Boron-Doped Nanocrystalline Diamond Electrodes for Neural Interfaces: In vivo Biocompatibility Evaluation.

Boron-doped nanocrystalline diamond (BDD) electrodes have recently attracted attention as materials for neural electrodes due to their superior physical and electrochemical properties, however their biocompatibility remains largely unexplored. In this work, we aim to investigate the in vivo biocompatibility of BDD electrodes in relation to conventional titanium nitride (TiN) electrodes using a rat subcutaneous implantation model. High quality BDD films were synthesized on electrodes intended for use as an implantable neurostimulation device. After implantation for 2 and 4 weeks, tissue sections adjacent to the electrodes were obtained for histological analysis. Both types of implants were contained in a thin fibrous encapsulation layer, the thickness of which decreased with time. Although the level of neovascularization around the implants was similar, BDD electrodes elicited significantly thinner fibrous capsules and a milder inflammatory reaction at both time points. These results suggest that BDD films may constitute an appropriate material to support stable performance of implantable neural electrodes over time.

Influence of fibrous encapsulation on electro-chemical properties of TiN electrodes.

The aim of this study was to investigate how the electrochemical properties of porous titanium nitride stimulation electrode are affected by fibrous encapsulation in vivo. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry and voltage transient (VT) measurements were performed in vivo and in phosphate buffered saline, where the encapsulation process is absent. EIS was used as a non-invasive measurement to follow the inflammation, healing and encapsulation process. EIS showed that the healing and encapsulation process lasted 3-4 weeks. The VTs increased during the first 3-4 weeks, after which they stabilized. The charge storage capacity (CSC) decreased most during the first 3-4 weeks. The increasing VTs and decreasing CSC during the first 3-4 weeks after implantation of the in vivo electrodes seem related to healing and fibrous encapsulation. It is suggested that the charge injection pathway during the encapsulation process changes, which implies that charge injection limits are underestimated with conventional methods.

Electrochemical properties of titanium nitride nerve stimulation electrodes: an in vitro and in vivo study.

The in vivo electrochemical behavior of titanium nitride (TiN) nerve stimulation electrodes was compared to their in vitro behavior for a period of 90 days. Ten electrodes were implanted in two Göttingen minipigs. Four of these were used for electrical stimulation and electrochemical measurements. Five electrodes were kept in Ringer's solution at 37.5°C, of which four were used for electrical stimulation and electrochemical measurements. The voltage transients measured in vivo were 13 times greater than in vitro at implantation and they continued to increase with time. The electrochemical properties in vivo and the tissue resistance (Rtissue) followed a similar trend with time. There was no consistent significant difference between the electrochemical properties of the in vivo and in vitro electrodes after the implanted period. The differences between the in vivo and in vitro electrodes during the implanted period show that the evaluation of electrochemical performance of implantable stimulation electrodes cannot be substituted with in vitro measurements. After the implanted period, however, the performance of the in vivo and in vitro electrodes in saline was similar. In addition, the changes observed over time during the post-implantation period regarding the electrochemical properties of the in vivo electrodes and Rtissue were similar, which indicates that these changes are due to the foreign body response to implantation.

Acute urodynamic effects of posterior tibial nerve stimulation on neurogenic detrusor overactivity in patients with MS.

OBJECTIVES: The aim of this study was to investigate whether acute electrical stimulation of the posterior tibial nerve could suppress detrusor contractions in multiple sclerosis (MS) patients with neurogenic detrusor overactivity. METHODS: Two successive slow-fill cystometries (16 ml/min) were carried out in eight MS patients with neurogenic detrusor overactivity. The first filling served as control without stimulation. In the second filling, electrical stimulation using needle electrodes was applied automatically to the posterior tibial nerve when the detrusor pressure exceeded 10 cm H(2)O. An additional filling in which the needle electrodes were replaced by surface electrodes was carried out in three patients. RESULTS: The control filling showed detrusor overactivity in eight patients, but electrical stimulation of the posterior tibial nerve failed to suppress detrusor contractions in all tested patients. CONCLUSIONS: Although neuromodulative effects may be obtained with therapeutic electrical stimulation of the posterior tibial nerve, no acute effects were demonstrated. For this reason, electrical stimulation of pudendal afferents remains the only option if acute suppression of a detrusor contraction is required.

Event driven electrical stimulation of the dorsal penile/clitoral nerve for management of neurogenic detrusor overactivity in multiple sclerosis.

AIMS: The aim of this study was to evaluate the effect of automatic event driven electrical stimulation on the dorsal penile/clitoral nerve for management of neurogenic detrusor overactivity in patients suffering from Multiple Sclerosis. METHODS: A total of 10 patients participated in the study. Detrusor pressure was recorded during physiological filling of the bladder and electrical stimulation was applied with surface electrodes whenever the detrusor pressure exceeded 10 cm H(2)O. RESULTS: In seven of the eight patients, where neurogenic detrusor overactivity was observed an average of 12 detrusor contractions could be inhibited by stimulation. In one patient, however, stimulation failed to inhibit the detrusor contractions. The average increase in bladder volume from first suppressed detrusor contraction until leakage was 94% (range: 22-366%). On average, the time from first suppressed contraction until leakage was 15 min and 50 sec (range: 4 min 58 sec-32 min 5 sec) with an average physiological filling rate of 8 ml/min. Urgency was effectively suppressed at the onset of stimulation. CONCLUSIONS: The results indicate that involuntary detrusor contractions in patients with multiple sclerosis can effectively be inhibited with event driven stimulation, hereby improving bladder capacity and reducing the number of incontinence episodes. However, the used method for detecting detrusor contractions is not suitable in a chronic setting and alternative techniques needs to be investigated if stimulation should be applied automatically.