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PubMedDate not supplied

Modelling of the solvent evaporation method for the preparation of controlled release acrylic microspheres using neural networks.

The purpose of the present study was to model the solvent evaporation procedure for the preparation of acrylic microspheres by using artificial neural networks (ANNs) to obtain an understanding of the selected preparative variables. Three preparative variables, the concentration of the dispersing agent (sucrose stearate), the stirring rate of emulsion system, and the ratio of polymers (Eudragit RS-L) were studied, each at different levels, as input variables. The response (output) variables examined to characterize microspheres and drug release were the size of the microspheres and T63.2%, the time at which 63.2% of drug is released. The results were also analysed by the multiple linear regression (MLR) to provide a comparison with the ANN methodology. Although both ANN and MLR methods were found to be similar in characterizing the process studied, the results showed that an ANN method gave a better prediction than the MLR method. For the size values of the microspheres, the predictability of the ANN model was quite high (R2 = 0.9602) based on the input variables. A relationship between these variables and size values of microspheres was also obtained by the MLR model (R2 = 0.9050). The performances of both models for the release data from microspheres based on the same input variables were at the level of 53%. According to the results, the ANN methodology can provide an alternative to the traditional regression methods, as a flexible and accurate method to study process and formulation factors.

Acrylic Resins↗
PubMed2006

Important parameters for the manufacture of slow-release matrix pellets with an aqueous dispersion of quaternary poly(meth)acrylates in the rotary fluidized bed.

The manufacture of slow-release matrix pellets with an aqueous dispersion of quaternary poly(meth)acrylates was investigated in the rotary fluidized bed. By considering the moisture content of the fluidized bed to be the key process parameter, it was measured on-line throughout the whole manufacturing process. A specially designed sampling device opened new ways to apply NIR spectrometry in laboratory scale processes. It was shown that reproducibly improved pellet properties can be achieved by reproducing the moisture content of the (rotary) fluidized bed. Moisture plateaus proved to be a suitable way to optimize the sphericity of the pellets. Premoisturizing was found to be a very effective tool to achieve slow-release dissolution of the model drug theophylline.

Acrylic Resins↗
PubMed2006

Controlled release of a poorly water-soluble drug from hot-melt extrudates containing acrylic polymers.

Controlled release tablets containing a poorly water-soluble drug, indomethacin (IDM), acrylic polymers (Eudragit RD 100, Eudragit L 100, or Eudragit S 100), and triethyl citrate (TEC) were prepared by hot-melt extrusion. The physicochemical and IDM release properties of the controlled release hot-melt extrudates were investigated. Indomethacin (IDM) was found to be both thermally and chemically stable following hot-melt extrusion processing and displayed a plasticizing effect on Eudragit RL PO as demonstrated by a decrease in the glass transition temperatures of the polymer. The inclusion of either Pluronic F68, Eudragit L 100, or Eudragit S 100 in the powder blend containing Eudragit RD 100 prior to processing increased the rate of release of the IDM from the extrudates. An increase in the media pH and a decrease in the granule particle size also increased the rate of release of IDM. The inclusion of TEC up to 8% in the granule formulation or compressing the granules into tablets had no significant effect on the drug release rate. Indomethacin (IDM) was transformed from a crystalline Form I into an amorphous form in the Eudragit RD 100 granules following hot-melt extrusion. The thermal processing facilitated the formation of a solid solution with a continuous matrix structure that was shown to control drug diffusion from the extrudates.

Acrylic Resins↗
PubMed1997

Time-resolved EPR studies on the reaction rates of peroxyl radicals of poly(acrylic acid) and of calf thymus DNA with glutathione. Re-examination of a rate constant for DNA.

Electron paramagnetic resonance (EPR) signals of peroxyl radicals of poly(acrylic acid), PAA, and of single- and double-stranded DNA were generated at 293 K and pH 6.6 by in situ photolysis of O2-saturated aqueous solutions containing the macromolecules and H2O2. From time-resolved EPR measurements upper limits for the rate constants of reaction of glutathione (GSH) with the peroxyl radicals of PAA [kb < or = (0.8 +/- 0.2) x 10(2) dm3 mol-1S-1] and of single- and double-stranded DNA from calf thymus [kb < or = (2 +/- 2) x 10(2) dm3 mol-1S-1] were determined. The low value of kb for reaction of GSH with DNA peroxyl radicals is in agreement with the observed lack of protective effect of the thiol in radiation-induced DNA strand break reactions (Liphard et al. 1990).

