Microfabricated Biocapsules Provide Short-Term Immunoisolation of Insulinoma Xenografts

This study examines the viability and functionality of two insulinoma cell lines, RIN (1048) and βTC6F7, encapsulated within microfabricated biocapsules. Surface and bulk micromachining are integrated in the biocapsule fabrication process, resulting in a diffusion membrane with uniform pore size distribution as well as mechanical and chemical stability, surrounded by an anisotropically-etched silicon wafer, which serves as the encapsulation cavity. Insulinoma cells (4500 cells/biocapsule) were enclosed within these microfabricated biocapsules and subjected to a static incubation study after either implantation in BALB-C mice or incubation in vitro. Examination of retrieved microfabricated biocapsules revealed an insulin stimulatory index of approximately 1.5 for encapsulated RIN cells and 3.6 for encapsulated βTC6F7 cells for biocapsules with 18 nm pore sized microfabricated membranes, similar to indices of biocapsules incubated in vitro. There was an 80% decrease in cell stimulatory response between in vitro and in vivo 66 nm-biocapsules as compared to 20% for 18 nm-biocapsules, indicating that the immunoisolatory effectiveness depends greatly on achieving uniform pore sizes in the size range of 18 nm or smaller. The present study demonstrates the feasibility of using microfabricated biocapsules for the immunoisolation of insulinoma cells lines. The microfabricated biocapsule may serve as an alternative to conventional polymeric based biocapsules for possible use as in vivo insulin secreting bioreactor.