Electrostatic layer-by-layer nanoassembly on biological microtemplates: platelets

Platelets were coated with 78-nm silica nanoparticles, 45-nm fluorescent nanospheres, or bovine immunoglobulin G (IgG) through layer-by-layer assembly by alternate adsorption with oppositely charged linear polyions. Sequential deposition on platelet surfaces of cationic poly(dimethyldiallylammonium chloride) and anionic poly(styrene sulfonate) was followed by adsorption of nanoparticles or immunoglobulins. Nano-organized shells of platelets were demonstrated by transmission electron microscopy and fluorescence microscope images. Bovine IgG was assembled on platelets, as verified with anti-bovine IgG-FITC labeling. Localized targeting of anti-IgG shelled platelets was also demonstrated. An ability to coat blood cells with nano-organized shells can have applications in cardiovascular research and targeted drug delivery.

Influence of the surface characteristics of PVM/MA nanoparticles on their bioadhesive properties

The aim of this work was to investigate the influence of the cross-linkage of poly(methylvinylether-co-maleic anhydride) (PVM/MA) nanoparticles with increasing amounts of 1,3-diaminopropane (DP) and, eventually, bovine serum albumin (BSA) on their gastrointestinal transit and bioadhesive properties. The fluorescently-labelled formulations were orally administered to rats and, at different times, the amount of nanoparticles in both the lumen content and adhered to the gut mucosa were quantified. The gut transit was evaluated by calculating the gastric (k(ge)) and intestinal (k(ie)) emptying rates. The adhered fraction of nanoparticles in the whole gut was plotted versus time and, from these curves, the intensity, capacity and extent of the adhesive interactions were estimated. The bioadhesive potential of PVM/MA was much higher when formulated as nanoparticles (NP) than in the solubilised form in water. However, k(ge) and k(ie) increased by increasing the extent of cross-linkage of nanoparticles with DP, while the capacity to develop adhesive interactions and the intensity of the adhesive phenomenon were significantly higher for non-hardened than for DP-cross-linked carriers. In contrast, the BSA-coating of cross-linked nanoparticles significantly decreased k(ge) and k(gi), whereas the intensity of the bioadhesive phenomenon was significantly higher than for NP. In summary, the adhesivity of the nanoparticles appears to modulate their gastrointestinal transit profile.

O2-Cu/ZIF-8@Ce6/ZIF-8@F127 Composite as a Tumor Microenvironment-Responsive Nanoplatform with Enhanced Photo-/Chemodynamic Antitumor Efficacy

Hypoxia and overexpression of glutathione (GSH) are typical characteristics of the tumor microenvironment, which severely hinders cancer treatments. Here, we design a novel biodegradable therapeutic system, O₂-Cu/ZIF-8@Ce6/ZIF-8@F127 (OCZCF), to simultaneously achieve GSH depletion and O₂-enhanced combination therapy. Notably, the doped Cu²⁺ doubles the O₂ storage capacity of the ZIF-8 matrix, which makes OCZCF an excellent pH-sensitive O₂ reservoir for conquering tumor hypoxia, enhancing the photodynamic therapy (PDT) efficiency of chlorin e6 (Ce6) under 650 nm laser irradiation. Moreover, the released Cu²⁺ can act as a smart reactive oxygen species protector by consuming intracellular GSH. The byproduct Cu⁺ will undergo highly efficient Fenton-like reaction to achieve chemodynamic therapy (CDT) in the presence of abundant H₂O₂. The accompanying O₂ will further alleviate hypoxia. The in vitro and in vivo experimental data indicate that OCZCF could cause remarkable tumor inhibition through enhanced synergetic PDT and CDT, which may open up a new path for cancer therapy.

