Alginate-polylysine-alginate microcapsules: effect of size reduction on capsule properties

Microencapsulation of parathyroid cells via electric field and non-surgical transplantation approach

PURPOSE

Hypoparathyroidism is a rare disease with low PTH, mostly seen as a consequence of neck surgery. Current management is the prescription of calcium and vitamin D, but the definitive treatment is parathyroid allotransplantation, which frequently triggers an immune response, thus cannot achieve the expected success. To overcome this problem, encapsulation of allogeneic cells is the most promising method. By optimizing the standard alginate cell encapsulation technique with parathyroid cells under high-voltage application, the authors reduced the size of parathyroid-encapsulated beads and evaluated these samples in vitro and in vivo.

METHODS

Parathyroid cells were isolated, and standard-sized alginate macrobeads were prepared without any electrical field application, while microbeads in smaller sizes (< 500 µm), by the application of 13 kV. Bead morphologies, cell viability, and PTH secretion were evaluated in vitro for four weeks. For the in vivo part, beads were transplanted into Sprague-Dawley rats, and after retrieval, immunohistochemistry and PTH release were evaluated in addition to the assessment of cytokine/chemokine levels.

RESULTS

The viability of parathyroid cells in micro- and macrobeads did not differ significantly. However, the amount of in vitro PTH secretion from microencapsulated cells was significantly lower than that from macroencapsulated cells, although it increased throughout the incubation period. Immunohistochemistry of PTH staining in both of the encapsulated cells identified as positive after retrieval.

CONCLUSION

Contrary to the literature, a minimal in vivo immune response was developed for alginate-encapsulated parathyroid cells, regardless of bead size. Our findings suggest that injectable, micro-sized beads obtained using high-voltage may be a promising method for a non-surgical transplantation approach.

Controlled release of adeno-associated virus from alginate hydrogel microbeads with enhanced sensitivity to ultrasound

Adeno-associated virus (AAV)-based gene therapy holds promise as a fundamental treatment for genetic disorders. For clinical applications, it is necessary to control AAV release timing to avoid an immune response to AAV. Here we propose an ultrasound (US)-triggered on-demand AAV release system using alginate hydrogel microbeads (AHMs) with a release enhancer. By using a centrifuge-based microdroplet shooting device, the AHMs encapsulating AAV with tungsten microparticles (W-MPs) are fabricated. Since W-MPs work as release enhancers, the AHMs have high sensitivity to the US with localized variation in acoustic impedance for improving the release of AAV. Furthermore, AHMs were coated with poly-l-lysine (PLL) to adjust the release of AAV. By applying US to the AAV encapsulating AHMs with W-MPs, the AAV was released on demand, and gene transfection to cells by AAV was confirmed without loss of AAV activity. This proposed US-triggered AAV release system expands methodological possibilities in gene therapy.

Alginate-Based Oral Delivery Systems to Enhance Protection, Release, and Absorption of Catalase

