Biocompatible alginate from freshly collected Laminaria pallida for implantation

Multiscale investigation of viscoelastic properties of aqueous solutions of sodium alginate and evaluation of their biocompatibility

In order to get better knowledge of mechanical properties from microscopic to macroscopic scale of biopolymers, viscoelastic bulk properties of aqueous solutions of sodium alginate were studied at different scales by combining macroscopic shear rheology (Hz), diffusing-wave spectroscopy microrheology (kHz-MHz) and Brillouin spectroscopy (GHz). Structural properties were also directly probed by small-angle X-ray scattering (SAXS). The results demonstrate a change from polyelectrolyte behavior to neutral polymer behavior by increasing polymer concentration with the determination of characteristic sizes (persistence length, correlation length). The viscoelastic properties probed at the phonon wavelength much higher than the ones obtained at low frequency reflect the variation of microscopic viscosity. First experiments obtained by metabolic activity assays with mouse embryonic fibroblasts showed biocompatibility of sodium alginate aqueous solutions in the studied range of concentrations (2.5-10 g L-1) and consequently their potential biomedical applications.

Recent Development of Alginate-Based Materials and Their Versatile Functions in Biomedicine, Flexible Electronics, and Environmental Uses

Alginate is a natural polysaccharide that is easily chemically modified or compounded with other components for various types of functionalities. The alginate derivatives are appealing not only because they are biocompatible so that they can be used in biomedicine or tissue engineering but also because of the prospering bioelectronics that require various biomaterials to interface between human tissues and electronics or to serve as electronic components themselves. The study of alginate-based materials, especially hydrogels, have repeatedly found new frontiers over recent years. In this Review, we document the basic properties of alginate, their chemical modification strategies, and the recent development of alginate-based functional composite materials. The newly thrived functions such as ionically conductive hydrogel or 3D or 4D cell culturing matrix are emphasized among other appealing potential applications. We expect that the documentation of relevant information will stimulate scientific efforts to further develop biocompatible electronics or smart materials and to help the research domain better address the medicine, energy, and environmental challenges faced by human societies.

Alginate from Sargassum siliquosum Simultaneously Stimulates Innate Immunity, Upregulates Immune Genes, and Enhances Resistance of Pacific White Shrimp (Litopenaeus vannamei) Against White Spot Syndrome Virus (WSSV)

Although alginate is known as an immunostimulant in shrimp, the comprehensive and simultaneous study on its activity to resolve the relationship of the hematological parameters, upregulation of immune-related gene expression, and resistance to pathogen has not been found in shrimp. We performed experiments to evaluate the effect and mechanism of alginate from S. siliquosum on Pacific white shrimp immune system. Hematological parameters were examined after oral administration of Na alginate in the shrimp. White spot syndrome virus (WSSV) was injected to the shrimp at 14 days, and its copy number was examined quantitatively (qRT-PCR). Immune-related gene expression was evaluated by qRT-PCR. Alginate increased some hematological immune parameters of shrimp. Before WSSV infection, expression levels of Toll and lectin genes were upregulated. The lectin gene were upregulated post infection, and the Toll gene in all the treatments were downregulated, except the shrimps fed with alginate at 6.0 g kg-1 at 48 h post infection (hpi). The shrimps fed with alginate at 6.0 g kg-1 were the most resistant and gave the least WSSV copy number at 48 hpi. Resistance of shrimps fed the alginate-supplemented diets against WSSV was significantly higher compared to that of the control treatment with 56% and 10% of survival rates, respectively. Oral administration of alginate did not affect the growth and total protein plasma. At 120 h post challenge, alginate treatment at 6.0 g kg-1 exhibited the highest survival rate. It is concluded that oral administration of alginate enhanced the innate immunity by upregulating immune-related gene expression. Consequently, the enhancement of the shrimp innate immunity improves the resistance against WSSV infection.

Novel injectable gallium-based self-setting glass-alginate hydrogel composite for cardiovascular tissue engineering

Composite biomaterials offer a new approach for engineering novel, minimally-invasive scaffolds with properties that can be modified for a range of soft tissue applications. In this study, a new way of controlling the gelation of alginate hydrogels using Ga-based glass particles is presented. Through a comprehensive analysis, it was shown that the setting time, mechanical strength, stiffness and degradation properties of this composite can all be tailored for various applications. Specifically, the hydrogel generated through using a glass particle, wherein toxic aluminium is replaced with biocompatible gallium, exhibited enhanced properties. The material's stiffness matches that of soft tissues, while it displays a slow and tuneable gelation rate, making it a suitable candidate for minimally-invasive intra-vascular injection. In addition, it was also found that this composite can be tailored to deliver ions into the local cellular environment without affecting platelet adhesion or compromising viability of vascular cells in vitro.

Effects of Ultra-Purified Alginate Gel Implantation on Meniscal Defects in Rabbits

BACKGROUND

Many tissue-engineered methods for meniscal repair have been studied, but their utility remains unclear.

HYPOTHESIS

Implantation of low-endotoxin, ultra-purified alginate (UPAL) gel without cells could induce fibrocartilage regeneration on meniscal defects in rabbits.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-two mature Japanese White rabbits were divided into 2 groups of 21 animals each. In each animal, a cylindrical defect measuring 2 mm in diameter was created with a biopsy punch on the anterior horn of the medial meniscus. In the control group, no treatment was applied on the left medial meniscal defect. In the UPAL gel group, the right medial meniscal defect was injected with the UPAL gel and gelated by a CaCl₂ solution. Samples were evaluated at 3, 6, and 12 weeks postoperatively. For biomechanical evaluation, 6 additional samples from intact animals were used for comparison.

