Cell-encapsulated hydrogels with complex three-dimensional (3D) structures were fabricated from photopolymerizable poly(ethylene glycol) diacrylate (PEGDA) using modified 'top-down' and 'bottoms-up' versions of a commercially available stereolithography apparatus (SLA). Swelling and mechanical properties were measured for PEGDA hydrogels with molecular weights (M(w)) ranging from 700 to 10 000 Daltons (Da). Long-term viability of encapsulated NIH/3T3 cells was quantitatively evaluated using an MTS assay and shown to improve over 14 days by increasing the M(w) of the hydrogels. Addition of adhesive RGDS peptide sequences resulted in increased cell viability, proliferation, and spreading compared to pristine PEG hydrogels of the same M(w). Spatial 3D layer-by-layer cell patterning was successfully demonstrated, and the feasibility of depositing multiple cell types and material compositions into distinct layers was established.

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Cell-based biohybrid actuators are integrated systems that use biological components including proteins and cells to power material components by converting chemical energy to mechanical energy. The latest progress in cell-based biohybrid actuators has been limited to rigid materials, such as silicon and PDMS, ranging in elastic moduli on the order of mega (10(6)) to giga (10(9)) Pascals. Recent reports in the literature have established a correlation between substrate rigidity and its influence on the contractile behavior of cardiomyocytes (A. J. Engler, C. Carag-Krieger, C. P. Johnson, M. Raab, H. Y. Tang and D. W. Speicher, et al., J. Cell Sci., 2008, 121(Pt 22), 3794-3802, P. Bajaj, X. Tang, T. A. Saif and R. Bashir, J. Biomed. Mater. Res., Part A, 2010, 95(4), 1261-1269). This study explores the fabrication of a more compliant cantilever, similar to that of the native myocardium, with elasticity on the order of kilo (10(3)) Pascals. 3D stereolithographic technology, a layer-by-layer UV polymerizable rapid prototyping system, was used to rapidly fabricate multi-material cantilevers composed of poly(ethylene glycol) diacrylate (PEGDA) and acrylic-PEG-collagen (PC) mixtures. The incorporation of acrylic-PEG-collagen into PEGDA-based materials enhanced cell adhesion, spreading, and organization without altering the ability to vary the elastic modulus through the molecular weight of PEGDA. Cardiomyocytes derived from neonatal rats were seeded on the cantilevers, and the resulting stresses and contractile forces were calculated using finite element simulations validated with classical beam equations. These cantilevers can be used as a mechanical sensor to measure the contractile forces of cardiomyocyte cell sheets, and as an early prototype for the design of optimal cell-based biohybrid actuators.

A spatially organized three‐dimensional (3D) co‐culture of multiple cell types is required to recapitulate cellular interactions and microenvironments in complex tissues. Although there are limited reports for 3D patterning of cells and materials, approaches to examine functional interactions of 3D spatially patterned multiple cell types are lacking entirely. This is mostly due to difficulties in controlling the physical arrangement of cells in a 3D matrix and the physical properties of the cell‐encapsulating matrix, while keeping the cells alive and functional for extended periods of time. In this study, an automated maskless fabrication technique is combined with a tunable polymer blend to spatially organize primary hippocampus neurons (HNs) and skeletal muscle myoblast cells (MCs) in a 3D hydrogel matrix with tunable mechanical and degradation properties. The spatial organization of these multiple cell types revealed that the presence of MCs resulted in increased cholinergic functionality of the HNs, as quantified by their choline acetyltransferase activity. The presence of a factor alone is not sufficient, but its spatiotemporal control is necessary; a condition that is possibly true for many cellular interactions. Therefore, the system described here offers a different approach to examine such previously unknown interactions. The approach proposed in this study can be used to examine interactions between many different cell types and shift the 3D fabrication paradigm to a next level, which is to fabricate tissues that are not only viable but also functional.

