Retention of trypsin activity in spermine alginate microcapsules

Studies on non-gelatinous & thermo-responsive chitosan with the N-isopropylacrylamide by RAFT methodology for control release of levofloxacin

The non-gelatinous and thermo-responsive properties were introduced in chitosan by incorporating the chain of poly(N-isopropylacrylamide) via reversible addition-fragmentation chain transfer (RAFT) polymerization. To achieve this, the reaction was carried out at 80 °C by modifying the chitosan(CS) with RAFT agent as a macroinitiator (CS-RAFT), where the amine group of CS was protected with phthalic anhydride and then reacted with 4-cyano-4-[(dodecyl sulfanyl thiocarbonyl)sulfanyl]-pentanoic acid (CDSTSP) to form CS-RAFT agent. Further, the addition of NIPAAm chains onto CS-RAFT was carried out in N,N'-dimethylformamide (DMF) solvent by using 2,2'-azobisisobutyronitrile (AIBN) as an initiator in N₂ atmosphere. The controlled addition of NIPAAm chains on to CS was confirmed by ¹H NMR spectroscopy, further, a kinetic study was performed to get the characteristic features of the RAFT reaction. The product was characterized by ¹H NMR, FT-IR, UV-Visible spectroscopy, XRD, SEM, and TGA analyses. The product in aqueous solution showed LCST at 2.0 mg/mL on 33 ± 0.1 °C. Further, beads were prepared with the sodium alginate and loaded the water-soluble levofloxacin drug (60% w/w loading was achieved). The drug delivery process was studied in-vitro at 37 ± 0.1 °C & pH 7.4, which shown controlled release of drug up to 32 h and it was 71% of the loaded levofloxacin.

Biocompatible Coatings from Smart Biopolymer Nanoparticles for Enzymatically Induced Drug Release

Nanoparticles can be used as a smart drug delivery system, when they release the drug only upon degradation by specific enzymes. A method to create such responsive materials is the formation of hydrogel nanoparticles, which have enzymatically degradable crosslinkers. Such hydrogel nanoparticles were prepared by ionotropic gelation sodium alginate with lysine-rich peptide sequences-either α-poly-L-lysine (PLL) or the aggrecanase-labile sequence KKKK-GRD-ARGSV↓NITEGE-DRG-KKKK. The nanoparticle suspensions obtained were analyzed by means of dynamic light scattering and nanoparticle tracking analysis. Degradation experiments carried out with the nanoparticles in suspension revealed enzyme-induced lability. Drugs present in the polymer solution during the ionotropic gelation can be encapsulated in the nanoparticles. Drug loading was investigated for interferon-β (IFN-β) as a model, using a bioluminescence assay with MX2Luc2 cells. The encapsulation efficiency for IFN-β was found to be approximately 25%. The nanoparticles suspension can be used to spray-coat titanium alloys (Ti-6Al-4V) as a common implant material. The coatings were proven by ellipsometry, reflection-absorption infrared spectroscopy, and X-ray photoelectron spectroscopy. An enzyme-responsive decrease in layer thickness is observed due to the degradation of the coatings. The Alg/peptide coatings were cytocompatible for human gingival fibroblasts (HGFIB), which was investigated by CellTiterBlue and lactate dehydrogenase (LDH) assay. However, HGFIBs showed poor adhesion and proliferation on the Alg/peptide coatings, but these could be improved by modification of the alginate with a RGD-peptide sequence. The smart drug release system presented can be further tailored to have the right release kinetics and cell adhesion properties.

Polymeric nanoparticles and microparticles for the delivery of peptides, biologics, and soluble therapeutics

Biologically derived therapeutics, or biologics, are the most rapidly growing segment of the pharmaceutical marketplace. However, there are still unmet needs in improving the delivery of biologics. Injectable polymeric nanoparticles and microparticles capable of releasing proteins and peptides over time periods as long as weeks or months have been a major focus in the effort to decrease the frequency of administration. These particle systems fit broadly into two categories: those composed of hydrophilic and those composed of hydrophobic polymeric scaffolds. Here we review the factors that contribute to the slow and controlled release from each class of particle, as well as the effects of synthesis parameters and product design on the loading, encapsulation efficiency, biologic integrity, and release profile. Generally, hydrophilic scaffolds are ideal for large proteins while hydrophobic scaffolds are more appropriate for smaller biologics without secondary structure. Here we also introduce a Flash NanoPrecipitation method that has been adopted for encapsulating biologics in nanoparticles (40-200nm) at high loadings (50-75wt.%) and high encapsulation efficiencies. The hydrophilic gel interior and hydrophobic shell provide an opportunity to combine the best of both classes of injectable polymeric depots.

