Improvement of the biocompatibility of alginate/poly-L-lysine/alginate microcapsules by the use of epimerized alginate as a coating

4D Bioprinting via Molecular Network Contraction for Membranous Tissue Fabrication

Generation of thin membranous tissues (TMT), such as the cornea, epidermis, and periosteum, presents a difficult fabrication challenge in tissue engineering (TE). TMTs consist of several cell layers that are less than 100 µm in thickness per layer. While traditional methods provide the necessary resolution for TMT fabrication, they require significant handling and incorporation of several layers is limited. Extrusion bioprinting offers precise control over deposition of different biomaterials and cell populations within the same construct but lacks the resolution to generate biomimetic TMTs. For the first time, a 4D bioprinting strategy that allows for the generation of cell-laden TMTs is developed. Anionic gelatin methacrylate (GelMA) hydrogels are treated with cationic poly-l-lysine (PLL), which induces charge attraction, microscale network collapse, and macroscale hydrogel shrinking. The impact of shrinking on hydrogel properties, print resolution, and cell viability is presented. Additionally, this work suggests that a novel mechanism is occurring, where PLL exhibits a contractile force on GelMA and PLL molecular weight drives GelMA shrinking capabilities. Finally, it is shown that this phenomenon can occur while maintaining an encapsulated cell population. These findings address a critical barrier by generating macroscale tissue structures with their microscale TMT counterparts in the same print.

The Diffusive Properties of Hydrogel Microcapsules for Cell Encapsulation

Hydrogel microcapsules have been used for decades to encapsulate cells and treat diseases ranging from neurodegenerative disorders to more systemic applications like Type I Diabetes. This cell encapsulation modality has been developed through more cumulative experiments than perhaps any other, owing to the relative ease of accessing the required materials, the commercial availability of droplet-generating instrumentation, and the mild microenvironment and unique permeability properties of hydrogels that are difficult to attain with alternative encapsulation systems employing thermoplastic materials. Because of their size and shape, microcapsules have an inherent advantage over macroencapsulation devices due to the more favorable surface area to volume ratio, which allows for greater efficiency in the amount of cellular cargo that is entrapped and enhanced nutrient exchange and efflux of secreted products. Unfortunately, with this significant positive benefit comes the caveat of difficult or impractical retrievability, highlighting the paradox that is particularly relevant as differentiated stem cell sources become more readily available. This chapter focuses on several techniques that can be used to evaluate the permeability and pore structure of hydrogel microcapsules, including a simplistic model for describing the diffusive behavior of alginate-polycation-alginate (APA) microcapsules with a liquid core, and an ancillary method to evaluate the ultrastructure of the APA membrane including morphometric analysis.

Sulfated alginate microspheres associate with factor H and dampen the inflammatory cytokine response

Alginate microspheres show promise for cell-encapsulation therapy but encounter challenges related to biocompatibility. In the present work we designed novel microbeads and microcapsules based on sulfated polyalternating MG alginate (SMG) and explored their inflammatory properties using a human whole blood model. SMG was either incorporated within the alginate microbeads or used as a secondary coat on poly-l-lysine (PLL)-containing microcapsules, resulting in reduction of the inflammatory cytokines (IL-1β, TNF, IL-6, IL-8, MIP-1α). The sulfated alginate microbeads exhibited a complement inert nature with no induction of terminal complement complex (TCC) above the values in freshly drawn blood and low surface accumulation of C3/C3b/iC3b. Conversely, SMG as a coating material lead to substantial TCC amounts and surface C3/C3b/iC3b. A common thread was an increased association of the complement inhibitor factor H to the alginate microbeads and microcapsules containing sulfated alginates. Factor H was also found to associate to non-sulfated alginate microbeads in lower amounts, indicating factor H binding as an inherent property of alginate. We conclude that the dampening effect on the cytokine response and increased factor H association points to sulfated alginate as a promising strategy for improving the biocompatibility of alginate microspheres.

STATEMENT OF SIGNIFICANCE

Alginate microspheres are candidate devices for cell encapsulation therapy. The concept is challenged by the inflammatory host response, and modification strategies for improved biocompatibility are urgently needed. One potential strategy is using sulfated alginates, acting as versatile heparin analogues with similar anti-inflammatory properties. We designed novel alginate microspheres using sulfated alginate with an alternating sequence mimicking glycosominoglycans. Evaluation in a physiologically relevant human whole blood model revealed a reduction of inflammatory cytokines by a sulfated alginate coating, and sulfated alginate microbeads were complement inert. These effects were correlated with a strong factor H association, which may represent the mechanistic explanation. This novel approach could improve the biocompatibility of alginate microspheres in vivo and present a new strategy toward clinical use.

