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PubMed2005

The long-term mechanical integrity of non-reinforced PEEK-OPTIMA polymer for demanding spinal applications: experimental and finite-element analysis.

Polyetheretherketone (PEEK) is a novel polymer with potential advantages for its use in demanding orthopaedic applications (e.g. intervertebral cages). However, the influence of a physiological environment on the mechanical stability of PEEK has not been reported. Furthermore, the suitability of the polymer for use in highly stressed spinal implants such as intervertebral cages has not been investigated. Therefore, a combined experimental and analytical study was performed to address these open questions. A quasi-static mechanical compression test was performed to compare the initial mechanical properties of PEEK-OPTIMA polymer in a dry, room-temperature and in an aqueous, 37 degrees C environment (n=10 per group). The creep behaviour of cylindrical PEEK polymer specimens (n=6) was measured in a simulated physiological environment at an applied stress level of 10 MPa for a loading duration of 2000 hours (12 weeks). To compare the biomechanical performance of different intervertebral cage types made from PEEK and titanium under complex loading conditions, a three-dimensional finite element model of a functional spinal unit was created. The elastic modulus of PEEK polymer specimens in a physiological environment was 1.8% lower than that of specimens tested at dry, room temperature conditions (P<0.001). The results from the creep test showed an average creep strain of less than 0.1% after 2000 hours of loading. The finite element analysis demonstrated high strain and stress concentrations at the bone/implant interface, emphasizing the importance of cage geometry for load distribution. The stress and strain maxima in the implants were well below the material strength limits of PEEK. In summary, the experimental results verified the mechanical stability of the PEEK-OPTIMA polymer in a simulated physiological environment, and over extended loading periods. Finite element analysis supported the use of PEEK-OPTIMA for load-bearing intervertebral implants.

Benzophenones↗

PubMed2006

Molar-mass characterization of cationic polymers for gene delivery by aqueous size-exclusion chromatography.

PURPOSE: This study was performed to develop a reliable aqueous size-exclusion chromatography (SEC) method to obtain the absolute molar masses and distributions of various cationic polymers used in gene delivery. METHODS: Water-soluble cationic [2-(dimethylamino) ethyl methacrylate] polymers (PDEs) with different molar masses and low polydispersities were synthesized by living polymerization and these were used to optimize the SEC conditions. Online coupled multiangle light scattering (MALS) detection was applied to obtain the absolute molar masses. Narrow fractions of high molar mass were obtained by semipreparative SEC. RESULTS: It was found that 0.3 M NaAc (pH 4.4) is a suitable eluent in combination with Shodex OHpak SB columns for SEC analysis of PDEs and other cationic polymers, such as poly(L-lysine) and poly(ethylene imine). The absolute molar masses of different PDEs were determined directly using SEC-MALS. A calibration curve was established using narrow PDEs. CONCLUSIONS: A reliable routine method for molar-mass characterization of cationic polymers was established. Because standards of known molar masses with narrow distributions are not commercially available for most polymers used in pharmaceutics and biotechnology, the procedure described in this work can also be applied for molar-mass characterization of other water-soluble polymers.

Cations↗

PubMed1991

Kinetics of the multi-step catalytic degradation of a polymer to its constituent subunits.

The stepwise catalytic degradation of a polymer to its constituent subunits results in many molecules of polymers of shorter chain length. Using the Law of Mass Action, ordinary differential equations for each species can be obtained from the set of elementary reactions and these can be integrated to obtain species concentrations as a function of time. A special case of catalytic degradation of polymers, in which one subunit is released at each step, is examined. A mathematical dissertation on the kinetics of the series of reactions involved is presented. The solution of the set of differential equations involve tedious computations and cannot be easily adapted to the analysis of experimental data. Two additional methods of analysis are described. The first one makes use of the property that for any intermediary polymer whose initial and final concentrations are zero, the integral of its concentration with respect to time is inversely proportional to the degradation rate constant. Stepwise calculation of the rate constants can thus be obtained by determining the area under the concentration-time trajectories while the degradation rate constant of the first polymer is known. The second method makes use of the property that the maximum concentration attained by any individual intermediary polymer is inversely proportional to its degradation constant. These methods have the advantage of being simple since the degradation constants can be obtained stepwise from experimental data.

Catalysis↗

PubMed1977

Effect of rapid curing procedures on polymer implant materials.

This investigation of standard curing methods for PMMA implants has demonstrated that alternate means of using the air oven may produce good strength properties along with a considerable degree of porosity, when desired, in a relatively short period of time. Curing of polymers in a pressure pot offers few advantages owing to the length of time required to produce, at best, equivalent strength for the porous materials. The method also poses dangers inherent in the use of superheated salt solution or hot glycerin. The autoclave is widely used in dental offices for sterilizing and will fully and consistently cure polymers within 30 minutes. The best properties for the PMMA resin were achieved with this method (61 MPa or 9,130 p.s.i., tensile strength). The microwave oven has become relatively inexpensive in recent years, and it offers time savings of up to 90 per cent which would be beneficial in implant dentistry or in dental laboratory procedures in general. The exact condition for curing particular polymers must be carefully determined to adjust the time of irradiation in order not to under- or overcure the polymer object. Curing polymers which contain intrinsic foaming agents under pressure conditions slightly reduced the total pore volume. But, pore volume and pore diameter in the large-bead polymers are determined predominantly by packing conditions, not curing conditions. Biologic tolerance to materials cured by these methods in primates is presently being evaluated.

Chemical Phenomena↗

PubMed1982

Solubility parameter, specific molar cohesion, and the solubility of ethylene oxide in polymers.

The polarity of polymers is commonly characterized by their solubility parameter to describe their interaction with small molecules or by their specific molar cohesion to describe interchain attraction. A linear relation between these two parameters is demonstrated. Ethylene oxide (EO) is used to sterilize containers and devices containing plastics or elastomers. The solubility parameter concept is applicable to the sorption of EO by such polymers provided crystallinity and rubbery/glassy state are taken into account. The delta value of EO, calculated from the temperature dependence of its vapour pressure, is 10.8 (cal/cm3)1/2. The highest EO solubility is in polyvinyl chloride and polycarbonate, whose solubility parameters match that of EO closely. The solubility in other polymers decreases as their solubility parameters diverge increasingly from 10.8. At comparable delta values, polymers in the rubbery state dissolve 6000 to 8000 ppm EO more than polymers in the glassy state. EO solubility in the amorphous fraction of polymers above their glass transition temperatures ranges from 20 800 ppm for plasticized polyvinyl chloride (delta = 9.2) to 800 ppm for polytetrafluorethylene (delta = 6.2).

Ethylene Oxide↗

PubMed1987

Synthesis and biodegradation of polymers derived from aspartic acid.

The synthesis of copolymers derived from aspartic acid hydrochloride, their characterization and their hydrolytic degradation and biodegradation by Aspergillus niger and E. coli have been described. The alpha-amino dicarboxylic acid has been copolymerized with 1,2-ethane diol, 1,3-butane diol, 1,4-butane diol, 1,6-hexane diol and glycerol to get copolyesters I, II, III, IV and V respectively. The polymer samples have been characterized by their number average molecular weight (Mn), elemental analysis and their i.r. spectra. The copolyester V is crosslinked. All of the copolyesters I-V undergo slow hydrolytic degradation in aqueous solution at ambient temperatures as studied by the measurement of the decrease in reduced viscosity and increase in specific conductance of their aqueous solutions. They are also degraded in aqueous suspension by the fungus Aspergillus niger and by the bacterium E. coli. Degradation by Aspergillus niger mainly depends on the polarity of the polymers, the more polar polymers being less degradable. On the other hand, degradation by E. coli is primarily dependent upon the alpha-NH2 group contents of the polymers, the alpha-NH2 group rich polymers being more degradable. The possible use of these polymers as biodegradable drug carriers has been suggested.

Aspartic Acid↗

PubMed1992

Biodegradable polymers. II. Degradation characteristics of hydrolysis-sensitive poly[(organo)phosphazenes].

