Effects of alginate composition on the growth and overall metabolic activity of betaTC3 cells

Microencapsulation of porcine thyroid cell organoids within a polymer microcapsule construct

Hypothyroidism is a common condition of hormone deficiency, and oral administration of thyroid hormones is currently the only available treatment option. However, there are some disadvantages with this treatment modality including compliance challenges to patients. Therefore, a physiologically based alternative therapy for hypothyroidism with little or no side-effects is needed. In this study, we have developed a method for microencapsulating porcine thyroid cells as a thyroid hormone replacement approach. The hybrid wall of the polymer microcapsules permits thyroid hormone release while preventing immunoglobulin antibodies from entry. This strategy could potentially enable implantation of the microcapsule organoids containing allogeneic or xenogeneic thyroid cells to secret hormones over time without the need for immunosuppression of recipients. Porcine thyroid cells were isolated and encapsulated in alginate-poly-L-ornithine-alginate microcapsules using a microfluidic device. The porcine thyroid cells formed three-dimensional follicular spheres in the microcapsules with decent cell viability and proliferation. Thyroxine release from the encapsulated cells was higher than from unencapsulated cells ( P < 0.05) and was maintained during the entire duration of experiment (>28 days). These results suggest that the microencapsulated thyroid cell organoids may have the potential to be used for therapy and/or drug screening.

Engineered multilayer ovarian tissue that secretes sex steroids and peptide hormones in response to gonadotropins

Although hormone replacement therapy is an option for the loss of ovarian function, hormone delivery through pharmacological means results in various clinical complications. The present study was designed to deliver sex steroids by a functional construct fabricated using encapsulation techniques. Theca and granulosa cells isolated from ovaries of 21-day old rats were encapsulated in multilayer alginate microcapsules to recapitulate the native follicular structure. Cells encapsulated in two other schemes were used as controls to assess the importance of the multilayer structure. The endocrine functions of the encapsulated cells were assessed in vitro for a period of 30 days. Encapsulated cells showed sustained viability during long-term in vitro culture with those encapsulated in multilayer capsules secreting significantly higher and sustained concentrations of 17 β-estradiol (E(2)) than the two other encapsulation schemes (p < 0.05, n = 6) in response to follicle-stimulating hormone (FSH) and luteinizing hormone (LH). In addition, cells in the multilayer microcapsules also secreted activin and inhibin in vitro. In contrast, when granulosa and theca cells were cultured in 2D culture, progesterone (P(4)) secretion increased while E(2) secretion decreased over a 30-day period. In summary, we have designed a multilayer engineered ovarian tissue that secretes sex steroids and peptide hormones and responds to gonadotropins, thus demonstrating the ability to recapitulate native ovarian structure ex vivo.

Islet transplantation and encapsulation: an update on recent developments

Human islet transplantation can provide good glycemic control in diabetic recipients without exogenous insulin. However, a major factor limiting its application is the recipient's need to adhere to life-long immunosuppression, something that has serious side effects. Microencapsulating human islets is a strategy that should prevent rejection of the grafted tissue without the need for anti-rejection drugs. Despite promising studies in various animal models, the encapsulated human islets so far have not made an impact in the clinical setting. Many non-immunological and immunological factors such as biocompatibility, reduced immunoprotection, hypoxia, pericapsular fibrotic overgrowth, effects of the encapsulation process and post-transplant inflammation hamper the successful application of this promising technology. In this review, strategies are discussed to overcome the above-mentioned factors and to enhance the survival and function of encapsulated insulin-producing cells, whether in islets or surrogate β-cells. Studies at our center show that barium alginate microcapsules are biocompatible in rodents, but not in humans, raising concerns over the use of rodents to predict outcomes. Studies at our center also show that the encapsulation process had little or no effect on the cellular transcriptome of human islets and on their ability to function either in vitro or in vivo. New approaches incorporating further modifications to the microcapsule surface to prevent fibrotic overgrowth are vital, if encapsulated human islets or β-cell surrogates are to become a viable therapy option for type 1 diabetes in humans.

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

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

Hydrogel-based microfluidic systems for co-culture of cells

Currently, in vivo cellular microenvironments are not well modeled using traditional cell culture methods. Microfluidic technology provides the tools to mimic in vivo environments for cell culture. We use alginate hydrogels to reversibly trap and release cells for incubation. The porous nature of alginate gels resembles the natural extracellular matrix and allows the transport of nutrients and waste. This property makes it an ideal cell trapping and culturing material. Here, we present reversible immobilization of human fetal lung fibroblasts (HFL1) and human hepatocellular liver carcinoma cell (Hep G2) inside microfluidic channels and demonstrate the possibility of co-culturing these two cell types within different alginate gel layers.

Chondrocyte-alginate bioconstructs: An nuclear magnetic resonance relaxation study

Proton nuclear magnetic resonance (NMR) relaxometry can give informations about hydrogel scaffold properties. As these properties can be modified with culture time and conditions according to scaffold biodegradability and new tissue biosynthesis, the aim of this research was to test the efficiency of this noninvasive NMR technique in the follow-up of 3D cultures for tissue engineering. The distributions of proton relaxation times T1 and T2 have been measured on cylindrical gel samples of different types of alginate, in the presence or absence of hyaluronate, in gels or bioconstructs with encapsulated chondrocytes cultured for 30 days in normal or reduced weight conditions. It was found that T2 increases with the mannuronate/guluronate ratio in alginate samples and with the presence of hyaluronate. The distributions of both T1 and T2 result wider for bioconstructs cultured in normal gravity than for those cultured in reduced weight conditions. Neither cell growing nor collagen production but only GAG neosynthesis have been demonstrated in our experimental conditions. In conclusion, T2 is sensitive to the gel properties (possibly to the rigidity of macromolecular components). The homogeneity of bioconstructs can be monitored by the distribution of T1 and T2. We propose that nonspatially resolved NMR relaxometry can efficiently be used in monitoring tissue development in a biodegradable scaffold for tissue engineering.

