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PubMed1988

Fatigue testing of acrylic bone cements: statistical concepts and proposed test methodology.

In order to determine the fatigue behavior of a material, a standard procedure and methodology must be proposed and validated. This article describes a standard test method and statistical analysis for describing the fatigue properties of acrylic bone cement. It is proposed that bone cement fatigue data can be subjected to probability of failure (P) analysis and the establishment of a distribution function describing the data. It is also proposed that an Olgive type curve can be used to describe the stress (S) vs. cycles to failure (N) data. These two data sets can then be combined to determine the P-S-N relationship which fully describes the fatigue characteristics of the material.

Acrylates↗
PubMed1988

Fatigue properties of acrylic bone cement: S-N, P-N, and P-S-N data.

The determination of the fatigue properties of a material is a fundamental criteria in the engineering design process. The fatigue properties are governed by a number of factors, one of which is the inherent scatter in the data. In order to take into account this scatter in the results, the concept of the probability of failure (P) is introduced and interconnected with the well known stress (S) versus number of cycles to failure (N) data. This report determines the S-N curve, P-N curve, and P-S-N contour for the three leading acrylic bone cements: Surgical Simplex P, Zimmer LVC, and Zimmer Regular. Tensile specimens were fabricated according to ASTM D638 specifications and tested in uniaxial, zero-tension fatigue. The resulting stress versus number of cycles to failure data was subjected to a nonlinear least-squares analysis to determine the mathematical expression of the fatigue curve. Statistical analysis showed excellent fit of the data to the predicted curve for estimation of the endurance limit of each cement. The results indicated that Zimmer LVC had the highest endurance limit while the limit of Simplex-P and Zimmer Regular were significantly lower. No significant difference was noted in the endurance limit between Simplex-P and Zimmer Regular. The probability of failure at each stress level was determined with respect to fatigue distribution functions. Using the normal distribution function and previous S-N data, the P-S-N contour was generated for each cement. The P-S-N contour fully describes the fatigue characteristics of the material.

Acrylates↗
PubMed1989

Fatigue of acrylic bone cement--effect of frequency and environment.

This study was conducted to investigate some fundamental fatigue testing variables as they apply to the response characteristics of acrylic bone cement. Cyclic loading under load control was conducted at frequencies of 1, 2, 5, 10, and 20 Hz in air at room temperature. At a tensile stress range of 0.3-20.0 MPa the fatigue life increased linearly with logarithmic frequency. The effect of conditioning and testing in saline at both room temperature and 37 degrees C at similar stress levels and a frequency of 10 Hz were also examined. When compared to dry testing at room temperature, testing in saline at 37 degrees C resulted in a reduction in fatigue life while testing in saline at room temperature produced an increase in fatigue life. Of a number of statistical distributions considered, the Weibull was found to be the most appropriate in documenting the findings of this investigation. A companion fractographic investigation of the failure surfaces demonstrated distinct regions of crack growth and fast fracture.

Acrylates↗
PubMed2004

Effect of composition of interpenetrating polymer network hydrogels based on poly(acrylic acid) and gelatin on tissue response: a quantitative in vivo study.

The local tissue response of the biomaterial is the most important criteria for determination of its biocompatibility. In the present study, full and semi-interpenetrating polymer networks (IPN) based on polyacrylic acid (AAc) and gelatin (Ge) crosslinked with 0.5 mol % N,N'-methylene bisacrylamide (BAm) and 4% glutaraldehyde (GA), respectively, were evaluated for tissue response in rats. IPNs with varying ratios of AAc and Ge were implanted subcutaneously in rats. Gentamicin sulfate (GS)-loaded IPN samples were also studied to evaluate the possible therapeutic use of these polymers. The site of implantation was biopsied and processed for light microscopy (LM) with image analysis for assessment of tissue reaction at 2-, 6-, and 12-week intervals. The tissue reaction was evaluated as a function of composition and time. The degree of neutrophil, lymphocyte and macrophage infiltration, fibrosis, granuloma formation, integration with extracellular matrix, vascular proliferation, and damage of adjacent structures were assessed. Polymers with >66% crosslinked Ge (Gx) showed persistence of acute inflammatory reaction till 3 months, with marked tissue injury and fibrosis. On the other hand, high crosslinked AAc (Ax) content showed chronic inflammatory reaction with high macrophage infiltration. Macrophages took active part in phagocytosis, degradation, and removal of polymers without granuloma formation or significant giant cell reaction. The IPNs with acrylic acid and gelatin in the ratio of 1:1 showed least tissue reaction and thus appeared to be most biocompatible. The majority of the polymers showed integration with extracellular matrix and growth of capillaries in and around the polymer. The heamogram, liver and renal function tests, and histology of vital organs were all normal. GS loading showed no additional local or systemic reaction suggesting the potential usefulness of the hydrogels as carrier for drugs such as GS.

