Hydrophilic Polymer Matrices Research Articles

Recent development in thermoplastic/wood composites and nanocomposites: A review

Thermoplastic composites filled with wood-base fillers have gained increasing attention, because compared to virgin polymers they have many advantages of light weight, high strength and stiffness, low cost, biodegradability and renewability. These advantages let them find a large dispersal in many areas of technical applications. However, poor interfacial interaction between hydrophilic wood-base fillers and hydrophobic polymer matrices should be improved to get reasonable physical properties for their wide applications. The interfacial interaction could be improved by addition of coupling agents and chemical modifications of wood-base fillers. To improve physical properties of the thermoplastic/wood composites, further nanofillers can be incorporated. This review summarizes recent developments in thermoplastic/wood composites and deals with wood-base fillers for thermoplastics, various interface modification methods and various thermoplastic/wood composites as well as nanocomposites. This review can provide reasonable future perspectives in this research area and stimulate development of new innovative thermoplastic/wood composites as well as nanocomposites.

Transcrystallization at the surface of graphene-modified chitosan fibers

Incompatibility between hydrophilic chitosan (CS) fiber and hydrophobic polymer matrices leads to unsatisfactory properties of the composites. The crystallization of polymer on the fiber surface is a promising way to increase interfacial interactions. Here, we coated CS fiber surfaces with graphene oxide via electrostatic self-assembly to improve interfacial interactions between the polymer and the CS fiber. Structures of the CS fiber before and after graphene coating were characterized by various methods. The formation of a polypropylene (PP) transcrystalline (TC) layer on the CS fiber surface was investigated. It is suggested that at low crystallization temperatures the fiber induced TC phase forms faster than at high temperature. There exist α and β crystal of PP in the TC phase formation process as demonstrated by x-ray diffraction. The polarized light optical microscope results demonstrate that graphene coated CS fiber can also enhance the TC phase nucleation ability of poly(l-lactide).

Optimization of Melatonin Dissolution from Extended Release Matrices Using Artificial Neural Networking.

Efficacy of melatonin in treating sleep disorders has been demonstrated in numerous studies. Being with short half-life, melatonin needs to be formulated in extended-release tablets to prevent the fast drop of its plasma concentration. However, an attempt to mimic melatonin natural plasma levels during night time is challenging. In this work, Artificial Neural Networks (ANNs) were used to optimize melatonin release from hydrophilic polymer matrices. Twenty-seven different tablet formulations with different amounts of hydroxypropyl methylcellulose, xanthan gum and Carbopol®974P NF were prepared and subjected to drug release studies. Using dissolution test data as inputs for ANN designed by Visual Basic programming language, the ideal number of neurons in the hidden layer was determined trial and error methodology to guarantee the best performance of constructed ANN. Results showed that the ANN with nine neurons in the hidden layer had the best results. ANN was examined to check its predictability and then used to determine the best formula that can mimic the release of melatonin from a marketed brand using similarity fit factor. This work shows the possibility of using ANN to optimize the composition of prolonged-release melatonin tablets having dissolution profile desired.

A unified multicomponent stress-diffusion model of drug release from non-biodegradable polymeric matrix tablets

We propose a new transport model of drug release from hydrophilic polymeric matrices, based on Stefan-Maxwell flux laws for multicomponent transport. Polymer stress is incorporated in the total mixing free energy, which contributes directly to the diffusion driving force while leading to time-dependent boundary conditions at the tablet interface. Given that hydrated matrix tablets are dense multicomponent systems, extended Stefan-Maxwell (ESM) flux laws are adopted to ensure consistency with the Onsager reciprocity principle and the Gibbs-Duhem thermodynamic constraint. The ESM flux law for any given component takes into account the friction exerted by all other species and is invariant with respect to reference velocity, thus satisfying Galilean translational invariance. Our model demonstrates that penetrant-induced plasticization of polymer chains partially or even entirely offsets the steady decline of chemical potential gradients at the tablet-medium interface that drive drug release. Utilizing a Flory-Huggins thermodynamic model, a modified form of the upper convected Maxwell constitutive equation for polymer stress and a Fujita-type dependence of mutual diffusivities on composition, depending on parameters, Fickian, anomalous or case II drug transport arises naturally from the model, which are characterized by quasi-power-law release profiles with exponents ranging from 0.5 to 1, respectively. A necessary requirement for non-Fickian release in our model is that the matrix stress relaxation time is comparable to the time scale for water diffusion. Mutual diffusivities and their composition dependence are the most decisive factors in controlling drug release characteristics in our model. Regression of the experimental polymer dissolution and drug release profiles in a system of Theophylline/cellulose (K15M) demonstrate that API-water mutual diffusivity in the presence of excipient cannot generally be taken as a constant.

