Water Soluble Polymers for Immunoisolation II: Evaluation of Multicomponent Microencapsulation Systems

Bio-Encapsulation for the Immune-Protection of Therapeutic Cells

The design of new technologies for treatment of human disorders is a complex and difficult task. The aim of this article is to explore state of art discussion of various techniques and materials involve in cell encapsulations. Encapsulation of cells within semi-permeable polymer shells or beads is a potentially powerful tool, and has long been explored as a promising approach for the treatment of several human diseases such as lysosomal storage disease (LSD), neurological disorders, Parkinsons disease, dwarfism, hemophilia, cancer and diabetes using immune-isolation gene therapy.

Cytotoxicity study of novel water-soluble chitosan derivatives applied as membrane material of alginate microcapsules

The majority of cell encapsulation systems applied so far are based on polyelectrolyte complexes of alginate and polyvalent metal cations. Although widely used, these systems suffer from the risk of disintegration. This can be partially solved by applying chitosan as additional outer membrane. However, chitosan can be dissolved in water only at a low pH, which limits its use in the field of bioencapsulation. In this study, novel primary and tertiary amine chitosan derivatives have been synthesized, which may be dissolved at pH 7.0, and retain the ability to effectively form additional membrane on the surface of alginate beads. As aqueous solutions tertiary amines dimethylamino-1-propyl-chitosan and dimethylethylamine-chitosan with linear hydrochloride aliphatic chains had the lowest toxicity, whereas dimethylpropylamine-chitosan, diethylaminoethyl-chitosan, and diisopropylaminoethyl-chitosan with branched hydrochloride aliphatic were cytotoxic to the majority of tested cells. When applied as polyelectrolyte complexation agent on the surface of alginate beads, none of the derivates had any negative effect on the metabolic activity of encapsulated beta-cells.

Encapsulation of human articular chondrocytes into 3D hydrogel: phenotype and genotype characterization

This chapter is intended to provide a summary of the current materials used in cell encapsulation technology as well as methods for evaluating the performance of cells encapsulated in a polymeric matrix. In particular, it describes the experimental procedure to prepare a hydrogel matrix based on natural polymers for encapsulating and culturing human articular chondrocytes with the interest in cartilage regeneration. Protocols to evaluate the viability, proliferation, differentiation, and matrix production of embedded cells are also described and include standard protocols such as the MTT and [3H] Thymidine assays, reverse transcription polymerase chain reaction (RT-PCR) technique, histology, and immunohistochemistry analysis. The assessment of cell distribution within the 3D hydrogel construct is also described using APoTome analysis.

Genipin Cross-Linked Polymeric Alginate-Chitosan Microcapsules for Oral Delivery: In-Vitro Analysis

We have previously reported the preparation of the genipin cross-linked alginate-chitosan (GCAC) microcapsules composed of an alginate core with a genipin cross-linked chitosan membrane. This paper is the further investigation on their structural and physical characteristics. Results showed that the GCAC microcapsules had a smooth and dense surface and a networked interior. Cross-linking by genipin substantially reduced swelling and physical disintegration of microcapsules induced by nongelling ions and calcium sequestrants. Strong resistance to mechanical shear forces and enzymatic degradation was observed. Furthermore, the GCAC membranes were permeable to bovine serum albumin and maintained a molecular weight cutoff at 70 KD, analogous to the widely studied alginate-chitosan, and alginate-poly-L-lysine-alginate microcapsules. The release features and the tolerance of the GCAC microcapsules in the stimulated gastrointestinal environment were also investigated. This GCAC microcapsule formulation offers significant potential as a delivery vehicle for many biomedical applications.

Polymethylene-co-guanidine based capsules: A mechanistic study of the formation using alginate and cellulose sulphate

Capsules have been prepared based on a polyanion blend of sodium alginate and sodium cellulose sulphate, gelled in the presence of calcium chloride and sodium chloride. In a second step a membrane was formed via the addition of polymethylene-co-guanidine (PMCG), an oligocation. A mechanistic study examined the influences of pH, ionic strength, gelation and reaction times as well as the molar mass of the polyanions on the transport and mechanical properties. The ratio of alginate-to-cellulose sulphate in the polyanion blend was also varied and it was found that both mechanical resistance to compression as well as the pore size of the membrane decreased as the percentage of cellulose sulphate was reduced. The maximum mechanical strength was observed to correspond to the minimum in viscosity of the polyanion blend with, for low NaCl levels, a 3:1 alginate:cellulose sulphate level providing the largest resistance to deformation. The ability to decouple the molar mass cut-off and mechanical resistance is viewed as an important advantage of alginate/cellulose sulphate/PMCG capsules. Capsules were transplanted into mice to a maximum of 102 days, after which animals were sacrificed and capsules retrieved. Over 90% of the capsules were recovered from the peritoneal cavity with the mechanical properties of the explanted capsules observed to decrease as a function of implantation time, likely as a result of ion exchange. The capsules were, however, relatively free from any rejection which is a quite unusual result for cation containing systems. It is believed that the reason PMCG-based microcapsules function well in vivo is that they provide a net negative charge on the surface. Higher molar mass polycations such as poly-L-lysine provide a net positive charge, inducing inflammation.

