Experimental assessment of the effects of sublethal salinities on growth performance and stress in cultured tra catfish (Pangasianodon hypophthalmus)

The effects of a range of different sublethal salinities were assessed on physiological processes and growth performance in the freshwater 'tra' catfish (Pangasianodon hypophthalmus) juveniles over an 8-week experiment. Fish were distributed randomly among 6 salinity treatments [2, 6, 10, 14 and 18 g/L of salinity and a control (0 g/L)] with a subsequent 13-day period of acclimation. Low salinity conditions from 2 to 10 g/L provided optimal conditions with high survival and good growth performance, while 0 g/L and salinities >14 g/L gave poorer survival rates (p < 0.05). Salinity levels from freshwater to 10 g/L did not have any negative effects on fish weight gain, daily weight gain, or specific growth rate. Food conversion ratio, however, was lowest in the control treatment (p < 0.05) and highest at the maximum salinities tested (18 g/L treatment). Cortisol levels were elevated in the 14 and 18 g/L treatments after 6 h and reached a peak after 24-h exposure, and this also led to increases in plasma glucose concentration. After 14 days, surviving fish in all treatments appeared to have acclimated to their respective conditions with cortisol levels remaining under 5 ng/mL with glucose concentrations stable. Tra catfish do not appear to be efficient osmoregulators when salinity levels exceed 10 g/L, and at raised salinity levels, growth performance is compromised. In general, results of this study confirm that providing culture environments in the Mekong River Basin do not exceed 10 g/L salinity and that cultured tra catfish can continue to perform well.

An in vitro release study of indomethacin from nanoparticles based on methyl methacrylate/glycidyl methacrylate copolymers

Indomethacin was coupled onto some macromolecular nanostructures based on methyl methacrylate copolymers with glycidyl methacrylate and tested as a model drug. The polymeric matrices were synthesized by radical emulsion copolymerization with and without the presence of a continuous external magnetic field of 1500 Gs intensity. Mathematical analysis of the release data was performed using Higuchi, Peppas-Korsmeyer equations. NIR chemical imaging (NIR-CI) was used to provide information about the spatial distribution of the components in the studied nanostructures. This opportunity was used to visualize the spatial distribution of bioactive substances (indomethacin) into the polymeric matrix, as well as to evaluate the degree of chemical and/or physical heterogeneity of the bioactive samples. The release rate dependence on the synthesis conditions as well as on the chemical compositions of the tested polymeric systems, it was also evidenced.

Immobilization of type-I collagen and basic fibroblast growth factor (bFGF) onto poly (HEMA-co-MMA) hydrogel surface and its cytotoxicity study

Type-I collagen and bFGF were immobilized onto the surface of poly (HEMA-co-MMA) hydrogel by grafting and coating methods to improve its cytotoxicity. The multi-layered structure of the biocompatible layer was confirmed by FTIR, AFM and static water contact angles. The layers were stable in body-like environment (pH 7.4). Human skin fibroblast cells (HSFC) were seeded onto Col/bFGF-poly (HEMA-co-MMA), Col-poly (HEMA-co-MMA) and poly (HEMA-co-MMA) films for 1, 3 and 5 day. MTT assay was performed to evaluate the extraction toxicity of the materials. Results showed that the cell attachment, proliferation and differentiation on Col/bFGF-poly (HEMA-co-MMA) film were higher than those of the control group, which indicated the improvement of cell-material interaction. The extraction toxicity of the modified materials was also lower than that of the unmodified group. The protein and bFGF immobilized poly (HEMA-co-MMA) hydrogel might hold great promise to be a biocompatible material.

Ultrastructural evaluation of in vitro mineralized calcium phosphate phase on surface phosphorylated poly(hydroxy ethyl methacrylate-co-methyl methacrylate)

The in vitro functionality of surface phosphorylated poly(hydroxy ethyl methacrylate-co-methyl methacrylate), poly(HEMA-co-MMA) to induce bioinspired mineralization of calcium phosphate phase is evaluated. The primary nucleation of calcium phosphate on the surface phosphorylated copolymer occurs within 3 days of immersion when immersed in 1.5x simulated body fluid and the degree of mineralization is proportional to the hydroxy ethyl methacrylate content in the copolymer. The calcium phosphate phase is identified as hydroxyapatite by X-Ray diffraction analysis. The transmission electron microscopic evaluation combined with selected area diffraction pattern and energy dispersive analysis exemplified that the primary nuclei of amorphous calcium phosphate transforms to crystalline needle like calcium rich apatite, within a period of 3 days immersion in simulated body fluid. The atomic force microscopic results corroborate the c-axis growth of the crystals within 3 days immersion in SBF.

Adsorption of human salivary mucin MG1 onto glow-discharge plasma treated acrylic resin surfaces

It has been suggested that altering the surface properties of acrylic resin material may change the nature of the adsorbed pellicle affecting denture retention and microbial adherence. This study aimed at evaluating the adsorption of salivary high molecular-weight mucins, a major component of denture pellicle, onto modified acrylic resin surfaces. (Poly) methylmethacrylate specimens were treated by glow discharge plasma technique, using hydrophilic 2-Hydroxyethylmethacrylate monomer or oxygen (O(2)) gas and hydrophobic Hexamethyldisiloxane monomer, at different discharge powers. Acrylic samples were incubated with high-molecular weight mucin, MG1 purified from saliva, the adsorbed fractions were transferred to nitrocellulose membranes by slot-blot technique, stained by periodic acid-Schiff and colour intensities were analysed by a colour densitometer. Higher amounts of mucins were adsorbed on all the surfaces modified by glow-discharge plasma treatment. Within the limitations of this study, it was concluded that glow-discharge plasma altered the surfaces of acrylic resin denture base materials and significantly increased the adsorption of high molecular-weight mucins at varying levels depending on plasma parameters.