Poly(d,llactide–co-ethyl ethylene phosphate)s as new drug carriers

Many biodegradable polymers have been developed for controlled drug delivery. The plethora of drug therapies and types of drugs demand different formulations, fabrications conditions and release kinetics. No one single polymer can satisfy all the requirements. To extend the properties of poly(D,L-lactide) (PLA), we synthesized copolymers of PLA and poly(ethylethylene phosphate) (PEEP) by ring-opening polymerization using Al(Oipr)3 as the initiator. The copolymers were structurally characterized by IR and 1H NMR. DSC data confirmed the formation of random microphase structure in all the copolymers, and showed a decrease of Tg from 43.2 to -22.6 degrees C when the molar content of ethylethylene phosphate (EEP) increased from 5 to 40%. The hydrophilicity of the copolymers increased with EEP content. In contrast to the degradation behavior of PLA, disc samples made of PLAEEP90 showed a linear weight loss profile in PBS (pH 7.4) at 37 degrees C. BSA microspheres using PLAEEP90 were prepared by double-emulsion method, yielding a loading level of 4.3% and a loading efficiency of 75%. The BSA release profile consisted of an initial burst (9%) on the first day, followed by a daily 4% release for the following 40 days, resulting in 91% of the BSA release in a near linear manner. The released BSA remained intact according to SDS-PAGE data. Cytotoxicity and histopathology studies showed low toxicity in HeLa cells and good tissue biocompatibility in mouse brain, respectively. PLAEEP is a promising biodegradable polymer for controlled drug delivery.

Effects of sevelamer hydrochloride and calcium acetate on the oral bioavailability of ciprofloxacin

BACKGROUND

The oral bioavailability of ciprofloxacin is significantly decreased when administered with calcium carbonate. Sevelamer hydrochloride is a phosphate-binding cationic polymer that is devoid of calcium. The authors conducted a 3-way, randomized, crossover study to determine the effects of sevelamer hydrochloride and calcium acetate on the relative oral bioavailability of ciprofloxacin.

METHODS

Fifteen healthy volunteers were assigned randomly to receive each of the following oral regimens: ciprofloxacin 750 mg, alone (Arm A); ciprofloxacin 750 mg plus 7 sevelamer hydrochloride 403 mg capsules (Arm B); ciprofloxacin 750 mg plus 4 calcium acetate 667 mg tablets (Arm C). Serial blood and urine samples were obtained over 24 hours, and ciprofloxacin concentrations were determined by high-performance liquid chromatography. Pharmacokinetic data were analyzed using noncompartmental methods, and maximum serum concentration (Cmax) and area under the serum concentration time curve from 0 to infinity (AUC(0- infinity )) were tested for bioequivalence after log transformation of the data. The relative oral bioavailability of ciprofloxacin was calculated as AUC(0- infinity ), Arm B or Arm C/AUC(0- infinity ), Arm A.

RESULTS

The Cmax and AUC(0- infinity ) of ciprofloxacin were significantly decreased when administered concomitantly with sevelamer hydrochloride or calcium acetate (P < 0.05), and bioequivalence was not achieved for either parameter. The relative oral bioavailability of ciprofloxacin was decreased by 48% with sevelamer hydrochloride and 51% with calcium acetate (P < 0.05).

CONCLUSION

The relative oral bioavailability of ciprofloxacin is significantly decreased when administered with sevelamer hydrochloride or calcium acetate. Concomitant administration of these drugs may decrease clinical efficacy and promote bacterial resistance to ciprofloxacin.

Development of novel 5-FU-loaded poly(methylidene malonate 2.1.2)-based microspheres for the treatment of brain cancers

In order to treat malignant brain tumors by local delivery of antineoplastic agents, the feasibility of 5-fluorouracil (5-FU)-sustained release biodegradable microspheres with a novel material, poly(methylidene malonate 2.1.2), was investigated using an emulsion/extraction method. This polymer was expected to present a slow degradation rate, thus leading to a long term local delivery system. Microparticles were successfully obtained and characterized in terms of drug loading, size, morphology and release profile. The size of the particles was between 40 and 50 microm, which was compatible with a stereotactic injection through a needle. Sufficient drug loadings were obtained (i.e. compatible with the preparation of therapeutic 5-FU doses in a minimal volume of injection), and perfectly spherical microspheres were observed. The respective influences of the polymer molecular weight, the polymer concentration, and the emulsion time on the release profiles were studied using a 2(3) factorial design. In the same objective, the solvent extraction time was extended while keeping all the previous parameters fixed at their optimal values. The in vitro study of these different parameters allowed a reduction of the initial burst release, with a percentage of 5-FU released after 24 h that was lowered from 90 to 65%, and the achievement of a long term drug delivery system, since the release was still ongoing after 43 days. Moreover, the microparticles could be gamma-sterilized (25 kGy) without modification of the release kinetics. Thus, the requested specifications to perform animal experiments were attained.

