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PubMed1998

Reduced protein adsorption on novel phospholipid polymers.

We have synthesized phospholipid polymers containing 2-methacryloyloxyethyl phosphorylcholine (MPC) units as novel blood compatible polymers and have evaluated their interactions with blood components. It was found that in the absence of anticoagulants, blood clotting was delayed and blood cell adhesion and activation were effectively prevented on the MPC copolymer surface. A little amount of protein adsorbed on the MPC copolymer from human plasma was compared with conventional polymers, and the amount was reduced with increasing MPC unit fraction. To clarify the reason for the little protein adsorption on the MPC copolymer, the water structure in the hydrated polymer was examined with attention to the free water fraction. Hydration of the polymers occurred when they were immersed in water. The thermal analysis of these hydrated polymers revealed that the free water fractions in the poly(MPC-co-n-butyl methacrylate (BMA)) and poly(MPC-co-n-dodecyl methacrylate) were significantly larger than those in the poly(2-hydroxyethyl methacrylate(HEMA)). The conformation of proteins adsorbed on poly(HEMA) changed considerably but that on poly(MPC-co-BMA) was almost the same as the native state. We concluded from these results that the proteins are hardly adsorbed and do not change their original conformation on the polymer surfaces which possess a high free water fraction such as phospholipid polymers.

Adsorption↗

PubMed2003

Local immunotherapy with interleukin-2 delivered from biodegradable polymer microspheres combined with interstitial chemotherapy: a novel treatment for experimental malignant glioma.

OBJECTIVE: Local delivery of carmustine (BCNU) from biodegradable polymers prolongs survival against experimental brain tumors. Moreover, paracrine administration of interleukin-2 (IL-2) has been shown to elicit a potent antitumor immune response and to improve survival in animal brain tumor models. We report the use of a novel polymeric microsphere delivery vehicle to release IL-2. We demonstrate both in vitro release of cytokine from the microspheres and histological evidence of the inflammatory response elicited by IL-2 released from the microspheres in the rat brain. These microspheres are used to deliver IL-2, and biodegradable polymer wafers are used to deliver BCNU, directly at the site of an intracranially implanted glioma in the rat. The two agents administered locally show a synergistic effect. METHODS: Fischer 344 rats challenged intracranially with 9L gliosarcoma received an intracranial implant of either empty microspheres or microspheres containing IL-2 (IL-2 MS). Five days later, animals in each group were randomized to receive polymer implants loaded with 0, 3.8, or 10% BCNU at the tumor site. RESULTS: Animals that received the combination of IL-2 MS and 3.8% BCNU polymer (median survival, 28.5 d) or IL-2 MS and 10% BCNU polymer (median survival, 45.5 d) showed significantly improved survival compared with animals that received monotherapy with IL-2 microspheres (median survival, 24 d), 3.8% BCNU polymer (median survival, 24 d), or 10% BCNU polymer (median survival, 32.5 d). Control animals had a median survival of 18 days. The combination of either 3.8 or 10% BCNU polymer with IL-2 MS resulted in 7 and 25% long-term survivors, respectively. CONCLUSION: By showing synergy of IL-2 and BCNU in an animal glioma model and using a reproducible synthetic delivery system for each agent (i.e., one that did not rely on genetically engineered cells or viruses), we hope that the combination of local immunotherapy and chemotherapy can take an important step closer to clinical application in patients with malignant brain tumors.

Animals↗

PubMed2004

Smart polymer-streptavidin conjugates.

The conjugation of stimuli-responsive, or "smart," polymers to streptavidin is described. The polymer is synthesized with a thiol-reactive end-group, which is used to end-graft the polymer to cysteine or lysine side-chains that are genetically engineered into controlled positions on the streptavidin surface. The conjugation positions are chosen on the basis of their location relative to the binding site, together with the criteria that they be solvent accessible and thus reactive. The polymer composition can be controlled to impart responsiveness to temperature, pH, and/or specific wavelengths of light. These signals are sent to the polymer, which serves as an antennae and actuator to gate biotin or biotinylated protein association with the streptavidin binding sites. The molecular switching and gating activity is directed by the reversible polymer transition between a hydrophilic, expanded coil and a more hydrophobic, collapsed state that is smaller in volume. The differences in the polymer steric properties serve to block or allow ligand access to the binding site. The control of polymer molecular weight is a particularly important design parameter for these molecular gates.

