ISSN:0920-5063    

DOI:10.1163/156856200744291

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Professor Bamford was regarded by many as the greatest British polymer chemist of the twentieth century and when Bam passed away in November 1999 tribute was quite rightly made to his considerable achievements in the field of polymer science. The aim of this paper is to highlight Bam's contribution to biomaterials research that occupied his attention for over 15 years after his official retirement. In particular a review of the synthetic methods employed by Bam for the modification of polymers to improve haemocompatibility and to function as affinity separation membranes for protein purification is presented.

ISSN:0920-5063    

DOI:10.1163/156856200744336

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In the literature, many papers deal with the behavior of proteins in aqueous media in the presence of poly(ethylene glycol) (PEG) molecules or poly(ethylene oxide) (PEO) segments, physically adsorbed onto, or covalently attached to, macromolecules or to solid surfaces. In particular, it is well known that PEO segments make foreign materials stealthy, i.e. they are much less detected by the immune system either through humoral reactions or, at the cell level, through opsonins. Revisiting the literature led us to challenge the largely accepted opinion that the decreased recognition of PEO segment-bearing foreign macromolecules and particles by the mononuclear phagocyte system is primarily the consequence of the repulsion of all blood proteins by PEG segments through the excluded volume effect. This challenge is based on the finding that albumin and PEG are compatible in phosphate-buffered saline at room temperature and at concentrations comparable to those measured by others on the surface of PEO segment-bearing species, whereas fibrinogen and PEG phase-separated and were incompatible despite the much lower concentration of the latter protein. According to literature and to these observations, it is proposed that the stealth effect induced by PEO segments is primarily due to the compatibility between PEO segments of intermediate molar mass and albumin, thus rendering PEO-bearing macromolecules or surfaces to look like native albumin. Under such conditions, the hospitality offered by PEG macromolecules or PEO segments to albumin, the dominant plasma protein, results in a 'chameleon' effect that prevents the activation of other PEG-compatible or-incompatible plasma proteins or cells involved in foreign body recognition and elimination. PEG with molar masses >8000 did not accommodate albumin in agreement with the excluded volume phenomenon.

ISSN:0920-5063    

DOI:10.1163/156856200744345

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have developed a new mucoadhesive drug delivery formulation based on an ionic complex of partially neutralized poly(acrylic acid) (PAA) and a highly potent beta blocker drug, levobetaxolol · hydrochloride (LB · HCl), for use in the treatment of glaucoma. PAA was neutralized with sodium hydroxide to varying degrees of neutralization. Aqueous solutions containing concentrations of LB · HCl equivalent to the degree of PAA neutralization were added to the PAA solutions and formed insoluble complexes, which were isolated. The complex formation was followed by turbidimetric titration, and the complexes were characterized by IR and1H NMR spectroscopy. Complexes were prepared with varying degrees of drug loading, such that the same PAA chain would have free COOH groups for mucoadhesion along with ionic complexes of LB · H+with COO-groups. Thin films of the complexes dissociated to release the drug by ion exchange with synthetic tear fluid. The films shrunk continuously during release of the drug and dissolved completely in 1 h. Solid inserts of these films could be useful as a mucoadhesive ophthalmic drug delivery system.

ISSN:0920-5063    

DOI:10.1163/156856200744354

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

PEG hydrogels cross-linked by a hydrolyzable polyrotaxane were prepared and their hydrolytic erosion characterized in terms of supramolecular dissociation of the polyrotaxane. The hydrolyzable polyrotaxane, in which many α-cyclodextrins (α-CDs) are threaded onto a poly(ethylene glycol) (PEG) chain capped with L-phenylalanine via ester linkages, was used as a multifunctional cross-linker: the PEG network was covalently bound to hydroxyl groups of α-CDs in the polyrotaxane. The contact angle and water content of the hydrogels were varied with the polyrotaxane content in the feed.In vitrohydrolysis study revealed that the time to reach complete gel erosion was shortened by increasing the polyrotaxane content in the feed in relation to the decreased number of chemical crosslinks between PEG and α-CDs in the polyrotaxane. The hydrogel degradation in a physiological condition was found to be followed by bulk mechanism. These findings suggest that changing the preparative conditions such as polyrotaxane content will make it possible to control programmed gel erosion for tissue engineering.

ISSN:0920-5063    

DOI:10.1163/156856200744363

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The aim of this work was to determine whether encapsulation of a non steroidal antiinflammatory agent within nanocapsules could reduce local toxicity after intramuscular injection. Diclofenac-loaded nanocapsules were prepared by deposition of poly( rac -lactic acid) polymer, and administered intramuscularly to male Wistar rats. Plasma creatine phosphokinase (CPK) activity and histological examination were used to assess local tissue damage. Following a single intramuscular injection of diclofenac (0.8 mg), CPK activity was shown to depend on both the type of dosage form and, in the case of nanocapsules, on the chemical nature of the central oily core. Lower CPK activity was observed with nanocapsules prepared from Miglyol 810fi, a caprylic/capric triglyceride, while nanocapsules prepared from benzyl benzoate, either empty or containing diclofenac, exhibited the same CPK activity as the drug solution. Histopathological examination performed three days after administration of free diclofenac or nanocapsules containing diclofenac prepared from Miglyol 810firevealed that a much more intense inflammation was obtained with the solution than with nanocapsules. In conclusion, when appropriately formulated, nanocapsules can considerably reduce the muscular damage caused by diclofenac.

