Investigation of a novel freeze-thaw process for the production of drug delivery hydrogels

Composite Cryogels Based on Hydroxyapatite and Polyvinyl Alcohol and the Study of Physicochemical and Mechanical Properties

Nowadays, due to the increasing number of diseases and injuries related to bone tissue, there is an acute problem of creating a material that could be incorporated into the bone tissue structure and contribute to accelerated bone regeneration. Such materials can be represented by a polymeric matrix that holds the material in the bone and an inorganic component that can be incorporated into the bone structure and promote accelerated bone regeneration. Therefore, in this work we investigated polyvinyl alcohol-based composite cryogels containing an in situ deposited inorganic filler, hydroxyapatite. The freezing temperature was varied during the synthesis process. The composition of the components was determined by infrared spectroscopy and the phase composition by X-ray phase analysis, from which it was found that the main phase of the composite is hydroxyapatite and that the particle size decreases with increasing freezing temperature. The elemental composition of the surface is dominated by carbon, oxygen, phosphorus and calcium; no impurities of other elements not typical for polyvinyl alcohol/ hydroxyapatite cryogels were found. Higher mechanical properties and melting points were observed at -15 °C. Cryogenic treatment parameters did not affect cell viability; however, cell viability was above 80% in all samples.

Hydrogels: Properties and Applications in Biomedicine

Hydrogels are crosslinked polymer chains with three-dimensional (3D) network structures, which can absorb relatively large amounts of fluid. Because of the high water content, soft structure, and porosity of hydrogels, they closely resemble living tissues. Research in recent years shows that hydrogels have been applied in various fields, such as agriculture, biomaterials, the food industry, drug delivery, tissue engineering, and regenerative medicine. Along with the underlying technology improvements of hydrogel development, hydrogels can be expected to be applied in more fields. Although not all hydrogels have good biodegradability and biocompatibility, such as synthetic hydrogels (polyvinyl alcohol, polyacrylamide, polyethylene glycol hydrogels, etc.), their biodegradability and biocompatibility can be adjusted by modification of their functional group or incorporation of natural polymers. Hence, scientists are still interested in the biomedical applications of hydrogels due to their creative adjustability for different uses. In this review, we first introduce the basic information of hydrogels, such as structure, classification, and synthesis. Then, we further describe the recent applications of hydrogels in 3D cell cultures, drug delivery, wound dressing, and tissue engineering.

Potential of Oil Palm Empty Fruit Bunch Resources in Nanocellulose Hydrogel Production for Versatile Applications: A Review

Oil palm empty fruit bunch (OPEFB) is considered the cheapest natural fiber with good properties and exists abundantly in Malaysia. It has great potential as an alternative main raw material to substitute woody plants. On the other hand, the well-known polymeric hydrogel has gathered a lot of interest due to its three-dimensional (3D) cross-linked network with high porosity. However, some issues regarding its performance like poor interfacial connectivity and mechanical strength have been raised, hence nanocellulose has been introduced. In this review, the plantation of oil palm in Malaysia is discussed to show the potential of OPEFB as a nanocellulose material in hydrogel production. Nanocellulose can be categorized into three nano-structured celluloses, which differ in the processing method. The most popular nanocellulose hydrogel processing methods are included in this review. The 3D printing method is taking the lead in current hydrogel production due to its high complexity and the need for hygiene products. Some of the latest advanced applications are discussed to show the high commercialization potential of nanocellulose hydrogel products. The authors also considered the challenges and future direction of nanocellulose hydrogel. OPEFB has met the requirements of the marketplace and product value chains as nanocellulose raw materials in hydrogel applications.

Chitosan-Graft-Poly(N-Isopropylacrylamide)/PVA Cryogels as Carriers for Mucosal Delivery of Voriconazole

The objective of this study was to prepare and characterize physically crosslinked gel formulations of chitosan (CS)-graft-poly(N-isopropyl acrylamide) (PNIPAAm) and polyvinyl alcohol (PVA) for smart delivery of an antifungal drug, Voriconazole, for mucosal applications. For this purpose, cryogels of CS-g-PNIPAAm/PVA and CS/PVA were tested by means of texture profile analysis and rheology to determine optimal matrix properties for topical application. The ratio of 75/25 v/v % CS-g-PNIPAAm/PVA was selected to be used for formulation since it gave low compressibility and hardness (1.2 and 0.6 N) as well as high adhesion properties and non-Newtonian flow behavior. The cryogels and formulations were further characterized by means of FTIR spectroscopy, swelling behavior, texture analysis, scanning electron microscopy (SEM), thermal (differential scanning calorimetry (DSC) and TGA), and rheological behavior. The drug loading capacity and in vitro release profile of the drug, storage stability, and cytotoxicity tests were also performed for the gel formulation. The FTIR, DSC, and TGA results verified the successful formation of cryogels. Swelling studies revealed a pH-dependent swelling ability with a maximum swelling degree of 1200% in acid and 990% in phosphate buffer (pH = 7.4). Thermal studies showed that CS-g-PNIPAAm/PVA 75/25 had higher thermal stability proving the structural complexity of the polymer. The loading capacity of Voriconazole was found to be 70% (w/w). The in vitro release profiles of Voriconazole showed Fickian release behavior for CS-g-PNIPAAm/PVA 75/25 gel with an approximate delivery of 38% within 8 h, slower than matrices containing unmodified chitosan. The storage stability test exhibited that the gel formulation was still stable even after aging for two months. Moreover, the cell culture assays revealed a non-toxic character of the polymeric matrix. Overall results showed that the CS-g-PNIPAAm/PVA 75/25 hydrogel has the potential to be used as a smart polymeric vehicle for topical applications.