Acrylamides↗

PubMed2005

Removing carious dentin using a polymer instrument without anesthesia versus a carbide bur with anesthesia.

BACKGROUND: The authors describe a new rotary polymer instrument that selectively removes infected dentin. This instrument has the potential to prepare selected cavities without the need for local anesthesia (LA). Patient acceptance has not been investigated in a clinical trial. METHODS: In this open-label clinical study, the authors enrolled 20 subjects with two Class I carious lesions and randomly assigned them to receive one restoration with the polymer instrument and no LA and the second restoration with a carbide bur and LA. Both procedures were completed in one appointment. Subjects completed dental history, dental anxiety and situational pain questionnaires. At specific points during the procedure, subjects rated their perception of the intensity of cold, heat, pain, pressure, vibration, fear and anxiety. On completion of the restorative procedures and at 48-hour and one-week telephone contacts, subjects indicated which procedure they preferred. RESULTS: During treatment with the polymer instrument, subjects indicated that they experienced slightly more pain, pressure, vibration and anxiety, but not more heat, cold or fear. Immediately after the procedure, 14 (70 percent) of 20 respondents (binomial test; P = .11) said that they would prefer having no LA and use of the polymer instrument for future dental work. The number of subjects indicating this preference increased to 15 (P < .05) at both the 48-hour and one-week contacts. One subject requested rescue LA during the polymer instrument treatment. CONCLUSIONS: A significant number of subjects preferred the rotary polymer instrumentation with no LA to the carbide bur instrumentation with LA. They held this preference despite experiencing slightly, but reliably, more pain and pressure when treated with the polymer instrument. CLINICAL IMPLICATIONS: A polymer (bur-like) rotary instrument with cutting ability limited to infected dentin can be used in Class I cavity preparations without the need for LA.

Adult↗

PubMed2005

Polymer-drug conjugates: towards a novel approach for the treatment of endrocine-related cancer.

The last decade has seen successful clinical application of polymer-protein conjugates (e.g. Oncaspar, Neulasta) and promising results in clinical trials with polymer-anticancer drug conjugates. This, together with the realisation that nanomedicines may play an important future role in cancer diagnosis and treatment, has increased interest in this emerging field. More than 10 anticancer conjugates have now entered clinical development. Phase I/II clinical trials involving N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin (PK1; FCE28068) showed a four- to fivefold reduction in anthracycline-related toxicity, and, despite cumulative doses up to 1680 mg/m2 (doxorubicin equivalent), no cardiotoxicity was observed. Antitumour activity in chemotherapy-resistant/refractory patients (including breast cancer) was also seen at doxorubicin doses of 80-320 mg/m2, consistent with tumour targeting by the enhanced permeability (EPR) effect. Hints, preclinical and clinical, that polymer anthracycline conjugation can bypass multidrug resistance (MDR) reinforce our hope that polymer drugs will prove useful in improving treatment of endocrine-related cancers. These promising early clinical results open the possibility of using the water-soluble polymers as platforms for delivery of a cocktail of pendant drugs. In particular, we have recently described the first conjugates to combine endocrine therapy and chemotherapy. Their markedly enhanced in vitro activity encourages further development of such novel, polymer-based combination therapies. This review briefly describes the current status of polymer therapeutics as anticancer agents, and discusses the opportunities for design of second-generation, polymer-based combination therapy, including the cocktail of agents that will be needed to treat resistant metastatic cancer.

Antineoplastic Agents↗

PubMed2004

DNA-conjugated polymers for self-assembled DNA chip fabrication.

We developed two DNA-conjugated polymers, one based on polyallylamine and the other on polyacrylic acid, for use in DNA chips. A 30-mer single-stranded DNA probe and thioctic acid were covalently attached to polyallylamine as sidechains. The same single-stranded DNA and 3-(pyridyldithio)propionyl hydrazide were covalently attached to polyacrylic acid as sidechains. Both DNA-conjugated polymers could be specifically immobilized onto a gold sensor substrate by a self-assembly technique. The interactions between fully matched DNA and each DNA-conjugated polymer were investigated by surface plasmon resonance. A gold surface modified with either DNA-conjugated polymer recognized fully matched DNA much better than unmatched DNA. The hybridization selectivity and efficiency of DNA-conjugated polyallylamine was optimized by adjusting the pH so as to reduce the effects of cationic polymer sidechains. The hybridization selectivity and efficiency of DNA-conjugated polymers were higher than those of a conventional immobilized thiol-based DNA. The coating of DNA-conjugated polymers reduced nonspecific adsorption of DNA by the gold substrate. DNA-conjugated polyacrylic acid was more selective toward fully matched DNA than was DNA-conjugated polyallylamine. Therefore, DNA-conjugated polymers show promise for application in novel DNA chips.

