Effect of oral exposure on chemical, physical, mechanical, and morphologic properties of clear orthodontic aligners

INTRODUCTION

The dental industry is heavily committed to developing more esthetic solutions for orthodontic treatments. Invisalign is a system of transparent orthodontic aligners introduced as an alternative to conventional orthodontic fittings with brackets and metal wires. This study aimed to assess the chemical, physical, mechanical and morphologic changes in these polymeric aligners after exposure to the oral environment.

METHODS

Twenty-four Invisalign orthodontic aligners were equally divided into 2 groups: an in vivo aged group in which patients used aligners for 14 days and the reference group, unexposed to the oral environment. Different experimental techniques were used to study the chemical structure, the color changes and translucency, the density and subsequent volume of the aligners, mechanical properties, surface roughness, morphology and elemental composition. The data were subjected to several statistical analyses.

RESULTS

Clear orthodontic aligners exhibit chemical stability but undergo a statistically significant optical change in color and translucency. There was a gradual increase in the water absorption rate and the dimensional variation of the polymer, indicating a strong correlation among these factors. The mechanical properties of the polymer showed a statistically significant decrease in its elastic modulus and hardness. There was a slight tendency toward increased surface roughness of the material, but no statistical differences were found between reference and aged groups. The surface morphology of the used aligners demonstrates microcracks, distortions and biofilm formation.

CONCLUSION

Intraoral aging adversely affected the physical, mechanical, and morphologic properties of the Invisalign appliance.

High-Density, Long-Lasting, and Multi-region Electrophysiological Recordings Using Polymer Electrode Arrays

The brain is a massive neuronal network, organized into anatomically distributed sub-circuits, with functionally relevant activity occurring at timescales ranging from milliseconds to years. Current methods to monitor neural activity, however, lack the necessary conjunction of anatomical spatial coverage, temporal resolution, and long-term stability to measure this distributed activity. Here we introduce a large-scale, multi-site, extracellular recording platform that integrates polymer electrodes with a modular stacking headstage design supporting up to 1,024 recording channels in freely behaving rats. This system can support months-long recordings from hundreds of well-isolated units across multiple brain regions. Moreover, these recordings are stable enough to track large numbers of single units for over a week. This platform enables large-scale electrophysiological interrogation of the fast dynamics and long-timescale evolution of anatomically distributed circuits, and thereby provides a new tool for understanding brain activity.

Comparison of a Lyophilized Drug Product to Other Solid and Liquid Media for the Extraction of Elastomeric Oligomers from a Butyl Rubber Stopper

Lyophilization is commonly used to extend the shelf life of pharmaceutical products that are otherwise unstable when stored as a liquid formulation. However, the ability of a lyophilized drug, or other solid medium, to leach or extract substances from a pharmaceutical packaging material is not well characterized. To provide insight into this area of uncertainty, the extraction properties of a lyophilized drug product, the lyophilized drug product reconstituted in water, and several other solid and liquid media of varying polarity were determined using a glass vial with a butyl rubber stopper as a representative pharmaceutical packaging system. The results obtained in this study show that the extracting power of a medium, whether solid or liquid, was primarily a function of polarity. Thus, the amount of each extractable observed for the lyophilized and reconstituted drug product were in trend with the other solid and liquid media, respectively. Nevertheless, it was notable that the lyophilized drug product was able to leach substances from the stopper in quantifiable amounts, whereas the reconstituted drug product contained no detectable leachables. Using a mathematical relationship, it was determined that the extraction power of the lyophilized drug product was equivalent to a 50/50 isopropanol/water solution.LAY ABSTRACT: Freeze drying is commonly used to extend the shelf life of pharmaceutical products that are otherwise unstable when stored as a liquid formulation. However, the propensity for substances to migrate from a pharmaceutical packaging material and into a solid drug formulation is not well characterized. To provide insight into this area of uncertainty, the migration of substances from a glass vial with a butyl rubber stopper and into a lyophilized drug product, the drug product reconstituted with water, as well as several solid and liquid media of varying polarity were assessed. The results obtained in this study show that the extracting power of a medium, whether solid or liquid, was primarily a function of polarity and thus could be related to one another. Furthermore, the results for the freeze-dried and reconstituted drug products were in trend with the other solid and liquid media tested, respectively, and showed that the freeze-dried drug was able to leach substances from the stopper in measureable amounts, whereas the reconstituted drug product contained no substances that had originated from the stopper.

High-throughput quantification of stabilizers in polymeric materials by flow injection tandem mass spectrometry

RATIONALE

High-throughput methods for identification and quantification of stabilizers in plastic materials are of significant importance in order to evaluate the suitability of materials of unknown origin for specific application areas, to clarify reasons for failure of materials, or for comparison of materials from different sources.

METHODS

In the present study, a highly sensitive and rapid flow injection method coupled to selected reaction monitoring mass spectrometry (MS) for comprehensive analysis of 21 polymer stabilizers in polyolefins is demonstrated. A critical factor for this approach is the choice of ionization mode, as no separation was performed prior to MS detection. Differences between several ionization techniques regarding matrix effects are reported.

RESULTS

Atmospheric pressure chemical ionization was found to be the most suitable ionization technique, with no significant matrix effects observed. The developed method has a linear dynamic range over two to three orders of magnitude with correlation coefficients better than 0.99 for all studied analytes. Following a multistep sample preparation protocol, the method allowed quantification down to minimum values of between 0.0001 and 0.04 wt% depending on the type of stabilizer. Results were compared to an established chromatographic approach and showed very good correlation (bias below 7.5%).

CONCLUSIONS

The applicability of the optimized method could be demonstrated for both the qualitative and quantitative determination of polymer stabilizers in polyolefins. Furthermore, the described approach yields a complete analysis in a much shorter time than can be achieved with commonly applied chromatographic methods.

