Tailored Biocompatible Polyurethane-Poly(ethylene glycol) Hydrogels as a Versatile Nonfouling Biomaterial

Polyurethane-based hydrogels are relatively inexpensive and mechanically robust biomaterials with ideal properties for various applications, including drug delivery, prosthetics, implant coatings, soft robotics, and tissue engineering. In this report, a simple method is presented for synthesizing and casting biocompatible polyurethane-poly(ethylene glycol) (PU-PEG) hydrogels with tunable mechanical properties, nonfouling characteristics, and sustained tolerability as an implantable material or coating. The hydrogels are synthesized via a simple one-pot method using commercially available precursors and low toxicity solvents and reagents, yielding a consistent and biocompatible gel platform primed for long-term biomaterial applications. The mechanical and physical properties of the gels are easily controlled by varying the curing concentration, producing networks with complex shear moduli of 0.82-190 kPa, similar to a range of human soft tissues. When evaluated against a mechanically matched poly(dimethylsiloxane) (PDMS) formulation, the PU-PEG hydrogels demonstrated favorable nonfouling characteristics, including comparable adsorption of plasma proteins (albumin and fibrinogen) and significantly reduced cellular adhesion. Moreover, preliminary murine implant studies reveal a mild foreign body response after 41 days. Due to the tunable mechanical properties, excellent biocompatibility, and sustained in vivo tolerability of these hydrogels, it is proposed that this method offers a simplified platform for fabricating soft PU-based biomaterials for a variety of applications.

Cellular shape reinforces niche to stem cell signaling in the small intestine

Niche-derived factors regulate tissue stem cells, but apart from the mechanosensory pathways, the effect of niche geometry is not well understood. We used organoids and bioengineered tissue culture platforms to demonstrate that the conical shape of Lgr5⁺ small intestinal stem cells (ISCs) facilitate their self-renewal and function. Inhibition of non-muscle myosin II (NM II)-driven apical constriction altered ISC shape and reduced niche curvature and stem cell capacity. Niche curvature is decreased in aged mice, suggesting that suboptimal interactions between old ISCs and their niche develop with age. We show that activation of NM IIC or physical restriction to young topology improves in vitro regeneration by old epithelium. We propose that the increase in lateral surface area of ISCs induced by apical constriction promotes interactions between neighboring cells, and the curved topology of the intestinal niche has evolved to maximize signaling between ISCs and neighboring cells.

Four Food and Drug Administration draft guidance documents and the REGROW Act: A litmus test for future changes in human cell- and tissue-based products regulatory policy in the United States?

Modern regenerative medicine research has expanded well past the development of traditional drugs and medical devices with many promising new therapies encompassing an increasingly diverse range of substances, notably cell-based therapies. These substantial recent developments and the progress in the health care and therapeutics fields necessitate a new regulatory framework agile enough to accommodate these unique therapies and acknowledge their differences with traditional pharmaceuticals. In the United States, recent proposed changes in the regulatory framework for autologous human cells, tissues, and cellular and tissue-based products (HCT/Ps) and their perceived risk-benefit analysis for patients remain controversial in the scientific field. To provide perspective on of the current status of the most recent attempts to redefine and conceptualize these changes in the United States, we will examine 4 draft guidance documents implemented by the Food and Drug Administration in interpreting relevant concepts and terminology pertaining to HCT/Ps: the Bipartisan Policy Center think tank report, "Advancing Regenerative Cellular Therapy: Medical Innovation for Healthier Americans," the proposed REGROW Act for HCT/Ps, and the current 24 Food and Drug Administration-approved HCT/Ps and related products in the United States.

High-throughput screening of microscale pitted substrate topographies for enhanced nonviral transfection efficiency in primary human fibroblasts

Optimization of nonviral gene delivery typically focuses on the design of particulate carriers that are endowed with desirable membrane targeting, internalization, and endosomal escape properties. Topographical control of cell transfectability, however, remains a largely unexplored parameter. Emerging literature has highlighted the influence of cell-topography interactions on modulation of many cell phenotypes, including protein expression and cytoskeletal behaviors implicated in endocytosis. Using high-throughput screening of primary human dermal fibroblasts cultured on a combinatorial library of microscale topographies, we have demonstrated an improvement in nonviral transfection efficiency for cells cultured on dense micropit patterns compared to smooth substrates, as verified with flow cytometry. A 25% increase in GFP(+) cells was observed independent of proliferation rate, accompanied by SEM and confocal microscopy characterization to help explain the phenomenon qualitatively. This finding encourages researchers to investigate substrate topography as a new design consideration for the optimization of nonviral transfection systems.