Polyphosphazenes with hydrolytic labile substituents have potential as biodegradable materials. By proper choice of the substituents, polymers can be prepared which can degrade to harmless products. The rate of biodegradation and the nature of the degradation products can be widely varied by changing the chemical composition of the polymers. The degradation properties of a series of new polyphosphazene derivatives are discussed. The synthesis of phosphazene polymers with variable amounts of ethyl 2-(O-glycyl)lactate or ethyl 2-(O-alanyl)lactate as cosubstituents was described previously. These polymers were prepared by partial reaction of poly[(dichloro)phosphazene] with the corresponding amine compound. Total halogen replacement was achieved by subsequent introduction of glycine ethyl ester cosubstituents. The degradation characteristics of these polymers in organic solution or in vitro was investigated. It was demonstrated that the introduction of hydrolysis-sensitive side-groups along the polymer chain results in an increased degradability of the poly[(amino acid ester)phosphazenes]. A plausible mechanism for the hydrolysis of these materials is proposed. The main hydrolysis pathway of poly[(amino acid ester)phosphazene] devices in vitro involves release of the amino acid ester side-group followed by hydrolysis of the ester with formation of the amino acid and ethanol. Initial hydrolysis of the ester bond with subsequent release of glycine cannot be excluded but is probably predominant.

Biocompatible Materials↗

PubMed1994

Engineering of cartilage tissue using bioresorbable polymer carriers in perfusion culture.

Bioresorbable polymer fleeces with a high internal surface area were used as temporary matrices to establish three-dimensional cultures of isolated human articular chondrocytes. The polymer surface was coated with poly-L-lysine to support cell attachment. The resulting cell-polymer tissues were cultured in perfusion culture chambers to achieve a constant supply of nutrients by diffusion. Retention and accumulation of extracellular matrix components synthesized by the chondrocytes were improved by encapsulation of the cell-polymer integrate in agarose gel. The cell-polymer tissues formed abundant collagen fibrils in vitro with a typical cross-triation clearly visible in electron microscopy analysis. Chondrocytes and intercellular matrix stained positively with monoclonal antibodies specific for differentiated chondrocytes and type II collagen. Synthesis of proteoglycans and collagen was also evident by further analysis with alcian blue and azan staining of cell-polymer tissue sections. The presented experimental tissue culture technique offers a novel concept for the in vitro formation of vital cartilage implants for reconstructive surgery or treatment of destructive joint diseases and possibly for the in vitro engineering of human tissues in general, with applications in drug testing and replacement of animal experiments.

Adult↗

PubMed1996

Mechanisms of polymer degradation and erosion.

The most important features of the degradation and erosion of degradable polymers in vitro are discussed. Parameters of chemical degradation, which is the scission of the polymer backbone, are described such as the type of polymer bond, pH and copolymer composition. Examples are given how these parameters can be used to control degradation rates. Degradation leads finally to polymer erosion, the loss of material from the polymer bulk. The resulting changes in morphology, pH, oligomer and monomer properties as well as crystallinity are illustrated with selected examples. Finally, a brief survey on approaches to polymer degradation and erosion is given.

Biocompatible Materials↗

PubMed1983

Comparison of tissue distribution of cadmium in mice intravenously injected with metallothionein and a polymer of metallothionein.

Polymers of cadmium metallothionein I and II were prepared and used for distribution studies. Mice were intravenously injected with comparable doses of cadmium as chloride, metallothionein and metallothionein-polymer and were killed at 3 h and 24 h after injection. A considerably higher concentration of cadmium was found in the plasma and spleen of animals exposed to metallothionein-polymer than other groups, while the cadmium concentration in the kidney was less than, but in the liver was greater than those injected with cadmium-metallothionein. Gel filtration of liver and kidney cytosols showed that metallothionein is the most stable form of cadmium in the tissues. The injected polymer was degraded into the monomer within 24 h in tissues. The high concentration of polymer in plasma indicates a slow clearance of cadmium in this form. The increased antigenicity of metallothionein-polymer may be related to its slow clearance from blood and increased deposition in spleen.

Animals↗

PubMed2005

Thiomers: a new generation of mucoadhesive polymers.

Thiolated polymers or designated thiomers are mucoadhesive basis polymers, which display thiol bearing side chains. Based on thiol/disulfide exchange reactions and/or a simple oxidation process disulfide bonds are formed between such polymers and cysteine-rich subdomains of mucus glycoproteins building up the mucus gel layer. Thiomers mimic therefore the natural mechanism of secreted mucus glycoproteins, which are also covalently anchored in the mucus layer by the formation of disulfide bonds-the bridging structure most commonly encountered in biological systems. So far the cationic thiomers chitosan-cysteine, chitosan-thiobutylamidine as well as chitosan-thioglycolic acid and the anionic thiomers poly(acylic acid)-cysteine, poly(acrylic acid)-cysteamine, carboxy-methylcellulose-cysteine and alginate-cysteine have been generated. Due to the immobilization of thiol groups on mucoadhesive basis polymers, their mucoadhesive properties are 2- up to 140-fold improved. The higher efficacy of this new generation of mucoadhesive polymers in comparison to the corresponding unmodified mucoadhesive basis polymers could be verified via various in vivo studies on various mucosal membranes in different animal species and in humans. The development of first commercial available products comprising thiomers is in progress. Within this review an overview of the mechanism of adhesion and the design of thiomers as well as delivery systems comprising thiomers and their in vivo performance is provided.

