Antifouling Photograftable Zwitterionic Coatings on PDMS Substrates.

The foreign body response (FBR) to implantable materials can negatively impact performance of medical devices such as the cochlear implant. Engineering surfaces that resist the FBR could lead to enhanced functionality including potentially improving outcomes for cochlear implant recipients through reduction in fibrosis. In this work, we coat poly(dimethylsiloxane) (PDMS) surfaces with two zwitterionic polymers, poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA), using a simultaneous photografting/photo-cross-linking process to produce a robust grafted zwitterionic hydrogel. reduce nonspecific protein adsorption, the first step of the FBR. The coating process uses benzophenone, a photografting agent and type II photoinitiator, to covalently link the cross-linked zwitterionic thin film to the PDMS surface. As the concentration of benzophenone on the surface increases, the adhesive strength of the zwitterionic thin films to PDMS surfaces increases as determined by shear adhesion. Additionally, with increased concentration of the adsorbed benzophenone, failure of the system changes from adhesive delamination to cohesive failure within the hydrogel, demonstrating that durable adhesive bonds are formed from the photografting process. Interestingly, antifouling properties of the zwitterionic polymers are preserved with significantly lower levels of nonspecific protein adsorption on zwitterion hydrogel-coated samples compared to uncoated controls. Fibroblast adhesion is also dramatically reduced on coated substrates. These results show that cross-linked pSBMA and pCBMA hydrogels can be readily photografted to PDMS substrates and show promise in potentially changing the fibrotic response to implanted biomaterials.

Tuning Surface and Topographical Features to Investigate Competitive Guidance of Spiral Ganglion Neurons.

Cochlear Implants (CIs) suffer from limited tonal resolution due, in large part, to spatial separation between stimulating electrode arrays and primary neural receptors. In this work, a combination of physical and chemical micropatterns, formed on acrylate polymers, are used to direct the growth of primary spiral ganglion neurons (SGNs), the inner ear neurons. Utilizing the inherent temporal and spatial control of photopolymerization, physical microgrooves are fabricated using a photomask in a single step process. Biochemical patterns are generated by adsorbing laminin, a cell adhesion protein, to acrylate polymer surfaces followed by irradiation through a photomask with UV light to deactivate protein in exposed areas and generate parallel biochemical patterns. Laminin deactivation was shown increase as a function of UV light exposure while remaining adsorbed to the polymer surface. SGN neurites show alignment to both biochemical and physical patterns when evaluated individually. Competing biochemical and physical patterns were also examined. The relative guiding strength of physical cues was varied by independently changing both the amplitude and the band spacing of the microgrooves, with higher amplitudes and shorter band spacing providing cues that more effective guide neurite growth. SGN neurites aligned to laminin patterns with lower physical pattern amplitude and thus weaker physical cues. Alignment of SGNs shifted toward the physical pattern with higher amplitude and lower periodicity patterns which represent stronger cues. These results demonstrate the ability of photopolymerized microfeatures to modulate alignment of inner ear neurites even in the presence of conflicting physical and biochemical cues laying the groundwork for next generation cochlear implants and neural prosthetic devices.

Photopolymerizable Zwitterionic Polymer Patterns Control Cell Adhesion and Guide Neural Growth.

Developing materials that reduce or eliminate fibrosis encapsulation of neural prosthetic implants could significantly enhance implant fidelity by improving the tissue/electrode array interface. Here, we report on the photografting and patterning of two zwitterionic materials, sulfobetaine methacrylate (SBMA) and carboxybetaine methacrylate (CBMA), for controlling the adhesion and directionality of cells relevant to neural prosthetics. CBMA and SBMA polymers were photopolymerized and grafted on glass surfaces then characterized by X-ray photoelectron spectroscopy, water contact angle, and protein adsorption. Micropatterned surfaces were fabricated with alternating zwitterionic and uncoated bands. Fibroblasts, cells prevalent in fibrotic tissue, almost exclusively migrate and grow on uncoated bands with little to no cells present on zwitterionic bands, especially for CBMA-coated surfaces. Astrocytes and Schwann cells showed similarly low levels of cell adhesion and morphology changes when cultured on zwitterionic surfaces. Additionally, Schwann cells and inner ear spiral ganglion neuron neurites aligned well to zwitterionic patterns.