Biomedical subjects

D R Kipke

Publications and source records attributed to D R Kipke.

5 recordsLinked to original sources

PubMed2001

Calcium alginate gel: a biocompatible and mechanically stable polymer for endovascular embolization.

The development and optimization of calcium alginate for potential use in endovascular occlusion was investigated by testing its in vitro and in vivo mechanical stability and biocompatibility. The compressive resistance, rheology, and polymer yield of reacted alginate, and the polymer viscosity of unreacted alginate, were assessed. Biocompatibility was tested by injecting calcium alginate into the kidney capsule of rats. The reactivity of alginates with various structures and levels of purity were compared visually and histologically. Results suggest that calcium alginate is a biocompatible and mechanically stable gel for endovascular applications. Purified alginates exhibited compressive strength of 22 kPa and above at 40% compression, with no significant loss in elasticity. Purified alginate strength was significantly higher than that of crude alginates (p < 0.08). Purified alginates also exhibited significantly lower tissue reaction than crude alginates (p < 0.05). Of the alginates tested, purified high guluronic acid alginates (PHG) exhibited optimal strength and polymer yield, increased biocompatibility, and decreased viscosity. Clinical embolization treatments may be improved with the development of stable and biocompatible polymers such as calcium alginate. Possible uses of improved endovascular polymers include treating arteriovenous malformations (AVMs), aneurysms, blood flow to tumors, and vascular hemorrhaging.

Alginates↗

PubMed2001

Flexible polyimide-based intracortical electrode arrays with bioactive capability.

The promise of advanced neuroprosthetic systems to significantly improve the quality of life for a segment of the deaf, blind, or paralyzed population hinges on the development of an efficacious, and safe, multichannel neural interface for the central nervous system. The candidate implantable device that is to provide such an interface must exceed a host of exacting design parameters. We present a thin-film, polyimide-based, multichannel intracortical Bio-MEMS interface manufactured with standard planar photo-lithographic CMOS-compatible techniques on 4-in silicon wafers. The use of polyimide provides a mechanically flexible substrate which can be manipulated into unique three-dimensional designs. Polyimide also provides an ideal surface for the selective attachment of various important bioactive species onto the device in order to encourage favorable long-term reactions at the tissue-electrode interface. Structures have an integrated polyimide cable providing efficient contact points for a high-density connector. This report details in vivo and in vitro device characterization of the biological, electrical and mechanical properties of these arrays. Results suggest that these arrays could be a candidate device for long-term neural implants.

Animals↗

PubMed1999

Long-term neural recording characteristics of wire microelectrode arrays implanted in cerebral cortex.

This paper describes a detailed protocol for obtaining chronic, multi-site unit recordings in cerebral cortex of awake animals for periods of three months or more. The protocol includes details for making relatively simple and inexpensive implantable multichannel electrodes that consist of arrays of separate microwires. The results reported in this paper suggest that a viable implant will have discriminable unit activity on about 80% of the electrodes, resulting in, on average, the simultaneous unit recording of upwards of 60 units during a daily recording session. The active electrodes during one recording session tend to remain active in subsequent recording sessions for several weeks. Using the methods described here, implants have been constructed which incorporate several different electrode materials, coatings, sizes, and electrode separation within a single array. These microwire electrode arrays provide the basic technology for obtaining unit recordings for several months. This provides a model system for studying biocompatibility of neural implants, which is a critical component for the development of neural implants that have an indefinite working span.

Action Potentials↗

PubMed1998

Mechanisms of the cochlear nucleus octopus cell's onset response: synaptic effectiveness and threshold.

Octopus cells are one of the principal cell types in the mammalian posteroventral cochlear nucleus. These cells respond to the onset of a toneburst with a precisely timed spike followed by little, if any, sustained activity. While experimental studies have partially characterized the cell, the mechanisms of this onset response are not well understood. The present study involved a model-based investigation that analyzed the responses of a compartmental model of the octopus cell in terms of synaptic effectiveness and dynamic spike threshold. The simulations demonstrate that properties of the onset response (first-spike latency, temporal precision of the first spike, and sustained firing rate) can be predicted from the values of these cell properties for a wide range of model configurations. These relationships were further analyzed through the development of mathematical expressions for synaptic effectiveness and dynamic spike threshold. This computational analysis resulted in a relatively simple explanation of the onset response, as well as predictions of the responses of octopus cells to nontonal, complex stimuli.

Auditory Perception↗

PubMed1991

Shared-stimulus driving and connectivity in groups of neurons in the dorsal cochlear nucleus.

Extracellular spike discharges were recorded from ensembles of up to five neurons simultaneously in the DCN of guinea pig using solid-state, thin-film, multichannel electrodes having up to five recording sites spanning up to 600 microns. Responses from 73 unit pairs were collected of which 54 had both units responding to pseudorandom wideband noise stimulation. Shared-stimulus driving was present in 78% (42/54) of the unit pairs and could be attributed to an overlap in their spectral sensitivities. Effective connectivity was indicated for 87% (47/54) of the unit pairs. Wideband noise proved more useful than tonebursts for investigating shared-stimulus driving and connectivity because it evoked widespread, but not overly synchronous, responses in the ensembles.

Acoustic Stimulation↗