Development of controlled-release matrix tablet of risperidone: influence of Methocel®- and Ethocel®-based novel polymeric blend on in vitro drug release and bioavailability

Controlled-release (CR) matrix tablet of 4 mg risperidone was developed using flow bound dry granulation-slugging method to improve its safety profile and compliance. Model formulations F1, F2, and F3, consisting of distinct blends of Methocel® K100 LV-CR and Ethocel® standard 7FP premium, were slugged. Each batch of granules (250-1,000 μm), obtained by crushing the slugs, was divided into three portions after lubrication and then compressed to 9-, 12-, and 15-kg hard tablets. In vitro drug release studies were carried out in 0.1 N HCl (pH 1.2) and phosphate buffer (pH 6.8) using a paddle dissolution apparatus run at 50 rpm. The CR test tablet, containing 30% Methocel® and 60% Ethocel® (F3) with 12-kg hardness, exhibited pH-independent zero-order release kinetics for 24 h. The drug release rate was inversely proportional to the content of Ethocel®, while the gel layer formed of Methocel® helped in maintaining the integrity of the matrix. Changes in the hardness of tablet did not affect the release kinetics. The tablets were reproducible and stable for 6 months at 40 ± 2°C/75 ± 5% relative humidity. Risperidone and its active metabolite, 9-hydroxyrisperidone, present in the pooled rabbit's serum, were analyzed with HPLC-UV at λ(max) 280 nm. The CR test tablet exhibited bioequivalence to reference conventional tablet in addition to the significantly (p < 0.05) optimized peak concentration, C(max), and extended peak time, T (max), of the active moiety. There was a good association between drug absorption in vivo and drug release in vitro (R(2) = 0.7293). The successfully developed CR test tablet may be used for better therapeutic outcomes of risperidone.

Biodegradability evaluation of polymers by ISO 14855-2

Biodegradabilities of polymers and their composites in a controlled compost were described. Polycaprolactone (PCL) and poly(lactic acid) (PLA) were employed as biodegradable polymers. Biodegradabilities of PCL and PLA samples in a controlled compost were measured using a Microbial Oxidative Degradation Analyzer (MODA) according to ISO 14855-2. Sample preparation method for biodegradation test according to ISO/DIS 10210 was also described. Effects of sizes and shapes of samples on biodegradability were studied. Reproducibility of biodegradation test of ISO 14855-2 by MODA was confirmed. Validity of sample preparation method for polymer pellets, polymer film, and polymer products of ISO/DIS 10210 for ISO 14855-2 was confirmed.

Elastomeric surgical sealant for hemostasis of cardiovascular anastomosis under full heparinization

PURPOSE

We developed a novel surgical sealant, a viscous diisocyanated prepolymer, applicable to arterial hemostasis. The purpose of this study is to evaluate hemostatic effect of this surgical sealant under heparinized conditions.

METHODS

The effectiveness of this sealant was verified by applying it to the end-to-end anastomosis of canine carotid arteries. Five mongrel dogs were used. After a complete heparinization, the carotid arteries were clamped, divided, and end-to-end anastomoses were performed with four simple interrupted sutures. The sealant was coated on the anastomosis. After 5 min the clamps were removed and the hemostatic effect was evaluated. Three dogs were immediately subjected to macroscopic evaluation. Two dogs were subjected to angiography after 3 months and 16 months, respectively.

RESULTS

No bleeding occurred in any of the anastomoses immediately after the removal of the clamp. Macroscopic finding revealed no leakage of the sealant into the lumen. Carotid angiography revealed patent anastomoses without stenosis.

CONCLUSION

A novel surgical sealant exhibited rapid and potent hemostatic effect on a moisturized tissue under full heparinization.

Platelet Activation during Haemodialysis: Comparison of Cuprammonium Rayon and Polysulfone Membranes

BACKGROUND/AIM

Haemodialysis-treated patients are at a high risk of developing cardiovascular disease. Part of this risk may be attributable to the type of the dialysis membrane used. We evaluated whether different dialysis membranes differ with respect to platelet activation.

METHODS

In a randomized crossover trial, the platelet activation was measured in 14 patients treated with two different dialyzers (cuprammonium rayon membrane and polysulfone membrane). We compared the platelet activation over the dialyzer and between dialyzers after several weeks of dialysis.

RESULTS

There were no differences between the two dialyzers in platelet activation over the dialyzer. After 2 weeks, however, the expression of CD62P, CD63, and PAC-1 was statistically significantly lower after cuprammonium membrane treatment than after polysulfone membrane treatment (mean fluorescence intensity in arbitrary units 8.0 vs. 11.1, 2.64 vs. 4.01, and 5.61 vs. 9.74, respectively).

CONCLUSION

Dialysis with a polysulfone membrane seems to lead to more platelet activation than dialysis with a cuprammonium membrane.

Interspinous process devices in the lumbar spine

A growing number of interspinous process devices have been introduced to the lumbar spine implant market. Implant designs vary from static spacers to dynamized devices. Furthermore, they are composed of a range of different materials including bone allograft, titanium, polyetheretherketone, and elastomeric compounds. The common link between them is the mechanical goal of distracting the spinous processes to affect the intervertebral relationship. In contrast, the purported clinical goals are more variable, ranging from treatment of degenerative spinal stenosis, discogenic low back pain, facet syndrome, disk herniations, and instability. Though some clinical data exist for some of these devices, defining the indications for these minimally invasive procedures will be crucial. Indications should emerge from thoughtful consideration of data from randomized controlled studies.

Early Failure of Bioabsorbable Anterior Cervical Fusion Plates

STUDY DESIGN

Case report with forensic failure analysis.

OBJECTIVE

To determine the failure modes of 3 explanted 70:30 PLDLA Mystique (Medtronic Sofamor Danek, Memphis, TN) graft containment plates retrieved from revision surgery for early device failure.

SUMMARY OF BACKGROUND DATA

To reduce the problems of stress-shielding and radiopacity associated with metallic systems, bioabsorbable polymers have been used in anterior cervical discectomy and fusion procedures. Degradation of mechanical properties in vivo is a major concern when using bioabsorbable systems. Three of 6 patients who underwent anterior cervical discectomy with instrumented fusion, using Mystique graft containment systems experienced early failure requiring revision to alternate hardware.

METHODS

Devices were retrieved after failure and analyzed by light microscopy and environmental scanning electron microscopy. Simulations were performed with an unused plating system to induce damage for comparison with the retrieved devices. A detailed case review was performed to identify possible sources of extraordinary loading or damage.

RESULTS

One plating system failed at 6 weeks postimplantation due to fatigue fracture of the screws. Crack initiation sites were identified at the interface of the thread root and mold line of the screw. Another plating system failed at 16 weeks postimplantation due to the coalescence of radial microcracking between holes in the plate, leading to catastrophic failure of the plate. The final plating system failed during the implantation surgery, when the screw fractured in torsion.

