Transformation of Biomass DNA into Biodegradable Materials from Gels to Plastics for Reducing Petrochemical Consumption.

Ancient biomass is the main source for petrochemicals including plastics, which are inherently difficult to be degraded, increasingly polluting the earth's ecosystem including our oceans. To reduce the consumption by substituting or even replacing most of the petrochemicals with degradable and renewable materials is inevitable and urgent for a sustainable future. We report here a unique strategy to directly convert biomass DNA, at a large scale and with low cost, to diverse materials including gels, membranes, and plastics without breaking down DNA first into building blocks and without polymer syntheses. With excellent and sometimes unexpected, useful properties, we applied these biomass DNA materials for versatile applications for drug delivery, unusual adhesion, multifunctional composites, patterning, and everyday plastic objects. We also achieved cell-free protein production that had not been possible by petrochemical-based products. We expect our biomass DNA conversion approach to be adaptable to other biomass molecules including biomass proteins. We envision a promising and exciting era coming where biomass may replace petrochemicals for most if not all petro-based products.

Developing mechanically robust, triazole-zwitterionic hydrogels to mitigate foreign body response (FBR) for islet encapsulation.

Zwitterionic hydrogels such as those based on polycarboxybetaine (PCB) or polysulfobetaine (PSB) have potential for various biomedical applications, due to their biocompatibility and low biofouling properties. However, the poor mechanical properties of zwitterionic hydrogels developed to date remain a challenge, severely limiting their practical uses. To improve the mechanical properties without compromising their zwitterionic feature or biocompatibility, we designed a new class of zwitterionic hydrogels by introducing triazole moieties into the hydrogel monomers that could form energy-dissipating π-π stacking. Compared to conventional zwitterionic hydrogels, the triazole-zwitterionic (TR-ZW) ones exhibited similarly excellent antifouling properties, but were much more mechanically robust with higher stretchability (250% tensile strain), better compression-resistance (89% compressive strain and 65% compression for at least 10 cycles without any crack) and better folding-resistance. In addition, upon subcutaneous implantation in mice, the TR-ZW hydrogels induced significantly lower foreign body responses (FBR) (i.e. less fibrosis and more blood vessel formation relative to a poly(2-hydroxyethyl methacrylate) hydrogel control). As an example of their potential applications, we showed the use of the TR-ZW hydrogels for islet encapsulation and transplantation and demonstrated diabetes correction up to ~1 month in mice in the convenient subcutaneous site.

Engineering transferrable microvascular meshes for subcutaneous islet transplantation.

The success of engineered cell or tissue implants is dependent on vascular regeneration to meet adequate metabolic requirements. However, development of a broadly applicable strategy for stable and functional vascularization has remained challenging. We report here highly organized and resilient microvascular meshes fabricated through a controllable anchored self-assembly method. The microvascular meshes are scalable to centimeters, almost free of defects and transferrable to diverse substrates, ready for transplantation. They promote formation of functional blood vessels, with a density as high as ~220 vessels mm-2, in the poorly vascularized subcutaneous space of SCID-Beige mice. We further demonstrate the feasibility of fabricating microvascular meshes from human induced pluripotent stem cell-derived endothelial cells, opening a way to engineer patient-specific microvasculature. As a proof-of-concept for type 1 diabetes treatment, we combine microvascular meshes and subcutaneously transplanted rat islets and achieve correction of chemically induced diabetes in SCID-Beige mice for 3 months.

Physical confinement induces malignant transformation in mammary epithelial cells.

The physical microenvironment of tumor cells plays an important role in cancer initiation and progression. Here, we present evidence that confinement - a new physical parameter that is apart from matrix stiffness - can also induce malignant transformation in mammary epithelial cells. We discovered that MCF10A cells, a benign mammary cell line that forms growth-arrested polarized acini in Matrigel, transforms into cancer-like cells within the same Matrigel material following confinement in alginate shell hydrogel microcapsules. The confined cells exhibited a range of tumor-like behaviors, including uncontrolled cellular proliferation and invasion. Additionally, 4-6 weeks after transplantation into the mammary fad pads of immunocompromised mice, the confined cells formed large palpable masses that exhibited histological features similar to that of carcinomas. Taken together, our findings suggest that physical confinement represents a previously unrecognized mechanism for malignancy induction in mammary epithelial cells and also provide a new, microcapsule-based, high throughput model system for testing new breast cancer therapeutics.

Conformal Hydrogel Coatings on Catheters To Reduce Biofouling.

Reducing biofouling while increasing lubricity of inserted medical catheters is highly desirable to improve their comfort, safety, and long-term use. We report here a simple method to create thin (∼30 µm) conformal lubricating hydrogel coatings on catheters. The key to this method is a three-step process including shape-forming, gradient cross-linking, and swell-peeling (we label this method as SGS). First, we took advantage of the fast gelation of agar to form a hydrogel layer conformal to catheters; then, we performed a surface-bound UV cross-linking of acrylamide mixed in agar in open air, purposely allowing gradual oxygen inhibition of free radicals to generate a gradient of cross-linking density across the hydrogel layer; and finally, we caused the hydrogel to swell to let the non-cross-linked/loosely attached hydrogel fall off, leaving behind a surface-bound, thin, and mostly uniform hydrogel coating. This method also allowed easy incorporation of different polymerizable monomers to obtain multifunctionality. For example, incorporating an antifouling, zwitterionic moiety sulfobetaine in the hydrogel reduced both in vitro protein adsorption and in vivo foreign-body response in mice. The addition of a biocidal N-halamine monomer to the hydrogel coating deactivated both Staphylococcus aureus ( S. aureus) and Escherichia coli ( E. coli) O157:H7 within 30 min of contact and reduced biofilm formation by 90% compared to those of uncoated commercial catheters when challenged with S. aureus for 3 days. The lubricating, antibiofouling hydrogel coating may bring clinical benefits in the use of urinary and venous catheters as well as other types of medical devices.

Dynamic DNA material with emergent locomotion behavior powered by artificial metabolism.

Metabolism is a key process that makes life alive-the combination of anabolism and catabolism sustains life by a continuous flux of matter and energy. In other words, the materials comprising life are synthesized, assembled, dissipated, and decomposed autonomously in a controlled, hierarchical manner using biological processes. Although some biological approaches for creating dynamic materials have been reported, the construction of such materials by mimicking metabolism from scratch based on bioengineering has not yet been achieved. Various chemical approaches, especially dissipative assemblies, allow the construction of dynamic materials in a synthetic fashion, analogous to part of metabolism. Inspired by these approaches, here, we report a bottom-up construction of dynamic biomaterials powered by artificial metabolism, representing a combination of irreversible biosynthesis and dissipative assembly processes. An emergent locomotion behavior resembling a slime mold was programmed with this material by using an abstract design model similar to mechanical systems. Dynamic properties, such as autonomous pattern generation and continuous polarized regeneration, enabled locomotion along the designated tracks against a constant flow. Furthermore, an emergent racing behavior of two locomotive bodies was achieved by expanding the program. Other applications, including pathogen detection and hybrid nanomaterials, illustrated further potential use of this material. Dynamic biomaterials powered by artificial metabolism could provide a previously unexplored route to realize "artificial" biological systems with regenerating and self-sustaining characteristics.

Designing a retrievable and scalable cell encapsulation device for potential treatment of type 1 diabetes.

Cell encapsulation has been shown to hold promise for effective, long-term treatment of type 1 diabetes (T1D). However, challenges remain for its clinical applications. For example, there is an unmet need for an encapsulation system that is capable of delivering sufficient cell mass while still allowing convenient retrieval or replacement. Here, we report a simple cell encapsulation design that is readily scalable and conveniently retrievable. The key to this design was to engineer a highly wettable, Ca2+-releasing nanoporous polymer thread that promoted uniform in situ cross-linking and strong adhesion of a thin layer of alginate hydrogel around the thread. The device provided immunoprotection of rat islets in immunocompetent C57BL/6 mice in a short-term (1-mo) study, similar to neat alginate fibers. However, the mechanical property of the device, critical for handling and retrieval, was much more robust than the neat alginate fibers due to the reinforcement of the central thread. It also had facile mass transfer due to the short diffusion distance. We demonstrated the therapeutic potential of the device through the correction of chemically induced diabetes in C57BL/6 mice using rat islets for 3 mo as well as in immunodeficient SCID-Beige mice using human islets for 4 mo. We further showed, as a proof of concept, the scalability and retrievability in dogs. After 1 mo of implantation in dogs, the device could be rapidly retrieved through a minimally invasive laparoscopic procedure. This encapsulation device may contribute to a cellular therapy for T1D because of its retrievability and scale-up potential.