Contribution of polymeric materials to progress in xenotransplantation of microencapsulated cells: a review

Cell microencapsulation and subsequent transplantation of the microencapsulated cells require multidisciplinary approaches. Physical, chemical, biological, engineering, and medical expertise has to be combined. Several natural and synthetic polymeric materials and different technologies have been reported for the preparation of hydrogels, which are suitable to protect cells by microencapsulation. However, owing to the frequent lack of adequate characterization of the hydrogels and their components as well as incomplete description of the technology, many results of in vitro and in vivo studies appear contradictory or cannot reliably be reproduced. This review addresses the state of the art in cell microencapsulation with special focus on microencapsulated cells intended for xenotransplantation cell therapies. The choice of materials, the design and fabrication of the microspheres, as well as the conditions to be met during the cell microencapsulation process, are summarized and discussed prior to presenting research results of in vitro and in vivo studies. Overall, this review will serve to sensitize medically educated specialists for materials and technological aspects of cell microencapsulation.

Mesenchymal stem cells and alginate microcarriers for craniofacial bone tissue engineering: A review

Craniofacial bone is a complex structure with an intricate anatomical and physiological architecture. The defects that exist in this region therefore require a precise control of osteogenesis in their reconstruction. Unlike traditional surgical intervention, tissue engineering techniques mediate bone development with limited postoperative risk and cost. Alginate stands as the premier polymer in bone repair because of its mild ionotropic gelation and excellent biocompatibility, biodegradability, and injectability. Alginate microcarriers are candidates of choice to mediate cells and accommodate into 3-D environment. Several studies reported the use of alginate microcarriers for delivering cells, drugs, and growth factors. This review will explore the potential use of alginate microcarrier for stem cell systems and its application in craniofacial bone tissue engineering.

An improved model for exploring the effect of physicochemical properties of alginate-based microcapsules on their fibrosis formation in vivo

An effectivein vitromodel established forexploring the effect ofthephysicochemical properties of alginate-based microcapsules on their fibrosis formation.

Stabilization challenges and formulation strategies associated with oral biologic drug delivery systems

Delivery of proteins to mucosal tissues of GI tract typically utilize formulations which protect against proteolysis and target the mucosal tissues. Using case studies from literature and the authors' own work, the in-process stability and solid state storage stability of biopharmaceuticals formulated in delivery systems designed for oral delivery to the GI tract will be reviewed. Among the range of delivery systems, biodegradable polymer systems for protection and controlled release of proteins have been the most studied; hence these systems will be covered in greater depth. These delivery systems include polymeric biodegradable microspheres or nanospheres that contain proteins or vaccines, which are designed to reduce the number of administrations/inoculations and the total protein dose required to achieve the desired biological effect. Specifically, this review will include a landscape survey of the systems that have been studied, the manufacturing processes involved, stability through the manufacturing process, key pharmaceutical formulation parameters that impact stability of the encased proteins, and storage stability of the encapsulated proteins in these delivery systems.

Multipotent stromal cells derived from common marmoset Callithrix jacchus within alginate 3D environment: Effect of cryopreservation procedures

Multipotent stromal cells derived from the common marmoset monkey Callithrix jacchus (cjMSCs) possess high phylogenetic similarity to humans, with a great potential for preclinical studies in the field of regenerative medicine. Safe and effective long-term storage of cells is of great significance to clinical and research applications. Encapsulation of such cell types within alginate beads that can mimic an extra-cellular matrix and provide a supportive environment for cells during cryopreservation, has several advantages over freezing of cells in suspension. In this study we have analysed the effect of dimethyl sulfoxide (Me2SO, 2.5-10%, v/v) and pre-freeze loading time of alginate encapsulated cjMSCs in Me2SO (0-45 min) on the viability and metabolic activity of the cells after freezing using a slow cooling rate (-1°C/min). It was found that these parameters affect the stability and homogeneity of alginate beads after thawing. Moreover, the cjMSCs can be frozen in alginate beads with lower Me2SO concentration of 7.5% after 30 min of loading, while retaining high cryopreservation outcome. We demonstrated the maximum viability, membrane integrity and metabolic activity of the cells under optimized, less cytotoxic conditions. The results of this study are another step forward towards the application of cryopreservation for the long-term storage and subsequent applications of transplants in cell-based therapies.

Advances in biocompatibility and physico-chemical characterization of microspheres for cell encapsulation

Cell encapsulation has already shown its high potential and holds the promise for future cell therapies to enter the clinics as a large scale treatment option for various types of diseases. The advancement in cell biology towards this goal has to be complemented with functional biomaterials suitable for cell encapsulation. This cannot be achieved without understanding the close correlation between cell performance and properties of microspheres. The ongoing challenges in the field of cell encapsulation require a critical view on techniques and approaches currently utilized to characterize microspheres. This review deals with both principal subjects of microspheres characterization in the cell encapsulation field: physico-chemical characterization and biocompatibility. The up-to-day knowledge is summarized and discussed with the focus to identify missing knowledge and uncertainties, and to propose the mandatory next steps in characterization of microspheres for cell encapsulation. The primary conclusion of this review is that further success in development of microspheres for cell therapies cannot be accomplished without careful selection of characterization techniques, which are employed in conjunction with biological tests.

Using manganese-enhanced MRI to assess optic nerve regeneration

Experimental visual pathway lesion in the form of optic nerve (ON) crush or transection injury results in massive death of retinal ganglion cells (RGCs) and permanent loss of synaptic connections (Berkelaar et al., J Neurosci 14:4368-4374, 1994). Despite the fact that RGC axon regeneration is inhibited in a manner typical of other CNS lesions, the rodent ON injury model is one of the few models where robust axon regeneration has been achieved after therapeutic intervention (Berry et al., Restor Neurol Neurosci 26:147-174, 2008). However, assessment of the efficacy of therapeutic approaches in promoting ON regeneration has traditionally relied on histological methods, which necessitate the sacrifice of experimental animals and thus preclude longitudinal in vivo monitoring of individual subjects. Manganese-enhanced MRI (MEMRI) utilizes the paramagnetic properties and uptake and transport mechanisms of manganese ions (Mn(2+)) by neurons, thus enabling serial in vivo monitoring of the entire axonal projections (Sandvig et al., J Magn Reson Imaging 34:670-675, 2011; Thuen et al., J Magn Reson Imaging 4:492-500, 2005; Pautler et al., Magn Res Med 50:33-39, 2003; Saleem et al., Neurotechnique 34:685-700, 2000). The above properties of Mn(2+) render MEMRI a highly suitable technique for assessment of ON regeneration after injury, especially with a view to in vivo monitoring of neuronal connectivity and axon-regenerative responses to treatment. In this chapter, we provide a generic protocol for ON lesioning and MEMRI application for assessment of ON regeneration in rodents.

Microencapsulated cell tracking

Microencapsulation of therapeutic cells has been widely pursued to achieve cellular immunoprotection following transplantation. Initial clinical studies have shown the potential of microencapsulation using semi-permeable alginate layers, but much needs to be learned about the optimal delivery route, in vivo pattern of engraftment, and microcapsule stability over time. In parallel with noninvasive imaging techniques for 'naked' (i.e. unencapsulated) cell tracking, microcapsules have now been endowed with contrast agents that can be visualized by (1) H MRI, (19) F MRI, X-ray/computed tomography and ultrasound imaging. By placing the contrast agent formulation in the extracellular space of the hydrogel, large amounts of contrast agents can be incorporated with negligible toxicity. This has led to a new generation of imaging biomaterials that can render cells visible with multiple imaging modalities.

Systematic study of alginate-based microcapsules by micropipette aspiration and confocal fluorescence microscopy

Micropipette aspiration and confocal fluorescence microscopy were used to study the structure and mechanical properties of calcium alginate hydrogel beads (A beads), as well as A beads that were additionally coated with poly-L-lysine (P) and sodium alginate (A) to form, respectively, AP and APA hydrogels. A beads were found to continue curing for up to 500 h during storage in saline, due to residual calcium chloride carried over from the gelling bath. In subsequent saline washes, micropipette aspiration proved to be a sensitive indicator of gel weakening and calcium loss. Aspiration tests were used to compare capsule stiffness before and after citrate extraction of calcium. They showed that the initial gel strength is largely due to the calcium alginate gel cores, while the long term strength is solely due to the poly-L-lysine-alginate polyelectrolyte complex (PEC) shells. Confocal fluorescence microscopy showed that calcium chloride exposure after PLL deposition led to PLL redistribution into the hydrogel bead, resulting in thicker but more diffuse and weaker PEC shells. Adding a final alginate coating to form APA capsules did not significantly change the PEC membrane thickness and stiffness, but did speed the loss of calcium from the bead core.

Impact of alginate composition: from bead mechanical properties to encapsulated HepG2/C3A cell activities for in vivo implantation

Recently, interest has focused on hepatocytes' implantation to provide end stage liver failure patients with a temporary support until spontaneous recovery or a suitable donor becomes available. To avoid cell damage and use of an immunosuppressive treatment, hepatic cells could be implanted after encapsulation in a porous biomaterial of bead or capsule shape. The aim of this study was to compare the production and the physical properties of the beads, together with some hepatic cell functions, resulting from the use of different material combinations for cell microencapsulation: alginate alone or combined with type I collagen with or without poly-L-lysine and alginate coatings. Collagen and poly-L-lysine increased the bead mechanical resistance but lowered the mass transfer kinetics of vitamin B12. Proliferation of encapsulated HepG2/C3A cells was shown to be improved in alginate-collagen beads. Finally, when the beads were subcutaneously implanted in mice, the inflammatory response was reduced in the case of alginate mixed with collagen. This in vitro and in vivo study clearly outlines, based on a systematic comparison, the necessity of compromising between material physical properties (mechanical stability and porosity) and cell behavior (viability, proliferation, functionalities) to define optima hepatic cell microencapsulation conditions before implantation.

Alginate microbeads are complement compatible, in contrast to polycation containing microcapsules, as revealed in a human whole blood model

Alginate microbeads and microcapsules are presently under evaluation for future cell-based therapy. Defining their inflammatory properties with regard to humans is therefore essential. A lepirudine-based human whole blood model was used as an inflammation predictor by measuring complement and leukocyte stimulation. Alginate microbeads were complement-compatible since they did not activate complement as measured by the soluble terminal complement complex (sTCC), Bb or the anaphylatoxins C3a and C5a. In addition, alginate microbeads were free of surface adherent leukocytes. In contrast, microcapsules containing poly-L-lysine (PLL) induced elevated levels of sTCC, Bb, C3a and C5a, surface active C3 convertase and leukocyte adhesion. The soluble PLL induced elevated levels of sTCC and up-regulated leukocyte CD11b expression. PMCG microcapsules containing poly(methylene-co-guanidine) complexed with sodium alginate and cellulose sulfate triggered a fast sTCC response and C3 deposition. The PMCG microcapsules were still less activating than PLL-containing microcapsules as a function of time. The amounts of anaphylatoxins C3a and C5a were diminished by the PMCG microcapsules, whereas leukocyte adherence demonstrated surface activating properties. We propose the whole blood model as an important tool for measuring bioincompatibility of microcapsules and microbeads for future applications as well as determining the mechanisms leading to inflammatory reactions.

Alginate as an immobilization material for MAb production via encapsulated hybridoma cells

Alginate has been widely used in various applications since its first extraction. What makes this biopolymer useful is its high biocompatibility and humid gelation conditions. Both of these features bring it into prominence as an ideal immobilization material. However, there are some complicated aspects of cell immobilization using alginate biopolymers. This review discusses and clarifies these crucial points, using as an example the bioprocessing of highly fragile cells (hybridoma cells). The review focuses on the cultivation and production of alginate encapsulated cells.

Progress technology in microencapsulation methods for cell therapy

Cell encapsulation in microcapsules allows the in situ delivery of secreted proteins to treat different pathological conditions. Spherical microcapsules offer optimal surface-to-volume ratio for protein and nutrient diffusion, and thus, cell viability. This technology permits cell survival along with protein secretion activity upon appropriate host stimuli without the deleterious effects of immunosuppressant drugs. Microcapsules can be classified in 3 categories: matrix-core/shell microcapsules, liquid-core/shell microcapsules, and cells-core/shell microcapsules (or conformal coating). Many preparation techniques using natural or synthetic polymers as well as inorganic compounds have been reported. Matrix-core/shell microcapsules in which cells are hydrogel-embedded, exemplified by alginates capsule, is by far the most studied method. Numerous refinement of the technique have been proposed over the years such as better material characterization and purification, improvements in microbead generation methods, and new microbeads coating techniques. Other approaches, based on liquid-core capsules showed improved protein production and increased cell survival. But aside those more traditional techniques, new techniques are emerging in response to shortcomings of existing methods. More recently, direct cell aggregate coating have been proposed to minimize membrane thickness and implants size. Microcapsule performances are largely dictated by the physicochemical properties of the materials and the preparation techniques employed. Despite numerous promising pre-clinical results, at the present time each methods proposed need further improvements before reaching the clinical phase.

Practical recombinant hybrid mussel bioadhesive fp-151

Mussel adhesive proteins (MAPs) have received increased attention as potential environmentally friendly adhesives under aqueous conditions and in medicine. However, attempts to produce functional recombinant MAPs (mainly foot protein type 1, fp-1) by several expression systems have failed. Even though we previously reported a functional expression of recombinant foot protein type 5 (fp-5) with significant adhesive ability in Escherichia coli, its practical use was limited by several problems such as low production yield, low purification yield, and high levels of post-purification insolubility. Here, to overcome these limitations, we designed and constructed the novel type of hybrid mussel bioadhesive fp-151, a fusion protein comprising six fp-1 decapeptide repeats at each fp-5 terminus. Using micro- and bulk-scale characterization and mammalian cell-adhesion analyses, we demonstrate that fp-151 has the potential to be a practical bioadhesive with strong adhesive ability, a simple purification process ( approximately 1g-purified protein per 1l-pilot-scale fed-batch bioreactor culture), proper manipulation properties ( approximately 330g/l solubility), and high biocompatibility.

Efficacy of Bioactive Polypeptides on Bleeding and Intra-Abdominal Adhesions

BACKGROUND

Perioperative bleeding and postoperative adhesions are two problems encountered in abdominal surgery. Commercial products are available that decrease both bleeding and development of abdominal adhesions, but no products are effective in both situations. The combination of differently charged bioactive polypeptides, administered intraperitoneally, has previously been shown effective in decreasing postoperative adhesions. The present study is a pilot examination of the effects on perioperative bleeding and postoperative adhesions, applying the polypeptide concept.

METHODS

Standardized wounds in the liver and spleen were induced in 52 NMRI mice. The amounts of bleeding and postoperative adhesions were measured after 1 and 7 days, respectively. Separate animals were examined after 8 weeks for long-term healing of the parenchymal wounds.

RESULTS

Both parenchymal bleeding and the extent of adhesions significantly decreased (p = 0.001 and p = 0.029, respectively) as compared to controls. Histology after 8 weeks showed no clear signs of impaired or altered healing.

CONCLUSION

Intraperitoneal administration of differently charged polypeptides significantly decreased postoperative bleeding and postoperative adhesions. Bioactive polypeptides appear promising in the promotion of peritoneal healing and merits further studies.

Recombinant mussel adhesive protein Mgfp-5 as cell adhesion biomaterial

Mytilus galloprovincialis foot protein type-5 (Mgfp-5) is one of the mussel adhesive proteins that participate in adhesion with the substratum. We previously reported the production of recombinant Mgfp-5 in Escherichia coli and showed that the recombinant protein had superior adhesion abilities versus those of Cell-Tak, a commercially available mussel adhesive protein mixture. In the present work, we investigated the feasibility of using recombinant Mgfp-5 as a cell adhesion agent. Purified and tyrosinase-modified recombinant Mgfp-5 was used to adhere living anchorage-independent cells such as insect Drosophila S2 cells and human MOLT-4 cells onto glass slides. Our results revealed that these cell lines efficiently attached to recombinant Mgfp-5-coated glass surfaces, and that surface-immobilized S2 cells were viable and able to undergo cell division for up to 1 week. Cytochemical studies with 4',6-diamidino-2-phenylindole (DAPI) staining of nuclei and immunofluorescence for secreted foreign human erythropoietin (hEPO) from recombinant S2 cells and quantitative comparative analyses of S2 cell binding ability with Cell-Tak and poly-L-lysine, the main cell adhesion agent, were performed to demonstrate successful usage of recombinant Mgfp-5 for cell biological applications. Collectively, these results indicate that recombinant Mgfp-5 may be a useful new cell adhesion biomaterial for anchorage-independent cells.

Novel treatment in peritoneal adhesion prevention: protection by polypeptides

OBJECTIVE

To evaluate a novel antiadhesive polypeptide complex containing a combination of poly-L-glutamate and poly-L-lysine in order to study its effectiveness and mechanisms in the prevention of postoperative abdominal adhesions in mice.

MATERIAL AND METHODS

The length of peritoneal adhesions was measured and expressed in percentage of the wound length in a standardized peritoneal injury model and evaluated 7 days and 4 weeks after adhesion induction. The test compound was administered intraperitoneally following surgery. Peritoneal swabs, including the wound area, were stained in order to determine the peritoneal location and clearance of the polypeptides. Electron microscopy was performed to analyze the wound surface and the ultra-structural changes of the phagocytes in cell culture. Moreover, flow cytometry was used to evaluate the effect on macrophage phagocytic function.

RESULTS

The poly-L-lysine and poly-L-glutamate combination significantly decreased peritoneal adhesions both at 7 days' (p < 0.001) and 4 weeks' (p < or = 0.001) follow-up. From the first day, the compound was found in the wound, after which this was gradually rebuilt, and covered with mesothelial cells. The macrophages phagocytosed the test compound particles, resulting in significant cell growth, and large phagocytic vacuoles.

CONCLUSIONS

The intraperitoneal administration of poly-L-lysine and poly-L-glutamate resulted in a significant decrease in experimental postoperative peritoneal adhesions.

Increasing anastomosis safety and preventing abdominal adhesion formation by the use of polypeptides in the rat

BACKGROUND AND AIMS

Postoperative adhesions can potentially be reduced using different anti-adhesive agents, though these drugs tend to compromise healing of an intestinal anastomosis. No method that significantly increases anastomosis safety is known at present. The aim of the study was to develop a concept of preventing postoperative adhesions using differently charged bioactive polypeptides, also considering healing and safety of an intestinal anastomosis.

