David J. Edell

Bio: David J. Edell is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Chemical vapor deposition & Thin film. The author has an hindex of 17, co-authored 22 publications receiving 2006 citations. Previous affiliations of David J. Edell include Harvard University.

Factors influencing the biocompatibility of insertable silicon microshafts in cerebral cortex

Abstract: Issues that determine the biocompatibility of insertable microelectrode arrays were investigated. Results from a limited number of tests indicated that there was minimal tissue response along the sides of the shafts when shafts were well sharpened, had sufficiently small tip angles, and were clean. Tissue was usually more reactive at the tips of the shafts. It was concluded that silicon microshafts of appropriate shaft and tip design were biocompatible along the sides of the shaft, but that relatively severe reactions could be anticipated at the tips. >

Method and apparatus for preferential neuron stimulation

Abstract: The invention provides a method for preferentially stimulating neural somas over neural axons located around the somas but not integral with the somas. In the invention, a positive electrical pulse is applied to a region of neural tissue consisting of one or more neural somas to be stimulated and neural axons, and due to the physiology of the somas, they are preferentially stimulated by the electrical pulse over the neural axons not integral with the somas to be stimulated. The preferential soma stimulation provided by the invention achieves the advantage of locally focusing external stimulation such that it may be directed to particular soma locations for indicating location-dependent sensory information. Thus the pulse scheme of the invention may be employed in prosthetic applications directed to, for example, the retinal ganglia neural tissue.

Chemical vapor deposition of fluorocarbon polymer thin films

Abstract: Provided are methods for forming a fluorocarbon polymer thin film on the surface of a structure. In one method, a monomer gas, preferably hexafluoropropylene oxide is exposed to a source of heat having a temperature sufficient to pyrolyze the monomer gas and produce a source of reactive CF2 species in the vicinity of the structure surface. The structure surface is maintained substantially at a temperature lower than that of the heat source to induce deposition and polymerization of the CF2 species on the structure surface. In another method a pulsed plasma is used to produce reactive CF2 species. The monomer gas pyrolysis and plasma excitation methods can be carried out individually, sequentially, or simultaneously. Flexible thin films can be produced on wires, twisted wires, neural probes, tubing, complex microstructures, substrates, microfabricated circuits, and other structures. The films have a compositional CF2 fraction of at least about 50 %, a dielectric constant of less than about 1.95, and a cross-linking density of less than about 35 %.

A Peripheral Nerve Information Transducer for Amputees: Long-Term Multichannel Recordings from Rabbit Peripheral Nerves

Abstract: A micromachined silicon technology is being developed for the purpose of sensing information from the stumps of amputated mammalian peripheral nerves. Information on long-term biocompatibility, anatomy, and physiology related to the structural design of this sensor is presented. Pertinent materials, fabrication, and surgical implantation issues are discussed. Noise, signal amplitude, and receptive field are considered as the prime determinants of the design of an appropriate electrode contact geometry for the structure. The selectivity of the device is also discussed in terms of the fine structure of the regenerated nerve. Examples of waveforms recorded from rabbit peripheral nerves using this sensor are presented and discussed in terms of electrical and physiological parameters. Possible use of the sensor as a source for a binary code suitable for communication of information to a computer is presented along with discussion of the limitations of the current technology and possible future applications.

Growth of fluorocarbon polymer thin films with high CF2 fractions and low dangling bond concentrations by thermal chemical vapor deposition

Abstract: Thermal chemical vapor deposition was used to deposit fluorocarbon films with chemical resemblance to bulk polytetrafluoroethylene. X‐ray photoelectron spectroscopy revealed that the films deposited from thermal decomposition of hexafluoropropylene oxide had fluorine to carbon ratios of 2.0 and CF2 fractions of 90% along with 10% of CF3 and CF moieties. Electron spin resonance results found the dangling bond density to be 1.2×1018 spins/cm3, low compared to conventional plasma polymerized films. Low dangling bond densities were achieved by using a clean source of CF2 in the absence of plasma source.

Neural stimulation and recording electrodes.

Abstract: Electrical stimulation of nerve tissue and recording of neural electrical activity are the basis of emerging prostheses and treatments for spinal cord injury, stroke, sensory deficits, and neurological disorders. An understanding of the electrochemical mechanisms underlying the behavior of neural stimulation and recording electrodes is important for the development of chronically implanted devices, particularly those employing large numbers of microelectrodes. For stimulation, materials that support charge injection by capacitive and faradaic mechanisms are available. These include titanium nitride, platinum, and iridium oxide, each with certain advantages and limitations. The use of charge-balanced waveforms and maximum electrochemical potential excursions as criteria for reversible charge injection with these electrode materials are described and critiqued. Techniques for characterizing electrochemical properties relevant to stimulation and recording are described with examples of differences in the in vitro and in vivo response of electrodes.

Low dielectric constant materials for microelectronics

Abstract: The ever increasing requirements for electrical performance of on-chip wiring has driven three major technological advances in recent years. First, copper has replaced Aluminum as the new interconnect metal of choice, forcing also the introduction of damascene processing. Second, alternatives for SiO2 with a lower dielectric constant are being developed and introduced in main stream processing. The many new resulting materials needs to be classified in terms of their materials characteristics, evaluated in terms of their properties, and tested for process compatibility. Third, in an attempt to lower the dielectric constant even more, porosity is being introduced into these new materials. The study of processes such as plasma interactions and swelling in liquid media now becomes critical. Furthermore, pore sealing and the deposition of a thin continuous copper diffusion barrier on a porous dielectric are of prime importance. This review is an attempt to give an overview of the classification, the character...

Plasma-surface modification of biomaterials

Abstract: Plasma-surface modification (PSM) is an effective and economical surface treatment technique for many materials and of growing interests in biomedical engineering This article reviews the various common plasma techniques and experimental methods as applied to biomedical materials research, such as plasma sputtering and etching, plasma implantation, plasma deposition, plasma polymerization, laser plasma deposition, plasma spraying, and so on The unique advantage of plasma modification is that the surface properties and biocompatibility can be enhanced selectively while the bulk attributes of the materials remain unchanged Existing materials can, thus, be used and needs for new classes of materials may be obviated thereby shortening the time to develop novel and better biomedical devices Recent work has spurred a number of very interesting applications in the biomedical field This review article concentrates upon the current status of these techniques, new applications, and achievements pertaining to biomedical materials research Examples described include hard tissue replacements, blood contacting prostheses, ophthalmic devices, and other products