No abstract

The usage of gelatin hydrogel is limited due to its instability and poor mechanical properties, especially under physiological conditions. Divalent metal ions present in gelatin such as Ca2+ and Fe2+ play important roles in the gelatin molecule interactions. The objective of this study was to determine the impact of divalent ion removal on the stability and mechanical properties of gelatin gels with and without chemical crosslinking. The gelatin solution was purified by Chelex resin to replace divalent metal ions with sodium ions. The gel was then chemically crosslinked by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Results showed that the removal of divalent metal ions significantly impacted the formation of the gelatin network. The purified gelatin hydrogels had less interactions between gelatin molecules and form larger-pore network which enabled EDC to penetrate and crosslink the gel more efficiently. The crosslinked purified gels showed small swelling ratio, higher crosslinking density and dramatically increased storage and loss moduli. The removal of divalent ions is a simple yet effective method that can significantly improve the stability and strength of gelatin hydrogels. The in vitro cell culture demonstrated that the purified gelatin maintained its ability to support cell attachment and spreading.

No abstract

A new type of nitric oxide (NO)-releasing material is described that utilizes S-nitrosothiols anchored to tiny fumed silica (FS) particles as the NO donor system. The synthetic procedures suitable for tethering three different thiol species (cysteine, N-acetylcysteine, and N-acetylpenicillamine) to the surface of FS polymer filler particles are detailed. The thiol-derivatized particles are converted to their corresponding S-nitrosothiols by reaction with t-butylnitrite. The total NO loading on the resulting particles range from 21-138 nmol/mg for the three different thiol-derivatized materials [S-nitrosocysteine-(NO-Cys)-FS, S-nitroso-N-acetylcysteine (SNAC)-FS, and S-nitroso-N-acetylpenicillamine (SNAP)-FS], with SNAP-FS yielding the highest NO loading. NO can be generated from these particles when suspended in solution via the addition of copper(II) ions, ascorbate, or irradiation with visible light. The SNAC-FS and SNAP-FS particles can be blended in polyurethane and silicone rubber matrixes to create films that release NO at controlled rates. Polyurethane films containing SNAC-FS submerged in phosphate-buffered saline (pH 7.4) generate NO surface fluxes approximately 0.1-0.7x10(-10) mol cm-2 min-1 and SNAP-FS films generate NO fluxes of approximately 0-7.5x10(-10) mol cm-2 min-1 upon addition of increasing amounts of copper ions. Silicone rubber films containing SNAC-FS or SNAP-FS do not liberate NO upon exposure to copper ions or ascorbate in phosphate-buffered saline solution. However, such films are shown to release NO at rates proportional to increasing intensities of visible light impinging on the films. Such photoinitiated NO release from these composite materials offers the first NO-releasing hydrophobic polymers with an external on/off trigger to control NO generation.

This report describes the first hydrophobic nitric oxide (NO)-releasing material that utilizes light as an external on/off trigger to control the flux of NO generated from cured polymer films. Fumed silica polymer filler particles were derivatized with S-nitroso-N-acetyl-dl-penicillamine and blended into the center layer of trilayer silicone rubber films. Nitric oxide is generated upon irradiation with light, and fluxes increase with increasing power of incident light. The ability to precisely control NO generation from this material has the potential to answer fundamental questions about the levels of NO needed to achieve desired therapeutic affects in different biomedical applications.