Preparation and characterization of polyacrylic acid-hydroxyapatite nanocomposite by microwave-assisted synthesis method.

Polyacrylic acid, polyalkenoic acids in general, form the liquid ionomer phase of glass ionomer cements, which are frequently used in root restorations in dentistry. It is possible to obtain these ionomers with a fast, energy-efficient, high reaction efficiency and a clean method with microwave irradiation method. In this study, polyacrylic acid and its composite with nano HAp have been synthesized by microwave (MW) irradiation. The two-process parameters that were tested are MW intensity and reaction time. The polymerization was carried out at 110 °C up to 40 min and yield over 92% was produced in 30 min. The average molar mass of PAA was found as 11960 Da using a high-resolution mass spectrometer (TOF-MS). On the other hand, hydroxyapatite (HAp) nanoparticles have been prepared via the sol-gel procedure using potassium dihydrogen phosphate and calcium nitrate tetrahydrate as the precursors for phosphorus and calcium, respectively. XRD, EDS analysis revealed that the particles contain calcium deficient hydroxyapatite (Ca10-x(HPO4)x(PO4)6-x(OH)2-x (HAp) crystals with beta-TCP phase. Morphological observation by SEM measurement proved that the crystal particles of the HAp are very regular and granular, and their size is 25-45 nm in the longitudinal section. These particles were used in composite preparation with PAA. The yield of the composite obtained by heating at 500 W, 30 min was found to be 90%. From the FTIR and 1H-NMR results, it was observed that there was not only a physical but also an electrostatic interaction between HAp and PAA. The thermal behavior of PAA and its composite with nano HAp were determined by the thermogravimetric analyzer (TGA). The results showed that anhydride formation or decarboxylation occurred at a lower temperature, confirming the interaction between PAA and HAp. The polymerization rate is much faster with microwave heating than conventional heating. Microwave irradiation enables rapid energy transfer and high-energy efficiency, hence, a faster reaction rate.

Evaluation of the effects of two novel irrigants on intraradicular dentine erosion, debris and smear layer removal.

OBJECTIVES: To evaluate the effects of copolymer of acrylic acid and maleic acid (Poly[AA-co-MA]) and calcium hypochlorite (Ca(OCl)2) on root canal dentin using scanning electron microscope (SEM). MATERIALS AND METHODS: Twenty-four single-rooted teeth were instrumented and the apical and coronal thirds of each root were removed, leaving the 5 mm middle thirds, which were then separated into two pieces longitudinally. The specimens were randomly divided into six groups and subjected to each irrigant for 5 min as follows: G1, Ca(OCl)2; G2, Poly(AA-co-MA); G3, Ca(OCl)2 + Poly(AA-co-MA); G4, sodium hypochlorite (NaOCl); G5, ethylenediaminetetraacetic acid (EDTA); G6, NaOCl+EDTA. The specimens were prepared for SEM evaluation. Smear layer, debris and erosion scores were recorded by two blinded examiners. One image from G3 was analyzed with energy dispersive spectroscopy (EDS) on suspicion of precipitate formation. Data were analyzed using the Kruskal-Wallis and Dunn tests. RESULTS: G1 and G4 showed the presence of debris and smear layer and they were statistically different from G2, G3, G5 and G6 where debris and smear layer were totally removed (p < 0.05). In G1 and G4, erosion evaluation could not be done because of debris and smear layer. G2, G3 and G5 showed no erosion, and there was no significant difference between them. G6 showed severe erosion and was statistically different from G2, G3 and G5 (p < 0.05). EDS microanalysis showed the presence of Na, P, and Ca elements on the surface. CONCLUSIONS: Poly(AA-co-MA) is effective in removing the smear layer and debris without causing erosion either alone or with Ca(OCl)2.

Activity of glucose oxidase immobilized onto Fe3+ attached hydroxypropyl methylcellulose films.

Hydroxypropyl methylcellulose (HMPC) insoluble films were prepared by (60)Co-γ irradiation of 10% (w/w) aqueous solutions of hydroxypropyl methylcellulose. The adsorption of Fe(3+) onto HPMC films was studied in the range of pH 3.0-7.0. The effect of initial concentrations of Fe(3+) solutions on adsorption capacity was studied in the range of 100-1000 ppm. Maximum adsorption capacity was found as 250 mg Fe(3+)/g dry HPMC film at pH 5.0. The structure and the morphology of Fe(3+)-attached HPMC film were evaluated by using FTIR/ATR and SEM-EDX methods. Glucose oxidase (GOX) immobilization on both pristine HPMC and maximum Fe(3+)-attached HPMC film was investigated in aqueous solutions containing different amount of GOX and at different pHs. Maximum GOX adsorption capacity was found as 500 mg/g Fe(3+)-attached HPMC film. Residual activity of GOX on pristine HPMC and Fe(3+)-attached HPMC films was investigated with changing pH. While maximum residual GOX activity was observed at pH 6.0 for free enzyme, it was obtained by HPMC and Fe(3+)-attached HPMC at pH 7.0. GOX desorption studies were achieved by using pH 6.0 buffer (I=0.02 M) and 0.1 M EDTA solutions. The long-term stability and activity studies of GOX, which is immobilized onto Fe(3+)-attached HPMC films are still under our investigation.

Synthesis, characterization and drug release behavior of poly(1-vinyl 1,2,4-triazole) hydrogels prepared by gamma irradiation.

Crosslinked poly(1-vinyl 1,2,4-triazole) (PVTAz) hydrogels in the form of rod and hollow cylinder (thin and thick wall) have been prepared by (60)Co γ-radiation initiated simultaneous polymerization and crosslinking of 1-vinyl 1,2,4-triazole in the presence of water. In binary aqueous systems, the degree of gelation decreased with the increasing water content. The swelling results obtained by using different form of hydrogels showed that the thin wall hollow cylinder hydrogels perform better than other hydrogels. Structural, morphological and thermal characterizations of the hydrogels were carried out with several techniques, including Fourier transform infrared spectroscopy, scanning electron microscopy, swelling measurements, thermogravimetry, and differential scanning calorimetry. The effects of time, pH, temperature, ionic strength, and salt and solvent type on the swelling behavior of thin wall hollow cylinder hydrogels were also investigated. Swelling equilibrium was attained in 2 days. Thin wall hollow cylinder PVTAz hydrogels originally swelled to 3000% (by volume), and depending on the pH value, no sharp change was observed on the swelling curve. Swelling values of hydrogels showed that the swelling ratio increase with the increasing temperature in the range of 4-20°C. The swelling ratios of the gels decreased with increasing ionic strength. Hydrogels have shown the maximum contraction in the presence of LiCl. 5-Fluorouracil (5-FU) was loaded on PVTAz hydrogels by using incorporation and adsorption methods. Both methods show the similar release profiles. Time-dependent release of 5-FU was achieved within 48 h by the success of 65%. All these results showed that PVTAz hydrogels are suitable for the release of 5-FU in the applications of long-term cancer treatment.