Stability of Asp(B28) Insulin Exposed to Modified and Unmodified Polypropylene.

Polypropylene (PP) plates have been modified with two different hydrophilic polymeric materials, poly(N,N-dimethylacrylamide) (poly(DMAAm)) and poly(poly(ethylene glycol)methacrylate) (poly(PEGMA)) in order to reduce insulin adsorption when the plates were exposed to insulin aspart (Asp(B28) insulin). The influence of surface modification on the chemical and physical stability of Asp(B28) insulin was evaluated by two chromatographic methods, size exclusion chromatography (SEC) and reverse phase high pressure liquid chromatography (RP-HPLC) and the Thioflavin T assay. A clear difference in the stability of Asp(B28) insulin was observed between the three tested surfaces. PP coated with poly(DMAAm) resulted in a poor chemical stability and a significantly improved physical stability compared with unmodified PP. In addition to this a lower phenol concentration was observed for the poly(DMAAm) coating. The results from the poly(PEGMA) coating looked very promising with respect to the stability of Asp(B28) insulin in comparison with the data from unmodified PP and the poly(DMAAm) coating. Two hydrophilic coatings have been tested and surprisingly a difference in Asp(B28) insulin stability was observed. Therefore, Asp(B28) insulin adsorption and stability will be influenced by more than the hydrophilicity of the surface.

Formulation and Evaluation of Sustained Release Matrix Tablets of Nifedipine

Conventional drug delivery system for treating the angina and hypertension are not much effective as the drug do not reach the site of action in appropriate amounts. Thus potent and guarded therapy of this angina and hypertension disorder using specific drug delivery system is a challenging task to the pharmaceutical professionals. Most oftenly used method of regulating the drug release is to include it in a matrix system because of their pliability, hydrophilic polymer matrices are widely used in oral controlled drug delivery to obtain a desirable drug release pattern, methodical, and broad regulatory compliance. Formulation of Nifedipine sustained release matrix tablet was prepared by the polymers blend with to get desirable drug release profile. Evaluation parameters of formulated tablets were hardness, friability, thickness, drug content uniformity weight variation, and the in vitro drug release rate pattern. Formulation prepared with HPMC K100M showed 97% of drug release at 24 hrs and with Eudragit indicates 99% of drug release at 20 hrs release of Nifedipine drug.

Prediction of Polymorphic Transformations of Paracetamol in Solid Dispersions

A novel approach employing variable-temperature X-ray powder diffraction (VTXRPD) was used to exploit its suitability as an off-line predictive tool to study the polymorphic transformations of paracetamol (PMOL) in melt-extruded hydrophilic polymer matrices. Physical mixtures (PMs) and extruded formulations of PMOL with either polyvinyl caprolactam graft copolymer (Soluplus®) or vinylpyrrolidone-vinyl acetate copolymer (Kollidon®) in the solid state were characterized by using differential scanning calorimetry, hot-stage microscopy, and scanning electron microscopy. The experimental findings from VTXRPD showed that the stable Form I (monoclinic) of PMOL transformed to the metastable polymorph Form II (orthorhombic) at temperatures varying from 112°C to 120°C, in both the PMs and extrudates suggesting an effect of both temperature and identity of the polymers. The findings obtained from VTXRD analysis for both the PMs and the extruded formulations were confirmed by in-line near-infrared (NIR) monitoring during the extrusion processing. In the NIR study, PMOL underwent the same pattern of polymorphic transformations as those detected using VTXPRD. The results of this study suggest that VTXRPD can be used to predict the polymorphic transformation of drugs in polymer matrices during extrusion processing and provides a better understanding of extrusion processing parameters.

