Model systems mimicking the extracellular matrix (ECM) have greatly helped in quantifying cell migration in three dimensions and elucidated the molecular determinants of cellular motility in morphogenesis, regeneration, and disease progression. Here we tested the suitability of proteolytically degradable synthetic poly(ethylene glycol) (PEG)-based hydrogels as an ECM model system for cell migration research and compared this designer matrix with the two well-established ECM mimetics fibrin and collagen. Three-dimensional migration of dermal fibroblasts was quantified by time-lapse microscopy and automated single-cell tracking. A broadband matrix metalloproteinase (MMP) inhibitor and tumor necrosis factor-alpha, a potent MMP-inducer in fibroblasts, were used to alter MMP regulation. We demonstrate a high sensitivity of migration in synthetic networks to both MMP modulators: inhibition led to an almost complete suppression of migration in PEG hydrogels, whereas MMP upregulation increased the fraction of migrating cells significantly. Conversely, migration in collagen and fibrin proved to be less sensitive to the above MMP modulators, as their fibrillar architecture allowed for MMP-independent migration through preexisting pores. The possibility of molecularly recapitulating key functions of the natural extracellular microenvironment and the improved protease sensitivity makes PEG hydrogels an interesting model system that allows correlation between protease activity and cell migration.

OLED Fabrication and Measurements: Pre-patterned indium tin oxide (ITO) substrates with an effective individual device area of 3.14 mm 2 were cleaned by sonication in a detergent solution for 3 min and then washed with large amount of doubly distilled water. Further sonication in ethanol for 3 min followed before blowing dry with a stream of nitrogen. The ITO substrates were then treated with O 2 plasma for one minute before being loaded into the vacuum chamber. The organic layers were deposited thermally at a rate of 0.1± 0.3 nm s ±1 under a pressure of~2 10 ±5 torr in an Ulvac Cryogenic deposition system. An alloy of Mg and Ag (ca. 10:1, 50 nm) was deposited as the cathode, which was capped with 100 nm of Ag. The current±voltage±luminance was measured in ambient with a Keithley 2400 Source meter and a Newport 1835C Optical meter equipped with 818ST silicon photodiode [19] The related Ir(piq) 3 complex was briefly mentioned in a recent conference paper by S. Ohada and co-workers. The device based on this complex gave a maximum bightness 10 000 cd m ±2 at J = 365 mA cm [20] The red iridium phosphors in this study have a 1-(phenyl)isoquinoline framework. In our new findings, iridium complexes bearing a 3-(phenyl)-isoquinoline framework also show an efficient yellow phosphorescence emission (565 nm) with a maximum brightness 65 000 cd m Cell-Responsive Synthetic Hydrogels** By Matthias P. Lutolf, George P. Raeber, Andreas H. Zisch, Nicola Tirelli, and Jeffrey A. Hubbell* An important part of tissue function relies on the dynamic dialog that exists between cells and their extracellular matrices (ECM): the ECM is active, presenting bound adhesion sites that interact with cell-surface receptors, [1] and it is responsive to signals presented by cells, locally degrading under the influence of proteases at the surface of the migrating cell.[2±4] While artificial biomaterial matrices used in cell culture and tissue engineering have been developed to be responsive to physical [5±9] and even biochemical [10±14] stimuli, they do not widely address this concept of responsiveness to cellular stimuli. We mimicked these features in synthetic hydrogel networks, for application in both cell biology and tissue engineering, [15±17] incorporating pendant receptor-binding sites so that cells can exert traction [18] and crosslinking protease-sensitive degradation sites so that cells can create a path to enable forward movement. [19] Our results demonstrate that synthetic materials can be responsive to cellular influences in vitro and in vivo, including here, as an example, inducing and responding to angiogenic invasion. We formed polymer networks in situ using conjugate addition reactions. We linked molecular building blocks performing either structural (poly(ethylene glycol), PEG) or biological (oligopeptides) function (Scheme 1). Vinyl sulfone (VS)-functionalized multiarmed telechelic PEG macromers reacted with thiolate groups of cysteine-containing peptides by conjugate addition, [20] a reaction that is highly selective versus b...

Local, controlled induction of angiogenesis remains a challenge that limits tissue engineering approaches to replace or restore diseased tissues. We present a new class of bioactive synthetic hydrogel matrices based on poly(ethylene glycol) (PEG) and synthetic peptides that exploits the activity of vascular endothelial growth factor (VEGF) alongside the base matrix functionality for cellular ingrowth, that is, induction of cell adhesion by pendant RGD-containing peptides and provision of cell-mediated remodeling by cross-linking matrix metalloproteinase substrate peptides. By using a Michael-type addition reaction, we incorporated variants of VEGF121 and VEGF165 covalently within the matrix, available for cells as they invade and locally remodel the material. The functionality of the matrix-conjugated VEGF was preserved and was critical for in vitro endothelial cell survival and migration within the matrix environment. Consistent with a scheme of locally restricted availability of VEGF, grafting of these VEGF-modified hydrogel matrices atop the chick chorioallontoic membrane evoked strong new blood vessel formation precisely at the area of graft-membrane contact. When implanted subcutaneously in rats, these VEGF-containing matrices were completely remodeled into native, vascularized tissue. This type of synthetic, biointeractive matrix with integrated angiogenic growth factor activity, presented and released only upon local cellular demand, could become highly useful in a number of clinical healing applications of local therapeutic angiogenesis.

We present here the biological performance in supporting tissue regeneration of hybrid hydrogels consisting of genetically engineered protein polymers that carry specific features of the natural extracellular matrix, cross-linked with reactive poly(ethylene glycol) (PEG). Specifically, the protein polymers contain the cell adhesion motif RGD, which mediates integrin receptor binding, and degradation sites for plasmin and matrix-metalloproteinases, both being proteases implicated in natural matrix remodeling. Biochemical assays as well as in vitro cell culture experiments confirmed the ability of these protein-PEG hydrogels to promote specific cellular adhesion and to exhibit degradability by the target enzymes. Cell culture experiments demonstrated that proteolytic sensitivity and suitable mechanical properties were critical for three-dimensional cell migration inside these synthetic matrixes. In vivo, protein-PEG matrixes were tested as a carrier of bone morphogenetic protein (rhBMP-2) to heal critical-sized defects in a rat calvarial defect model. The results underscore the importance of fine-tuning material properties of provisional therapeutic matrixes to induce cellular responses conducive to tissue repair. In particular, a lack of rhBMP or insufficient degradability of the protein-PEG matrix prevented healing of bone defects or remodeling and replacement of the artificial matrix. This work confirms the feasibility of attaining desired biological responses in vivo by engineering material properties through the design of single components at the molecular level. The combination of polymer science and recombinant DNA technology emerges as a powerful tool for the development of novel biomaterials.