Unacceptable biodegradation of polyethylene in vivo

The chemical characterization of 19 retrieved ultra-high-molecular-weight polyethylene tibial plateaux, six new ones and one raw bar was performed by means of infrared spectroscopy. The surface and bulk oxidation and biodegradation indexes were calculated. The raw bar has a measurable oxidation, which increases on the bulk and on the surfaces of the new plateaux. In the retrieved plateaux, the average oxidation index increases further both on the bulk and on the surfaces; the worse values were present on the worn area. Similar results were found for the biodegradation index. The data show that the biotic in vivo degradation is promoted by the oxidation present on the new plateaux and that it occurs through a different mechanism, abiotic thermal-, photo-, gamma-radiation oxidation, evaluated by the oxidation index.

High-temperature migration of antioxidants from polyolefins

Migration rates of radiolabelled antioxidants, Irganox-1010 (I-1010) and Irganox-1076 (I-1076), were measured from low- and high-density polyethylenes (LDPE, HDPE) and polypropylene (PP) at temperatures up to 135 degrees C. Water, 8 and 95 per cent aqueous ethanol and corn oil were employed as food simulating liquids (FSL). The experiments were conducted in a high-pressure cell in a manner that allowed contact between the polyolefin plaque and the FSL only during the test period and not while being heated. The migrations of the antioxidants varied with the square root of time, and the Fickian diffusion coefficients could be correlated with temperature in an Arrhenius fashion. Under comparable test conditions, antioxidant migrations were largest from PP for aqueous simulants, but for non-aqueous simulants the highest losses were from LDPE. In both instances lowest losses were from HDPE. In most instances there was little difference between the migration behaviour of I-1010 and I-1076. A few tests were conducted to measure the antioxidant migrations to foods. The losses were usually larger than those to water but below those to corn oil.

Sevelamer, a phosphate-binding polymer, is a non-absorbed compound

OBJECTIVE

To examine the absorption, distribution and excretion of sevelamer hydrochloride in rats and humans.

PARTICIPANTS

Twelve male Sprague-Dawley rats were used in the animal study, and twenty human volunteers participated in the clinical trial.

METHODS

In the animal study, six rats received a single oral dose of [(3)H]sevelamer and six rats were pretreated with unlabelled sevelamer in the diet for 28 days followed by a single dose of [(3)H]sevelamer on day 29. Total urine and faeces were collected at intervals up to 72 hours post dose, and tissues were obtained at the time of sacrifice. In the clinical trial, subjects received a single oral dose of [(14)C]sevelamer following 28 days of pretreatment with unlabelled sevelamer. Blood, urine and faeces samples were collected at intervals up to 96 hours.

RESULTS

In the rat study, no significant urinary excretion of radioactivity was observed. The average recovery of radioactivity in the faeces was 98% in the single-dose group and greater than 100% in the group pretreated with unlabelled sevelamer for 28 days. A total of less than 0.1% of the dose was found in the tissues. In the human study, no detectable amount of (14)C was found in the blood of any subject at any time. The majority of subjects had no detectable amounts of (14)C recovered in the urine. In subjects where (14)C was recovered in the urine, less than 0.02% was detected, a level equivalent to the free (14)C detected in the [(14)C]sevelamer preparation. On average, greater than 99% of the administered dose was recovered in the faeces of the subjects.

CONCLUSION

These studies demonstrate that sevelamer is a non-absorbed compound.

