Water Soluble Polymers for Pharmaceutical Applications

Unprecedented Acid-Promoted Polymerization and Gelation of Acrylamide: A Serendipitous Discovery

Dilute acid polymerizes degassed, aqueous acrylamide with concomitant gelation, without the need for added free radical initiator or cross-linking agent. This reaction is accelerated by sonication or UV irradiation, but inhibited by adventitious oxygen or the addition of a free radical inhibitor, suggesting an acid-accelerated free radical process. The resulting hydrogels are thixotropic in nature and partially disrupted by the addition of chaotropic agents, indicating the importance of hydrogen bonding to the 3D network. This discovery was made while trying to prepare pectin-polyacrylamide hydrogels. We observed that pectin initiated the gelation of acrylamide, but only if the aqueous pectin samples had a pH lower than ca. 5.

The role of SeDeM for characterizing the active substance and polyvinyilpyrrolidone eliminating metastable forms in an oral lyophilizate-A preformulation study

A preformulation study of an oral lyophilisate with cetirizine dihydrochloride (CTZ) as active ingredient, mannitol and PVP K30 as bulking agents is presented. CTZ shown a humidity content of 0.150% and a spontaneous hygroscopicity of 0.200% (both determined by SeDeM diagram), demonstrating an adequate stability behavior in solid form. A design of experiments (DoE) performed with both mannitol and PVP K30, followed by a simple factorial design (3²) has determined the optimum combination of excipients and CTZ, and showed that a higher proportion of PVP K30 was able to prevent metastable forms generated by mannitol.

Synthesis, Optical, and Structural Studies of Iron Sulphide Nanoparticles and Iron Sulphide Hydroxyethyl Cellulose Nanocomposites from Bis-(Dithiocarbamato)Iron(II) Single-Source Precursors

In this study, Fe(II) complexes of phenyldithiocarbamate, dimethyldithiocarbamate and imidazolyldithiocarbamate were used as single-source precursors to prepare iron sulphide nanoparticles by thermolysis in oleic acid/octadecylamine (ODA) at 180 °C. The nanoparticles were dispersed into hydroxyethyl cellulose (HEC) to prepare iron sulphide/HEC nanocomposites. Ultraviolet-Visible (UV-Vis), Photoluminescence (PL), Fourier Transform Infrared (FTIR), powder X-ray diffraction (pXRD), high-resolution transmission electron microscopy (HRTEM), Field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS) were used to characterize the iron sulphide nanoparticles and corresponding HEC nanocomposites. The absorption spectra studies revealed that the nanoparticles were blue shifted due to quantum confinement and the optical band gaps of the nanoparticles are 4.85 eV for FeS1, 4.36 eV for FeS2, and 4.77 eV for FeS3. The emission maxima are red-shifted and broader for the nanoparticles prepared from phenyldithiocarbamate. Rod-like and spherically shaped iron sulphide particles were observed from the HRTEM images. The crystallite sizes from the HRTEM images are 23.90-38.89 nm for FeS1, 4.50-10.50 nm for FeS2, and 6.05-6.19 nm for FeS3 iron sulphide nanoparticles, respectively. pXRD diffraction patterns confirmed that FeS1 is in the pyrrhotite-4M crystalline phase, FeS2 is in the pyrrhotite phase, and FeS3 is in the troilite phase of iron sulphide. The phases of the iron sulphide nanoparticles indicate that the nature of the precursor complex affects the obtained crystalline phase. FTIR spectra studies confirmed the incorporation of the nanoparticles in the HEC matrix by the slight shift of the O-H and C-O bonds and the intense peaks on the nanoparticles. FESEM images of the iron sulphide nanoparticles showed flake-like or leaf-like morphologies with some hollow spheres. The EDS confirmed the formation of iron sulphide nanoparticles by showing the peaks of Fe and S.

Orally Disintegrating Tablets Containing Melt Extruded Amorphous Solid Dispersion of Tacrolimus for Dissolution Enhancement

In order to improve the aqueous solubility and dissolution of Tacrolimus (TAC), amorphous solid dispersions of TAC were prepared by hot melt extrusion with three hydrophilic polymers, Polyvinylpyrrolidone vinyl acetate (PVP VA64), Soluplus^® and Hydroxypropyl Cellulose (HPC), at a drug loading of 10% w/w. Molecular modeling was used to determine the miscibility of the drug with the carrier polymers by calculating the Hansen Solubility Parameters. Powder X-ray diffraction and differential scanning calorimetry (DSC) studies of powdered solid dispersions revealed the conversion of crystalline TAC to amorphous form. Fourier transform Infrared (FTIR) spectroscopy results indicated formation of hydrogen bond between TAC and polymers leading to stabilization of TAC in amorphous form. The extrudates were found to be stable under accelerated storage conditions for 3 months with no re-crystallization, indicating that hot melt extrusion is suitable for producing stable amorphous solid dispersions of TAC in PVP VA64, Soluplus^® and HPC. Stable solid dispersions of amorphous TAC exhibited higher dissolution rate, with the solid dispersions releasing more than 80% drug in 15 min compared to the crystalline drug giving 5% drug release in two hours. These stable solid dispersions were incorporated into orally-disintegrating tablets in which the solid dispersion retained its solubility, dissolution and stability advantage.

Microspherical Particles of Solid Dispersion of Polyvinylpyrrolidone K29-32 for Inhalation Administration

Inhalation administration is a promising alternative to the invasive drug delivery methods. The particle size required for ideal drug aerosol preparation is between 1 and 3 μm. The application of microspherical particles of solid dispersions enhances bioavailability of poorly soluble drugs due to the solubilization. In the present work, the spray drying process of the production of microspherical particles of solid dispersions of polyvinylpyrrolidone K29-32 with model hydrophobic drug, phenacetin, was optimized using the results of DSC, PXRD, and viscometry. The diameter of the obtained particles is within 1–3 μm range. The Gibbs energy of dissolution in water was shown to be negative for the mixture with polymer/phenacetin mass ratio 5 : 1. We have demonstrated that the optimal size distribution for the inhalation administration is obtained for microspherical particles produced using spray caps with 7.0 μm hole size. The dissolution rates of phenacetin from the produced microspherical particles were faster than that of drug powder. As evidenced by powder X-ray diffraction data, phenacetin stayed in amorphous state for 4 months in microspherical particles of solid dispersions. According to the obtained results, strategic application of the spray drying process could be beneficial for the improvement of the pharmaceutical properties of model drug, phenacetin.

Novel membranes from physico-chemically modified deproteinized natural rubber latex: development, characterisation and drug permeation

Novel blend membranes from physico-chemically modified deproteinized natural rubber latex for drug release applications.

Electrochemical Sunset Yellow Biosensor Based on Photocured Polyacrylamide Membrane for Food Dye Monitoring

An enzyme-based electrochemical biosensor was investigated for the analysis of Sunset Yellow synthetic food dye. A glassy carbon electrode was coated with a poly(acrylamide-co-ethyl methacrylate) membrane to immobilize laccase using a single-step photopolymerization procedure. Poly(acrylamide-co-ethyl methacrylate) membrane was demonstrated to have acceptable water absorption and suitable for biosensor application. Sunset Yellow biosensor exhibited a linear response range from 0.08 to 10.00 µM with a detection limit of 0.02 µM. This biosensor was successfully used to determine Sunset Yellow in soft drinks with recoveries of 99.0-101.6%. The method was validated using high-performance liquid chromatography, indicating the biosensor can be as a promising alternative method for Sunset Yellow detection.

Re-evaluation of celluloses E 460(i), E 460(ii), E 461, E 462, E 463, E 464, E 465, E 466, E 468 and E 469 as food additives

Following a request from the European Commission, the EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) was asked to deliver a scientific opinion re-evaluating the safety of microcrystalline cellulose (E 460(i)), powdered cellulose (E 460(ii)), methyl cellulose (E 461), ethyl cellulose (E 462), hydroxypropyl cellulose (E 463), hydroxypropyl methyl cellulose (E 464), ethyl methyl cellulose (E 465), sodium carboxy methyl cellulose (E 466), enzymatically hydrolysed carboxy methyl cellulose (E 469) and cross-linked carboxy methyl cellulose (E 468) as food additives. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the Scientific Committee on Food (SCF) established an acceptable daily intake (ADI) 'not specified' for unmodified and modified celluloses. Celluloses are not absorbed and are excreted intact in the faeces; in addition, microcrystalline cellulose, powdered and modified celluloses could be fermented by the intestinal flora in animals and humans. Specific toxicity data were not always available for all the celluloses evaluated in the present opinion and for all endpoints. Given their structural, physicochemical and biological similarities, the Panel considered it possible to read-across between all the celluloses. The acute toxicity of celluloses was low and there was no genotoxic concern. Short-term and subchronic dietary toxicity studies performed with E 460(i), E 461, E 462, E 463, E 464, E 466 and E 469 at levels up to 10% did not indicate specific treatment related adverse effects. In chronic toxicity studies performed with E 460(i), E 461, E 463, E 464, E 465 and E 466, the no observed adverse effect level (NOAEL) values reported ranged up to 9,000 mg/kg body weight (bw) per day. No carcinogenic properties were detected for microcrystalline cellulose and modified celluloses. Adverse effects on reproductive performance or developmental effects were not observed with celluloses at doses greater than 1,000 mg/kg bw by gavage (often the highest dose tested). The combined exposure to celluloses (E 460-466, E 468 and E 469) at 95th percentile of the refined (brand-loyal) exposure assessment for the general population was up to 506 mg/kg bw per day. The Panel concluded that there was no need for a numerical ADI and that there would be no safety concern at the reported uses and use levels for the unmodified and modified celluloses (E 460(i); E 460(ii); E 461-466; E 468 and E 469). The Panel considered an indicative total exposure of around 660-900 mg/kg bw per day for microcrystalline, powdered and modified celluloses.

Reverse-phase high performance liquid chromatography (RP-HPLC) as a powerful tool to characterise complex water-soluble copolymer architectures

A novel analytical method, based on RP-HPLC, for the characterisation of monomer distribution in charged water-soluble copolymers.

Enhancing the Solubility of Fenofibrate by Nanocrystal Formation and Encapsulation

Development of techniques to enhance bioavailability of drugs having poor water solubility is a big challenge for pharmaceutical industry. Solubility can be enhanced by particle size reduction and encapsulation using hydrophilic polymers. Fenofibrate (FF) is a drug for regulating lipids. Multi-fold enhancement in solubility of FF has been achieved by nanocrystal formation in the present study. Nanoparticles were prepared by an evaporation-assisted solvent-antisolvent interaction (EASAI) approach. Water-soluble polymers, viz. polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and hydroxypropyl methylcellulose (HPMC), were used to encapsulate and thus control the particle size of FF nanocrystals. Spherical particles having average particle size well below 30 nm could be prepared under optimum conditions. Almost complete release of the drug molecules from the polymer-stabilized nanocrystals within 2 h was clearly evident from the in vitro drug release studies. Infrared (FTIR) spectroscopy indicated the absence of solvent impurities and any strong interaction between the drug and stabilizers. The polymorphic form of raw-FF was retained in the nanoparticles as per the X-ray diffraction (XRD) patterns. Lower crystallinity of the nanoformulated samples compared to raw-FF was confirmed by differential scanning calorimetric (DSC) studies.

The Preparations and Water Vapor Barrier Properties of Polyimide Films Containing Amide Moieties

Flexible displays are a systematic revolution in the field of display, in which high-performance and high-barrier polymer substrates are considered to be one of the most important key materials. In this work, high water vapor barrier polyimides containing amide moieties were synthesized via the ternary polymerization of 4,4'-diaminobenzailide (DABA), 4,4'-diaminodipheny ether (ODA), and 3,3',4,4'-biphenyl-tetracarboxylic acid dianhydride (BPDA) followed by thermal imidization. The relationship between the content of amide moieties and the water vapor barrier property of the prepared polyimides was studied by means of density test, water absorbing test, water contact angle test, water vapor permeation test, fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), thermogravimetry coupled with fourier transform infrared spectrometry (TG-FTIR), wide-angle X-ray diffraction analysis (WXRD), mechanical performance test, etc. The results show that the introduction of amide groups into polyimide (PI) main chains can improve the water vapor barrier properties of the polyimides effectively. The water vapor transmission rate (WVTR) of the polyimide films can be improved from 8.2365 g·(m²·24 h)-1 to 0.8670 g·(m²·24 h)-1 with the increasing content of amide moieties.

Nanostructure of Poly(Acrylic Acid) Adsorption Layer on the Surface of Activated Carbon Obtained from Residue After Supercritical Extraction of Hops

The nanostructure of poly(acrylic acid) (PAA) adsorption layer on the surface of mesoporous-activated carbon HPA obtained by physical activation of residue after supercritical extraction of hops was characterized. This characterization has been done based on the analysis of determination of adsorbed polymer amount, surface charge density, and zeta potential of solid particles (without and in the PAA presence). The SEM, thermogravimetric, FTIR, and MS techniques have allowed one to examine the solid surface morphology and specify different kinds of HPA surface groups. The effects of solution pH, as well as polymer molecular weight and concentration, were studied. The obtained results indicated that the highest adsorption on the activated carbon surface was exhibited by PAA with lower molecular weight (i.e., 2000 Da) at pH 3. Under such conditions, polymeric adsorption layer is composed of nanosized PAA coils (slightly negatively charged) which are densely packed on the positive surface of HPA. Additionally, the adsorption of polymeric macromolecules into solid pores is possible.

Thermosensitive hydrogels a versatile concept adapted to vaginal drug delivery

Vaginal drug delivery represents an attractive strategy for local and systemic delivery of drugs otherwise poorly absorbed after oral administration. The rather dense vascular network, mucus permeability and the physiological phenomenon of the uterine first-pass effect can all be exploited for therapeutic benefit. However, several physiological factors such as an acidic pH, constant secretion, and turnover of mucus as well as varying thickness of the vaginal epithelium can impact sustained drug delivery. In recent years, polymers have been designed to tackle challenges mentioned above. In particular, thermosensitive hydrogels hold great promise due to their stability, biocompatibility, adhesion properties and adjustable drug release kinetics. Here, we discuss the physiological and anatomical uniqueness of the vaginal environment and how it impacts the safe and efficient vaginal delivery and also reviewed several thermosensitive hydrogels deemed suitable for vaginal drug delivery by addressing specific characteristics, which are essential to engage the vaginal environment successfully.

Recent advances in the use of nanoparticles for allergen-specific immunotherapy

The number of patients suffering from allergic asthma and rhinoconjunctivitis has increased dramatically within the last decades. Allergen-specific immunotherapy (AIT) is the only available cause-oriented therapy so far. AIT reduces symptoms, but has also a disease-modifying effect. Disadvantages are a long-lasting procedure, and in a few cases potential systemic adverse reactions. Encapsulation of allergens or DNA vaccines into nanostructures may provide advantages compared to the conventional AIT with noncapsulated allergen extracts: The protein/DNA molecule can be protected from degradation, higher local concentrations and targeted delivery to the site of action appear possible, and most importantly, recognition of encapsulated allergen by the immune system, especially by IgE antibodies, is prevented. AIT with nanoparticles (NPs) may offer a safer and potentially more efficient way of treatment for allergic diseases. In this review, we summarize the use of biodegradable NPs consisting of synthetic or natural polymers, liposomes, and virus-like particles as well as nonbiodegradable NPs like dendrimers, and carbon- or metal-based NPs for AIT. More or less successful applications of these NPs in prophylactic as well as therapeutic vaccination approaches in rodents or other animals as well as first human clinical trials are discussed in detail.

Radical Copolymerization Kinetics of Bio-Renewable Butyrolactone Monomer in Aqueous Solution

The radical copolymerization kinetics of acrylamide (AM) and the water-soluble monomer sodium 4-hydroxy-4-methyl-2-methylene butanoate (SHMeMB), formed by saponification of the bio-sourced monomer γ-methyl-α-methylene-γ-butyrolactone (MeMBL), are investigated to explain the previously reported slow rates of reaction during synthesis of superabsorbent hydrogels. Limiting conversions were observed to decrease with increased temperature during SHMeMB homopolymerization, suggesting that polymerization rate is limited by depropagation. Comonomer composition drift also increased with temperature, with more AM incorporated into the copolymer due to SHMeMB depropagation. Using previous estimates for the SHMeMB propagation rate coefficient, the conversion profiles were used to estimate rate coefficients for depropagation and termination (kt). The estimate for kt,SHMeMB was found to be of the same order of magnitude as that recently reported for sodium methacrylate, with the averaged copolymerization termination rate coefficient dominated by the presence of SHMeMB in the system. In addition, it was found that depropagation still controlled the SHMeMB polymerization rate at elevated temperatures in the presence of added salt.

Production of Electrospun Fast-Dissolving Drug Delivery Systems with Therapeutic Eutectic Systems Encapsulated in Gelatin

Fast-dissolving delivery systems (FDDS) have received increasing attention in the last years. Oral drug delivery is still the preferred route for the administration of pharmaceutical ingredients. Nevertheless, some patients, e.g. children or elderly people, have difficulties in swallowing solid tablets. In this work, gelatin membranes were produced by electrospinning, containing an encapsulated therapeutic deep-eutectic solvent (THEDES) composed by choline chloride/mandelic acid, in a 1:2 molar ratio. A gelatin solution (30% w/v) with 2% (v/v) of THEDES was used to produce electrospun fibers and the experimental parameters were optimized. Due to the high surface area of polymer fibers, this type of construct has wide applicability. With no cytotoxicity effect, and showing a fast-dissolving release profile in PBS, the gelatin fibers with encapsulated THEDES seem to have promising applications in the development of new drug delivery systems.

Film forming PVA-based cleaning systems for the removal of corrosion products from historical bronzes

This paper presents an innovative poly(vinyl)alcohol-based film forming system, specifically devised for the controllable and selective cleaning of copper-based artifacts. Traditional cleaning procedures are commonly performed using mechanical and/or chemical methods. Unfortunately, both these methods present some limitations related to both the poor selectivity and invasiveness in case of the mechanical procedure, and to the scarce control over the involved reactions when dealing with a chemical approach. The innovative system proposed in this work allows combining the advantages of chemical and mechanical treatments thanks to the confinement of a complexing agent (EDTA) within a fluid, polymeric matrix, that is able to form a solid thin film upon drying. After treatment, the polymeric film can be completely removed from the artwork through a gentle peeling action. In this contribution, the film formation mechanism was investigated by means of thermal analysis and rheology; the role of plasticizers, volatile solvent fraction, and quantity of loaded EDTA is also discussed. Finally, the results of cleaning tests performed on artificially aged samples, and on a real case study, the “Fontana dei Mostri Marini” by Pietro Tacca in Florence, are presented.

Dispersion of the Photosensitizer 5,10,15,20-Tetrakis(4-Sulfonatophenyl)-porphyrin by the Amphiphilic Polymer Poly(vinylpirrolidone) in Highly Porous Solid Materials Designed for Photodynamic Therapy

The ability of the amphiphilic and biocompatible poly(vinylpyrrolidone) to avoid self-aggregation of the photosensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous solution in the presence of the biocompatible polycation chitosan, polymer that induces the dye self-aggregation, is shown. This is related to the tendency of the dye to undergo preferential solvation by the amphiphilic polymer. Importantly, the dispersant ability of this polymer is transferred to the solid state. Thus, aerogels made of the biocompatible polymers chitosan and chondroitin sulfate, and containing the photosensitizer dispersed by the amphiphilic polymer have been synthesized. Production of reactive oxygen species by the aerogel containing the amphiphilic polymer was faster than when the polymer was absent, correlating with the relative concentration of dyes dispersed as monomers. The aerogels presented here constitute low cost biocompatible materials bearing a conventional photosensitizer for photodynamic therapy, easy to produce, store, transport, and manage in clinical practice.

pH-Sensitive drug delivery system based on hydrophobic modified konjac glucomannan

Amphiphilic aliphatic amines grafted konjac glucomannan (KGM-g-AH₈, KGM-g-AH₁₂ and KGM-g-AH₁₈) micelles were prepared via a simple two-step synthesis with Schiff's base as the "switch" to achieve intracellular acid-triggered curcumin release. The KGM-g-AH₈ self-assembled into spherical nano-micelles (107.6±11.6nm) in an aqueous medium, and presented high curcumin loading capacity as well as good physical stability in 28 days. The in vitro curcumin release behaviors proved the controlled release property and the endosomal/lysosomal pH response of KGM-g-AH₈ micelles. The cytotoxicity and cellular uptake studies were also investigated to exhibit the intracellular pH-sensitivity, safety and biocompatibility of KGM-g-AH₈ micelles. This research focuses on the feasibility of KGM-based micelles to be extrapolated as promising strategies for cancer therapy and offers new potential options for intracellular drug delivery.

Design and characteristics of gellan gum beads for modified release of meloxicam

The aim of the presented work was to design, formulate and evaluate the properties of low-acyl gellan macro beads with the potential application as carriers for oral delivery of meloxicam (MLX) in the prophylaxis of colorectal cancer. The beads were obtained by means of ionotropic gelation technique. Calcium chloride (1.0%, 9.0 × 10^-2 M) was used as the cross-linking agent. Nine different polymer, drug and surfactant (Tween^®80) mixtures were used for production of the beads. The quantitative compositions of the mixtures were generated with the application of the Design of Experiments (DoE) modulus from the STATISTICA Software. The prepared formulations revealed 7.2-27.0% of drug loading and 29.2-50.7% drug encapsulation efficiency. It turned out that 0.5% amount of gellan gum in the mixtures was not sufficient to obtain spherical beads. The morphology and surface of the dried beads were analyzed by SEM. Raman spectra confirmed that MLX did not undergo structural changes during production of the beads. The swelling behavior and degradation of the beads were evaluated in three simulated gastrointestinal fluids at different pH (1.2; 4.5; 6.8). The MLX in vitro release studies were conducted on USP apparatus IV, working in the open loop mode. The obtained results showed that MLX release from the dried beads was pH-dependent. The formulations obtained from mixtures containing 1.0 and 1.5% of gellan may be considered as oral dosage forms for MLX, intended to omit the stomach and release the drug in the distal parts of the gastrointestinal tract.

PEGylated Anionic Magnetofluorescent Nanoassemblies: Impact of Their Interface Structure on Magnetic Resonance Imaging Contrast and Cellular Uptake

Controlling the interactions of functional nanostructures with water and biological media represents high challenges in the field of bioimaging applications. Large contrast at low doses, high colloidal stability in physiological conditions, the absence of cell cytotoxicity, and efficient cell internalization represent strong additional needs. To achieve such requirements, we report on high-payload magnetofluorescent architectures made of a shell of superparamagnetic iron oxide nanoparticles tightly anchored around fluorescent organic nanoparticles. Their external coating is simply modulated using anionic polyelectrolytes in a final step to provide efficient magnetic resonance imaging (MRI) and fluorescence imaging of live cells. Various structures of PEGylated polyelectrolytes have been synthesized and investigated, differing from their iron oxide complexing units (carboxylic vs phosphonic acid), their structure (block- or comblike), their hydrophobicity, and their fabrication process [conventional or reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization] while keeping the central magnetofluorescent platforms the same. Combined photophysical, magnetic, NMRD, and structural investigations proved the superiority of RAFT polymer coatings containing carboxylate units and a hydrophobic tail to impart the magnetic nanoassemblies (NAs) with enhanced-MRI negative contrast, characterized by a high r₂/r₁ ratio and a transverse relaxation r₂ equal to 21 and 125 s^-1 mmol^-1 L, respectively, at 60 MHz clinical frequency (∼1.5 T). Thanks to their dual modality, cell internalization of the NAs in mesothelioma cancer cells could be evidenced by both confocal fluorescence microscopy and magnetophoresis. A 72 h follow-up showed efficient uptake after 24 h with no notable cell mortality. These studies again pointed out the distinct behavior of RAFT polyelectrolyte-coated bimodal NAs that internalize at a slower rate with no adverse cytotoxicity. Extension to multicellular tumor cell spheroids that mimic solid tumors revealed the successful internalization of the NAs in the periphery cells, which provides efficient deep-imaging labels thanks to their induced T₂* contrast, large emission Stokes shift, and bright dotlike signal, popping out of the strong spheroid autofluorescence.

Characterizing viscoelasticity of unhydrolyzed chicken sternal cartilage extract suspensions: Towards development of injectable therapeutics formulations

Exogenous delivery of cartilage extract is being explored as a promising candidate for knee arthritis treatment as it biomimics native cartilage tissue characteristics. In this study, we report on the rheological characterization of aqueous suspensions constituted from a powdered form of unhydrolyzed chicken sternum extract. The effect of particle size (as-received vs. milled), suspension fluid (water vs. PBS), and temperature (37°C vs. 4°C), on the viscoelastic properties of the sternum extract based particulate suspensions were evaluated. Results showed that these suspensions exhibit shear-thinning characteristics as shear rate (γ̇) increases, while viscosity (η), storage (G'), and loss (G″) moduli of the suspensions increased with increasing particulate loading (ϕ: 2.5-10wt%). Reducing the as-received particle size by milling decreased G', G, and η of the suspensions and increased the influence of ϕ on these properties, possibly due to improved particle packing. Replacing water with PBS had no significant effect on the rheological properties, but temperature reduction from 37°C to 4°C increased G', G", and η of the suspensions and lowered the impact of powder loading on viscoelastic properties. The suspension's time-dependent response was typical of viscoelastic materials, characterized by an asymptotical approach to a final stress (stress relaxation) or strain (creep). Results were fit to a power-law model for creep, a general relaxation model for exponential decay in stress, Carreau-Yasuda models for flow curves, and a two-parameter Liu model to identify the maximum powder loading (ϕ_m). Among the various forces involved in particle-particle interactions within these suspensions, electrostatic forces appeared to dominate the most. Such characterization of the viscoelastic nature of these suspensions would help in formulating stable injectable cartilage extract based therapeutics for in vivo applications.

pH Sensitive Hydrogels in Drug Delivery: Brief History, Properties, Swelling, and Release Mechanism, Material Selection and Applications

Improving the safety efficacy ratio of existing drugs is a current challenge to be addressed rather than the development of novel drugs which involve much expense and time. The efficacy of drugs is affected by a number of factors such as their low aqueous solubility, unequal absorption along the gastrointestinal (GI) tract, risk of degradation in the acidic milieu of the stomach, low permeation of the drugs in the upper GI tract, systematic side effects, etc. This review aims to enlighten readers on the role of pH sensitive hydrogels in drug delivery, their mechanism of action, swelling, and drug release as a function of pH change along the GI tract. The basis for the selection of materials, their structural features, physical and chemical properties, the presence of ionic pendant groups, and the influence of their pKa and pKb values on the ionization, consequent swelling, and targeted drug release are also highlighted.

Superabsorbent hydrogels made from bio-sourced butyrolactone monomer in aqueous solution

A study of the radical polymerization kinetics of sodium 4-hydroxy-4-methyl-2-methylene butanoate with acrylamide in aqueous solution provides insights to the performance of superabsorbent hydrogels synthesized with equilibrium degree of swelling in the range of 6700–59 000%.