ISSN:0920-5063    

DOI:10.1163/156856200744372

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The objective of this study is to examine whether or not bone formation at a skull bone defect induced by gelatin microspheres incorporating transforming growth factor (TGF)-β1 is promoted by prevention of fibrous tissues into the defect. The 6-mm diameter bone defect of rabbit skulls was applied with gelatin microspheres incorporating TGF-β1 or free TGF-β1 and physically covered by a barrier membrane. When the bone formation at the defect was assessed 6 weeks postoperatively, combinational application of gelatin microspheres incorporating 0.1 μg of TGF-β1 with the barrier membrane induced bone formation at the skull defect, in marked contrast to that of 0.1 μg of free TGF-β1 and empty gelatin microspheres. Complete defect closure was histologically observed by the newly formed bone tissue. Without the barrier membrane, gelatin microspheres incorporating TGF-β1 were less effective in inducing bone formation, whereas free TGF-β1 and empty gelatin microspheres were ineffective. The skull defect was occupied by fibrous tissue infiltrated in place of bone tissue. The bone mineral density at the skull defect applied with gelatin microspheres incorporating TGF-β1 plus the membrane was significantly higher than that of gelatin microspheres incorporating TGF-β1 alone. The present data indicated that physical protection from the soft tissue infiltration enabled gelatin microspheres incorporating TGF-β1 to synergistically enhance the osteoinductive ability at the skull defect.

ISSN:0920-5063    

DOI:10.1163/156856200744381

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Stimuli-sensitive hydrogels (or smart hydrogels) are hydrogels that swell or shrink in response to small changes in environmental conditions in which they are placed. While the extent of swelling or shrinking may be large, the kinetics of such changes is slow, since the diffusion of water into and out of the hydrogel is a slow process. To obtain fast responses, we have prepared superporous hydrogels (SPHs) that can swell or shrink extremely fast regardless of their dimensions. The swelling and shrinking are orders of magnitude faster than expected for a nonporous hydrogel of the same dimensions. Water molecules are taken up into the SPHs by capillary forces, and this makes water uptake much faster than diffusion. The swelling ratio of the poly(acrylamide- co -acrylic acid) (p(AM-co-AA)) SPHs was dependent on the pH and ionic strength of the medium. The effect of pH was most pronounced and the effect of ionic strength was observed at all pH values. SPHs made at pH around 5 showed transient maximum swelling when exposed to pH 1.2 medium due to the transient low hydrogen ion concentration inside the swelling SPHs. The p(AM-co-AA) SPHs showed repeated swelling and shrinking by alternating the medium pH between 1.2 and 7.5, and the changes in swelling ratio was quite fast occurring in a matter of a minute. This fast sensitivity may make the stimuli sensitive hydrogels useful in many applications not previously possible. These materials can be used for applications where a single-piece hydrogel is more advantageous than hydrogel microparticulates.

ISSN:0920-5063    

DOI:10.1163/156856200744390

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Antibacterial immunoliposomes have been prepared using covalently bound antibody, raised to the cell surface of the bacteriumStreptococcus oralis(S. oralis), and incorporating the bactericides chlorhexidine and Triclosan™. A regrowth assay, in which the ability of a bacterial biofilm immobilised on polystyrene to grow after exposure to a test solution, was undertaken to study the action of the antibacterial immunoliposomes. The antibacterial anti-oralisimmunoliposomes show enhanced growth inhibition ofS. oralis, compared to free bactericide, using low bactericide concentrations. For short exposure times to the biofilms, antibacterial anti-oralisimmunoliposomes can show several times enhanced growth inhibition ofS. oraliscompared to free bactericide. Antibacterial anti-oralisimmunoliposomes inhibit the growth ofS. oralismore than that of other oral bacteria. The extent of growth inhibition by antibacterial anti-oralisimmunoliposomes is linearly related to the number of immunoliposomes targeted to the biofilm surface.

ISSN:0920-5063    

DOI:10.1163/156856200744408

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Hydrophobically-modified dextran (dextran-phenoxy, DexP) and dextran-phénoxy- poly(oxyethylene) (DexP-POE) copolymers have been used to modify the surface properties and the stability of polystyrene nanoparticles. We examined the effect of phenoxy group and POE chain concentrations on their adsorption behaviour. The adsorbed amount was determined by the standard depletion method and the layer thickness of the adsorbed layer by photon correlation spectroscopy and electrokinetic measurements. The results show that the hydrophobic interaction is the driving force during the adsorption while the layer thickness correlates with the interfacial concentration of grafted POE chains. The effects of adsorbed layers on the properties of latex dispersions have been characterized in terms of the stability of the dispersions toward added electrolyte and temperature. The conformation of the adsorbed copolymers is discussed in relation to layer thickness and colloidal stability of suspensions.

ISSN:0920-5063    

DOI:10.1163/156856200744309

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor