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PubMed2004

Tensile properties of soft contact lens materials.

The strength of contact lens materials is an important consideration with respect to resistance to damage during lens handling and long term durability, and may govern some aspects of in-eye lens performance. The tensile properties of hydrogel contact lenses manufactured from eight different materials were examined in a series of clinical and laboratory experiments using the Instron 1122 Universal Testing Instrument. Lenses from the following eight materials (and nominal water contents) were used: HEMA/VP 40%, HEMA/VP 55%, HEMA/VP 70%, VP/MMA 55%, VP/MMA 70%, HEMA 40%, HEMA/MAA 55% and HEMA/MAA 70% (HEMA: 2-hydroxy-ethyl methacrylate, VP: vinyl pyrrolidone, MMA: methyl methacrylate, MAA: methacrylic acid). Tensile strength, elongation-at-break and Young's modulus were measured. A technique was devised that enables three parallel-sided specimens of identical width to be cut from a single contact lens with good accuracy. It was found that materials made from HEMA/MAA--although having a very low tensile strength and elongation-at-break--exhibit only a moderate Young's modulus. Materials made from HEMA/VP exhibit high-to-moderate tensile strength, high elongation-at-break and moderate-to-low Young's modulus. Materials made from VP/MMA exhibit high tensile strength and high-to-moderate elongation-at-break, but the Young's modulus is high for the 55% water content and low for the 70% water content materials. The HEMA 40% material exhibits a moderate tensile strength, a low elongation-at-break and a high Young's modulus. This experiment highlights the necessity of developing an accepted standard test methodology for contact lens material stiffness evaluation, in order to derive useful comparative information. Six subjects were fitted with the same lenses for one day. In vitro measurements of total diameter and back optic zone radius were taken at 35 degrees C before lens fitting and after 6h of lens wear. Lens water content, the relative change in lens total diameter (%deltaTD) and relative change in lens back optic zone radius (%deltaBOZR) were calculated and correlated with the tensile properties of the eight hydrogel lens materials. It is concluded that hydrogel materials with high stiffness and strength display less tendency to change their geometric parameters and materials with a high water content do not necessarily have the weakest mechanical properties.

Journal Article↗

PubMed2004

Water properties of soft contact lens materials.

The properties of water in soft contact lenses such as the water content, free-to-bound water ratio, and the extent to which soft lenses dehydrate during wear, are key determinants of their in eye performance and oxygen transmissibility characteristics. This study describes clinical and laboratory experiments that were conducted in order to examine the state of water in eight soft contact lenses manufactured from different materials. Specifically, lenses made from the following eight materials (and nominal water contents) were used: HEMA/VP 40%, HEMA/VP 55%, HEMA/VP 70%, VP/MMA 55%, VP/MMA 70%, HEMA 40%, HEMA/MAA 55% and HEMA/MAA 70% [HEMA = 2-hydroxy-ethyl methacrylate, VP = vinyl pyrrolidone, MMA = methyl methacrylate, MAA = methacrylic acid]. Differential scanning calorimetry (DSC) was used for measuring the free water content in the materials listed above. Some noticeable differences in water properties among soft contact lens materials having approximately the same water contents were revealed. Low water content materials exhibited a simple endotherm and all water melted around 0 degrees C. On the other hand, medium and high water content materials exhibited multiple melting endotherms, representing a broad range of interactions between water and the polymer. Low water content soft contact lenses have approximately the same amount of bound water as those with much higher water contents. Six subjects were then fitted with the same lenses for one day. In vitro measurements of water content and oxygen transmissibility were taken at 35 degrees C, both before lens fitting and after 6 h of lens wear. Water content and oxygen transmissibility were correlated with the water properties of the soft contact lens materials. The relative change in lens water content (%deltaWC) and relative change in lens oxygen transmissibility (%deltaDk/t) were calculated and correlated with the water properties of the eight soft contact lens materials. It was concluded that (a) oxygen transmissibility, free water content and free-to-bound water ratio are increased when the water content of a contact lens is increased and (b) water content, free water content and free-to-bound water ratio cannot be used for the prediction of soft contact lens dehydration in vivo.