Probing the S100 protein family through genomic and functional analysis

The EF-hand superfamily of calcium binding proteins includes the S100, calcium binding protein, and troponin subfamilies. This study represents a genome, structure, and expression analysis of the S100 protein family, in mouse, human, and rat. We confirm the high level of conservation between mammalian sequences but show that four members, including S100A12, are present only in the human genome. We describe three new members of the S100 family in the three species and their locations within the S100 genomic clusters and propose a revised nomenclature and phylogenetic relationship between members of the EF-hand superfamily. Two of the three new genes were induced in bone-marrow-derived macrophages activated with bacterial lipopolysaccharide, suggesting a role in inflammation. Normal human and murine tissue distribution profiles indicate that some members of the family are expressed in a specific manner, whereas others are more ubiquitous. Structure-function analysis of the chemotactic properties of murine S100A8 and human S100A12, particularly within the active hinge domain, suggests that the human protein is the functional homolog of the murine protein. Strong similarities between the promoter regions of human S100A12 and murine S100A8 support this possibility. This study provides insights into the possible processes of evolution of the EF-hand protein superfamily. Evolution of the S100 proteins appears to have occurred in a modular fashion, also seen in other protein families such as the C2H2-type zinc-finger family.

Tailoring the swelling pressure of degrading dextran hydroxyethyl methacrylate hydrogels

Swelling pressure measurements were performed on degrading dextran hydroxyethyl methacrylate (dex-HEMA) hydrogels. In these networks, the cross-links are hydrolyzable carbonate ester bonds formed between methacrylate groups and dextran molecules. It is demonstrated that dex-HEMA gels made in the presence of a known amount of free dextran chains exhibit osmotic properties similar to those of partially degraded dex-HEMA gels. The swelling pressure, Pi(sw), of degrading dex-HEMA gels is controlled primarily by the cross-linked dex-HEMA polymer and the free dextran molecules, while the contribution of short poly-HEMA fragments (produced in the degradation process) is negligible. It is found that Pi(sw) only slightly changes during the first 15 days of degradation. Close to the end of the degradation process, however, a much faster increase in Pi(sw) is observed. The swelling pressure profile of these gels strongly depends on the concentration of the cross-linked dex-HEMA and its chemical composition (amount of HEMA groups per 100 glucose units).

Enhanced anaerobic degradation of polymeric azo compounds by Escherichia coli in the presence of low-molecular-weight redox mediators

The effects of the redox mediator lawsone (2-hydroxy-1,4-naphthoquinone) on the ability of Escherichia coli to reduce anaerobically polymeric azo compounds were analysed. Two types of polymeric azo compounds were tested, that have been proposed as putative tools for the site-specific targeting of drugs to the colon. The first group of polymers consisted basically of linear chains of polymethacrylic acid or polymethylmethacrylate which were interrupted by subunits of 4,4'-bis(methacryloylamino)azobenzene. These polymers differed significantly in their hydrophilicity according to the relative proportion of polymethacrylic acid used for the polymerization procedure. The second group of polymers consisted of almost water-insoluble poly(ether-ester)azo polymers that were composed of 4-(6-hydroxyhexyl)oxy-phenylazobenzoate and 16-hydroxyhexadecanoate. The addition of lawsone to the anaerobically incubated cultures of E. coli resulted in a pronounced increase in the reduction rates of the water-soluble poly(methacrylate-co-4,4'-bis(methacryloylamino)azobenzene) and in a much smaller, but significant, increase in the reduction rates of the hydrophobic poly(ether-ester)azo polymers. An increase in the amount of azo groups resulted, for the hydrophobic poly(ether-ester)azo polymers, in an increased reduction rate in the presence of the redox mediator lawsone.

Biocompatibility of NDGA-polymerized collagen fibers. II. Attachment, proliferation, and migration of tendon fibroblasts in vitro

The material properties of collagen fibers polymerized with nordihydroguaiaretic acid (NDGA) are equivalent to native tendon, suggesting that NDGA crosslinking may provide a viable approach to stabilizing collagenous materials for use in repairing ruptured, lacerated, or surgically transected fibrous tissues, such as tendons and ligaments (Koob & Hernandez, Biomaterials, in press). The present study evaluated the biocompatibility of these fibers with cultured bovine tendon fibroblasts. Fibroblast attachment, migration, and proliferation on NDGA-crosslinked materials were compared to those on prepolymerized type I tendon collagen constructs as well as on tissue-culture-treated plastic. Fibroblast attachment on NDGA-crosslinked collagen fibrils was equivalent to attachment on plates coated with collagen alone. Over a period of 8 days in culture, attached fibroblasts proliferated on NDGA-crosslinked collagen at a rate identical to that of fibroblasts attached to native collagen. In order for the biomaterial effectively to bridge gaps in fibrous tissues, fibroblasts must be able to migrate and replicate on the bridging fiber. Control and crosslinked fibers were inserted in calf tendon explants, with a portion of the fiber extending out of the sectioned end of the tendon. Explants were cultured for 9 weeks, and the number of cells was measured at weekly intervals. Cells appeared on the fibers after 1 week of culture. By 2 weeks, cells had colonized the entire fiber. The number of cells continued to increase throughout the 9 weeks in culture, forming a layer several cells thick. Histologic analysis indicated that the fibroblasts populating the fibers appeared to originate in the epitenon. There was no difference in the rate of fibroblast migration and replication, nor in the ultimate number of colonizing cells, between control collagen fibers and NDGA-crosslinked fibers. NDGA-crosslinked fibers may provide a means of bridging gaps in ruptured, lacerated, or surgically transected tendons by providing a mechanically competent scaffold on which tendon fibroblasts can migrate, attach, and proliferate.

[Heat of polymerization of bone cement can induce cardiac arrest]

Total hip arthroplasty is associated with cardiopulmonary complications including cardiac arrest. We present one of four cases of cardiac arrest, two of the cases were fatal. The pathogenesis suggested to explain these complications is venous air embolism, generated by the methylmethacrylate bone cement polymerization causing thermal blood damage. To prevent this happening cortical bone allotransplantation around the prosthesis and bone cement with a low temperature of polymerization may be used.

