Biomedical subjects

Patrick A Tresco

Publications and source records attributed to Patrick A Tresco.

At least 19 recordsLinked to original sources

PubMed2006

Acute microelectrode array implantation into human neocortex: preliminary technique and histological considerations.

OBJECT: Researchers at The Center for Neural Interfaces at the University of Utah have designed and produced a silicon-based high-density microelectrode array that has been used successfully in mammalian models. The authors investigate the ability to transfer array insertion techniques to humans and examine the acute response of human cortical tissue to array implantation. METHODS: Six patients who were scheduled to undergo temporal lobectomy surgery were enrolled in an Institutional Review Board-approved protocol. Before the patients underwent lateral temporal cortical resection, one or two high-density microelectrode arrays were implanted in each individual by using a pneumatic insertion device. Cortical tissue was then excised and preserved in formalin. The specimens were sectioned and stained for histological examination. Pneumatic insertion of a microelectrode array into human cortex in the operating room was feasible. There were no clinical complications associated with implantation and no evidence of significant insertion-related hemorrhage. Tissue responses ranged from mild cortical deformity to small focal hemorrhages several millimeters below the electrode tines. Based on initial results, the insertion device was modified. A footplate that mechanically isolates a small area of cortex and a calibrated micromanipulator were added to improve the reproducibility of insertion. CONCLUSIONS: A high-density microelectrode array designed to function as a direct cortical interface device can be implanted into human cortical tissue without acute clinical complications. Further modifications to the insertion device and array design are ongoing and future work will assess the functional significance of the tissue reactions observed.

Electrodes, Implanted↗

PubMed2006

Fabrication and characterization of permeable degradable poly(DL-lactide-co-glycolide) (PLGA) hollow fiber phase inversion membranes for use as nerve tract guidance channels.

Biodegradable permeable poly(DL-lactide-co-glycolide) (PLGA) hollow fiber membranes (HFMs) were fabricated using a wet phase inversion technique. By varying several parameters, such as the spinneret size, solvent and non-solvent pair, polymer concentration, flow rate, precipitation method, drop height, and small molecular pore-forming agents, PLGA HFMs with variable sizes, surface morphologies, porosities, and diffusive permeability were obtained. Under simulated physiological conditions in vitro, PLGA HFMs exhibited a degradation profile to accommodate nervous system regeneration and axonal outgrowth. While accelerated degradation resulted in substantial molecular weight loss starting at 2 weeks and loss of selective permeability at 3 weeks, PLGA HFMs maintained gross structural integrity in the first 4 weeks, followed by sharp weight loss at 6 weeks and complete disappearance at about 8 weeks. When compared to the raw PLGA material in a pellet form, which underwent heterogeneous degradation, the PLGA HFMs exhibited a homogeneous degradation where the surface and bulk degraded at approximately the same rate, and an overall lower degradation rate. Our results indicate that using a wet phase inversion technique, degradable HFMs with variable size, inner and outer surface morphologies, porosity, and permeability with potential applications for nerve tract guidance conduits can be fabricated.

Animals↗

PubMed2006

Effect of filament diameter and extracellular matrix molecule precoating on neurite outgrowth and Schwann cell behavior on multifilament entubulation bridging device in vitro.

At present there is no clinically effective treatment for injuries or pathological processes that disrupt the continuity of axons in the mature central nervous system. However, a number of studies suggest that a tremendous potential exists for developing biomaterial based therapies. In particular, biomaterials in the form of bridging substrates have been shown to support at least some level of axonal regeneration across the lesion site, but display a limited capacity for directing axons toward their targets. To improve the directionality and outgrowth rate of the axonal regeneration process, filaments and tubes appear promising, but the technology is far from optimized. As a step toward optimization, the influence of filament diameter and various extracellular matrix coatings on nerve regeneration was evaluated in this article using a dorsal root ganglion (DRG) explant model. An increasing pattern of alignment and outgrowth of neurites in the direction parallel the long axis of the packed filament bundles with decreasing filament diameters ranging from supracellular and beyond (500 to 100 mum), cellular (30 mum), down to subcellular size (5 mum) was observed. Such effects became most prominent on filament bundles with individual filament diameters in the range of cellular size and below (5 and 30 mum) where highly directional and robust neuronal outgrowth was achieved. In addition, laminin-coated filaments that approached the size of spinal axons support significantly longer regenerative outgrowth than similarly treated filaments of larger diameter, and exceed outgrowth distance on similarly sized filaments treated with fibronectin. These data suggested the feasibility of using a multifilament entubulation bridging device for supporting directional axonal regeneration.