Journal Article↗

PubMed2006

Colloidal crystallization of colloidal silica modified with ferrocenyl group-contained polymers in organic solvents.

Surface modification of colloidal silica with ferrocenyl-grafted polymer and colloidal crystallization of the particles in organic solvent were studied. Poly(methyl methacrylate-co-vinylferrocene)-grafted silica never formed colloidal crystals in polar solvent, such as acetone, acetonitrile, ethanol and N,N-dimethylformamide (DMF), while poly(methyl methacrylate-co-ferrocenyl acrylate)-grafted silica gave colloidal crystallization in DMF. The particles prepared by grafting of poly(N,N-dimethylacrylamide-co-vinylferrocene), with vinylferrocene (Vfc) mole fraction of 1/13 and 1/23, were observed to give the crystallization in ethanol and DMF over particle volume fraction of 0.058. Further, silica modified with copolymer of Vfc and N-vinyl-2-pyrrolidone, N-vinylcarbazole or N-isopropylacrylamide formed colloidal crystals in ethanol and DMF. Especially, poly(N-isopropylacrylamide-co-Vfc)-grafted silica, which was composed of the highest mole fraction of vinylferrocene, 1/3, afforded colloidal crystallization in ethanol over particle volume fraction of 0.053. Relatively high polar vinylferrocene copolymer grafting of silica resulted in colloidal polymerization in organic solvents.

Amides↗

PubMed2006

Visualizing the conversion of carbamazepine in aqueous suspension with and without the presence of excipients: a single crystal study using SEM and Raman microscopy.

Visual observations of the hydration process of single carbamazepine (CBZ) crystals in water and in various excipient solutions [(1% w/v) - hydroxypropyl cellulose (HPC), poly(vinyl pyrrolidone) (PVP), sodium carboxymethylcellulose (CMC) at pH 7.5 and 3.0, and polyethylene glycol (PEG)] using scanning electron microscopy (SEM) are reported in this paper. Raman microscopy was used to confirm the chemical structures of the unconverted CBZ and the CBZ dihydrate (DH) needles. It was found that defect structures were a more important driving force than the nature of crystal faces for the initiation of the hydration, but face differences became obvious after 6 h immersion. The biggest crystal face grown from methanol, (100), was the slowest one to be covered with DH needles. A comparison of the molecular arrangements along the three crystal faces [(100), (010) and (001)] was carried out using crystal structure visualization software, and fewer polar groups exposed on the (100) face than on the (001) and (010) faces were found, explaining the comparatively weak interaction of the (100) face with water during hydration. Furthermore, investigation of the influence of excipients on the hydration of CBZ showed that both HPC and PVP strongly inhibited conversion, and no conversion of CBZ to DH was found after 18 h immersion in water. PEG and CMC (pH 7.5) were less potent inhibitors than HPC and PVP, and DH needles were observed on all the faces except the (100) face after 18 h immersion. No conversion was detected for the crystal immersed in CMC solution at pH 3.0. This is likely to be caused by the decreased polarity of CMC in water at pH 3.0 (pKa,cmc = 4.3), and thus a higher surface adsorption of CMC to the CBZ crystals in dispersion. The influence of excipients on the conversion of CBZ observed in this study agreed well with our previous quantitative studies using Raman spectroscopy. In this study, visual observation using electron microscopy has been demonstrated to be a unique and powerful tool to improve our understanding of polymorphic conversions of CBZ in aqueous suspension.

Carbamazepine↗

PubMed2003

Permeation of ciclopirox across porcine hoof membrane: effect of pressure sensitive adhesives and vehicles.