CONCLUSIONS

Stress concentrations at the screw head-shaft interface and thread-shaft interface reduce the fatigue performance of bioabsorbable screws. Hydrolysis of the polymer may also play a role in the reduction of resistance to crack initiation and propagation.

An in vitro comparison of the force decay generated by different commercially available elastomeric chains and NiTi closed coil springs

This in vitro study was designed to compare the forces generated by commercially available elastomeric chains and NiTi closed coil springs, and to determine their force decay pattern. Forty elastomeric chains and forty NiTi closed coil springs were divided into 4 groups according to the following manufacturers: (1) Morelli®, (2) Abzil®, (3) TP Orthodontics® and (4) American Orthodontics®. The specimens were extended to twice their original length and stored in artificial saliva at 37°C. Initial force was measured by means of an Instron universal testing machine and then at 1, 4, 7, 14, 21, and 28 days. The results revealed that the elastomeric chains delivered a mean initial force of 347 g for Morelli®, 351 g for American Orthodontics®, 402 g for Abzil®, and 404 g for TP Orthodontics®. The NiTi closed coil springs generated a mean initial force of 196 g for American Orthodontics®, 208 g for TP Orthodontics®, 216 g for Abzil®, and 223 g for Morelli®. The mean percentage of force decay observed after 28 days for the elastomeric chains was 37.4% for TP Orthodontics®, 48.1% for American Orthodontics®, 65.4% for Morelli®, and 71.6% for Abzil®. After 28 days, the NiTi closed coil springs presented a mean percentage of force decay of 22.6% for American Orthodontics®, 29.8% for Abzil®, 30.6% for Morelli®, and 45.8% for TP Orthodontics®. At the end of the study, significant differences were observed between the elastomeric chains and the NiTi closed coil springs. The results indicated that the studied NiTi closed coil springs are more adequate for dental movement than the elastomeric chains.

Randomized Trial of a Nonpolymer-Based Rapamycin-Eluting Stent Versus a Polymer-Based Paclitaxel-Eluting Stent for the Reduction of Late Lumen Loss

BACKGROUND

Although drug-eluting stents (DESs) constitute a major achievement in preventing restenosis, concerns remain regarding the increased inflammatory and thrombogenic responses associated with the polymers used. Recently, we showed that a nonpolymer on-site coating with rapamycin not only is feasible and safe but also leads to a dose-dependent reduction in restenosis.

METHODS AND RESULTS

To assess whether polymer-free stents coated on-site with 2% rapamycin solution are inferior to polymer-based paclitaxel-eluting stents for the prevention of restenosis, we randomly assigned a total of 450 patients with de novo lesions in native coronary vessels, excluding the left main trunk, to either the polymer-free, rapamycin-coated Yukon DES (rapamycin stent) or the polymer-based, paclitaxel-eluting Taxus stent (paclitaxel stent). The primary end point was in-stent late lumen loss. Secondary end points were angiographic restenosis and target lesion revascularization. The study was designed to test the noninferiority of the rapamycin stent compared with the paclitaxel stent with respect to late lumen loss according to a noninferiority margin of 0.13 mm. Follow-up angiography was completed in 81% of the patients. The mean difference in in-stent late lumen loss between the rapamycin-stent group and the paclitaxel-stent group was 0.002 mm, and the upper limit of the 1-sided 95% confidence interval was 0.10 mm (P=0.02 from test for noninferiority). No significant differences were observed regarding angiographic restenosis rates (14.2% with the rapamycin stent and 15.5% with the paclitaxel stent) and target lesion revascularization rates due to restenosis (9.3% in both groups).

CONCLUSIONS

The polymer-free, rapamycin-coated stent has an antirestenotic effect that is not inferior to that observed with the polymer-based paclitaxel-eluting stent.

[Elaboration of biodegradable polymer substrate for cultivation of human dermal fibroblasts]

The influence of polylactic acid (PLA) surface films on the pattern of cell behavior was studied. The human dermal fibroblasts were cultivated on PLA covered glasses. The hydrophobic nature of PLA films depends on the availability of polymer solvent in the film preparation. PLA films obtained from a more polar solvent--aceton--appeared to be more hydrophilic than those obtained from methylene chloride. More hydrophilic polymer films also appeared to be more preferable for cell cultivation, and human dermal fibroblasts demonstrated a better adhesion and proliferation on hydrophilic rather than on hydrophobic PLA films.

[Shape-memory polymers for biomedical engineering applications]

The latest progress in shape-memory polymer for biomedical engineering applications was summarized in this paper. The mechanism responsible for shape memory effect was analyzed in reference to the polymer structure. Also introduced and reviewed were the characteristics of some shape-memory polymers (polyurethane polycaprolactone and polylactide) and their applications in medical engineering.

Indicator Products: A New Tool for Lifetime Prediction of Polymeric Materials

The possible correlation between the degree of degradation in the polymer matrix and the release of indicator products was investigated. The degree of degradation was measured by following the molar mass changes by size exclusion chromatography, while indicator products were analyzed by gas chromatography-mass spectrometry. The degree of degradation in polyethylene and polyethylene vinyl acetate matrix after thermooxidation was found to be in correlation with the amount of dicarboxylic acids and lactones formed during aging, while the degree of degradation in photooxidized polyethylene could be predicted from the amount of dicarboxylic acids. The relative amount of lactones compared to the relative amount of dicarboxylic acids increased if the oxidation temperature was increased. However, the total amount of indicator products was in correlation with the remaining number average molar mass and the number of chain scissions caused by oxidation. The amount of butanedioic acid and butyrolactone correlated well with the total amount of dicarboxylic acids and lactones, respectively. Thus, instead of the whole compound classes, butanedioic acid or butyrolactone alone could be used as indicators of oxidation. The detected correlation offers a novel tool for making lifetime predictions and studying the long-term properties of polymeric materials.

