Nima Roohpour

Investigation into the structural, morphological, mechanical and thermal behaviour of bacterial cellulose after a two-step purification process.

Bacterial cellulose (BC) is a natural hydrogel, which is produced by Acetobacter xylinum (recently renamed Gluconacetobacter xylinum) in culture and constitutes of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. Here, a two-step purification process is presented that significantly improves the structural, mechanical, thermal and morphological behaviour of BC sheet processed from these hydrogels produced in static culture. Alkalisation of BC using a single-step treatment of 2.5 wt.% NaOH solution produced a twofold increase in Youngs modulus of processed BC sheet over untreated BC sheet. Further enhancements are achieved after a second treatment with 2.5 wt.% NaOCl (bleaching). These treatments were carefully designed in order to prevent any polymorphic crystal transformation from cellulose I to cellulose II, which can be detrimental for the mechanical properties. Scanning electron microscopy and thermogravimetric analysis reveals that with increasing chemical treatment, morphological and thermal stability of the processed films are also improved.

Synthesis and characterization of a novel N-vinylcaprolactam-containing acrylic acid terpolymer for applications in glass-ionomer dental cements

In this study a novel N-vinylcaprolactam (NVC)-containing copolymer of acrylic-itaconic acid was synthesized, characterized and incorporated into Fuji IX conventional glass-ionomer cement (GIC). Subsequently, the effects of incorporation of synthesized terpolymer on the mechanical properties of GIC were studied. The synthesized terpolymer was characterized using (1)H nuclear magnetic resonance, Fourier transform infrared and Raman spectroscopy. The viscosity and molecular weight of the terpolymer were also measured. The compressive strength (CS), diametral tensile strength (DTS) and biaxial flexural strength (BFS) of the modified GICs were evaluated after 24h and 1week of immersion in distilled water at 37 degrees C. The handling properties (working and setting times) of the resulting modified cements were also evaluated. One-way analysis of variance was used to study the statistical significance of the mechanical strengths and handling properties in comparison to the control group. The results showed that NVC-containing GIC samples exhibited significantly higher (P<0.05) DTS (38.3+/-10.9MPa) and BFS (82.2+/-12.8MPa) in comparison to Fuji IX GIC (DTS=19.6+/-11.4MPa; BFS=41.3+/-10.5MPa). The experimental cement also showed higher but not statistically significant values for CS compared to the control material (CS for NVC-containing sample=303+/-32.8MPa; CS for Fuji XI=236+/-41.5MPa). Novel NVC-containing GIC has been developed in this study, with a 28% increase in CS. The presented GIC is capable of doubling the DTS and BFS in comparison to commercial Fuji IX GIC. The working properties of NVC-containing glass-ionomer formulations are comparable and are acceptable for water-based cements.

A review of powder modifications in conventional glass-ionomer dental cements

Glass-ionomer dental cements (GICs) have proven to be useful in several areas of dentistry such as restorative dentistry. Glass-ionomers are aqueous cements formed by the reaction of an acidic polymer and a basic glass in the presence of water. The oral environment presents many challenges to the longevity of restorative materials. Glass-ionomer cements have many properties that are clinically useful and promote longevity. Importantly, GICs adhere to moist tooth structure without any pretreatment, and provide a prolonged period of fluoride release, which inhibits recurrent tooth decay (caries). These properties together with acceptable aesthetics and biocompatibility make these materials popular and desirable for medical and dental applications. However, glass-ionomer dental cements have limitations that prevent broader clinical adaptation such as poor mechanical properties and moisture sensitivity. Many significant changes and modifications to the chemistry of the acidic polymers and basic glasses and to the formulation of the cements have been made to address these limitations. In this review, advances in the development of the basic glasses and other reinforcing agents will be discussed. An overview of the chemistry of glass-ionomer cements will be discussed followed by an in-depth discussion of the chemistry of novel basic glasses and reinforcing additives.

Injectable in situ forming drug delivery system based on poly(ε-caprolactone fumarate) for tamoxifen citrate delivery: Gelation characteristics, in vitro drug release and anti-cancer evaluation

The present study deals with the preparation and characterization of an injectable and in situ forming drug delivery system based on photocrosslinked poly(epsilon-caprolactone fumarate) (PCLF) networks loaded with tamoxifen citrate (TC). Networks were made of PCLF macromers, a photoinitiation system (comprising initiator and accelerator) and the active ingredient N-vinyl-2-pyrrolidone (NVP) as a crosslinker and reactive diluent. Shrinkage behavior, equilibrium swelling and sol fraction ratios of photocrosslinked PCLF gels were determined as functions of NVP content. It was shown that the crosslinking is facilitated up to a certain concentration of NVP and most of NVP remained unreacted above this value. In vitro drug release, biocompatibility evaluation and activity against MCF-7 breast cancer cell line were also investigated. Accurate but simple bipartite expressions were also derived that enable rapid determination of effective diffusion coefficients of TC in photocrosslinked PCLF/NVP disks. Cytotoxicity assay showed that while the photocrosslinked PCLF network with optimum NVP content exhibits no significant cytotoxicity against MCF-7 and L929 cell lines, 40-60% of the MCF-7 cells were killed after incubation with TC-loaded devices.

Antimicrobial, Mechanical and Thermal Studies of Silver Particle-Loaded Polyurethane

Silver-particle-incorporated polyurethane films were evaluated for antimicrobial activity towards two different bacteria: Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Distributed silver particles sourced from silver nitrate, silver lactate and preformed silver nanoparticles were mixed with polyurethane (PU) and variously characterized by field emission scanning electron microscopy (FESEM), fourier transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD) and contact angle measurement. Antibacterial activity against E.coli was confirmed for films loaded with 10% (w/w) AgNO3, 1% and 10% (w/w) Ag lactate and preformed Ag nanoparticles. All were active against S. aureus, but Ag nanoparticles loaded with PU had a minor effect. The apparent antibacterial performance of Ag lactate-loaded PU is better than other Ag ion-loaded films, revealed from the zone of inhibition study. The better performance of silver lactate-loaded PU was the likely result of a porous PU structure. FESEM and FTIR indicated direct interaction of silver with the PU backbone, and XRD patterns confirmed that face-centred cubic-type silver, representative of Ag metal, was present. Young’s modulus, tensile strength and the hardness of silver containing PU films were not adversely affected and possibly marginally increased with silver incorporation. Dynamic mechanical analysis (DMA) indicated greater thermal stability.

Structural characterization and physical properties of P2O5-CaO-Na2O-TiO2 glasses by Fourier transform infrared, Raman and solid-state magic angle spinning nuclear magnetic resonance spectroscopies.

Phosphate-based glasses have been investigated for tissue engineering applications. This study details the properties and structural characterization of titanium ultra-phosphate glasses in the 55(P(2)O(5))-30(CaO)-(25-x)(Na(2)O)-x(TiO(2)) (0≤x≤5) system, which have been prepared via melt-quenching techniques. Structural characterization was achieved by a combination of X-ray diffraction (XRD), and solid-state nuclear magnetic resonance, Raman and Fourier transform infrared spectroscopies. Physical properties were also investigated using density, degradation and ion release studies; additionally, differential thermal analysis was used for thermal analysis of these glasses. The results show that with the addition of TiO(2) the density and glass transition temperature increased whereas the degradation and ion release properties are decreased. From XRD data, TiP(2)O(7) and CaP(2)O(6) were detected in 3 and 5 mol.% TiO(2)-containing glasses. Magic angle spinning nuclear magnetic resonance results confirmed that as TiO(2) is incorporated into the glass; the amount of Q(3) increases as the amount of Q(2) consequently decreases, indicating increasing polymerization of the phosphate network. Spectroscopy results also showed that the local structure of glasses changes with increasing TiO(2) content. As TiO(2) is incorporated into the glass, the phosphate connectivity increases, indicating that the addition of TiO(2) content correlates unequivocally with an increase in glass stability.

Synthesis and characterisation of enhanced barrier polyurethane for encapsulation of implantable medical devices

Polymeric membranes have been used as interfaces between implantable devices and biological tissues to operate as a protective barrier from water exchanging and to enhance biocompatibility. Polyurethanes have been used as biocompatible membranes for decades. In this study, copolymers of polyether urethane (PEU) with polydimethylsiloxane (PDMS) were synthesised with the goal of creating materials with low water permeability and high elasticity. PDMS was incorporated into polymer backbone as a part of the soft segment during polyurethane synthesis and physical properties as well as water permeability of resulting copolymer were studied in regard to PDMS content. Increase in PDMS content led to increase of microphase separation of the copolymer and corresponding increase in elastic modulus. Surface energy of the polymer was decreased by incorporating PDMS compared to unmodified PEU. PDMS in copolymer formed a hydrophobic surface which caused reduction in water permeability and water uptake of the membranes. Thus, PDMS containing polyurethane with its potent water resistant properties demonstrated a great promise for use as an implantable encapsulation material.

