The goal of this work was to evaluate tissue-device interactions due to\r\nimplantation of a mechanically operated drug delivery system onto the posterior sclera.\r\nTwo test devices were designed and fabricated to model elements of the drug delivery\r\ndeviceââ?¬â?one containing a free-spinning ball bearing and the other encasing two articulating\r\ngears. Openings in the base of test devices modeled ports for drug passage from device to\r\nsclera. Porous poly(tetrafluoroethylene) (PTFE) membranes were attached to half of the\r\ngear devices to minimize tissue ingrowth through these ports. Test devices were sutured\r\nonto rabbit eyes for 10 weeks. Tissue-device interactions were evaluated histologically and\r\nmechanically after removal to determine effects on device function and changes in\r\nsurrounding tissue. Test devices were generally well-tolerated during residence in the\r\nanimal. All devices encouraged fibrous tissue formation between the sclera and the device,\r\nfibrous tissue encapsulation and invasion around the device, and inflammation of the\r\nconjunctiva. Gear devices encouraged significantly greater inflammation in all cases and a\r\nlarger rate of tissue ingrowth. PTFE membranes prevented tissue invasion through the\r\ncovered drug ports, though tissue migrated in through other smaller openings. The torque\r\nrequired to turn the mechanical elements increased over 1000 times for gear devices, but\r\nonly on the order of 100 times for membrane-covered gear devices and less than 100 times\r\nfor ball bearing devices. Maintaining a lower device profile, minimizing microscale motion on the eye surface and covering drug ports with a porous membrane may minimize\r\ninflammation, decreasing the risk of damage to surrounding tissues and minimizing\r\ndisruption of device operation.
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