Evaluation of biocompatibility of polypyrrole in vitro and in vivo

In this study, the biocompatibility of the electrically conductive polymer polypyrrole (PPy) with nerve tissue was evaluated in vitro and in vivo. The extraction solution of PPy powder, which was synthesized chemically, was tested for acute toxicity, subacute toxicity, pyretogen, quantitative measure of cell viability, hemolysis, allergen, and micronuclei. The PPy membrane was synthesized electrochemically on the indium tin oxide conductive borosilicate glass. The dorsal root ganglia from 1-3-day-old Sprague-Dawley rats were cultured above PPy membrane and observed by light or scanning electron microscopy. The PPy-silicone tube (PPy membrane on the inner surface of the silicone tube) also synthesized electrochemically was used to bridge across 10-mm sciatic nerve gap in rats. Twenty-four weeks after the operation to rats, the regenerated tissues were observed by electrophysiological and histological techniques. PPy extraction solution showed no evidence of acute and subacute toxicity, pyretogen, hemolysis, allergen, and mutagenesis, and the Schwann cells from the PPy extraction solution group showed better survival rate and proliferation rate as compared with the saline solution control group. The migration of the Schwann cells and the neurite extension from dorsal root ganglia on the surface of PPy membrane-coated glass was better than those of bare glass. There was only lightly inflammation during 6 months of the postoperation, when the PPy-silicone tube bridged across the gap of the transected sciatic nerve. The regeneration of nerve tissue in the PPy-silicone tube was slightly better than that in the plain silicone tube by means of electrophysiological and histological examination. The results of this study indicate that PPy has a good biocompatibility with rat peripheral nerve tissue and that PPy might be a candidate material for bridging the peripheral nerve gap.

Dynamic Effects of a 9 mm Missile on Cadaveric Skull Protected by Aramid, Polyethylene or Aluminum Plate: An Experimental Study

BACKGROUND

Most military helmets are designed to prevent penetration by small firearms using composite materials in their construction. However, the transient deformation of the composite helmet during a non penetrating impact may result in severe head injury.

METHOD

Two experimental designs were undertaken to characterize the extend of injuries imparted by composite panels using in protective helmets. In the first series, 21 dry skulls were protected by polyethylene plates, with gaps between the protective plate and skull ranging from 12 to 15 mm. In another design, using 9 cadavers, heads were protected by aluminum, aramid, or polyethylene plates. Specimens were instrumented with pressure gauges to record the impact response. The ammunition used in these experiments was 9 mm caliber and had a velocity of 400 m/s. A macroscopic analysis of the specimens quantified fractures and injuries, which were then related to the measured pressures.

RESULTS

Protective plates influenced both the levels of injury and the intracranial pressure. Injuries were accentuated as the plates was changed from aluminum to composite materials and ranged from skin laceration to extensive skull fractures and brain contusion. Fractures were associated with brain parenchymal pressures in excess of 560 kPa and cerebrospinal fluid pressure of 150 kPa. An air gap of a few millimeters between the plate and the head was sufficient to decrease these internal pressures by half, significantly reducing the level of injury.

CONCLUSIONS

Ballistic helmets made of composite materials could be optimized to avoid extensive transient deformation and thus reduce the impact and blunt trauma to the head. However, this deformation cannot be completely removed, which is why the gap between the helmet and the head must be maintained at more than 12 mm.

Comparison of linear-linear and hyperbranched-linear dental composite

Linear polymers have been commonly used as dental composite. However the aim of this work is to use hyperbranched polymer in an attempt to produce dental composite. The reason is because the dendritic molecules have shown low viscosity at higher molecular weight compared to the linear counterparts. Therefore, this work attempts to substitute the linear polymer with as much of hyperbranched polymer in the dental composite that would pass the required ISO 4049:1998(E) "Dentistry - Resin-based filling material". Several formulations of dental composites were used, i.e. combinations of linear-linear and linear-hyperbranched polymers for comparison. Following this, physical and mechanical characterisation were conducted based on the ISO standards such as water sorption and water solubility. Other characterisation such as polymerisation shrinkage and Vickers hardness were also evaluated. It was found that different types of resins give different physical and mechanical properties. The maximum achievable hyperbranched polymer, which passes the required ISO standard, that can be incorporated in the linear polymer to form dental composite is 43% wt.

Conventional blood sampling versus On-Line Clearance Monitoring

On-line Clearance Monitoring (OCM) calculates the Kt/V during a dialysis session using a module incorporated into the Fresenius 4008 H/S haemodialysis machine (1). The method is based on repeated increments in dialysate sodium concentrations followed by measuring the change of dialysate sodium concentration after the dialysate has passed through the kidney. OCM is a patient friendly, non-invasive and easy method for measuring Kt/V. Kt/V calculated on single-pool urea kinetics according to Daugirdas was compared to Kt/V measured by OCM in thirty stable patients on chronic haemodialysis. Patients were dialysed using a dialyser with either a high-flux polysulfone or a haemophane membrane. In four patients OCM was measured in ten consecutive sessions to assess the intra-individual variation in OCM. The calculated Kt/V was compared to Kt/Vocm in three patients at five consecutive dialysis sessions to measure the intra-individual correlation. A linear correlation was present between Kt/Vocal and Kt/Vac for both the polysulfone and haemophane membrane. Intra-individual Kt/Vocm showed very stable values with an average variation of less than 5%. Intra-individual correlation between calculated Kt/V and Kt/Vocm was high.

A study to compare a new self-adherent soft silicone dressing with a self-adherent polymer dressing in stage II pressure ulcers

Pressure ulcers are common among elderly nursing home residents. To be effective in managing these wounds, a dressing should maintain a moist environment, facilitate healing, absorb exudate, remain in place for a number of days, and prevent trauma to the surrounding skin. An 8-week, open, randomized, multicenter, controlled study was conducted to compare the effects of a new self-adherent soft silicone dressing and a self-adherent hydropolymer dressing on Stage II pressure ulcers. Thirty-eight (38) residents participated in the study. Eighteen residents (mean age 83.8 years, range 74.9 to 95.1 years) were randomized to wound management with a soft silicone dressing, and the ulcers of 20 residents (mean age 82.5 years, range 66.4 to 91.9 years) were managed with a hydropolymer dressing. Wound healing, wound and surrounding skin characteristics, and ease of dressing removal were measured and documented. During the study, eight (44%) ulcers in the soft silicone group and 10 (50%) in the hydropolymer dressing group healed. Both dressings were changed approximately once a week and no differences in signs of inflammation, amount of exudate and odor, or incidence of leakage were observed. Damage to the surrounding skin, maceration, and dressing removal difficulties were less common with the soft silicone dressing. Differences in tissue damage between the two dressings were significant during weeks 1, 2, and 3 (P < 0.05). Studies with a larger sample size are needed to confirm these findings.

