Abstract

FR.10.02

Concept of a pressure-controlled microstent for glaucoma therapy

Wolfram Schmidt1, Christine Schultze1, Diana Buß2, Ulrike Ruppin1, Oliver Stachs2, Marian Löbler1, Katrin Sternberg1, Boris Chichkov3, Rudolf Guthoff2, Klaus-Peter Schmitz1
1Institut für Biomedizinische Technik, Universität Rostock, Rostock, 2Universitäts-Augenklinik Rostock, 3Department of Nanotechnology, Laserzentrum Hannover e.V., Hannover

Objective
A pressure-controlled microstent shall permanently normalize the intraocular pressure (IOP) for open-angle glaucoma therapy by drainage into the suprachoroidal space. The complex requirements ask for new technical solutions as well as for an improved understanding of specific cell-biological processes at the implant’s surface to develop effective local-drug-delivery (LDD) concepts and surface modifications.
Methods
Fluid-mechanical requirements were derived from physiological data and the analysis of commercial glaucoma implants. Technological basics for the production of suitable structures are refined ultra-short-pulse laser technology and 2-photon polymerisation (2PP).
All known glaucoma implants induce unwanted cell proliferation resulting in loss of function. It is assumed that the activity of fibroblasts is low in the suprachoroidal space. However, it was seen that LDD concepts are required to control cell proliferation. Fibroblasts from sclera and choroidea were isolated und cultured as the most relevant cell types for in vitro investigation. Potential materials and drugs were investigated by cell viability tests for biocompatibility or suppression of cell viability.
Results
The fluidmechanical analysis leads to smallest stent lumina (ID=50 µm) at anatomical suitable implant lengths (7-10mm). Only pressure control can manage the individual conditions with changing IOP.
Finite-Element analysis of valves showed the need for highly flexible structures. This can be achieved by combining basic structures with micromechanically active valves added by 2PP.
The polymers P(3HB) and P(4HB) show perfect in vitro and in vivo biocompatibility. Ormocers which are best suited for 2PP are also highly biocompatible. The antiproliferative drug Triamcinolon Acetonid opens a wide therapeutic window to impair fibroblast growth without affecting the growth of cornea keratocytes.
The surgical procedure was established by implantation of P(3HB) and P(4HB) drainage tubes in rabbit eyes connecting the anterior chamber with the suprachoroidal space. Highly flexible implants are required for correct placement within the eye.
Conclusions
The new concept of the microstent combines biomechanical approaches, technologies for micro-fabrication and current LDD concepts and opens new perspectives for glaucoma therapy.

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