RESULTS

The macroscopic score was significantly greater in the UPAL gel group than in the control group at 3 weeks (mean ± SE: 5.6 ± 0.82 vs 3.4 ± 0.83, P = .010), 6 weeks (5.9 ± 0.72 vs 2.5 ± 0.75, P = .026), and 12 weeks (5.2 ± 1.21 vs 1.0 ± 0.63, P = .020). The histological score was significantly greater in the UPAL group than in the control group at 3 weeks (2.1 ± 0.31 vs 1.2 ± 0.25, P = .029) and 12 weeks (2.2 ± 0.55 vs 0.3 ± 0.21, P = .016). The mean stiffness of the reparative tissue in the UPAL gel group was significantly greater than that in the control group at 6 weeks (24.325 ± 3.920 N/mm vs 8.723 ± 1.190 N/mm, P = .006) and at 12 weeks (27.804 ± 6.169 N/mm vs not applicable [because of rupture]).

CONCLUSION

The UPAL gel enhanced the spontaneous repair of fibrocartilage tissues in a cylindrical meniscal defect in rabbits.

CLINICAL RELEVANCE

These results imply that the acellular UPAL gel may improve the repair of traumatic meniscal injuries.

Chondrogenic differentiation of mouse induced pluripotent stem cells using the three-dimensional culture with ultra-purified alginate gel

As articular cartilages have rarely healed by themselves because of their characteristics of avascularity and low cell density, surgical intervention is ideal for patients with cartilaginous injuries. Because of structural characteristics of the cartilage tissue, a three-dimensional culture of stem cells in biomaterials is a favorable system on cartilage tissue engineering. Induced pluripotent stem cells (iPSCs) are a new cell source in cartilage tissue engineering for its characteristics of self-renewal capability and pluripotency. However, the optimal cultivation condition for chondrogenesis of iPSCs is still unknown. Here we show that a novel chondrogenic differentiation method of iPSCs using the combination of three-dimensional cultivation in ultra-purified alginate gel (UPAL gel) and multi-step differentiation via mesenchymal stem cell-like cells (iPS-MSCs) could efficiently and specifically differentiate iPSCs into chondrocytes. The iPS-MSCs in UPAL gel culture sequentially enhanced the expression of chondrogenic marker without the upregulation of that of osteogenic and adipogenic marker and histologically showed homogeneous chondrogenic extracellular matrix formation. Our results suggest that the pluripotency of iPSCs can be controlled when iPSCs are differentiated into iPS-MSCs before embedding in UPAL gel. These results lead to the establishment of an efficient three-dimensional system to engineer artificial cartilage tissue from iPSCs for cartilage regeneration. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1086-1093, 2019.

Microencapsulated adult porcine islets transplanted intraperitoneally in streptozotocin-diabetic non-human primates

BACKGROUND

Xenogeneic donors would provide an unlimited source of islets for the treatment of type 1 diabetes (T1D). The goal of this study was to assess the function of microencapsulated adult porcine islets (APIs) transplanted ip in streptozotocin (STZ)-diabetic non-human primates (NHPs) given targeted immunosuppression.

METHODS

APIs were encapsulated in: (a) single barium-gelled alginate capsules or (b) double alginate capsules with an inner, islet-containing compartment and a durable, biocompatible outer alginate layer. Immunosuppressed, streptozotocin-diabetic NHPs were transplanted ip with encapsulated APIs, and graft function was monitored by measuring blood glucose, %HbA1c, and porcine C-peptide. At graft failure, explanted capsules were assessed for biocompatibility and durability plus islet viability and functionality. Host immune responses were evaluated by phenotyping peritoneal cell populations, quantitation of peritoneal cytokines and chemokines, and measurement of anti-porcine IgG and IgM plus anti-Gal IgG.

RESULTS

NHP recipients had reduced hyperglycemia, decreased exogenous insulin requirements, and lower percent hemoglobin A1c (%HbA1c) levels. Porcine C-peptide was detected in plasma of all recipients, but these levels diminished with time. However, relatively high levels of porcine C-peptide were detected locally in the peritoneal graft site of some recipients at sacrifice. IV glucose tolerance tests demonstrated metabolic function, but the grafts eventually failed in all diabetic NHPs regardless of the type of encapsulation or the host immunosuppression regimen. Explanted microcapsules were intact, "clean," and free-floating without evidence of fibrosis at graft failure, and some reversed diabetes when re-implanted ip in diabetic immunoincompetent mice. Histology of explanted capsules showed scant evidence of a host cellular response, and viable islets could be found. Flow cytometric analyses of peritoneal cells and peripheral blood showed similarly minimal evidence of a host immune response. Preformed anti-porcine IgG and IgM antibodies were present in recipient plasma, but these levels did not rise post-transplant. Peritoneal graft site cytokine or chemokine levels were equivalent to normal controls, with the exception of minimal elevation observed for IL-6 or IL-1β, GRO-α, I-309, IP-10, and MCP-1. However, we found central necrosis in many of the encapsulated islets after graft failure, and explanted islets expressed endogenous markers of hypoxia (HIF-1α, osteopontin, and GLUT-1), suggesting a role for non-immunologic factors, likely hypoxia, in graft failure.

CONCLUSIONS

With donor xenoislet microencapsulation and host immunosuppression, APIs corrected hyperglycemia after ip transplantation in STZ-diabetic NHPs in the short term. The islet xenografts lost efficacy gradually, but at graft failure, some viable islets remained, substantial porcine C-peptide was detected in the peritoneal graft site, and there was very little evidence of a host immune response. We postulate that chronic effects of non-immunologic factors, such as in vivo hypoxic and hyperglycemic conditions, damaged the encapsulated islet xenografts. To achieve long-term function, new approaches must be developed to prevent this damage, for example, by increasing the oxygen supply to microencapsulated islets in the ip space.