Preparation of blood-compatible hollow fibers from a polymer alloy composed of polysulfone and 2-methacryloyloxyethyl phosphorylcholine polymer

Blood-compatible hollow fibers were successfully prepared from a polymer alloy composed of polysulfone (PSf) and the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer. To improve the hydrophilicity, fouling-resistance characteristics, and blood compatibility of the PSf hollow fiber in a hemodialyzer, an MPC polymer that can be blended with PSf was synthesized in order to prepare the polymer alloy (PSf/MPC polymer). The contents of the MPC polymer blended in the PSf were 7 and 15 wt%. The PSf/MPC polymer hollow fiber could be prepared by both wet and dry-wet processing methods. The hollow fiber took an asymmetric structure, that is, the hollow-fiber membrane had a dense skin layer on the porous sponge-like structure. The mechanical strength was higher than that of conventional PSf hollow fibers for hemodialysis. The surface characterization of the PSf/MPC polymer hollow fiber by x-ray photoelectron spectroscopy revealed that the MPC units were concentrated at the surface. The permeability for solutes through the PSf/MPC polymer hollow fibers was measured for 4 h. The permeabilities of both a low-molecular-weight compound and protein were greater than those of the PSf hollow fibers. The amount of adsorbed protein was lower on the PSf/MPC polymer hollow fiber when compared to that of the PSf hollow fiber. Moreover, platelet adhesion was also effectively inhibited on the PSf/MPC polymer hollow fiber. Based on these results, the addition of the MPC polymer to the PSf is a very useful method to improve the functions and blood compatibility of the hollow fiber.

Polymeric alkenoxy amino acid surfactants: I. Highly selective class of molecular micelles for chiral separation of beta-blockers

Two amino acid-based alkenoxy micelle polymers were synthesized for this study. These include polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL) and polysodium N-undecenoxy carbonyl-L-isoleucinate (poly-L-SUCIL). The polymerization time and concentration of the synthesized micelle polymers were optimized by (1)H-nuclear magnetic resonance (NMR) and capillary electrophoresis (CE) experiments. Detailed physicochemical properties ((1)H NMR, critical micelle concentration (CMC), optical rotation, partial specific volume, aggregation number, and polarity) were determined, and these molecular micelles were introduced as a pseudostationary phase in micellar electrokinetic chromatography to study the molecular recognition and to develop a method for simultaneous separation of eight chiral beta-blockers. It is found that poly-L-SUCL gives overall better chiral resolution and wider chiral window than poly-L-SUCIL. After optimizing the type of micelle polymer, injection size and temperature, simultaneous separation and enantioseparation of eight beta-blockers were achieved in less than 35 min. A comparison with the amide-type surfactants of the same polar head group and alkyl chain length showed that carbamate-type surfactants always work better than the corresponding amide-type surfactant.

Enhanced functional performance characteristics of a new polysulfone membrane for high-flux hemodialysis

Elimination of uremic solutes with molecular weights up to 60 kD, without significant loss of albumin is an important therapeutic goal to optimize outcomes in chronic hemodialysis patients. To characterize a newly developed polysulfone dialyzer (APS-650) a comparative analysis was performed with a highly advanced polysulfone dialyzer (F-60S) including 22 stable chronic hemodialysis patients. Diffusive clearances were determined, and albumin loss was calculated. The elimination profile of uremic solutes up to 32.0 kD was assessed in vivo by sieving coefficients, clearances, and reduction ratios of beta(2)-microglobulin (11.8 kD), myoglobin (17.2 kD), prolactin (23.0 kD), and alpha(1)-microglobulin (32.0 kD). Hemocompatibility was tested in serial measurements of total white blood cell count, platelet count, C3a, and neutrophil elastase. No significant albumin loss was detected. Significantly higher sieving coefficients, clearances, and reduction ratios for proteins with molecular weight up to 32.0 kD were demonstrated with the newly developed polysulfone membrane. Both polysulfone membranes were equal concerning hemocompatibility parameters. The APS-650 dialyzer allowed optimized hemodialysis treatment with respect to clearance of medium-sized uraemic solutes by high-flux dialysis.

Biological safety testing of polymers

The extent of testing polymer-containing medical devices is subject to a range of considerations and needs to be determined on a case-by-case basis. This article reports on recent areas of concern for device materials including biodegradation and immunogenicity potential.

The use of poly-L-lactic acid in lumbar interbody cages: design and biomechanical evaluation in vitro

Cage design and cage material may play a crucial role in the incidence of postoperative complications reported with current non-absorbable interbody cage devices. Bioabsorbable poly-L-lactic acid cage devices may have potential benefits. The purpose of this study was to determine the required strength of poly-L-lactic acid cages for use in experimental goat studies and to evaluate the mechanical properties of different cage designs in situ. The yield and ultimate strength of native goat motion segments (L1-L6) were determined; the yield strength was used as a design parameter for the cages. The mechanical behaviour of two types of poly-L-lactic acid cages, the influence of endplate perforation, differences between toothed and smooth cages, and the influence of cage filling were biomechanically tested and compared to native motion segments. Only axial compression until failure of the motion segments was performed. Dual energy X-ray absorptiometry was used to determine bone mineral content. The yield and ultimate strength of the native motion segments were 3.5 and 7.0 kN, respectively. Based on these data, flexible and stiff poly-L-lactic acid cages were designed with strengths of 3.5 and 7 kN, respectively. Poly-L-lactic acid cages, whether with or without bone graft and perforating the endplates, did not reduce the compressive strength of motion segments as compared to native segments. However, toothed titanium cages, with the same geometry, negatively influenced the segments' compressive strength, which effect was reduced using smooth titanium cages.

