Biocompatibility of mannuronic acid-rich alginates

Transport of biological molecules in surfactant-alginate composite hydrogels

Obstructed transport of biological molecules can result in improper release of pharmaceuticals or biologics from biomedical devices. Recent studies have shown that nonionic surfactants, such as Pluronic® F68 (F68), positively alter biomaterial properties such as mesh size and microcapsule diameter. To further understand the effect of F68 (incorporated at concentrations well above the critical micelle concentration (CMC)) in traditional biomaterials, the transport properties of BSA and riboflavin were investigated in F68-alginate composite hydrogels, formed by both internal and external cross-linking with divalent cations. Results indicate that small molecule transport (represented by riboflavin) was not significantly hindered by F68 in homogeneously (internally) cross-linked hydrogels (up to an 11% decrease in loading capacity and 14% increase in effective diffusion coefficient, D(eff)), while protein transport in homogeneously cross-linked hydrogels (represented by BSA) was significantly affected (up to a 43% decrease in loading capacity and 40% increase in D(eff)). For inhomogeneously cross-linked hydrogels (externally cross-linked by CaCl(2) or BaCl(2)), the D(eff) increased up to 50 and 83% for small molecules and proteins, respectively. Variation in the alginate gelation method was shown to affect transport through measurable changes in swelling ratio (30% decrease) and observable changes in cross-linking structure as well as up to a 3.6- and 11.8-fold difference in D(eff) for riboflavin and BSA, respectively. Aside from the expected significant changes due to the cross-linking method utilized, protein transport properties were altered due to mesh size restrictions (10-25 nm estimated by mechanical properties) and BSA-F68 interaction (DLS). Taken as a whole, these results show that incorporation of a nonionic surfactant at concentrations above the CMC can affect device functionality by impeding the transport of large biological molecules.

Truly nonionic polymer shells for the encapsulation of living cells

Engineering surfaces of living cells with natural or synthetic compounds can mediate intercellular communication and provide a protective barrier from hostile agents. We report on truly nonionic hydrogen-bonded LbL coatings for cell surface engineering. These ultrathin, highly permeable polymer membranes are constructed on living cells without the cationic component typically employed to increase the stability of LbL coatings. Without the cytotoxic cationic PEI pre-layer, the viability of encapsulated cells drastically increases to 94%, in contrast to 20% viability in electrostatically-bonded LbL shells. Moreover, the long-term growth of encapsulated cells is not affected, thus facilitating efficient function of protected cells in hostile environment.

Effect of oxygen levels on proteoglycan synthesis by intervertebral disc cells

STUDY DESIGN

the response of cells from the annulus fibrosus (AF) and nucleus pulposus (NP) to varying oxygen (O2) concentrations was examined when cultured in alginate.

OBJECTIVE

to study the effect of O2 concentration on AF and NP cells.

SUMMARY OF BACKGROUND DATA

AF and NP cells possess different metabolic profiles in situ. However, it is not clear whether this difference is maintained in in vitro culture conditions. AF and NP cells can respond differently in the different systems, which may differ from the in vivo environment in terms of nutrient supply and O2 levels. In vivo, O2 levels vary from 1% to 5% within the intervertebral disc, and there is evidence that disc cell metabolism can vary with O2 concentrations.

METHODS

an alginate scaffold was seeded with bovine AF or NP cells and maintained in culture for up to 18 days under different O2 concentrations. The sulfated glycosaminoglycan (GAG) content in the culture medium and the expression of aggrecan, type I (COL1A2) and II (COL2A1) collagen genes were analyzed at day 9 and day 18.

RESULTS

in both NP and AF cells cultured either in normoxia (21% O2) or in hypoxia (5% and 1% O2), the GAG content of the culture medium increased with time, though the rate of increase was diminished in 5% O2. With a decrease in O2 levels, the expression of aggrecan mRNA increased in NP cells. There was little effect of O2 on aggrecan mRNA level in AF cells. However, there was a slight decrease with time. Interestingly, aggrecan mRNA levels did not reflect GAG release for either NP or AF cells. There was no effect with time or O2 levels on COL2A1 message in NP cells. The highest Aggrecan/COL2 message ratio for NP cells was with 1% O2, suggesting this to be the best condition for maintaining the NP phenotype. COL1A2 gene expression in NP and AF cells increased with time, but showed little change with O2 levels in NP cells. The highest COL2/COL1 ratio in NP cells was also observed with 1% O2. Finally, NP cells tended to remain localized in the alginate beads, whereas AF cells tended to migrate from the beads.

