Physicochemical Characterization of Poly(ethylene glycol) Plasticized Poly(methyl vinyl ether-co-maleic acid) Films

The influence of the poly(ethylene glycol) (PEG) plasticizer content and molecular weight on the physicochemical properties of films cast from aqueous blends of poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) was investigated with tensile mechanical testing, thermal analysis, and attenuated total reflectance/Fourier transform infrared spectroscopy. Unplasticized films and those containing high copolymer contents were very difficult to handle and proved difficult to test. PEG with a molecular weight of 200 Da was the most efficient plasticizer. However, films cast from aqueous blends containing 10% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 4 : 3 and those cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 2 : 1 possessed mechanical properties most closely mimicking those of a formulation we have used clinically in photodynamic therapy. Importantly, we found previously that films cast from aqueous blends containing 10% (w/w) PMVE/MA performed rather poorly in the clinical setting, where uptake of moisture from patients' skin led to reversion of the formulation to a thick gel. Consequently, we are now investigating films cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000, where the copolymer/plasticizer ratio is 2 : 1, as possible Food and Drug Administration approved replacements for our current formulation, which must currently be used only on a named patient basis as its plasticizer, tripropylene glycol methyl ether, is not currently available in pharmaceutical grade

Preparation and characterization of Poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution-casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X- ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X-ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc.

Rheological Evaluation of the Isothermal Cure Characteristics of Medical Grade Silicone Elastomers

Silicone elastomer systems have been shown to offer potential for the fabrication of medical devices and sustained release drug delivery devices comprising low molecular weight drugs and protein therapeutics. For drug delivery systems in particular, there is often no clear rationale for selection of the silicone elastomer grade, particularly in respect of optimizing the manufacturing conditions to ensure thermal stability of the active agent and short cycle times. In this study, the cure characteristics of a range of addition-cure and condensation-cure, low-consistency, implant-grade silicone elastomers, either as supplied or loaded with the model protein bovine serum albumin (BSA) and the model hydrophilic excipient glycine, were investigated using oscillatory rheology with a view to better understanding the isothermal cure characteristics. The results demonstrate the influence of elastomer type, cure temperature, protein loading, and glycine loading on isothermal cure properties. By measuring the cure time required to achieve tan delta values representative of early and late-stage cure conditions, a ratio t(1)/t(2) was defined that allowed the cure characteristics of the various systems to be compared. Sustained in vitro release of BSA from glycine-loaded silicone elastomer covered rod devices was also demonstrated over 14 days. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2320-2327, 2010

Effect of the incorporation of hydroxy-terminated liquid silicones on the cure characteristics, morphology, and release of a model protein from silicone elastomer-covered rods

Silicone elastomer systems have previously been shown to offer potential for the sustained release of protein therapeutics. However, the general requirement for the incorporation of large amounts of release enhancing solid excipients to achieve therapeutically effective release rates from these otherwise hydrophobic polymer systems can detrimentally affect the viscosity of the precure silicone elastomer mixture and its curing characteristics. The increase in viscosity necessitates the use of higher operating pressures in manufacture, resulting in higher shear stresses that are often detrimental to the structural integrity of the incorporated protein. The addition of liquid silicones increases the initial tan delta value and the tan delta values in the early stages of curing by increasing the liquid character (G '') of the silicone elastomer system and reducing its elastic character (G'), thereby reducing the shear stress placed on the formulation during manufacture and minimizing the potential for protein degradation. However, SEM analysis has demonstrated that if the liquid character of the silicone elastomer is too high, the formulation will be unable to fill the mold during manufacture. This study demonstrates that incorporation of liquid hydroxy-terminated polydimethylsiloxanes into addition-cure silicone elastomer-covered rod formulations can both effectively lower the viscosity of the precured silicone elastomer and enhance the release rate of the model therapeutic protein bovine serum albumin. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Multiaxial Deformation of Polyethylene and Polyethylene/Clay Nanocomposites: In Situ Synchrotron Small Angle and Wide Angle X-Ray Scattering Study