Contribution of the polymer standards' polydispersity to the observed band broadening in size-exclusion chromatography

The contribution of the polydispersity of polymer standards to the observed band broadening in size-exclusion chromatography was evaluated. Initially, theoretical predictions based on an equation by Knox et al. were found to overestimate this contribution, greatly due to the fact that the polydispersity values specified by the manufacturers are upper limits and therefore too high to be applied in this context. An improved estimate of the polydispersity values was obtained from the size-exclusion chromatography results and these new values were used to reassess the polydispersity contribution to band broadening. For two of three columns tested the best molar-mass-distribution parameters, i.e. those the least affected by extra-column and intra-column band broadening effects, can be obtained for polymers with a molar mass in the effective range of the given column and at rather low mobile-phase flow rates. At those conditions, for low-molar-mass polymers, the estimated polydispersity index values approach the theoretical ones derived from a Poisson distribution.

Comparison of bacterial colonization rates of antiseptic impregnated and pure polymer central venous catheters in the critically ill

A study was performed on critically ill patients to evaluate the rate of colonization and catheter-related sepsis using antiseptic bonded (Arrowguard Arrow International) versus smooth pure polymer (Infectguard MedexMedical Ltd) central venous catheters. Two hundred and thirty-two catheters were inserted into 181 patients. Indications for removal included local or systemic infection, the catheter was no longer required and patient death. No statistical difference in colonization rate was found between the two types of catheter.

Mechanical characteristics of an absorbable copolymer internal fixation pin

Absorbable internal fixation is gaining acceptance among foot and ankle surgeons. While absorbable pins made of poly-L-lactic acid, polyglycolic acid, or poly-p-dioxanone are generally effective as applied in the foot, their strength loss profiles and degradation characteristics may not be optimally matched to the healing process. This study investigated a novel absorbable oriented copolymer pin, with unique absorption characteristics, made of 82% poly-L-lactic acid and 18% polyglycolic acid, to determine its suitability for use in fixation in the foot. The pins were incubated in a 37 degrees C buffer bath that simulated in vivo conditions and were mechanically tested in four-point bend and shear at time intervals up to 12 weeks. In vitro strength loss profiles demonstrated peak strength retention (flexural and shear) for about 8 weeks, with 50% of properties remaining by 12 weeks. The initial Young's modulus of the pins was approximately 7 GPa. The mathematical relationship between pin strength and pin diameter was discussed, providing the surgeon with helpful criteria for making an implant selection. The degradation time course of these pins appears to compliment the known healing dynamics of bone, making them a suitable choice for use in foot surgery.

Precise control of PLG microsphere size provides enhanced control of drug release rate

An important limitation in the development of biodegradable polymer microspheres for controlled-release drug delivery applications has been the difficulty of specifically designing systems exhibiting precisely controlled release rates. Because microparticle size is a primary determinant of drug release, we developed a methodology for controlling release kinetics employing monodisperse poly(D,L-lactide-co-glycolide) (PLG) microspheres. We fabricated 20-, 40- and 65-microm diameter rhodamine-containing microspheres and 10-, 50- and 100-microm diameter piroxicam-containing microspheres at various loadings from 1 to 20%. In vitro release kinetics were determined for each preparation. Drug release depended strongly on microsphere diameter with 10- and 20-microm particles exhibiting concave-downward release profiles while larger particles resulted in sigmoidal release profiles. Overall, the rate of release decreased and the duration increased with increasing microsphere size. Release kinetics from mixtures of uniform microspheres corresponded to mass-weighted averages of the individual microsphere release kinetics. Appropriate mixtures of uniform microspheres were identified that provided constant (zero-order) release of rhodamine and piroxicam for 8 and 14 days, respectively. Mixing of uniform microspheres, as well as control of microsphere size distribution, may provide an improved methodology to tailor small-molecule drug-release kinetics from simple, biodegradable-polymer microparticles.

[Current questions of sanitary supervision and control of safety of using polymer materials destined for contact with food products]

New directive and normative documents on state sanitary supervision of a safety of use of plastic of "alimentary" destination are analysed in article.

Flow cytometric evaluation of material-induced platelet and complement activation

Flow cytometry is used to characterize the activation state of platelets and leukocytes within whole blood after contact for 4 h at 37 degrees C with various materials under conditions of low shear. The contact involved adding heparinized whole blood to small diameter tubes that were connected to two arms extending from a rocking platform. For all surfaces (polyethylene, polypropylene, Silastic, PVA hydrogel) tested there was strong evidence of platelet activation in the bulk blood: platelet-derived microparticles. P-selectin expression and platelet-leukocyte aggregates. Only contact with PVA hydrogel surfaces led to dramatic increases in CD11b up-regulation on monocytes and neutrophils that was inhibited by complement inhibition (sCRI). Flow cytometry was also used to evaluate the effectiveness of various agents to inhibit material-induced complement activation. The assay involved incubating 10 microm polystyrene beads for 1 h with serum at 37 degrees C before isolating the beads so as to label them with a monoclonal antibody against a neoantigen on SC5b-9. The beads were then identified by flow cytometry and the fluorescence associated with their SC5b-9 level recorded. The ability of C1-INH, pentamidine and benzamidine to moderately inhibit SC5b-9 levels suggests a role for classical complement activation in material-induced complement activation.

SuperSkin: the management of skin susceptible to breakdown

Few studies have been undertaken in the area of skin protection, even though maintaining tissue viability in the event of incontinence, shear forces and the potential for exudate to macerate periwound areas remains a challenge for any nurse caring for patients. This article outlines and discusses the problems associated with overhydrated tissues and shear forces and the potential for SuperSkin liquid film dressing, marketed by CliniMed, to provide a solution.

Relative ultrasonographic echogenicity of standard, dimpled, and polymeric-coated needles

PURPOSE

To use quantitative ultrasonographic measurements to compare the effect of a polymeric coating designed to increase needle echogenicity to commercially available needles.

MATERIALS AND METHODS

Commercially available standard smooth and dimpled echogenic tip 21-gauge needles established reference levels of echogenicity in gelatin-based and turkey breast phantoms. Examples of both types of needles were coated with a thin polymeric film that utilizes entrapped microbubbles of air on its surface to increase echogenicity. Samples of each type in both coated and noncoated versions were placed in phantoms in matched positions and imaged with clinical ultrasound machines. Similar numbers of each category were evaluated at various angles of insonation for a total of 109 images. Similar numbers of each category were imaged at 5-minute intervals for up to 38 minutes for a total of 226 images. Images were recorded, digitized, and evaluated for relative echo strength in arbitrary echogenic brightness units.