A hydrophobic interaction site for lysozyme binding to polyethylene glycol and model contact lens polymers

Proton nuclear magnetic resonance (1H-NMR) spectroscopy is used to identify a preferred binding site for uncharged hydrophilic polymers on the surface of hen egg-white lysozyme. Chemical shift titrations show that exchangeable proton signals from amino acids Arg-61, Trp-62, Trp-63, Arg-73, Lys-96 and Asp-101 are selectively perturbed upon binding of poly(ethylene oxide), poly(ethylene glycol) and poly(ethylene-co-propylene oxide). The greatest binding-induced chemical shift changes are observed for Trp-62, Arg-61 and Arg-73 at the edge of the active site cleft of the protein, consistent with a predominantly hydrophobic interaction mode involving the polymer ethylene moieties. The more hydrophilic species poly(dihydroxypropyl methacrylate) causes similar but substantially smaller chemical shift effects than the other polymers, confirming the nature of the interaction. A dissociation constant of 76+/-5 mM is determined for the poly(ethylene glycol)-lysozyme complex. The relatively low affinity of the protein-polymer interactions compared to oligosaccharide substrate binding suggests that lysozyme activity is minimally affected by these materials.

Embedding of bone samples in methylmethacrylate: an improved method suitable for bone histomorphometry, histochemistry, and immunohistochemistry

Methylmethacrylate (MMA) embedding of undecalcified bone biopsies is a technique widely used for bone histomorphometry. However, conventional MMA embedding causes almost complete loss of enzyme activity and protein antigenicity in the tissues. Recently, an MMA embedding technique has been reported that preserves enzyme activity and antigenic determinants in bone tissue. We describe here a modification of this embedding method. For our modified MMA embedding process, commercially available methacrylates can be used without purification, and the histologic quality of bone sections is comparable to that of conventionally MMA-embedded bone specimens. The technique reported here can be employed for embedding of larger bone samples and is suitable for histochemical and immunohistological applications as well as for routine bone histomorphometry. By addition of methylbenzoate during infiltration and polymerization of the plastic, the antigenicity of the tissue was improved. As applications of this novel technique, demonstration of alkaline phosphatase and tartrate-resistant acid phosphatase as well as positive labeling of Kupffer cells and osteoclasts with the monoclonal antibody ED1 in sections of liver, tibiae, and vertebrae of 3-month-old rats was demonstrated. The method described here might be useful for the inclusion of histochemical and immunohistological methods into bone histomorphometry.

The Microsponge Delivery System (MDS): a topical delivery system with reduced irritancy incorporating multiple triggering mechanisms for the release of actives

The Microsponge Delivery System (MDS) is a unique technology for the controlled release of topical agents and consists of macroporous beads, typically 10-25 microns in diameter, loaded with active agent. When applied to the skin, the MDS releases its active ingredient on a time mode and also in response to other stimuli (rubbing, temperature, pH, etc). MDS technology is being used currently in cosmetics, over-the-counter (OTC) skin care, sunscreens and prescription products. By delivering the active gradually to the skin, MDS-benzoyl peroxide formulations, for example, have excellent efficacy with minimal irritation. These are typical benefits from the use of the MDS.

Protein A carrying monosize PMMA microbeads for the removal of HIgG from human plasma

Protein A-incorporated polymethylmethacrylate (PMMA) microbeads were investigated for specific removal of HIgG from human plasma. The microbeads were prepared by a phase inversion polymerization, and activated by periodate oxidation. Protein A was then incorporated by covalent binding onto these microbeads through hydroxyl groups coming from the stabilizer. The amount of incorporated protein A was controlled by the initial concentrations of protein A in the immobilization medium and pH. The maximum protein A immobilization of 0.615 mg protein A/g PMMA, was observed at a pH of 9.5 corresponding to an initial protein A concentration of 0.1 mg/ml. There was no HIgG adsorption onto the plain PMMA microbeads, while high HIgG adsorptions of up to 32 mg HIgG/g PMMA were achieved with human plasma.

Cell growth on insulin/RGDS-coimmobilized poly(methyl methacrylate) films

The tetrapeptide, Arg-Gly-Asp-Ser (RGDS), which corresponds to a core sequence of cell adhesion proteins, was coimmobilized with insulin on to surface-hydrolyzed poly(methyl methacrylate) film. Adhesion of STO mouse fibroblast cells was enhanced by the immobilization of RGDS, but not of insulin. On the other hand, growth of the cells was accelerated by the insulin immobilization, but not by the RGDS immobilization. Coimmobilization of insulin and RGDS did not affect cell adhesion but accelerated cell growth remarkably. This acceleration effect is considered to be attributable to a prolonged interaction of immobilized insulin and insulin receptor by adhesion enhancement, and to a postulated interaction between activated insulin receptor and integrin.

Annexin V-coated intraocular lenses

PURPOSE

To assess whether annexin V-coated poly(methyl methacrylate) (PMMA) intraocular lenses (IOLs) prevent postoperative inflammation in rabbit eyes.

SETTING

Department of Ophthalmology, Hôpital Purpan, Toulouse, France.

METHODS

Thirteen IOLs coated with annexin V were implanted in 13 rabbit eyes; the contralateral eyes received uncoated IOLs. Postoperative fibrin was quantitated by daily slitlamp examination until the anterior chamber was completely clear. Results were analyzed using a Wilcoxon test. Ocular toxicity was evaluated by light and electron microscopy.

RESULTS

Eyes with the annexin V-coated IOLs had less severe inflammation on the first postoperative day, and the inflammation resolved more quickly than in eyes with uncoated IOLs (P < .05). No annexin V was released postoperatively, nor were there signs of ocular toxicity.

CONCLUSION

Annexin V-coated lenses effectively reduced postoperative inflammation in rabbit eyes.

In vitro bacterial adherence to hydrogel and poly(methyl methacrylate) intraocular lenses

PURPOSE

To compare the in vitro adherence of Staphylococcus epidermidis to poly-(hydroxyethyl methacrylate) (polyHEMA) or hydrogel intraocular lenses (IOLs) and poly(methyl methacrylate) (PMMA) IOLs.