Base Sequence↗

PubMed1992

The intracerebral distribution of BCNU delivered by surgically implanted biodegradable polymers.

The local concentration and distribution of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) within normal brain tissue were studied following surgical implantation of biodegradable polymer containing BCNU in New Zealand White rabbits. Cylindrical discs of poly(bis(p-carboxyphenoxy)-propane:sebacic acid) copolymer in a 20:80 formulation were made containing [3H]-inulin or [3H]-BCNU labeled in the methylene hydrogens of the chloroethyl groups. These were implanted in the brains of 56 New Zealand White rabbits. The animals were sacrificed 3, 7, 14, or 21 days later and the brains were rapidly removed, frozen, and prepared for quantitative autoradiography. Autoradiographs from coronal sections bisecting the polymer were analyzed to determine both the proportion of the brain section exposed to the tracer and the local drug concentrations as a function of distance from the polymer. Tritiated BCNU was also injected directly into the brains of eight additional rabbits, and local brain concentrations were studied over time. The results of this study demonstrate that approximately 50% of the area of the brain sections was exposed to radiolabeled compound 3 days after BCNU-polymer implantation, 15% at 7 days, and less than 10% at 14 and 21 days. Polymer discs containing 600 micrograms BCNU generated 6 mM concentrations of BCNU in brain tissue 10 mm from the polymer at 3 and 7 days. Pharmacological studies demonstrated that approximately 25% of the tritium label was associated with intact BCNU 3 days following polymer implantation. Radiolabeled inulin delivered by polymer remained dispersed throughout the ipsilateral hemisphere for 14 days. Direct injection of [3H]-BCNU into brain parenchyma resulted in widely distributed tracer at 1 and 3 hours with rapid disappearance thereafter. It is concluded that local delivery of BCNU to brain tissue with this polymeric drug delivery system results in sustained high local concentrations of BCNU which may be of value in the treatment of patients with brain tumors.

Animals↗

PubMed1999

Biodegradable implants from poly-(alpha-hydroxy acid) polymers for isoniazid delivery.

SETTING: In vitro and in vivo study of an isoniazid (INH) drug delivery system. OBJECTIVE: To develop a system for the treatment of tuberculosis using a subcutaneous polymer implant with a large drug load released slowly over a long period. INH delivery by biodegradable poly-(alpha-hydroxy acid) polymers was evaluated using ground polymer and compression molded implants. DESIGN: Rate of drug release and structural stability of the implant in an aqueous environment were measured, as were in vivo evaluations of the duration of measurable levels of INH in serum and urine. RESULTS: Factors that influenced the suitability of an implant in an in vitro system included polymer molecular weight and crystallinity, polymer and drug particle size, drug loading dose, and press temperature and pressure. The implant characteristics that most closely approached optimal conditions include a polymer of 100% L-lactide with low intrinsic viscosity, polymer particle size <75 micron, and INH particle = 126-180 micron, INH loading dose not to exceed 46%, and press conditions of 70 degrees C and 345000 kPa. Studies of subcutaneous implants in rabbits and baboons show that INH is released from the implant for 15 to 26 weeks. CONCLUSIONS: An INH-containing polymer was developed that was structurally stable in an aqueous environment and that released INH over a period of at least 15 weeks. Studies with infected animals will be necessary to determine the dose required for prophylaxis and treatment of active disease.

Animals↗

PubMedDate not supplied

Equilibrium strengths of denture polymers subjected to long-term water immersion.

PURPOSE: This study characterized the effect of water immersion on the strength of denture polymers. MATERIALS AND METHODS: Four denture-base polymers and four denture-reline polymers were tested for flexural strength at proportional limits (FSpl) at 24 hours and at monthly intervals. The equilibrium strength of each polymer was estimated. RESULTS: The denture polymers took from 24 hours to 4 months to reach their equilibrium strength. The equilibrium strengths of the denture polymers were significantly different. CONCLUSION: Water immersion affected the strength of most denture polymers. Different denture polymers behaved differently in response to water immersion.

Analysis of Variance↗

PubMedDate not supplied

Some mechanical properties of a highly cross-linked, microwave-polymerized, injection-molded denture base polymer.