RESULTS

Coating increased peak echogenicity over the entire needle to a level that closely approximates the peak echogenicity of dimpled needle tips (means: dimpled = 834, coated smooth = 803, coated dimpled = 823; P = .54). Smooth is lower than this group at 468 (P = .0001). Representative area echogenicity increased with coating or dimpling (smooth = 377 vs coated smooth = 778, coated dimpled = 690, dimpled = 775; P = .0001). Coating increased peak values 74% and area values 95% compared to smooth. Decreased angles of insonation moderately reduced echogenicity on coated smooth, coated dimpled, and dimpled, while it decreased to below good visibility threshold on standard smooth needles. The echogenicity of the coated needles fades in saline with time (1%/min).

CONCLUSION

Objective measurements show that this coating significantly increases echogenicity of entire needles to match that obtained with a dimpled tip.

Multisorbent tubes for collecting volatile organic compounds in spacecraft air

The sampling capability of Tenax-TA tubes, used in the National Aeronautics and Space Administration's solid sorbent air sampler to trap and concentrate contaminants from air aboard spacecraft, was improved by incorporating two sorbents within the tubes. Existing tubes containing only Tenax-TA allowed highly volatile compounds to "break through" during collection of a 1.5 L air sample. First the carbon molecular sieve-type sorbents Carboxen 569 and Carbosieve S-III were tested for their ability to quantitatively trap the highly volatile compounds. Breakthrough volumes were determined with the direct method, whereby low ppm levels of methanol or Freon 12 in nitrogen were flowed through the sorbent tubes at 30 mL/min, and breakthrough was detected by gas chromatography. Breakthrough volumes for methanol were about 9 L/g on Carboxen 569 and 11 L/g on Carbosieve S-III; breakthrough volumes for Freon 12 were about 7 L/g on Carboxen 569 and > 26 L/g on Carbosieve S-III. Next, dual-bed tubes containing either Tenax-TA/Carbosieve S-III, Tenax-TA/Carboxen 569, or Carbotrap/Carboxen 569 to a 10-component gas mixture were exposed, in dry and in humidified air (50% relative humidity), and percentage recoveries of each compound were determined. The Tenax-TA/Carboxen 569 combination gave the best overall recoveries (75-114% for the 10 compounds). Acetaldehyde had the lowest recovery (75%) of the 10 compounds, but this value was still an improvement over either the other two sorbent combinations or the original single-sorbent tubes.

Treatment of a patient with a deep leg ulcer using Biatain Adhesive

This article looks at the use of Biatain Adhesive, a new foam dressing from Coloplast which is manufactured by incorporating 3D polymer structures within the central pad. It is now available on the Drug Tariff. The article discusses the treatment of exuding wounds and highlights the benefits of Biatain Adhesive by focusing on the case of an 84-year-old woman who had a history of long-standing leg ulcers where previous dressings had failed to promote healing.

Radiopaque polymeric materials for medical applications. Current aspects of biomaterial research

The aim of this review is to give an overview and some insight into different radiopaque polymeric materials that are currently used as medical implants or inserts. The advantages and limitations of each radiopaque polymeric material are summarized. The main method used to make medical implants radiologically visible is based on blending polymers with conventional radiopaque agents, blends which usually are a physical mixture of acrylic derivatives and inorganic salts. Other methods reported involve either the formation of single-phase radiopaque polymer salt complexes somehow preventing the release of the radiopacifying element by entrapment of the complex in a crosslinked network, or radiopaque polymerized monomers characterized by a radiopacifying element associated with the monomer unit prior to polymerization. In the near future, research will certainly concentrate on biocompatible radiopaque polymers with covalently bound opaque elements leading to stable polymers with properties equivalent to the nonopaque, parent polymer.

[Comparison of different finishing methods for composites and compomers. Profilometric analysis]

BACKGROUND

Reconstructions with aesthetical materials neither finished nor polished can be extremely irregular and wrinkled. For this reason they represent an ideal basis for the growing of pigmentation which come from food remainings and the nestle of bacteria on the plaque. The finishing of aesthetical materials is a fundamental step in conservative dentistry. The finishing session regarding the aesthetical restorations should be considered and planned at the moment of their insertion in the prepared hollows. The finishing should not be considered an option, but the conclusion of all the conservative treatment. Purpose of the search is to examine and assess, through a technical equipment measuring the superficial wrinkledness of the materials, the action of 4 systems of finishing and polishing on two aesthetical materials widely used in the daily practice by dental surgeons: a compomer (Compoglass, Vivadent) and a composite (Spectrum, Dentsply).

METHODS

For each of these two materials some little slabs model have been prepared, choosing the universal colour in the colorimetric scale. The two types of filling materials have been compared with 4 systems of finishing and polishing: Sof-Lex Pop-on (3M), Enhance system (Dentsply), Hawe Micro Disc (Howe Neos), Heawe Gommini Polisher (Heawe Neos). The total working time did not overcome 1 minute. The little slabs have been obtained, pressing the resin between two slides used in microscopy. In the hope to guarantee in the different samples, a uniform thickness, we have used a technical device. On each covering slide we have put a weight of 0.5 kg for 5 minutes. The thickness of the little slabs obtained was 2 mm. Thus, pressed between the two slides, the aesthetical material has been photopolymerized according to the time suggested by Manufacturing Industries. The sizes concerning the wrinkledness of samples subjected to different treatments have been carried out using a pointed profilometer with high sensitivity. (Tencor-P10). This instrument used in the National Laboratory of Catania, called INFN, is able to graphitize the wrinkledness of a surface "survbeying" it with a diamond ultramicrometric point.

RESULTS

All tested systems gradually produce the upper layers of the materials less suitable to resist the assault of plaque bacteria as time passed. The 3M coarse and medium grain Disks are very abrasive and for this reason the surface of the materials is ill-shaped. Those disks with fine and extra fine grain, smooth the tracks left by previous disks. As they have been always used according to their decreasing granulometry, the disks are used only for removing small composite pieces in excess and to improve micromorphology of the restauration. The "Gommini" are less abrasive than Disks. In a few minutes and often with only one step they produce a much regular and polished fillings surface.

CONCLUSIONS

The "Gommini" have a preference when the last photopolymerization has left a regular layer, with a very good micromorphology. Actually, "Gommini" do not remove much material, but they continue to smooth the outline of the reconstruction. Disks are not classified as being of first quality in the finishing of composites and compomers.