Polyvinylamine-based capsules: A mechanistic study of the formation using alginate and cellulose sulphate

Capsules based on sodium alginate (SA) and sodium cellulose sulphate (SCS), have been prepared using polyvinylamines (PVAm) of varying intrinsic viscosities. The resulting capsules are relatively dense in nature, revealing a bursting force which is four times that observed for the classical SA/SCS/polymethylene-co-guanidine chemistry. Molar mass cutoffs were typically in the 10-70 kDa range. A mechanistic study was carried out where the reaction time, ionic strength and pH of the reaction mixture, as well as the stoichiometry of the polyanion blend and the PVAm molar mass were varied. It is postulated that both the SA-PVAm and the SCS-PVAm binary interactions contribute to the mechanical properties and the permeability of the resulting capsules. The polyvinylamine-based chemistry offers interesting alternatives to the PMCG system in that it provides a means to produce capsules at low, or zero, ionic strengths. Subtle changes in the pH, or the SA:SCS ratio, can also be used to tune the bursting force quite sensitively. The most appropriate capsules, for transplantation, would likely be formed at polyanion levels of 1.2 wt% with a PVAm molar mass below 17 kDa.

Natural origin biodegradable systems in tissue engineering and regenerative medicine: present status and some moving trends

The fields of tissue engineering and regenerative medicine aim at promoting the regeneration of tissues or replacing failing or malfunctioning organs, by means of combining a scaffold/support material, adequate cells and bioactive molecules. Different materials have been proposed to be used as both three-dimensional porous scaffolds and hydrogel matrices for distinct tissue engineering strategies. Among them, polymers of natural origin are one of the most attractive options, mainly due to their similarities with the extracellular matrix (ECM), chemical versatility as well as typically good biological performance. In this review, the most studied and promising and recently proposed naturally derived polymers that have been suggested for tissue engineering applications are described. Different classes of such type of polymers and their blends with synthetic polymers are analysed, with special focus on polysaccharides and proteins, the systems that are more inspired by the ECM. The adaptation of conventional methods or non-conventional processing techniques for processing scaffolds from natural origin based polymers is reviewed. The use of particles, membranes and injectable systems from such kind of materials is also overviewed, especially what concerns the present status of the research that should lead towards their final application. Finally, the biological performance of tissue engineering constructs based on natural-based polymers is discussed, using several examples for different clinically relevant applications.

Reaction of chitosan with genipin and its fluorogenic attributes for potential microcapsule membrane characterization

This study investigates the fluorogenic characteristics of the chitosan-genipin reaction for applications in microencapsulation research. Results showed that the chitosan-genipin reaction generated a colored and fluorescent product, with optimal excitation and emission wavelengths at 369 and 470 nm, respectively. Furthermore, it was found that reaction conditions affected the fluorescence intensity of the product. Mixture at the ratio of 4:1 (chitosan: genipin by weight) fluoresced the most. It also fluoresced stronger if the reaction occurred at higher temperature, with the intensity of 10.4 x 10(5) CPS at 37 degrees C, 5.9 x 10(5) CPS at 20 degrees C, and 2.5 x 10(5) CPS at 4 degrees C. As well, the fluorescence of the mixture developed gradually over time, attaining the emission maxima of 2.9 x 10(5), 7.6 x 10(5), and 10.0 x 10(5) CPS in 1, 6, and 18 h, respectively. Chitosan-coated alginate microcapsules were prepared without prior labeling, to which subsequent genipin treatment was applied in order to examine the potential of using genipin in microcapsule characterization. Chitosan bound to the alginate beads interacted with genipin, from which the resultant fluorescent signals allowed for clear visualization of the chitosan coating under confocal laser scanning microscopy. The relative fluorescence intensity across the chitosan membrane was found to be considerably higher than the controls (175 vs. 50). The membrane thickness measured was 29.2 +/- 7.3 microm. These findings demonstrate a convenient and effective way of characterizing chitosan-based microcapsules using genipin as a fluorogenic marker, a technique that will be useful in microcapsule research and other biomedical applications.

Engineering and material considerations in islet cell transplantation

The successful application and optimization of cell transplantation will require quantitative engineering design and analysis of cells and materials in which relevant biological processes remain complex and incompletely defined. This report primarily reviews the engineering and material considerations in islet cell transplantation, including established biological constraints and biohybrid devices for cell delivery, as well as available barrier materials and the associated processing strategies directed at the control of solute transport, barrier permeability, and host responses at the biological-material interface. Also described are current areas of investigation with particular promise as enabling technologies for accelerating the clinical effectiveness of islet cell transplantation.