Comparison of Silver-Coated Dressing (Acticoat???), Chlorhexidine Acetate 0.5% (Bactigrass??), and Silver Sulfadiazine 1% (Silverdin??) for Topical Antibacterial Effect in Pseudomonas Aeruginosa-Contaminated, Full-Skin Thickness Burn Wounds in Rats

Acticoat (Smith and Nephew, Istanbul, Turkey), chlorhexidine acetate 0.5%, and silver sulfadiazine 1% were compared to assess the antibacterial effect of their application on experimental burn wounds in contaminated with Pseudomonas aeruginosa in rats. All treatment modalities were effective against P. aeruginosa because there were significant differences between treatment groups and control groups. The mean eschar concentrations did not differ significantly between Acticoat and chlorhexidine acetate groups, but there were significant differences between the silver sulfadiazine group and the other treatment groups, indicating that silver sulfadiazine significantly eliminated P. aeruginosa more effectively in the tissues than did the other two agents. All treatment modalities were sufficient to prevent the P. aeruginosa from invading to the muscle and from causing systemic infection. In conclusion, silver sulfadiazine is the most effective agent in the treatment of the P. aeruginosa-contaminated burn wounds; Acticoat can be considered as a treatment choice because of its peculiar ability of limiting the frequency of replacing wound dressings.

The encapsulation and intracellular delivery of trehalose using a thermally responsive nanocapsule

The thermally responsive wall permeability of an empty core-shell structured Pluronic nanocapsule (together with its temperature dependent size and surface charge) was successfully utilized for encapsulation, intracellular delivery, and controlled release of trehalose, a highly hydrophilic small (M(W) = 342 D) molecule (a disaccharide of glucose) that is exceptional for long-term stabilization of biologicals (particularly at ambient temperatures). It was found that trehalose can be physically encapsulated in the nanocapsule using a soaking-freeze-drying-heating procedure. The nanocapsule is capable of physically withholding trehalose with negligible release in hours for cellular uptake at 37 degrees C when its wall permeability is low. A quick release of the encapsulated sugar can be achieved by thermally cycling the nanocapsule between 37 and 22 degrees C (or lower). A significant amount of trehalose (up to 0.3 M) can be delivered into NIH 3T3 fibroblasts by incubating the cells with the trehalose-encapsulated nanocapsules at 37 degrees C for 40 min. Moreover, cytotoxicity of the nanocapsule for the purpose of intracellular delivery of trehalose was found to be negligible. Altogether, the thermally responsive nanocapsule is effective for intracellular delivery of trehalose, which is critical for the long-term stabilization of mammalian cells at ambient temperatures and the eventual success of modern cell-based medicine.

Preparation and characterization of novel poly(methylidene malonate 2.1.2.)-made nanoparticles

Poly(methylidene malonate 2.1.2.) (PMM 2.1.2.) nanoparticles were prepared in phosphate buffer through emulsion polymerization of monomeric units; the kinetics of the reaction was monitored by spectrophotometry at 400 nm. Average nanoparticle sizes, molecular weights, and biodegradability of this potential drug carrier were determined under various conditions. As previously demonstrated for other similar monomers, i.e. IHCA or IBCA, pH influenced the physico-chemical characteristics of the nanoparticles obtained. Ethanol release from the ester-bearing side chains indicated that the polymers were susceptible to hydrolysis when incubated in basic pH or in rat plasma. A secondary degradation pathway, yielding formaldehyde through a reverse Knoevenagel's reaction, was minimal. Cytotoxicity studies of this new vector, in vitro, against L929 fibroblast cells demonstrated that PMM 2.1.2. nanoparticles were better tolerated than other poly(alkylcyanoacrylate) (PACA) carriers. Pharmacokinetic studies were also carried out to observe the fate of 14C-labelled PMM 2.1.2. nanoparticles after intravenous administration to rats. Forty eight hour post-injection, more than 80% of the radioactivity was recovered in urine and faeces. The body distribution of the polymer was estimated by measuring the radioactivity associated with liver, spleen, lung and kidneys. Five minutes after injection, a maximum of 24 +/- 2% of the total radioactivity was detected in the liver and less than 0.4% in the spleen. The liver-associated radioactivity decreased according to a biphasic profile and less than 8% of the total radioactivity remained after 6 days.

