Fourier transform infrared spectroscopic studies of human serum albumin microcapsules prepared by interfacial cross-linking with terephthaloylchloride: influence of polycondensation pH on spectra and relation with microcapsule morphology and size

Study of the interfacial viscoelasticity of human serum albumin microcapsules using a viscoelasto-electrohydrodynamic technique

Crosslinked proteins are widely used as the encapsulating membranes in microcapsules for many biomedical and food industries. The interfacial rheological properties of these capsules are due to the complex microstructure of cross-linked globular proteins owing to structural changes at quaternary, tertiary and secondary levels. These changes in structure can be induced by high protein concentration, hydrophobic-hydrophillic interfaces, and pH. In this work, the interfacial viscoelastic rheological properties of human serum albumin (HSA) microcapsules are estimated using a novel electrodeformation technique exhibiting creep and oscillatory responses. Insights into the microstructure-rheology relationship are obtained using FTIR and SEM studies. The results show a complex dependence of the interfacial properties on the size, concentration and pH of the capsules. An interplay of inter-molecular interactions, adsorption and multilayer formation, accessibility to reactive functional groups, and dependence on the relative content of alpha helix, beta sheet and beta turn is observed. The interfacial rheological properties are estimated using the Burger model and creep is found to sensitively affect the rheological properties due to irreversible changes in microstructure. Furthermore, the electrodeformation technique allows analysis of interfacial rheology at high frequencies, 10 Hz to 1 kHz, which is otherwise not easily possible with conventional rheometers.

Microencapsulation for the Therapeutic Delivery of Drugs, Live Mammalian and Bacterial Cells, and Other Biopharmaceutics: Current Status and Future Directions

Microencapsulation is a technology that has shown significant promise in biotherapeutics, and other applications. It has been proven useful in the immobilization of drugs, live mammalian and bacterial cells and other cells, and other biopharmaceutics molecules, as it can provide material structuration, protection of the enclosed product, and controlled release of the encapsulated contents, all of which can ensure efficient and safe therapeutic effects. This paper is a comprehensive review of microencapsulation and its latest developments in the field. It provides a comprehensive overview of the technology and primary goals of microencapsulation and discusses various processes and techniques involved in microencapsulation including physical, chemical, physicochemical, and other methods involved. It also summarizes the state-of-the-art successes of microencapsulation, specifically with regard to the encapsulation of microorganisms, mammalian cells, drugs, and other biopharmaceutics in various diseases. The limitations and future directions of microencapsulation technologies are also discussed.

Coating alginate microspheres with a serum albumin-alginate membrane: application to the encapsulation of a peptide

Calcium alginate gel microspheres coated with a human serum albumin (HSA)-alginate membrane were prepared adapting a transacylation method previously applied to large beads. The procedure involved emulsification of an aqueous solution of sodium alginate and propylene glycol alginate (PGA) in an oily phase, followed by addition of CaCl(2). The resulting gel microspheres were transferred in an aqueous solution of HSA. The addition of 0.5 M NaOH started the reaction between PGA and HSA, producing amide bonds and forming a membrane around the particles. An optimization study was conducted, notably exploring the addition of HSA to the internal phase. The microcapsules were studied with respect to morphology (optical and scanning electron microscopy) and size (laser granulometry), in comparison with uncoated gel microspheres. Biocompatibility was checked in osteoblast cultures. Lysine-arginine-phenylalanine-lysine (KRFK) was encapsulated and the release kinetics was studied in vitro. The method provided stable microspheres (size around 60 microm), with a membrane surviving a treatment with citrate and resisting lyophilization. The microcapsules were shown biocompatible. The release of KRFK was slower (release time>8 days) than that of uncoated microspheres. These microcapsules might be useful as peptide containers to be combined with prosthetic materials for improving osteointegration.