The purpose of this study was to investigate the effects of various pressure sensitive adhesives (PSA) on the penetration of ciclopirox across porcine hoof membrane. In addition, the influence of various vehicles on the permeation of ciclopirox from a PSA matrix across porcine hoof membrane was evaluated using a plastic penetration chamber containing poloxamer gel at 32 degrees C. Ciclopirox in poloxamer gel was extracted, derivatized and analyzed by HPLC. Ciclopirox showed highest permeability from an acrylic adhesive with a hydroxyl functional group, and this was followed by styrene-isoprene-styrene, styrene-butadiene-styrene, silicone and polyisobutylene adhesives in order. In addition, N-methyl-2-pyrrolidone (NMP), polypropylene glycol 400 (PPG 400), dimethylsulfoxide (DMSO), Labrasol, mercaptoethanol and Transcutol showed excellent permeation enhancing effects in a styrene-isoprene-styrene adhesive. A porcine hoof membrane treated with NMP changed from the non-helical phase to the helical phase, and another treated with DMSO showed a S=O peak shift to lower wavelength.

Adhesives↗

PubMed2005

In situ gelling, bioadhesive nasal inserts for extended drug delivery: in vitro characterization of a new nasal dosage form.

The purpose of this study was the preparation and characterization of sponge-like, in situ gelling inserts based on bioadhesive polymers. Hydrophilic polymers (carrageenan, Carbopol, chitosan, hydroxypropyl methylcellulose (HPMC) K15M and E5, sodium alginate, sodium carboxy methylcellulose (NaCMC), polyvinyl pyrrolidone (PVP) 90, xanthan gum) were dissolved with/without the model drug oxymetazoline HCl in demineralized water and lyophilized into small inserts. The drug release, water uptake, mechanical properties, X-ray diffraction and bioadhesion potential of the nasal inserts were investigated. A sponge-like structure of nasal inserts was formed with amorphous, but not with crystalline polymers during the freeze-drying process. The insert hardness increased with the glass transition temperature of the polymer (PVP25<PVP30<PVP90). The bioadhesion potential was governed by the polymer ability to interact with mucin/agar (highest for carrageenan, Carbopol, xanthan gum and NaCMC). Inserts prepared from low molecular weight polymers resulted in polymer dissolution and fast drug release (HPMC E5, Na-alginate, PVP90). The drug release from inserts prepared from high molecular weight polymers (carrageenan, Carbopol, chitosan, HPMC K15M, NaCMC, xanthan gum) was a complex interplay of osmotic forces, water uptake and electrostatic interactions between drug and polymer. The drug release decreased with higher polymer content and increased drug loading of the insert. Bioadhesive nasal inserts have a high potential as new nasal dosage form for extended drug delivery.

Adhesiveness↗

PubMed2005

Stability and degradation profiles of Spantide II in aqueous solutions.

Spantide II is an 11 amino acid peptide that has been shown to be a potential anti-inflammatory agent. The stability and degradation profiles of Spantide II in aqueous solutions were evaluated with the long-term objective of developing topical formulations of this compound for various skin disorders. The stability profile of Spantide II at various temperature and pH conditions was monitored by high performance liquid chromatography (HPLC) and the resulting degradation products were identified by liquid chromatography-mass spectroscopy (LC-MS). Forced degradation of Spantide II was performed at extreme acidic (pH <2.0) and alkaline (pH >10.0) conditions and by addition of hydrogen peroxide (oxidizing agent). The degradation pattern of Spantide II followed pseudo first-order kinetics. The shelf life (T90%) of Spantide II in aqueous ethanol (50%) was determined to be 230 days at 25 degrees C. Spantide II was susceptible to degradation at pH <2 and pH >5 and showed maximum stability at pH 3-5. The stability under various pH conditions indicates that Spantide II was most stable at pH 3.0 with a half-life of 95 days at 60 degrees C. Spantide II degradation was attributed to hydrolysis of peptide bonds [Pro2-(pyridyl)Ala3, (nicotinoyl)Lys1-Pro2, Pro4-PheCl2(5), Trp7-Phe8, Phe8-Trp9, Nle11-NH2), racemization of the peptide fragments that resulted from hydrolysis, cleavage and formation of (nicotinoyl)Lys1-Pro2 diketopiperazine. In the presence of an oxidizing agent, Pro(2,4) residues degraded by ring opening to form glutamyl-semialdehyde and by bond cleavage at Pro4 to form 2-pyrrolidone, while Phe(5,8) degraded to form 2-hydroxyphenylalanine. Spantide II was found to be stable in aqueous medium with T90% of 230 days. The major degradation pathways of Spantide II were identified as hydrolysis, racemization, cleavage and formation of diketopiperazine.

