ISSN:0006-3592    

DOI:10.1002/bit.260430702

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe nervous system presents a challenge to the field of tissue engineering because some of its complex neurochemical and neuroanatomical architecture is just beginning to be understood. A combination of advances in molecular neurobiology, gene transfer techniques, and the concomitant advances in the engineering of biomaterials at a molecular level, are making tissue engineering in the nervous system possible. Due to the vast range of fields that this highly interdisciplinary task spans, any review is bound to be somewhat limited. Given that, this review attempts to cover some solutions engineered for: (a) the functional replacement of a missing neuroactive component; (b) the rescue or regeneration of degenerated neural tissue; and (c) the building of intelligent neural cell‐based biosensors and simple in vitro neural circuits based on controlled neural cell attachment to electrically relevant substrates. © 1994 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260430703

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractComponents of the extracellular matrix are believed to guide both nerve cells and neurites to their targets during embryogenesis and, therefore, might be useful for controlling regeneration of nervous tissue in adults. To study the influence of extracellular conditions on neurite outgrowth and cell motility, PC12 cells were suspended in three‐dimensional gels containing (i) collagen (0.4 to 2 mg/mL), (ii) collagen (1 mg/mL) with added fibronectin or laminin (1 to 100 μg/mL), and (iii) agarose (7 mg/mL) with added collagen (0.001 to 1 mg/mL). Neurite outgrwoth was stimulated with nerve growth factor (NGF) and both the extent of neurite outgrowth ad cell aggregation were quantitated over 10 to 12 days in culture. The extent of neurite outgrowth was greatest at the lowest collagen concentration tested (0.4 mg/mL) and decreased with increasing concentration. The addition of laminin or fibronectin altered the extent of neurite outgrowth in collagen gels, but the differences were small. Although no neurite growth was observed in pure agarose gels, considerable neurite outgrowth occurred with the addition of small amounts (≥0.01 mg/mL) of collagen. Mean aggregate size increased more quickly in gels with lower concentrations of collagen. For cells in 1.0 mg/mL collagen, a four‐ to fivefold increase in aggregate volume was seen between days 2 and 10 o the culture period, whereas the increase in DNA content during this same period was less than twofold, suggesting that the cells were aggregating, not multiplying. These results suggest that the composition of the matrix supporting nerve cells has a significant effect on both neurite outgrowth and cell motility. © 1994 John Wiley&So

ISSN:0006-3592    

DOI:10.1002/bit.260430704

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractPoly(acrylonitrile‐co‐vinyl chloride) (PAN/VC) anisotropic membranes were chemically modified with poly(ethylene oxide) (PEO) (5000 and 20,000 g/mol) by one of two aqueous reactions: (a) acid hydrolysis of the nitrile group to a carboxylic acid with which amine‐terminated PEO (PEO‐NH2) reacted or (b) base reduction of the nitrile group to an amine with which PEO‐succinimide (PEO‐SC) reacted. Approximately 1.3% of the bulk material was modified with PEO‐NH2whereas 1.8 to 3.5% was modified with PEO‐SC as determined by proton nuclear magnetic resonance (1H NMR) and attenuated total reflectance Fourier transform infrared (ATR FTIR) spectra. Approximately 50 to 75% less bovine serum albumin (BSA) adsorbed to PEO‐grafted single skin fibers than to unmodified PAN/VC. Transport properties of modified and unmodified fibers were compared by passive diffusion, convective nominal molecular weight cutoff, and hydraulic permeability. Neither hydraulic permeability nor nominal molecular weight cutoff of BSA changed appreciably after surface modification with PEO indicating that pore structure was not adversely affected by the chemistry involved in grafting poly(ethylene oxide). However, in the absence of any membrane conditioning, the apparent diffusion of α‐chymotrypsinogen (24,000 g/mol) was enhanced in PEO‐grafted PAN/VC fibers possibly as a result of reduced sorption of the permeating protein. In vivo biocompatibility in the brain tissue of rats was judged by histological assessment of the host's cellular response to fibers implanted for 30 days; biocompatibility of both PAN/VC and PAN/VC‐g‐PEO was satisfactory but improved slightly with PEO grafting.

ISSN:0006-3592    

DOI:10.1002/bit.260430705

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIt is well established that vascularization is required for effective bone healing. This implies that blood flow and interstitial fluid (ISF) flow are required for healing and maintenance of bone. The fact that changes in bone blood flow and ISF flow are associated with changes in bone remodeling and formation support this theory. ISF flow in bone results from transcortical pressure gradients produced by vascular and hydrostatic pressure, and mechanical loading. Conditions observed to alter flow rates include increases in venous pressure in hypertension, fluid shifts occurring in bedrest and microgravity, increases in vascularization during the injury‐healing response, and mechanical compression and bending of bone during exercise. These conditions also induce changes in bone remodeling. Previously, we hypothesized that interstitial fluid flow in bone, and in particular fluid shear stress, serves to mediate signal transduction in mechanical loading‐ and injury‐induced remodeling. In addition, we proposed that a lack or decrease of ISF flow results in the bone loss observed in disuse and microgravity. The purpose of this article is to review ISF flow in bone and its role in osteogenesis. © 1994 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260430706

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWell‐characterized osteoblasts provide a successful in vitro model to study bone‐biomaterial interactions. Knowledge of the events occurring at this tissue‐biomaterial interface could lead to the design of improved orthopedic/dental biomaterials which elicit specific and desirable responses from surrounding cells/tissues, optimize function of osteoblasts (the boneforming cells), and enhance long‐term bone‐implant bonding. © 1994 John Wiley