Skin adhesives and skin adhesion. 1. Transdermal drug delivery systems

The use of pressure-sensitive adhesives (PSAs) for skin-contact applications is discussed. The requirements of such adhesives in various applications are examined in detail. Commercially available classes of PSAs used for skin-contact applications are the acrylics, the polyisobutylenes, and the silicones. The main application examined in this review is transdermal drug delivery. The roles played by the PSA in two types of transdermal designs are described. Correlations between in vivo and ex vivo measurements of adhesion are discussed. Also, the reported human studies of various commercially available transdermals are examined critically, with a view to assessing the relative performance capabilities of each type of transdermal design. Finally, a comprehensive listing of currently commercialized transdermals is given.

Breaking strength and diameter of absorbable sutures after in vivo exposure in the rat

Although absorbable sutures are commonly used in clinical practice, the rate of decay of strength in various tissues has not been studied. The purpose of this study was to assess breaking strength (BS) and diameter of monofilament (chromic gut, polydiaxanone, Maxon, Monocryl) and multifilament (Vicryl, Dexon, Polysorb) absorbable sutures implanted in various sites and measured at specific time intervals. A 15 cm length of 4-0 suture from a single lot of each material was implanted in the pleural space, rectus abdominus muscle, subcutaneous tissue, intravascular space, peritoneal cavity, and stomach lumen in the rat. A precipitous decrease in BS was noted in all multifilament sutures after 7 days, and in chromic gut and Monocryl sutures after 1 day. Polydiaxanone and Maxon sutures maintained the highest BS over the 28-day period, 71 per cent and 59 per cent of their initial BS, respectively. Suture diameter remained essentially unchanged except for chromic gut and the multifilament sutures which exhibited increased diameter. This increase was attributed to inflammatory tissue infiltration.

Blood compatible polymers in intensive care units: state of the art and current aspects of biomaterials research

The use of artificial organs in cases of acute renal failure, acute respiratory distress syndrome (ARDS) and multiorgan dysfunction syndrome (MODS) has lead to a significant reduction of mortality. However, the interaction between body and biomaterials results in the activation of the coagulation system and in the induction of systemic inflammatory response syndrome. The necessary anticoagulation may be contraindicated and may even further increase the risk for the patient. This article evaluates the currently applied polymeric materials used in intensive care units (ICU) and gives a possible outlook into future developments. It is emphasized that systematic interdisciplinary research of physicians and biomaterial scientists is essential for the successful development of new polymers with improved biocompatibility. For this purpose a brief overview of analytical techniques for surface characterization is given, and future developments to a fully biocompatible polymer are described.

High-precision genotyping by denaturing capillary electrophoresis

Genotyping, as applied to linkage mapping, human identification, or mapping of genetic traits, mandates electrophoretic separation systems that enable a user to identify alleles with high precision to obtain a correct genotype. For 2-bp microsatellites or short tandem repeats (STRs), standard deviations of +/-0.3 nucleotide are required to ensure with 99.7% probability the identity or dissimilarity of tested alleles. A complete system, consisting of commercially available laser-induced fluorescence capillary electrophoresis (ABI PRISM 310) and performance optimized polymer 4 (POP-4), was evaluated for microsatellite separations. POP-4 is a low viscosity polymer for use in uncoated fused microbore silica capillaries. It separates DNA fragments that differ in size by 1 nucleotide up to 250 nucleotides and that differ in size by 2 nucleotides for fragments up to at least 350 nucleotides in length in about 30 min. The presence of denaturants and, more importantly, operation at 60 degrees C was mandatory for high-precision and high-resolution sizing operation. Reproducible separation performance was achieved in excess of 100 injections per capillary with resulting standard deviations in the range of 0.04 to 0.17 nucleotide. Comparative sizing of known CEPH (Centre d'Etudes du Polymorphisme Humaine) samples performed at 22 independent test sites showed the usefulness of the system for genotyping with standard deviations of 0.24 nucleotide, or better.

Repair of soft tissue to bone using a biodegradable suture anchor

The medial collateral ligaments of 18 New Zealand rabbits were surgically detached from bone. In one knee, the ligament was repaired using a biodegradable suture anchor composed of a co-polymer of lactic and glycolic acid. The contralateral medial collateral ligament was not repaired. Animals were sacrificed at 4, 8, and 12 weeks after the operation, and the knee that had the ligament repair was compared with the contralateral control knee. All knees were tested manually tested for stability to valgus stress and then prepared for histologic examination. Medial collateral ligaments repaired using the biodegradable suture anchor demonstrated stability to valgus stress and anatomic healing at the bone-tendon junction. Resorption of the implant was virtually complete by 12 weeks. All specimens demonstrated less inflammatory reaction to the suture anchor than to the attached Vicryl suture. This contrasts with the control group, which was grossly unstable and demonstrated scarring in this nonanatomic position. These results demonstrate efficacy of this particular material of biodegradable implant and justify further investigative efforts.

Physical, biological and handling characteristics of surgical suture material: a comparison of four different multifilament absorbable sutures

OBJECTIVE

Four different braided absorbable surgical materials (Dexon, Dexon II Bicolor, Vicryl and Polysorb) 2/0 USP, which basically share the same indications, were studied in vitro and in vivo with regard to their physical properties as well as tissue compatibility and surgical handling. Analyzing the results the authors tried to determine the most useful suture in surgical practice.

METHOD

Physical tests to determine tensile strength, knot-breaking strength and knot security were carried out. Additionally an in vivo model (Wistar rat) was used to compare histocompatibility and loss of function due to hydrolytic resorption. Furthermore, a handling test was carried out by trained surgeons.

RESULTS

Polysorb had the highest linear tensile strength but also the fastest loss of function following tissue implantation, whereas Vicryl showed the slowest loss of function. Similar results were obtained with regard to the knot-breaking strength. After pulsatile stressing Dexon II Bicolor and Dexon showed the highest irreversible elongation followed by Vicryl and Polysorb. Polysorb had the best knotting characteristics, scoring highest also in the handling study.

CONCLUSIONS

The authors conclude that with Polysorb all features and properties of braided suture material have reached a high level of quality. This suture combines the positive characteristics of monofilament with those of multifilament materials, thus coming closest to being the 'optimal suture'.