PURPOSE: The impact strength and the flexural properties of denture base materials are of importance in predicting their clinical performance upon sudden loading. This study compares the impact and transverse strengths and the flexural modulus of three denture base polymers. MATERIALS AND METHODS: The investigation included a relatively new microwave-polymerized polyurethane-based denture material processed by an injection-molding technique, a conventional microwave-polymerized denture material, and a heat-polymerized compression-molded poly(methyl methacrylate) (PMMA) denture material. Impact strength was determined using a Charpy-type impact tester. The transverse strength and the flexural modulus were assessed with a three-point bending test. The results were subjected to statistical analysis using a one-way analysis of variance and the Scheffé test for comparison. RESULTS: The impact strength of the microwave-polymerized injection-molded polymer was 6.3 kl/m2, while its flexural strength was 66.2 MPa. These values were lower than those shown by the two compression-molded PMMA-based polymers. The differences were statistically significant. The flexural modulus of the new denture material was 2,832 MPa, which was higher than the conventional heat-polymerized polymer but was comparable to the other microwave-polymerized PMMA-based polymer. The difference in the flexural modulus was statistically significant. CONCLUSION: In terms of the impact and flexural strengths, the new microwave-polymerized, injection-molded, polyurethane-based polymer offered no advantage over the existing heat- and microwave-polymerized PMMA-based denture base polymers. However, it has a rigidity comparable to that of the microwave-polymerized PMMA polymer.

Acrylic Resins↗

PubMedDate not supplied

Comparative evaluation of plastic, hydrophobic and hydrophilic polymers as matrices for controlled-release drug delivery.

PURPOSE: The present study was undertaken to investigate the effect of plastic, hydrophilic and hydrophobic types of polymers and their content level on the release profile of drug from matrix systems. As the physico-chemical nature of the active ingredients influence the drug retarding ability of these polymers, three different drugs were used to evaluate their comparative release characteristics in similar matrices. METHODS: Matrix tablets of theophylline, diclofenac sodium and diltiazem HCl using Kollidon SR, Carnauba wax and Hydroxypropyl methylcellulose (HPMC-15cps) were prepared separately by direct compression process. The USP Basket method was selected to perform the dissolution test carried out in 250 ml 0.1N HCl for first two hours and 1000 ml phosphate buffer of pH 6.8 for ten hours. RESULTS: Statistically significant differences were found among the drug release profile from different classes of polymeric matrices. The release kinetics was found to be governed by the type and content of polymer in the matrix system. Higher polymeric content (75%) in the matrix decreased the release rate of drug because of increased tortuosity and decreased porosity. At lower polymeric level (25%), the rate and extent of drug release was elevated. Carnauba wax was found to cause the strongest retardation of drug. On the otherhand, highest drug release was from HPMC matrices while Kollidon SR gave an intermediate release profile between these two polymers. Release rate was also found to be the function of physico-chemical nature of drug molecule. Theophylline and diltiazem HCl, being soluble in nature, released faster than diclofenac sodium from all matrix systems. The release mechanism was explored and explained with biexponential equation. Release profile showed a tendency to follow zero-order kinetics from HPMC matrix systems whereas Fickian (Case I) transport was predominant mechanism of drug release from Kollidon SR matrix system. The mean dissolution time (MDT) was calculated for all the formulations and the highest MDT value was obtained with Carnauba wax for all the drugs under investigation. CONCLUSIONS: The results generated in this study showed that the profile and kinetics of drug release were functions of polymer type, polymer level and physico-chemical nature of drug. A controlled plasma level profile of drug can be obtained by judicious combination of polymers and modulation of polymer content in the matrix system.

Chemistry, Pharmaceutical↗

PubMed1992

Comparison of toxicity rankings of six aircraft cabin polymers by lethality and by incapacitation in rats.