Trophic effects of adipose-tissue-derived and bone-marrow-derived mesenchymal stem cells enhance cartilage generation by chondrocytes in co-culture

AIMS

Combining mesenchymal stem cells (MSCs) and chondrocytes has great potential for cell-based cartilage repair. However, there is much debate regarding the mechanisms behind this concept. We aimed to clarify the mechanisms that lead to chondrogenesis (chondrocyte driven MSC-differentiation versus MSC driven chondroinduction) and whether their effect was dependent on MSC-origin. Therefore, chondrogenesis of human adipose-tissue-derived MSCs (hAMSCs) and bone-marrow-derived MSCs (hBMSCs) combined with bovine articular chondrocytes (bACs) was compared.

METHODS

hAMSCs or hBMSCs were combined with bACs in alginate and cultured in vitro or implanted subcutaneously in mice. Cartilage formation was evaluated with biochemical, histological and biomechanical analyses. To further investigate the interactions between bACs and hMSCs, (1) co-culture, (2) pellet, (3) Transwell® and (4) conditioned media studies were conducted.

RESULTS

The presence of hMSCs-either hAMSCs or hBMSCs-increased chondrogenesis in culture; deposition of GAG was most evidently enhanced in hBMSC/bACs. This effect was similar when hMSCs and bAC were combined in pellet culture, in alginate culture or when conditioned media of hMSCs were used on bAC. Species-specific gene-expression analyses demonstrated that aggrecan was expressed by bACs only, indicating a predominantly trophic role for hMSCs. Collagen-10-gene expression of bACs was not affected by hBMSCs, but slightly enhanced by hAMSCs. After in-vivo implantation, hAMSC/bACs and hBMSC/bACs had similar cartilage matrix production, both appeared stable and did not calcify.

CONCLUSIONS

This study demonstrates that replacing 80% of bACs by either hAMSCs or hBMSCs does not influence cartilage matrix production or stability. The remaining chondrocytes produce more matrix due to trophic factors produced by hMSCs.

Combined De-Algination Process as a Fractionation Strategy for Valorization of Brown Macroalga Saccharina japonica

A combined process, de-algination followed by enzymatic saccharification, was designed to produce alginate and glucose from Saccharina japonica consecutively. The process conditions of de-algination were optimized separately for each stage of acidification and alkaline extraction. Collectively, the de-algination yield was 70.1% under the following optimized conditions: 2.4 wt% of Na2CO3, 70 °C, and 100 min with the acidified S. japonica immersed in a 0.5 wt% H2SO4 solution for 2 h at room temperature. The glucan content in the de-alginated S. japonica increased to 38.0%, which was approximately fivefold higher than that of the raw S. japonica. The enzymatic hydrolysis of the de-alginated S. japonica almost completed in 9 h, affording 5.2 g (96.8% of glucan digestibility) of glucose at a de-alginated S. japonica loading of 14.2 g.

Investigating the Synergistic Effects of Combined Modified Alginates on Macrophage Phenotype

Understanding macrophage responses to biomaterials is crucial to the success of implanted medical devices, tissue engineering scaffolds, and drug delivery vehicles. Cellular responses to materials may depend synergistically on multiple surface chemistries, due to the polyvalent nature of cell⁻ligand interactions. Previous work in our lab found that different surface functionalities of chemically modified alginate could sway macrophage phenotype toward either the pro-inflammatory or pro-angiogenic phenotype. Using these findings, this research aims to understand the relationship between combined material surface chemistries and macrophage phenotype. Tumor necrosis factor-α (TNF-α) secretion, nitrite production, and arginase activity were measured and used to determine the ability of the materials to alter macrophage phenotype. Cooperative relationships between pairwise modifications of alginate were determined by calculating synergy values for the aforementioned molecules. Several materials appeared to improve M1 to M2 macrophage reprogramming capabilities, giving valuable insight into the complexity of surface chemistries needed for optimal incorporation and survival of implanted biomaterials.

Innate immune-stimulating and immune genes up-regulating activities of three types of alginate from Sargassum siliquosum in Pacific white shrimp, Litopenaeus vannamei

The Total Haemocyte Count (THC), phenoloxidase (PO), Superoxide Dismutase (SOD) activity, Phagocytic Activity/Index and Total Protein Plasma (TPP) were examined after feeding the white shrimp Litopenaeus vannamei with diets supplemented with three different types of alginates (acid, calcium and sodium alginates). Immune-related genes expression was evaluated by quantitative Real Time PCR (qRT-PCR). Results indicated that the immune parameters directly increased according to the doses of alginates and time. The 2.0 g kg(-1) of acid and sodium alginate treatments were gave better results. Four immune-related genes expression i.e. LGBP, Toll, Lectin, proPO were up regulated. It is therefore concluded that the supplementation of alginate of Sargassum siliquosum on the diet of L. vannamei enhanced the innate immunity as well as the expression of immune-related genes. It is the first report on the simultaneous evaluation of three alginate types to enhance innate immune parameters and immune-related genes expression in L. vannamei.

Therapeutic effects of intra-articular ultra-purified low endotoxin alginate administration on an experimental canine osteoarthritis model

OBJECTIVE

This study aimed to elucidate the therapeutic effects of intra-articular administration of ultra-purified low endotoxin alginate (UPLE-alginate) on osteoarthritis (OA) using a canine anterior cruciate ligament transection (ACLT) model.

DESIGN

We used 20 beagle dogs. ACLT was performed on the left knee of each dog and a sham operation was performed on the right knee as a control. All animals were randomly divided into the control (saline) and therapeutic (UPLE-alginate) groups. Animals in the control and therapeutic groups received weekly injections with 0.7 mL normal saline or 0.7 mL 0.5% UPLE-alginate, respectively, from 0 to 3 weeks after ACLT or sham operation. At 9 weeks after ACLT, the knee joints of all animals were observed using arthroscopy. All animals were euthanized at 14 weeks after ACLT and evaluated using morphologic assessment, histologic assessment, and biomechanical testing.

RESULTS

Arthroscopic findings showed intact cartilage surface in both groups. Morphologic findings in the therapeutic group showed milder degeneration compared with those of the control group, but there were no significant differences between groups. Histologic scores of the medial femoral condyle (MFC) and lateral femoral condyle (LFC) were better in the therapeutic group than the control group (MFC: p = 0.009, LFC: p = 0.009). Joint lubrication did not differ significantly between groups.