Evaluation of polyethylene terephthalate cyclic trimer migration from microwave food packaging using temperature-time profiles

The polymer polyethylene terephthalate (PET) is widely used for packaging food that will be heated or cooked in the PET container. A procedure was developed to predict the potential of PET to migrate from the container into the food. Migration experiments using crystallized polyethylene terephthalate (CPET) and corn oil were performed at 115, 146 and 176 degrees C. From these experiments diffusion coefficients were calculated for the cyclic trimer in PET. By using an Arrhenius plot to obtain the diffusion coefficient and a temperature versus time plot of a microwave susceptor-heated CPET tray, it was possible to predict migration of the cyclic trimer into corn oil under microwave conditions. Predicted values were in good agreement with measured results.

Interaction of triclosan with eukaryotic membrane lipids

The possibility that triclosan and PVM/MA (polyvinylmethyl ether/maleic acid) copolymer, additives to dentrifrices, could interact with eukaryotic membrane lipids was studied by two methods: first, by determining the pressure/molecular area isotherms at 37 degrees C of glycerophospholipid monolayers, using the Langmuir technique; and second, by phase-transition parameters in liposomes of the same lipids, using differential scanning calorimetry (DSC). Triclosan interacted, in a concentration-independent manner, with monolayers of saturated phosphatidylcholines (PC; i.e. markers of the outer membrane leaflet of eukaryotic cells). Triclosan and PVM/MA copolymer mixtures were shown to clearly interact in a concentration-dependent manner with PC. Triclosan was found to interact with liposomes of saturated and unsaturated phosphatidylcholines and phosphatidylserines (PS; i.e. markers of the inner membrane leaflet of eukaryotic cells), and saturated ethanolamines (PE; i.e. markers of the inner membrane leaflet of eukaryotic cells), resulting in a decrease of the lipid melting temperature (Tm). PVM/MA copolymer changed the Tm of PS, PC, and PE in different manners. By adding PVM/MA or triclosan-PVM/MA copolymer mixtures to 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoserine (SOPS) no lipid transitions were detected. A biphasic change of the PC transition temperature resulted when triclosan or triclosan PVM/MA copolymer mixtures were added, indicating domain formation and change of the lipid polymorphism.

Increase in permeability and phospholipase A2 activity of colonic mucosa in Crohn's colitis

Patients with Crohn's colitis were investigated regarding the relationship between intestinal inflammation, mucosal activity of phospholipase A2 and intestinal permeability to different-sized polyethylene glycols (PEG). Mucosal specimens for phospholipase A2 were obtained at colonoscopy and PEG (590-942 daltons) were deposited in the descending colon. Colonic absorption was measured as urinary output of deposited PEG. Colonic absorption of PEG was higher in these patients, even when the colitis was in remission at colonoscopy, than in ileal Crohn's disease or control patients. Mucosal phospholipase A2 activity was increased in active colitis, but in the patients with endoscopic remission it was at the same level as in the controls or in the patients with ileal Crohn's disease. The observations suggest that increased intestinal permeability may be a primary factor in activation of mucosal phospholipase A2 activity and in intestinal inflammation.

An anionic charge barrier in the guinea pig cochlea

A charge barrier has been found in the glomerular basement membrane of the kidney and plays an important role in the filtration of solutes. In the present study, we used electron microscopy to localize anionic sites of a similar charge barrier in the guinea pig cochlea. Polyethyleneimine (PEI) was used as a cationic marker to detect anionic sites. Our results showed a localization of PEI with regular interspaces, indicating the anionic sites to the charge in the capillary basement membrane of the stria vascularis and the spiral ligament, and in the basal lamina of Reissner's membrane and the spiral prominence. This charge barrier, as well as structural size barrier, may play an important role in the maintenance of normal inner ear functions.

Topical Application of Ionic Polymers Affects Skin Permeability Barrier Homeostasis

We previously demonstrated that the external electric potential affected skin barrier homeostasis. On the other hand, topical application of an ionic polymer formed a diffusion electric double layer on the surface of the skin. Thus, we evaluated effects of topical application of ionic polymers on the damaged skin barrier. Application of a nonionic polymer did not affect barrier recovery. Application of sodium salts of anionic polymers accelerated barrier recovery, while that of cationic polymers delayed it. Topical application of a sodium-exchange resin accelerated barrier recovery, but application of a calcium-exchange resin had no effect even when the resins had the same structure. Application of a chloride-exchange resin delayed barrier recovery. Topical application of ionic polymers influenced skin barrier homeostasis.

