Polysaccharide hydrogels for protein drug delivery

Thermophilic Exopolysaccharide Films: A Potential Device for Local Antibiotic Delivery

Natural polysaccharides being investigated for use in the field of drug delivery commonly require the addition of sugars or pretreated biomass for fabrication. Geobacillus sp. strain WSUCF1 is a thermophile capable of secreting natural polymers, termed exopolysaccharides (EPSs), cultivated from cost-effective, non-treated lignocellulosic biomass carbon substrates. This preliminary investigation explores the capabilities of a 5% wt/wt amikacin-loaded film constructed from the crude EPS extracted from the strain WSUCF1. Film samples were seen to be non-cytotoxic to human keratinocytes and human skin-tissue fibroblasts, maintaining cell viability, on average, above 85% for keratinocytes over 72-h during a cell viability assay. The drug release profile of a whole film sample revealed a steady release of the antibiotic up to 12 h. The amikacin eluted by the EPS film was seen to be active against Staphylococcus aureus, maintaining above a 91% growth inhibition over a period of 48 h. Overall, this study demonstrates that a 5% amikacin-EPS film, grown from lignocellulosic biomass, can be a viable option for preventing or combating infections in clinical treatment.

Dextran-polylactide micelles loaded with doxorubicin and DiR for image-guided chemo-photothermal tumor therapy

Image-guided chemo-photothermal therapy based on near-infrared (NIR) theranostic agents has found promising applications in treating tumors. In this multimodal treatment, it is of critical importance to image real-time distribution of photothermal agents in vivo and to monitor therapeutic outcomes for implementing personalized treatment. In this study, an optimally synthesized dextran-polylactide (DEX-PLA) copolymer was assembled with doxorubicin (DOX) and DiR, a kind of NIR dye, to construct desirable micelles ((DiR + DOX)/DEX-PLA) for performing image-guided chemo-photothermal therapy. These (DiR + DOX)/DEX-PLA micelles had good physical and photothermal stability in aqueous media and showed high photothermal efficiency in vivo. Based on the H22-tumor-bearing mouse model, (DiR + DOX)/DEX-PLA micelles were found to accumulate inside tumors sustainably and to emit strong fluorescence signals for more than three days. The (DiR + DOX)@DEX-PLA micelles together with NIR laser irradiation were able to highly inhibit tumor growth or even eradicate tumors with one injection and two dose-designated 5-minute laser irradiations at the tumor site during 14 days of treatment. Furthermore, they showed almost no impairment to the body of the treated mice. These (DiR + DOX)@DEX-PLA micelles have confirmative translational potential in clinical tumor therapy on account of their persistent image-guided capacity, high antitumor efficacy and good in vivo safety.

Recent Progress on Polysaccharide-Based Hydrogels for Controlled Delivery of Therapeutic Biomolecules

A plethora of applications using polysaccharides have been developed in recent years due to their availability as well as their frequent nontoxicity and biodegradability. These polymers are usually obtained from renewable sources or are byproducts of industrial processes, thus, their use is collaborative in waste management and shows promise for an enhanced sustainable circular economy. Regarding the development of novel delivery systems for biotherapeutics, the potential of polysaccharides is attractive for the previously mentioned properties and also for the possibility of chemical modification of their structures, their ability to form matrixes of diverse architectures and mechanical properties, as well as for their ability to maintain bioactivity following incorporation of the biomolecules into the matrix. Biotherapeutics, such as proteins, growth factors, gene vectors, enzymes, hormones, DNA/RNA, and antibodies are currently in use as major therapeutics in a wide range of pathologies. In the present review, we summarize recent progress in the development of polysaccharide-based hydrogels of diverse nature, alone or in combination with other polymers or drug delivery systems, which have been implemented in the delivery of biotherapeutics in the pharmaceutical and biomedical fields.