ISSN:0006-3592    

DOI:10.1002/bit.260430707

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractBone tissue is a complex multilevel composite which has the ability to sense ad respond to its mechanical environment. It is believed that bone cells called osteocytes within the bone matrix sense the mechanical environment and determine whether structural alterations are needed. At present it is not known, however, how loads are transferred from the whole bone level to cells. A computational procedure combining representative volume element (RVE) based homogenization theory with digital imaging is proposed to estimate strains at various levels of bone structure. Bone tissue structural organization and RVE based analysis are briefly reviewed. The digital image based computational procedure was applied to estimate strains in individual trabeculae (first‐level microstructure). Homogenization analysis of an idealized model was used to estimate strains at one level of bone structure around osteocyte lacunae (second‐level trabecular microstructure). The results showed that strain at one level of bone structure is amplified to a broad range at the next microstructural level. In one case, a zeor‐level tensile principal strain of 495 μE engendered strains ranging between ‐1000 and 7000 μE in individual trabeculae (first‐level microstructure). Subsequently, a first‐level tensile principal strains of 1325 μE within an inidividual trabecula engendered strains ranging between 782 and 2530 μE around osteocyte lacunae. Lacunar orientation was found to influence strains around osteocyte lacunae much more than lacunar ellipticity. In conclusion, the computational procedure combining homogenization theory with digital imaging can proveide estimates of cell level strains within whole bones. Such results may be used to bridge experimental studies of bone adaptation at the whole bone and cell culture level. © 1994 John

ISSN:0006-3592    

DOI:10.1002/bit.260430708

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn vitro cultivation of cartilage cells (chondrocytes) on biodegradable polyglycolic acid (PGA) scaffolds resulted in implants which could potentially be used to repair damaged joint cartilage or for reconstructive surgery. Cell growth kinetics were studied to define conditions under which the cellularity of implants made from isolated calf chondrocytes reached that of the parent calf cartilage. In static cultures, condrocyte growth rates decreased as either implant thickness or implant cell density increased. Over 4 weeks of cultivation, implant permeability to glucose decreased to 3% that of the plain polymer scaffold; this effect was attributed to the decrease in effective implant porosity associated with cartilage tissue regeneration.In a well‐mixed culture, implants 1 cm in diameter by 0.3 cm thick maintained high cell growth rates over 7 weeks and hard normal cell densities. Regenerated cartilage with these dimensions is large enough to resurface small joints such as the trapezium bone at the base of the human thumb. Such implants could not be grown statically, since cell growth stopped at 3–4 weeks and cell densities remained below normal. Optimization of the tissue culture environment is thus essential in order to cultivate clinically useful cartilage implants in vitro. © 1994 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260430709

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractCartilage implants for potential in vivo use for joint repair or reconstructive surgery can be created in vitro by growing chondrocytes on biodegradable polymer scaffolds. Implants 1 cm in diameter by 0.176 cm thick were made using isolated calf chondrocytes and polyglucolic acid (PGA). By 6 weeks, the total amount of glycosaminoglycan (GAG) and collagen (types I and II) increased to 46% of the implant dry weight; there was a corresponding decrease in the mass of PGA. Implant biochemical and histological compositions depended on initial cell density, scaffold thickness, and the methods of cell seeding and implant culture. Implants seeded at higher initial cell densities reached higher GAG contents (total and per cell), presumably due to cooperative cell‐to‐cell interactions. Thicker implants had lower GAG and collagen contents due to diffusional limitations.Implants that were seeded and cultured under mixed conditions grew to be thicker and more spatially uniform with respect to the distribution of cells, matrix, and remaining polymer than those seeded and/or cultured statically. Implants from mixed cultures had a 20‐40‐μm thick superficial zone of flat cells and collagen oriented parallel to the surface and a deep zone with perpendicular columns of cells surrounded by GAG Mixing during cell seeding and culture resulted in a more even cell distribution ad enhanced nutrient diffusion which could be related to a more favorable biomechanical environment for chondrogenesis. Cartilage with appropriate for and function for in vivo implantation ca thus be created by selectively stimulating the growth and differentiated function of chondrocytes (i.e., GAG and collagen synthesis) through optimization of the in vitro culture environment. © 1994 John Wiley&

ISSN:0006-3592    

DOI:10.1002/bit.260430710

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe effects of cyclical expansion and elaxation of the vessel wall on endothelial cell metabolism have been modeled using a uniaxial strain device and cultured endothelial cell monolayers. Also, the effects of stopping and then restarting cyclic strain on metabolite secreation rates were determined. Secretion rates of prostacyclin (PGI2), endothelin, tissue plasminogen activator (t‐PA), and plasminogen activator inhibitor‐type 1 (PaI‐1) by endothelial cells were constant over24‐h periods The secreation of both PGI2and endothelin was enhanced in cells exposed to high physiological levels of cyclical strain (10% at 1Hz) compared with controls, while tPA production was unaltered. These results were true for both human and bovine endothelial cells. Characterization of the response of human endothelial cells to cyclical strain made evaluation of stretch effects on PAl‐1 secretion possible. A nearly twofold increase in PAl‐1 secretion by cells exposed to arterial levels of strain was observed. Endothelin secretion remained elevated even after strain was stopped for 12 h, while PGl2secretion returned to control values upon cessation of cyclic stretch. These results indicate that physiological levels of cyclic mechanical strain ca significantly modulate secretion of vasoactive metabolited form endothelial cells. The changes sen secretion are, in some cases, quite different from those caused by arterial levels of fluid shear stress exposure. © 1994 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260430711

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY