Use Of Microencapsulation Research Articles

Energy Storage in Lightweight Aggregate and Pervious Concrete Infused with Phase Change Materials

This study explores the feasibility of utilizing pervious concrete (PC) incorporating diverse lightweight aggregates (LWAs) integrated with phase change materials (PCM) for applications where forced air cooling would be advantageous. The use of such a component provides latent and sensible heat that can cool forced air applications, offsetting ambient temperature increases that occur during the day. Macro- and microencapsulation techniques were used to incorporate inorganic PCM in the PC. The macro-encapsulation technique involved enclosure of PCM within a stable shell prior to addition into the concrete. The microencapsulation technique involved the impregnation of PCM into porous lightweight aggregate. To overcome the PCM reaction with the concrete constituents, an epoxy coating was utilized. The design of the PCM concrete mix and comprehensive laboratory assessment of porosity, water permeability, PCM absorption capacity, compressive strength, and microstructure of the LWAs are detailed. The test results indicate that LWAs have high PCM impregnation rates ranging from 32 % to 57 % by volume. The compressive strengths of PC using LWAs were reduced by 25 % to 65 % when using microencapsulation. The use of microencapsulation was found to reduce the pressure drop under air flow due to the increase in aggregate size as a result of the coating thickness. PCM-PC with a shell thickness of 100 mm, resulted in a pressure drop of less than 100 Pa at a velocity of 0.35 m/s. The use of macro-encapsulated PCM in PC was sensitive to the phase of the PCM, where the liquid phase reduced the compressive strength by 67 %. The failure occurred within the macro-encapsulated PCM at the liquid phase temperatures and at the interface between the encapsulated PCM at solid phase temperatures. The heat transfer provided by the LWA infused PCM when used in a packed aggregate bed or in PC, was shown to match expected latent and sensible heat estimates based on the thermal properties of the materials. This systematic investigation provides valuable insights into LWAs and PCM performance in pervious concrete, offering a comprehensive understanding of their interaction in cooling applications.

Innovations in bio-engineering and cell-based approaches to address immunological challenges in islet transplantation.

Human allogeneic pancreatic islet transplantation is a life-changing treatment for patients with severe Type 1 Diabetes (T1D) who suffer from hypoglycemia unawareness and high risk of severe hypoglycemia. However, intensive immunosuppression is required to prevent immune rejection of the graft, that may in turn lead to undesirable side effects such as toxicity to the islet cells, kidney toxicity, occurrence of opportunistic infections, and malignancies. The shortage of cadaveric human islet donors further limits islet transplantation as a treatment option for widespread adoption. Alternatively, porcine islets have been considered as another source of insulin-secreting cells for transplantation in T1D patients, though xeno-transplants raise concerns over the risk of endogenous retrovirus transmission and immunological incompatibility. As a result, technological advancements have been made to protect transplanted islets from immune rejection and inflammation, ideally in the absence of chronic immunosuppression, to improve the outcomes and accessibility of allogeneic islet cell replacement therapies. These include the use of microencapsulation or macroencapsulation devices designed to provide an immunoprotective environment using a cell-impermeable layer, preventing immune cell attack of the transplanted cells. Other up and coming advancements are based on the use of stem cells as the starting source material for generating islet cells 'on-demand'. These starting stem cell sources include human induced pluripotent stem cells (hiPSCs) that have been genetically engineered to avoid the host immune response, curated HLA-selected donor hiPSCs that can be matched with recipients within a given population, and multipotent stem cells with natural immune privilege properties. These strategies are developed to provide an immune-evasive cell resource for allogeneic cell therapy. This review will summarize the immunological challenges facing islet transplantation and highlight recent bio-engineering and cell-based approaches aimed at avoiding immune rejection, to improve the accessibility of islet cell therapy and enhance treatment outcomes. Better understanding of the different approaches and their limitations can guide future research endeavors towards developing more comprehensive and targeted strategies for creating a more tolerogenic microenvironment, and improve the effectiveness and sustainability of islet transplantation to benefit more patients.

CHARACTERISTICS AND APPLICATION OF BIOPOLYMERS FOR MICROENCAPSULATION OF BIOLOGICALLY ACTIVE SUBSTANCES

In the feeding of highly productive agricultural animals and poultry, an important role belongs to the quality and safety of compound feed products, for the production of which premixes or preparations of biologically active substances are used. Increasingly, probiotic supplements based on live microorganisms are used in the feeding of farm animals and poultry, which, among other things, provide stable immunity to infectious diseases without using antibiotics in the diet. As a result, the general condition improves and the productivity of animals and the quality of livestock products increase. Today, one of the urgent issues is the stabilization of probiotic microorganisms. Thus, the microencapsulation technology allows you to cover the particles of the probiotic supplement with an individual shell to obtain a product with a directed effect and an adjustable time of release of the constituent substance. The article deals with protein metabolism during feeding of highly productive breeds of cattle. Methods of cell stabilization and advantages of stabilized forms of probiotics are presented. Technologies and types of shell materials widely used for microencapsulation of probiotics are analyzed. The use of a specific microencapsulation technology or material depends on the properties of the specific probiotic strain. Organic and inorganic substances, synthetic materials and natural biodegradable polymers are used to stabilize the cells of microorganisms. The most popular biopolymers used for microencapsulation are considered in detail - alginates, carrageenans, chitosan, starch, gum arabic, pectin, gelatin, whey protein. The structural composition, production methods, functional characteristics, volumes of global production of the considered biopolymers are given. The use of microencapsulation of probiotic microorganisms with natural biopolymers for the purpose of stabilizing probiotics in animal feed is an innovative approach.

Bioinformatically predicted emulsifying peptides and potato protein hydrolysate improves the oxidative stability of microencapsulated fish oil

The aim of this study was to investigate the potential of potato proteins and peptides as emulsifiers in the microencapsulation of fish oil by spray-drying. Microcapsules were produced using a potato protein extract, and fractions enriched in patatin and protease inhibitors. Furthermore, bioinformatically predicted emulsifier peptides from abundant potato proteins and a hydrolysate, obtained through targeted proteolysis of the extract, were investigated. During 28 days of storage at 25 °C, peptides and the hydrolysate exhibited better emulsifying properties and higher encapsulation efficiencies compared to native proteins and sodium caseinate. Significant differences (p < 0.05) were observed in the peroxide value (PV) and secondary volatile oxidation products between the microcapsules produced with peptides and native proteins. Microcapsules produced with peptides and hydrolysate showed the highest oxidative stability, not exceeding a PV of 10 meq/kg oil, and with concentrations of volatiles below the odor threshold in oil for five of the six studied compounds. These results show the emulsifying potential of potato peptides and hydrolysate for use in microencapsulation of hydrophobic bioactive ingredients such as fish oil.

Use of Microencapsulation of Aromatic Plants and Spices as a Strategy for Salt Reduction for Food and Cooking

ABSTRACT Excessive salt intake is highly prevalent worldwide, posing as a risk factor for cardiovascular diseases. Scientific evidence supports the need for salt reduction in food. This project aimed for application of microencapsulation of aromas of aromatic plants and spices to decrease/exclude salt. Product was applied in school and adult meals in two canteens. Participants fulfilled a questionnaire for hedonic, salt and overall evaluation. Results for sensorial evaluation show no significant differences for most of the parameters (overall evaluationchildren – MCMc = 7,5, SD = ±1,6; MIMc = 8,2, SD = ±1,3; saltchildren – MCSc = 2,9, SD = ±0,7; MISc = 2,6, SD = ±0,7; overall evaluationadults MCM = 6,8, SD = ±1,1; MIM = 6,5, SD = ±1,3; saltadults – MCM = 3,1, SD = ±0,5; MIM = 2,75, SD = ±0,5)), evidencing good acceptance. This product constitutes a strategy for salt reduction/elimination in catering and people’s homes.

Strategy to increase the lipid stability of the microbial oil produced by Umbelopsis isabellina for food purposes: Use of microencapsulation by external ionic gelation

Oleaginous microorganisms, including the fungus Umbelopsis isabellina, have emerged as a biotechnological alternative to obtain polyunsaturated fatty acid-rich oils, which are strongly linked to energy purposes (biofuel) than the food industry. Considering the composition of microbial oil and its use by the food industry, it is necessary to investigate strategies that increase its lipid stability. Ergo, this pioneering study aimed to microencapsulate the oil produced by Umbelopsis isabellina and evaluate its oxidative stability throughout the storage period against factors such as temperature and luminosity. The microbial oil was microencapsulated through the external ionic gelation technique, producing an encapsulation efficiency of 80% and proving to be a suitable method because it maintained oil composition. Combining microencapsulation and refrigerated storage led to the best effects on storage time, increasing the evaluated lipid stability through the peroxide values and conjugated diene formation. Moreover, saturated and monounsaturated fatty acid content increased, and polyunsaturated fatty acid content decreased during storage for both the free and microencapsulated oil, regardless of storage temperature, although microencapsulation reduced the changes. The results primarily demonstrate how microencapsulation prolongs the oxidative stability and unsaturated fatty acid content of the microbial oil by reducing its reactions to external environmental factors, thus facilitating its use in the food industry.

MICROENCAPSULATION OF FUNCTIONAL COMPONENTS IN THE FOOD TECHNOLOGY: PARTIALLY OPTIMISTIC VIEW

This work deals with the use of microencapsulation of biologically active compounds (BAC) as an alternative method of protection and prolongation of their functional properties in the food products. The main methods for the formation of microcapsules (MC) are considered. Biopolymer materials, suitable for MCs production, are outlined. Some technological solutions, suitable for microencapsulation and successfully used in other industries, present interest only for laboratory researches in the food science, but are not suitable for industrial scale food production. It is discussed why the methods of simple and complex coacervation, liposomal entrapment are thermodynamically advantageous for obtaining microcapsules in comparison with others. To achieve further progresses of microencapsulation in food technologies, the direct integration of the microencapsulation into the food production technological cycle is necessary. Products should initially have a texture and consistency that allow microcapsules to be resistant to premature aggregation. MCs should not exfoliate or break down, while execute their functions of protection and targeted delivery of biologically active compounds. Only high viscous colloidal systems, as traditional fermented dairy products (kefir, yoghurts, ice cream, curd and cheese) and fruit juices with pulp, are mostly suitable for supplementation of them by BACs using microencapsulation.

Influence of Microencapsulation on Fermentative Behavior of Hanseniaspora osmophila in Wine Mixed Starter Fermentation

In recent years, as a consequence of the re-evaluation of the role of non-Saccharomyces yeasts, several studies have been conducted on the use of controlled mixed fermentations with Saccharomyces and different non-Saccharomyces yeast species from the winemaking environment. To benefit from the metabolic particularities of some non-Saccharomyces yeasts, the management of a non-Saccharomyces strain in mixed fermentation is a crucial step, in particular the use of procedures addressed to increase the persistence of non-Saccharomyces strains during the fermentative process. The use of microencapsulation for cell immobilization might represent a strategy for enhancing the competitiveness of non-Saccharomyces yeasts during mixed fermentation. This study was aimed to assess the fermentative performance of a mixed starter culture, composed by a wild Hanseniaspora osmophila strain (ND1) and a commercial Saccharomyces cerevisiae strain (EC1118). For this purpose, free and microencapsulated cells of ND1 strain were tested in co-culture with EC1118 during mixed fermentations in order to evaluate the effect of the microencapsulation on fermentative behavior of mixed starter and final wine composition. The data have shown that H. osmophila cell formulation affects the persistence of both ND1 and EC1118 strains during fermentations and microencapsulation resulted in a suitable system to increase the fermentative efficiency of ND1 strain during mixed starter fermentation.