Acrylic Resins↗
PubMed2004

Biocompatibility of chemoenzymatically derived dextran-acrylate hydrogels.

The biocompatibility of chemoenzymatically generated dextran-acrylate hydrogels has been evaluated in vitro, using human foreskin fibroblasts, and in vivo, by subcutaneous and intramuscular implantation in Wistar rats for up to 40 days. In vitro tests show that hydrogel extracts only minimally reduced (<10%) the mitochondrial metabolic activity of fibroblasts. Direct contact of the hydrogels with cells induced a cellular proliferation inhibition index (CPII) of 50-80%, compared with a control, whereas through indirect contact, the CPII values were <16%, suggesting that the high CPII values achieved in the direct assay test were likely due to mechanical stress or limitations in oxygen diffusion. Hence, the hydrogels were noncytotoxic. Moreover, cell-material interaction studies show that these hydrogels were nonadhesive. Finally, histologic evaluation of tissue response to subcutaneous and intramuscular implants showed acceptable levels of biocompatibility, as characterized by a normal cellular response and the absence of necrosis of the surrounding tissues of the implant. In the first 10 days, the foreign-body reaction in the intramuscular implantation was more severe than in subcutaneous implantation, becoming identical after 30 days. In both cases, dextran hydrogels did not show signs of degradation 6 weeks postimplantation and were surrounded by a thin fibrous capsule and some macrophages and giant cells. This response is typical with a number of nondegradable biocompatible materials. These results indicate that dextran hydrogels are biocompatible, and may have suitable applications as implantable long-term peptide/protein delivery systems or scaffolds for tissue engineering.

Acrylates↗
PubMed2005

Oxidative and hydrolytic stability of a novel acrylic terpolymer for biomedical applications.

Oxidative and hydrolytic biostability assessment was carried out on a novel acrylic material made of hexamethyl methacrylate (HMA), methyl methacrylate (MMA), and methacrylic acid (MAA). To simulate the in vivo microenvironment, solutions of H2O2/CoCl2 and buffered solutions of cholesterol esterase (CE) and phospholipase A2 (PLA) were used. As controls, film specimens were incubated in deionized water. Samples were incubated in these solutions at 37 degrees C for 10 weeks before physical and mechanical properties were evaluated by size exclusion chromatography (SEC), 1H- nuclear magnetic resonance (1H-NMR), acid-base titration, and Instron tensile testing. The results from this study indicate excellent biostability of HMA-MMA-MAA terpolymers and thus their potential for use in biomedical devices for long-term implantation.

Acrylic Resins↗
PubMed2007

Acrylic bone cements with bismuth salicylate: Behavior in simulated physiological conditions.

In a previous work, we reported the development of acrylic bone cement formulations for application in percutaneous vertebroplasty, by using bismuth salicylate (BS) as the radiopaque agent. Our objective was to obtain high radiopacity along with a therapeutical effect produced by the release of salicylic acid in situ. To follow that study, the setting kinetics and static and dynamical mechanical properties of the BS cements were studied in simulated physiological conditions. Moreover, radiopacity after various times of immersion in saline and the wettability of the cements surfaces were determined. The study finished with the analysis of the biological response. From the results, it can be concluded that physiological conditions did not affect negatively to the cements performance, since all BS-loaded cements fulfilled the ISO standard requirements. Radiopacity of the formulations was maintained over time and cements with BS were found to be biocompatible.