CONCLUSION

both NP and AF cells showed little change in GAG production with O2 levels ranging from 1% to 21%. Disc cell metabolism is not impaired at low O2 concentrations, which appear beneficial to matrix composition. Furthermore, low oxygen may promote a gelatinous NP matrix, whereas increased oxygen levels may promote a fibrous matrix.

Wound Healing Versus Regeneration: Role of the Tissue Environment in Regenerative Medicine

One of the major challenges in the field of regenerative medicine is how to optimize tissue regeneration in the body by therapeutically manipulating its natural ability to form scar at the time of injury or disease. It is often the balance between tissue regeneration, a process that is activated at the onset of disease, and scar formation, which develops as a result of the disease process that determines the ability of the tissue or organ to be functional. Using biomaterials as scaffolds often can provide a "bridge" for normal tissue edges to regenerate over small distances, usually up to 1 cm. Larger tissue defect gaps typically require both scaffolds and cells for normal tissue regeneration to occur without scar formation. Various strategies can help to modulate the scar response and can potentially enhance tissue regeneration. Understanding the mechanistic basis of such multivariate interactions as the scar microenvironment, the immune system, extracellular matrix, and inflammatory cytokines may enable the design of tissue engineering and wound healing strategies that directly modulate the healing response in a manner favorable to regeneration.

Islet grafting and imaging in a bioengineered intramuscular space

BACKGROUND

Because the hepatic portal system may not be the optimal site for islet transplantation, several extrahepatic sites have been studied. Here, we examine an intramuscular transplantation site, bioengineered to better support islet neovascularization, engraftment, and survival, and we demonstrate that at this novel site, grafted beta cell mass may be quantitated in a real-time noninvasive manner by positron emission tomography (PET) imaging.

METHODS

Streptozotocin-induced rats were pretreated intramuscularly with a biocompatible angiogenic scaffold received syngeneic islet transplants 2 weeks later. The recipients were monitored serially by blood glucose and glucose tolerance measurements and by PET imaging of the transplant site with [11C] dihydrotetrabenazine. Parallel histopathologic evaluation of the grafts was performed using insulin staining and evaluation of microvasularity.

RESULTS

Reversal of hyperglycemia by islet transplantation was most successful in recipients pretreated with bioscaffolds containing angiogenic factors when compared with those who received no bioscaffolds or bioscaffolds not treated with angiogenic factors. PET imaging with [11C] dihydrotetrabenazine, insulin staining, and microvascular density patterns were consistent with islet survival, increased levels of angiogenesis, and with reversal of hyperglycemia.

CONCLUSIONS

Induction of increased neovascularization at an intramuscular site significantly improves islet transplant engraftment and survival compared with controls. The use of a nonhepatic transplant site may avoid intrahepatic complications and permit the use of PET imaging to measure and follow transplanted beta cell mass in real time. These findings have important implications for effective islet implantation outside of the liver and offer promising possibilities for improving islet survival, monitoring, and even prevention of islet loss.

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.

Direct effect of alginate purification on the survival of islets immobilized in alginate-based microcapsules

Alginate purification has been shown to decrease the host immune response to implanted alginate-based microcapsules, but the direct effect of contaminants on islet cell survival remains unknown. Wistar rat islets were immobilized in calcium alginate beads made with crude vs. purified alginate and then incubated in CMRL culture medium. Islet survival was evaluated at 1, 4, 7, 14 and 27 days post-encapsulation. Islet viability was investigated using a dual staining assay (propidium iodide and orange acridine). The islet cell necrosis and the proportion of apoptotic cells were quantified under optical microscopy and with a TUNEL assay, respectively. Islets immobilized in purified alginate were more viable, and had fewer necrotic centers, a smaller area of central necrosis and a lower number of apoptotic cells. At day 14 and 27 post-encapsulation, respectively, 48% and 23% of islets were viable with purified alginate vs. 18% and 8% with crude alginate (p<0.05). At day 14, the surface area of central necrosis and the number of necrotic islets were more important with the impure alginate (65% vs. 45% and 73% vs. 53%, respectively; p<0.05). We conclude that alginate purification improves the survival of islets that are immobilized in alginate-based microcapsules. These findings indicate that caution should be taken in the interpretation of in vivo experiments, as the results could be explained by either a direct effect on islet survival or a modification of the host reaction, or both. Moreover, it suggests that the effect on islet viability should be assessed during the development of biomaterials for cell encapsulation.

Adsorption of human immunoglobulin to implantable alginate-poly-L-lysine microcapsules: effect of microcapsule composition

Alginate-poly-L-lysine-alginate (APA) microcapsules continue to be the most widely studied device for the immuno-protection of transplanted therapeutic cells. Producing APA microcapsules having a reproducible and high level of biocompatibility requires an understanding of the mechanisms of the immune response towards the implants. Here, we investigate the adsorption of immunoglobulins (IgG, IgM, and IgA) onto the surface of APA microcapsules in vitro after their exposure to human serum and peritoneal fluid. Immunoglobulins (Ig) are considered to be opsonizing proteins, thus they tend to mediate inflammation when adsorbed to foreign surfaces. Ig adsorption was monitored using direct immunofluorescence. The amount of Ig adsorbed to the microcapsule surface was not significantly influenced by the guluronic acid content nor the purity level of the alginate, although microcapsules of intermediate-G purified alginate corresponded with the lowest adsorption levels. Ig adsorption was negligible when the poly-L-lysine membrane was omitted, suggesting that positive charges at the microcapsule surface are responsible for binding Ig.

Preparation of injectable 3D-formed beta-tricalcium phosphate bead/alginate composite for bone tissue engineering

A novel, injectable bone tissue engineering material was developed that consisted of beta-tricalcium phosphate (beta-TCP) beads as the solid phase and alginate as the gel phase. To prepare the instantaneously formed composite scaffold, an aqueous calcium chloride solution was dried on the surface of beta-TCP beads and crosslinked with an alginic acid sodium solution, thereby forming stable beta-TCP beads and alginate gel which were injectable via a syringe. This biodegradable composite was a three-dimensional (3D) material that could be used as an injectable scaffold for bone tissue engineering. In particular, the composite with 2.0 wt% alginate concentration exhibited a compressive strength of 69 kPa in dry conditions, which was significantly higher than that exhibited by 1.0 wt%. Furthermore, mesenchymal stem cells (MSC) were 3D-cultured within the composite and then investigated for osteogenic markers. MSC-loaded composite was subjected to scanning electron microscope (SEM) examination and implanted subcutaneously for in vivo experiment. Results showed that the scaffold provided support for osteogenic differentiation. In light of the encouraging results obtained, this novel injectable composite material may be useful for bone tissue engineering.

Encapsulated porcine islet transplantation: an evolving therapy for the treatment of type I diabetes

BACKGROUND

Allogeneic tissue-based therapies for Type I diabetes have demonstrated efficacy but are limited due to tissue-sourcing constraints, as the number of patients exceeds that of tissue donors. Porcine islets derived from designated pathogen-free sources could be an alternative, particularly if delivered in a way that evades the host immune system's rejection.

METHODS

This review focuses on approaches designed to protect xenogeneic islets from immune rejection by provision of perm-selective barriers.

RESULTS

Designated pathogen-free herds could provide a supply of wild-type porcine islets that are well tolerated when administered in a suitable protective delivery vehicle. Such barrier systems have enabled amelioration of diabetes in a variety of animal models and preliminary evidence suggests that similar results could be attained in humans.

CONCLUSION

With advances in biomaterial design, source tissue selection, and the evolution of critical cell processing techniques, contemporary encapsulated porcine islet therapies offer a new level of clinical promise.

Controlled delivery of platelet-rich plasma-derived growth factors for bone formation

Platelet-rich plasma (PRP) represents an autologous source of growth factors essential for bone regeneration. The clinical efficacy of PRP is, however, unpredictable, and this is likely due to the inefficient and inconsistent delivery of PRP-derived growth factors. Previous investigations have shown that current methods of PRP preparation result in a premature release of the relevant bone stimulatory factors. As successful bone regeneration requires multiple factors presented in a physiologic temporal and spatial cascade, the objective of this study is to control the bioavailability of PRP-derived growth factors using a hydrogel carrier system. Specifically, the release of platelet-derived growth factor, transforming growth factor beta-1, and insulin-like growth factor from two types of alginate carriers was compared over time. The effects of the released factors on the growth and alkaline phosphatase (ALP) activity of human osteoblast-like cells were also evaluated. It was found that factor release profiles varied as function of carrier type, and binding of growth factors to the alginate matrix also modulated their release. The bioactivity of released factors was maintained in vitro and they promoted cell proliferation and ALP activity. These results demonstrate the potential of this autologous multifactor delivery system for controlling the bioavailability of PRP-derived factors. Future studies will focus on optimizing this system to increase the clinical efficacy of PRP by matching the distribution and temporal sequencing of PRP-derived factors to the bone healing cascade.

Effect of alginate composition and gelling cation on micro-bead swelling

PURPOSE

The purpose of this study was to determine the roles of alginate composition and gelling cations on bead swelling, which affects its durability.

METHOD

Using a 2-channel droplet generator, microspheres were generated with 1.5% solutions of low viscosity high-mannuronic acid (LVM), medium viscosity high-mannuronic acid (MVM), low viscosity high-guluronic acid (LVG) and medium viscosity high-guluronic acid (MVG) alginate. They were gelled by cross-linking with 1.1% solution of either BaCl2 or CaCl2. The diameters of the micro-beads were measured and recorded on day 0. The micro-beads were subsequently washed and incubated in saline at 37 degrees C for 2 weeks with size assessment every 2 days. The data were normalized by calculation of the percentage change from control (day 0) for all groups of micro-beads.

RESULTS

Diameters of all beads were between 550 and 700 microm on day 0. Viscosity had no effect on swelling of Ba++- and Ca++-alginate micro-beads. Ca++-alginate micro-beads were more prone to swelling than the corresponding Ba++-alginate beads. High G-Ba++ beads had only a modest increase in size over time, in contrast to the high M-Ba++.

CONCLUSION

Alginate composition and the gelling cation have significant effects on bead swelling.

Effect of alginate composition and gelling cation on microbead swelling

PURPOSE

The purpose of this study was to determine the roles of alginate composition and gelling cations on bead swelling, which affects its durability.

METHOD

Using a 2-channel droplet generator, microspheres were generated with 1.5% solutions of low viscosity high-mannuronic acid (LVM), medium viscosity high-mannuronic acid (MVM), low viscosity high-guluronic acid (LVG) and medium viscosity high-guluronic acid (MVG) alginate. They were gelled by cross-linking with 1.1% solution of either BaCl2 or CaCl2. The diameters of the microbeads were measured and recorded on day 0. The microbeads were subsequently washed and incubated in saline at 37 degrees C for 2 weeks with size assessment every 2 days. The data were normalized by calculation of the percentage change from control (day 0) for all groups of microbeads.

RESULTS

Diameters of all beads were between 550-700 microns on day 0. Viscosity had no effect on swelling of Ba++- and Ca++-alginate microbeads. Ca++-alginate microbeads were more prone to swelling than the corresponding Ba++-alginate beads. High G-Ba++ beads had only a modest increase in size over time, in contrast to the high M-Ba++.

CONCLUSION

Alginate composition and the gelling cation have significant effects on bead swelling.

Characterization of microglial attachment and cytokine release on biomaterials of differing surface chemistry

The clinical usefulness of central nervous system recording electrodes is currently limited by inconsistent long-term performance that is believed to be governed by the brain tissue response to the implant. In this study, we observed persistent macrophage biomarker expression at the biotic-abiotic interface surrounding implanted electrodes over a 12-week indwelling period. Using the cell type-specific marker CD11b to examine the cells attached to electrodes retrieved over the indwelling period, we found that most of the cells were activated microglia, the resident macrophage of brain tissue, indicating that the implanted electrodes behave as a persistent inflammatory stimulus. To determine the potential usefulness of different materials as coatings for implanted electrodes, we examined brain-derived microglial cell attachment and cytokine release on a number of medically relevant materials. Our results suggest that activated microglia attach to many of the materials used as external coatings for electrode manufacture, and likely serve as a source of pro-inflammatory and neurotoxic cytokines that may be responsible for reducing the biocompatibility of such implants. Our results also indicate that low protein-binding coatings may be useful in reducing microglial attachment upon implantation in brain tissue and may provide a means of improving electrode biocompatibility.