High-water-content and resilient PEG-containing hydrogels with low fibrotic response.

Hydrogels such as those based on polyethylene glycol (PEG) are broadly used in biomedicine where high water contents, robust mechanical properties such as resilience and favorable interactions with the body are often simultaneously desirable. However, the mechanical properties of conventional hydrogels often degrade rapidly after swelling or with increasing water content, limiting their potential in many applications. Here we describe a new class of PEG-containing hydrogels that remain highly resilient after maximum swelling. We achieved the hydrogels by incorporating reversible "dual" hydrogen bonding into highly coiled, elastic PEG networks. These hydrogels, due to their high water content and high mechanical resilience, can form highly permeable, yet durable and easy-to-handle cell delivery devices without any additional structural support. In addition, optimization of chemical composition resulted in hydrogels with superior bio-inertness, inducing much less fibrosis upon subcutaneous implantation in mice than a polyhydroxyethylmethacrylate (PHEMA) hydrogel control. STATEMENT OF SIGNIFICANCE: Hydrogels such as polyethylene glycol (PEG)-based ones are broadly used in the biomedical world. Examples include wound dressings, tissue scaffolds, medical implants, biosensors and drug or cell delivery devices. In many of these applications, robust mechanical property, high water content (or facile mass transfer) and favorable interactions with the body are often simultaneously desirable. However, the mechanical property of hydrogels often degrades rapidly after swelling or with increasing water content. Here we report a new class of PEG-based hydrogels that simultaneously possess high water content, high mechanical resilience and low fibrotic response upon subcutaneous implantation in mice. These hydrogels may therefore find broad applications in biomedicine.

Dynamic self-organization of microwell-aggregated cellular mixtures.

Cells with different cohesive properties self-assemble in a spatiotemporal and context-dependent manner. Previous studies on cell self-organization mainly focused on the spontaneous structural development within a short period of time during which the cell numbers remained constant. However the effect of cell proliferation over time on the self-organization of cells is largely unexplored. Here, we studied the spatiotemporal dynamics of self-organization of a co-culture of MDA-MB-231 and MCF10A cells seeded in a well defined space (i.e. non-adherent microfabricated wells). When cell-growth was chemically inhibited, high cohesive MCF10A cells formed a core surrounded by low cohesive MDA-MB-231 cells on the periphery, consistent with the differential adhesion hypothesis (DAH). Interestingly, this aggregate morphology was completely inverted when the cells were free to grow. At an initial seeding ratio of 1 : 1 (MDA-MB-231 : MCF10A), the fast growing MCF10A cells segregated in the periphery while the slow growing MDA-MB-231 cells stayed in the core. Another morphology developed at an inequal seeding ratio (4 : 1), that is, the cell mixtures developed a side-by-side aggregate morphology. We conclude that the cell self-organization depends not only on the cell cohesive properties but also on the cell seeding ratio and proliferation. Furthermore, by taking advantage of the cell self-organization, we purified human embryonic stem cells-derived pancreatic progenitors (hESCs-PPs) from co-cultured feeder cells without using any additional tools or labels.

Detection of outer membrane vesicles in Synechocystis PCC 6803.

It has been well established that many species of Gram-negative bacteria release nanoscale outer membrane vesicles (OMVs) during normal growth. Furthermore, the roles of these structures in heterotrophic bacteria have been extensively characterized. However, little is known about the existence or function of OMVs in photoautotrophs. In the present study, we report for the first time the production of OMVs by the model photosynthetic organism Synechocystis sp. PCC 6803, a species of biotechnological importance. We detected extracellular proteins and lipids in cell-free supernatants derived from Synechocystis culture, yet the cytoplasmic and thylakoid membrane markers NADH oxidase and chlorophyll were absent. This indicated that the extracellular proteins and lipids derived from the outer membrane, and not from cell lysis. Furthermore, we identified spherical structures within the expected size range of OMVs in Synechocystis culture using scanning electron microscopy. Taken together, these results suggest that the repertoire of Gram-negative bacteria that are known to produce OMVs may be expanded to include Synechocystis PCC6803. Because of the considerable genetic characterization of Synechocystis in particular, our discovery has the potential to support novel biotechnological applications as well.