Biofriendly bonding processes for nanoporous implantable SU-8 microcapsules for encapsulated cell therapy

Cell microencapsulation with synthetic polymers

The encapsulation of cells into polymeric microspheres or microcapsules has permitted the transplantation of cells into human and animal subjects without the need for immunosuppressants. Cell-based therapies use donor cells to provide sustained release of a therapeutic product, such as insulin, and have shown promise in treating a variety of diseases. Immunoisolation of these cells via microencapsulation is a hotly investigated field, and the preferred material of choice has been alginate, a natural polymer derived from seaweed due to its gelling conditions. Although many natural polymers tend to gel in conditions favorable to mammalian cell encapsulation, there remain challenges such as batch to batch variability and residual components from the original source that can lead to an immune response when implanted into a recipient. Synthetic materials have the potential to avoid these issues; however, historically they have required harsh polymerization conditions that are not favorable to mammalian cells. As research into microencapsulation grows, more investigators are exploring methods to microencapsulate cells into synthetic polymers. This review describes a variety of synthetic polymers used to microencapsulate cells.

In vitro and in vivo evaluation of SU-8 biocompatibility

SU-8 negative photoresist is a high tensile strength polymer that has been used for a number of biomedical applications that include cell encapsulation and neuronal probes. Chemically, SU-8 comprises, among other components, an epoxy based monomer and antimony salts, the latter being a potential source of cytotoxicity. We report on the in vitro and in vivo evaluation of SU-8 biocompatibility based on leachates from various solvents, at varying temperatures and pH, and upon subcutaneous implantation of SU-8 substrates in mice. MTT cell viability assay did not exhibit any cytotoxic effects from the leachates. The hemolytic activity of SU-8 is comparable to that of FDA approved implant materials such as silicone elastomer, Buna-S and medical steel. In vivo histocompatibility study in mice indicates a muted immune response to subcutaneous SU-8 implants.

Applications of Semiconductor Fabrication Methods to Nanomedicine: A Review of Recent Inventions and Techniques

We live in a world of convergence where scientific techniques from a variety of seemingly disparate fields are being applied cohesively to the study and solution of biomedical problems. For instance, the semiconductor processing field has been primarily developed to cater to the needs of the ever decreasing transistor size and cost while increasing functionality of electronic circuits. In recent years, pioneers in this field have equipped themselves with a powerful understanding of how the same techniques can be applied in the biomedical field to develop new and efficient systems for the diagnosis, analysis and treatment of various conditions in the human body. In this paper, we review the major inventions and experimental methods which have been developed for nano/micro fluidic channels, nanoparticles fabricated by top-down methods, and in-vivo nanoporous microcages for effective drug delivery. This paper focuses on the information contained in patents as well as the corresponding technical publications. The goal of the paper is to help emerging scientists understand and improvise over these inventions.

Epoxy insulated carbon fiber and carbon nanotube fiber microelectrodes

Carbon-fiber microelectrodes (CFMEs) are typically constructed from glass capillaries pulled to a fine taper or from a polyimide-coated capillary that is 90 μm in outer diameter. Here, a new fabrication method is developed to insulate carbon-fiber microelectrodes with a thin epoxy coating. A polytetrafluoroethylene (Teflon) mold was laser etched with channels 30-40 μm deep and wide and each channel filled with Armstrong C7 epoxy. A carbon fiber was laid into each channel so that the fiber extended past the mold, and the epoxy cured in an oven. One end of the fiber was trimmed to about 100 μm to form a cylindrical carbon-fiber microelectrode, while the other end was attached to a pin and connected to a potentiostat. Epoxy-insulated electrodes were tested with fast-scan cyclic voltammetry. For dopamine, the sensitivity is similar to glass and polyimide-coated capillary electrodes with a linear range of 0.1 to 10 μM and a LOD of 24 nM. SU-8 epoxy was tested as an alternative insulator because it cures at a lower temperature using light, but it was more brittle. Carbon nanotube fibers were also successfully insulated with epoxy. Epoxy- insulated CFMEs were used to detect stimulated dopamine release in vivo. Epoxy-insulated electrodes are smaller in diameter than polyimide-coated capillary electrodes and amenable to mass production. They are advantageous for use in higher order mammals, where glass is not permitted, and with alternative electrode materials, such as carbon nanotube fibers, that cannot be fabricated in a capillary puller.