A review of polyelectrolyte modifications in conventional glass-ionomer dental cements

Glass-ionomer dental restorative cements have proven to be quite practical in different areas of dentistry. An aqueous polyelectrolyte system, glass-ionomer cements have exceptional properties such as a prolonged period of fluoride release which inhibits recurrent caries, adhesion to moist tooth structure without any pretreatment, satisfactory aesthetics and biocompatibility. This makes these cements very popular and attractive for restorative dentistry and also for orthopedics. However, they have some disadvantages such as poor mechanical strength and moisture sensitivity in the early stages of setting. Lately there have been significant modifications in the formulation of the powder and liquid of the glass-ionomer cements, leading to improved mechanical and handling properties of the material. This paper is the second paper of its series, which reviews the modifications to the polymeric component of glass-ionomer dental cements. In this manuscript, the poly(acrylic acid) (PAA) based polymers currently used in glass-ionomer cements are reviewed. Different methods of reinforcement of the glass-ionomer cements by modification of the polymeric liquid; including new acrylic acid copolymers, amino acid containing polyelectrolyte, N-vinylpyrrolidone and N-vinylcaprolactam modified terpolymers are described. The paper discusses the advantages and disadvantages of different modifications and illustrates the future aspects of the materials chemistry.

Synthesis and characterization of a novel fast-set proline-derivative-containing glass ionomer cement with enhanced mechanical properties

In this study, a methacryloyl derivative of l-proline was synthesized, characterized and incorporated into a conventional glass ionomer cement (GIC) with a polyacid composition. Subsequently, the effects of incorporation of synthesized N-methacryloyl-proline and terpolymer on the GICs mechanical and working properties were studied. 1-Methacryloylpyrrolidone-2-carboxylic acid was synthesized and used in a polymerization reaction with acrylic acid and itaconic acid in order to form terpolymer which was used in Fuji II commercial GIC formulations. Chemical structural characterization of the resulting products was performed using (1)H nuclear magnetic resonance and Fourier transform infrared spectroscopy. The viscosity and molecular weight of the terpolymer were also measured. The mechanical strength properties of the modified GICs were evaluated after 24h or 1 week of immersion in distilled water at 37 degrees C. Analysis of variance was used to study the statistical significance of the mechanical strengths and working properties, and to compare them with a control group. Results showed that N-methacryloyl-proline modified GICs exhibited significantly higher compressive strength (CS; 195-210MPa), higher diametral tensile strength (DTS; 19-26MPa) and higher biaxial flexural strength (38-46MPa) in comparison to Fuji II GIC (161-166MPa in CS, 12-14MPa in DTS and 13-18MPa in biaxial flexural strength). The working properties (setting and working time) of the modified samples showed that the modified cement was a fast-set cement. It was concluded that a novel amino acid-containing GIC has been developed in this study with 27%, 94% and 170% increases in values for compressive, diametral tensile and biaxial flexural strength, respectively, in comparison to commercial Fuji II GIC.

Synthesis of N-vinylpyrrolidone modified acrylic acid copolymer in supercritical fluids and its application in dental glass-ionomer cements.

Compressed fluids such as supercritical CO2 offer marvellous opportunities for the synthesis of polymers, particularly in applications in medicine and dentistry. It has several advantages in comparison to conventional polymerisation solvents, such as enhanced kinetics and simplified solvent removal process. In this study, poly(acrylic acid-co-itaconic acid-co-N-vinylpyrrolidone) (PAA-IA-NVP), a modified glass-ionomer polymer, was synthesised in supercritical CO2 (sc-CO2) and methanol as a co-solvent. The synthesised polymer was characterized by 1H-NMR, Raman and FT-IR spectroscopy and viscometry. The molecular weight of the final product was also measured using static light scattering method. The synthesised polymers were subsequently used in several glass ionomer cement formulations (Fuji II commercial GIC) in which mechanical strength (compressive strength (CS), diametral tensile strength (DTS) and biaxial flexural strength (BFS)) and handling properties (working and setting time) of the resulting cements were evaluated. The polymerisation reaction in sc-CO2/methanol was significantly faster than the corresponding polymerisation reaction in water and the purification procedures were simpler for the former. Furthermore, glass ionomer cement samples made from the terpolymer prepared in sc-CO2/methanol exhibited higher CS and DTS and comparable BFS compared to the same polymer synthesised in water. The working properties of glass ionomer formulations made in sc-CO2/methanol were comparable and in selected cases better than the values of those made from polymers synthesised in water.