Probing the biomechanical contribution of the endothelium to lymphocyte migration: diapedesis by the path of least resistance.

Immune cell trafficking requires the frequent breaching of the endothelial barrier either directly through individual cells ('transcellular' route) or through the inter-endothelial junctions ('paracellular' route). What determines the loci or route of breaching events is an open question with important implications for overall barrier regulation. We hypothesized that basic biomechanical properties of the endothelium might serve as crucial determinants of this process.

Why the dish makes a difference: quantitative comparison of polystyrene culture surfaces.

There is wide anecdotal recognition that biological cell viability and behavior can vary significantly as a function of the source of commercial tissue culture polystyrene (TCPS) culture vessels to which those cells adhere. However, this marked material dependency is typically resolved by selecting and then consistently using the same manufacturer's product - following protocol - rather than by investigating the material properties that may be responsible for such experimental variation. Here, we quantified several physical properties of TCPS surfaces obtained from a wide range of commercial sources and processing steps, through the use of atomic force microscopy (AFM)-based imaging and analysis, goniometry and protein adsorption quantification.

Macromolecular crowding directs extracellular matrix organization and mesenchymal stem cell behavior.

Microenvironments of biological cells are dominated in vivo by macromolecular crowding and resultant excluded volume effects. This feature is absent in dilute in vitro cell culture. Here, we induced macromolecular crowding in vitro by using synthetic macromolecular globules of nm-scale radius at physiological levels of fractional volume occupancy.

Pericyte actomyosin-mediated contraction at the cell-material interface can modulate the microvascular niche.

Pericytes physically surround the capillary endothelium, contacting and communicating with associated vascular endothelial cells via cell-cell and cell-matrix contacts. Pericyte-endothelial cell interactions thus have the potential to modulate growth and function of the microvasculature. Here we employ the experimental finding that pericytes can buckle a freestanding, underlying membrane via actin-mediated contraction.

Autocrine-controlled formation and function of tissue-like aggregates by primary hepatocytes in micropatterned hydrogel arrays.

The liver carries out a variety of essential functions regulated in part by autocrine signaling, including hepatocyte-produced growth factors and extracellular matrix (ECM). The local concentrations of autocrine factors are governed by a balance between receptor-mediated binding at the cell surface and diffusion into the local matrix and are thus expected to be influenced by the dimensionality of the cell culture environment. To investigate the role of growth factor and ECM-modulated autocrine signaling in maintaining appropriate primary hepatocyte survival, metabolic functions, and polarity, we created three-dimensional cultures of defined geometry using micropatterned semisynthetic polyethylene glycol-fibrinogen hydrogels to provide a mechanically compliant, nonadhesive material platform that could be modified by cell-secreted factors.

Photoelectrochemical complexes for solar energy conversion that chemically and autonomously regenerate.

Naturally occurring photosynthetic systems use elaborate pathways of self-repair to limit the impact of photo-damage. Here, we demonstrate a complex consisting of two recombinant proteins, phospholipids and a carbon nanotube that mimics this process. The components self-assemble into a configuration in which an array of lipid bilayers aggregate on the surface of the carbon nanotube, creating a platform for the attachment of light-converting proteins.

Calpain- and talin-dependent control of microvascular pericyte contractility and cellular stiffness.

Pericytes surround capillary endothelial cells and exert contractile forces modulating microvascular tone and endothelial growth. We previously described pericyte contractile phenotype to be Rho GTPase- and α-smooth muscle actin (αSMA)-dependent. However, mechanisms mediating adhesion-dependent shape changes and contractile force transduction remain largely equivocal.

Tuning adhesion failure strength for tissue-specific applications.

Soft tissue adhesives are employed to repair and seal many different organs, which range in both tissue surface chemistry and mechanical challenges during organ function. This complexity motivates the development of tunable adhesive materials with high resistance to uniaxial or multiaxial loads dictated by a specific organ environment. Co-polymeric hydrogels comprising aminated star polyethylene glycol and dextran aldehyde (PEG:dextran) are materials exhibiting physico-chemical properties that can be modified to achieve this organ- and tissue-specific adhesion performance.

Stop-flow lithography for the production of shape-evolving degradable microgel particles.

Microgel particles capable of bulk degradation have been synthesized from a solution of diacrylated triblock copolymer composed of poly(ethylene glycol) and poly(lactic acid) in a microfluidic device using stop-flow lithography (SFL). It has been previously demonstrated that SFL can be used to fabricate particles with precise control over particle size and shape. Here, we have fabricated hydrogel particles of varying size and shape and examined their mass-loss and swelling behavior histologically and mechanically.

Collagen's triglycine repeat number and phylogeny suggest an interdomain transfer event from a Devonian or Silurian organism into Trichodesmium erythraeum.

Two competing effects at two vastly different scales may explain collagen's current translation length. The necessity to have long molecules for maintaining mechanical integrity at the organism and supraorganism scales may be limited by the need to have small molecules capable of robust self-assembly at the nanoscale. The triglycine repeat regions of all 556 currently cataloged organisms with collagen-like genes were ranked by length.