CONCLUSION

Intra-articular administration of UPLE-alginate in the early stage of OA slowed disease progression in canines. UPLE-alginate may have potential as a therapeutic agent for OA patients and reduce the number of patients who need to undergo total joint arthroplasty.

Microenvironment-dependent respiration of T-47D cells cultured in alginate biostructures

OBJECTIVES

The main objective of this paper was to investigate whether the oxygen consumption rate (OCR) of cells entrapped in alginate hydrogels depends on presence of soluble factors present in foetal bovine serum (FBS).

MATERIALS AND METHODS

Pericellular oxygen concentrations were measured using a photochemical oxygen sensor inserted into bioconstructs made from different formulations of alginate, containing T-47D cells. Cell count was corrected for viability as determined by cell uptake and exclusion of standard live/dead fluorophores, in sections of freshly prepared biostructures. Based on concentration data, OCR of the embedded cells was calculated according to a simple algorithm.

RESULTS

OCR was found to vary significantly between the different formulations investigated. Inclusion of high concentrations of FBS in the biostructure matrices elicited significantly higher OCRs, in guluronate-rich gels similar to those previously found in monolayer culture. Guluronate-rich gels also generally permitted highest OCR. Respiration also had a falling tendency with increasing alginate concentration and elastic modulus.

CONCLUSIONS

Presence of FBS in biostructure matrices elicited higher OCR in T-47D cells. Formulation of biostructures must consider differential diffusion of macromolecular substances.

Reduction of inflammatory reaction in the use of purified alginate microcapsules

Alginate, a polysaccharide extracted from brown seaweed, remains the most widely used biomaterial for immobilizing cells to be transplanted, because of the good viability of the encapsulated cells and the relatively ease of processing for cell encapsulation. However, the main drawback is the immune reaction in vivo. To overcome this problem, we have demonstrated a modified Korbutt method for alginate purification. After alginate microcapsules were manufactured, NIH/3T3 fibroblast cells were seeded in purified and non-purified alginate microcapsules, and the cell proliferation was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide assay. Reverse transcriptase-polymerase chain reaction was performed to assess the mRNA expression of RAW 264.7 macrophage cells for inflammation cytokines such as TNF-α. Purified and non-purified alginate microcapsules were implanted into Wister rats, and subsequently extracted after 1-2 weeks. Tissues surrounding the implants were harvested and underwent histological evaluation through H&E staining and immunohistochemical evaluation through ED-1 staining. In this result, contaminated materials in the purified alginate were eliminated by purification process. Thereby, density of inflammatory cell decreased about 30% more than non-purified alginate and thickness of fibrotic wall decreased about three times. In concluding, the purified alginate is anticipated to be highly potent for numerous biomaterial applications.

Evaluation of biocompatibility and anti-glioma efficacy of doxorubicin and irinotecan drug-eluting bead suspensions in alginate

INTRODUCTION

Chemotherapeutic drug-eluting beads (DEBs) are microspheres that are in clinical use for intraarterial chemoembolisation of liver cancer. Here we report on the biocompatibility and anti-tumour efficacy of DEBs after intratumoral application in a rat BT4Ca glioma model.

METHODS AND RESULTS

Doxorubicin and irinotecan-eluting DEBs were suspended in a Ca(2+)-free aqueous alginate solution that provides a sol-gel transition when injected into the Ca(2+) rich brain tissue. In this way the DEBs are immobilised at the implantation site. Forced elution studies in vitro using a USP-4 flow-through apparatus demonstrated that the alginate excipient helped to reduce the burst effect and rate the elution from the beads. From the in vivo evaluation, doxorubicin DEBs demonstrated a significant local toxicity, while irinotecan-loaded DEBs showed good local tissue compatibility. Doxorubicin at higher concentrations and irinotecan-loaded DEBs were found to decrease tumour volume, increase survival time and decrease the Ki67 proliferation index of the tumour. Doxorubicin was shown by fluorescent microscopy to diffuse into the peritumoral tissue, but also penetrates along white matter tracts, to more distant areas.

DISCUSSION

We conclude that the alginate suspension of irinotecan DEBs can be considered safe and effective in a clinical setting.

Viability of human umbilical cord–derived mesenchymal stem cells in G-rich and M-rich alginates

In this study, the effect of pharmaceutical-grade alginates on the cell viability of human mesenchymal stem cells derived from umbilical cord was examined and their use in tissue engineering applications was evaluated. The effects of the ratio of the copolymer building blocks (guluronic and mannuronic acids) and their interactions with divalent calcium, the purity of alginates (proteins and polyphenol content), and gelation factors (calcium concentration and sol content) were examined. The high guluronic acid content in the alginates improved the viability of the human mesenchymal stem cells derived from umbilical cord and supported cell growth significantly. It was confirmed that the sol fraction of alginate reduced cell viability. Cells in the presence of alginate beads cross-linked with 50 and 100 mM calcium chloride showed maximum viability; the protein and polyphenol content of the alginates did not affect the viability of the human mesenchymal stem cells derived from umbilical cord, while the monomer ratio did have an obvious effect.

Nanofibers resulting from cooperative electrostatic and hydrophobic interactions between peptides and polyelectrolytes of opposite charge

We investigated whether cationic peptides that contain hydrophobic side chains were able to stabilize themselves via hydrophobic interactions between neighboring peptide molecules upon electrostatic binding to oppositely charged polyelectrolytes. The interaction mechanism was examined through a model system consisting of the anionic polyelectrolyte alginate and the cationic decapeptide ozarelix. The interaction resulted in the formation of highly ordered complexes that were noticeable upon visual inspection. These complexes were then investigated by microscopic techniques and shown to exhibit a branched network structure. Cryogenic-temperature transmission electron microscopy (cryo-TEM) and negative staining TEM revealed that the molecular interactions between alginate and ozarelix led to the formation of nanofibers. The rodlike nanofibers had a diameter distribution of 4-8 nm. Isothermal titration calorimetry was used to determine the thermodynamic parameters of the alginate-ozarelix interaction. The binding constant was found to be on the order of 10(6) M(-1), indicating a high binding affinity. The interaction of the peptide with the polyelectrolyte triggered profound changes in the conformation of ozarelix, which was confirmed by UV spectroscopy and circular dichroism. On the basis of these experimental results, a theoretical modeling study of the alginate-ozarelix interaction was conducted to gain a better molecular-level understanding of the complex structure. It revealed that, upon binding of ozarelix to alginate, new intermolecular and intramolecular aromatic interactions between the ozarelix molecules occurred. These interactions changed the conformation of the peptide, a modification in which the aromatic side chains played a major role. Our results indicate that the cationic peptides interact with the polyanions via electrostatic interactions, but are additionally stabilized via hydrophobic interactions. This binding mode may serve as a powerful tool to extend the duration of drug release in hydrogel drug delivery systems.

Repair of articular cartilage defects with a novel injectable in situ forming material in a canine model

We developed an ultra-purified in situ forming gel as an injectable delivery vehicle of bone marrow stromal cells (BMSCs). Our objective was to assess reparative tissues treated with autologous BMSCs implanted using the injectable implantation system into osteochondral defects in a canine model. Forty-eight osteochondral defects in the patella groove of the knee joint were created in 12 adult beagle dogs (two defects in each knee). The defects were divided into a defect group (n = 16), an acellular novel material implantation (material) group (n = 16), and a BMSCs implantation using the current vehicle system (material with BMSCs) group (n = 16). The reparative tissues at 16 weeks postoperatively were assessed through gross, histological, and mechanical analyses. The reparative tissues of the material with BMSCs group were substituted with firm and smooth hyaline-like cartilage tissue that was perfectly integrated into the host tissues. This treatment group obviously enhanced the subchondral bone reconstruction. The compressive modulus of the reparative tissues was significantly higher in the material with BMSCs group than the other groups. This study demonstrated that the implantation of BMSCs using our novel in situ forming material induced a mature hyaline-like cartilage repair of osteochondral defects in a canine model.

A cellular implantation system using an injectable ultra-purified alginate gel for repair of osteochondral defects in a rabbit model

We developed a novel cellular implantation system using an in situ forming ultra-purified alginate gel with quite low endotoxity. The aims of this study were to determine the superiority of chondrogenic potential of bone marrow stromal cells (BMSCs) cultured in the purified alginate gel compared with a commercial grade gel, and to assess reparative tissues treated with BMSCs implanted using the developed system into cartilage defects in rabbit knees. The effects of each alginate gel on cellular proliferation and chondrogenesis of rabbit BMSCs were determined by in vitro assessments. Using our purified alginate gel, a novel vehicle system for injecting BMSCs into osteochondral defects without periosteal patch was successfully established in this animal models. The in vitro analyses demonstrated that the purification of alginate significantly enhanced the cellular proliferation and chondrogenic differentiation of BMSCs. The in vivo assessments suggested that the implantation of BMSCs with the developed system using the purified alginate gel histologically and mechanically improved the reparative tissue of osteochondral defects. This system using the purified alginate gel shows the clinical potential for arthroscopically injectable implantation of BMSCs for the treatment of cartilaginous lesions.

Role of protein contaminants in the immunogenicity of alginates

Alginate is widely used for cell microencapsulation and transplantation. There is a lack of standardization of alginate purity and composition. In a previous study, we compared different alginate purification methods and concluded that polyphenol and endotoxin contaminants were eliminated efficiently but residual protein contaminants persisted with all of the methods under evaluation. The objective of this study was to test the hypothesis that residual proteins play a role in the immunogenicity of certain alginate preparations. Using preparative size exclusion chromatography (SEC) and a large scale purification protocol that was derived from the findings obtained with SEC, we substantially decreased the protein content of alginate preparations. When implanted into mouse peritoneum, barium alginate beads made of alginates that were purified using SEC or the derived large scale protocol induced significantly less pericapsular cell adhesion than those made with control alginates. In conclusions, these results suggest that removing residual protein contamination may decrease the immunogenicity of certain alginate preparations. The measurement of proteins could be used as a screening method for evaluating alginate preparations.

Allotransplantation of sulphate glucomannan-alginate barium (SGA)-microencapsulated rat islets for the treatment of diabetes mellitus

To offer a more effective microencapsulation technique of islets for the treatment of diabetes, we have developed a new type of microcapsule comprising sulphate glucomannan-alginate barium (SGA). We compared it with traditional microencapsulated APA (alginate-poly-L-lysine-alginate) and ABa (Ba(2+)-alginate) microencapsulated islets. These three types of microencapsulated islets were prepared and cultured in vitro and we studied their morphology and activity. To determine their effects on insulin secretion and cytokine production (MCP-1, IL-1, IFN-gamma, TNF-alpha) the islets were transplanted into diabetic rats. There was no difference in the morphologies of the three types of microencapsulated islets or their insulin secretory capacity in vitro. However, the SGA microencapsulated islets had higher activity and produced more insulin than the APA and ABa microencapsulated islets after transplantation. Normoglycemia was maintained for longer in the SGA-transplanted group than in the other two groups. The concentrations of cytokines in the peritoneal fluid were significantly decreased in the SGA group, as was the infiltration of inflammatory cells around the microcapsules. In conclusion, the novel SGA microencapsulated islets can maintain normoglycemia in diabetic rats without immunosuppression for longer than APA and ABa microencapsulated islets.