Acrylates↗
PubMed2007

Influence of the activator in an acrylic bone cement on an array of cement properties.

In all but one of the acrylic bone cement brands used in cemented arthroplasties, N,N-dimethyl-4-toluidine (DMPT) serves as the activator of the polymerization reaction. However, many concerns have been raised about this activator, all related to its toxicity. Thus, various workers have assessed a number of alternative activators, with two examples being N,N-dimethylamino-4-benzyl laurate (DMAL) and N,N-dimethylamino-4-benzyl oleate (DMAO). The results of limited characterization of cements that contain DMAL or DMAO have been reported in the literature. The present work is a comprehensive comparison of cements that contain one of these three activators, in which the values of a large array of their properties were determined. These properties range from the setting time and maximum exotherm temperature of the curing cement to the variation of the loss elastic modulus of the cured cement with frequency of the applied indenting force in dynamic nanoindentation tests. The present results, taken in conjunction with those presented in previous reports by the present authors and co-workers on other properties of these cements, indicate that both DMAL and DMPT are suitable alternatives to DMPT.

Acrylic Resins↗
PubMed2005

Manipulation of nanoneedle and nanosphere apatite/poly(acrylic acid) nanocomposites.

Colloidal apatitic nanosphere of 2-5 nm in diameter was synthesized in the presence of poly(acrylic acid), PAA. PAA, which has long been recognized as an inhibitor in the synthesis of hydroxyapatite, is used as a structure-directing agent for the synthesis of calcium-deficient apatite (CDHA) in this study. Experimental observation suggests a critical amount of the low-molecular-weight PAA, above which morphological evolution of CDHA nanoparticles from needle to sphere was observed. This reveals that the PAA acts as an inhibitor for the growth of CDHA crystals. Further incorporation of PAA of high molecular weight formed a highly optically transparent nanocomposite, even with the nanospherical apatite loading up to 35 wt %, suggesting no agglomeration. This was further justified through transmission electron microscopy (TEM), where the CDHA nanospheres were uniformly distributed in the PAA-CDHA nanocomposites. No interfacial crevices were visually observed, indicating a highly compatible interface between the inorganic CDHA and organic PAA phase.

Acrylic Resins↗
PubMed1991

Kinetic investigation of penicillin G acylase from a mutant strain of Escherichia coli ATCC 11105 immobilized on oxirane-acrylic beads.

Highly purified penicillin G acylase from a mutant derivative of Escherichia coli ATCC 11105 was immobilized on oxirane-acrylic beads by covalent binding via oxirane groups. The highest specific activity, (322 U g-1 dry matrix at 40 degrees C and at pH 8.0) was obtained by using an enzyme solution having 13.8 U mg-1 specific activity and 72.73 mg total protein. The efficiency of immobilization was 95.8%. Kinetic parameters of immobilized penicillin G acylase were determined at the same pH and temperature by a preparation having 8.1 mg bound protein. The Km value and substrate inhibition constant of the enzyme were found to be 11.36 mmol dm-3 and 680 mmol dm-3 penicillin G respectively. Phenylacetic acid and 6-aminopenicillanic acid were estimated as the competitive and non-competitive inhibitors of the enzyme and their inhibition constants were found to be 90 mmol dm-3 phenylacetic acid and 76.1 mmol dm-3 for 6-aminopenicillanic acid. The activation energy of the hydrolytic reaction was calculated to be 7.75 kcal mol-1. The immobilized enzyme showed highest activity at pH 8.0 and at 55 degrees C. The enzyme was stable when incubated at 4 degrees C for one day at a pH range of 5.0 to 9.0. Thermal stability (over 30 min) was observed up to 40 degrees C but decreased at higher temperatures and was almost absent at 60 degrees C. A 95% conversion rate was observed at 28 degrees C and at 40 degrees C with 60 and 30 min operation times respectively. Operational stability of the enzyme was improved further with dithiothreitol treatment. Activity loss was around 5% following 20 cycles of repeated use of the enzyme at 40 degrees C. No significant loss of activity was observed at 28 degrees C when the enzyme was used for 20 cycles. 6-Aminopenicillanic acid in the reaction mixture was observed to be stable during conversion reactions which were carried out at both temperatures.