Treatment of alopecia by transplantation of hair follicle stem cells and dermal papilla cells encapsulated in alginate gels

The affected individual of hair loss demands help, because hair is viewed as a sign of youth and good health. Nowadays treatment of alopecia includes drug therapy and hair transplantation. Some drugs may promote hair growth, at least temporarily, but the treatment is effective only in milder alopecia, instead of extensive alopecia. Furthermore, the side effect of long period medication could not be avoided. Hair transplantation involves harvesting small pieces of hair-bearing scalp grafts from a donor site and relocating them to a bald area. This method does not increase the number of existing hairs, but only redistributes them. The operation is sophisticated and time-consuming, thus the patient suffers a lot during the process. The discovery of hair follicle stem cells (FSC) brings gospel to the affected individual of hair loss because of its capacity of generating new hair when they interact with mesenchymal dermal papilla cells (DPC). Besides, both FSC and DPC have strong proliferative capacity and the patient's own cells could be expanded considerably in vitro. Thus we hypothesize that the microencapsulation of the two kinds of cells in alginate gels could be implanted into the bald scalp of the patient since alginate gels is effective in cell transplantation. The strategy may provide a more convenient and valid alternative to hair loss if the hypothesis proved to be practical.

Extraction and physicochemical characterization of Sargassum vulgare alginate from Brazil

Alginate fractions from Sargassum vulgare brown seaweed were characterized by (1)H NMR and fluorescence spectroscopy and by rheological measurements. The alginate extraction conditions were investigated. In order to carry out the structural and physicochemical characterization, samples extracted for 1 and 5h at 60 degrees C were further purified by re-precipitation with ethanol and denoted as SVLV (S. vulgare low viscosity) and SVHV (S. vulgare high viscosity), respectively. The M/G ratio values for SVLV and SVHV were 1.56 and 1.27, respectively, higher than the ratio for most Sargassum spp. alginates (0.19-0.82). The homopolymeric blocks F(GG) and F(MM) of these fractions characterized by (1)H NMR spectroscopy were 0.43 and 0.55 for SVHV and 0.36 and 0.58 for SVLV samples, respectively, these values typically being within 0.28-0.77 and 0.07-0.41, respectively. Therefore, the alginate samples from S. vulgare are much richer in mannuronic block structures than those from other Sargassum species. Values of M(w) for alginate samples were also calculated using intrinsic viscosity data. The M(w) value for SVLV (1.94 x 10(5)g/mol) was lower than that for SVHV (3.3 x 10(5)g/mol). Newtonian behavior was observed for a solution concentration as high as 0.7% for SVLV, while for SVHV the solutions behaved as a Newtonian fluid up to 0.5%. The optimal conditions for obtaining the alginates from S. vulgare were 60 degrees C and 5h extraction. Under these conditions, a more viscous alginate in higher yield was extracted from the seaweed biomass.

Preliminary investigation of calcium alginate gel as a biocompatible material for endovascular aneurysm embolization in vivo

OBJECTIVE

We sought to expand our assessment of calcium alginate as an embolic agent in an aneurysm model in swine that survived from 30 to 90 days. The objective of this study was to assess the biocompatibility and stability of calcium alginate in aneurysms in vivo.

METHODS

Ten models were created from a venous pouch sutured to the carotid artery, simulating flow to a side-wall aneurysm. Eight swine received complete embolizations, and two were less than 50% embolized to be used as controls. Alginate and calcium chloride were injected from concentric-tube microcatheters to form a mass that filled the aneurysm pouch.

RESULTS

Angiography and histology verified complete aneurysm occlusion and neck healing up to 90 days in eight swine. Both control animal aneurysms ruptured within 8 days. No animals showed evidence of downstream calcium alginate gel propagation. A minor bioactive response to the alginate gel was noted at 30 days, and fibrous tissue grew over the aneurysm orifice, sealing off the defect. No degenerative or inflammatory response was observed. At 90 days, moderate fibrous tissue surrounded the alginate. Tissue growth across the aneurysm neck remained complete and stable with no signs of neointimal growth into the parent vessel.

CONCLUSION

Calcium alginate was an effective endovascular occlusion material that filled the aneurysm and provided an effective template for tissue growth across the aneurysm neck after 30 days and up to 90 days. Complete filling of the aneurysm with calcium alginate ensures stability, biocompatibility, and optimal healing for up to 90 days in swine.

Tissue compatibility of interfacial polyelectrolyte complexation fibrous scaffold: evaluation of blood compatibility and biocompatibility

Interfacial polyelectrolyte complexation (PEC) fiber has been proposed as a biostructural unit and biological construct for tissue engineering applications, with its ability to incorporate proteins, drug molecules, DNA nanoparticles, and cells. In this study, we evaluated the biocompatibility and blood compatibility of PEC fiber in order to assess its potential for in vivo applications in tissue engineering. Although chitosan-alginate PEC fibrous scaffold was found to be thrombogenic, the blood compatibility of the scaffold could be significantly improved by incorporating a small amount of heparin in the polyelectrolyte solution during fiber formation. The platelet microparticle production and platelet adhesion on the chitosan-alginate-heparin fibrous scaffold were comparable to those on the resting control. In vitro cytotoxicity test showed that the scaffold was not toxic to human mesenchymal stem cells (hMSCs). In the in vivo biocompatibility test in rats, no acute inflammation was observed in the subcutaneously or intramuscularly implanted specimens. Good cell infiltration and vascularization were observed after 2 months of implantations. Enhanced extracellular matrix (ECM) deposition was observed when hMSCs were cultured in the transforming growth factor-beta3 (TGF-beta3)-encapsulated PEC fibrous scaffold in vitro, or when the TGF-beta3-encapsulated PEC was implanted intramuscularly in vivo. The results showed that this versatile PEC fibrous scaffold could be used in various tissue engineering applications for its good biocompatible and blood compatible properties.

Induction of lymphocytes activated marker CD69 following exposure to chitosan and alginate biopolymers

CD69 is a very early cell activation antigen expressed on the surface of activated immune cells. It can appear within 1-2h of activation and exhibits maximal expression levels between 18 and 24h after stimulation. In this work, the expression profile of CD69 in mice splenocytes was evaluated following exposure to the biopolymers, chitosan or alginate and the immunostimulatory factors, CpG ODN 1826 or concanavalin A. We have shown that both polymers are able to upregulate expression of CD69 on B cells and CD4+ T-lymphocytes, with alginate as the least potent stimulus. Moreover, the expression of the CD69 molecule on CD8+ T-lymphocytes was observed only in splenocytes cultured with chitosan. However, activation of lymphocytes did not result in cell proliferation. On the other hand, CpG ODN proved to be a potent B cell stimulator, as evidenced by the upregulation of CD69, but had less effect on T-cells. These results, together with previous discoveries reported in scientific literature, may contribute to the clarification of the adjuvant effect, which has been attributed to chitosan and alginate formulations or to the biopolymers itself.

The Effect of 3D Construction Culture of Human Chondrocytes Using Alginate Sponge

In this study, we investigated the effect of the use of alginate sponge as a chondrocyte-3D scaffold for the construction of a cartilage graft. Alginate sponge was made by 5% alginic acid which was crosslinked by CaCl2. Chondrocytes were obtained from a nasal septum after the operation and cultured in 3D alginate sponge. For analysis of cell differentiation, we have checked aggrecan, collagen type I and II using RT-PCR and performed the histological and scanning electron microscopy analysis. Our experiments showed that alginate sponge of 5% promoted sufficient chondrocyte proliferation and differentiation, resulting in the formation of a specific cartilage matrix. The sponge presents new perspectives with respect to in vitro production of "artificial" cartilage. We conclude that the alginate sponges have potential as a scaffold for cartilage tissue engineering.

