摘要:

Festschrift remark-It was an honor to be invited to honor Allan Hoffman on the occasion of his 60th birthday. It seems like yesterday that Allan and I shared an office in old Building 12 on the M.I.T. campus. At that time Allan had lost a bout with a snow covered mountain while on skis, and consequently moved about awkwardly in our already small room on crutches with a heavy cast. Despite these impediments, he carried on his classroom activities with typical energy. It was even earlier that at M.I.T., under the supervision of Ed Gilliland and myself, he carried out his doctoral research on the radiation grafting of styrene to polyethylene. Both he and I have dabbled in radiation chemistry on and off since then-he far more than I. Neither of us at that epoch had much idea about biomaterials or medical applications of materials-at least I did not-perhaps Allan had it in the back of his mind. The University of Washington, Seattle, is recognized as one of the great centers of biomedical engineering in the world, both in scope and in depth, and Allan has played a stellar role in the evolution of Seattle's reputation. He has also developed a reputation for outstanding work in biomaterials and is one of the most visible and internationally recognized leaders in the field.

ISSN:0920-5063    

DOI:10.1163/156856294X00617

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Fluorinated ethylenepropylene copolymer (FEP) and polyvinylidene fluoride (PVDF) can generate static and transient electrical charges, respectively, after bulk molecular rearrangements induced by electrical charging techniques. Neurons cultured on electrically active FEP and PVDF show increased levels of nerve fiber outgrowth compared to electrically neutral material. The purpose of the present study was to determine if the addition of charged surface groups to the surfaces of FEP and PVDF would modify the influence of bulk electrical charges on cultured neurons. Mouse neuroblastoma (Nb2a) cells were cultured on electrically charged and uncharged FEP and PVDF substrates with covalently modified surfaces containing hydroxyl (OH) and amine (NH2) groups. Surface chemical modification was performed on the entire surface or in discrete striped regions. Nb2a cells cultured on electrically active FEP and PVDF showed greater levels of differentiation than cells on electrically neutral substrates. The presence of NH2groups attenuated these responses in serum-containing media. Cells attached to NH2rich surfaces generally displayed a flatter morphology and tended to remain attached for longer time periods. Cells cultured on stripe-modified substrates in serum-containing media showed a strong preferential attachment to modified regions, especially on NH2stripes. In summary, bulk electrical charges are more important than surface charges in stimulating Nb2a cell differentiation. Surface groups serve to modulate neuronal morphology and confer specific attachment promoting properties in serum-containing media. The development of an optimal neuronal regeneration template may require the incorporation of specific bulk and surface properties.

ISSN:0920-5063    

DOI:10.1163/156856294X00626

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A method of covalent immobilization of microorganisms (marine luminescent bacteria and yeast) in polymeric hydrogels is described. It is shown that cell immobilization leads to the creation of materials having properties of both synthetic polymers and physiologically active systems. Application of systems containing covalent immobilized yeast and photobacteria in biotechnological and other processes is proposed.

ISSN:0920-5063    

DOI:10.1163/156856294X00635

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Although bone has a remarkable capacity for regenerative growth, there are many clinical situations in which the bony repair process is impaired. TGF-β1is a 25 kD homodimeric protein which modulates the growth and differentiation of many cell types. The ability of TGF-β1, to promote bone formation suggests that it may have potential as a therapeutic agent in disease of bone loss. However, there still exists a need for an effective method of delivering TGF-β1to the site of an osseous defect for the promotion of bone healing. This paper describes a novel biodegradable controlled release system for TGF-β1comprised of poly (DL-lactic-co-glycolic acid) (PLPG) and demineralized bone matrix (DBM). The amount and activity of TGF-βIreleased was determined using several methods including125I-labeled TGF-β1as a tracer, an enzyme linked immunosorbent assay (ELISA) and a growth inhibitory assay (GIA). Protein was released from the devices for time periods of more than 600 h. The amount of TGF-β1released was directly proportional to both the TGF-β1loading and the weight percent of DBM in the device. The release kinetics could be further controlled by applying polymeric coatings of varying porosity to the devices. The GIA indicated that between 80 and 90% of the TGF-β1released from the delivery system retained its bioactivity. The PLPG and DBM existed in phase separated domains within the device as determined by differential scanning calorimetry. Scanning electron microscopy suggested that the devices were sufficiently porous to allow bone ingrowth.

ISSN:0920-5063    

DOI:10.1163/156856294X00644

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this work (Part I), surface modified styrene polymers as new microcarrier material for animal cell culture were extensively investigated. The first synthesis steps-carried out by chloromethylation, sulphonation and nitration of the polystyrene matrix-resulted in precursors with a defined surface layer thickness. The obtained hydrophobic bulk phase showed a limited absorption of hydrophilic media components compared to polysaccharides matrices like dextran. By varying reaction conditions for microcarrier synthesis and/or by using similar styrene type polymer matrices like polyvinyltoluene, the specific density (1.028-1.05 g/cm3) of the microcarrier matrix was adjusted without problems. Chemical varying of the microcarrier surface by reaction of the precursors with different amines, saccharides or proteins led to new microcarriers with optimal conditions for cell adhesion and cell growth. All biological investigations were carried out with a BHK 21 (c-13) cell line. Detailed results will be discussed and summarized in Part II of this work.