Insulin secretion dynamics of free and alginate-encapsulated insulinoma cells

This study investigates the effect of alginate/poly-L: -lysine/alginate (APA) encapsulation on the insulin secretion dynamics exhibited by an encapsulated cell system. Experiments were performed with the aid of a home-built perfusion apparatus providing a 1 min temporal resolution. Insulin profiles were measured from: (i) murine insulinoma betaTC3 cells encapsulated in calcium alginate/poly-L: -lysine/alginate (APA) beads generated with high guluronic (G) or high mannuoric (M) content alginate, and (ii) murine insulinoma betaTC-tet cells encapsulated in high M APA beads and propagated in the presence and absence of tetracycline. Results show that encapsulation in APA beads did not affect the insulin secretion profile shortly post-encapsulation. However, remodeling of the beads due to cell proliferation affected the insulin secretion profiles; and inhibiting remodeling by suppressing cell growth preserved the secretion profile. The implications of these findings regarding the in vivo function of encapsulated insulin secreting cells are discussed.

Modeling of encapsulated cell systems

Tissue engineered substitutes consisting of cells in biocompatible materials undergo remodeling with time as a result of cell growth and death processes. With inert matrices that do not directly influence cell growth, remodeling is driven mainly by the concentration of dissolved oxygen (DO). Insulin-secreting cell lines encapsulated in alginate-based beads and used as a pancreatic substitute represent such a case. Beads undergo remodeling with time so that an initially homogeneous distribution of cells is eventually replaced by a dense peripheral ring of primarily viable cells, whereas inner cells are mostly necrotic. This paper develops and analyzes a mathematical model of an encapsulated cell system of spherical geometry that tracks the viable and dead cell densities and the concentration of DO within the construct as functions of radial position and time. Model simulations are compared with experimental histology data on cell distribution. Correlations are then developed between the average intrabead DO concentration (AIDO) and the total viable cell number, as well as between AIDO and the radial cell and DO distributions in beads. As AIDO can be measured experimentally by incorporating a perfluorocarbon emulsion in the beads and acquiring (19)F nuclear magnetic resonance (NMR) spectroscopic data, these correlations can be used to track the remodeling that occurs in the construct in vitro and potentially in vivo. The usefulness of mathematical models in describing the dynamic changes that occur in tissue constructs with time, and the value of these models at obtaining additional information on the system when used interactively with experimental measurements, are discussed.

Effects of alginate encapsulation on mitochondrial activity

The long-term objective of our research is to study the biochemical consequences of primary genetic defects of the Pyruvate Dehydrogenase Complex, a key mitochondrial enzyme complex, by NMR spectroscopy. An established method to obtain energetic and metabolic information from intact cells involves the use of 31P and 13C NMR spectroscopic techniques. NMR spectra from live and fully functional cells can be obtained from cells encapsulated within alginate beads and maintained in a perfusion bioreactor throughout the NMR experiment. However, before spectroscopic studies can commence, the effects of alginate encapsulation on the general metabolism and mitochondrial activity of fibroblasts need to be determined. in this study we report glucose consumption and flow cytometry measurements (with the fluorescent markers MitoTracker GreenFM and Nonyl-acridine Orange to determine the mitochondrial status and mass) of healthy human fibroblasts encapsulated in a mannuronic acid-rich alginate matrix. The results show that alginate encapsulation of fibroblasts does not affect the glucose consumption, the mitochondrial integrity, or the mitochondrial mass during 21 days of in vitro culture.

The role of the CaCl2–guluronic acid interaction on alginate encapsulated βTC3 cells

Previously we demonstrated that alginate composition has a significant effect on the growth of encapsulated betaTC3 cells and consequently on the overall metabolic and secretory activities of the encapsulated cultures. Based on these results we postulated that the mechanical properties of alginate were not responsible for the observed effects but rather, changes in the strength of the alginate gel network caused by changes in the number of alginate strands held together in the "egg-box" model are responsible for the observed effects. In this study we address this hypothesis with a series of experiments in which the strength of this interaction is manipulated by varying the calcium concentration either at the time of gelation or during culture maintenance. Our data show that increasing the concentration of the CaCl2 solution used at the time of gelation, thus increasing the strength of the alginate gel network, impedes the growth characteristics of betaTC3 cells encapsulated in a high guluronic acid content alginate. This effect is amplified by maintaining a constant supply of calcium ions during culture thus sustaining the interaction between guluronic acid residues and calcium ions. However, preparations of betaTC3 cells encapsulated in an alginate with high mannuronic acid content are not affected by changes in CaCl2 concentration due to the low percentage of consecutive guluronic acid residues. Therefore, the present data show that the strength of the alginate gel network is an important factor that influences the growth characteristics of encapsulated cell preparations.

Encapsulated islets in diabetes treatment

Encapsulation of insulin-producing cells in semipermeable membranes has the potential to provide an effective treatment for insulin-dependent diabetes with little or no immunosuppression of the host. Improvements in alginate, a marine polysaccharide commonly used for cell encapsulation, have revived interest in this material. However, serious obstacles, including a reliable cell source and a better understanding of immune acceptance issues, remain to be addressed before a clinically applicable therapeutic procedure based on encapsulated cells becomes available.