Effects of preparative parameters on the properties of chitosan hydrogel beads containing Candida rugosa lipase

The influences of the pH, tripolyphosphate (TPP) concentration, and ionic strength of the gelling medium on the entrapment efficiency, release, and activity of lipase in chitosan hydrogel beads were studied. A solution of Candida rugosa lipase was prepared in a 1.5% w/v chitosan and 1% (v/v) acetic acid medium, and dropped into a TPP solution. Release of lipase in pH 7.2 Tris buffer was monitored over 36 h using the micro BCA protein assay. The activity of the entrapped enzyme was assayed using the Sigma lipase activity method. Following preliminary studies, an experimental design was followed to develop mathematical models that describe bead characteristics as functions of the pH and the TPP concentration in the gelling medium. The pH and the TPP concentration each had an effect on the entrapment, retention, and activity of lipase. Entrapped lipase retained a high degree of activity in multiple reactions. The ionic strength, in the range studied, exerted a minimal effect on bead characteristics. Statistical analysis allowed optimization within the factor space with respect to maximizing the enzyme entrapment efficiency and activity, and also minimizing the amount released after 36 h in the Tris buffer.

Alginate in drug delivery systems

Alginates are established among the most versatile biopolymers, used in a wide range of applications. The conventional use of alginate as an excipient in drug products generally depends on the thickening, gel-forming, and stabilizing properties. A need for prolonged and better control of drug administration has increased the demand for tailor-made polymers. Hydrocolloids like alginate can play a significant role in the design of a controlled-release product. At low pH hydration of alginic acid leads to the formation of a high-viscosity "acid gel." Alginate is also easily gelled in the presence of a divalent cation as the calcium ion. Dried sodium alginate beads reswell, creating a diffusion barrier decreasing the migration of small molecules (e.g., drugs). The ability of alginate to form two types of gel dependent on pH, i.e., an acid gel and an ionotropic gel, gives the polymer unique properties compared to neutral macromolecules. The molecule can be tailor-made for a number of applications. So far more than 200 different alginate grades and a number of alginate salts are manufactured. The potential use of the various qualities as pharmaceutical excipients has not been evaluated fully, but alginate is likely to make an important contribution in the development of polymeric delivery systems. This natural polymer is adopted by Ph.Eur. It can be obtained in an ultrapure form suitable for implants. This review discusses the present use and future possibilities of alginate as a tool in drug formulation.

Water-based microsphere delivery system for proteins

This paper describes formulation of a model protein, horseradish peroxidase (HRP), in a water based microcapsule delivery system and demonstrates the utility of this delivery system for proteins. Aqueous solutions (1 mg/mL) of the enzyme were separately blended with aqueous solutions of the neutral sodium salt of the anionic polymer iota carrageenan (0.6 mM in repeat unit). These blends were instilled as uniform microdroplets into aqueous solutions of a series of eleven mono-, di-, or oligo-amines (as neutral hydrochloride or acetate salts). Essentially instantaneous salt exchange interaction of the sodium salt of anionic polymer with amine hydrochloride resulted in formation of microparticles of amine/polymer complex. The enzyme was captured in the resulting capsules. The particles were washed by repeated centrifugation and resuspension in water and their particle size distribution was determined. HRP in washed pelleted microspheres was analyzed for fragmentation/aggregation by SDS-PAGE and size exclusion chromatography, for unfolding by fluorescence spectroscopy, and for specific enzymatic activity, capture efficiency and release studies by absorbance spectroscopy. Dependent on amine employed, capture efficiencies ranged from 1 to 72%. Encapsulation produced no adverse effect on protein size as no molecular fragments or aggregates were visible below or above 44 kDa. The tryptophan fluorescence spectrum of the protein did not change after encapsulation indicating no conformational change in tertiary structure. There was an apparent substrate diffusion related reduction in activity of encapsulated HRP, but almost 100% of activity was recovered on lysis of the capsules. It is concluded that water based charged film encapsulation used as a drug delivery system for proteins does not alter structural conformation or specific activity of the model protein tested and provides protein release at a constant rate.

Amine composition influences apparent activity of enzyme in charged film microcapsules

It has been shown that, when captured in charged film microcapsules prepared from spermine alginate, intact viruses retain infectivity, isolated viral proteins retain immunogenicity, and trypsin retains enzymatic activity. However, it was unclear whether the greater anionic strength of hemisulfate residues such as those in carrageenan might alter protein conformation and activity unfavourably in comparison with the lesser influence of alginate carboxylates. Further, the influence of the structure of the amine used to prepare the capsules was largely unknown. To examine these questions, trypsin, used as a model protein, was encased in microcapsules prepared from iota-carrageenan and oligoamines drawn from either the homologous series spermine, spermidine, putrescine or ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine. The gross structures of encapsulated and native trypsin were compared by denaturing electrophoresis and their enzymatic activity by the method of Hummel. In all encapsulations SDS PAGE gave no evidence of alteration of protein structure. When encapsulated, the apparent activity of trypsin was reduced by about 60 to 75%, but when the capsules were lysed in hypertonic saline activity was restored. This apparent reduction in activity is attributed to the diffusional barrier imposed by the encapsulating membrane but it should be recognized that it may be the result of reversible denaturation.