In vivo evaluation of EPO-secreting cells immobilized in different alginate-PLL microcapsules

Alginates are the most employed biomaterials for cell encapsulation due to their abundance, easy gelling properties and apparent biocompatibility. However, as natural polymers different impurities including endotoxins, proteins and polyphenols can be found in their composition. Several purification protocols as well as different batteries of assays to prove the biocompatibility of the alginates in vitro have been recently developed. However, little is known about how the use of alginates with different purity grade may affect the host immune response after their implantation in vivo. The present paper investigates the long-term functionality and biocompatibility of murine erythropoietin (EPO) secreting C2C12 cells entrapped in microcapsules elaborated with alginates with different properties (purity, composition and viscosity). Results showed that independently of the alginate type employed, the animals presented elevated hematocrit levels until day 130, remaining at values between 70-87%. However, histological analysis of the explanted devices showed higher overgrowth around non-biomedical grade alginate microcapsules which could be directly related with higher impurity content of this type of alginate. Although EPO delivery may be limited by the formation of a fibrotic layer around non-biomedical grade alginate microcapsules, the high EPO secretion of the encapsulated cells together with the pharmacodynamic behaviour and the angiogenic and immune-modulatory properties of EPO result in no direct correlation between the biocompatibility of the alginate and the therapeutic response obtained.

Alginate Hydrogels as Biomaterials

[Image: see text] Alginate hydrogels are proving to have a wide applicability as biomaterials. They have been used as scaffolds for tissue engineering, as delivery vehicles for drugs, and as model extracellular matrices for basic biological studies. These applications require tight control of a number of material properties including mechanical stiffness, swelling, degradation, cell attachment, and binding or release of bioactive molecules. Control over these properties can be achieved by chemical or physical modifications of the polysaccharide itself or the gels formed from alginate. The utility of these modified alginate gels as biomaterials has been demonstrated in a number of in vitro and in vivo studies.Micro-CT images of bone-like constructs that result from transplantation of osteoblasts on gels that degrade over a time frame of several months leading to improved bone formation.

Radiopaque Alginate Microcapsules for X-ray Visualization and Immunoprotection of Cellular Therapeutics

Alginate-poly-L-lysine-alginate (APA) microcapsules have been explored as vehicles for therapeutic drug and cell delivery. The permselectivity of these capsules provides a unique means of controlled drug release and immunoisolation of encapsulated cells. Immunoisolation is especially attractive as it abrogates the need for chronic immunosuppressive therapy and opens up the possibility for the delivery of numerous cell sources including xenogeneic grafts. APA microcapsules containing cellular therapeutics have proven effective in the short-term treatment of a wide range of diseases requiring enzyme or endocrine replacement therapy, including type I diabetes. If these microcapsules could be noninvasively monitored with X-ray imaging modalities (i.e., fluoroscopy, CT, and digital subtraction angiography), questions such as the ideal transplantation site, the best means of delivery, and the long-term survival of grafts could be better addressed. We have developed two novel alginate-based radiopaque microcapsule formulations containing either barium sulfate (Ba X-Caps) or bismuth sulfate (Bi X-Caps). As compared to conventional, nonradiopaque APA capsules, Ba X-Caps and Bi X-Caps containing human cadaveric islets resulted in a decrease in cellular viability of less than 5% up to 14 days after encapsulation. Both radiopaque capsules were found to be permeable to lectins < or =75 kDa, but were impermeable to lectins > or =120 kDa, thus ensuring the blockage of the penetration of antibodies while allowing free diffusion of insulin and nutrients. The glucose-responsive insulin secretion of the radiopaque encapsulated human islets was found to be unaltered compared to that of unlabeled controls, with human C-peptide levels ranging from 3.21 to 2.87 (Ba X-Caps) and 3.23 to 2.87 (Bi X-Caps) ng/islet at 7 and 14 days postencapsulation, respectively. Using fluoroscopy, both Ba X-Caps and Bi X-Caps could be readily visualized as single radiopaque entities in vitro. Furthermore, following transplantation in vivo in mice and rabbits, single capsules could be identified with no significant change in contrast for at least 2 weeks. This study represents the first attempt at making radiopaque microcapsules for X-ray guided delivery and imaging of cellular therapeutics. While human cadaveric islets were used as a proof-of-principle, these radiopaque capsules may have wide ranging therapeutic applications for a variety of cell types.

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.