Facile fabrication of hyaluronated starch nanogels for efficient docetaxel delivery

In this study, we designed and synthesized polysaccharidic nanogels comprising starch cross-linked with hyaluronic acid. These hyaluronated starch nanogels were prepared by cross-linking primary hydroxyl groups in polysaccharides (starch and hyaluronic acid) and epoxide groups in 1,4-butanediol diglycidyl ether (used as a cross-linking agent). The nanogels take advantage of hyaluronic acid as a specific ligand for CD44 receptors overexpressed on tumors and the hyaluronic acid/starch core as a compartment for the encapsulation of docetaxel (as model antitumor drug). Here, hyaluronic acid can be enzymatically degraded by tumor cell–specific enzyme (e.g. hyaluronidase-1), which could significantly accelerate docetaxel release from the nanogels. Our experimental results demonstrate that the nanogels promote the release of docetaxel content in the presence of hyaluronidase-1 enzyme. As a result, the nanogels selectively inhibited MCF-7 (with CD44 receptor and hyaluronidase-1 enzyme) tumor cell growth in vitro, suggesting their therapeutic potential for efficient tumor ablation.

Cellulose-based hydrogel materials: chemistry, properties and their prospective applications

Hydrogels based on cellulose comprising many organic biopolymers including cellulose, chitin, and chitosan are the hydrophilic material, which can absorb and retain a huge proportion of water in the interstitial sites of their structures. These polymers feature many amazing properties such as responsiveness to pH, time, temperature, chemical species and biological conditions besides a very high-water absorption capacity. Biopolymer hydrogels can be manipulated and crafted for numerous applications leading to a tremendous boom in research during recent times in scientific communities. With the growing environmental concerns and an emergent demand, researchers throughout the globe are concentrating particularly on naturally derived hydrogels due to their biocompatibility, biodegradability and abundance. Cellulose-based hydrogels are considered as useful biocompatible materials to be used in medical devices to treat, augment or replace any tissue, organ, or help function of the body. These hydrogels also hold a great promise for applications in agricultural activity, as smart materials and some other useful industrial purposes. This review offers an overview of the recent and contemporary research regarding physiochemical properties of cellulose-based hydrogels along with their applications in multidisciplinary areas including biomedical fields such as drug delivery, tissue engineering and wound healing, healthcare and hygienic products as well as in agriculture, textiles and industrial applications as smart materials.

Characterization of Cassava Fibre for Potential Wound Dressing Application

Wound dressing is the application of a sterile pad to protect a wound from further harm and promote healing. Over the past decades, various materials including calcium alginate, hydrogel, hydrocolloid and gauze based wound dressing materials have been developed. Unfortunately, shortcomings such as potential allergic reaction, high cost, short shelf life and scarcity have been associated with their use. In developing countries such as Ghana, sterilized gauze is commonly used in wound dressing but it causes scar formation and traumatic pain during removal. In addressing the issues of cost and availability, there may be local materials like cassava (Manihot esculenta) with the ability to aid in wound healing. Cassava is a cheap staple crop grown in Africa which is rich in carbohydrate, fibre and minerals. This research characterized three genotypes of cassava (IITA-TMS-GAEC-160006 (IT6), IITA-TMS-GAEC-160004 (IT4) and Afisiafi (Afi)). These genotypes have been studied in terms of their fibre content, fluid absorption capacity, hemolytic ability and their ability to promote rapid blood coagulation (coagulation time). Fibre samples were soaked in deionized (DI) water and PBS (Phosphate buffered saline) and at different time intervals the swollen samples were weighed. Fibre samples were also brought into contact with human blood and toxicity of samples determined. The results reveal that the rate of absorption of fluid by fibres in both DI water and PBS ranges between 0.66-0.93 g/min and fibres are generally non-toxic to blood cells. The fibre properties were compared with gauze and from these, some genotypes of cassava fibre were recommended for further research towards the design of a wound dressing material.

