There is a significant medical need for tough biodegradable polymer adhesives that can adapt to or recover from various mechanical deformations while remaining strongly attached to the underlying tissue. We approached this problem by using a polymer poly(glycerol-co-sebacate acrylate) and modifying the surface to mimic the nanotopography of gecko feet, which allows attachment to vertical surfaces. Translation of existing gecko-inspired adhesives for medical applications is complex, as multiple parameters must be optimized, including: biocompatibility, biodegradation, strong adhesive tissue bonding, as well as compliance and conformability to tissue surfaces. Ideally these adhesives would also have the ability to deliver drugs or growth factors to promote healing. As a first demonstration, we have created a gecko-inspired tissue adhesive from a biocompatible and biodegradable elastomer combined with a thin tissue-reactive biocompatible surface coating. Tissue adhesion was optimized by varying dimensions of the nanoscale pillars, including the ratio of tip diameter to pitch and the ratio of tip diameter to base diameter. Coating these nanomolded pillars of biodegradable elastomers with a thin layer of oxidized dextran significantly increased the interfacial adhesion strength on porcine intestine tissue in vitro and in the rat abdominal subfascial in vivo environment. This gecko-inspired medical adhesive may have potential applications for sealing wounds and for replacement or augmentation of sutures or staples.chemical cross-link ͉ medical adhesive ͉ nanotopography ͉ surgical suture

Directed differentiation of embryonic stem (ES) cells is useful for creating models of human disease and could potentially generate a wide array of functional cell types for therapeutic applications. Methods to differentiate ES cells often involve the formation of cell aggregates called embryoid bodies (EBs), which recapitulate early stages of embryonic development. EBs are typically made from suspension cultures, resulting in heterogeneous structures with a wide range of sizes and shapes, which may influence differentiation. Here, we use microfabricated cell-repellant poly(ethylene glycol) (PEG) wells as templates to initiate the formation of homogenous EBs. ES cell aggregates were formed with controlled sizes and shapes defined by the geometry of the microwells. EBs generated in this manner remained viable and maintained their size and shape within the microwells relative to their suspension counterparts. Intact EBs could be easily retrieved from the microwells with high viability (>95%). These results suggest that the microwell technique could be a useful approach for in vitro studies involving ES cells and, more specifically, for initiating the differentiation of EBs of greater uniformity based on controlled microenvironments.

Protein-based hydrogels have emerged as promising alternatives to synthetic hydrogels for biomedical applications, owing to the precise control of structure and function enabled by protein engineering. Nevertheless, strategies for assembling 3D molecular networks that carry the biological information encoded in fulllength proteins remain underdeveloped. Here we present a robust protein gelation strategy based on a pair of genetically encoded reactive partners, SpyTag and SpyCatcher, that spontaneously form covalent isopeptide linkages under physiological conditions. The resulting "network of Spies" may be designed to include celladhesion ligands, matrix metalloproteinase-1 cleavage sites, and full-length globular proteins [mCherry and leukemia inhibitory factor (LIF)]. The LIF network was used to encapsulate mouse embryonic stem cells; the encapsulated cells remained pluripotent in the absence of added LIF. These results illustrate a versatile strategy for the creation of information-rich biomaterials.protein biomaterials | stem cell encapsulation | cell fate control H ydrogels made from natural or synthetic polymers have been investigated for many years as scaffolds for encapsulated cells (1). The past decade has witnessed a growing trend in hydrogel design that calls for systems capable of controlling the behavior of encapsulated cells by providing, sensing, and responding to biological signals (2). This design criterion demands a new level of craftsmanship from scientists and engineers who wish to incorporate biomolecular species, which may range in size and complexity from small molecules to multidomain proteins, into biomaterials (3). A promising approach to this challenge uses bio-orthogonal chemistry to introduce the species of interest with spatial and temporal control (4-7).Here we discuss an alternative approach, based on the design and expression of artificial proteins that are programmed to form covalent molecular networks, which offers important advantages in the engineering of dynamic biomaterials systems (8, 9). The method requires no chemical reagents, proceeds efficiently under mild conditions (e.g., in aqueous solution at physiological pH, in the presence of ambient levels of oxygen, and at temperatures ranging from 4 to 37°C), allows introduction of biological information in modular fashion, and enables encapsulation of cells without loss of viability.The recent discovery of naturally occurring isopeptide bonds in Gram-positive bacterial adhesins (10) inspired Howarth and coworkers (11, 12) to design a pair of reactive protein partners (SpyTag and SpyCatcher) by splitting the second immunoglobulinlike collagen adhesin domain (CnaB2) of the fibronectin-binding protein (FbaB) of Streptococcus pyogenes. SpyTag-SpyCatcher chemistry forms a specific isopeptide bond between Asp-117 of SpyTag and Lys-31 of SpyCatcher. In a previous study, we demonstrated that placing SpyTag and SpyCatcher at carefully chosen locations within elastin-like proteins (ELPs) enabled efficient synthesis of unusual nonlinea...

The study of hematopoietic colony-forming units using semisolid culture media has greatly advanced the knowledge of hematopoiesis. Here we report that similar methods can be used to study pancreatic colony-forming units. We have developed two pancreatic colony assays that enable quantitative and functional analyses of progenitor-like cells isolated from dissociated adult (2-4 mo old) murine pancreas. We find that a methylcellulose-based semisolid medium containing Matrigel allows growth of duct-like "Ring/ Dense" colonies from a rare (∼1%) population of total pancreatic single cells. With the addition of roof plate-specific spondin 1, a wingless-int agonist, Ring/Dense colony-forming cells can be expanded more than 100,000-fold when serially dissociated and replated in the presence of Matrigel. When cells grown in Matrigel are then transferred to a Matrigel-free semisolid medium with a unique laminin-based hydrogel, some cells grow and differentiate into another type of colony, which we name "Endocrine/Acinar." These Endocrine/Acinar colonies are comprised mostly of endocrine-and acinar-like cells, as ascertained by RNA expression analysis, immunohistochemistry, and electron microscopy. Most Endocrine/Acinar colonies contain beta-like cells that secrete insulin/C-peptide in response to D-glucose and theophylline. These results demonstrate robust self-renewal and differentiation of adult Ring/Dense colony-forming units in vitro and suggest an approach to producing beta-like cells for cell replacement of type 1 diabetes. The methods described, which include microfluidic expression analysis of single cells and colonies, should also advance study of pancreas development and pancreatic progenitor cells. extracellular matrix proteins | Sry-related HMG box (Sox) 9 | Promonin 1 (CD133) | neurogenin 3 | dickkopf1 (Dkk1)

Metabolic labeling of proteins with the methionine (1) surrogate azidonorleucine (2) can be targeted exclusively to specified cells through expression of a mutant methionyl-tRNA synthetase (MetRS). In complex cellular mixtures, proteins made in cells that express the mutant synthetase can be tagged with affinity reagents (for detection or enrichment) or fluorescent dyes (for imaging). Proteins made in cells that do not express the mutant synthetase are neither labeled nor detected.