Acrylates↗
PubMed1993

Effect of polymer matrix on penicillin acylase immobilization on copolymers of butyl acrylate and ethylene glycol dimethacrylate.

Copolymers of butyl acrylate and ethylene glycol dimethacrylate with various degree of crosslinking and aminolysis were used for penicillin acylase immobilization. The amount and activity of the bound protein decreased with the decrease of crosslinking when copolymers having nearly constant degrees of aminolysis were compared. The increase of the carrier amino group content increased the ability to bind the protein (by glutaraldehyde method) without a proportional rise of enzyme activity. The comparative studies of immobilization effect and performance of the derivatives showed 40% crosslinked EGDMA, having an amino group content of 0.67 mmol g-3, to be the carrier of choice. This selected carrier was tested for active protein immobilization by use of crude acylase preparation. It was shown that up to a protein concentration of 9 mg cm-3 in the immobilization mixture the active protein was preferentially bound to the polymer matrix. It was indicated also that the derivative stability was mostly affected by multipoint attachment of the enzyme to the carrier surface.

Acrylates↗
PubMed1993

Immobilization of penicillin acylase on copolymer of butyl acrylate and ethylene glycol dimethacrylate.

The effects of glutaraldehyde, enzyme concentrations and reactants volumes, ionic strength, pH value and carrier particle diameter on immobilization of penicillin acylase onto acrylic carriers were studied. The activity of immobilized enzyme preparations was also studied over a range of pH values and temperatures and thermal and pH stabilities were determined. The use of the immobilized preparation for penicillin G hydrolysis in a batch reactor was investigated. The immobilized enzyme gave a significant reduction in hydrolysis time compared to hydrolysis by the native enzyme.

Acrylates↗
PubMed1990

A reduced-modulus acrylic bone cement: preliminary results.

Excessive local contact stress is implicated as an important factor in the initiation of the loosening process after total joint arthroplasties. A reduced-modulus acrylic bone cement, which decreases the bone-cement interface stresses, was developed to test this hypothesis. The formulation consists of butylmethacrylate beads, having a glass transition temperature of 27 degrees C, in a methylmethacrylate matrix. This cement, polybutylmethylmethacrylate (PBMMA), has an elastic modulus one-eighth that of standard PMMA bone cement, 0.27 vs. 2.1 GPa, at body temperature. In vivo use in a pilot study using the sheep total hip arthroplasty model shows a reduction in the rate of loosening of femoral components when compared both radiographically and mechanically with PMMA controls.

Acrylic Resins↗
PubMed2004

Influence of methacrylic and acrylic acid polymers on the release performance of weakly basic drugs from sustained release hydrophilic matrices.

Weakly basic drugs and their salts exhibit a drop in aqueous solubility at high pH conditions, which can result in low and incomplete release of these drugs from sustained release formulations. The objective of this study is to modulate matrix microenvironmental pH by incorporation of acidic polymers and thus enhance the local solubility and release of basic drugs in high pH environment. Two weakly basic drugs, papaverine hydrochloride and verapamil hydrochloride with widely different pKa and aqueous solubilities at the pH of interest (6.8), were investigated for their release from hydrophilic matrices and the effect of a methacrylic (Eudragit L100-55) and an acrylic acid polymer (Carbopol 71G), were studied. For papaverine HCl, release increased with an increase in the levels of the acidic polymer used. Direct measurement of matrix pH using microelectrodes illustrated that the mechanism of release enhancement was based on modulation of microenvironmental pH. For verapamil HCl, incorporation of L100-55 resulted in release retardation due to an interaction between the anionic polymer and the cationic drug and the extent of retardation increased with an increase in the polymer level. The interaction product was characterized by NIR, FT-IR, and MTDSC techniques. Verapamil HCl release from Carbopol 71G based matrix tablets was higher than that from conventional hydroxypropyl methylcellulose (HPMC) based matrices, without any incorporated acidic additives.