Synthesis and optimization of a novel polymeric micelle based on hyaluronic acid and phospholipids for delivery of paclitaxel, in vitro and in-vivo evaluation

Novel polymeric micelles were synthesized based on hyaluronic acid (HA) and phospholipids (PEs) including 1,2-dimiristoyl phosphatidylethanolamine (DMPE) and 1,2-distearoyl phosphatidylethanolamine (DSPE). The newly developed micelles evaluated for the physicochemical properties including structural analysis by means of FTIR. Micelles were optimized for delivery of paclitaxel (PTX). The D-optimal design was applied in order to reach micelles with high entrapment efficiency (EE %) and minimum size, simultaneously. In this design the independent variables were the co-polymer type, the drug to polymer ratio and the formulation temperature, whereas the dependent variables were EE% and micelle size. The EE% of the optimized micelles was 46.8% and 59.9% for HA-DMPE and HA-DSPE micelles, respectively. The size of the optimized micelles was in the range of around 250 nm. In vitro release study of the optimized micelles showed that PTX was released from HA-DMPE and HA-DSPE micelles as long as 23 h and 34 h, respectively. Differential scanning calorimetry (DSC) studies showed a conversion of the crystalline PTX molecules into the amorphous form in the micelles. In vivo real time image analysis showed that micellar system was mostly accumulated in the liver, spleen and heart. Accelerated stability studies represented that PTX loaded micelle formulations were stable both physically and chemically at least in 6 months' time.

Injectable biodegradable hydrogels: progress and challenges

Over the past decades, injectable hydrogels have emerged as promising biomaterials because of their biocompatibility, excellent permeability, minimal invasion, and easy integration into surgical procedures. These systems provide an effective and convenient way to administer a wide variety of bioactive agents such as proteins, genes, and even living cells. Additionally, they can be designed to be degradable and eventually cleared from the body after completing their missions. Given their unique characteristics, injectable biodegradable hydrogels have been actively explored as drug reservoir systems for sustained release of bioactive agents and temporary extracellular matrices for tissue engineering. This review provides an overview of state-of-the-art strategies towards constructing a rational design of injectable biodegradable hydrogels for protein drug delivery and tissue engineering. We also discuss the use of injectable hydrogels for gene delivery systems and biomedical adhesives.

Polysaccharide-based micelles for drug delivery

Delivery of hydrophobic molecules and proteins has been an issue due to poor bioavailability following administration. Thus, micelle carrier systems are being investigated to improve drug solubility and stability. Due to problems with toxicity and immunogenicity, natural polysaccharides are being explored as substitutes for synthetic polymers in the development of new micelle systems. By grafting hydrophobic moieties to the polysaccharide backbone, self-assembled micelles can be readily formed in aqueous solution. Many polysaccharides also possess inherent bioactivity that can facilitate mucoadhesion, enhanced targeting of specific tissues, and a reduction in the inflammatory response. Furthermore, the hydrophilic nature of some polysaccharides can be exploited to enhance circulatory stability. This review will highlight the advantages of polysaccharide use in the development of drug delivery systems and will provide an overview of the polysaccharide-based micelles that have been developed to date.

Self-assembled DNA-based giant thrombin nanoparticles for controlled release

Protein-aptamer interactions have been used in a wide range of fields, including medical diagnosis and protein delivery. Herein, we report a method for thrombin delivery with thrombin-binding aptamer (TBA), which is one of the well-known aptamers for thrombin, by generating giant thrombin nanoparticles (GTNPs). GTNPs can be synthesized by crosslinking thrombin with DNA nanostructures that possess several TBA molecules. To generate GTNPs, two different DNA nanostructures were used. Y-shaped DNA with TBA and X-shaped DNA with TBA were used for 250 and 650 nm GTNPs, respectively. Controlled release of thrombin from GTNPs was performed by adding complementary DNA (cDNA) to TBA. To investigate thrombin release from GTNPs, the sizes of the GTNPs were measured using dynamic light scattering, atomic force microscopy (AFM), and scanning electron microscopy (SEM). We confirmed a decrease in the size of GTNPs with various concentrations of cDNA, suggesting the release of thrombin. Based on these results, we expect that our method can be used to control the amount of thrombin released effectively. Our method is also widely applicable for effective protein delivery.

Materials for diabetes therapeutics

This review is focused on the materials and methods used to fabricate closed-loop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies-(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and be permeable to small molecules and proteins, such as insulin. Several polymers and fabrication methods of artificial pancreases are discussed: microencapsulation, conformal coatings, and planar sheets. We also review the two components of a completely synthetic pancreas. Several types of glucose sensing systems (including materials used for electrochemical, optical, and chemical sensing platforms) are discussed, in addition to various polymer-based release systems (including ethylene-vinyl acetate, polyanhydrides, and phenylboronic acid containing hydrogels).

Concanavalin A immobilized poly(ethylene glycol dimethacrylate) based affinity cryogel matrix and usability of invertase immobilization

Concanavalin A (Con A) immobilized supermacroporous poly(ethylene glycol dimethacrylate) [poly(EGDMA)] monolithic cryogel column was prepared by radical cryocopolymerization of EGDMA as a monomer and N,N'-methylene-bisacrylamide as a crosslinker. Bioligand Con A was then immobilized by covalent binding onto poly(EGDMA) cryogel via glutaraldehyde activation [Con A-poly(EGDMA)]. Con A-poly(EGDMA) cryogel was characterized by swelling studies and scanning electron microscopy. The monolithic cryogel contained a continuous polymeric matrix having interconnected pores of 10-50 μm size. The equilibrium swelling degree of the cryogel was 15.01 g H₂O/g dry cryogel. Con A-poly(EGDMA) cryogel was used in the adsorption/desorption of invertase from aqueous solutions. The maximum amount of invertase adsorption from aqueous solution in acetate buffer was 55.45 mg/g polymer at pH 5.0. Con A-poly(EGDMA) cryogels were used for repetitive adsorption/desorption of invertase without noticeable loss in invertase adsorption capacity after 10 cycles.

Manipulation of Polyhydroxybutyrate Properties through Blending with Ethyl-Cellulose for a Composite Biomaterial

Polyhydroxybutyrate (PHB) is widely used as a biomaterial in medical and tissue-engineering applications, a relatively high crystallinity limits its application. Blending PHB with ethyl-cellulose (EtC) was readily achieved to reduce PHB crystallinity and promote its degradation under physiological conditions without undue influence on biocompatibility. Material strength of composite films remained unchanged at 6.5±0.6 MPa with 40% (w/w) EtC loadings. Phase separation between the two biopolymers was determined with PHB crystallinity decreasing from 63% to 47% for films with the same loading. This reduction in crystallinity supported an increase in the degradation rates of composite films from 0.39 to 0.81% wk−1for PHB and its composite, respectively. No significant change in morphology and proliferation of olfactory ensheathing cells were observed with the composites despite significant increases in average surface roughness (Ra) of the films from 2.90 to 3.65 μm for PHB and blends with 80% (w/w) EtC, respectively.

Human growth hormone expressed in tobacco cells as an arabinogalactan-protein fusion glycoprotein has a prolonged serum life

Therapeutic proteins with molecular weights lower than 40 kDa often have short serum half-lives due to their susceptibility to serum proteases and rapid renal clearance. Chemical derivatization, such as PEGylation, or expression as serum albumin fusions increases molecular mass and overcome these problems but at the expense of decreased bioactivity. Here we applied a new method that yields biologically potent recombinant human growth hormone (rhGH) with increased serum half-life when expressed as an arabinogalactan-protein (AGP) in tobacco BY-2 cells. Thus, rhGH was expressed with 10 repeats of the AGP glycomodule Ser-Hyp (SO) at the C-terminus (rhGH-(SO)(10)). We also expressed rhGH as an AGP-enhanced green fluorescent protein (EGFP) fusion, designated rhGH-(SO)(10)-EGFP, to assess the cellular distribution of the glycoprotein, which was mainly extracellular. Recombinant hGH-(SO)(10) bound the hGH receptor with an affinity similar to that of a rhGH standard, stimulated the same intracellular signaling pathway as hGH, but possessed an in vivo serum half-life more than sixfold that of the hGH control. Furthermore, rhGH-(SO)(10) gave a 500 fold greater secreted yield than the non-glycosylated control rhGH that was also targeted for secretion. Detailed analysis of the rhGH-(SO)(10) glycans indicated a conserved structure with relatively little microheterogeneity and an average size of 25 monosaccharide residues. These results were consistent with earlier work expressing interferon alpha 2b as an AGP chimera and further demonstrate the feasibility of this approach to the production of long-acting, biologically potent therapeutic proteins by plant cells.

Impregnation of tubular self-assemblies into dextran hydrogels

Amine groups are the building units of proteins. The incorporation of amine groups into polyethylene glycol diacrylate (PEGDA) hydrogel through dextran-allyl isocyanate-ethylamine (Dex-AE) enhances sustained protein release by introducing effective interactions. To investigate such an interaction effect and to improve protein release, we impregnated self-assembled tubular structures from dextran-bromoethylamine (Dex-BH) and dextran-chloroacetic acid (Dex-CA) into Dex-AE/PEGDA hydrogel. The morphology data obtained from scanning electron microscopy (SEM) reveal that pure PEGDA hydrogel had no effect on the distribution of the self-assembled tubules; the introduction of Dex-AE brought about the dispersion of these tubules, and an increase in Dex-AE content led to more evenly distributed structures. Moreover, the implantation of the self-assembled tubules had no distinct effect on the swelling capacity of the hybrid self-assembly embedded hydrogels. The in vitro albumin release study was carried out in a pH 7.4 buffer solution; the results show that the implantation of the self-assembly into the hydrogels reduced the burst release and prolonged the protein release time. These findings demonstrate that the impregnation of tubular self-assembly into hydrogel makes the hybrid hydrogel an excellent protein delivery system.

Effects of precursor and cross-linking parameters on the properties of dextran-allyl isocyanate-ethylamine/poly(ethylene glycol diacrylate) biodegradable hydrogels and their release of ovalbumin

In this paper, we studied the effects of molecular weight of poly(ethylene glycol diacrylate) (PEGDA) precursor, the degree of substitution (DS) of both allyl isocyanate (AI) and amine groups in dextran-based precursor (Dex-AE), and photoinitiator concentration on Dex-AE/PEGDA hydrogel formation and its ovalbumin (OVA) release. FT-IR spectra showed chemical bond interaction between amine and urethane groups of the hydrogel carriers with OVA. The increase in PEGDA molecular weight led to a faster OVA release because of a more open gel network structure. The study on the DS of AI in Dex-AE precursor showed that an increase in AI did not result in a prominent gel network structure difference. However, the urethane groups in Dex-AE precursor showed some interactions with OVA and, thus, resulted in a slower release rate. The incorporation of amine group into Dex-AE precursor did not affect the gel network structure, but reduced the OVA release rate, and the level of reduction increased with an increasing amine group substitution into the Dex-AE precursor. This reduction could be attributed to the interaction between the amine groups in the gel carrier and OVA. An increase in the photoinitiator concentration showed no effect on the gel network structure or OVA release.