Polymeric aircraft cabin materials have the potential to produce toxic gases in fires. Lethality (LC50) in animal models is a standard index to rank polymers on the basis of their combustion toxicity. However, the use of times-to-incapacitation (ti) may be more realistic for predicting relative escape times from a fire. Therefore, LC50 and ti for polymers, polyamide (I), polystyrene (II), Nylon 6/6 (III), polysulfone (IV), polyethylene (V) and chlorinated polyethylene (VI), of different chemical classes were determined and compared. Male rats, 12/fuel loading, were exposed to the pyrolysis products from selected weights of each polymer for 30 min in a 265-L combustion/exposure system, and LC50 values were determined following a 14-d observation period. For each polymer, ti was measured at 16 g and at its respective LC50 using the inability of rats (n greater than or equal to 12) to walk in rotating cages as a criterion for incapacitation. LC50 (45.7-87.5 mg/L) of the polymers had the order of I less than II approximately III less than IV less than V less than VI, while their ti (6.6-21.1 min) at 16 g (60 mg/L) had the order of III approximately I less than V approximately II less than VI less than IV. Based on ti at LC50, polymers were grouped into III & V; I, II & VI; and IV. LC50 and ti did not exhibit the same relative toxic hazard rankings for these polymers; ti were also not equal at the LC50 concentrations. These findings demonstrate the possible involvement of different mechanisms of action for the combustion products of these polymers at the selected end points.

Aircraft↗

PubMed2004

Effects of low-level hydrophobic substitution on conditioning properties of cationic cellulosic polymers in shampoo systems.

A new class of cationic conditioning polymers (Polymer SL) has been prepared and evaluated in shampoo formulations. Polymer SL is a family of high viscosity quaternized hydroxyethyl cellulose (HEC) polymers with cationic substitution of trimethyl ammonium and dimethyldodecyl ammonium (Figure 1). SL compositions benefit from hydrophobic character to deliver superior conditioning performance in hair care applications. At the same time, low levels of hydrophobes have been chosen to assure good compatibility with surfactant systems without the complications of associative thickening. The polymers have been evaluated in clear shampoo formulations and two-in-one silicone containing shampoos using objective lab methods and subjective panel evaluation on hair tresses. Commercial conditioning polymers: Polyquaternium-10 (PQ-10) (UCARE Polymer LR-30M) and Guar Hydroxypro-pyltrimethylammonium Chloride (Jaguar C-13S) were used as performance benchmarks. The new hydrophobically-modified cationic polymers demonstrated superior performance in all major categories of conditioning and showed improved silicone deposition from two-in-one systems. Moreover, they retained other good qualities of their PQ-10 structural analogs such as enabling crystal clear formulations and showing no build-up or volume-down effects on hair. These new olymers were also found to be efficient conditioning agents in different surfactant systems with or without silicones.

Cellulose↗

PubMed1991

Piroxicam-natural polymers interactions.

The interaction of the anti-inflammatory drug, piroxicam, with some naturally occurring polymers-viz gamma-globulin, bovine serum-albumin, bovine synovial fluid and casein was characterized in this study. This was done using equilibrium dialysis method where the dialysis membrane was permeable only to the drug molecules while polymers and formed complex(es) cannot pass through. The amount of permeable piroxicam molecules was determined spectrophotometrically. It was found out that increasing the concentration of piroxicam was accompanied by an increase in the amount of piroxicam bound to the investigated natural polymers. The maximum binding capacity of the investigated polymers for the drug as revealed by Langmuir plots, could be arranged in ascending manner as follows: synovial fluid, albumin, casein and gamma-globulin. The binding parameters K (association constant) and n (the number of binding sites available on the polymer) were determined using Sandberg plots. It was found that two classed of binding sites were involved in the interaction of piroxicam with gamma-globulin, albumin and casein. Increasing salt concentration was accompanied by a decrease in piroxicam binding with the investigated polymers till a constant value of ionic strength (0.6 mole/liter). This result may suggest the ionic nature in binding of piroxicam with the investigated polymers. It was concluded that piroxicam is strongly bound to the investigated natural polymers with different degree of binding, such binding may affect the pharmacological effect of piroxicam. An in-vivo absorption study was performed on eight male healthy volunteers to compare the bioavailability of piroxicam in presence and absence of casein using plasma data after 100 mg single dose treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1987

Osmometric study of the subunit dissociation of hemoglobin Porto Alegre [beta 9(A6)Ser----Cys] dissulfide polymer.

The hemoglobin Porto Alegre (HbPA) disulfide polymer dodecamer and the HbPA, HbA disulfide polymer octamer subunit dissociation by NaCl was studied by measuring the osmotic pressure of CO-hemoglobin solutions at pH = 6.9 and 20 degrees C. The dissociation equilibrium constants were evaluated from the osmotic pressure data. The subunit dissociation of the two types of disulfide polymers follows a reaction of the type A3 in equilibrium 3A. The HbPA disulfide polymer dodecamer appears to be more susceptible to NaCl induced dissociation than is normal HbA and less resistant to dissociation on protein dilution. The HbPA, HbA disulfide polymer octamer appears to be much more susceptible to dissociation on protein dilution than is the HbPA disulfide polymer dodecamer and normal HbA. The standard free energy of dissociation of the HbPA disulfide polymer at 2 M NaCl is delta GOD(25 degrees C) = 12 kcal/mole. The type of dissociation reaction (A3 in equilibrium with 3A) support the conclusion that the HbPA disulfide polymer has a quaternary molecular structure of a closed ring of three tetramers.