Acrylic Resins↗
PubMed2006

Template-assisted synthesis of nanogels from Pluronic-modified poly(acrylic acid).

A series of novel polymeric nanogels with core-shell morphology was developed. Block ionomer complexes of comb-graft poly(ethylene oxide)-b-poly(polypropylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) copolymers (Pluronic-PAA) and divalent metal cations were utilized as micellar templates for the synthesis of nanogels with sizes ranging from 100 to 200 nm in diameter. The Pluronic-PAA nanogels were confirmed to possess ionic cross-linked PAA cores and flexible hydrophilic shells from the Pluronic copolymer chains. The ionic character of the core provided for pH-dependent swelling/collapse behavior of the nanogels. These prepared nanogels are expected to be of utility as carriers for charged therapeutic or diagnostic agents.

Acrylates↗
PubMed1986

Review of the toxicity of multifunctional acrylates.

Multifunctional acrylates and methacrylates (MFA) represent a class of materials with considerable chemical reactivity that are used in many applications with opportunity for contact exposure. They represent appreciable eye and skin contact hazards, and several members of the class may be absorbed from skin to cause systemic effects. A number of MFAs have been identified as sensitizers. While the acute toxicity of MFAs is certain, the effects of repeated or chronic exposure are less clear. Data are presented that suggest that MFAs are not appreciable fetotoxic or teratogenic hazards and do not elicit a strong carcinogenic response following chronic dermal exposure. The use of these data for product safety purposes and research needs is discussed.

Acrylates↗
PubMed2001

Influence of curing on the adhesive and thermomechanical properties of an applied acrylic polymer.

The objective of the current study was to investigate the relationship between polymer adhesion and post-coating thermal treatment. A novel adhesion technique was used to quantify the adhesive properties of applied acrylic films. Differential scanning calorimetry was used to determine the glass transition temperature of the applied polymer. Post-coating thermal treatment, or curing, was found to significantly influence the adhesive and thermomechanical properties of the applied film coating. Adhesion of triethyl citrate-plasticized films to tablets increased during storage at elevated temperatures, equilibrating within four hours. The glass transition temperature of the applied triethyl citrate-plasticized coatings also increased during curing. Equilibration of polymer properties was found to be dependent on the hydrophobicity of the plasticizer incorporated into the coating formulation, with longer curing times required for films containing the hydrophobic plasticizer tributyl citrate. The curing temperature was shown to influence polymer properties, with stronger film-tablet adhesion and higher glass transition temperatures resulting when the coated tablets were stored at higher temperatures. Substrate hydrophobicity was also found to influence the curing process, suggesting that the mechanisms involved in film formation and polymer-substrate adhesion may contribute to the internal stresses within the film.

Acrylic Resins↗
PubMed1991

Cytogenetic studies of ethyl acrylate using C57BL/6 mice.

The clastogenicity of ethyl acrylate (EA) was examined in vivo by injecting i.p. five male C57BL/6 mice per dose group with either 125, 250, 500 or 1000 mg/kg EA dissolved in saline. Controls received solvent only. Acrylamide (100 mg/kg), because of its similarity in structure and mode of action to EA, was used as a positive control. Twenty-four hours after injection, the animals were anesthetized and the spleens aseptically removed. Splenocytes were isolated on density gradients and cultured with concanavalin A to stimulate cell division. In half the cultures bromodeoxyuridine was added at 21 h for analysis of chromosome aberrations (CAs) in first division cells and sister chromatid exchange (SCE) in second division cells. In the remaining cultures cytochalasin B was added to produce binucleated cells for scoring of micronuclei (MN). There was no significant increase in SCE or CAs at any of the doses of EA examined. At the highest dose examined (1000 mg/kg), EA did cause a small but significant increase in binucleated cell MN. Acrylamide caused an increase in MN and SCEs in splenocytes. Because others have found EA to be clastogenic in vitro, isolated splenocytes were exposed to a wide range of concentrations of EA during the G0 stage of the cell cycle or 23 h after mitogen stimulation during the late G1 or early S phase of the cell cycle. Although EA was toxic for both exposure regimens, significant increases in chromatid-type aberrations were found only when the target cells were treated 23 h after mitogenic stimulation. No statistically significant increase in SCE frequency was found after either treatment regimen. These data suggest that EA is only clastogenic at near toxic concentrations during a specific stage of the cell cycle.