Effects of sterilization on poly(ethylene glycol) hydrogels

The past few decades have witnessed a dramatic increase in the development of polymeric biomaterials. These biomaterials have to undergo a sterilization procedure before implantation. However, many sterilization procedures have been shown to profoundly affect polymer properties. Poly(ethylene glycol) hydrogels have gained increasing importance in the controlled delivery of therapeutics and in tissue engineering. We evaluated the effect of ethylene oxide (EtO), hydrogen peroxide (H(2)O(2)), and gamma sterilization of poly(ethylene glycol) hydrogels on properties relevant to controlled drug delivery and tissue engineering. We observed that the release of cyclosporine (CyA) (an immunosuppressive drug that is effective in combating tissue rejection following organ transplantation) was significantly affected by the type of sterilization. However, that was not the case with rhodamine B, a dye. Hence, the drug release characteristics were observed to be dependent not only on the sterilization procedure but also on the type of agent that needs to be delivered. In addition, differences in the swelling ratios for the sterilized and unsterilized hydrogels were statistically significant for 1:1 crosslinked hydrogels derived from the 8000 MW polymer. Significant differences were also observed for gamma sterilization for 1:1 crosslinked hydrogels derived from the 3350 MW polymer and also the 2:1 crosslinked hydrogels derived from the 8000 MW polymer. Atomic force microscopy (AFM) studies revealed that the roughness parameter for the unsterilized and EtO-sterilized PEG hydrogels remained similar. However, a statistically significant reduction of the roughness parameter was observed for the H(2)O(2) and gamma-sterilized samples. Electron spin resonance (ESR) studies on the unsterilized and the sterilized samples revealed the presence of the peroxy and the triphenyl methyl carbon radical in the samples. The gamma and the H(2)O(2)-sterilized samples were observed to have a much higher concentration of the radical pecies when compared with the EtO and the unsterilized samples.

New Polysaccharide-based Microparticles Crosslinked with Siloxane: Interactions with Biologically Active Substances

The interaction of microparticles of carboxymethyl pullulan crosslinked with siloxane (provided by a new crosslinking agent: 3-(glycid oxypropyl) trimethoxysilane) with biologically active molecules, such as enzymes (lysozyme) and drugs (propranolol, quinidine) was studied. The anionic amphiphilic supports retained through electrostatic and/or hydrophobic forces, variable amounts of the substances as a function of their structure, such as crosslinking degree and amount of uncrosslinked alkylsilane chains. The absorption of lysozyme on the supports followed the Langmuir isotherm, which allowed the calculation of constants k1 and k2. Both retention and in vitro release behavior of these support potential applications in controlled drug release as well as immobilization and purification of enzymes.

Peptide- and protein-mediated assembly of heparinized hydrogels

Polymeric hydrogels have demonstrated significant promise in biomedical applications such as drug delivery and tissue engineering. A continued direction in hydrogel development includes the engineering of the biological responsiveness of these materials, via the inclusion of cell-binding domains and enzyme-sensitive domains. Ligand-receptor interactions offer additional opportunities in the design of responsive hydrogels, and strategies employing protein- polysaccharide interactions as a target may have unique relevance to materials intended to mimic the extracellular matrix (ECM). Accordingly, we have developed approaches for producing hydrogels via noncovalent interactions between heparin and heparin-binding peptides/proteins, and have demonstrated that such matrices are capable of both passive and receptor-mediated growth factor delivery. Further modification of these materials via the integration of these noncovalent strategies with chemical crosslinking methods will expand the range of their potential use and is under exploration. The combination of these approaches offers broad opportunities for the production of responsive matrices for biomedical applications.

Heparin-mimetic sulfated peptides with modulated affinities for heparin-binding peptides and growth factors

Heterogeneity in the composition and in the polydispersity of heparin has motivated the development of homogeneous heparin mimics, and peptides of appropriate sequence and chemical function have therefore recently emerged as potential replacements for heparin in selected applications. Here, we report the assessment of the binding affinities of multiple sulfated peptides (SPs) for a set of heparin-binding peptides (HBPs) and for vascular endothelial growth factor isoform 165 (VEGF165); these binding partners have application in the selective immobilization of proteins and in hydrogel formation through non-covalent interactions. Sulfated peptides were produced via solid-phase methods, and their affinity for the HBPs and VEGF165 was assessed via affinity liquid chromatography (ALC), surface plasmon resonance (SPR), and in selected cases, isothermal titration calorimetry (ITC). The shortest peptide, SP(a), showed the highest affinity binding of HBPs and VEGF165 in both ALC and SPR measurements, with slight exceptions. Of the investigated HBPs, a peptide based on the heparin-binding domain of human platelet factor 4 showed greatest binding affinities toward all of the SPs, consistent with its stronger binding to heparin. The affinity between SP(a) and PF4(ZIP) was indicated via SPR (K(D)=5.27 microM) and confirmed via ITC (K(D)=8.09 microM). The binding by SP(a) of both VEGF and HBPs suggests its use as a binding partner to multiple species, and the use of these interactions in assembly of materials. Given that the peptide sequences can be varied to control binding affinity and selectivity, opportunities are also suggested for the production of a wider array of matrices with selective binding and release properties useful for biomaterials applications.