Hemoglobin A↗

PubMed1996

Polymer-iodine inactivation of the human immunodeficiency virus.

BACKGROUND: Hospital and laboratory equipment that come in contact with body fluids of patients with human immunodeficiency virus (HIV) are potentially infective and require special measures for decontamination and disposal. Human immunodeficiency virus is sensitive to several chemicals but requires a continuous exposure to the disinfectant to effective inactivation. Polymers have the capacity to release viricidal chemicals in a sustained fashion for prolonged periods of time, and may be used to coat patient care items before their use. Iodine was chosen because of its universal antimicrobial potential; it was incorporated into polyurethane polymers and the effectiveness of the polymer-iodine against HIV-1 3B was assayed. STUDY DESIGN: Iodine was loaded into polyurethane polymers by two different methods: polyurethane-complexing, where the iodine is released through a desorption mechanism, and polyurethane-matrixing, where the iodine is released through a diffusion mechanism. The pharmacokinetics of the iodine release were studied in each case. Twenty-four-well viral culture plates used for HIV-1 3B assays were coated with both types of polyurethane-iodine polymers. Their effectiveness against HIV was assessed by MT4 cell viability and reverse transcriptase assays. RESULTS: The polymer-iodine combination remained stable as long as it was dry: the iodine release started only when the plates came in contact with an aqueous environment. The release from the polyurethane-iodine complex was large and rapid, resulting in inactivation of the HIV-1 3B within 15 to 30 minutes, as determined both by reverse transcriptase and the MT4 cytopathic cell cultures assays. The release from the polyurethane-iodine matrix was slower and had no significant antiviral effect. CONCLUSIONS: The polyurethane polymer provided a sustained release of iodine that effectively inactivated HIV. The coating may be applied at the time of manufacturing to specific hospital and laboratory items that are to come in contact with blood from patient-contaminated fluids. This technology is attractive for decontamination, especially in situations where appropriate and rapid disposal of medical waste is not readily available. Further research is in progress to speed the release of the iodine from the polymer and the subsequent inactivation of the virus.

Delayed-Action Preparations↗

PubMed1996

Polymers, Dk, and contact lenses: now and in the future.

PURPOSE: The polymers used in conventional contact lenses are briefly reviewed as are the factors that contribute to their gas permeability. The chemistry and gas permeability of future hydrogel contact lenses are discussed. RESULTS: Interchain packed zones in polymers are less permeable than the amorphous zones. Polymers with thick bulky groups in rigid gas permeable lenses hinder interchain packing, allowing oxygen and carbon dioxide to diffuse through the polymer voids. Also, the flexibility of the siloxane groups facilitates the diffusion of gases. In hydrogel contact lenses, the polymer segments are separated by the aqueous phase. The gas diffusivity increases with hydration, but is limited by the rigid polymer network. Research on new hydrogel contact lenses aims to develop hydrogels with gas permeability enhancing polymers. In these hydrogels, the gas permeability depends not only on their hydration but also on the permeation of the gas through the polymer phase. CONCLUSIONS: The new hydrogel contact lenses will contain highly permeable polysiloxane domains. A potential problem with the new hydrogels is decreased wettability due to the migration of hydrophobic moieties to the lens surface.

Compliance↗

PubMed1996

Flocculation of Esch. coli with cationic polymers: a model for the dose curve based on charge.

Continuously grown cells from a glucose limited chemostat were flocculated with four different cationic polymers. The polymer was added to the cells either dropwise or as a slug at the start of the flocculation period. Dose curves for each polymer type and using each method of polymer addition were constructed. It was evident that classical overdose was possible with all four polymers if slug addition was used. Continuous addition produced dose curves overdose was possible with all four polymers if slug addition was used. Continuous addition produced dose curves with no overdosing except when low molecular weight, low charge density polymer was used. The dose curves could be combined if they were based on amount of charge added. The dose curve was not linear, but fitted a logarithmic model well. Charge density was much more important than MW of the polymer.

Biotechnology↗