of a tissuecontacting biomedical implant and subsequently infect the surrounding tissue. Such an implant must typically be removed and replaced with significant impact on both the patient and the health-care system. Many strategies are thus being explored to inhibit bacterial colonization of synthetic surfaces. Among them is the creation of antifouling coatings that resist bacterial adhesion [1-10]. In particular, hydrogels and gel-like surfaces have been and continue to be widely studied for use in biomaterials applications because of their ability to control surface interactions with various types of cells. Among materials used for antifouling applications is poly(ethylen
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