Acrylic Resins↗

PubMed2005

Cyclic strain increases fibroblast proliferation, matrix accumulation, and elastic modulus of fibroblast-seeded polyurethane constructs.

Rapid induction of matrix production and mechanical strengthening is essential to the development of bio-artificial constructs for repair and replacement of load-bearing connective tissues. Toward this end, we describe the development of a mechanical bioreactor and its application to investigate the influence of cyclic strain on fibroblast proliferation, matrix accumulation, and the mechanical properties of fibroblast-seeded polyurethane constructs (FSPC). Human fibroblasts were cultured in 10% serum-containing conditions within three-dimensional, porous elastomeric substrates under static conditions and a model regime of cyclic strain (10% strain, 0.25 Hz, 8 h/day), with and without ascorbic acid supplementation. After one week, the combination of cyclic strain and ascorbic acid resulted in significantly increased construct elastic modulus (>110%) relative to either condition alone. In contrast, cyclic strain alone was sufficient to stimulate significant increases in fibroblast proliferation. Mechanical strengthening of FSPCs was accompanied by increased type I collagen and fibronectin matrix accumulation and distribution, and significantly increased gene expression for type I collagen, TGFbeta-1, and CTGF. These results suggest that strain-induced conditioning in vitro leads to mechanical strengthening of fibroblast/material constructs, most likely resulting from increased collagen matrix deposition, secondary to strain-induced increases in cytokine production.

Ascorbic Acid↗

PubMed2005

Response of brain tissue to chronically implanted neural electrodes.

Chronically implanted recording electrode arrays linked to prosthetics have the potential to make positive impacts on patients suffering from full or partial paralysis. Such arrays are implanted into the patient's cortical tissue and record extracellular potentials from nearby neurons, allowing the information encoded by the neuronal discharges to control external devices. While such systems perform well during acute recordings, they often fail to function reliably in clinically relevant chronic settings. Available evidence suggests that a major failure mode of electrode arrays is the brain tissue reaction against these implants, making the biocompatibility of implanted electrodes a primary concern in device design. This review presents the biological components and time course of the acute and chronic tissue reaction in brain tissue, analyses the brain tissue response of current electrode systems, and comments on the various material science and bioactive strategies undertaken by electrode designers to enhance electrode performance.

Animals↗

PubMed2005

A cell encapsulation device for studying soluble factor release from cells transplanted in the rat brain.

The transplantation of a variety of naturally occurring and genetically modified cell types has been shown to be an effective experimental method to achieve sustained delivery of therapeutic molecules to specific target areas in the brain. To acquire a better understanding of dosing, implant mechanism of action, and how certain cell types affect remodeling of central nervous system (CNS) tissue, a refillable cell encapsulation device was developed for introducing cells into the brain while keeping them physically isolated from contact with brain tissue with a semipermeable membrane. The stereotactically placed device consists of a hollow fiber membrane (HFM), a polyurethane grommet with watertight cap that snaps into a precisely drilled hole in the rat skull, and a removable cell-containing insert. The cell-containing insert can be introduced or removed in a time-dependent manner to study the influence of soluble factors released from transplanted cells. The study describes the device design and validates its utility using a well-established cell transplantation model of Parkinson's disease.

Animals↗

PubMed2005

Substrate curvature influences the direction of nerve outgrowth.