Acrylamide↗
PubMed2002

A clinical trial of light cure acrylic resin for orthodontic use.

OBJECTIVE: To ascertain whether or not the less porous surface associated with visible light cure appliances and the absence of free monomer had any measurable affect upon mucosal erythema, and to assess the durability of such appliances in a clinical context. DESIGN: A prospective randomized trial of visible light cure (Triad VLC) and autopolymerizing (Orthoresin) acrylic resin used as orthodontic base plate materials. SETTING: University Dental Hospital and School. SUBJECTS: Fifty subjects from a consecutively enrolled sample of 69 (19 drop outs) for removable appliance therapy (23 VLC, 27 AP). OUTCOME MEASURES: Erythema meter scores and appliance breakages. RESULTS: No statistical difference in mucosal erythema between the two materials was found. Fifty-two per cent of VLC appliances broke during a 6-month period, as opposed to 7 per cent of AP appliances. CONCLUSIONS: VLC appears to have no clinically beneficial effect on the oral mucosa compared with AP. VLC appliances are currently not sufficiently durable to make them a viable alternative to AP appliances.

Acrylic Resins↗
PubMed2000

Application of a hybrid CFD-PBPK nasal dosimetry model in an inhalation risk assessment: an example with acrylic acid.

The available inhalation toxicity information for acrylic acid (AA) suggests that lesions to the nasal cavity, specifically olfactory degeneration, are the most sensitive end point for developing a reference concentration (RfC). Advances in physiologically based pharmacokinetic (PBPK) modeling, specifically the incorporation of computational fluid dynamic (CFD) models, now make it possible to estimate the flux of inhaled chemicals within the nasal cavity of experimental species, specifically rats. The focus of this investigation was to apply an existing CFD-PBPK hybrid model in the estimation of an RfC to determine the impact of incorporation of this new modeling technique into the risk assessment process. Information provided in the literature on the toxicity and mode of action for AA was used to determine the risk assessment approach. A comparison of the approach used for the current U.S. Environmental Protection Agency (U.S. EPA) RfC with the approach using the CFD-PBPK hybrid model was also conducted. The application of the CFD-PBPK hybrid model in a risk assessment for AA resulted in an RfC of 79 ppb, assuming a minute ventilation of 13.8 l/min (20 m(3)/day) in humans. This value differs substantially from the RfC of 0.37 ppb estimated for AA by the U.S. EPA before the PBPK modeling advances became available. The difference in these two RfCs arises from many factors, with the main difference being the species selected (mouse vs. rat). The choice to conduct the evaluation using the rat was based on the availability of dosimetry data in this species. Once these data are available in the mouse, an assessment should be conducted using this information. Additional differences included the methods used for estimating the target tissue concentration, the uncertainty factors (UFs) applied, and the application of duration and uncertainty adjustments to the internal target tissue dose rather than the external exposure concentration.

Acrylates↗
PubMed1998

Clinical value of computer-generated acrylic skull replicas produced by laser lithography.

To determine for what deformity and utility the computer-generated acrylic (CGA) skull replica has the greatest value, we analyzed retrospectively a consecutive series of patients with craniomaxillofacial deformities (N = 54) whose treatment involved the utilization of CGA skull replicas. Application of the CGA skull replica was divided retrospectively into four groups: (1) use as an aid for preoperative analysis of osseous deformity, (2) use as material for preoperative surgical simulation, (3) use as a navigational aid during an operation, and (4) use as a negative template. Based on the aspects of these utilizations, we evaluated for what deformity the CGA skull replica was useful. Analysis of the data led us to conclude the following. First, the CGA skull replica is a valuable tool in craniomaxillofacial surgery, especially for patients with asymmetrical deformities and delicate convexities and concavities of the skull surface. Second, the largest function that CGA skull replicas can satisfy is standardization of craniomaxillofacial surgery. In carrying out preoperative surgical simulation utilizing a replica, drawing osteotomy lines on it, sterilizing it, and then bringing it to the operating table for consultation whenever required during an operation, we are able to proceed with greater precision and speed than if it was not available.