Acrylic Resins↗
PubMed1976

Drug release from methyl acrylate-methyl methacrylate copolymer matrix III: stimultaneous release of noninteracting drug-excipient mixtures.

The simultaneous release of mixtures of noninteracting chemicals incorporated in a methyl acrylate-methyl methacrylate copolymer was studied. Different mixtures of dextrose-methapyrilene hydrochloride and sodium chloride-methapyrilene hydrochlodire in the plastic were compressed into tablets, and single-surface release was obtained in 0.N HCI at 37 degrees. The amounts of both drug and excipients released per unit surface rate constants were analysed in terms of the solubility, diffusion coefficient, concentrations of each chemical, and porosity and tortuosity of the tablets. It was concluded that for each tablet system the individual solid-liquid boundaries of the incorporated chemicals had merged together, and the release could be explained by Higuchi's square foot of time relationship.

Acrylates↗
PubMed1983

Acrylic microspheres in vivo VIII: distribution and elimination of polyacryldextran particles in mice.

The disposition of different 14C-labeled, biodegradable polyacryldextran microparticles after intravenous injection has been studied in the mouse. The particles were rapidly cleared from the circulatory system by the reticuloendothelial system. They were predominantly (60-80%) found in the liver and spleen and to some extent in the bone marrow. Large particle aggregates were found in the lungs 6 hr postinjection. After redistribution, the particles were eliminated from the organs with an apparent t 1/2 of 12-30 weeks, depending on the composition of the particles. Highly cross-linked particles with 2% acrylic groups (DTC = 11-2-75) had a half-life similar to that of polyacrylamide particles (TC = 8-25). The metabolism rate was also correlated with the degradation in vitro with isolated rat lysosomes. After intravenous injection of small 14C-labeled polyacrylamide particles (0.2-0.5 micron), significant amounts of radioactivity were detected in the bile and gallbladder.

Acrylic Resins↗
PubMed1984

Effects of acrylic acid polymer and its arrangement on drug release from a wax matrix.

The release of phenacetin from a wax matrix was improved by the addition of an acrylic acid polymer. Increasing the amount of polymer increased the release rate of phenacetin due to the formation of pores and channels in the matrix resulting from leaching of the polymer. The leaching was affected by the pH of the dissolution medium as well as by the methods used to prepare the granules. The polymer in ordered powder mixes behaved differently from that uniformly dispersed in a wax matrix. The drug appeared to be released by an approximate zero-order process at pH 7.5 from tablets containing the polymer.

Acrylates↗
PubMed1994

Sustained-release oral delivery of theophylline by use of polyvinyl alcohol and polyvinyl alcohol-methyl acrylate polymers.

Crystalline polyvinyl alcohol (PVA) polymer and low-crystallinity polyvinyl alcohol-methyl acrylate copolymer (PVA-MA) were examined as sustained-release tablet excipients with theophylline as a model drug. By blending of different proportions of the crystalline polymer and the low-crystallinity copolymer, it was possible to affect the release characteristics of the tablets. Tablets made with crystalline PVA provided instant release of theophylline in vitro. Tablets made with a larger proportion of PVA-MA relative to PVA provided a very prolonged release profile in vitro. A formulation containing PVA-MA:PVA:theophylline in a ratio of 1:9:10 provided sustained-release profiles in vitro and in vivo in dogs. The dissolution release profile of this PVA-blend tablet formulation in vitro agreed extremely well with the percentage of bioavailable dose absorbed over time in vivo. The formulation provided a plateau of levels in plasma over 16 h. The oral bioavailability of theophylline from this formulation in dogs was approximately 80% and was equivalent to that obtained after administration of Theo-Dur, a marketed extended-release theophylline tablet from Key Pharmaceuticals.

Absorption↗