Nerve outgrowth in the developing nervous system utilizes a variety of attractive and repulsive molecules found in the extracellular environment. In addition, physical cues may play an important regulatory role in determining directional outgrowth of nervous tissue. Here, by culturing nerve cells on filamentous surfaces and measuring directional growth, we tested the hypothesis that substrate curvature is sufficient to influence the directional outgrowth of nerve cells. We found that the mean direction of neurite outgrowth aligned with the direction of minimum principle curvature, and the spatial variance in outgrowth direction was directly related to the maximum principle curvature. As substrate size approached the size of an axon, adherent neurons extended processes that followed the direction of the long axis of the substrate similar to what occurs during development along pioneering axons and radial glial fibers. A simple Boltzmann model describing the interplay between adhesion and bending stiffness of the nerve process was found to be in close agreement with the data suggesting that cell stiffness and substrate curvature can act together in a manner that is sufficient to direct nerve outgrowth in the absence of contrasting molecular cues. The study highlights the potential importance of cellular level geometry as a fidelity-enhancing cue in the developing and regenerating nervous system.

Animals↗

PubMed2005

Neuronal cell loss accompanies the brain tissue response to chronically implanted silicon microelectrode arrays.

Implantable silicon microelectrode array technology is a useful technique for obtaining high-density, high-spatial resolution sampling of neuronal activity within the brain and holds promise for a wide range of neuroprosthetic applications. One of the limitations of the current technology is inconsistent performance in long-term applications. Although the brain tissue response is believed to be a major cause of performance degradation, the precise mechanisms that lead to failure of recordings are unknown. We observed persistent ED1 immunoreactivity around implanted silicon microelectrode arrays implanted in adult rat cortex that was accompanied by a significant reduction in nerve fiber density and nerve cell bodies in the tissue immediately surrounding the implanted silicon microelectrode arrays. Persistent ED1 up-regulation and neuronal loss was not observed in microelectrode stab controls indicating that the phenotype did not result from the initial mechanical trauma of electrode implantation, but was associated with the foreign body response. In addition, we found that explanted electrodes were covered with ED1/MAC-1 immunoreactive cells and that the cells released MCP-1 and TNF-alpha under serum-free conditions in vitro. Our findings suggest a potential new mechanism for chronic recording failure that involves neuronal cell loss, which we speculate is caused by chronic inflammation at the microelectrode brain tissue interface.

Animals↗

PubMed2005

Impedance characterization of microarray recording electrodes in vitro.

The mechanisms underlying performance degradation of chronically implanted silicon microelectrode arrays in the central nervous system (CNS) remain unclear. Humoral and cellular components of the brain foreign body response were evaluated to determine whether their presence on the electrode surface results in increased electrical impedance. Iridium oxide microelectrode recording arrays were electrically characterized in saline, culture media with 10% fetal bovine serum, and coated with various CNS cell types isolated from rat brain. Electrochemical impedance spectroscopy and cyclic voltammetry were performed using a three-electrode system. Potential cycling caused an immediate decrease in electrical impedance, which increased with time toward precycling values, with the effect of cycling remaining significant for several days. The addition of serum caused a significant increase in impedance of up to 28% relative to the saline control. Microelectrodes coated with various cell types known to participate in the foreign body response caused a 20%-80% increase in impedance immediately after contact that remained constant or gradually increased for several weeks. Our findings suggest that the attachment of molecular and cellular species following microelectrode implantation into brain tissue likely contribute to increases in impedance, but do not appear sufficient to hinder recording performance.

Action Potentials↗

PubMed2004

Chronic response of adult rat brain tissue to implants anchored to the skull.