Preparation and in vitro evaluation of melatonin-loaded HA/PVA gel formulations

Melatonin-loaded hyaluronic acid (HA) and poly(vinyl alcohol) (PVA) gels were prepared by using freeze-thaw technique and an emulsion method followed by freeze-thaw technique to produce a new synergistic system for topical application. Freeze-thaw hydrogels and emulgels were characterized by means of Fourier transform infrared spectroscopy, rheology and swelling tests. The porous structure of the hydrogels was shown by scanning electron microscopy observations and thermal properties were tested by differential scanning calorimetry measurements. Bioadhesion and in vitro release characterization of formulations were performed by texture profile analysis and dialysis bag method, respectively. The pore size of both formulations was ranging from 900 nm to 30 μm. Melatonin showed a good compatibility with the polymeric matrices as the pores were smaller for the drug-loaded systems. In vitro release studies showed that the release was improved by emulgel formulations. After 24 h, the release percentage was found to be 13.240% ± 1.094 and 15.192% ± 2.270 for hydrogel and emulgel, respectively. Emulgels had better bioadhesion properties than simple freeze-thaw samples. As a conclusion, regarding the in vitro characterization studies HA and PVA hydrogel and emulgel formulations and their lyophilized forms could be promising systems for topical application of melatonin.

Investigating a new drug delivery nano composite membrane system based on PVA/PCL and PVA/HA(PEG) for the controlled release of biopharmaceuticals for bone infections

The capability for sustained and gradual release of pharmaceuticals is a major requirement in the development of a guided antimicrobial bacterial control system for clinical applications. In this study, PVA gels with varying constituents that were manufactured via a refreeze/thawing route, were found to have excellent potential for antimicrobial delivery for bone infections. Cefuroxime Sodium with poly(ethylene glycol) was incorporated into 2 delivery systems poly(e-caprolactone) (PCL) and hydroxyapatite (HA), by a modified emulsion process. Our results indicate that the Cefuroxime Sodium released from poly(e-caprolactone) in PVA was tailored to a sustained release over more than 45 days, while the release from hydroxyapatite PVA reach burst maximum after 20 days. These PVA hydrogel-systems were also capable of controlled and sustained release of other biopharmaceuticals.

SWELLING DESWELLING STUDIES AFTER FREEZE–THAW TREATMENT OF NANOSILICA REINFORCED POLY (VINYL ALCOHOL)-BASED ORGANIC–INORGANIC HYBRID HYDROGEL

Aqueous nanosilica sol (particle size range: 9–13 nm, pH: 9.0) was added at various low concentration range (0.5–2 wt.%) into aqueous poly (vinyl alcohol) (PVA) of different molecular weight (98% hydrolyzed, 20 wt.%) (pH: 5.0) at room temperature under constant stirring to synthesize organic-inorganic hybrid hydrogels in presence of sodium lauryl sulphate as a silica dispersant. Buffer tablets were added to arrest the pH at 9.0 (to prevent any silica aggregation due to change in pH). The resultant hybrids were cast on Teflon sheets and dried in an oven at 50°C to drive out all the unbound water. Those films were then subjected to freese-thaw treatment continuously for 5 h. The freese-thawed films appeared opaque. The swelling-de swelling experiments with the hydrogels were carried out in distilled water at room temperature and consequently allowed to de-swell naturally. Those observations were correlated with the microstructures of the hybrid hydrogels.

A novel model for diffusion based release kinetics using an inverse numerical method

We developed and analyzed an inverse numerical model based on Fick's second law on the dynamics of drug release. In contrast to previous models which required two state descriptions of diffusion for long- and short-term release processes, our model is valid for the entire release process. The proposed model may be used for identifying and reducing experimental errors associated with measurements of diffusion based release kinetics. Knowing the initial and boundary conditions, and assuming Fick's second law to be appropriate, we use the methods of Lagrange multiplier along with least-square algorithms to define a cost function which is discretized using finite difference methods and is optimized so as to minimize errors. Our model can describe diffusion based release kinetics for static and dynamic conditions as accurately as finite element methods, but results are obtained in a fraction of CPU time. Our method can be widely used for drug release procedures and for tissue engineering/repair applications where oxygenation of cells residing within a matrix is important.