Water-based nanoparticulate polymeric system for protein delivery

This article features a new production technology for nanoparticles comprised of multicomponent polymeric complexes that are candidates for delivery vehicles of biological molecules such as proteins and drugs. Biocompatible and mostly natural polymers are fabricated into thermodynamically stable nanoparticles insoluble in water and buffered media, in the absence of organic solvents, using two types of processing: batch and continuous. Careful choice of construction materials and the superposition of several interacting principles during their production allow for the customization of the physicochemical properties of the structures. Detailed experiments in batch and continuous systems allowed time-dependent stoichiometric characterization of the production process and an understanding of fundamental assembly principles of such supramolecular structures. Continuous-flow production is shown to provide more consistent data in terms of product quality and consistency, with further possibility of process development and commercialization. The development of nanoparticles using the described methodology is expected to lead to a flexible nanoparticle drug delivery system for medical applications, which has particular bearing to the slow release of drugs, antigens (for vaccine design), and genes (for gene therapy). Several chemistries of particles are presented.

Carrageenan-oligochitosan microcapsules: optimization of the formation process(1)

The formation of new microcapsules based on polyelectrolyte complexes between carrageenans and oligochitosan has been investigated. The optimization of the process, which includes the selection of the most suitable solvent and investigation of the influence of reaction conditions on capsule properties, is presented. Iota-carrageenan (1.2-2% wt.) prepared in HEPES buffer was found to be the most suitable for the formation of mechanically stable capsules. These new capsules combine extremely high deformability (>90%) and elasticity with permeability control and can be applied in various bioencapsulation technologies. It has been shown that the reaction time influences the mechanical properties, whereas carrageenan concentration and the temperature during the capsule formation effect both mechanical and porosity characteristic of the membrane. Moreover, the temperature influences the kinetics of the diffusion through the complex iota-carrageenan/oligochitosan membrane. In general egress is faster above the sol-gel transition point, indicating applicability in thermo-induced releasing systems.

Technology of mammalian cell encapsulation

Entrapment of mammalian cells in physical membranes has been practiced since the early 1950s when it was originally introduced as a basic research tool. The method has since been developed based on the promise of its therapeutic usefulness in tissue transplantation. Encapsulation physically isolates a cell mass from an outside environment and aims to maintain normal cellular physiology within a desired permeability barrier. Numerous encapsulation techniques have been developed over the years. These techniques are generally classified as microencapsulation (involving small spherical vehicles and conformally coated tissues) and macroencapsulation (involving larger flat-sheet and hollow-fiber membranes). This review is intended to summarize techniques of cell encapsulation as well as methods for evaluating the performance of encapsulated cells. The techniques reviewed include microencapsulation with polyelectrolyte complexation emphasizing alginate-polylysine capsules, thermoreversible gelation with agarose as a prototype system, interfacial precipitation and interfacial polymerization, as well as the technology of flat sheet and hollow fiber-based macroencapsulation. Four aspects of encapsulated cells that are critical for the success of the technology, namely the capsule permeability, mechanical properties, immune protection and biocompatibility, have been singled out and methods to evaluate these properties were summarized. Finally, speculations regarding future directions of cell encapsulation research and device development are included from the authors' perspective.

Development of cellulose sulfate-based polyelectrolyte complex microcapsules for medical applications

Microencapsulation, as a tool for immunoisolation for allogenic or xenogenic implants, is a rapidly growing field. However most of the approaches are based on alginate/polylysine capsules, despite this system's obvious disadvantages such as its pyrogenicity. Here we report a different encapsulation system based on sodium cellulose sulfate and polydiallyldimethyl ammonium chloride for the encapsulation of mammalian cells. We have characterized this system regarding capsule formation, strength and size of the capsules as well as viability of the cells after encapsulation. In addition, we demonstrate the efficacy of these capsules as a "microfactory" in vitro and in vivo. Using encapsulated hybridoma cells we were able to demonstrate long-term release of antibodies up to four months in vivo. In another application we could show the therapeutic relevance of encapsulated genetically modified cells as an in vivo activation center for cytostatic drugs during tumor therapy.

New multicomponent capsules for immunoisolation

A new generation of microcapsules based on the use of oligomers which participate in polyelectrolyte complexation reactions has been developed. These freeze-thaw stable capsules have been applied as a bioartificial pancreas and have resulted in normoglycemia for periods of six months in concordant xenotransplantations. The new chemistry permits the control of permeability and mechanical properties over a wide range and can be adapted both to microcapsule and hollow fiber geometries rendering it a robust tool for encapsulation in general. Methods, and metrics, for the characterization of the mechanical properties and permeability of microcapsules are presented.