SETTING

Lions Eye Institute, Perth, Western Australia.

METHODS

One-piece hydrogel lenses and one-piece PMMA lenses were suspended for 60 minutes in standardized suspensions of a well-characterized strain of S. epidermidis and then sonicated in a known quantity of balanced salt solution to remove the adherent bacteria. Quantitative cultures of the sonicates were performed and the results analyzed statistically.

RESULTS

The mean bacterial adherence of S. epidermidis to the PMMA IOLs (58,400 CFU) was more than 20 times greater than that to the hydrogel IOLs (1953 CFU). The difference was statistically significant (P < .001).

CONCLUSIONS

Adherence of S. epidermidis to hydrogel IOLs is significantly lower than to PMMA IOLs. This suggests that the risk of postoperative endophthalmitis after cataract extraction and IOL implantation may be lower with the use of hydrogel IOLs.

Corpectomy and stabilization with methylmethacrylate in patients with metastatic disease of the spine: a technical note

Corpectomy with methylmethacrylate reconstruction and stabilization in patients with metastatic disease of the spine has been performed for several years. Stainless steel Steinmann pins or K-wires are commonly used to facilitate fixation of the acrylic to the vertebral bodies above and below the resection site. The use of these ferromagnetic substances precludes the optimal use of magnetic resonance imaging in the postoperative period. We now report the use of commercially available titanium screws in conjunction with the methylmethacrylate to eliminate this problem and provide for improved postoperative imaging.

[Alterations of cardiac function and metabolism in the rat heart-lung preparation by methyl methacrylate (MMA) and their protection by ulinastatin]

We have assessed the deleterious effects of methyl methacrylate (MMA) on cardiac function and metabolism in the isolated heart-lung preparation and their protection by ulinastatin. Twenty-four male Wistar rats were prepared for the heart-lung model. They were randomly divided into 3 groups. In the MMA (M) and ulinastatin (U) groups, MMA 1000 micrograms.ml-1 was administered 7 minutes after the start of perfusion. At the end of the experimental period, the hearts were freeze-clamped and then myocardial high energy phosphates, lactate and glycogen were measured. Cardiac output decreased significantly in the M and U groups. Po2 of the perfusion blood in the M and U groups was significantly lower than that in the control (C) group. Myocardial ATP in the M and U groups was significantly lower than that in the C group. ADP and AMP in the M and U groups were higher than those in the C group. Although there was no significant difference in lactate levels among the 3 groups, glycogen in the U and C groups was significantly higher than that in the M group. MMA 1000 micrograms.ml-1 is much higher than the blood level (0.05-31.89 micrograms.ml-1) reported clinically in patients who had femoral prosthesis. Ulinastatin increased myocardial glycogen content which had been reduced by MMA. This may suggest that ulinastatin has a protective effect on heart damaged by MMA.

Influence of the dialyzer membrane material on sodium transport in hemodialysis

Traditionally Gibbs-Donnan coefficients based on the mean charge of plasma proteins are used as the only correction factor in equations describing sodium transport across the dialyzer membrane. This ignores the possible impact of the membrane material. Correction coefficients (CC) of the whole dialyzer were measured during in vivo dialysis as a quotient of dialysate to plasma sodium in an equilibrated state for different membrane materials used in commercially available dialyzers. Their mean value and correlation with total plasma protein content (TPP) were evaluated. CC for the six materials evaluated differed both in the intercept and slope of the regression line CC versus TPP: Cuprophan 1: CC = 1.0253 - 0.00017 x TPP; Hemophan 1: CC = 1.119 - 0.00175 x TPP; Hemophan 2: CC = 1.095 - 0.00111 x TPP; PMMA: CC = 1.0353 - 0.00044 x TPP; SCE:CC = 1.114 - 0.00145 x TPP; and Cuprophan 1:CC = 1.0562 - 0.00065 x TPP. The observed differences are attributed to the different charge densities of the membrane materials and suggest that for a precise description of sodium transport, the role of the membrane material needs to be considered.

Influence of hemodialysis membranes on gene expression and plasma levels of interleukin-1 beta

Plasma levels of interleukin-1 beta (IL-1 beta) were measured in 10 normal subjects, in 11 nondialyzed end-stage renal failure (ESRD) patients, and in 22 hemodialysis (HD) patients. Of the HD patients, 7 were dialyzed with Cuprophan (CU), 7 with polymethylmethacrylate (PMMA), and 8 with polysulphone (PS) dialyzers. In normal controls, nondialyzed ESRD patients, and HD equipped with CU, PAMM, and PS dialyzers, plasma levels of IL-1 beta were 10.73 +/- 5.24 pg/ml, 9.97 +/- 3.61 pg/ml, 13.17 +/- 4.04 pg/ml, 15.16 +/- 6.16 pg/ml, and 13.96 +/- 5.47 pg/ml, respectively. There were no statistically significant differences among the groups (p > or = 0.05). In contrast, the gene expression of IL-1 beta for peripheral blood mononuclear cells (PBMC) by in situ hybridization showed differences among the groups. The gene for IL-1 beta for PBMC appears in HD equipped with different membranes, but not in cases of nondialyzed uremic patients and normal subjects. With computer imaging analysis, we carried out quantitative analysis of cells in in situ hybridization with an area of positive spots to an area of total cells. In HD with CU, PMMA, and PS, the results were 10.64 +/- 1.07, 3.34 +/- 0.74, and 3.27 +/- 0.64%, respectively. The levels of IL-1 beta gene expression in CU were higher than that in PMMA or PS. There were statistically significant differences (p < or = 0.001) between CU and PMMA or PS and no significant difference between the PMMA and PS (p > or = 0.05). We suggest measuring the gene expression of cytokines for PBMC and which may be better than measuring cytokine levels only for investigating the blood compatibility of dialyzers, which may help in understanding chronic complications of the dialysis procedure.