Design, characterization, and evaluation of meloxicam gel prepared by suspension and solution polymerization using solubility parameter as the basis for development

Meloxicam gel was designed based on the matching of the solubility parameter (delta) of the drug with that of the polymer and subsequently with skin for improved dermal delivery of meloxicam. The delta of meloxicam (11.48 (cal/cm(3))(0.5)) determined by solubility measurement was matched statistically to the solubility parameter of monomers, n-vinyl-2-pyrrolidone, polyvinyl alcohol (PVA), hydroxyl ethyl methacrylate, ethylene glycol methacrylate (EGMA) determined by intrinsic viscosity measurement. Consequently gels were formulated by polymerization in selected solvent blend of water/ethyl acetate (20:80) in which the drug showed maximum solubility. Thus, F1-F16 formulations designed were evaluated for physicochemical properties, textural analysis, and in vitro drug release. On the basis of optimum characteristics, F2 (PVA, delta = 16.96 (cal/cm(3))(0.5)) and F8 (EGMA, delta = 18.35 (cal/cm(3))(0.5)) formulated by suspension polymerization were selected and subjected to skin irritation and topical anti-inflammatory studies. The formulation F8 demonstrated significant (p < 0.05) of anti-inflammatory activity in comparison to marketed piroxicam gel and was free from irritation.

The use of novel organic gels and hydrogels in protein crystallization

The use of an organic solvent-based gel prepared from polyethylene oxide and a polyvinyl alcohol hydrogel for protein crystallization was investigated. The preparation, properties and application of the gels for protein crystallization are described, and the advantages and limitations of the approach are discussed. The gels are compared with agar, which is a popular aqueous gel used for protein crystallization. The growth behaviour and diffraction quality of crystals prepared in these gel media were evaluated for two model soluble proteins, thaumatin and lysozyme, and for two bacterial membrane proteins, TolC and AcrB.

Development and characterisation of an agar--polyvinyl alcohol blend hydrogel

Numerous authors have reported on hydrogel technologies providing products suitable for applications in biomedical, personal care as well as in nano-sensor applications. Hydrogels fabricated from single polymers have been extensively investigated. However, in many cases a single polymer alone cannot meet divergent demands in terms of both properties and performance. In this work, hydrogels were prepared by physically blending the natural polymer agar with polyvinyl alcohol in varying ratios to produce a new biosynthetic polymer applicable for a variety of purposes. Hydrogen bonding was observed to take place between the polyvinyl alcohol and the agar molecules in the composite materials leading to changes in the thermal, mechanical and swelling characteristics of the composite hydrogels. The composite hydrogels exhibited a slightly higher melting temperature than pure agar (116.81 degrees C). Irreversible compressive damage was found to occur at lower strain levels during compression testing of the dehydrated samples consisting of higher PVOH concentrations. Rheological analysis of hydrated sample revealed G' values of between 5000 and 10,000 Pa for the composite blends, with gels containing higher PVOH percentages exhibiting poorer mechanical strength.

Controlled release of insulin from PLGA nanoparticles embedded within PVA hydrogels

A simple and versatile delivery platform for peptide and protein based on physically cross-linked poly (vinyl alcohol) (PVA) hydrogels containing insulin-loaded poly (lactic-co-glycolic acid) (PLGA) nanoparticles was successfully fabricated. The particle morphology and size were characterized by SEM and laser light scattering method, respectively. Results showed that these particles had a mean diameter of 615 nm with a narrow size distribution and homogeneous particle production. The protein encapsulation efficiency was 72.6%. When insulin-loaded PLGA nanoparticles were administered intraperitoneally as a single dose (20 U/kg) to streptozotocin-induced diabetic mouse, blood glucose levels of these mice decreased and it could be sustained at such levels over 24 h. In vitro release further indicated that entrapment of the nanoparticles into the PVA hydrogels causes a reduction in both the release rate and the total amount of insulin released, which suggesting that PLGA nanoparticles entrapped into the PVA hydrogels showed more suitable controlled release kinetics for protein delivery.

Preparation of a novel freeze thawed poly(vinyl alcohol) composite hydrogel for drug delivery applications

We describe a drug delivery system based on a physically cross-linked poly(vinyl alcohol) (PVA) hydrogel for the release of Theophylline (TH). A composite was created by freezing an aqueous solution of PVA/NaOH onto a PVA/poly(acrylic acid) substrate. This formed a strong interface and demonstrated greater physical strength than the hydrogel alone. Such systems have potential for a variety of localised controlled drug delivery applications, for example, as coatings for implantable devices. Importantly, the results suggest that a versatile synthetic platform is possible that may provide different functional materials or combination of such. The resultant samples were characterised using optical microscopy, modulated differential scanning calorimetry (MDSC) and dissolution testing. The microstructure of the gels was examined using micro-thermal analysis (microTA) which is a combination of atomic force microscopy and thermal analysis. TH was found to have an effect on the crystalline structure and dissolution showed a Fickian release, suggesting that swelling and crystallinity were the controlling mechanisms.