METHODS

An ileocolic anastomosis was performed under both "clean" and "septic" conditions in the rat. The treatment group received intraperitoneal poly-L-lysine and poly-L-glutamate, while controls received sodium chloride. Abdominal adhesions, anastomosis leakage and burst pressure were analysed after 1, 3, 5 and 7 days in the clean anastomosis model and after 7 days in the septic model.

RESULTS

A significant decrease (p<0.01) in the amount of adhesions was seen in animals treated with polypeptides after 1, 3 and 5 days, while no difference was seen after 7 days. The anastomosis demonstrated a significantly higher burst pressure as evaluated at days 1 and 3 (p<0.05 and p<0.01, respectively) in the polypeptide-treated animals, while no difference was seen between the groups at day 5 or 7.

CONCLUSION

The use of differently charged polypeptides administered intraperitoneally after surgery resulted in a significant decrease in the extent of postoperative adhesions. Furthermore, an increase in intestinal anastomosis safety, based on improved burst pressure during the first 3 days, i.e. the critical period during the healing process, was noted. No adverse effects were seen in surgery during septic conditions.

Bacterial alginates: from biosynthesis to applications

Alginate is a polysaccharide belonging to the family of linear (unbranched), non-repeating copolymers, consisting of variable amounts of beta-D-mannuronic acid and its C5-epimer alpha- L-guluronic acid linked via beta-1,4-glycosidic bonds. Like DNA, alginate is a negatively charged polymer, imparting material properties ranging from viscous solutions to gel-like structures in the presence of divalent cations. Bacterial alginates are synthesized by only two bacterial genera, Pseudomonas and Azotobacter, and have been extensively studied over the last 40 years. While primarily synthesized in form of polymannuronic acid, alginate undergoes chemical modifications comprising acetylation and epimerization, which occurs during periplasmic transfer and before final export through the outer membrane. Alginate with its unique material properties and characteristics has been increasingly considered as biomaterial for medical applications. The genetic modification of alginate producing microorganisms could enable biotechnological production of new alginates with unique, tailor-made properties, suitable for medical and industrial applications.

Alginate-based microcapsules for immunoisolation of pancreatic islets

Transplantation of microencapsulated cells is proposed as a therapy for the treatment of a wide variety of diseases since it allows for transplantation of endocrine cells in the absence of undesired immunosuppression. The technology is based on the principle that foreign cells are protected from the host immune system by an artificial membrane. In spite of the simplicity of the concept, progress in the field of immunoisolation has been hampered for many years due to biocompatibility issues. During the last years important advances have been made in the knowledge of the characteristics and requirements capsules have to meet in order to provide optimal biocompatibility and survival of the enveloped tissue. Novel insight shows that not only the capsules material but also the enveloped cells should be hold responsible for loss of a significant portion of the immunoisolated cells and, thus, failure of the grafts on the long term. Microcapsules without cells can be produced as such that they remain free of any significant foreign body response for prolonged periods of time in both experimental animals and humans. New approaches in which newly discovered inflammatory responses are silenced bring the technology of transplantation of immunoisolated cells close to clinical application.

Present and Future Developments in Hepatic Tissue Engineering for Liver Support Systems : State of the art and future developments of hepatic cell culture techniques for the use in liver support systems

The liver is the most important organ for the biotransformation of xenobiotics, and the failure to treat acute or acute-on-chronic liver failure causes high mortality rates in affected patients. Due to the lack of donor livers and the limited possibility of the clinical management there has been growing interest in the development of extracorporeal liver support systems as a bridge to liver transplantation or to support recovery during hepatic failure. Earlier attempts to provide liver support comprised non-biological therapies based on the use of conventional detoxification procedures, such as filtration and dialysis. These techniques, however, failed to meet the expected efficacy in terms of the overall survival rate due to the inadequate support of several essential liver-specific functions. For this reason, several bioartificial liver support systems using isolated viable hepatocytes have been constructed to improve the outcome of treatment for patients with fulminant liver failure by delivering essential hepatic functions. However, controlled trials (phase I/II) with these systems have shown no significant survival benefits despite the systems' contribution to improvements in clinical and biochemical parameters. For the development of improved liver support systems, critical issues, such as the cell source and culture conditions for the long-term maintenance of liver-specific functions in vitro, are reviewed in this article. We also discuss aspects concerning the performance, biotolerance and logistics of the selected bioartificial liver support systems that have been or are currently being preclinically and clinically evaluated.

Polymer Chemistry in Diabetes Treatment by Encapsulated Islets of Langerhans: Review to 2006

Polymeric materials have been successfully used in numerous medical applications because of their diverse properties. For example, development of a bioartificial pancreas remains a challenge for polymer chemistry. Polymers, as a form of various encapsulation device, have been proposed for designing the semipermeable membrane capable of long-term immunoprotection of transplanted islets of Langerhans, which regulate the blood glucose level in a diabetic patient. This review describes the current situation in the field, discussing aspects of material selection, encapsulation devices, and encapsulation protocols. Problems and unanswered questions are emphasized to illustrate why clinical therapies with encapsulated islets have not been realized, despite intense activity over the past 15 years. The review was prepared with the goal to address professionals in the field as well as the broad polymer community to help in overcoming final barriers to the clinical phase for transplantation of islets of Langerhans encapsulated in a polymeric membrane.

Deletion of the tissue response against alginate-pll capsules by temporary release of co-encapsulated steroids

Transplantation of encapsulated living cells is a promising approach for the treatment of a wide variety of diseases. Large-scale application of the technique, however, is hampered by inflammatory responses against the capsules. In the present study, we investigate whether tissue responses against alginate-PLL-alginate capsules can be modulated by co-encapsulation and temporary release of immunomodulating factors such as dexamethasone. Such an approach may be mandatory in order to increase the function and survival of encapsulated tissue since it has been shown that the tissue response can be caused by many, insurmountable factors. In an in vitro assay, we demonstrated an antiproliferative effect of dexamethasone-containing capsules on L929-mouse-fibroblasts. Subsequently, capsules prepared of purified alginate with or without solved dexamethasone were implanted in the peritoneal cavity of rats and retrieved one month later for histological evaluation. Most of the capsules without dexamethasone proved to be overgrown and adherent to the abdominal organs whereas with co-encapsulated dexamethasone the majority of the capsules were found freely floating in the peritoneal cavity without overgrowth. We conclude that co-encapsulation of dexamethasone has a profound effect on fibroblasts and macrophages adherence to immunoisolating capsules.

Effect of poly-L-lysine coating on macrophage activation by alginate-based microcapsules: Assessment using a newin vitromethod

The characteristics of the microcapsule surface, which interacts directly with the host macrophages, may have a role in the biocompatibility of alginate-poly-L-lysine (PLL)-alginate (APA) microcapsule. The objectives of the study were: 1) to develop and validate a simple, rapid, and sensitive in vitro method for assessing microcapsule biocompatibility, based on microcapsule coincubation with macrophages and measurement, by reverse transcriptase-polymerase chain reaction, of cytokine mRNA expression, and 2) to evaluate the effect of alginate purification and PLL coating on macrophage activation. The mRNA expression of tumor necrosis factor-alpha and interleukin-1beta was significantly higher when macrophages were coincubated with beads made with nonpurified compared with purified alginate (p<0.01, p<0.05, respectively) and negative control (p<0.001) or with APA microcapsules compared with non-PLL-coated alginate beads and negative control (p<0.001). The mRNA expression of interleukin-6 differed significantly only when APA microcapsules were compared with a negative control (p<0.05). These results confirm that alginate purification improves microcapsule biocompatibility, and suggest that PLL is not completely covered and/or neutralized by the second alginate incubation and thus has a role in the host macrophage activation. The assay is sensitive to both alginate contaminants and microcapsule surface characteristics and may be a useful tool for the development of biocompatible microcapsules.

History, challenges and perspectives of cell microencapsulation

Cell microencapsulation continues to hold significant promise for biotechnology and medicine. The controlled, and continuous, delivery of therapeutic products to the host by immunoisolated cells is a potentially cost-effective method to treat a wide range of diseases. Although there are several issues that need to be addressed, including capsule manufacture, properties and performance, in the past few years, a stepwise analysis on the essential obstacles and limitations has brought the whole technology closer to a realistic proposal for clinical application. This paper summarizes the current situation in the cell encapsulation field and discusses the main events that have occurred along the way.

Prospects for Delivery of Recombinant Angiostatin by Cell-Encapsulation Therapy

Implantation of encapsulated nonautologous cells that have been genetically modified to secrete proteins with tumor suppressor properties represents an alternative nonviral strategy to cancer gene therapy. We report an approach to raise the yield of recombinant proteins from encapsulated cells substantially. We hypothesized that by optimizing the encapsulation procedure, the production efficacy from the encapsulated cells could be increased. HEK 293 EBNA cells were genetically engineered to produce angiostatin. Encapsulation was performed by varying bead size, cellular density, homogeneity, and ion composition of the gel. The morphology and viability of the cells and the release of angiostatin were studied. Computer software was developed for three-dimensional imaging and quantification of cell viability. Angiostatin production was assessed at 3, 6, and 11 weeks using enzyme-linked immunosorbent assay (ELISA). Inhomogeneous gels facilitated cell growth and viability. The most efficient inhomogeneous microcapsules were generated by reducing the size and cellular density of the beads. The viability and the production of angiostatin were 3 to 5 times higher than in the homogeneous capsules. Significant amounts of viable cells were present in both homogeneous and inhomogeneous beads after 6 months of culture. The stability of the alginate matrix was greatly enhanced by gelling in the presence of barium. In conclusion, the viability and production efficacy of recombinant angiostatin from alginate-encapsulated cells can be increased considerably by optimizing the encapsulation procedure. The development of such optimized microcapsules brings cell-encapsulation therapy further towards clinical use in cancer therapy.