Using quantitative immunohistological methods, we examined the brain tissue response to hollow fiber membranes (HFMs) that were either implanted intraparenchymally, as in a cell encapsulation application, or were attached to the skull as in a biosensor application (transcranially). We found that the reaction surrounding transcranially implanted HFMs was significantly greater than that observed with intraparenchymally implanted materials including increases in immunoreactivity against GFAP, vimentin, ED-1 labeled macrophages and microglia, and several extracellular matrix proteins including collagen, fibronectin, and laminin. In general, these markers were elevated along the entire length of transcranially implanted HFMs extending into the adjacent parenchyma up to 0.5 mm from the implant interface. Intraparenchymal implants did not appear to have significant involvement of a fibroblastic component as suggested by a decreased expression of vimentin, fibronectin and collagen-type I at the implant tissue interface. The increase in tissue reactivity observed with transcranially implanted HFMs may be influenced by several mechanisms including chronic contact with the meninges and possibly motion of the device within brain tissue. Broadly speaking, our results suggest that any biomaterial, biosensor or device that is anchored to the skull and in chronic contact with meningeal tissue will have a higher level of tissue reactivity than the same material completely implanted within brain tissue.

Acrylic Resins↗

PubMed2004

Contact guidance induced organization of extracellular matrix.

The scarring response following injury to the central nervous system disrupts the anatomical organization of nervous tissue posing a barrier to the regeneration of axons. In the present study, using materials with nanometer level surface features we examined whether matrix organization could be controlled by engineering meningeal cell asymmetry. Following 5 days in culture, the organization of meningeal cells along with their cytoskeletal elements and extracellular matrix proteins was evaluated. Meningeal cell morphology was markedly affected by nanometer level substrate topography. Cell alignment increased with increasing surface roughness. In addition, linear arrays of extracellular matrix were expressed that appeared related to cellular orientation. When cultured on substrates with topographical features of less than 10 nm neither cells nor their extracellular matrix showed organizational asymmetry. However, as oriented surface roughness increased, cellular and matrix asymmetrical organization became more pronounced reaching a threshold at 345 nm. These results suggest that biomaterial surface topography or other methods of altering the orientation of cells may be used to engineer orientation into the secreted extracellular matrix and as such may be a potential strategy for developing organized cell-derived matrix as a bridging material for nerve repair or other regenerative applications.

Animals↗

PubMed2004

Design and validation of a bioreactor for engineering vocal fold tissues under combined tensile and vibrational stresses.

Criteria are outlined for the design of a bioreactor that can simulate the vibrational stresses in vocal fold movement during speech. Requirements are 0-1 mm amplitudes in the 20-200 Hz frequency range, a variable on-off stress regime, and maintenance of tissue viability over several days. The bioreactor uses dual drivers, one for low frequency (or static) strains, and another for high-frequencies vibrational strains. Response is linear at the driving end for an input of 0-5 V. The amplitude decreases linearly with frequency at constant input voltage, and the phase changes by nearly 180 degrees over the 20-200 Hz range. Human vocal fold fibroblasts were cultured in a polymer substrate and subjected to static and vibrational forces. The results indicate that vibratory strain alters the expression levels of many extracellular matrix-related genes, as well as the spatial distribution of cells and matrix.

Bioreactors↗

PubMed2004

Resorption rate and biocompatibility characteristics of two polyester ventilation tubes in a guinea pig model.