Six-month survival of microencapsulated pig islets and alginate biocompatibility in primates: proof of concept

BACKGROUND

Pig islets xenotransplantation remains associated with a strong humoral and cellular xenogeneic immune responses. The aim of this study was to assess the long-term biocompatibility of alginate encapsulated pig islets after transplantation in primates.

METHODS

Adult pig islets encapsulated in alginate under optimal conditions (n=7) or not (n=5) were transplanted under the kidney capsule of nondiabetic Cynomolgus maccacus. Additional primates received empty capsules (n=1) and nonencapsulated pig islets (n=2) as controls. Capsule integrity, cellular overgrowth, pig islet survival, porcine C-peptide and anti-pig IgM/IgG antibodies were examined up to 6 months after implantation.

RESULTS

Nonencapsulated islets and islets encapsulated in nonoptimal capsules were rapidly destroyed. In seven primates receiving perfectly encapsulated pig islets, part of the islets survived up to 6 months after implantation without immunosuppression. Porcine C-peptide was detected after 1 month in 71% of the animals. The majority of grafts (86%) were intact and completely free of cellular overgrowth or capsule fibrosis. Explanted capsules, after 135 (n=2/2) and 180 (n=2/3) days, demonstrated residual insulin content and responses to glucose challenge (stimulation index of 2.2). Partial islet survival was obtained despite an elicited anti-pig IgG humoral response.

CONCLUSIONS

Optimal alginate encapsulation significantly prolonged adult pig islet survival into primates for up to 6 months, even in the presence of antibody response.

Polysaccharide biological response modifiers

Biological response modifiers (BRMs) are substances which augment immune response. BRMs can be cytokines which are produced endogenously in our body by immune cells or derivatives of bacteria, fungi, brown algae, Aloe vera and photosynthetic plants. Such exogeneous derivatives (exogeneous BRMs) can be nucleic acid (CpG), lipid (lipotechoic acid), protein or polysaccharide in nature. The receptors for these exogeneous BRMs are pattern recognition receptors. The binding of exogeneous BRMs to pattern recognition receptors triggers immune response. Exogenous BRMs have been reported to have anti-viral, anti-bacterial, anti-fungal, anti-parasitic, and anti-tumor activities. Among different exogeneous BRMs, polysaccharide BRMs have the widest occurrence in nature. Some polysaccharide BRMs have been tested for their therapeutic properties in human clinical trials. An overview of current understandings of polysaccharide BRMs is summarized in this review.

Biodegradable scaffolds – delivery systems for cell therapies

The use of cells as therapies for disease, repair and regeneration of tissues is one of the new challenges in modern therapeutics. To facilitate the ability to localise, condition and protect cells, biodegradable scaffolds are being developed that will improve the efficiency of these treatments. Thus, cell delivery systems, either scaffolds or capsules, play a pivotal role in the success of these techniques. This review discusses these novel approaches. The selection of scaffold materials is addressed alongside issues of biocompatibility. The current research developments in smart scaffolds, which focus on the formation of biomimetic scaffolds, new fabrication techniques capable of controlling architecture and microstructure of scaffolds, and the production of injectable and in situ crosslinked scaffolds, are outlined. Finally, the continuing challenges that will drive future research in the cell therapies are highlighted.

Immobilization and hybridization of DNA in a sugar polyacrylate hydrogel

Using a non-contact microarrayer, amine-terminated probe oligonucleotides representing 20-, 50-, and 70-mer fragments of the fliC gene were covalently coupled into three-dimensional regions in a "sugar polyacrylate" hydrogel based on poly(6-acryloyl-beta-O-methyl galactopyranoside-co-aminopropyl methacrylamide). The arrayer deposited the solution containing ssDNA probes in discrete regions on the surface of the gel (i.e. as a droplet with a ca. 450 microm diameter), allowing penetration and attachment of the ss DNA within the three dimensional region of the gel. The attachment was mediated by the homobifunctional crosslinker bis-succinimidyl suberate. Confocal microscopy showed the density of attached probe DNA was greatest in the interior-most regions of the gel volume. Target ssDNA (20- and 70-mer) was able to diffuse through the gel and undergo successful hybridization with the probes. For target ssDNA in the concentration range 0.19 microM to 6.0 microM, there was a linear correlation between DNA concentration and the fluorescence of the gel region where hybridization occurred.