Progress and challenges for cell encapsulation in brain tumour therapy

Cell encapsulation provides a method to circumvent the host immune system by encapsulating cells or tissues in immunoisolating, semipermeable membranes before implantation. The technology has been widely studied with an aim of developing bio-organs transplantable into patients without the need of immunosuppression, and in cancer therapy, the principle of cell encapsulation may be further exploited. Encapsulated recombinant cells represent factories or bioreactors for the production of therapeutic proteins. By implanting the bioreactors in the vicinity of the tumour, long-term local de novo delivery of the therapeutic proteins may be achieved. Malignant brain tumours such as glioblastoma multiforme (GBM) remain highly lethal neoplasms, refractory to current therapies. Researchers and medical professionals are working on developing translational therapies to combat these aggressive tumours. Numerous clinical trials on gene therapy for glioma patients have been conducted over the last decade, but the results have largely been disappointing. Cell encapsulation represents an alternative method for local delivery of therapeutic proteins with antineoplastic properties to glioma patients. The concept has not yet reached clinical trials, but encouraging results have been achieved in rats bearing gliomas when implanting endostatin-secreting encapsulated cells into the rat brain. This review primarily focuses on the recent progress that has been made with cell encapsulation technology. In addition, the challenges this field faces before clinical application in brain tumour patients is discussed.

Visualization of alginate-poly-L-lysine-alginate microcapsules by confocal laser scanning microscopy

Confocal laser scanning microscopy (CLSM) was used to study the distribution of polymers and cross-linking ions in alginate-poly-L-lysine (PLL) -alginate microcapsules made by fluorescent-labeled polymers. CLSM studies of Ca-alginate gel beads made in the presence and absence of non-gelling sodium ions revealed a more inhomogeneous distribution of alginate in beads formed in the absence of non-gelling ions. In the formation of alginate-PLL capsules, the polymer gradients in the preformed gel core were destabilized by the presence of non-gelling ions in the washing step and in the PLL solution. Ca-alginate gels preserved the inhomogeneous structure by exposure to ion-free solution in contrast to exposure to non-gelling ions (Na(+)). By exchanging Ca(2+) with Ba(2+) (10 mM), extremely inhomogeneous gel beads were formed that preserved their structure during the washing and exposure to PLL in saline. PLL was shown to bind at the very surface of the alginate core, forming a shell-like membrane. The thickness of the PLL-layer increased about 100% after 2 weeks of storage, but no further increase was seen after 2 years of storage. The coating alginate was shown to overlap the PLL layer. No difference in binding could be observed among coating alginates of different composition. This paper shows an easy and novel method to study the distribution of alginate and PLL in intact microcapsules. As the labeling procedures are easy to perform, the method can also be used for a variety of other polymers in other microencapsulation systems.

The effect of capsule composition in the reversal of hyperglycemia in diabetic mice transplanted with microencapsulated allogeneic islets

The transplantation of microencapsulated islets may allow reversal of hyperglycemia in the absence of immunosuppression. Poly-L-lysine (PLL) on capsules may potentiate the fibrotic reaction against implanted capsules. The aims of this study were to investigate how the biocompatibility of such capsules affects their function in vivo and to compare their efficacy relative to naked islets after intraperitoneal transplantation to nude or immune competent mice. Alloxan-diabetic C57BL/6 wild-type or nude (nu/nu) mice were transplanted with naked BALB/c islets, empty capsules, or microencapsulated BALB/c islets. Three types of capsules were used, one containing a high guluronic acid (G) alginate and PLL, one with a high mannuronic acid (M) alginate and PLL, and one high M alginate capsule with no PLL. Hyperglycemia in nude mice was reversed after transplantation of naked islets or islets encapsulated in a capsule containing high M alginate. Nude mice transplanted with islets encapsulated in the high G capsules showed only a transient reversal of hyperglycemia. In an allogeneic system, naked BALB/c islets were rejected by day 10 after transplantation, whereas the islets encapsulated in high M capsules continued to function for at least a month. When PLL was excluded from the capsules, the grafts functioned for up to 8 weeks. Islets microencapsulated in high G alginate capsules fail to reverse hyperglycemia for more than a few days in nude mice. However, islets in high M alginate capsules can reverse hyperglycemia in nude and immune competent mice. Islets microencapsulated in PLL-free high M alginate capsules function for 8 weeks in immune competent mice.