Epo delivery by genetically engineered C2C12 myoblasts immobilized in microcapsules

ver the last half century, the use of erythropoietin (Epo) in the management of malignancies has been extensively studied. Originally viewed as the renal hormone responsible for red blood cell production, many recent in vivo and clinical approaches demonstrate that various tissues locally produce Epo in response to physical or metabolic stress. Thus, not only its circulating erythrocyte mass regulator activity but also the recently discovered nonhematological actions are being thoroughly investigated in order to fulfill the specific Epo delivery requirements for each therapeutic approach.

A gel-forming poly-L: -guluronic acid produced from no guluronate-rich marine algae using new hydrolysis method: test for endovascular embolization

To prepare a gel-forming poly-L-guluronic acid (Poly-G) from no guluronate-rich Laminaria japonica, a new hydrolysis method was employed with a lower HCl concentration (0.025-0.15 M) and a shorter treatment time (5 min). The Poly-Gs were set to measure purity, presence of poly-L-guluronic block, molecular weight distribution, polymer yield, viscosity, and compressive gel strength. Finally, the Poly-G was tested to embolize the renal vascular system by using a rabbit model and angiography. Optimized Poly-G could be selected with respect to wt% concentration, polymer yield, gel-forming stability, viscosity, and gel strength as an endovascular embolizing agent. Overall, 0.4-0.6% of 0.03 M-Poly-G obtained from acid treatment with 0.03 M of HCl had molecular weights greater than 80 kDa, and the best gelling capacity with an injectable viscosity (30-120 cP). It was successfully delivered into the vascular bed of a rabbit kidney and was shown angiographically to embolize the renal vascular system.

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.

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.

Expression of Human Calcitonin by Microencapsulated Recombinant Myoblasts

A novel approach to treat post-menopausal osteoporosis is proposed by engineering cell lines for the secretion of human calcitonin (hCT) and which would then be suitable for implantation in different allogeneic hosts. Mouse myoblast were transfected with the cDNA for hCT using the liposome-based gene delivery technique and clones secreting of human calcitonin were isolated. Human calcitonin expression was detected by ELISA. Western blot and immunohistochemical analyses also confirmed the plasmid, pcDNA3-hCT, had been transfected into the cells. Upon enclosure in microcapsules, which are biocompatible membranes that permit exit of therapeutic proteins but not entry of immune mediators, the myoblasts continued to secrete human calcitonin into the culture medium. These results demonstrate the feasibility of using these encapsulated recombinant myoblasts to deliver human calcitonin and the potential of allergenic gene therapy for postmenopausal osteoporosis.

Biocompatibility of alginate–poly-l-lysine microcapsules for cell therapy☆

Cell microencapsulation holds promise for the treatment of many diseases by the continuous delivery of therapeutic products. The biocompatibility of the microcapsules and their biomaterials components is a critical issue for the long-term efficacy of this technology. The objective of this paper is to provide detailed information about the principal factors affecting the biocompatibility of alginates and alginate-poly-l-lysine microcapsules, which are the most frequently employed biomaterials and encapsulation devices for cell immobilization, respectively. Some of these factors include the alginate composition and purification, the selection of the polycation, the interactions between the alginates and the polycation, the microcapsule fabrication process, the uniformity of the devices and the implantation procedure. Improved knowledge will lead to the production of standardized transplantation-grade biomaterials and biocompatible microcapsules.

Evaluation of alginate purification methods: effect on polyphenol, endotoxin, and protein contamination

Alginate, a polysaccharide extracted from brown seaweed, is widely used for the microencapsulation of islets of Langerhans, allowing their transplantation without immunosuppression. This natural polymer is known to be largely contaminated. The implantation of islets encapsulated using unpurified alginate leads to the development of fibrotic cell overgrowth around the microcapsules and normalization of the blood glucose is restricted to a very short period if it is achieved at all. Several research groups have developed their own purification method and obtained relatively good results. No comparative evaluation of the efficiencies of these methods has been published. We conducted an evaluative study of five different alginate preparations: a pharmaceutical-grade alginate in its raw state, the same alginate after purification according to three different published methods, and a commercially available purified alginate. The results showed that all purification methods reduced the amounts of known contaminants, that is, polyphenols, endotoxins, and proteins, although with varying efficiencies. Increased viscosity of alginate solutions was observed after purification of the alginates. Despite a general efficiency in decreasing contamination levels, all of the purified alginates contained relatively high residual amounts of protein contaminants. Because proteins may be immunogenic, these residual proteins may have a role in persisting microcapsule immunogenicity.

Effect of Viscous Injectable Pure Alginate Sol on Cultured Fibroblasts

BACKGROUND

Alginates have a wide variety of potential clinical applications, including use in cell encapsulation, drug delivery, and tissue engineering. Although the compounds are typically used in the form of a calcium hydrogel, alginates in this form possess several disadvantages, including low biodegradability, induction of foreign body reactions, and cytotoxicity secondary to Ca2+ efflux and contamination with bioincompatible substances. Thus, the goal of the present study was to develop a new method of obtaining sterilized, pure, highly viscous alginate sol from seaweed alginates and to determine its utility as an injectable antiadhesion drug.

METHODS

Viscous injectable pure alginate sol was produced from a commercially available sodium alginate, and its molecular and physical characteristics were analyzed. The biological properties of the viscous injectable pure alginate sol were analyzed using cultured fibroblasts prepared from the dorsal skin of neonatal rats to determine its biocompatibility and its effects on cell proliferation, cell migration, and collagen lattice contraction.

RESULTS

The mannuronic acid-to-glucuronic acid ratio of viscous injectable pure alginate sol, as determined by nuclear magnetic resonance studies, was 1.2, and its viscosity at 5 percent was 17,800 mPa. Purification used to produce viscous injectable pure alginate sol decreased contamination by insoluble particles by 20 percent and decreased polyphenol concentration by 17 percent. In vitro analyses with cultured fibroblasts demonstrated that viscous injectable pure alginate sol had excellent biodegradability and biocompatibility and that viscous injectable pure alginate sol inhibited fibroblast proliferation and migration. Furthermore, assessment of collagen contraction with floating fibroblast-loaded collagen lattices indicated that viscous injectable pure alginate sol enhanced wound healing in surrounding connective tissues.

CONCLUSIONS

The authors conclude that viscous injectable pure alginate sol can inhibit scar formation by presenting a physical barrier to invading fibroblasts and by enhancing wound healing of surrounding tissues.

Long-Term Expression of Erythropoietin from Myoblasts Immobilized in Biocompatible and Neovascularized Microcapsules

The present paper investigates the long-term functionality of an ex vivo gene therapy approach based on cell microencapsulation for the continuous delivery of erythropoietin (EPO) without implementation of immunosuppressive protocols. Polymer microcapsules (0.5 ml) loaded with EPO-secreting C(2)C(12) myoblasts and releasing 15,490 +/- 600 IU EPO/24 h were implanted in the peritoneum and subcutaneous tissue of syngeneic and allogeneic mice. High and constant hematocrit levels were maintained for more than 100 days in all implanted mice. Capsules retrieved from the peritoneum were free-floating or forming small capsule clusters, and we detected only a weak fibroblast outgrowth in capsules adhered to organs, whereas capsules explanted from the subcutaneous region appeared altogether as a richly vascularized structure with no signs of major host reaction. Interestingly, the functionality of capsules implanted in the allogeneic mice persisted until day 210 after implantation. These results highlight the feasibility of cell encapsulation technology for the long-term delivery of EPO independent of the method of administration and the mouse strain.

Tissue engineering of articular cartilage under the influence of collagen I/III membranes and low oxygen tension

The objective of this study was to study the matrix production and phenotype stability of articular chondrocytes cultured on collagen I/III membranes (CM) under the influence of low oxygen tension (Po(2)). Primary bovine and osteoarthritic human chondrocytes were cultured for 2 weeks under 5-21% Po(2) on CM, in alginate, or as monolayers. Dedifferentiated cells were produced by 2-week monolayer culture under 21% Po(2). Collagen (Coll) type II and I expression was demonstrated immunohistochemically, by Western blotting (Coll II), and by semiquantitative RT-PCR; proteoglycan synthesis was demonstrated histochemically (toluidine blue); and biosynthetic activity was indicated by radiolabel incorporation ([(3)H]proline and [(35)S]sulfate). Bovine chondrocytes on CM showed an increase in Coll II expression and proteoglycan synthesis under low Po(2) conditions, whereas Coll I decreased. This oxygen-dependent phenotype-stabilizing effect was even more pronounced in alginate cultures. Biosynthesis of bovine and human chondrocytes was also increased by low Po(2), except for proline incorporation, which decreased in bovine CM cultures (low-oxygen effects were significantly higher in alginate than in CM cultures). Dedifferentiated chondrocytes reexpressed Coll II protein when cultured under low Po(2) on CM or in alginate only, but not under high Po(2) or in monolayer culture. We conclude that CM and, even more, alginate foster phenotype stability and cartilage-specific matrix production of bovine chondrocytes, especially when cultured under in vivo-like oxygen conditions.

Causes of limited survival of microencapsulated pancreatic islet grafts

Successful transplantation of pancreatic tissue has been demonstrated to be an efficacious method of restoring glycemic control in type 1 diabetic patients. To establish graft acceptance patients require lifelong immunosuppression, which in turn is associated with severe deleterious side effects. Microencapsulation is a technique that enables the transplantation of pancreatic islets in the absence of immunosuppression by protecting the islet tissue through a mechanical barrier. This protection may even allow for the transplantation of animal tissue, which opens the perspective of using animal donors as a means to solve the problem of organ shortage. Microencapsulation is not yet applied in clinical practice, mainly because encapsulated islet graft survival is limited. In the present review we discuss the principal causes of microencapsulated islet graft failure, which are related to a lack of biocompatibility, limited immunoprotective properties, and hypoxia. Next to the causes of encapsulated islet graft failure we discuss possible improvements in the encapsulation technique and additional methods that could prolong encapsulated islet graft survival. Strategies that may well support encapsulated islet grafts include co-encapsulation of islets with Sertoli cells, the genetic modification of islet cells, the creation of an artificial implantation site, and the use of alternative donor sources. We conclude that encapsulation in combination with one or more of these additional strategies may well lead to a simple and safe transplantation therapy as a cure for diabetes.

Chondrogenic differentiation of mesenchymal progenitor cells encapsulated in ultrahigh-viscosity alginate

One major problem of current cartilage repair techniques is that three-dimensional encapsulated mesenchymal progenitor cells frequently differentiate into hypertrophic cells that express type X collagen and osteogenic marker genes. Studies on wild-type cells of murine mesenchymal C3H10T1/2 progenitor cells as well as on cells transfected with cDNA encoding for bone morphogenetic protein (BMP)-2 or -4 in alginate revealed that the formation of markers for osteogenesis and chondrogenic hypertrophy apparently depended on the BMP-transfection. Cells were encapsulated in ultrahigh-viscosity, clinical grade alginate and differentiation was studied over a period of 17 days. Consistent with results published previously staining with haematoxylin-eosin or Alcian blue, immunohistochemical analysis, and quantitative RT-PCR confirmed the expression of chondrogenic markers (chondroitin-4- and -6-sulfate as well as type II collagen). Production of chondrogenic markers was particularly high in BMP-4 transfected cells. Hypertrophic chondrogenesis did not occur in BMP-4 transfected cells, as revealed by measurement of type X collagen, but could be demonstrated for wild-type cells and to some extent for BMP-2 transfected cells. The osteogenic markers, type I collagen, alkaline phosphatase, and Cbfa1 were upregulated in all cell lines even though the levels and the time of upregulation differed significantly. In any case, the markers were less and only very shortly expressed in BMP-4 transfected cells as revealed quantitatively by real time RT-PCR. Thus, the in vitro results suggested that BMP-4 is a very promising candidate for suppressing chondrogenic hypertrophy, while simultaneously enhancing the production of chondrogenic components.