Anti-Inflammatory Agents↗

PubMed2006

Rat epidermal keratinocyte organotypic culture (ROC) compared to human cadaver skin: the effect of skin permeation enhancers.

The objective of this study was to evaluate the response of the rat epidermal keratinocyte organotypic culture (ROC) to permeation enhancers, and to compare these responses to those in human cadaver skin. Different concentrations of two mixtures for enhancing permeation were investigated, sodium dodecyl sulfate:phenyl piperazine and methyl pyrrolidone:dodecyl pyridinium chloride, using skin impedance spectroscopy and two experimental compounds, the lipophilic corticosterone and the hydrophilic sucrose. The chemical irritation effects of the formulations were evaluated based on leakage of lactate dehydrogenase enzyme (LDH) and cellular morphological perturbation. This study provides evidence for direct correlations of permeation/permeation, impedance/impedance and permation/impedance between the culture model and human skin. The only exception was the enhancer induced permeation of sucrose which was 1-40-fold higher in ROC compared to human skin, reflecting the more disordered lipid organization in stratum corneum and consequently the greater number of polar pathways. LDH leakage and cellular morphology indicated that it was possible to differentiate between safe permeation enhancers from irritating agents. This is not only the first study to have compared the enhancer effects on a cultured skin model with human skin, but also it has demonstrated enhancer induced irritation using an artificial skin model.

Administration, Topical↗

PubMed2005

Suppression of choroidal neovascularization by intramuscular polymer-based gene delivery of vasostatin.

The purpose of this study was to evaluate the efficacy of gene delivery of angiogenesis inhibitor, vasostatin (VS), in suppressing experimental model of choroidal neovascularization (CNV). A mammalian expression vector carrying VS, pCMV3-VS, was constructed and evaluated for its ability to produce VS in transfected cells using western blot analysis and a cell viability assay. CNV was induced in Brown Norway rats by fundus argon laser photocoagulation and evaluated by fundus fluorescein angiography (FAG). Ten days post-laser treatment, gene delivery was achieved by intramuscular (IM) injection of poly-(N-vinyl pyrrolidone) (PVP) polymer conjugated with pCMV3-VS (PVP-VS) or a control vector (PVP-vector). Systemic VS expression was analysed by western blot analysis and enzyme linked immunosorbent assay (ELISA), and the extent of CNV was monitored by FAG analysis at different time intervals post-PVP treatment. Transfection of pCMV3-VS into muscle cells resulted in increased production and release of exogenous VS, which specifically inhibited the proliferation of endothelial cells. Besides, IM injection of PVP-VS, but not PVP-vector, led to elevated VS level in plasma for 30 days. After laser photocoagulation, rats injected with PVP-VS exhibited significantly lower incidence of CNV comparing with animals of control groups (P < 0.01) for at least 42 days. Moreover, rats treated with PVP-VS also showed a significant reduction in the CNV lesions compared with control groups (P < 0.001) for at least 42 days. Above all, no overt adverse effects were observed in rats received PVP-VS. These results demonstrate the potential of IM VS gene delivery for CNV treatment.

Angiogenesis Inhibitors↗

PubMed2004

Skin permeation of propranolol from polymeric film containing terpene enhancers for transdermal use.

To develop the suitable film formulations of propranolol hydrochloride (PPL) containing enhancers for transdermal use, polymeric film formulations were prepared by employing ethyl cellulose (EC) and polyvinyl pyrrolidone (PVP) as a film former, and dibutyl phthalate (DBP) as a plasticizer. Terpenes such as menthol and cineole, and propylene glycol (PG) were also employed as a chemical enhancer to improve the skin penetration of PPL. The film preparations were characterized in physical properties such as uniformity of drug content, thickness and moisture uptake capacity. Release and skin permeation kinetics of PPL from film preparations were examined in the in vitro studies using a Franz-type diffusion cell. The uniformity of drug content was evidenced by the low S.D. values for each film preparation. The moisture uptake capacity and drug release rate increased with the increase of PVP in each preparation. Enhancers examined in the present study also increased the moisture uptake capacity and release rate of PPL from the film preparations. Increasing the concentration of PPL from 1 to 2 mg/cm2 in the film enhanced the release rate of PPL, while no effect of enhancer concentrations on the release rate from the film preparations was observed. In vitro skin permeation study showed that cineole was the most promising enhancer among the enhancers examined in the present study and suggested that the suitable compositions of film preparation would be EC:PVP:PPL=6:3:4 with 10% (w/w) cineole and 7:2:4 with 10% (w/w) PG and cineole, which provided high skin permeation rates at 93.81+/-11.56 and 54.51+/-0.52 microg/cm2/h, respectively.

Administration, Cutaneous↗

PubMed2005

Preparation of mucoadhesive microspheres containing antimicrobial agents for eradication of H. pylori.

Mucoadhesive microspheres containing either amoxicillin or clarithromycin were prepared via the interpolymer complexation of poly(acrylic acid) (PAA) with poly(vinyl pyrrolidone) (PVP) and solvent diffusion method. The complexation between the PAA and PVP in an ethanol/water mixture was confirmed by the change in the transmittance of the solution as a function of repeating PAA and PVP unit ratio. The loading efficiency of clarithromycin in the complex microspheres was higher than that of amoxicillin due to the stronger interaction of clarithromycin with the PAA. The microspheres had a spherical shape with a smooth surface and the inside of the microspheres was completely filled. The dissolution rate of the complex microspheres was significantly slower than that of the PVP microspheres, particularly at pH 2.0. Amoxicillin and clarithromycin degraded significantly during the release study at pH 2.0. Therefore, their release rates were corrected using first order degradation rate constants. The amoxicillin release rates were similar regardless of the pH of the medium, while those of clarithromycin differed depending on the pH. The release mechanism of amoxicillin was mainly by a diffusion process and that of clarithromycin was via a dissolution process. The drug release rate from the complex microspheres was significantly lower than that from the PVP microspheres.

Adhesives↗

PubMed2005

Stabilizer choice for rapid dissolving high potency itraconazole particles formed by evaporative precipitation into aqueous solution.

The objective of this study was to investigate the influence of stabilizer type on the physicochemical properties, including dissolution, of ultra-high potency powders containing itraconazole (ITZ) formed by evaporative precipitation into aqueous solution (EPAS). ITZ was dissolved in dichloromethane, which was then atomized through a heated coil at 80 degrees C into an aqueous solution over precise periods of time. Stabilizers were present in either the aqueous, organic or both phases. The dispersions were centrifuged and the supernatant was removed. Three hydrophilic stabilizers were investigated, including polysorbate 80, polyvinyl pyrrolidone and poloxamer 407. Rapid dissolving ultra-high potency of ITZ powders was successfully produced. Greater than 80% of ITZ was dissolved in 5 min compared to only 13% of ITZ bulk powders. The resulting stabilizer-coated drug particles had high drug-to-stabilizer ratios greater than 12, corresponding to potencies (wt drug/wt drug+wt surfactant) as high as 93%. An increase in dissolution rate was correlated with the amount of stabilizer adsorbed and the wettability. The combination of polysorbate 80 and poloxamer 407 present in the aqueous and organic phases, respectively, was superior in achieving high wetting and rapid dissolving ITZ powders. The ability to control the adsorption behavior of stabilizers by using synergistic combinations affords the opportunity to achieve high dissolution rates with higher potencies compared to previously reported values.

Adsorption↗

PubMed2005

Use of compressed gas precipitation to enhance the dissolution behavior of a poorly water-soluble drug: generation of drug microparticles and drug-polymer solid dispersions.

