Electrically mediated neuronal guidance with applied alternating current electric fields.

Applied electric fields (EFs) have previously been presented as a potential method of inducing functional recovery after neural trauma. To date, most of this research has focused on the application of a direct current (DC) stimulus to produce the desired EF and induce neuronal growth. We propose that high duty-cycle alternating current (AC) stimulation is capable of inducing similar EFs within the spinal cord and eliciting a neural response with the added benefits of increased field propagation and lower power consumption. Through ex vivo tissue testing of porcine spinal columns and Xenopus laevis cell cultures, 80% duty-cycle AC stimulation was compared to DC stimulation for efficacy in field generation and induction of neurite growth. Results from ex vivo measurement show that AC stimulation is capable of producing EFs of greater magnitudes over an increased distance in the spinal cord than DC stimulation at the same current magnitude. Furthermore, stimulation of Xenopus laevis neuronal cultures with 80% duty-cycle rectangular waves indicated a significant increase in neurite length as compared to non-stimulated controls and cathodal preference, growth that was statistically similar to DC-stimulated cells. These results suggest high duty-cycle stimulation modalities to be applicable and perhaps preferable to DC stimulation in electrically mediated neuronal therapies.

Effects of a synthetic bioactive peptide on neurite growth and nerve growth factor release in chondroitin sulfate hydrogels.

Previous work has revealed robust dorsal root ganglia neurite growth in hydrogels of chondroitin sulfate. In the current work, it was determined whether addition of a synthetic bioactive peptide could augment neurite growth in these matrices via enhanced binding and sequestering of growth factors. Fluorescence recovery after photobleaching studies revealed that addition of peptide slowed nerve growth factor diffusivity in chondroitin sulfate gels, but not in control gels of hyaluronic acid. Furthermore, cultures of chick dorsal root ganglia in gels of hyaluronic acid or chondroitin sulfate revealed enhanced growth in chondroitin sulfate gels only upon addition of peptide. Taken together, these results suggest a synergistic nerve growth factor-binding activity between this peptide and chondroitin sulfate.

Preliminary characterization of a glucose-sensitive hydrogel.

We present proof-of-concept studies that display the potential for using a glucose-sensitive hydrogel as a continuous glucose sensor. A study to characterize the swelling ratio of the hydrogel at normal physiological and pathological hyperglycemic glucose levels was performed. The hydrogel exposed to the hyperglycemic glucose solution had a higher equilibrium swelling ratio than the hydrogel exposed to the normal glucose concentration solution. The diffusivity of a small molecule, fluorescein isothiocyanate (FITC), through a hydrogel exposed to a hyperglycemic solution was determined using fluorescence recovery after photobleaching (FRAP). The diffusivity was found to be 4.2 × 10(-14) m(2)/s, a value approximately four orders of magnitude smaller than the diffusivity of FITC in glucose solution. The permeability of the hydrogel after equilibration in a hyperglycemic solution was found to be 5.1 × 10(-17) m(2), in the range of 2-4% agarose gels.

Toward an implantable wireless cardiac monitoring platform integrated with an FDA-approved cardiovascular stent.

Continuous monitoring of blood pressure from a minimally invasive device in the pulmonary artery can serve as a diagnostic and early warning system for cardiac health. The foremost challenge in such a device is the wireless transfer of data and power from within the blood vessel to an external device while maintaining unrestricted flow through the artery. We present a miniaturized system, which is attached to the outer surface of a regular or drug-eluting FDA-approved stent. When expanded, the stent maintains a patent vessel lumen while allowing contact between the electronic sensors and the blood supply. The stent-based antenna can be used for both wireless telemetry and power transfer for the implanted electronics. Using the stent platform as both a radiating antenna and a structural support allows us to take advantage of an FDA-approved device whose safety and surgical procedure are well established. The electronics package has been reduced to an area of less than 1 mm(2), with a thickness under 300 mum. A minimally invasive implantation procedure allows the delivery of the stent-based implant in nearly any major vessel of the body. This article describes an initial prototype with two stents configured as a single dipole, a 2.4-GHz transmitter microchip, and a battery, and validates transcutaneous transmission through ex vivo and in vivo porcine studies. The results demonstrate the feasibility of a stent-based wireless platform for continuous monitoring of blood pressure.