OBJECTIVES: Determine the resorption rate and biocompatibility characteristics of 2 polyester ventilation tubes, and to determine whether soap and water exposure accelerates polyester tube degradation. STUDY DESIGN AND SETTING: 50/50 poly (D, L-lactide-co-glycolide; PLGA-50) and poly (L-lactide; PLA) polymers were placed into the tympanic membranes of Hartley pigmented guinea pigs. Integrity of the tubes was determined by weekly otoscopic examination. Biocompatibility was assessed by comparing auditory brainstem response (ABR) thresholds and by examining tympanic membrane changes following tube resorption. Shah minigrommet ventilation tubes were used as controls. In the second portion of this study, implanted PLGA-50 and PLA tubes were exposed weekly to a mixture of soap and water (1:5) until complete resorption was observed. Biocompatibility was assessed by periodic ABR testing and tympanic membrane examination. RESULTS: The PLA tubes remained in the tympanic membrane for a longer period (63.2 +/- 19.3 days) than the PLGA-50 (18.8 +/- 8.1 days). The tympanic membrane and resorbable tube interface demonstrated equivalent findings for auditory thresholds and tissue histopathology at the implant site compared to nonresorbable controls. The resorption behavior was not altered by exposure to soap and water. Tympanic membranes of all animals following tube degradation and soap water exposure were intact with minimal scarring and no signs of persistent foreign body response. The histological analysis showed that implantation of resorbable tubes was not accompanied by secondary infection with otorrhea through the tube, did not result in a permanent perforation or dislocation of the tube into the middle ear cavity, and was not followed by excess tympanosclerosis or localized or diffuse membrane atrophy. CONCLUSIONS AND SIGNIFICANCE: Resorbable polyester pressure equalization tubes demonstrate predictable resorption behavior and similar biocompatibility characteristics when compared with nonresorbable Shah minigrommet ventilation tubes. Exposure to soap water does not accelerate polyester tube degradation nor change the host tissue response during the indwelling period or after complete resorption. The data suggests that resorbable ventilation tubes are substantially equivalent to other FDA-approved tympanostomy devices with regard to safety and biocompatibility in the guinea pig model examined and may provide improved clinical performance by combining this approach with sustained release technology. EBM RATING: B-2.

Animals↗

PubMed2004

Basic fibroblast growth factor promotes neuronal survival but not behavioral recovery in the transected and Schwann cell implanted rat thoracic spinal cord.

It was investigated whether the addition of basic fibroblast growth factor (FGF-2) enhances the efficacy of a Schwann cell (SC) bridge to repair the transected spinal cord by assessing tissue sparing and neuronal survival near the graft-cord interfaces, axonal regeneration and myelination in the graft, and behavioral recovery up to 12 weeks post-grafting. Experimental animals received a bridge of SCs within fibrin containing 1 microg of FGF-2; control animals received a SC implant without FGF-2. Sparing of tissue in a 2.5-mm-long segment near the graft-cord borders was 69% in the rostral and 52% in the caudal cord at 6 weeks post-grafting, not significantly different from the control group. With FGF-2, survival of NeuN-positive cells was increased in the rostral cord: 24.4%, 20.4%, and 17.2% of the number of positive cells in the uninjured cord compared to 13.5%, 9.1%, and 8.9% in controls at 3, 6, and 12 weeks post-grafting, respectively. Similarly, in the caudal cord, survival of NeuN-positive cells was increased with FGF-2: 19.3%, 16.8%, and 14.5% compared to 10.8%, 5.6%, and 6.1% in controls. The staining intensity of glial fibrillary acidic protein was significantly higher at the interfaces of both cord stumps at 3 weeks with SC/FGF-2 grafts; chondroitin sulfate proteoglycan (CS-56) staining was more intense in the rostral cord but only at 6 weeks. Blood vessels in the FGF-2 grafts were larger and less regular in shape than those in control grafts. Axonal growth into the bridge was not improved by the addition of FGF-2. Retrogradely traced neurons were not found rostral to the implant, indicating that axons had not grown a few mm into the caudal spinal tissue. Recovery of hind limb function was similar in both groups. Despite the neuroprotective effects of FGF-2, improved effects on axonal regeneration and functional recovery were not observed.

Animals↗

PubMed2003

Directed nerve outgrowth is enhanced by engineered glial substrates.

In the present study, the influence of astrocyte alignment on the direction and length of regenerating neurites was examined in vitro. Astrocytes were experimentally manipulated by different approaches to create longitudinally aligned monolayers. When cultured on the aligned monolayers, dorsal root ganglion neurites grew parallel to the long axis of the aligned astrocytes and were significantly longer than controls. Engineered monolayers expressed linear arrays of fibronectin, laminin, neural cell adhesion molecule, and chondroitin sulfate proteoglycan that were organized parallel to one another, suggesting that a particular spatial arrangement of these molecules on the astrocyte surface may be necessary to direct nerve regeneration in vivo. In contrast, no bias in directional outgrowth was observed for neurites growing on unorganized monolayers. The results suggest that altering the organization of astrocytes and their scar-associated matrix at the lesion site may be used to influence the direction and the length of adjacent regenerating axons in the damaged brain and spinal cord.

