Biostability of micro-photodiode arrays for subretinal implantation

The use of an axisymmetric formulation of the Finite Volume Method for the thermal analysis of the retina and ocular tissues following implantation of retinal prosthesis

“…The present simulation values used general data available in literature (Hämmerle et al, 2002;Clements et al, 1999).…”

“…After 6 months, the passivation layer becomes very thin due to chemical degradation and after 12 months a considerable damage to the silicon is observed, while the electrodes do not show any detectable sign of morphological damage (Hämmerle et al, 2002).…”

“…For the subretinal device, we used the values obtained by Hämmerle et al (2002). The chip diameter was 3 mm and its thickness was 70 µm.…”

Ion Leaching from Implantable Medical Devices

“…These thin coatings must not leach toxic elements or compounds into the body and prevent the saline environment from affecting the electrical performance over decades of service life. As an example of where there are unanticipated differences between in-vivo and in-vitro testing, test data indicates silica coatings (frequently used as passivation materials on consumer electronics) are more rapidly dissolved in-vivo than in-vitro in 0.9 wt% saline compared with material that had been implanted in an animal [11]- [13]. 1 has an in-vivo dissolution rate of 600 to 1000 nm per year; whereas no significant damage (<90 nm/yr) 2 was found on in-vitro 3 exposed chips that had been immersed in saline for up to 21 months.…”

“…1 has an in-vivo dissolution rate of 600 to 1000 nm per year; whereas no significant damage (<90 nm/yr) 2 was found on in-vitro 3 exposed chips that had been immersed in saline for up to 21 months. The silica layer had dissolved in-vivo 4 within 6 to 12 months, damaging the underlying silicon layer [11]. Rojahn et al, also comments on the work of Hämmerle et al, and cites Fromherz as further evidence of rapid dissolution of silica when exposed to brain tissue [13].…”