Encapsulation of Lactobacillus casei in quince seed gum-alginate beads to produce a functional synbiotic drink powder by agro-industrial by-products and freeze-drying

A new functional synbiotic drink powder based on plant by-products (grape pulp, pomegranate and beetroot peels extracts), Lactobacillus casei, and the use of microencapsulation (by quince seed gum (QSG) and sodium alginate (Alg)) and freeze-drying technologies were produced and characterized. Evaluation of the functional properties of drink powders showed that the total phenolic content (TPC), oxygen radical absorbance capacity (ORAC) and DPPH radical scavenging activity were in the range of 19.78–21.35 mg GAE/g, 193.45–194.19 μmol TE/g and 67.34–71.14%, respectively. After freeze drying process, probiotic survival rate in the functional drink powders containing free Lactobacillus casei (FDP1) was 42.16%, and increased to 86.40% and 87.56% in the powders containing probiotic Alg-microcapsules (FDP2) and probiotic Alg-QSG microcapsules (FDP3), respectively. The production yield, moisture content, solubility, wettability, lightness, redness and yellowness of the drink powders (FDP1-3) were in the range of 10.95–13.16%, 4.94–5.17%, 85.25–88.29%, 21.56–22.12s, 51.86–53.70, 20.13–22.35 and 1.95–2.13, respectively. Based on the results, the Alg-QSG microcapsules maintained the L. casei viability of the recommended level of 106−7 CFU/g during the storage period of 60 days and made the drink powder (FDP3) as a functional synbiotic product.

The Use of Polymer and Surfactants for the Microencapsulation and Emulsion Stabilization

Polymer/surfactant mixtures have a wide range of industrial and technological applications, one of them being the use in microencapsulation and emulsion stabilization processes. These mixtures are able to form adsorption layers at the surface of oil droplets and so affect the emulsion stability, which depends on the polyelectrolyte/surfactant nature, concentrations ratio, method of the emulsification, etc. Polyelectrolytes alone show low surface activity in contrast to surfactants, which adsorb at the water/oil interface, making the droplets charged, but they are insufficient to stabilize emulsions. When an oppositely-charged polymer is added to the surfactant solution, a steric barrier is formed, which prevents coalescence and enhances the stability. The present review is devoted to the recent studies of the use of polymer/surfactant mixtures for the encapsulation of active ingredients and stabilization of single and double emulsions. Active ingredients are added to the oil phase prior to emulsification so that any subsequent dissolution of the core, like in other encapsulation protocols, can be omitted. By measuring the interfacial tension and dilational rheology it is possible to find optimum conditions for the emulsion formation and hence for encapsulation. Therefore, such systems have become a prominent approach for the encapsulation of active ingredients.

Preservation of Antioxidant Activity and Polyphenols in Chokeberry Juice and Wine with the Use of Microencapsulation

Black chokeberry (Aronia melanocarpa) juice and wine with high polyphenol contents were spray-dried using three types of coating material: maltodextrin, a mixture of maltodextrin with Arabic gum and hydroxypropyl-β-cyclodextrin. The microstructure and physiochemical properties of the spray-dried powders were systematically evaluated and compared. The degradation kinetics of polyphenols and antioxidant stability in microencapsulated juice and wine preparations from chokeberry were studied over 12 months under different storage conditions (8C, 25C in light and darkness). Results show that the type of encapsulant influenced powder morphology, microencapsulation efficiency, polyphenol content and its stability. Due to good polyphenol stability, the stored microcapsules showed very high antioxidant and antiradical activity both before and after storage. The results reveal that the antioxidant and antiradical stability of the juice polyphenol preparations was much lower than those of corresponding wine polyphenol microcapsules under all tested storage conditions. Practical Applications The interest in the production of stable polyphenol extracts or nonalcoholic products containing red wine polyphenols is still growing. Hence, both types of polyphenol preparations described in this research could have a promising double application in the food and pharmaceutical industries, providing health benefits due to their high antioxidant potential.

Microfluidic fabrication of bioactive microgels for rapid formation and enhanced differentiation of stem cell spheroids

A major challenge in tissue engineering is to develop robust protocols for differentiating ES and iPS cells to functional adult tissues at a clinically relevant scale. The goal of this study is to develop a high throughput platform for generating bioactive, stem cell-laden microgels to direct differentiation in a well-defined microenvironment. We describe a droplet microfluidics system for fabricating microgels composed of polyethylene glycol and heparin, with tunable geometric, mechanical, and chemical properties, at kHz rates. Heparin-containing hydrogel particles sequestered growth factors Nodal and FGF-2, which are implicated in specifying pluripotent cells to definitive endoderm. Mouse ESCs were encapsulated into heparin microgels with a single dose of Nodal and FGF-2, and expressed high levels of endoderm markers Sox17 and FoxA2 after 5days. These results highlight the use of microencapsulation for tailoring the stem cell microenvironment to promote directed differentiation, and may provide a straightforward path to large scale bioprocessing in the future. Statement of SignificanceMulticellular spheroids and microtissues are valuable for tissue engineering, but fabrication approaches typically sacrifice either precision or throughput. Microfluidic encapsulation in polymeric biomaterials is a promising technique for rapidly generating cell aggregates with excellent control of microenvironmental parameters. Here we describe the microfluidic fabrication of bioactive, heparin-based microgels, and demonstrate the adsorption of heparin-binding growth factors for enhancing directed differentiation of embryonic stem cells toward endoderm. This approach also facilitated a ∼90-fold decrease in consumption of exogenous growth factors compared to conventional differentiation protocols.

Probiotic Ferulic Acid Esterase Active Lactobacillus fermentum NCIMB 5221 APA Microcapsules for Oral Delivery: Preparation and in Vitro Characterization

Probiotics possess potential therapeutic and preventative effects for various diseases and metabolic disorders. One important limitation for the oral delivery of probiotics is the harsh conditions of the upper gastrointestinal tract (GIT) which challenge bacterial viability and activity. One proposed method to surpass this obstacle is the use of microencapsulation to improve the delivery of bacterial cells to the lower GIT. The aim of this study is to use alginate-poly-L-lysine-alginate (APA) microcapsules to encapsulate Lactobacillus fermentum NCIMB 5221 and characterize its enzymatic activity and viability through a simulated GIT. This specific strain, in previous research, was characterized for its inherent ferulic acid esterase (FAE) activity which could prove beneficial in the development of a therapeutic for the treatment and prevention of cancers and metabolic disorders. Our findings demonstrate that the APA microcapsule does not slow the mass transfer of substrate into and that of the FA product out of the microcapsule, while also not impairing bacterial cell viability. The use of simulated gastrointestinal conditions led to a significant 2.5 log difference in viability between the free (1.10 × 104 ± 1.00 × 103 cfu/mL) and the microencapsulated (5.50 × 106 ± 1.00 × 105 cfu/mL) L. fermentum NCIMB 5221 following exposure. The work presented here suggests that APA microencapsulation can be used as an effective oral delivery method for L. fermentum NCIMB 5221, a FAE-active probiotic strain.

Activity, stability and inhibition of a bioactive paper prepared by large-scale coating of laccase microcapsules

Enzyme immobilization on paper by large-scale processes may play a valuable role in the development of economical and widely distributed biosensors. In this study, we report on the coating of laccase from Trametes versicolor on papers using a laboratory coater (Cylindrical Laboratory Coater) that simulates realistic conditions similar to those obtained with industrial coaters. In order to achieve an efficient retention of laccase in the coating, the enzymes were incorporated in poly(ethyleneimine) microcapsules. The microcapsules were suspended in a starch-based coating suspension, applied on paper by blade coating at a rate of 500 and 800 m/min thereupon dried by evaporation using an IR lamp at 36 kW. A technique based on the colorimetric reaction between the laccase and its substrate, p-phenylenediamine (PPD), was developed to evaluate the activity of the immobilized enzyme. Our results show that the use of microencapsulation allows for better activity retention in papers over time at room temperature (50% loss after 28 days) compared to papers modified with free laccase (50% loss after 4 days). Microcapsules also decrease the inhibition of laccase by azide.