Macroporous gels prepared at subzero temperatures as novel materials for chromatography of particulate-containing fluids and cell culture applications

Macroporous gels (MGs) with a broad variety of morphologies are prepared using the cryotropic gelation technique, i. e. gelation at subzero temperatures. These highly elastic hydrophilic materials can be produced from practically any gel-forming system with a broad range of porosity extending from elastic and porous gels with pore sizes up to 1.0 microm to elastic and sponge-like gels with pore sizes up to 100 microm. The versatility of the cryogelation technique is demonstrated by use of different chemical reactions (hydrogen bond formation, chemical cross-linking of polymers, free radical polymerization) mainly in an aqueous medium. Appropriate control over solvent crystallization (formation of solvent crystals) and rate of chemical reaction during the cryogelation allows the reproducible preparation of cryogels with tailored properties. Different approaches, such as chemical modification of reactive groups, grafting of the pore surface with an appropriate polymer, or direct copolymerization with functional monomers are used for control of the surface chemistry of MGs. Typically, MGs with pore sizes up to 1.0 microm are produced in the shape of beads and MGs with pore size up to 100 microm are prepared as monoliths, discs, and sheets. The difference in porous structure of MGs defines the main applications of these porous materials. Elastic beaded MGs are mostly used as carriers for cell and enzyme immobilization or for capture of low-molecular weight targets from particulate-containing fluids in expanded-bed mode. However, the elastic and sponge-like MG monoliths with interconnected pores measuring hundreds of mum have been successfully used as monolithic columns for chromatography of particulate-containing fluids (crude cell homogenates, viruses, whole cells, wastewater effluents) and as three-dimensional scaffolds for mammalian cell culture applications.

Encapsulation of crosslinked subtilisin microcrystals in hydrogel beads for controlled release applications

Enzymes are less stable in harsh conditions and hence to overcome this nature, several methodologies are being developed. It was found that crosslinked enzyme crystals are the most promising strategy for the stabilization of the enzymes [Emilia Abraham, T., Jegan Roy, J., Bindhu, L.V., Jayakumar, K.K., 2004. Crosslinked enzyme crystals of glucoamylase as a potent catalyst for biotransformations. Carbohydr. Res. 339, 1099-1104; Navia, M., St. Clair, N., 1997. Crosslinked enzyme crystals. Biosens. Bioelectron. 12, 7]. A cost effective methodology of crystallization of protease (Bacillus subtilis) with ammonium sulphate (65%, w/v) and then crosslinking the crystals with glutaraldehyde (4%, v/v) in isopropanol for 20min gave a stable and active enzyme. SEM studies showed that the protease is in small cubic shaped crystals of 1-2 microm size. Crosslinked enzyme crystal (CLEC) of protease has good stability in polar and nonpolar organic solvents, such as hexane, toluene, benzene and carbon tetrachloride and it had high thermal stability up to 60 degrees C and hence can be used as a catalyst for the biotransformation of compounds which are not soluble in aqueous medium. The CLECs were entrapped in the alginate:guar gum (3:1) composite beads which were resistant to low pH conditions in the stomach and hence was found to be useful for the oral drug delivery. This method can be used to deliver the protein and peptide drugs which require high concentrations at the delivery stage, and which normally degrades in the stomach before reaching the jejunum. Application of these pH-sensitive beads for the controlled release of subtilisin in in vitro was studied and found to be a viable strategy.