Computational Chemistry Study on the Microscopic Interactions between Biomolecules and Hydrophilic Polymeric Materials

Controlling protein adsorption on polymeric surfaces is one of the major challenges for developing novel biomaterials. To clarify microscopic mechanisms on the suppression of protein adsorption, identification of crucial factors for achieving excellent biocompatibility is significant. In this study, free energy calculations are introduced to assess the biocompatibility of two types of material: poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(vinyl alcohol) (PVA). Free energy profiles are evaluated for an amino acid residue approaching their repeat unit in explicit water molecules from molecular dynamics simulations. Although PHEMA and PVA are generally both hydrophilic, the predicted profiles become remarkably different from each other. The profile for PHEMA shows nearly flat profiles, while the profile for PVA shows energetically stable minimum. These results theoretically demonstrate that hydrophilicity is not a crucial factor for achieving excellent biocompatibility, although it can be a prerequisite.

PEG-Stabilized Core–Shell Nanoparticles: Impact of Linear versus Dendritic Polymer Shell Architecture on Colloidal Properties and the Reversibility of Temperature-Induced Aggregation

Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely used experimentally and also clinically tested in diverse areas of biology and medicine. Applications include magnetic resonance imaging, cell sorting, drug delivery, and hyperthermia. Physicochemical surface properties are particularly relevant in the context of achieving high colloidal nanoparticle (NP) stability and preventing agglomeration (particularly challenging in biological fluids), increasing blood circulation time, and possibly targeting specific cells or tissues through the presentation of bioligands. Traditionally, NP surfaces are sterically stabilized with hydrophilic polymeric matrices, such as dextran or linear poly(ethylene glycol) brushes. While dendrimers have found applications as drug carriers, dispersants with dendritic ("dendrons") or hyperbranched structures have been comparatively neglected despite their unique properties, such as a precisely defined molecular structure and the ability to present biofunctionalities at high density at the NP periphery. This work covers the synthesis of SPIONs and their stabilization based on poly(ethylene glycol) (PEG) and oligo(ethylene glycol) (OEG) chemistry and compares the physicochemical properties of NPs stabilized with linear and dendritic macromolecules of comparable molecular weight. The results highlight the impact of the polymeric interface architecture on solubility, colloidal stability, hydrodynamic radius, and thermoresponsive behavior. Dendron-stabilized NPs were found to provide excellent colloidal stability, despite a smaller hydrodynamic radius and lower degree of soft shell hydration compared to linear PEG analogues. Moreover, for the same grafting density and molecular weight of the stabilizers, OEG dendron-stabilized NPs show a reversible temperature-induced aggregation behavior, in contrast to the essentially irreversible aggregation and sedimentation observed for the linear PEG analogues. This new class of dendritically stabilized NPs is believed to have a potential for future biomedical and other applications, in which stability, resistance to (or reversible) aggregation, ultrasmall size (for crossing biological barriers or inclusion in responsive artificial membranes), and/or high corona density of (bio)active ligands are key.

The influence of agitation sequence and ionic strength on in vitro drug release from hypromellose (E4M and K4M) ER matrices—The use of the USP III apparatus

Theophylline extended release (ER) matrices containing hypromellose (hydroxypropyl methylcellulose (HPMC) E4M and K4M were evaluated in media with a pH range of 1.2–7.5, using an automated USP type III, Bio-Dis dissolution apparatus. The objectives of this study were to evaluate the effects of systematic agitation, ionic strength and pH on the release of theophylline from the gel forming hydrophilic polymeric matrices with different methoxyl substitution levels. Tribo-electric charging of hypromellose, theophylline and their formulated blends containing E4M and K4M grades has been characterised, along with quantitative observations of flow, compression behaviour and particle morphology. Agitations were studied at 5, 10, 15, 20, 25, 30 dips per minute (dpm) and also in the ascending and descending order in the dissolution vials. The ionic concentration strength of the media was also varied over a range of 0–0.4M to simulate the gastrointestinal fed and fasted states and various physiological pH conditions. To study the effect of ionic strength on the hydrophilic matrices, agitation was set at 20 dpm. The charge results on individual components imply that the positively charged particles have coupled with the negatively charged particles to form a stable ordered mixture which is believed to result in a more homogeneous and stable system. The particle shape analysis showed the HPMC K4M polymer to have a more irregular morphology and a rougher surface texture in comparison to the HPMC E4M polymer, possibly a contributory factor to the gelation process. The results showed gelation occurred quicker for the K4M tablet matrices. Drug release increased with increased agitation. This was more pronounced for the E4M tablet matrices. The ionic strength also had more of an effect on the drug release from the E4M matrices. The experiments highlighted the resilience of the K4M matrices in comparison with the E4M matrices. The results thus show that despite similar viscosities of E4M and K4M, the methoxyl substitution makes a difference to their control of drug release and as such care and consideration should be given to the choice of polymer used for extended release. The use of systematic change of agitation method and ionic strength may indicate potential fed and fasted effects on drug release from hydrophilic matrices.

Preparation and characterization of surface modified electrospun membranes for higher filtration flux

Popular polymers such as polysulfone and poly(vinylidene fluoride) (PVDF) when electrospun into a membrane, have a much higher contact angle and hence are more hydrophobic when compared to the virgin polymeric material. In direct liquid penetration it is more beneficial if the membrane is hydrophilic so that the flux is not compromised and has less tendency to foul. Hence, this research is focused on generating a highly hydrophilic electrospun membrane (EM) based on PVDF material by blending this polymer with several different types of surface modifying macromolecules (SMMs) prepared from urethane pre-polymer with poly(ethylene glycol)s (PEGs) of various average molecular weights (400, 600, and 1000 Da) and poly(propylene glycol) of average molecular weights 3500 and 425 Da. One of the SMMs, with PEG 1000 Da, had a significant impact on the hydrophilic nature (0° SCA with water) of the EM as compared to the blend casted membrane. This could possibly be due to the orientation of the SMMs hydrophilic groups adopted during electrospinning on the surface, whereas they are either encapsulated or submerged in other SMMs. The water flux at a given pressure of blended EM was higher than the non-blended electrospun PVDF membrane. This study highlights the potential benefits of this new hydrophilic polymeric material in the membrane field, which can achieve high-flux rates at low pressure.

Hydrophobic surface modification of ramie fibers with ethanol pretreatment and atmospheric pressure plasma treatment

Incompatibility between hydrophilic natural cellulose fibers and hydrophobic thermoplastic polymer matrices leads to poor interfacial bonding in their composites. This study investigates how atmospheric pressure plasma jet (APPJ) treatment with ethanol pretreatment may improve ramie fiber surface properties for better adhesion to polypropylene. After soaking in ethanol for 10 min, ramie fibers are treated by helium plasma. For the plasma treated fibers, scanning electron microscopy shows increased fiber surface roughness due to plasma etching, which favors mechanical interlocking of the interface; X-ray photoelectron spectroscopy analysis indicates increased carbon contents and hydrophobic C–C bonds. Larger advancing water contact angles are found in dynamic water contact angle measurement. Microbond test shows an up to 50% increase of the interfacial shear strength of the fibers to polypropylene compared to the control, which may be attributed largely to the combined effects of the roughened fiber surface due to plasma etching and increased hydrophobicity of the fiber surface resulting from the reaction of ethanol molecules to cellulose in plasma treatment, thus improving their compatibility to polypropylene matrix.

Hierarchical Composites Made Entirely from Renewable Resources

Recent interest in the utilisation of greener materials has reinitiated the interest in natural fibres and/or fibrils as reinforcement for polymers. However, such bio-based composites often exhibit properties that fall short of expectations due to (i) inadequate processing conditions, resulting in filler agglomeration and poor filler dispersion within the matrix, (ii) variations in natural fibre properties, often due to geographical and seasonal variability, (iii) anisotropy of the natural fibres themselves, (iv) high linear coefficient of thermal expansion for natural fibres and (v) the incompatibility between typically hydrophilic natural fibres and hydrophobic polymer matrices resulting in poor interfacial adhesion between the phases. Chemical modification of natural fibres is often performed to enhance the fibre-matrix interface. A new type of modification, which involves depositing a coating of nanosized cellulose onto natural fibres or dispersing nano-sized cellulose in natural fibre reinforced composites, has been shown to improve the fibre-matrix interface and the overall mechanical performances of such composites, which we term hierarchical (nano)composites. Such composites are also known as multiscale, nanoengineered or nanostructured composites. This paper reviews the current progress of green hierarchical (nano)composites made entirely from renewable materials. As a backdrop, here we look at how nature organises structures across different length scales. We discuss techniques to achieve percolated nanofiller networks within the matrix, at low-medium loading fractions (typically 6–10 vol.%) and processing routes to achieve high loading fractions, then focus on those used to produce truly hierarchical structures in terms of their processing and resultant properties. By creating hierarchical structures within bio-based composite materials we expect to match and improve upon non-renewable polymers.

Polymer–drug interactions and wetting of solid dispersions

We demonstrate the ability of drugs to influence the wetting of solid dispersion tablets in unexpected ways. Five model drugs of different water solubility and ability to interact with the involved polymers were incorporated in hydrophilic polymer matrices, made of either hydroxypropyl methylcellulose (HPMC) or polyvinyl pyrrolidone (PVP). The physical mixtures of all combinations of drug and polymer presented surface hydrophobicities, as measured by the equilibrium advancing contact angle of water, which are expected for materials that do not influence the interactions of each other with water. However, the solid dispersions containing HPMC deviated from this regular behaviour and displayed contact angles below those of the pure compounds involved, either drug or polymer. This behaviour is explained by changed surface exposure of HPMC side groups, as a result of changes in intermolecular hydrogen bonds. In addition to water contact angle measurements, we employed NMR imaging to monitor the time course of water ingress and swelling.

Molecular modeling of interfaces between cellulose crystals and surrounding molecules: Effects of caprolactone surface grafting

A technical problem in cellulosic nanocomposite materials is the weak interaction between hydrophilic cellulose and hydrophobic polymer matrices. One approach to solve this difficulty is to chemically graft monomers of the matrix polymer onto the cellulose surface. An important question is to understand the effect such surface modification has on the interfacial properties. Semi-empirical approaches to estimate work of adhesion based on surface energies do not provide information on specific molecular interactions. Details about these interactions were obtained using molecular dynamics (MD) simulation. Cellulose interfaces with water and caprolactone medium were modeled with different amounts of grafted caprolactone. The modification lead to an increased work of adhesion between the surface and its surrounding medium. Furthermore, the MD simulations showed that the interaction between cellulose, both modified and non-modified, and surrounding medium is dominated by Coulomb interactions, predominantly as hydrogen bonds.

Water uptake of hydrophilic polymers determined by a thermal gravimetric analyzer with a controlled humidity chamber

The moisture uptake of several water-soluble polymers at different humidities was investigated with a thermal gravimetric analyzer equipped with a controlled humidity chamber. The water sorption of poly(acrylic acid) sodium salt, poly(ethylene glycol) and silica, which are known as super absorbers, were examined. In addition, various hydrophilic polymeric materials were selected according to their structural features. These included hydroxyl functions on the side chains (e.g. poly(2-hydroxyethyl methacrylate)), as well as acidic or basic functionalities (e.g. poly (dimethylaminoethyl methacrylate) or poly(vinylimidazole)). In addition, poly(2-methyl-2-oxazoline) (P(MeOx)) and poly(2-ethyl-2-oxazoline) (P(EtOx)), which are well-known hydrophilic polymers, were also investigated in this context. More significant weight percent changes were obtained for P(MeOx) (60% at 90% relative humidity (RH)) in comparison to P(EtOx) (35% at 90% RH) as a result of the slight difference in hydrophilicity of the structures. The effect of the chain length on the ability for water uptake was also investigated for both poly(oxazolines). Finally, thermoresponsive polymers with a lower critical solution temperature (LCST) behavior (e.g. poly(N-isopropylacrylamide) and poly(dimethylaminoethyl methacrylate)) were also examined. The measurements for the latter polymers were performed below and above the LCST of each polymer whereby the humidities are varied from 0 to 90% with steps of 10%. Upon increasing humidity, the results revealed relatively high water uptake values (8% and 22% for P(NIPAM) and for P(DMAEMA), respectively) below the LCSTs of the polymers and, contrastingly, a small weight loss above their LCSTs. The present results allow a deeper insight into important structure–property relationships (e.g. the influence of the polymer backbone, functional groups, LCST behavior, etc. on the water-uptake properties), and will in subsequent steps permit the directed design of tailor-made polymers for selected applications.