Acrylic Resins↗
PubMedDate not supplied

The effect of radiation on the shear strength of acrylic bone cement.

Bone loss due to secondary neoplastic disease of bone has frequently presented the orthopedic surgeon with difficult or insoluble problems of surgical management. Local radiation is the most effective, and widely used form of therapy for this type of metastatic disease. Levels of radiation in vitro comparable to therapeutic doses, as well as levels 6 times that commonly used in vivo on patients, demonstrate no significant effect on the mechanical properties of acrylic bone cement.

Acrylic Resins↗
PubMed1977

Stainless steel mesh-acrylic cranioplasty.

Twenty-four steel mesh-acrylic plates have been used for repair of skull defects in 1970-73. Three plates had to be removed due to complications, two due to infection and one due to an allergic reaction. The plate is easy to mould, strong, and light. The cosmetic results are excellent.

Acrylic Resins↗
PubMed1989

Titanium mesh and acrylic cranioplasty.

Since June 1985 100 cranioplasties have been carried out using titanium mesh and acrylic. There have been no complications and no infections. Titanium mesh is virtually radiolucent. Titanium is nonmagnetic and is the most biocompatible metal known.

Acrylic Resins↗
PubMed1989

Use of silicone-acrylate contact lenses for the control of myopia: results after two years of lens wear.

Although a number of reports have been published concerning the use of polymethyl methacrylate (PMMA) contact lenses for the control of myopia, there have been no reports of the use of gas permeable contact lenses for this purpose. In the study reported here, 100 myopic children between the ages of 8 and 13 years were fitted with Paraperm O2 plus silicone-acrylate contact lenses to be worn for a period of 3 years. Lenses were fitted by the alignment method, most lenses having diameters from 8.5 to 9.0 mm. At the end of 2 years 60 subjects remained in the study, 53 of whom were wearing their lenses on a regular basis and the other 7 were irregular wearers. Mean increases in myopia during the 2-year period were found to be 0.28 D for the subjects who wore their lenses regularly and 0.93 D for the irregular wearers, compared to 0.80 D for a group of 31 age-matched single vision spectacle lens wearers. Mean corneal refracting power was found to decrease (the cornea flattened) 0.33 D for the regular wearers as compared to an increase of 0.14 D for the irregular wearers and a decrease of 0.13 D for the spectacle wearers. Mean changes in axial length were an increase of 0.1 mm for the regular wearers, an increase of 0.4 mm for the irregular wearers, and an increase of 0.6 mm for the spectacle wearers.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylates↗
PubMed1990

Silicone-acrylate contact lenses for myopia control: 3-year results.

One hundred myopic children between the ages of 8 and 13 years were fitted with Paraperm O2plus silicone-acrylate contact lenses. After 3 years of lens wear, the mean increase in myopia for the 56 subjects remaining in the study was 0.48 D (+/- 0.70) D as compared with 1.53 (+/- 0.81) D for a group of spectacle-wearing myopes matched for initial age and initial refractive error. The mean change in corneal refracting power for the contact lens wearers was a decrease (corneal flattening) of 0.37 (+/- 0.32) D. Assuming that little or no corneal change would have occurred in the absence of the contact lenses, we may conclude that corneal flattening (as measured by the keratometer) accounts for less than half of the effect of contact lenses in controlling myopia progression. A possible explanation for this disparity is that although the keratometer provides a valid measurement of corneal refracting power for a "normal" cornea, it fails to provide a valid measurement for a cornea that has been flattened by wearing a contact lens.

Acrylates↗
PubMed1981

A hydrophilic acrylate implant for scleral buckling: technique and clinical experience.

A new hydrophilic acrylate implant developed for scleral buckling was used in 51 patients: as an accessory meridional piece under a solid silicone buckle in 25 and as a main buckling element in 26 (intrasclerally in 15 and episclerally in 11). Clinical observations six to 18 months after implantation showed the implants to be well tolerated in all cases. There was no infection, rejection, extrusion of the implant, or erosion of the eye coats. In two patients who had reoperations, smooth fibrous tissue encapsulating the implant including the scleral bed was present. Our observations indicate that this new material has all the characteristics of an ideal implant for scleral buckling.

Acrylates↗