Local antibacterial therapy for the management of orthopaedic infections. Pharmacokinetic considerations

Bone infection has long been a formidable foe of orthopaedic surgeons. The standard method of treating osteomyelitis generally consists of irrigation and debridement supplemented by pre- and postoperative antibiotics and intraoperative antimicrobial solutions. In the 1970s, Buchholz introduced the concept of local antibacterial therapy in the form of antibiotic impregnated bone cement to treated infected arthroplasties. From this, antibiotic impregnated beads were developed to treat local infections of bone and soft tissue. The advantage of these beads compared with parenteral therapy is that they deliver a high concentration of antibacterial locally while avoiding high systemic concentrations, thus avoiding adverse effects that are often associated with parenteral antibacterial therapy. Additionally, methylmethacrylate bone cement does not significantly affect the immune response of the body. This makes the use of antibiotic-impregnated polymethylmethacrylate (PMMA) beads highly effective either as an alternative to, or in conjunction with, systemic antibiotic treatment of infected arthroplasties, and localised bone and soft tissue infection. This article explores the indications for the use of local therapy as well as any advantages or disadvantages it may have over systemic antibacterial treatment. Additionally, there are important pharmacokinetic considerations for the optimal use of antibacterial agents in the treatment of osteomyelitis.

Swelling/deswelling of anionic copolymer gels

Studies of dynamic and equilibrium swelling of ionic gels are important in understanding the diffusion of physiologically important fluids in materials for site-specific controlled drug delivery applications. The dynamic and equilibrium swelling properties of dry glassy poly(2-hydroxyethyl methacrylate-co-methacrylic acid) and poly(2-hydroxyethyl methacrylate-co-acrylic acid) polymeric networks were studied as a function of pH, ionic strength, nature of the counterion and buffer composition. The mechanism of water diffusion in these gels became more anomalous as the pH of the swelling medium increased and as the ionic strength decreased at a constant pH > or = pKa,gel. The mechanism of water diffusion was Fickian in all unbuffered swelling media at pH 4.0, which is lower than the pKa,gel. The pKa,gel of these gels was between 5.5 and 6. At pH 4.0, the diffusion mechanism was independent of ionic strength. This swelling behaviour is explained in terms of the concept of ion osmotic swelling pressure and ion exchange kinetics.

Silicone rubber-hydrogel composites as polymeric biomaterials. VI. Transport properties in the water-swollen state

Permeation of inorganic salts in water-swollen silicone rubber-hydrogel composites consisting of a silicone rubber matrix and lightly cross-linked particles of poly(2-hydroxyethyl methacrylate), poly(2-hydroxyethyl methacrylate-co-methacrylic acid), poly(methacrylic acid), polyacrylamide or poly(acrylamide-co-methacrylic acid) hydrogels was investigated. The results, together with earlier data on permeation of non-ionic low-molecular-weight substances through the composite materials, were evaluated in terms of the free-volume diffusion theory. It was found that the materials with water content exceeding a certain limit are highly permeable to the salts, and that, as regards permeation properties, they behave as homogeneous water-swollen hydrogels. The dependence of electrical conductivity of the water-swollen composites on the hydrogel phase content was measured, and the results are discussed in relation to other transport properties and to the structure of the materials.

Adhesion and colonisation of Candida krusei on host surfaces

Candida krusei is an emerging pathogen, especially in immunocompromised hosts. As the adherence of this organism both to host epithelial surfaces and to catheter and prosthetic surfaces appears to be important in the pathogenesis of superficial as well as systemic candidoses, the adhesion of 20 oral isolates of C. krusei and five oral isolates of C. albicans was compared with the following substrates: cultured (HeLa) epithelial cells, buccal epithelial cells (BEC) from healthy adults and bone marrow transplant patients, and acrylic (polymethylmethacrylate) surfaces. Animal experiments in Sprague Dawley rats were also conducted to evaluate the relative oral carriage rate of the two Candida spp. C. krusei isolates adhered in far greater numbers to acrylic surfaces than to either of the cell surfaces. Significant intra-species differences in C. krusei adhesion for acrylic surfaces were noted between 74 (39%) of 190 pair comparisons in contrast to 18 (9.5%) of 190 with HeLa surfaces (p < 0.05). A positive correlation was also observed between the adhesion of C. krusei isolates to HeLa cells and acrylic surfaces. Five isolates of C. albicans showed very low adherence to HeLa surfaces when compared with BEC obtained from either healthy individuals or bone marrow transplant patients. The adherence of C. albicans to BEC from the healthy individuals was c. 12-fold greater than that of C. krusei, a figure similar to the relative murine oral carriage rate of the two Candida spp.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibiotic-leaching from polymethylmethacrylate beads

Aminoglycoside-impregnated polymethylmethacrylate beads, which are used to deliver antibiotic directly to infected sites in the musculoskeletal system, are available as a manufactured product or they can be mold-made by a pharmacy or hand-rolled by the orthopaedist in the operating suite. We investigated the leaching of antibiotic from each of these types of beads. Our hypothesis was that the elutions of antibiotic from the three types of beads are similar. Three study groups (hand-made, mold-made, and manufactured beads), each composed of four five-bead subsets, were formed so that twenty beads of each type were tested. Each bead was leached daily in a two-milliliter aliquot of normal saline solution throughout a sixty-day period, and the aminoglycoside concentration in twenty of these aliquots was determined. Analysis of variance showed no statistically significant differences when the antibiotic elutions within each subset, between the different subsets, and between the three groups were compared. The clinically important finding of this investigation is that the leaching characteristics of the three types of aminoglycoside-impregnated beads are equivalent when the beads have been fabricated out of comparable materials.