Biocompatibility Investigation of Polyethylene Glycol and Alginate-Poly-l-Lysine for Islet Encapsulation

The use of microencapsulation with alginate-poly-l-lysine (PLL) as the encapsulation material has been hampered by overgrowth of collagen around implanted capsules. Studies have shown that poly(ethylene glycol) (PEG) has higher biocompatibility than PLL. In this project, we examined the biocompatibility of PEG in comparison with PLL in the Lewis rat model. Capsules made from either PEG or PLL were implanted into Lewis rats in three anatomical sites: subcutaneous (SC), intramuscular (IM), and intra-epididymis (IE). After 2 or 4 weeks, capsules were retrieved, sectioned, and stained with Sirius Red for analysis of fibrotic overgrowth with ImageJ software. The results were statistically analyzed using either unpaired t test or analysis of variance (ANOVA). PEG demonstrated significantly better biocompatibility in SC, at both 2 and 4 weeks, and IE at 2 weeks (p < 0.0001). No significant differences were found in IM implantation at either time point (p = 0.36) between the two materials. However, there was significantly heavier fibrotic overgrowth around PEG capsules in IE than PLL capsules at 4 weeks (p < 0.01). When compared among the anatomical sites, IM implantation demonstrated significantly less fibrotic overgrowth than other sites for both materials (p < 0.01). In conclusion, PLL and PEG may induce different levels of fibrosis based on anatomical location and duration of implantation.

Can encapsulation lengthen the shelf-life of probiotic bacteria in dry products?

This study evaluated the use of microencapsulation to maintain probiotic Lactobacillus rhamnosus GG (LGG) viability during exposure to detrimentally high levels of water activity. Freeze-dried LGG was mixed into a whey protein solution and sprayed onto a core particle. A second batch was prepared by applying an extra layer of palm oil onto the LGG encapsulates. Viability of the LGG preparations was measured over time in an accelerated shelf-life study at 37 °C which included exposure to different water activities ( a w = 0.15 or 0.7), ambient oxygen, and incorporation of the probiotic in infant formula powder. Results showed that a high water activity (0.7) was detrimental to the survival of unencapsulated LGG, yielding more than a 10 log 10 loss in cell viability within 2 weeks. The presence of oxygen and infant formula conferred no additional effects. Encapsulation of LGG did not improve the survival of this strain under the conditions tested here. Although encapsulation is often mentioned as a quick-fix for preserving probiotic viability in dry and semi-dry products, more studies are needed which validate the broader potential of this approach at different shelf-life expectancies, water activities, and product matrices.

Islet alpha cell number is maintained in microencapsulated islet transplantation

Islet transplantation can reverse hyperglycaemia in Type 1 diabetes patients. One problem in islet transplantation is a loss of beta cell mass as well as blunted glucagon responses from the grafted islets. It has been suggested that alpha cell loss is associated with close contact of the alpha cells with the implantation organ. In the present study we made use of microencapsulation, where transplanted islets are not in direct contact with the host implantation site. After transplantation, the number of glucagon cells stained per microencapsulated islet section was increased whereas the number of insulin cells stained was decreased. DNA content of the islets was reduced, as was insulin content, whereas glucagon content was unchanged. This indicates that cell number in transplanted microencapsulated islets diminishes, which can be accounted for by loss of beta cells. However, in contrast to previous studies using non-encapsulated islets, alpha cell number seems to be maintained.

Proliferation, Viability, and Metabolism of Human Tumor and Normal Cells Cultured in Microcapsule

In this study, we investigated the effect of the microenvironment provided by alginate-poly-L-lysine-alginate (APA) microcapsule with liquefied or gelled core on the proliferation, viability, and metabolism of human cells, including anchorage-dependent MCF-7 breast cancer cells and primary fibroblasts, and anchorage-independent K-562 leukemia cells; cells in conventional culture were used as control. The growth pattern of cells in microcapsule was examined by phase-contrast micrography. The cell viability, proliferation, organization, and gene expression were evaluated by 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, hematoxylin and eosin staining, live/dead staining, 5-bromo-20-deoxyuridine labeling, and immunohistochemistry, respectively. Cell metabolism was determined by measuring glucose and lactate concentrations in medium. The results demonstrate that APA microcapsule with liquefied core provides a microenvironment for both anchorage-dependent and anchorage-independent cells to grow into a large cell aggregate and maintain cell viability at a constant level for a period of time. In conclusion, cells in APA microcapsule are alive and have proliferation potential with lower metabolism rate. APA microcapsule may be a useful tool for in vitro tumor cell modeling and anticancer drug screening as well as for cancer gene therapy. In addition, it lays a solid foundation for the use of microencapsulation in cell culture in vitro and cell implantation in vivo.