A unique in situ multiaxial deformation device has been designed and built specifically for simultaneous synchrotron small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) measurements. SAXS and WAXS patterns of high-density polyethylene (HDPE) and HDPE/clay nanocomposites were measured in real time during in situ multiaxial deformation at room temperature and at 55 degrees C. It was observed that the morphological evolution of polyethylene is affected by the existence of clay platelets as well as the deformation temperature and strain rate. Martensitic transformation of orthorhombic into monoclinic crystal phases was observed under strain in HDPE, which is delayed and hindered in the presence of clay nanoplatelets. From the SAXS measurements, it was observed that the thickness of the interlamellar amorphous region increased with increasing strain, which is due to elongation of the amorphous chains. The increase in amorphous layer thickness is slightly higher for the nanocomposites compared to the neat polymer. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 669-677, 2011

Rheological destructuring of aqueous gels composed of cellulose ethers following storage in the presence of redox agents

Despite their widespread use, there is a paucity of information concerning the effect of storage on the rheological properties of pharmaceutical gels that contain organic and inorganic additives. Therefore, this study examined the effect of storage (1 month at either 4 or 37 degrees C) on the rheological and mechanical properties of gels composed of either hydroxypropylmethylcellulose (3-5% w/w, HPMC) or hydroxyethylcellulose (3-5% w/w, HEC) and containing or devoid of dispersed organic (tetracycline hydrochloride 2% w/w) or inorganic (iron oxide 0.1% w/w) agents. The mechanical properties were measured using texture profile analysis whereas the rheological properties were analyzed using continuous shear rheometry and modeled using the Power Law model. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing polymer concentration (3-5% w/w) significantly increased the consistency, hardness, compressibility, and adhesiveness of the formulations due to increased polymer chain entanglement. Following storage (I month at 4 and 37 degrees C) the consistency and mechanical properties of additive free HPMC gets (but not HEC gels) increased, due to the time-dependent development of polymer chain entanglements. Incorporation of tetracycline hydrochloride significantly decreased and increased the rheological and mechanical properties of HPMC and HEC gels, respectively. Conversely, the incorporation of iron oxide did not affect these properties. Following storage, the rheological and mechanical properties of HPMC and HEC formulations were markedly compromised. This effect was greater following storage at 37 than at 4 degrees C and, additionally, greater in the presence of tetracycline hydrochloride than iron oxide. It is suggested that the loss of rheological/mechanical structure was due to chain depolymerization, facilitated by the redox properties of tetracycline hydrochloride and iron oxide. These observations have direct implications for the design and formulation of gels containing an active pharmaceutical ingredient. (c) 2005 Wiley Periodicals, Inc.

Texture profile analysis of bioadhesive polymeric semisolids: Mechanical characterization and investigation of interactions between formulation components

This study reports the use of texture profile analysis (TPA) to mechanically characterize polymeric, pharmaceutical semisolids containing at least one bioadhesive polymer and to determine interactions between formulation components. The hardness, adhesiveness, force per unit time required for compression (compressibility), and elasticity of polymeric, pharmaceutical semisolids containing polycarbophil (1 or 5% w/w), polyvinylpyrrolidone (3 or 5% w/w), and hydroxyethylcellulose (3, 5, or 10% w/w) in phosphate buffer (pH 6.8) were determined using a texture analyzer in the TPA mode (compression depth 15 mm, compression rate 8 mm s(-1) 15 s delay period). Increasing concentrations of polycarbophil, poly vinylpyrrolidone, and hydroxyethylcellulose significantly increased product hardness, adhesiveness, and compressibility but decreased product elasticity. Statistically, interactions between polymeric formulation components were observed within the experimental design and were probably due to relative differences in the physical states of polyvinylpyrrolidone and polycarbophil in the formulations, i.e., dispersed/dissolved and unswollen/swollen, respectively. Increased product hardness and compressibility were possibly due to the effects of hydroxyethylcellulose, polyvinylpyrrolidone, and polycarbophil on the viscosity of the formulations. Increased adhesiveness was related to the concentration and, more importantly, to the physical state of polycarbophil. Decreased product elasticity was due to the increased semisolid nature of the product. TPA is a rapid, straightforward analytical technique that may be applied to the mechanical characterization of polymeric, pharmaceutical semisolids. It provides a convenient means to rapidly identify physicochemical interactions between formulation components. (C) 1996 John Wiley & Sons, Inc.

