title: Biocompatibility of a polymer based on Off-Stoichiometry Thiol-Enes + Epoxy (OSTE+) for neural implants.
abstract: BACKGROUND
  The flexibility of implantable neural probes has increased during the last 10 years, starting with stiff materials such as silicone to more flexible materials like polyimide. We have developed a novel polymer based on Off-Stoichiometry Thiol-Enes + Epoxy (OSTE+, consisting of a thiol, two allyls, an epoxy resin and two initiators), which is up to 100 times more flexible than polyimide. Since a flexible neural probe should be more biocompatible than a stiff probe, an OSTE+ probe should be more biocompatible than one composed of a more rigid material. We have investigated the toxicity of OSTE+ as well as of OSTE+ that had been incubated in water for a week (OSTE+H2O) using MTT assays with mouse L929 fibroblasts. We found that OSTE+ showed cytotoxicity, but OSTE+H2O did not. Extracts were analyzed using LC-MS and GC-MS in order to identify leaked chemicals.
  
  
  RESULTS
  Most constituents were found in extracts of OSTE+, whereas only initiators were found in OSTE+H2O extracts. The detected levels of each chemical found in the LC-MS and the GC-MS analysis were below the toxicity level when compared to MTT assays of all the individual chemicals, except for one of the initiators that had an IC50 value close to the detected levels.
  
  
  CONCLUSIONS
  Our notion is that the toxicity of OSTE+ was caused by one of the initiators, by impurities in the constituents or by synergistic effects of low doses of leaked chemicals. However, our conclusion is that if OSTE+ is incubated for one week in water, OSTE+ is not cytotoxic and suitable for further in vivo studies.
authors.affiliation: Department of Biomedical Engineering, Lund University, Box 118, Lund, 221 00 Sweden ; NeuroNano Research Centre, Lund University, Medicon Village, Scheelevägen 8, Lund, 223 81 Sweden.
authors.forename: Fredrik
authors.initials: F
authors.lastname: Ejserholm
authors.affiliation: Department of Laboratory Medicine, Lund University, Box 118, Lund, 221 00 Sweden ; Department of Biology, Lund University, Box 118, Lund, 221 00 Sweden.
authors.forename: John
authors.initials: J
authors.lastname: Stegmayr
authors.affiliation: Department of Biology, Lund University, Box 118, Lund, 221 00 Sweden.
authors.forename: Patrik
authors.initials: P
authors.lastname: Bauer
authors.affiliation: NeuroNano Research Centre, Lund University, Medicon Village, Scheelevägen 8, Lund, 223 81 Sweden ; Department of Biology, Lund University, Box 118, Lund, 221 00 Sweden.
authors.forename: Fredrik
authors.initials: F
authors.lastname: Johansson
authors.affiliation: Department of Biomedical Engineering, Lund University, Box 118, Lund, 221 00 Sweden ; NeuroNano Research Centre, Lund University, Medicon Village, Scheelevägen 8, Lund, 223 81 Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Wallman
authors.affiliation: Department of Biomedical Engineering, Lund University, Box 118, Lund, 221 00 Sweden ; NeuroNano Research Centre, Lund University, Medicon Village, Scheelevägen 8, Lund, 223 81 Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Bengtsson
authors.affiliation: Department of Biology, Lund University, Box 118, Lund, 221 00 Sweden.
authors.forename: Stina
authors.initials: S
authors.lastname: Oredsson
keywords: Biocompatibility; In Vitro toxicity; LC-MS; Neural implant; Off-Stoichiometry Thiol-Enes + EpoxyOSTE+; Polymer