Evaluation of sodium alginate for bone marrow cell tissue engineering

Sodium alginate has applications as a material for the encapsulation and immobilisation of a variety of cell types for immunoisolatory and biochemical processing applications. It forms a biodegradable gel when crosslinked with calcium ions and it has been exploited in cartilage tissue engineering since chondrocytes do not dedifferentiate when immobilised in it. Despite its attractive properties of degradability, ease of processing and cell immobilisation, there is little work demonstrating the efficacy of alginate gel as a substrate for cell proliferation, except when RGD is modified. In this study we investigated the ability of rat bone marrow cells to proliferate and differentiate on alginates of differing composition and purity. The mechanical properties of the gels were investigated. It was found that high purity and high G-type alginate retained 27% of its initial strength after 12 days in culture and that comparable levels of proliferation were observed on this material and tissue culture plastic. Depending on composition, calcium crosslinked alginate can act as a substrate for rat marrow cell proliferation and has potential for use as 3D degradable scaffold.

Fabrication of homogeneously cross-linked, functional alginate microcapsules validated by NMR-, CLSM- and AFM-imaging

Cross-linked alginate microcapsules of sufficient mechanical strength can immunoisolate cells for the long-term treatment of hormone and other deficiency diseases in human beings. However, gelation of alginate by external Ba(2+) (or other divalent cations) produces non-homogeneous cross-linking of the polymeric mannuronic (M) and guluronic (G) acid chains. The stability of such microcapsules is rather limited. Here, we show that homogeneous cross-linking can be achieved by injecting BaCl(2) crystals into alginate droplets before they come into contact with external BaCl(2). The high effectiveness of this crystal gun method is demonstrated by confocal laser scanning microscopy and by advanced nuclear magnetic resonance imaging. Both techniques gave clear-cut evidence that homogeneous cross-linkage throughout the microcapsule is only obtained with simultaneous internal and external gelation. Atomic force microscopy showed a very smooth surface topography for microcapsules made by the crystal gun method, provided that excess Ba(2+) ions were removed immediately after gelation. In vitro experiments showed greatly suppressed swelling for crystal gun microcapsules. Even alginate extracted from Lessonia nigrescens (highly biocompatible) yielded microcapsules with long-term mechanical stability not hitherto possible. Encapsulation of rat islets, human monoclonal antibodies secreting hybridoma cells and murine mesenchymal stem cells transfected with cDNA encoding for bone morphogenetic protein (BMP-4) revealed that injection of BaCl(2) crystals has no adverse side effects on cell viability and function. However, the release of low-molecular weight factors (such as insulin) may be delayed when using alginate concentrations in the usual range.

Formation of cartilage matrix proteins by BMP-transfected murine mesenchymal stem cells encapsulated in a novel class of alginates

Proliferation and differentiation of wild-type, BMP-2 and BMP-4 transfected cells of C3H10T1/2, a mouse mesenchymal stem cell line that can differentiate into chondrocytes, were studied under monolayer (2D-) and encapsulation (3D-) conditions. Cells were encapsulated in a novel class of alginate. The alginate was of clinical grade (CG) because of complete removal of mitogenic and cytotoxic contaminants by chemical means. Compared to commercial alginates used so far for encapsulation it was characterized by ultra-high viscosity (UHV; viscosity of a 0.1% w/v solution of about 20 cP). In contrast to monolayer cultures, proliferation of cells was prevented when the cells were encapsulated in UHV/CG alginate at the same suspension density. As revealed by immunohistochemistry and quantitative RT-PCR, transfected and wild-type monolayer cells showed synthesis of type I collagen after transfer into differentiation medium, while culture in an alginate scaffold resulted in an upregulation of type II collagen and other hyaline cartilage proteins. BMP-4 transfected cells produced considerably more type II collagen than BMP-2 transfected and wild-type cells. BMP-4 transfected cells were also characterized by type I collagen production up to Day 10 and exhibited transient alkaline phosphatase activity levels that were much higher than the peak values observed for the other two cell lines. The coincidence of the ALP peak values with downregulation of type I collagen in BMP-4 transfected cells suggested that C3H10T1/2 cells differentiate into chondrocytes via a chondroprogenitor-like cell.

A novel class of amitogenic alginate microcapsules for long-term immunoisolated transplantation

In the light of results of clinical trials with immunoisolated human parathyroid tissue Ba2+-alginate capsules were developed that meet the requirements for long-term immunoisolated transplantation of (allogeneic and xenogeneic) cells and tissue fragments. Biocompatibility of the capsules was achieved by subjecting high-M alginate extracted from freshly collected brown algae to a simple purification protocol that removes quantitatively mitogenic and cytotoxic impurities without degradation of the alginate polymers. The final ultra-high-viscosity, clinical-grade (UHV/CG) product did not evoke any (significant) foreign body reaction in BB rats or in baboons. Similarly, the very sensitive pERK assay did not reveal any mitogenic impurities. Encapsulated cells also exhibited excellent secretory properties under in vitro conditions. Despite biocompatible material, pericapsular fibrosis is also induced by imperfect capsule surfaces that can favor cell attachment and migration under the release of material traces. This material can interact with free end monomers of the alginate polymers under formation of mitogenic advanced glycation products. Smooth surfaces, and thus topographical biocompatibility of the capsules (visualized by atomic force microscopy), can be generated by appropriate crosslinking of the UHV/CG-alginate with Ba2+ and simultaneous suppression of capsule swelling by incorporation of proteins and/or perfluorocarbons (i.e., medically approved compounds with high oxygen capacity). Perfluorocarbon-loaded alginate capsules allow long-term non-invasive monitoring of the location and the oxygen supply of the transplants by using 19F-MRI. Transplantation studies in rats demonstrated that these capsules were functional over a period of more than two years.