The effect of freeze-drying parameters on the cure characteristics of freeze-dried BSA-loaded silicone elastomer

To formulate therapeutic proteins into polymeric devices the protein is typically in the solid state, which can be achieved by the process of freeze-drying. However, freeze-drying not only risks denaturing the protein but it can adversely affect the cure characteristics of protein-loaded silicone elastomers. This study demonstrates that a variation in the parameters of the freeze-dryer can significantly affect the residual moisture content of freeze-dried BSA, which in turn has an effect on the bulk density and flow properties of the BSA. The bulk density and flow properties of the BSA subsequently affect the cure characteristics of BSA-loaded silicone elastomers. An increase in the residual moisture content results in the freeze-dried BSA having a decreased bulk density and poor flow properties which can have a detrimental effect on the cure characteristics of a freeze-dried BSA-loaded silicone elastomer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012

Recycled carbon fiber filled polyethylene composites

Composites of recycled carbon fiber (CF) with up to 30 wt % loading with polyethylene (PE) were prepared via melt compounding. The morphology of the composites and the degree of dispersion of the CF in the PE matrix was examined using scanning electron microscopy, and revealed the CF to be highly dispersed at all loadings and strong interfacial adhesion to exist between the CF and PE. Raman and FTIR spectroscopy were used to characterize the surface chemistry and potential bonding sites of recycled CF. Both the Young's modulus and ultimate tensile stress increased with increasing CF loading, but the percentage stress at break was unchanged up to 5 wt % loading, then decreased with further successive addition of CF. The effect of CF on the elastic modulus of PE was examined using the Halpin-Tsai and modified Cox models, the former giving a better fit with the values determined experimentally. The electrical conductivity of the PE matrix was enhanced by about 11 orders of magnitude on addition of recycled CF with a percolation threshold of 7 and 15 wt % for 500-mu m and 3-mm thick samples. (c) 2007 Wiley Periodicals, Inc.

Influence of a pore-forming agent on swelling, network parameters, and permeability of poly(ethylene glycol)-crosslinked poly(methyl vinyl ether-co-maleic acid) hydrogels:Application in transdermal delivery systems

We characterized hydrogels, prepared from aqueous blends of poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) and poly(ethylene glycol) (PEG 10,000 Daltons) containing a pore-forming agent (sodium bicarbonate, NaHCO ). Increase in NaHCO content increased the equilibrium water content (EWC) and average molecular weight between crosslinks (M ) of hydrogels. For example, the %EWC was 731, 860, 1109, and 7536% and the M was 8.26, 31.64, 30.04, and 3010.00 × 10 g/mol for hydrogels prepared from aqueous blends containing 0, 1, 2, and 5% w/w of NaHCO , respectively. Increase in NaHCO content also resulted in increased permeation of insulin. After 24 h, percentage permeation was 0.94, 3.68, and 25.71% across hydrogel membranes prepared from aqueous blends containing 0, 2, and 5% w/w of NaHCO , respectively. Hydrogels containing the pore-forming agent were fabricated into microneedles (MNs) for transdermal drug delivery applications by integrating the MNs with insulin-loaded patches. It was observed that the mean amount of insulin permeating across neonatal porcine skin in vitro was 20.62% and 52.48% from hydrogel MNs prepared from aqueous blends containing 0 and 5% w/w of NaHCO . We believe that these pore-forming hydrogels are likely to prove extremely useful for applications in transdermal drug delivery of biomolecules. © 2012 Wiley Periodicals, Inc.