Animals↗

PubMed2004

Control of heme peptide activity by using phase transition polymers modified with inhibitors.

Catalytic activity of a heme peptide (HP) modified-electrode for H(2)O(2) reduction was controlled by use of poly(N-isopropylacrylamide) modified with an inhibitory moiety, imidazole group. The polymers inhibited the catalytic activity below their lower critical solution temperature (LCST) where the polymers were dissolved and did not inhibit the activity above the LCST where the polymers were precipitated. A polymer with a longer side chain connecting with the imidazole group was more inhibitory than a polymer with a shorter side chain at temperatures below the LCST. Formation constants of dissolved HP-imidazole complexes were evaluated by spectroscopic means, and it was found that the polymers were more inhibitory than the corresponding monomers.

Acrylic Resins↗

PubMed2005

Cytotoxicity of thermosensitive polymers poly(N-isopropylacrylamide), poly(N-vinylcaprolactam) and amphiphilically modified poly(N-vinylcaprolactam).

Thermosensitive polymers poly(N-isopropylacrylamide) (PNIPAM), poly(N-vinylcaprolactam) (PVCL) and PVCL grafted with amphiphilic poly(ethylene oxide) (PEO) chains (PVCL-graft-C11EO42) were prepared and characterized and their putative cytotoxicity was evaluated. The cytotoxicity of these thermosensitive polymers and their monomers was investigated as a function of polymer concentration, incubation time and incubation temperature by using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) cytotoxicity tests in Caco-2 and Calu-3 cell cultures. Also, the influence of the chain end functionality on toxicity was examined. Viability (MTT) and cellular damage (LDH) of the cells were shown to be dependent on the surface properties of the polymers, hydrophilicity or hydrophobicity. Hydrophilic PVCL and PVCL-graft-C11EO42 were well tolerated at all polymer concentrations (0.1-10.0 mg/ml) after 3 h of incubation at room temperature and at physiological temperature (37 degrees C). The more hydrophobic PNIPAM induced more clear cellular cytotoxicity at 37 degrees C. The monomers N-isopropylacrylamide and vinylcaprolactam and PEO-macromonomer showed dramatically higher cytotoxicity values with respect to the corresponding polymers. Cell damage was directly dependent on concentration, temperature and incubation time.

Acrylic Resins↗

PubMed2005

Highly effective and slow-biodegradable network-type cationic gene delivery polymer: small library-like approach synthesis and characterization.

Over the past years, macromolecular biodegradable polymers have been attracting considerable attention as gene delivery vehicles due to their safety and many potential applications. In the process of developing such biopolymers, we synthesized a biodegradable, network-type poly(amino ester) polymer (nt-PAE), which showed desirable chemical properties and a mechanical durability with high transfection efficiency. A small library-like approach to polymer synthesis using melt polycondensation followed by surface modification with aminohexanoic acid resulted in the final polymer, nt-PAE. The network-type structure of nt-PAE consists of biodegradable ester linkages and tertiary amines embedded in the backbone, and primary amines positioned at the surface. Unlike other rapidly degrading ester polymers, the nt-PAE exhibited fairly slow degradation, as the polymer sustained its DNA complexing ability for 10 days under physiological buffer conditions. In addition, the transfection efficiency of the nt-PAE could be increased to the same level comparable with that of PEI even in the presence of serum. Low toxicity and high transfection efficiency with a slow degradation profile implies that the nt-PAE can be used as a valuable nonviral gene delivery system.

Biocompatible Materials↗

PubMed2005

Effects of synthetic polymer on the filamentous bacteria in activated sludge.