Fourier transform infrared spectroscopic studies of cross-linked human serum albumin microcapsules. 3. Influence of terephthaloyl chloride concentration on spectra and correlation with microcapsule morphology and size

Microcapsules were prepared from human serum albumin (HSA) by interfacial cross-linking with terephthaloyl chloride (TC). TC concentrations were increased from 0.5 to 5% w/v, while pH (9.8) and reaction time (30 min) were kept constant. Fourier transform infrared (FT-IR) spectra of lyophilized microcapsules were compared. Correlations were established with microcapsule morphology and size. The results were compared with those of previous studies exploring pH or reaction time and with those of parallel determinations of microcapsule free amino groups. With 0.5% TC, decreases of the ester-assigned 1724-cm-1 band area and of the carboxylate-assigned 1394-cm-1 band area were observed compared with pure HSA. This phenomenon was attributed to a removal of contaminating lipids of HSA. Increasing TC concentration resulted in a progressive increase of the band areas at 1724 cm-1 (esters) and 1795 cm-1 (anhydrides), in a further decrease of the 1394-cm-1 band area (carboxylates), and in marked alterations of teh 1340-1080-cm-1 region. These changes, which revealed the progressive acylation of hydroxy and carboxylate groups of HSA, were accompanied by an increase of the 1624-cm-1 band area (beta-sheet), reflecting interchain H-bonding due to cross-linking. As observed in the previous studies of pH and reaction time, important spectral changes corresponded to low values of -NH2 content, to a decrease in microcapsule mean size (from > 30 to < 15 microns), and to modifications of the membrane surface (made rough).

Fourier-transform infrared spectroscopic studies of cross-linked human serum albumin microcapsules. 2. Influence of reaction time on spectra and correlation with microcapsule morphology and size

Microcapsules were prepared from human serum albumin (HSA) through interfacial cross-linking with terephthaloyl chloride (TC). Reaction times were increased from 2 to 60 min, while pH (9.8) and TC concentration (2.5% w/v) were kept constant. Fourier-transform infrared (FT-IR) spectra of lyophilized microcapsules were compared. Correlations were established with microcapsule morphology and size, as had been done in a previous study exploring the effect of increasing pH values. Microcapsules obtained after 2 min had to be considered separately. Minor alterations were observed in the spectrum as compared with pure HSA. They consisted of a decrease of the ester-assigned 1724-cm-1 band and of the carboxylate-assigned 1394-cm-1 band, attributed to a removal of contaminating lipids of HSA, and an increase of the 1624-cm-1 band, attributed to interchain H bonding following acylation of the NH2 groups. Prolonging the reaction time resulted in a progressive increase of the bands at 1724 (esters), 1795 (anhydrides), and 1624 cm-1 (beta-sheet), in a further decrease of the 1394-cm-1 band (carboxylates), and in marked alterations of the 1340-1080-cm-1 region. These important changes, which appeared after 5 min, reflect the progressive acylation of the hydroxy and carboxylate groups of HSA. As in the previous series of pH-based assays, important spectral changes were shown to correspond to a decrease in microcapsule mean size (from 32 to < 15 microns) and in important modifications of the membrane surface, made rough.

Polyhydroxamic microcapsules prepared from proteins: a novel type of chelating microcapsules

Microcapsules were prepared from three proteins, namely human serum albumin (HSA), bovine fibrinogen and ovalbumin, by an interfacial crosslinking process using terephthaloylchloride. They were further treated with alkaline hydroxylamine in order to disrupt ester and anhydride bonds in the walls. All microcapsules survived the treatment. They exhibited a significant increase in size and became sensitive to trypsin. The hydroxylamine treatment also resulted in attachment of hydroxamic groups to the membrane, making the microcapsules capable of iron binding. These properties were evaluated after soaking microcapsules in a 140 mumol/l ferric solution and determination of iron in the supernantant. Lower amounts of iron were found to be complexed by HSA microcapsules (mean value: 29.3 mumol iron/g microcapsule dry weight) as compared with fibrinogen and ovalbumin microcapsules (43.7 and 44.9 mumol/g, respectively). Microcapsule chelating properties were further improved by esterification of the free carboxyl groups of the membrane with benzyl alcohol or ethanol using a carbodiimide, prior to the hydroxylamine treatment. Comparable values of iron binding were obtained from esterified and hydroxylamine-treated batches prepared from the three proteins (about 50 mumol iron/g).