ISSN:0920-5063    

DOI:10.1163/156856294X00653

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this work (Part II) the application of new polystyrene based microcarriers in cell culture technology is demonstrated. Carriers with a variety of surface modifications were tested as a growth support for cell line BHK 21. The growth behavior of the cells and cell to surface attachment were compared to Cytodex 3 (Pharmacia), which was used as a reference carrier. To select carriers with growth supporting surfaces, broad screening in petri dish experiments was carried out. Candidates with the highest growth rates were investigated in spinner flask experiments in further detail. Polystyrene carrier with a surface modification like triethylamine, maltamine or N-methylglucosamine were able to support growth as good or better as the reference carrier Cytodex 3. Economies of ingredients and ease in laboratory handling could make amine-modified polystyrenes a competitive alternative to currently commercially available microcarrier types.

ISSN:0920-5063    

DOI:10.1163/156856294X00662

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Aramid-silicone resins (PASs) consisting of aromatic polyamide (aramid) and poly(dimethylsiloxane) (PDMS) segments were synthesized by low temperature solution polycondensation. For the evaluation of blood compatibility in vitro, two kinds of experiments were carried out. One was the thromboxane B2(TXB2) release test from platelets attaching to PAS and Biomer®. The other was the observation of the platelet adhesion on the surfaces of PAS by scanning electron microscopy (SEM). The results indicated that PAS was bio-inert in vitro. The surface chemical composition of PAS films was investigated by means of electron probe micro analysis (EPMA), X-ray photoelectron spectroscopy (XPS), and dynamic contact angle measurements. The relationship between blood compatibility and surface composition of PAS is discussed.

ISSN:0920-5063    

DOI:10.1163/156856294X00671

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Hyaluronan, which is found in high concentrations in fetal tissues, has been suggested to play a major role in preventing scar formation in fetal wounds. We have developed a floating collagen fibrillar matrix (CFM) made out of reconstituted type I collagen for the purpose of evaluating the ability of hyaluronan to inhibit the fibroblast induced contraction of the matrix. When hyaluronan is covalently bound to collagen it appears to better support fibroblast proliferation and matrices are less contractible by these cells than when hyaluronan interacts only ionically. When hyaluronan is bridged between collagen fibrils by a network of extensive covalent crosslinks, contractibility by fibroblasts is abolished. These modified collagen matrices may prove to be very useful in the development of bioprostheses and implants.

ISSN:0920-5063    

DOI:10.1163/156856294X00680

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The mechanisms which control the release of dispersed water-soluble drugs from an initially dry hydrogel are complex. The release profile derives from a combination of several contributing factors which may change with time at different rates. It has been possible to isolate controlling factors and investigate their individual contributions to the release kinetics. The hydrogels presented in this paper owe their hydrophilicity to their poly(ethylene oxide) content. They swell and can absorb up to three times their dry weight in water. Having a glass transition temperature (Tg) below body temperature they are essentially different to those studied theoretically or experimentally, by other groups, which have Tgvalues above body temperature and are initially glassy. A range of diffusates was studied ranging from low water-soluble prostaglandin E2to highly water-soluble lithium chloride. Device geometry was restricted to approximations to infinite slabs with more than 85% total surface area over the top and bottom surfaces so that release was predominantly one-dimensional and the controlling variable was thickness. The increase in surface area with time, drug-solubility in the water-swelling matrix and the presence of crystallinity were shown to be important factors governing the profile and level of release rate with time. It was observed that the release profile could be separated into three parts, the most important being the middle section from early in the release until at least the half-life time. This period could be characterized by the exponential time function, tn. The diffusional exponent, n, is an important indicator of the release mechanism and ranged from 0.79 to 1, i.e. good anomalous to zero order. This is a highly desirable range of values for controlled release devices. The value of n decreases at late-time. The very early-time release can also show a burst or lag effect depending on the diffusate solubility and its loading in the xerogel.

ISSN:0920-5063    

DOI:10.1163/156856294X00699

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A pulsed RF plasma glow discharge is employed to demonstrate molecular level controllability of surface film deposits. Molecular composition of plasma deposited films is shown to vary in a significant manner with the RF duty cycle. Three fluorocarbon monomers are used to illustrate the process. All three exhibit a trend towards increased surface CF2content with decreasing pulsed RF duty cycle, including exclusion of oxygen. Significant variations in carbon-fluorine surface functionalities are obtained over a controllable range of film thickness. Film growth rate measurements reveal the occurrence of surface reactions during significant portions of the off portion of the duty cycle. Albumin adsorption on fluorocarbon-treated PET films is unchanged from PET controls for a 100-fold range of bulk concentrations and 60-fold range of adsorption times. However, increased retention of albumin is observed following incubation with protein-denaturing sodium dodecyl sulfate solution, the retention decreasing with increasing bulk concentration of albumin. The increased retention of albumin suggests the treated surfaces may have promise as biocompatible materials.

ISSN:0920-5063    

DOI:10.1163/156856294X00707

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor