An ultra melt-resistant hydrogel from food grade carbohydrates

© 2017 The Royal Society of Chemistry. We report a binary hydrogel system made from two food grade biopolymers, agar and methylcellulose (agar-MC), which does not require addition of salt for gelation to occur and has very unusual rheological and thermal properties. It is found that the storage modulus of the agar-MC hydrogel far exceeds those of hydrogels from the individual components. In addition, the agar-MC hydrogel has enhanced mechanical properties over the temperature range 25-85 °C and a maximum storage modulus at 55 °C when the concentration of methylcellulose was 0.75% w/v or higher. This is explained by a sol-gel phase transition of the methylcellulose upon heating as supported by differential scanning calorimetry (DSC) measurements. Above the melting point of agar, the storage modulus of agar-MC hydrogel decreases but is still an elastic hydrogel with mechanical properties dominated by the MC gelation. By varying the mixing ratio of the two polymers, agar and MC, it was possible to engineer a food grade hydrogel of controlled mechanical properties and thermal response. SEM imaging of flash-frozen and freeze-dried samples revealed that the agar-MC hydrogel contains two different types of heterogeneous regions of distinct microstructures. The latter was also tested for its stability towards heat treatment which showed that upon heating to temperatures above 120 °C its structure was retained without melting. The produced highly thermally stable hydrogel shows melt resistance which may find application in high temperature food processing and materials templating

Alkali-metal silicate binders and methods of manufacture

A paint binder is described which uses a potassium or sodium silicate dispersion having a silicon dioxide to alkali-metal oxide mol ratio of from 4.8:1 to 6.0:1. The binder exhibits stability during both manufacture and storage. The process of making the binder is predictable and repeatable and the binder may be made with inexpensive components. The high mol ratio is achieved with the inclusion of a silicon dioxide hydrogel. The binder, which also employs a silicone, is in the final form of a hydrogel sol

Ionically cross-linked alginate hydrogels as drug delivery systems for analgesics in broiler chickens : thesis presented in partial fulfilment of the requirement for the degree of Masters of Science in Chemistry at Massey University, Palmerston North, Manawatu, New Zealand

Treating birds with analgesic drugs requires continuous injections of near lethal concentrations to maintain the therapeutic dose in the blood plasma. This is due to birds having higher metabolic rates than mammals. Therefore, there is a need to develop drug delivery systems that can control and slow down the release of analgesics in birds. This study was designed to analyse the sustained release of the model analgesics, sodium salicylate and sodium aspirin, from ionically cross-linked alginate hydrogels, in in vitro and in vivo experiments using broiler chickens as the model bird. Analgesic loaded hydrogels separated into two layers, unlike the homogeneous blank hydrogels. This was labelled as the separation effect. Swelling studies indicated the absence of the insoluble cross-linked alginate material in the hydrogels where the separation effect occurred, with most of the hydrogels dissolving back into the medium. The highest equilibrium swelling percentage achieved in the loaded hydrogels was 68 %. In comparison, the highest equilibrium swelling percentage in the blank hydrogels was 622 %. In vitro drug release profiles showed that the hydrogels released up to 100% of the sodium salicylate within 3.33 hours. In contrast, the hydrogels containing sodium aspirin released only 35 % of the encapsulated drug. Hydrogels containing a drug concentration of 150 mg/mL were injected into the model birds at a dose rate of 150 mg/Kg. No chicken reacted negatively to the hydrogel injection. In vivo results indicate sustained release of the model analgesic from the hydrogels compared to the release from the aqueous solutions of the drug. The effective concentration for an analgesic effect of sodium salicylate was maintained by the group injected with an aqueous solution of sodium salicylate 18 hours after the injection. The groups injected with the hydrogel with the maximum calcium chloride content saw the largest sustained release, with the plasma concentration of sodium salicylate remaining over the effective concentration for up to 36 hours after the injection. Keywords: Sodium salicylate, sodium aspirin, hydrogel, analgesia, sustained release, broiler chicken

Self-healing metallo-supramolecular hydrogel based on specific Ni2+ coordination interactions of poly(ethylene glycol) with bistriazole pyridine ligands in the main chain

In this study, a supramolecular hydrogel formed by incorporating the 2,6-bis(1,2,3-triazol-4-yl)-pyridine (btp) ligand in the backbone of a polymer prepared by copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) "click" polyaddition reaction of 2,6-diethynylpyridine and diazido-poly(ethylene glycol) is reported. The hydrogelation is selectively triggered by the addition of Ni2+ ions to aqueous copolymer solutions. The gelation and rheological properties could be tuned by the change of metal to ligand ratio and polymer concentration. Interestingly, the hydrogel exhibits a fast (within 2 min) and excellent repeatable autonomic healing capacity without external stimuli. This self-healing behavior may find potential applications for the repairing of metal coatings, in the future

Photocurable Bioink for the Inkjet 3D Pharming of Hydrophilic Drugs.

Novel strategies are required to manufacture customized oral solid dosage forms for personalized medicine applications. 3D Pharming, the direct printing of pharmaceutical tablets, is an attractive strategy, since it allows for the rapid production of solid dosage forms containing custom drug dosages. This study reports on the design and characterization of a biocompatible photocurable pharmaceutical polymer for inkjet 3D printing that is suitable for hydrophilic active pharmaceutical ingredients (API). Specifically, hyaluronic acid was functionalized with norbornene moieties that, in the presence of poly(ethylene) glycol dithiol, Eosin Y as a photoinitiator, and a visible light source, undergoes a rapid step-growth polymerization reaction through thiol-ene chemistry. The engineered bioink was loaded with Ropinirole HCL, dispensed through a piezoelectric nozzle onto a blank preform tablet, and polymerized. Drug release analysis of the tablet resulted in 60% release within 15 min of tablet dissolution. The study confirms the potential of inkjet printing for the rapid production of tablets through the deposition of a photocurable bioink designed for hydrophilic APIs

Multifunctional enzymatically generated hydrogels for chronic wound application

The healing of chronic wounds requires intensive medical intervention at huge healthcare costs. Dressing materials should consider the multifactorial nature of these wounds comprising deleterious proteolytic and oxidative enzymes and high bacterial load. In this work, multifunctional hydrogels for chronic wound application were produced by enzymatic cross- linking of thiolated chitosan and gallic acid. The hydrogels combine several beneficial to wound healing properties, controlling the matrix metalloproteinases (MMPs) and myeloperoxidase (MPO) activities, oxidative stress, and bacterial contamination. In vitro studies revealed above 90% antioxidant activity, and MPO and collagenase inhibition by up to 98 and 23%, respectively. Ex vivo studies with venous leg ulcer exudates confirmed the inhibitory capacity of the dressings against MPO and MMPs. Additionally, the hydrogels reduced the population of the most frequently encountered in nonhealing wounds bacterial strains. The stable at physiological conditions and resistant to lysozyme degradation hydrogels showed high biocompatibility with human skin fibroblastsPeer ReviewedPostprint (author's final draft

The Use of Poly(vinyl alcohol)-based Hydrogels in Biomedical Applications

Polymers have found increasing favor in biomedical applications due to the greater control that researchers can exert over their properties. Researchers have focused on the development of therapies using biologically compatible polymers due to their ability to limit potentially harmful interactions with the body. This research has led to advances in tissue engineering, controlled and targeted drug delivery, and other biomedical fields, with the goal of improving both the effectiveness and accessibility of health care. Poly(vinyl alcohol) (PVA) hydrogels possess several chemical properties that make them well suited for biomedical applications. These include inertness and stability, biocompatibility, and pH-responsiveness. As a result, PVA based materials have been studied for potential applications in areas of biomedicine such as targeted drug delivery, tissue engineering, and wound healing. This thesis examines the properties of PVA and seeks to understand how the chemical and physical structure affects their properties. It then examines how these properties enhance their utility in potential biomedical applications. Finally, it reviews the research into development of PVA based materials for three different biomedical applications.Chemical Engineerin

Prescribed pattern transformation in swelling gel tubes by elastic instability

We present a study on swelling-induced circumferential buckling of tubular shaped gels. Inhomogeneous stress develops as gel swells under mechanical constraints, which gives rise to spontaneous buckling instability without external force. Full control over the post-buckling pattern is experimentally demonstrated. A simple analytical model is developed using elastic energy to predict stability and post-buckling patterns upon swelling. Analysis reveals that height to diameter ratio is the most critical design parameter to determine buckling pattern, which agrees well with experimental and numerical results.Comment: 32 pages, 7 figure