Animals↗

PubMed2003

Comparison of pure and mixed populations of human fetal-derived neural progenitors transplanted into intact adult rat brain.

We examined the influence of initial graft composition on the number, type, and distribution of human progenitor cells after transplantation into the anterior subventricular zone (SVZa) of normal adult rats. The grafted populations were derived from 19-week-old human cortical tissue grown under adherent conditions in the presence of fibroblast growth factor (FGF) and from a subpopulation of nestin-expressing cells, isolated using negative immunoselection methods, which exhibited properties of neural progenitors. Identical numbers of each were transplanted and the number and location of engrafted cells were compared 4 weeks later. We found a significantly greater number of presumptive neurons and astrocytes in animals that received mixed grafts compared to those enriched for progenitors. In addition, the number of human cells undergoing division was significantly greater in animals that received mixed grafts. The spatial distribution of grafted cells was not significantly different, suggesting that the patterns of cell migration were unaffected by transplant composition, whereas, a greater proportion of neurons was observed in the neurogenic areas of animals that received progenitor-enriched grafts. From a clinical perspective, our results suggest that the cellular composition of human fetal-derived transplants may be an important parameter that influences the number and pattern of differentiation of engrafted cells following transplantation in the mature CNS.

Animals↗

PubMed2003

Comparison of human fibroblast ECM-related gene expression on elastic three-dimensional substrates relative to two-dimensional films of the same material.

Three-dimensional elastic substrates were fabricated from a commercially available polyurethane with an internal porosity of approximately 70% and elastic modulus of 27.4+/-2.76 KPa and examined for suitability in vocal fold tissue engineering. Using immunohistochemistry, biomechanical testing, and RT-PCR; we examined human fibroblast viability, distribution and extracellular matrix related gene expression within substrates for periods up to 4 weeks. We found that cells were capable of colonizing the entire volume of a 5mm wide x 3mm deep x 20mm long substrate at high viability. Histological cross-sections showed extensive extracellular matrix deposited around the cells and throughout the pore structure of the substrates, which consisted of fibronectin and type I collagen. Cell seeded substrates displayed a significantly higher elastic modulus than unseeded controls similar to native tissue. The transfer of cell growth from two-dimensional to three-dimensional culture resulted in changes in ECM-related gene expression consistent with decreasing cell migration and increasing tissue formation. We found that fibroblasts cultured in three-dimensional substrates expressed significantly higher levels of mRNA for elastin and fibromodulin, while expressing significantly lower levels of mRNA for MMP-1 and hyaluronidase relative to two-dimensional substrates of the same material. The results suggest that three-dimensionally porous, Tecoflex-derived elastic biomaterials may be suitable substrates for engineering vocal fold tissue.

Actins↗

PubMed2002

Hollow fiber membrane diffusive permeability regulates encapsulated cell line biomass, proliferation, and small molecule release.

Using histological and HPLC methods, we examined the influence of hollow fiber membrane transport properties on encapsulated PC12 cell biomass, proliferation and the release of dopamine over 4 weeks in culture. Our data indicated that encapsulated cell biomass, the number of proliferating cells, and the quantity of dopamine released increased as a function of increasing hollow fiber encapsulation membrane diffusive permeability. Overall the percentage of viable cells and the biomass architecture, however, was not significantly affected by differences in membrane transport. When compared to membrane sieving properties, membrane diffusive transport and membrane hydraulic permeability were better indicators of biomass size, proliferating cell number, and dopamine release from encapsulated cells. Studies examining the sustained release of DA from membranes of differing permeability suggest that membrane diffusive permeability can be used to regulate the quantity of small molecules released per unit time at steady state, and should be considered when dosing is an important determinant of implant efficacy.

Acrylic Resins↗