We have employed baculovirus-mediated expression of the recombinant A. diadematus spider dragline silk fibroin rADF-4 to explore the role of the evolutionary conserved C-terminal domain in self-assembly of the protein into fiber. In this unique system, polymerization of monomers occurs in the cytoplasm of living cells, giving rise to superfibers, which resemble some properties of the native dragline fibers that are synthesized by the spider using mechanical spinning. While the C-terminal containing rADF-4 self-assembled to create intricate fibers in the host insect cells, a C-terminal deleted form of the protein (rADF-4-DeltaC) self-assembled to create aggregates, which preserved the chemical stability of dragline fibers, yet lacked their shape. Interestingly, ultrastructural analysis showed that the rADF-4-DeltaC monomers did form rudimentary nanofibers, but these were short and crude as compared to those of rADF-4, thus not supporting formation of the highly compact and oriented "superfiber" typical to the rADF-4 form. In addition, using thermal analysis, we show evidence that the rADF-4 fibers but not the rADF-4-DeltaC aggregates contain crystalline domains, further establishing the former as a veritable model of authentic dragline fibers. Thus, we conclude that the conserved C-terminal domain of dragline silk is important for the correct structure of the basic nanofibers, which assemble in an oriented fashion to form the final intricate natural-like dragline silk fiber.

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The objective of this study was to explore the use of reverse thermo-responsive (RTG) polymers for generating implants at their site of performance, following minimally invasive surgical procedures. Aiming at combining syringability and enhanced mechanical properties, a new family of injectable RTG-displaying polymers that exhibit improved mechanical properties was created, following two different strategies: (1) to synthesize high-molecular-weight polymers by covalenty joining poly(ethylene glycol) and poly(propylene glycol) chains using phosgene as the coupling molecule and (2) to cross-link poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblocks after end-capping them with triethoxysilane or methacrylate reactive groups. While the methacrylates cross-linked rapidly, the triethoxysilane groups enabled the system to cross-link gradually over time. The chain-extended PEO/PPO copolymers had molecular weights in the 39 000-54 000 interval and exhibited improved mechanical properties. Reverse thermo-responsive systems displaying gradually increasing mechanical properties were generated by cross-linking triethoxysilane-capped (EO)(99)-(PO)(67)-(EO)(99) (F127) triblocks. Over time, the ethoxysilane groups hydrolyzed and created silanol moieties that subsequently condensated. With the aim of further improving their mechanical behavior, F127 triblocks were reacted with methacryloyl chloride and the resulting dimethacrylate was subsequently cross-linked in an aqueous solution at 37 degrees C. The effect of the concentration of the F127 dimethacrylate on the mechanical properties and the porous structure of the cross-linked matrixes produced was assessed. Rheometric studies revealed that the cross-linked hydrogels attained remarkable mechanical properties and allowed the engineering of robust macroscopic constructs, such as large tubular structures. The microporosity of the matrixes produced was studied by scanning electron microscopy. Monolayered conduits as well as structures comprising two and three layers were engineered in vitro, and their compliance and burst strength were determined.

Biodegradable poly(N-isopropyl acrylamide) (poly-NIPAM) hydrogels with controlled molecular weight of the parent polymer and its degradation products were synthesized by atom transfer radical polymerization in the presence of a polycaprolactone-based di-chlorinated macroinitiator and polycaprolactone dimethacrylate. The phase transition temperature, swelling, hydrolytic degradability, and mechanical properties at 25 and 37°C were explored. A cytocompatibility study showed good NIH3T3 cell response over 5 days culture on the surface of the hydrogels, demonstrated by a consistent increase in cell proliferation detected by an Alamar Blue assay. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazo-lium bromide] results suggested that the hydrogels and their degradation products in the concentration range of 1–25 mg/ mL were not cytotoxic to NIH3T3 cells. A sphere-templating technique was utilized to fabricate biodegradable polyNIPAM scaffolds with monodisperse, pore size. Scaffolds with pore diameter of 48 ± 6 μm were loaded with A-10 smooth muscle cells and then warmed to 37°C entrapping cells in pores approximately 40 μm in diameter, a size we have found to be optimal for angiogenesis and biointegration. Due to their degradable nature, tunable molecular weight, highly interconnected morphology, thermally controlled monodisperse pore size, and temperature-induced volume expansion–contraction, the polyNIPAM-based scaffolds developed in this work will be valuable in tissue engineering.

Intraocular lens implantation after opacified natural lens removal is the primary treatment for cataracts in developed countries. Cataract surgery is generally considered safe, but entails significant risks in countries where sophisticated sterile operating theaters are not widely available. Post-operative infection (endophthalmitis) is a potential blinding complication. Infection often results from bacterial colonization of the new lens implant and subsequent antibiotic-tolerant biofilm formation. To combat this risk, we developed a polymeric hydrogel system that can deliver effective levels of antibiotic over an extended period of time within the globe of the eye. Norfloxacin™ antibiotic was loaded into cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA) gels, which were subsequently surface-modified with octadecyl isocyanate to produce a hydrophobic rate-limiting barrier controlling norfloxacin release. Octadecyl surface modification was characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). A 15-min modification leads to a uniform surface coating and near zero order release of norfloxacin from the matrix. Norfloxacin released from coated pHEMA kills Staphylococcus epidermidis in suspension and on a simulated medical implant surface. With these data, we demonstrate a new and effective system for sustained drug release from a hydrogel matrix with specific application for intraocular lens surgery.