Reactive Amine Functionalized Microelectrode Arrays Provide Short-Term Benefit but Long-Term Detriment to In Vivo Recording Performance

Intracortical microelectrode arrays (MEAs) are used for recording neural signals. However, indwelling devices result in chronic neuroinflammation, which leads to decreased recording performance through degradation of the device and surrounding tissue. Coating the MEAs with bioactive molecules is being explored to mitigate neuroinflammation. Such approaches often require an intermediate functionalization step such as (3-aminopropyl)triethoxysilane (APTES), which serves as a linker. However, the standalone effect of this intermediate step has not been previously characterized. Here, we investigated the effect of coating MEAs with APTES by comparing APTES-coated to uncoated controls in vivo and ex vivo. First, we measured water contact angles between silicon uncoated and APTES-coated substrates to verify the hydrophilic characteristics of the APTES coating. Next, we implanted MEAs in the motor cortex (M1) of Sprague-Dawley rats with uncoated or APTES-coated devices. We assessed changes in the electrochemical impedance and neural recording performance over a chronic implantation period of 16 weeks. Additionally, histology and bulk gene expression were analyzed to understand further the reactive tissue changes arising from the coating. Results showed that APTES increased the hydrophilicity of the devices and decreased electrochemical impedance at 1 kHz. APTES coatings proved detrimental to the recording performance, as shown by a constant decay up to 16 weeks postimplantation. Bulk gene analysis showed differential changes in gene expression between groups that were inconclusive with regard to the long-term effect on neuronal tissue. Together, these results suggest that APTES coatings are ultimately detrimental to chronic neural recordings. Furthermore, interpretations of studies using APTES as a functionalization step should consider the potential consequences if the final functionalization step is incomplete.

An evaluation of diabetic and pseudodiabetic glomerulosclerosis

Diabetic glomerulosclerosis must be either a primary manifestation or a secondary consequence of the metabolic abnormalities of diabetes. Several earlier reports have attempted to support the former hypothesis by describing cases of pathognomonic renal lesions in nondiabetic subjects; however, the clinical and pathologic data in these reports are inconclusive. We have reviewed our experience at the University of Virginia Hospital with 447 percutaneous renal biopsies performed over a period of four years from July 1973 through July 1977. Of these cases, only two appeared to represent diabetic glomerulosclerosis occurring in nondiabetic subjects. Upon further investigation, one case provided to be light chain disease demonstrated by immunofluorescence staining. The other case, on repeat renal biopsy, proved to be membranoproliferative glomerulonephritis. We conclude that a diagnosis of diabetic glomerulosclerosis must be viewed with suspicion in nondiabetic subjects. Suspected cases should be labeled pseudodiabetic glomerulosclerosis and investigated further.