The design of hydrogels that simultaneously report protease activity and remove excess protease from solution is elucidated. The hydrogels, based on amino-PEGA, combine enzyme-specific peptides flanked with FRET complimented by charged amino acid residues that facilitate protease uptake via short range electrostatic interactions. Enzymatic response was analysed using a combination of fluorescence spectroscopy, two-photon microscopy and UV/Vis spectroscopy. An optimised elastase-responsive hydrogel resulted in lowering of elastase levels below those typical of chronic wounds. The versatility of the modular-design approach was demonstrated by development of matrix metalloprotease and chymotrypsin sensitive systems.

Differences in the way human and mouse fibroblasts experience senescence in culture had long puzzled researchers. While senescence of human cells is mediated by telomere shortening, Parrinello et al. demonstrated that senescence of mouse cells is caused by extreme oxygen sensitivity. It was hypothesized that the striking difference in oxygen sensitivity between mouse and human cells explains their different rates of aging. To test if this hypothesis is broadly applicable, we cultured cells from 16 rodent species with diverse lifespans in 3% and 21% oxygen and compared their growth rates. Unexpectedly, fibroblasts derived from laboratory mouse strains were the only cells demonstrating extreme sensitivity to oxygen. Cells from hamster, muskrat, woodchuck, capybara, blind mole rat, paca, squirrel, beaver, naked mole rat and wild-caught mice were mildly sensitive to oxygen, while cells from rat, gerbil, deer mouse, chipmunk, guinea pig and chinchilla showed no difference in the growth rate between 3% and 21% oxygen. We conclude that, although the growth of primary fibroblasts is generally improved by maintaining cells in 3% oxygen, the extreme oxygen sensitivity is a peculiarity of laboratory mouse strains, possibly related to their very long telomeres, and fibroblast oxygen sensitivity does not directly correlate with species' lifespan.

We demonstrate the design of novel sensor particles that display fluorescence in the presence of elastase, an enzyme that is present at elevated levels in chronic (non-healing) wounds. Poly(ethyleneglycol acrylamide) hydrogel particles, approximately 200µm in diameter are used as a polymeric matrix, to which a peptide based sensing element is attached. This sensing element consists of a Förster resonance energy transfer (FRET) pair separated by an enzyme cleavable linker. In addition, negatively charged Glutamic acid (Glu) residues are incorporated into the hydrogel structure to facilitate diffusion of the positively charged enzyme into the hydrogel matrix. Enzymatic hydrolysis of the enzyme cleavable linker results in fluorescence of the donor molecule being switched on. We have shown that these particles can detect elastase to a concentration of 100ng/ml, a concentration found in chronic wound fluids. These particles simultaneously detect and address balances in elastase levels and may therefore find applications as smart wound dressings. Fig. 1 Sensor Design layout: FRET Donor is denoted by grey circle, FRET Acceptor is denoted by black circle, ECL is shown by black rectangle FRET Elastase Fluorescence Mater. Res. Soc. Symp. Proc. Vol. 1064