Adhesion of Staphylococcus aureus to surface-bound platelets: role of fibrinogen/fibrin and platelet integrins

Platelets adhering to artificial or biologic surfaces have been implicated in the pathogenesis of catheter infections or endocarditis; however, the ligands involved in Staphylococcus aureus interaction with adherent platelets remain incompletely understood. Radiolabeled S. aureus Cowan I were incubated with purified platelets adherent to polymethylmethacrylate (PMMA) coverslips and washed, and adhesion was determined. Platelets promoted adhesion of S. aureus approximately 30-fold compared with adhesion to albumin-PMMA. In the presence of both plasma (1% vol/vol) and platelets, adhesion was extensively promoted, with 30% (of inoculated) S. aureus adherent (150-fold increase). Platelet pretreatment with anti-GPIIb/IIIa monoclonal antibodies or inhibitors of platelet activation decreased plasma-enhanced adhesion, suggesting a role of platelet activation in S. aureus adhesion. Plasma-enhanced adhesion was sensitive to thrombin antagonists, proteinase inhibitors, heparin, or antifibrinogen antibodies, indicating that fibrinogen/fibrin is necessary for bridging between adherent platelets and S. aureus. In conclusion, S. aureus adhesion to immobilized platelets may play a role in the pathogenesis of invasive bloodstream infections or endocarditis.

An infrared study of the interaction of polymethyl methacrylate with the protein and mineral components of bone

We used Fourier transform infrared (FT-IR) microscopic mapping techniques to investigate the infiltration of polymethyl methacrylate (PMMA), a widely used medium for embedding biological tissues, into rat femur sections. Monitoring of the infrared absorbances of the PMMA carbonyl stretch, the protein amide I, and the apatite mineral phosphate stretch over a 225 x 975-microns region of the epiphyseal growth plate region of the rat femur enabled comparison of the relative amount of each component in distinct regions of the tissue. It was found that PMMA penetrates less into regions of greater mineral density and that the frequency of the PMMA carbonyl absorbance from the embedded tissue, 1729 cm-1, is identical to the free PMMA carbonyl frequency. This is consistent with a diffusion mechanism of infiltration of the PMMA, with no specific chemical interaction between the PMMA and the tissue components.

The effect of intramedullary polymethylmethacrylate on healing of intercalary cortical allografts in a canine model

The purpose of this study was to evaluate the effect of intramedullary polymethylmethacrylate (PMMA) bone cement on the healing of intercalary allografts. Thirteen adult beagles had bilateral intercalary femoral allografts implanted. The medullary canal of one randomly assigned allograft in each dog was filled with PMMA. Healing was followed clinically and femora were evaluated radiographically, biomechanically, histologically, and histomorphometrically 9 months after surgery. There was an increased percent of eroded surface at the endosteal area of the center region of grafts containing PMMA and there was an increased percent osteoblast surface in this area in grafts not containing PMMA. There was an increased percent eroded surface at the periosteal area in the center region in grafts not containing PMMA and there was an increased percent osteoblast surface at the periosteal area in the graft adjacent to the host junction in grafts containing PMMA. There was no significant difference between PMMA-treated and untreated allografts in any other parameters measured. The results from this study suggest that, although the pattern of incorporation is altered, intramedullary PMMA does not appear to effect allograft healing adversely.

In vitro and in vivo evaluation of antibiotic diffusion from antibiotic-impregnated polymethylmethacrylate beads

The elution of antibiotics from antibiotic-impregnated polymethylmethacrylate (PMMA) beads was measured in mongrel dogs. The antibiotics, used in mixture with Simplex cement, included cefazolin (Ancef; 4.5 g/40 g cement powder), ciprofloxacin (Cipro; 6 g/40 g powder), clindamycin (Cleocin; 6 g/40 g powder), ticarcillin (Ticar; 12 g/40 g powder), tobramycin (Nebcin; 9.8 g/40 g powder), and vancomycin (Vancocin; 4 g/40 g powder). After a pneumatic drill was used to dredge a trough in the tibia, five beads were implanted. During the next 28 days, seroma samples and serum samples were taken for antibiotic measurements. On Day 28, the dogs were killed, beads removed, and the seroma, serum, bone, and granulation tissue sampled. The results of the study showed that clindamycin, vancomycin, and tobramycin exhibited good elution characteristics and had consistently high levels in bone and granulation tissue.

The release of gentamicin after total hip replacement using low or high viscosity bone cement. A prospective, randomized study

Low viscosity bone cement is expected to give improved long term fixation of prosthetic components by increased intrusion into cancellous bone. Fixation is more difficult to achieve after revision for infection because of the inferior quality of the bone. We have compared the amount of gentamicin released from high viscosity and low viscosity bone cements in 41 patients undergoing total hip replacement. The concentration of gentamicin in serum and the wound secretion, and the amount recovered from the urine, was about three times higher for low viscosity cement. A possible explanation for this is an increase in surface area of the cement body because of improved intrusion of cement into bone. The improved mechanical fixation and the high concentration of gentamicin of the bone cement interface favours the use of low viscosity cement, especially in revision for deep infection.

Prostaglandin E2 levels in the membrane surrounding bulk and particulate polymethylmethacrylate in the rabbit tibia. A preliminary study

Fourteen mature New Zealand white female rabbits were allocated into two groups. Group 1 received a bolus doughy Simplex polymethylmethacrylate (PMMA) cement injected into the proximal tibia through a drill hole. Group 2 received an equal volume of particulate PMMA cement powder. The operated but nonimplanted left tibiae served as controls. The animals were killed after four months. The membrane surrounding the implant area was harvested aseptically and grown in tissue culture. The supernatants were assayed for prostaglandin E2 (PGE2) via radioimmunoassay. Bulk cement specimens produced on average 12.39 +/- 4.11 ng PGE2 on the right experimental side and 12.29 +/- 3.56 ng PGE2 on the left control side (not statistically different). Cement powder specimens produced 8.82 +/- 1.64 ng PGE2 on the right experimental side, which was statistically different from 4.21 +/- 0.88 ng PGE2 produced on the left control side. The ratio of PGE2 values for the right divided by the left side and the arithmetic difference between right and left sides were significantly higher in the particle group compared with the bulk group. Small, undigestable cement particles may be phagocytosed by foreign-body giant cells and histiocytes and then extruded into the extracellular compartment, along with substances such as PGE2. PGE2 has been implicated as the biologic mechanism for stimulating the bone lysis associated with prosthetic loosening.