Filamentous bulking is one of the solid-liquid separation problems always seen in activated sludge process. The addition of synthetic polymer is always one of the popular ways for the treatment plant operator to immediately solve the poor sludge settling problem. Therefore, it may be interesting to understand the effects of synthetic polymer on the filamentous bacteria in activated sludge. In this study, synthetic polymer was applied to a lab-scale wastewater treatment system with the filamentous bulking problem. The population structure of filamentous bacteria and sludge characteristics were investigated under different conditions. When synthetic polymer was added into the system, it was found that poor sludge settleability caused by filamentous bulking was temporarily solved and filamentous branches growing outside the flocs were damaged or inhibited. However, filamentous growth was still observed inside the flocs. After the addition of polymer was halted, filamentous branches extended out of the flocs immediately. Very serious filamentous bulking occurred and sludge settleability became much worse than that occurring before the addition of polymer. And, it took several weeks for the system to return to normal operation.

Bacteria↗

PubMed2004

Effect of the solvent on recognition properties of molecularly imprinted polymer specific for ochratoxin A.

A molecularly imprinted polymer specific for the mycotoxin ochratoxin A has been synthesised using a non-covalent approach. The polymer has shown an excellent affinity and specificity for the target template in aqueous solutions. The binding experiments, NMR study and molecular modelling have proven that the template recognition by polymer originates from the shape complementarity of binding sites. The binding mechanism is critically depended on factors that affect the polymer conformation. Thus the variation in buffer concentration, pH and presence of organic solvent, which affect the polymer swelling or shrinking, had a profound effect on the polymer recognition properties.

Binding Sites↗

PubMed2005

A molecularly imprinted polymer on indium tin oxide and silicon.

Molecular imprinting is a technique for creating artificial receptor sites in a polymer. Molecularly imprinted polymers (MIPs) are produced by forming a polymer around a molecule that is used as the template. Upon removal of the template, molecular holes remain which are specific in shape and size to the target molecule. In this research, a MIP was formed for theophylline using a copolymer of methacrylic acid and ethylene glycol dimethacrylate. The theophylline MIP was formed on two platforms: indium tin oxide (ITO) and silicon, which were used as the working electrode for cyclic voltammetry measurements. The presence of theophylline was measured using cyclic voltammetry and corresponded to the peak current on the cyclic voltammograms. The results of this research agreed with previous results of MIPs immobilized on an ITO platform. The peak currents of the MIP in the presence and absence of theophylline were compared to the blank polymer for each platform. The ratio of peak currents on ITO increased by a factor of 9.5 for the MIP compared to the non-imprinted polymer. Similarly, the ratio of peak currents on silicon increased by a factor of 6 compared to the non-imprinted polymer. This research demonstrated a procedure for evaluating a MIP layer on two different platforms.

Biosensing Techniques↗

PubMed2006

Novel biphasic separations utilising highly selective molecularly imprinted polymers as biorecognition solvent extraction agents.

Molecularly imprinted polymers (MIPs) represent a class of artificial receptors that promise an environmentally robust alternative to naturally occurring biorecognition elements of biosensing devices and systems. However, in general, the performance of conventional MIPs in aqueous environments is poor. In the study reported here, this limitation has been addressed by the novel application of MIPs as a solvent extraction solid phase in a biphasic solvent system. This paper describes a previously unreported use of MIPs as solvent extraction reagents, their successful application to aqueous sample media and the opportunities for utilisation of this unique system in novel biosensing and separation procedures. This study demonstrates the development of a novel biphasic solvent system utilising MIP in the extracting phase to enhance both efficiency and selectivity of a simple two phase liquid extraction. Monodisperse propranolol imprinted polymer microspheres [p(divinylbenzene-co-methacrylic acid)] were prepared by precipitation polymerisation. Initially, the affinity of the polymers for (R,S)-propranolol was assessed by established techniques whereby the MIP demonstrated greater affinity for the template than did the non-imprinted control polymer (NIP). Importantly, MIP performance was also assessed using the novel dual solvent system. The depletion of (R,S)-propranolol from the aqueous phase into the polymer containing organic phase was determined. When compared to control extractions containing no polymer the presence of MIP in the extracting solvent phase resulted in an increased extraction of (R,S)-propranolol from the aqueous phase. Importantly, this extraction was significantly greater in the presence of MIP when compared to NIP. This unique principle generates opportunities for MIP based extractions and chemical enrichments in industrial applications, offering commercial, ecological and practical advantages to traditional solvent extraction techniques. The technique is readily transferable to analytical microsystems utilising MIP recognition elements generating promising opportunities for MIP based sensing of aqueous sample media.

Biosensing Techniques↗