Biodegradation of poly(ethylene adipate) microcapsules in physiological media

Spherical reservoir-type microcapsules fabricated using a water/oil/water (W/O/W) double emulsion technique with solvent evaporation and composed of poly(ethylene adipate) (PEAD) blended with 20% poly-epsilon-caprolactone (PCL II) containing a range of bovine serum albumin (BSA) loadings were incubated in Hank's buffer, pH 7.4, newborn calf serum, 1.5% pancreatin and synthetic gastric juice containing 10% pepsin A over 30 days and their percentage weight loss (PWL) and changes in ultrastructural morphology monitored by gravimetry and stereoscan electron microscopy (SEM) respectively. The greatest PWL from microcapsules was observed after incubation in newborn calf serum (NCS) and pancreatin and decreased in the order NCS > pancreatin > synthetic gastric juice > Hank's buffer. Only microcapsules theoretically loaded with 5-20% BSA and incubated in synthetic gastric juice showed a significant increase in PWL with increasing percentage BSA loading. The structural biodegradation of PEAD microcapsules in both Hank's buffer and synthetic gastric juice was minimal whilst the morphological changes observed during incubation in NCS involved pitting of the membrane, some surface erosion and reduction in diameter, followed by microcapsule membrane disruption and loss of reservoir contents. Biodegradation in pancreatin was associated with surface flaking and loss of large fragments of the microcapsule membrane. Only in NCS and pancreatin, where one would expect to see the effects of enzyme activity in addition to simple ester hydrolysis, did biodegradation proceed to the stage where there was a loss of spherical shape and almost total disruption of the microcapsule structure within 30 days.

In vitro and in vivo evaluation of poly(methylidene malonate 2.1.2) microparticles behavior for oral administration

The goal of this paper was to investigate the fate of novel poly(methylidene malonate 2.1.2) microparticles with different surface properties, i.e. prepared with or without polyvinylalcohol (PVA), after oral administration, using in vitro cell culture and an in vivo mice model. Incubation of particles with Caco-2 cells induced no cytotoxicity except for the microparticles prepared without PVA at high concentrations. At subtoxic concentrations, microparticles were highly associated to cells, independently of particles concentrations, particles surface properties (with or without PVA) or incubation time. Confocal microscopy analysis revealed that adsorption was the main phenomenon leading to the association of particles to cells. However, association was greater at 37 degrees C than at 4 degrees C, suggesting that an active process, such as endocytosis, could also occur. In vivo, radiolabeled particles were mainly found in luminal content and also adsorbed onto the epithelium. After 24 hours, more than 15% of PVA-free microparticles were still present in the gastrointestinal tract, compared to 5% for particles prepared with PVA. However, histological evaluation revealed low uptake of particles by Peyer's patches. As a conclusion, this study provided a good correlation between in vitro and in vivo evaluation. These particles could be useful for oral sustained release and delivery of drugs to intestinal and colon epithelium.

Polychlorotrifluoroethylene (PCTFE) oligomer pharmacokinetics in Fischer 344 rats: development of a physiologically based model

The hydraulic fluid oil polychlorotrifluoroethylene (PCTFE) is hepato- and nephrotoxic in the rat. Male Fischer 344 rats were exposed to PCTFE either for a single 6-hr exposure (0.5 or 0.25 mg/liter) or daily 5 days/week, 6 hr/day, for 13 weeks (0.5, 0.25, or 0.01 mg/liter). Blood, tissue, and urinary PCTFE concentrations measured postexposure were used to develop a physiologically based pharmacokinetic (PB-PK) model. The PCTFE hydraulic fluid used was a mixture of trimeric and tetrameric oligomers with minor amounts of other chain lengths. The PB-PK model was designed to describe the behavior, not of individual oligomers, but of total mass for the trimer and tetramer in each tissue. Partition coefficients were estimated using the model to optimize tissue/blood concentration ratios measured at the end of the 13-week exposure. First-order metabolic rate constants for both trimeric (2.0 hr-1) and tetrameric (1.0 hr-1) portions were estimated by optimization against urinary fluoride data assuming release of 0.77 mole fluoride per mole trimer and 0.844 mole fluoride per mole tetramer metabolized. To obtain accurate simulation of pharmacokinetic data it was necessary to hypothesize two fat compartments with diffusion-limited exchange of PCTFE oligomer with the blood. Relative concentrations of trimer and tetramer in venous blood, liver, and fat after a single 6-hr exposure were proportional to inhaled concentrations. Tetramer accumulated preferentially with multiple exposure. Components of PCTFE were metabolized to carboxylic acids with release of fluoride. Due to their persistence tetrameric oligomers appear to be more important than trimeric oligomers as causative agents of PCTFE hepato- and nephrotoxicity in the rat.

