Biomedical device-related infection is a significant clinical problem caused by bacterial adhesion, followed by the formation of 3-dimensional matrices of bacterial cells and extracellular polymers, known as biofilms, on device surfaces, leading to potential sepsis or thrombosis, and potentially failure of the device or death of the patient. The current method to prevent these infections is to treat patients with high antibiotic concentrations, which can lead to antibiotic resistant strains and toxic effects. Therefore, using non-antibiotic anti-biofilm agents would be a preferable alternative. The goal of this project was to develop a new non-antibiotic based biomaterials design, where the biomaterial not only promotes healing by reducing inflammation, but also prevents biofilm formation by inhibiting bacterial colonization. A polyether-urethane PEU (Biospan®) matrix, a common blood contacting material used in many medical implants, was used here as the base polymer. PEU was modified to provide the sustained, controlled release of an anti-biofilm agent, specifically salicylic acid that has been shown to block biofilm formation without a bacterial cell toxic effect. Drug-loaded PEU materials were developed to control salicylic acid release rates as a function of the amount of pore-former agent (poly-ethylene glycol, PEG) and anti-biofilm drug loaded. Pore-former agents serve to form pores within the base polymer upon hydration, thus allowing the release of the therapeutic drugs. To measure the release rates of anti-biofilm therapy, the absorbance of the therapy released was measured periodically over two days. An optimum formulation consisting of Biospan®, PEG, and salicylic acid offered the longest effective period of sustained release as compared to control. The efficacy of the modified PEU polymers against Pseudomonas aeruginosa colonization was examined by direct counting of any adherent bacterial cells.

Hypospadias is a birth defect affecting 0.7% of male newborns in which the opening if the male urethra is in the anatomically incorrect position. Current reconstructive techniques result in worldwide complication rates reported to be as high as 50%. Problems with the implanted tissue used to reconstruct the opening have been attributed to these complications, and urologists agree that there is much room for improvement when it comes to hypospadias repair. We hypothesized that properly differentiated epithelial tissue can be reconstituted onto collagen-coated tubular scaffolds by the in vitro propagation of human epithelial cells derived from the biopsy of a male hypospadias patient. This autologous tissue would lower the rejection risk associated with the insertion of foreign tissue to the urethra and offer a greater chance that the implanted tissue integrates with the unaffected urethra. Rabbit urethras, which were identified as anatomically similar to human urethras, were chosen as models. A biodegradable poly-96L/4D-lactide (P-(96L/4D)-LA) copolymer fabricated into a tubular scaffold proved mechanically suitable for urethral reconstruction. We determined ideal conditions for lyophilizing, cross-linking, and sterilizing the collagen coating the scaffold, and designed a novel bioreactor to facilitate seeding urethral epithelial cells onto the coated scaffold. Toxicity testing of silicone glue used to build the bioreactor demonstrated that the glue would not kill urethral epithelial cells. At this time, we are conducting proof-of-principle experiments to determine the efficacy of our hypothesis. We have shown that epithelial cells adhere to the luminal side of our collagen-coated scaffolds, and we are currently identifying conditions that encourage optimal tissue growth.

Polymeric biomaterials used in clinical devices and implants that come in contact with blood typically have poor blood compatibility. Blood clots can form on the surfaces of these devices and break off, travel through the circulatory system, and can cause strokes and heart attacks. The adhesion, activation, and aggregation of blood platelets binding to proteins adsorbed on the biomaterials is the primary cause of these blood clots. Platelet adhesion is caused by prior adsorption of fibrinogen from blood plasma to the biomaterial surface. The aim of this project is the design and testing of a low-cost coating protocol that reduces fibrinogen binding and consequent platelet adhesion and thromboembolization. The polymer coatings are polyurethanes, which are known for their excellent physical properties compared to other polymeric biomaterials. Coating with this polymer was applied onto polyethylene sheets and tubing. A protocol was developed involving chromic acid etching of the polyethylene surface to increase wettability, followed by coating with polyurethane dissolved in a solvent. Requirements of the coating protocol are that they exhibit stability, uniformity, and complete coverage. Electron Spectroscopy for Chemical Analysis (ESCA) and dye staining methods were used for characterizing the coatings. Fibrinogen adsorption measured using iodine-125 radiolabeled fibrinogen is being used to assess the resistance of the coatings to fibrinogen adsorption. Finally, an alternative coating protocol involving coating of polyurethane tubes with our polyurethanes that resist fibrinogen adsorption is being evaluated as this approach is even more efficient as it does not require the hazardous chromate etching step.

Using biocombinatorial mutagenesis, we identify peptides with short amino acid sequences to solids of nanotechnology and medical interest. Through bioinformatics design and genetic tailoring, we enhance binding and assembly of these peptides as fundamental building blocks in synthesizing, assembling and forming nanostructured practical systems and devices. In this work, we specifically concentrate on a new gold binding peptide, AuBP1 (12 AAs) and study its binding affinity and material selectivity in tandem and linker-repeat forms to enhance its heterofunctionality. In particular, we use various linkers, such as PPP and GGG, to provide rigidity or flexibity, respectively to affect binding characteristics as well as self assembly behavior of these peptides. Both SPR (surface plasmon resonance spectroscopy) as well as AFM (atomic force microscopy) techniques are used to interrogate quantitatively molecular affinities at atomic and molecular scales of resolution. These peptides alone, conjugated to other GEPIs, or functional proteins are used as linkers for practical implementations such as in multiplexed nanoparticles, targeted immobilization of biomolecules, and biofunctionalization of surfaces for nanosensors, implant materials and nanodevices.