Biocompatibility and biofouling of MEMS drug delivery devices
The biocompatibility and biofouling of the microfabrication materials for a MEMS drug delivery device have been evaluated. The in vivo inﬂammatory and wound healing response of MEMS drug delivery component materials, metallic gold, silicon nitride, silicon dioxide, silicon, and SU-8 photoresist, were evaluated using the cage implant system. Materials, placed into stainless-steel cages, were implanted subcutaneously in a rodent model. Exudates within the cage were sampled at 4, 7, 14, and 21 days, representative of the stages of the inﬂammatory response, and leukocyte concentrations (leukocytes/ml) were measured. Overall, the inﬂammatory responses elicited by these materials were not signiﬁcantly different than those for the empty cage controls over the duration of the study. The material surface cell density (macrophages or foreign body giant cells, FBGCs), an indicator of in vivo biofouling, was determined by scanning electron microscopy of materials explanted at 4, 7, 14, and 21 days.
A wide variety of devices are being developed that take advantage of the materials and processing tools of microfabrication for applications in medicine and biology . As a result of the advances made by the microelectronics industry, the advantage of such devices consist of their microsize potentials and the ability to be manufactured in high volume with low unit cost. However, devices such as biological microelectromechanical systems (BioMEMS), ion sensing ﬁeld effect transistors (ISFET) or silicon-based microelectrodes had performed well in vitro, but experienced signiﬁcant biofouling in vivo, over time [5–7]. Silicon-based MEMS technology is starting to impact the drug delivery ﬁeld with the development of microneedles  and immunoisolating biocapsules . Quantitative biocompatibility and biofouling data are needed to aid not only in device material selection for medical applications, but also to further understand the in vivo interactions between the emerging technology and the biological environment
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