Growth hormone in polymethylmethacrylate cement

The in vitro release of human growth hormone (hGH) from polymethylmethacrylate bone cement was measured for up to 40 days using a specific enzyme-linked immunosorbent assay. In rabbits, hGH-loaded bone cement was inserted into one distal femur and plain cement was inserted into the contralateral distal femur as a control. The rabbits were killed at time intervals of one, two, and four months after surgery and the distal femurs embedded whole for histology. Quantitative histomorphometry indicated there was a greater percentage of osteoid present at the hGH-loaded cement surface than at the plain cement surface one month after implantation. The hGH released from bone cement may stimulate osteogenesis and new bone formation, thus improving the strength of the bone-cement interface.

Paraperm EW lens for extended wear

This paper reports the results of 372 patients fit with the Paraperm EW rigid gas permeable lens for extended wear. This lens material is a copolymer derived from siloxane and methylmethacrylate with an oxygen permeability (Dk) of 56 X 10(-11) at 37 degrees C. At the end of 1 year, 270 patients had completed the study with 94.8% achieving 20/25 or better vision. Complications included a 12.3% incidence of superficial limbal keratitis with staining, a 3.1% incidence of conjunctival injection, and a 1.5% incidence of observable corneal edema. The lens appears to be a significant addition to the possibilities available for fitting extended wear patients or those who desire occasional overnight lens wear.

Nuclear magnetic resonance spectroscopic studies of the interaction of methyl methacrylate and ethylene dimethacrylate with phosphatidylcholine liposomes as a model for biomembranes

The interaction of methyl methacrylate (MMA) and ethylene dimethacrylate (EDMA) with dipalmitoyl phosphatidylcholine (DPPC) liposomes was studied by 1H and 13C nuclear magnetic resonance spectroscopy (NMR). It was found that the changes in the 1H chemical shift of EDMA were larger than those of MMA when comparing membrane-bound state with free state and that the amount of EDMA incorporated into DPPC liposomes was approximately 74%, whilst MMA was approximately 41%. The major changes in chemical shifts of EDMA appeared to be due to its interaction with the acyl chains of DPPC liposomes.

[The role of rat liver microsomes in the metabolism of methylmethacrylate to formaldehyde]

Rat liver microsomal carboxylesterase catalyzed hydrolysis of butyl methacrylate (BMA), butyl acrylate (BA), methyl acrylate (MA) and methyl methacrylate (MMA). The rate of butanol formation from BA and BMA was 4-fold higher as compared with methanol production from MA and MMA. Methanol was oxidized to formaldehyde at the next step of microsomal metabolism. The rate of methanol oxidation was increased 2.2-fold after addition of the NADPH-generating system into the incubation medium. In the mixture containing MMA, NADPH-generating system and liver microsomes, preinduced with phenobarbital or methyl cholanthrene, the rate of formaldehyde generation was increased 7- and 2-fold, respectively, as compared with the analogous experiments involving liver microsomes of control rats. Production of methanol and generation of formaldehyde were not detected after incubation of MMA with inactivated microsomes. The microsomal MMA-methanol oxidizing system was inhibited by CO or after addition of microsomes from rats pretreated with CoCL2. Sodium azide (0.05 mM) decreased 8-fold the rate of formaldehyde generation.

Adsorption of proteins from artificial tear solutions to contact lens materials

A series of polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) were synthesized in order to find surfaces that would adsorb minimal amounts of protein. The adsorption of albumin, lysozyme and immunoglobulin G from a three-way mixture of these proteins in isotonic buffered saline to the polymers was measured using 125I-labeled proteins. Apparently high protein uptake on copolymers rich in HEMA was found to be due to sorption of unbound 125I by the polymers. 125I sorption by the polymers was minimized by dialysis of the protein solution to remove unbound 125I iodide and inclusion of 0.01 M sodium iodide to block uptake of residual 125I iodide. Using these improved protocols, minimal total protein uptake was observed on copolymers containing 50% or more HEMA. The majority of adsorbed protein on all p(MMA-HEMA) polymers was albumin. Total protein uptake was greatest on pMMA. Commercial contact lenses composed of copolymers of HEMA and N-vinyl pyrrolidone (NVP) or acrylamide (AAm) adsorbed small amounts of all proteins whereas copolymers of methacrylic acid (MAAc) and HEMA adsorbed much larger quantities of lysozyme. These results indicate that protein uptake by contact lens materials varies greatly with polymer composition. Artifactually high "adsorption" can occur if precautions are not taken to prevent uptake of unbound 125I.

In vitro complement-independent activation of human neutrophils by hemodialysis membranes: role of the net electric charge

Polymethylmethacrylate (PMMA) membranes with different net electric charges and percentage water contents (anionic 71%, neutral 70%, cationic 75%) were evaluated for their ability to stimulate plasma-free human polymorphonuclear neutrophils (PMN), and compared for potency to cuprophan (Cu), already described as being a potent trigger of PMN. The release of lysozyme, beta-glucuronidase, lactic dehydrogenase (LDH), and the generation of a platelet aggregating activity were studied in the supernatants from plasma-free human PMN incubated with different membranes. The PMN intracellular content of neutrophil cationic proteins (NCP), elastase, and cathepsin G were also studied by immunofluorescence using specific antisera on smears of PMN before and after incubation with each membrane. Only cationic, but not anionic or neutral PMMA induced a marked release of lysozyme (range 20-25% of the sonicated control, assumed as 100%), and beta-glucuronidase (40-43%), and marked depletion of the intracellular content of NCP, elastase, and cathepsin G, suggesting a degranulation process. Platelet aggregating activity was generated and referred to the release of platelet activating factor (PAF) only in the supernatants from PMN incubated with cationic, but not with anionic, or neutral PMMA membranes. These results indicate that modification of the net electric charge can per se turn PMMA, commonly recognized as inert, into a material with marked PMN activating effects, comparable to those of Cu, a highly reactive polymer.

