A rapidly formed supramolecular polypeptide-DNA hydrogel was prepared and used for in situ multilayer three-dimensional bioprinting for the first time. By alternative deposition of two complementary bio-inks, designed structures can be printed. Based on their healing properties and high mechanical strengths, the printed structures are geometrically uniform without boundaries and can keep their shapes up to the millimeter scale without collapse. 3D cell printing was demonstrated to fabricate live-cell-containing structures with normal cellular functions. Together with the unique properties of biocompatibility, permeability, and biodegradability, the hydrogel becomes an ideal biomaterial for 3D bioprinting to produce designable 3D constructs for applications in tissue engineering.

A new electrocatalyst, palladium nanoparticle-single-walled carbon nanotube (Pd-SWNTs) hybrid nanostructure, for the nonenzymatic oxidation of glucose was developed and characterized by X-ray diffraction (XRD) and the transmission electron microscope (TEM). The hybrid nanostructures were prepared by depositing palladium nanoparticles with average diameters of 4-5 nm on the surface of single-walled carbon nanotubes (SWNTs) via chemical reduction of the precursor (Pd(2+)). The electrocatalyst showed good electrocatalytic activity toward the oxidation of glucose in the neutral phosphate buffer solution (PBS, pH 7.4) even in the presence of a high concentration of chloride ions. A nonenzymatic amperometric glucose sensor was developed with the use of the Pd-SWNT nanostructure as an electrocatalyst. The sensor had good electrocatalytic activity toward oxidation of glucose and exhibited a rapid response (ca.3 s), a low detection limit (0.2 +/- 0.05 microM), a wide and useful linear range (0.5-17 mM), and high sensitivity (approximately 160 microA mM(-1) cm(-2)) as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, uric acid, 4-acetamidophenol, 3,4-dihydroxyphenylacetic acid, and so forth did not cause any interference due to the use of a low detection potential (-0.35 V vs SCE). The sensor can also be used for quantification of the concentration of glucose in real clinical samples. Therefore, this work has demonstrated a simple and effective sensing platform for nonenzymatic detection of glucose.

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We develop an enzyme-triggered permeable DNA hydrogel cover to envelop and release single cells in microwells. The porous structure of the DNA hydrogel allows nutrients and waste to pass through, leading to a cell viability as high as 98%. The design provides a general method to culture, monitor, and manipulate single cells, and has potential applications in cell patterning and studying cell communication.