Since stem cells emerged as a new generation of medicine, there are increasing efforts to deliver the stem cells to a target tissue via intravascular injection. However, the therapeutic stem cells lack a capacity to detect and adhere to the target tissue. Therefore, this study presents synthesis of a bioactive hyper-branched polyglycerol (HPG) which can non-invasively associate with stem cells and further guide them to target sites, such as inflamed endothelium. The overall process is analogous to the way in which leukocytes are mobilized to the injured endothelium.

With the emergence of microscale biotechnology, such as biomicroelectromechanical systems ("Bio-MEMS") and microfluidic-based microchips for sensing and diagnostics, polydimethylsiloxane (PDMS)-based elastomers have become very popular materials. [1] PDMS elastomers possess several features that are well suited for these applications: mechanical stability and elasticity, chemical inertness, optical transparency, gas permeability, ease of fabrication, and biocompatibility. [1d, 2] However, the extremely hydrophobic nature of PDMS often limits its applicability (e.g. poor aqueous fluid flow and nonspecific adhesion of biomolecules). [2] Various methods have been proposed to modify the PDMS surface to impart hydrophilicity, for example, UV or plasma treatment to oxidize the surface [3] and coating the surface with hydrophilic polymers. [4] However, the treated PDMS surfaces often recover their hydrophobic traits due to the migration of unreacted PDMS oligomers to the surface and the rearrangement of PDMS polymer chains. [2b, 5] We suggest that coating PDMS with hydrophilic materials would be more effective than the molecular level modifications. Hydrogels, which are networks of cross-linked polymers taking up large amounts of water, are therefore considered promising materials. Hydrogels can also be designed to present functionalities for specific purposes, such as in vitro cell culture, cell encapsulation, and molecular capture and release. [6] Therefore, PDMS coated with hydrogels with desired properties would significantly enhance the performance of PDMS-based devices. However, it is a significant challenge to attain and sustain the adhesion between hydrogel and PDMS, due to the stark discrepancy between the bulk properties of PDMS substrates and hydrogels.To meet this challenge, we describe a unique approach to tailor hydrogel adhesion to a PDMS substrate. Alginate, a naturally derived polysaccharide, was covalently linked to the PDMS surface. This attached alginate acted as a "glue" to allow the strong, permanent adhesion of the hydrogel onto the PDMS surface by 1) imparting hydrophilicity to improve compatibility with hydrogels, and 2) providing functional groups for the stable conjugation of hydrogels. The resulting hydrogel-coated PDMS substrate was used in the following two applications: 1) it served as an in vitro cell culture platform to study cellular behavior in response to cyclic mechanical strain, and 2) it was used in a microfluidic device with hydrogel-filled channels.The PDMS surface was chemically grafted with alginate following a series of modification steps: [7] step 1: oxidation to present hydroxy groups (OH-PDMS, Figure 1 a); step 2: silanization using 3-aminopropyltriethoxysilane to present primary amino groups (NH 2 -PDMS); and step 3: conjugation of alginate by carbodiimide-mediated amide coupling between amino groups on the PDMS surface and carboxylic acid groups of alginate (alginate-PDMS). The successive modifications of PDMS were confirmed with FTIR spectroscopy ( Figure S1 and Table...

This study presents a “living” microvascular stamp that releases multiple angiogenic factors and subsequently creates functional neovessels with the same pattern as that engraved in the stamp. The stamp consists of live cells that secrete angiogenic factors, an engineered hydrogel matrix that promotes cellular expression of angiogenic factors, and a three‐dimensional geometry that localizes the angiogenic factors within the pattern.

This study presents a multi-walled poly(ethylene glycol) diacrylate hydrogel tube formed by the simple self-folding of a bi-layered hydrogel patch. The gel tube has the capability to release encapsulated molecules through designated pathways in a sustained manner. Therefore, the gel tube encapsulating the vascular endothelial growth factor significantly increases the vascular densities and vessel diameters at an implantation site.