The classical anticonvulsant drug phenytoin (5,5-diphenyl hydantoin, C(15)H(12)N(2)O(2)) has been used as a model compound to investigate the possibility of enhancing the dissolution rate of poorly water-soluble drugs using dense gas antisolvent techniques. In a first step, microcrystals of neat phenytoin have been generated using the gas antisolvent (GAS) and precipitation with compressed antisolvent (PCA) processes, thereby assessing process performances and elucidating similarities and differences between the two techniques. In a second step, the PCA process has been used to generate solid dispersions of phenytoin in the hydrophilic polymer poly(vinyl-pyrrolidone)-K30 (PVP). In vitro dissolution results reveal a substantially better performance of the PCA-processed co-formulations compared to unprocessed phenytoin and to GAS- and PCA-precipitates of neat drug crystals. A comparison of the product quality of phenytoin-PVP co-formulations with solid dispersions obtained by spray drying convincingly underlines the potential of dense gas antisolvent techniques for the production of pharmaceutical formulations with enhanced oral bioavailability.

Chemical Precipitation↗

PubMed2006

Evaluation of chemical enhancers in the transdermal delivery of lidocaine.

The effect of various classes of chemical enhancers was investigated for the transdermal delivery of the anesthetic lidocaine across pig and human skin in vitro. The lipid disrupting agents (LDA) oleic acid, oleyl alcohol, butenediol, and decanoic acid by themselves or in combination with isopropyl myristate (IPM) showed no significant flux enhancement. However, the binary system of IPM/n-methyl pyrrolidone (IPM/NMP) improved drug transport. At 2% lidocaine dose, this synergistic enhancement peaked at 25:75 (v/v) IPM:NMP with a steady state flux of 57.6 +/- 8.4 microg cm(-2) h(-1) through human skin. This observed flux corresponds to a four-fold enhancement over a 100% NMP solution and over 25-fold increase over 100% IPM at the same drug concentration (p < 0.001). NMP was also found to co-transport through human skin with lidocaine free base and improve enhancement due to LDA. These findings allow a more rational approach for designing oil-based formulations for the transdermal delivery of lidocaine free base and similar drugs.

Administration, Cutaneous↗

PubMed2006

Synthesis and study of controlled release of ibuprofen from the new acrylic type polymers.

New acrylic type polymeric systems having degradable ester bonds linked to ibuprofen were synthesized and evaluated as materials for drug delivery. Methacryloyloxy(2-hydroxy)propyl-4-isobutyl-alpha-methylphenyl acetate (MOPE), a new methacrylic derivative of ibuprofen in which the drug is separated from the methacrylic backbone by an oxy(2-hydroxy)propylene spacer arm and hydrolytically labile ester bond, was synthesized from reaction of glycidyl methacrylate with ibuprofen. The resulting drug containing monomer was copolymerized with methacrylamide, 2-hydroxyethyl methacrylate, N-vinyl-2-pyrrolidone or n-butyl methacrylate by free radical polymerization method in N,N-di-methylformamide (DMF) solution, utilizing azobisisobutyronitrile as initiator at the temperature range 65-70 degrees C. The obtained polymers were characterized by FT-IR, 1H NMR and 13C NMR spectroscopy. Gel permeation chromatography (GPC) was used for determination of average molecular weights of drug-polymer conjugates and showed that the polydispersity indices of the polymers are in the range of 1.9-2.3. Drug release studies were performed by hydrolysis in buffered solutions (pH 1 and 8) at 37 degrees C. Detection of hydrolysis by UV spectroscopy at selected interval showed that the drug can be released by selective hydrolysis of the ester bond at the side of drug moiety. The release profiles indicated that the hydrolytic behavior of polymeric prodrugs is strongly based on the hydrophilicity of polymer and the pH of the hydrolysis solution. The hydrophilic polymers containing ibuprofen were hydrolyzed in buffer solutions rather than the hydrophobic polymers.

Acrylates↗

PubMed2006

Investigation into the influence of polymeric stabilizing excipients on inter-particulate forces in pressurised metered dose inhalers.