Utilising human embryonic stem cells as ‘catalysts’ for biological repair and regeneration. Challenges and some possible strategies

In recent years, much interest has been generated over the potential of human embryonic stem cells in transplantation medicine. The ground-breaking study of Fraidenraich and colleagues conclusively demonstrated that rescue of lethal cardiac defects in Id knockout mutant mouse embryos was not due to transplanted embryonic stem cells giving rise to functional new tissues within the defective embryonic heart. Instead, there is indirect evidence that the observed therapeutic effect was due to various secreted factors emanating from the transplanted cells. This therefore introduces the exciting prospect of utilizing human embryonic stem cells as "catalysts" to promote biological repair and regeneration in transplantation therapy. Nevertheless, the immunological barrier against allogenic transplantation, as well as the teratogenic potential of human embryonic stem cells poses major technical challenges. A possible strategy to overcome the immunological barrier may be to impose a temporary regimen of immunosuppressive drugs followed by their gradual withdrawal, once adequate tissue regeneration has been achieved. Other more novel alternatives include the use of microencapsulation to block interaction with the transplant recipient's immune system, and co-transplantation with bone marrow-derived mesenchymal stem cells, which have been demonstrated to possess immuno-suppressive properties. The teratogenic potential of human embryonic stem cells could possibly be alleviated by directing the differentiation of these cells to specific lineages prior to transplantation, or through mitotic inactivation. Co-transplantation with autologous adult stem cells may represent a novel strategy to further enhance the "catalytic" effects of human embryonic stem cells. The various factors secreted by human embryonic stem cells could then have a concentrated localized effect on relatively large numbers of co-transplanted autologous adult stem cells, which may in turn lead to enhanced repair and regeneration of the damaged tissue or organ. This new therapeutic strategy needs to rigorously investigated, in view of its potentially important clinical applications.

Transplanted human embryonic stem cells as biological ‘catalysts’ for tissue repair and regeneration

Human embryonic stem cells have tremendous potential in the newly emerging field of regenerative medicine. Recently, it was demonstrated that the rescue of lethal cardiac defects in Id knockout mutant mouse embryos was not due to the transplanted cells giving rise to functional new tissues within the defective embryonic heart. Instead, there is indirect evidence that the observed therapeutic effect was due to various secreted factors emanating from the transplanted cells. This therefore, introduces the exciting prospect of utilizing human embryonic stem cells as biological 'catalysts' to promote tissue repair and regeneration in transplantation therapy. However, the immunological barrier against allogenic transplantation, as well as the teratogenic potential of human embryonic stem cells poses major technical challenges. A possible strategy to overcome the immunological barrier may be to impose a temporary regimen of immunosuppressive drugs followed by their gradual withdrawal, once adequate tissue regeneration has been achieved. Other more novel alternatives include the use of microencapsulation to block interaction with the transplant recipient's immune system, and co-transplantation with bone marrow-derived mesenchymal stem cells, which have been demonstrated to possess immuno-suppressive properties. The teratogenic potential of human embryonic stem cells could possibly be alleviated by directing the differentiation of these cells to specific lineages prior to transplantation, or through mitotic inactivation (gamma irradiation or mitomycin C exposure). Co-transplantation with autologous adult stem cells may represent a novel strategy to further enhance the 'catalytic' effects of human embryonic stem cells. The various factors secreted by human embryonic stem cells could then have a concentrated localized effect on relatively large numbers of co-transplanted autologous adult stem cells, which may in turn lead to enhanced repair and regeneration of the damaged tissue or organ. Moreover, there is also a possibility that synergistic interactions between the co-transplanted human embryonic stem cells and autologous adult stem cells, may somehow produce signals for the recruitment and migration of additional endogenous adult stem cells within the recipient (i.e. peripheral blood circulation, bone marrow), which could further enhance organ/tissue regeneration. Hence, the potential use of human embryonic stem cells as biological 'catalysts' to stimulate tissue repair and regeneration, appears to hold tremendous promise in the field of regenerative medicine. This new therapeutic strategy needs to thoroughly investigated, in view of its potentially important clinical applications.