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2. Fabricating Complex Culture Substrates Using Robotic Microcontact Printing (R-µCP) and Sequential Nucleophilic Substitution

Author

Knight, Gavin T., Klann, Tyler, McNulty, Jason D., and Ashton, Randolph S.

Subjects
Tissue Culture Techniques, Tissue Engineering, technology, industry, and agriculture, Printing, Bioengineering, Robotics, Polyethylene Glycols
Abstract

In tissue engineering, it is desirable to exhibit spatial control of tissue morphology and cell fate in culture on the micron scale. Culture substrates presenting grafted poly(ethylene glycol) (PEG) brushes can be used to achieve this task by creating microscale, non-fouling and cell adhesion resistant regions as well as regions where cells participate in biospecific interactions with covalently tethered ligands. To engineer complex tissues using such substrates, it will be necessary to sequentially pattern multiple PEG brushes functionalized to confer differential bioactivities and aligned in microscale orientations that mimic in vivo niches. Microcontact printing (μCP) is a versatile technique to pattern such grafted PEG brushes, but manual μCP cannot be performed with microscale precision. Thus, we combined advanced robotics with soft-lithography techniques and emerging surface chemistry reactions to develop a robotic microcontact printing (R-μCP)-assisted method for fabricating culture substrates with complex, microscale, and highly ordered patterns of PEG brushes presenting orthogonal 'click' chemistries. Here, we describe in detail the workflow to manufacture such substrates.

Published
2014

5. Comparative study of chemical and physical foaming methods for injection-molded thermoplastic polyurethane.

Author

Kharbas, Hrishikesh A., McNulty, Jason D., Ellingham, Thomas, Thompson, Cyrus, Manitiu, Mihai, Scholz, Guenter, and Turng, Lih-Sheng

Subjects
*URETHANE foam manufacturing, *THERMOPLASTIC composites, *POLYURETHANES, *SURFACE active agents, *SUPERCRITICAL fluid chromatography
Abstract

Thermoplastic polyurethane is one of the most versatile thermoplastic materials being used in a myriad of industrial and commercial applications. Thermoplastic polyurethane foams are finding new applications in various industries including the furniture, automotive, sportswear, and packaging industries because of their easy processability and desirable customizable properties. In this study, three methods of manufacturing injection molded low density foams were investigated and compared: (1) using chemical blowing agents, (2) using microcellular injection molding with N2 as the blowing agent, and (3) using a combination of supercritical gas-laden pellets injection molding foaming technology and microcellular injection molding processes using co-blowing agents CO2 and N2. Thermal, rheological, microscopic imaging, and mechanical testing were carried out on the molded samples with increasing amounts of blowing agents. The results showed that the use of physical blowing agents yielded softer foams, while the use of CO2 and N2 as co-blowing agents helped to manufacture foams with lower bulk densities, better microstructures, and lower hysteresis loss ratios. Chemical blowing agent-foamed thermoplastic polyurethane showed an earlier onset of degradation. The average cell size decreased and the cell density increased with the use of co-blowing agents. A further increase in gas saturation levels showed a degradation of microstructure by cell coalescence. [ABSTRACT FROM AUTHOR]

Published
2017
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