A “self-pinning” adhesive based on responsive surface wrinkles

available in PMC 2012 January 1.Surface wrinkles are interesting since they form spontaneously into well-defined patterns. The mechanism of formation is well-studied and is associated with the development of a critical compressive stress that induces the elastic instability. In this work, we demonstrate surface wrinkles that dynamically change in response to a stimulus can improve interfacial adhesion with a hydrogel surface through the dynamic evolution of the wrinkle morphology. We observe that this control is related to the local pinning of the crack separation pathway facilitated by the surface wrinkles during debonding, which is dependent on the contact time with the hydrogel.National Science Foundation (U.S.) (NIRT grant 0609182)National Science Foundation (U.S.) (NIH grant DE013023)Center for Integration of Medicine and Innovative Technology (U.S. Army grant W81XWH-07-2-0011)Center for Integration of Medicine and Innovative Technology (NIH GM086433)University of Massachusetts (System)Massachusetts Technology Transfer CenterAmerican Heart Association (Grant 0835601D

Mechanotransduction and growth factor signalling to engineer cellular microenvironments

Engineering cellular microenvironments involves biochemical factors, the extracellular matrix (ECM) and the interaction with neighbouring cells. This progress report provides a critical overview of key studies that incorporate growth factor (GF) signalling and mechanotransduction into the design of advanced microenvironments. Materials systems have been developed for surface-bound presentation of GFs, either covalently tethered or sequestered through physico-chemical affinity to the matrix, as an alternative to soluble GFs. Furthermore, some materials contain both GF and integrin binding regions and thereby enable synergistic signalling between the two. Mechanotransduction refers to the ability of the cells to sense physical properties of the ECM and to transduce them into biochemical signals. Various aspects of the physics of the ECM, i.e. stiffness, geometry and ligand spacing, as well as time-dependent properties, such as matrix stiffening, degradability, viscoelasticity, surface mobility as well as spatial patterns and gradients of physical cues are discussed. To conclude, various examples illustrate the potential for cooperative signalling of growth factors and the physical properties of the microenvironment for potential applications in regenerative medicine, cancer research and drug testing

Developing a self-healing supramolecular nucleoside hydrogel

Low molecular weight gelator hydrogels provide a viable alternative to traditional polymer based drug delivery platforms, owing to their tunable stability and in most cases inherent biocompatibility. Here we report the first self-healing nucleoside hydrogel using N4-octanoyl-2′-deoxycytidine (0.5% w/v) for drug delivery. The hydrogel's cross-linked nanofibrillar structure, was characterised using oscillatory rheology and confirmed using SEM and TEM imaging. The potential of this gel for drug delivery was explored in vitro using fluorescently labelled tracers. Cell viability assays were conducted using pancreatic cell lines which tolerated the gels well; whilst no adverse effects on the viability or proliferation of cells were observed for fibroblast cell lines

Optical Waveguide-Enhanced Diffraction for Observation of Responsive Hydrogel Nanostructures

Optical diffraction measurements are reported for in situ observation of swelling and collapsing of responsive hydrogel nanostructures. The optical signal is enhanced by probing the surface carrying periodic arrays of hydrogel nanostructures by resonantly excited optical waveguide modes. UV-nanoimprint lithography is employed for the preparation of the arrays of nanopillars from photo-crosslinked N-isopropylacrylamide (pNIPAAm)-based hydrogel that are covalently tethered to a gold surface. The thermo-responsive properties of such pNIPAAm nanopillars that swell in 3D are compared to those of a thin film prepared from the identical material and that is allowed to swell predominantly in 1D. The nanopillars with a diameter of ≈100 nm and aspect ratio of 2 swell by a factor of ≈6 as determined by optical measurements supported by simulations that are compared to morphological characteristics obtained from atomic force microscopy. Bending of nanopillars above the lower critical solution temperature (LCST), erasure of the topographic structure by drying at temperature below the LCST, and recovery by subsequent swelling below the LCST and drying at temperature above the LCST are observed

Nanogrooved microdiscs for bottom-up modulation of osteogenic differentiation

Grooved topographical features have effectively modulated cell differentiation on two-dimensional substrates. To transpose patterning into a 3D environmment, nanogrooved microdiscs, "topodiscs", are produced as cell carriers for bottom-up cell-mediated assembly. While enhancing cell proliferation, topodiscs led to the formation of bone-like aggregates, even in culture medium lacking osteoinductive factors.publishe