Chemoselective enzymatic preparation of N-hydroxyalkylacrylamides, monomers for hydrophilic polymer matrices

A lipase-catalyzed procedure is described for the preparation of N-hydroxyalkylacrylamides useful among a number of electrophoretical applications such as capillary and gel electrophoresis. The N-hydroxyalkylacrylamides were prepared through an aminolysis reaction of alkanolamines on ethyl acrylate. The reaction was catalyzed by Candida antarctica lipase. The addition of radical inhibitors improved chemoselectivity and amides were obtained in high yield and purity at room temperature.

Flow Injection Analysis of Polymeric Excipients Used in Pharmaceutical Formulations

ABSTRACT Both hydrophobic and hydrophilic polymer matrices are used in pharmaceutical controlled-release formulations. In order to fully understand the functionality of the polymer in the drug delivery device, it is useful to study both the properties of the material before formulation and the behavior of the polymer in situ. A flow injection size exclusion chromatography approach is described that permits the rapid determination of polymer properties. Examples are given for the application of this method to real-time monitoring of the polymerization of poly(lactide-co-glycolide) and to the study of polymer release from swellable matrix tablets.

Effect of Water Absorption Rates on Fracture Toughness of Sisal Textile Fiber Reinforced Composites

Using natural fibers that are inexpensive, lightweight and biodegradable, as the reinforcement for composites is difficult due to their poor interfacial properties between hydrophilic fiber and hydrophobic polymer matrices. It is necessary to evaluate fracture toughness of natural fiber reinforced composites according to water absorption rates to improve mechanical performance of those. In this study, compact tension fracture test was conducted to evaluate fracture toughness with the various specimens. The value of fracture toughness has the tendency to decrease as water absorption rate increases. And different surface treatment methods and different polymer matrices have influence on the value of fracture toughness.

Image analysis studies of dimensional changes in swellable hydrophilic polymer matrices

AbstractStudies of the fronts which are created by the process of swelling, their movement and the effect of drug solubility on release mechanisms, are presented. Tablets comprising solely of hydroxypropyl methylcellulose (HPMC) (Metolose 90 SH 100 000 SR), HPMC with sodium diclofenac (relatively soluble in the buffer solution used) and HPMC with furosemide (insoluble in the buffer solution used) were prepared. The tablets were made by direct compression in a manual hydraulic press and the matrix swelling was studied by an optical analysis technique. During the experimental procedure measurements were taken of the gel layer dimensions, the movement of the swelling, and the erosion and diffusion fronts at different time points. These measurements allowed the investigation of the possible mechanisms involved in the swelling/release process. The results showed that the rate and mechanism of drug release from swellable matrices depends on the following factors: the dissolution, the diffusion of the drug, the translocation of undissolved drug particles in the gel layer, and the solubility of the drugs used. This is supported by the following: (a) the diffusion layer thickness, which is observed as a result of the presence of undissolved drug in the gel layer, increases in the case of the water insoluble drug furosemide and as a result the diffusion front converges on the erosion front; (b) from the analysis of the dissolution data it appears that sodium diclofenac is released as a result of diffusion via the gel layer as well as due to polymer relaxation and/or matrix erosion. Conversely, the release of furosemide is only dependent on the polymer relaxation and/or matrix erosion. Copyright © 2004 John Wiley & Sons, Ltd.