Glycidyl acrylate plasma glow discharged polymers

A homogeneous glycidyl acrylate polymer (GAP) has been grafted on to polytetrafluoroethylene (PTFE) and polyethylene (PE) using a modified plasma glow discharge technique with glycidyl acrylate. The polymeric layer appears to be extremely stable to acidic media and to common organic solvents. The modified surface can be derivatized via epoxy groups with hydroxy and amino compounds including sugars and amino sugars. These derivatized surfaces have been characterized by Fourier transform infrared (FTIR) spectroscopy and contact angle measurements. The wide variety of compounds which can be attached provides flexibility in the design of surfaces for the study of a range of biological interactions.

Failure property distributions for conventional and highly crosslinked ultrahigh molecular weight polyethylenes

To make stochastic (probabilistic) failure predictions of a conventional or highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) material, not only must a failure criterion be defined, but it is also necessary to specify a probability distribution of the failure strength. This study sought to evaluate both parametric and nonparametric statistical approaches to describing the failure properties of UHMWPE, based on the Normal and Weibull model distributions, respectively. Because fatigue and fracture properties of materials have historically been well described with the use of Weibull statistics, it was expected that a nonparametric approach would provide a better fit of the failure distributions than the parametric approach. The ultimate true stress, true strain, and ultimate chain stretch data at failure were analyzed from 60 tensile tests conducted previously. The ultimate load and ultimate displacement from 121 small punch tests conducted previously were also analyzed. It was found that both Normal and Weibull models provide a reasonable description of the central tendency of the failure distribution. The principal difference between the Normal and Weibull models can be appreciated in the predicted lower-bound response at the tail end of the distribution. The data support the use of both parametric and nonparametric methods to bracket the lower-bound failure prediction in order to simulate the failure threshold for UHMWPE.

Permeation of water through the polymeric components of boil-in-bag laminates

Diffusion coefficients and equilibrium uptake have been measured for water and 3% acetic acid in film of PETP, lldpe, nylon 6 and nylon 66, and also in some isocyanate adhesives. These materials are used in the construction of boil-in-bags for food. The three methods of measurement used were permeation from a bag, mass uptake, and the use of a novel technique using isotopically labelled water. The principal temperature of investigation has been 100 degrees C. Differences in the permeation parameters for water and 3% acetic acid were small for PETP, but surprisingly large for an inert material such as lldpe. With the nylons differences could readily be ascribed to the fact that these materials are bases. When immersed in boiling water there was no change in the degree of crystallinity of PETP, but lldpe and nylon 66 showed small increases.

Comparison between in vitro and in vivo UHMW-PE degradation

There is an increasing interest in orthopedics for clinical problems associated with wear and failure of ultra-high-molecular-weight (UHMW) polyethylene devices. Wear not only affects the implant performance but, more importantly, produces the release of particulate debris in the surrounding tissues and fluids. The debris in turn cause a deleterious biological response that can include an inflammatory reaction with subsequent loosening of the implant components. Surface wear is certainly promoted from the oxidation process that can occur during the prosthesis life. However, the oxidation mechanism involved during the implantation period has not been described yet for the UHMW-polyethylene devices. Here, the comparison of FT-IR spectra of a retrieved acetabular cup (9 years in a human body) and thin UHMW-PE films treated respectively with: H2O2, KO2/THF, and Fe[II]/H2O2 solutions indicates the effect of the high reactive hydroxyl radicals as the most important cause of in vivo polymer degradation.