In vitro measurement and computer modelling of the diffusion of antibiotic in bone cement

The diffusion coefficient for a particular antibiotic (benzyl penicillin) in various types of bone cement has been calculated from direct measurement of the passage of radio-labelled penicillin through thin sections of cement at intervals over a period of 90 days, assuming the transport processes to be Fickian. Since the concentration gradient across the test sample is not uniform in the earlier stages of the experiment, a finite-difference approximation to the diffusion equation was used to take account of the transient behaviour in determining the coefficient. This method of analysis may also be used to predict the release, as a function of time, from the surface of antibiotic-loaded bone cement and from implanted pre-loaded PMMA beads used to provide antibiotic cover following bone or joint surgery. Our computer-generated predictions appear to agree very well with previously published figures arising from in vivo and in vitro studies and we conclude therefore, that Fick's Law accurately describes the process, even when the cement mix is inhomogeneous. We have by this means a reliable method by which the diffusion coefficients for various combinations of cement, antibiotic and other additives may be retrospectively determined and compared.

Gentamicin-PMMA beads. Pharmacokinetic and nephrotoxicological study

Five patients treated with gentamicin-polymethylmethacrylate (PMMA) beads were monitored during the treatment of nine to 14 days. Kinetic data of the gentamicin delivery were gathered constantly by multiple samples of blood and urine. The treatment with 48-360 beads caused a gentamicin serum concentration of 0.03-0.4 micrograms/ml and a renal excretion rate of 3-40 micrograms/min. The total amount of gentamicin excreted after the whole treatment was 20%-70%, with an in vivo half-life of 5.7-10 days. The gentamicin appeared to be released constantly during the entire treatment (nine to 14 days); the beads are kinetically slow release carriers. Despite precise measurement of tubular and glomerular renal function, no nephrotoxicity could be demonstrated. This local antibiotic gentamicin therapy may use the blood bone barrier effectively as a protection of the body against a very high local gentamicin concentration.

Biocompatibility of different hemodialysis membranes: activation of complement and leukopenia

The ability of three hollow-fiber dialyzers (Cuprophane [CU], polymethylmethacrylate [PMMA], and polyacrylonitrile [PAN]) to activate complement and to induce leukopenia was studied prospectively in six patients on long-term hemodialysis. CU membranes caused the most intense complement activation with C3a, C3d, and C5a levels peaking 15 min after beginning dialysis. Total white blood cell (WBC) counts dropped simultaneously by 76%, and the decrease in leukocytes was inversely correlated with the levels of C3a and C5a. In contrast, PMMA membranes led only to slight complement activation with an associated fall in WBC counts of 29%, and PAN membranes induced very little complement activation without leukopenia. In vitro studies involving incubation of normal human plasma with each of the three membranes corroborated these findings. The results suggest that the biocompatibility of PMMA and PAN dialyzers is superior to CU.

[Determination of methylmethacrylate in expired gases after hip prosthesis cementing]

Total hip replacement using methylmethacrylate can induce early intraoperative hypoxaemia caused, according to some authors, by alveolar gas dilution by acrylic monomer vapour. In order to test this hypothesis, expired monomer was measured in ten patients undergoing total hip replacement carried out under narconeuroleptanalgesia. Methylmethacrylate was collected by adsorption on activated charcoal and measured by gas chromatography. The quality of expired monomer was 25 +/- 10 micrograms after cotyloid sealing. It is of 264 +/- 396 micrograms after femoral sealing; the most important excretion took place in the first three minutes, and its total duration may exceed 18 min. A simple calculation showed quite convincingly that the volume of expired monomer vapour was not sufficient to explain the hypoxaemia: impaired arterial oxygenation associated with the use of methylmethacrylate is not due to a dilution technique.

The clearance of gentamicin from antibiotic-loaded bone cement

The concentrations of Gentamicin in the serum, drainage fluid and urine were determined by radioimmunoassay in 40 patients after total hip replacement and 10 after knee replacement. Palacos R bone cement with added Gentamicin had been used to fix the prostheses in all cases. Two types of response were observed; in Group I the Gentamicin levels rose very rapidly, whereas in Group II a more gradual increase was seen. In all cases the level of Gentamicin had fallen to a negligible amount by the fifth day after operation.

Methylmethacrylate: tissue distribution and pulmonary damage in rats following acute inhalation

Distribution in blood, brain and lungs, and histopathologic changes in brain and lungs of rats following inhalation exposure to methylmethacrylate monomer (MMA) are reported. On exposing groups of four male rats to air containing 100 ppm of MMA, the concentration of MMA in the tissues determined by headspace gas chromatography, was found to be 11.14 +/- 1.05 mg % in blood, 25.24 +/- 2.04 micrograms/g in brain, 20.60 +/- 1.01 micrograms/g in lungs; these did not change significantly with different exposure periods. Interalveolar congestion/hemorrhage, pulmonary vasodilation and edema were observed with rats exposed for 2,3 and 4 hours but not for 1 hour. No histopathologic changes were seen in the brain of any of the exposed rats.

Distribution and elimination of coated polymethyl [2-14C]methacrylate nanoparticles after intravenous injection in rats

Surfactant-coated polymethyl [2-14C]methacrylate nanoparticles had significantly different time-course distribution patterns in rats than noncoated and albumin-coated particles. Blood concentrations of poloxamer 188-coated particles were 70-fold higher after 30 min, and the particles persisted at higher levels in the circulation for up to 2 h. The initial and final liver levels were significantly lower (38% after 30 min, 51% after 7 d) and spleen levels were significantly higher (21% after 30 min, 23% after 7 d) than non-coated particles (74% in the liver and 5% in the spleen after 7 d) and the albumin-coated particles (84% in the liver and 5% in the spleen after 7 d). Specific activity was somewhat higher for the surfactant-coated particles in other organs such as the lungs, kidneys, testicles, ovaries, and lymph nodes. The bovine serum albumin sorption behavior of polymethyl methacrylate nanoparticles was followed under various conditions, and adsorption was found to increase with increasing protein concentration and increasing temperature, reaching a maximum at the isoelectric point of pH 4.9 after approximately 12 h of incubation. The zeta potential of the particles decreased with increasing pH, and the change was more pronounced with the albumin-coated particles.