Colloid probe atomic force microscopy (AFM) was utilised to quantify the cohesive forces of salbutamol sulphate in a model non-pressurised fluorinated liquid (mHFA), in the presence of increasing concentrations of poly(ethylene glycol) (PEG; molecular weight (MW) 200, 400 and 600). In addition, samples of PEG 400 (0.05-0.5%, v/w), were analysed in the presence of 0.001% (w/w) of poly(vinyl pyrrolidone) (PVP). In the absence of any stabilizing agents, strong attractive forces were present between particles. Increasing the concentration of the different MW PEG solutions in the mHFA system (up to 0.5%, v/w), significantly decreased the force of interaction (ANOVA, p<0.05). The decrease in cohesion was particularly evident at very low concentrations of PEG (0.05-0.1%, v/w). Further data analysis (p<0.05) suggested that the reduction in the force of cohesion was dependent on the concentration and molecular weight of PEG. The addition of low concentration of PVP to the PEG 400-mHFA system had the most significant influence on drug particle cohesion. In the presence of PVP, increasing addition of PEG 400 (0.05-0.5%, v/w) to the mHFA, resulted in no significant reduction in the force of cohesion (p>0.05). Clearly, an understanding of the conformation of polymer molecules at interfaces is of vital importance when controlling the stability/flocculation behaviour of sterically stabilized pMDI suspensions. In this context, the use of the colloid probe AFM technique has provided a quantitative insight into the interactions of these complex systems and may be an invaluable asset during the early phase of formulation product development.

Albuterol↗

PubMed2006

Encapsulation efficiency and controlled release characteristics of crosslinked polyacrylamide particles.

Polyacrylamide (pAAm) particles crosslinked with N,N-methylenebis-acrylamide/ethylene glycol dimethacrylate (NNMBA/EGDMA) have been prepared in water-methanol medium by the dispersion polymerization using poly(vinyl pyrrolidone), PVP as a steric stabilizer. 5-fluorouracil an anticancer drug, has been loaded in situ into the crosslinked pAAm particles. Plain as well as drug loaded microparticles have been characterized by differential scanning calorimetry (DSC) and X-ray diffraction studies (XRD) and scanning electron microscopy (SEM). DSC and XRD studies have indicated a molecular level dispersion of the drug in pAAm particles during in situ loading and SEM pictures have shown the formation of spherical and oval-shaped particles. In vitro release of 5-fluorouracil from the crosslinked pAAm particles has been carried out in 7.4 pH buffer medium. Both encapsulation efficiency and release patterns are found to depend on the nature of the crosslinking agent, amount of crosslinking agent used and the amount of drug loaded. In vitro release studies indicated the controlled release of 5-fluorouracil up to 12 h.

Acrylamides↗

PubMed2006

The influence of PVP incorporation on moisture-induced surface crystallization of amorphous spray-dried lactose particles.

We have recently shown that atomic force microscopy (AFM) may be an appropriate method for characterisation of the re-crystallization of amorphous particles. In this study, spray-dried composite particles consisting of lactose and polyvinyl pyrrolidon (PVP) were characterised by AFM and electron spectroscopy for chemical analysis (ESCA), and their response on increasing the relative humidity (RH) was investigated. The PVP content in the particles used was 0, 5 or 25 wt.% of either PVP K17 or PVP K90. All composite particles were found to be enriched with PVP at the surface. The incorporation of PVP in the particles influenced the way the particles responded to an increase in RH. The specific RH interval in which the surface of the particles smoothened and the RH where crystallization could be detected, increased with an increase in the amount and molecular weight of the PVP in the particles. The crystallization kinetics of single particles was analysed with AFM and by utilising the JMAK equation. The rate constant for this transformation increased in an exponential manner with increasing RH. Furthermore, above the RH needed for the crystallization to occur, the exponential increase in the crystallization rate was larger for particles with higher polymer content which indicates that the stabilising effect decreases as the water content in the particles becomes higher. In this study we report a method for determination of crystallization kinetics on single composite particles, which is valuable when evaluating the effect of stabilisers in amorphous powders.

Crystallization↗