Oxidative stress, overproduction of reactive oxygen species (ROS), plays an important role in the development of inflammatory bowel diseases. Catalase has great therapeutic potential by scavenging hydrogen peroxide, one of the ROSs produced in cellular metabolisms. However, in vivo application to scavenge ROS is currently limited especially in oral administrations. Here, we introduced an alginate-based oral drug delivery system that effectively protected catalase from the simulated harsh conditions of the gastrointestinal (GI) tract, released it in the small intestine mimicked condition, and enhanced its absorption via M cells, highly specialized epithelium cells in the small intestine. First of all, catalase was encapsulated in alginate-based microparticles with different amounts of polygalacturonic acid or pectin, which achieved an encapsulation efficiency of more than 90%. It was further shown that catalase was released from alginate-based microparticles in a pH-dependent manner. Results indicated that alginate-polygalacturonic acid microparticles (60 wt % Alg:40 wt % Gal) released 79.5 ± 2.4% of encapsulated catalase at pH 9.1 in 3 h, while they only released 9.2 ± 1.5% of encapsulated catalase at pH 2.0. Even when catalase was encapsulated in microparticles (60 wt % Alg:40 wt % Gal) and exposed to pH 2.0 followed by pH 9.1, it still retained 81.0 ± 11.3% enzyme activity compared to that in microparticles prior to the pH treatment. We then investigated the efficiency of RGD conjugation to catalase on the catalase uptake by M-like cells, the coculturing of human epithelial colorectal adenocarcinoma; Caco-2 cells and B lymphocyte; Raji cells. RGD-catalase protected M-cells more efficiently from the cytotoxicity of H₂O₂, a typical ROS. RGD conjugation to catalase enhanced the uptake by M-cells with 87.6 ± 0.8% RGD-catalase, whereas 11.5 ± 9.2% of RGD-free catalase passed across M-cells. From the results of protection, release, and absorption of model therapeutic proteins from the harsh pH conditions, alginate-based oral drug delivery systems will have numerous applications for the controlled release of drugs that are easily degradable in the GI tract.

Microfluidically fabricated fibers containing pancreatic islets and mesenchymal stromal cells improve longevity and sustained normoglycemia in diabetic rats

Type 1 diabetes mellitus is an autoimmune disease characterized by the loss of pancreatic isletβcells. Insulin injections and pancreas transplants are currently available therapies. The former requires daily insulin injections, while the latter is constrained by donor organ availability. Islet transplantation is a promising alternative treatment for type 1 diabetes mellitus that may overcome the limitations of previous techniques. Two challenges, however, must be addressed: limited cell retention as a result of the immune response and limited function of the transplanted cells that survive. To address these problems, we developed a microfluidic technology for a one-step generation of islet-laden fibers to protect them from the immune response. This approach enables continuous generation of microfibers with a diameter suitable for islet encapsulation (275µm). We, then, transplanted islet-laden fibers into diabetic Wistar rats. While islet-laden fibers alone were unable to restore normoglycemia in diabetic rats, adding mesenchymal stromal cells (MSCs) restored normoglycemia for an extended time. It increased the animals' lifespan by up to 75 d. Additionally, it improved the glucose-stimulated response of islets to the point where there was no significant difference between the treatment group and the healthy animals. Additionally, the presence of MSCs suppressed the immune response, as seen by decreased levels of pro-inflammatory cytokines such as tumor necrosis factor-α. Taken together, these fibers including islet and MSCs provide a versatile platform for concurrently improving cell preservation and functioning followingin vivotransplantation.

Alginate Microsphere Encapsulation of Drug-Loaded Nanoparticles: A Novel Strategy for Intraperitoneal Drug Delivery

Alginate hydrogels have been broadly investigated for use in medical applications due to their biocompatibility and the possibility to encapsulate cells, proteins, and drugs. In the treatment of peritoneal metastasis, rapid drug clearance from the peritoneal cavity is a major challenge. Aiming to delay drug absorption and reduce toxic side effects, cabazitaxel (CAB)-loaded poly(alkyl cyanoacrylate) (PACA) nanoparticles were encapsulated in alginate microspheres. The PACAlg alginate microspheres were synthesized by electrostatic droplet generation and the physicochemical properties, stability, drug release kinetics, and mesothelial cytotoxicity were analyzed before biodistribution and therapeutic efficacy were studied in mice. The 450 µm microspheres were stable at in vivo conditions for at least 21 days after intraperitoneal implantation in mice, and distributed evenly throughout the peritoneal cavity without aggregation or adhesion. The nanoparticles were stably retained in the alginate microspheres, and nanoparticle toxicity to mesothelial cells was reduced, while the therapeutic efficacy of free CAB was maintained or improved in vivo. Altogether, this work presents the alginate encapsulation of drug-loaded nanoparticles as a promising novel strategy for the treatment of peritoneal metastasis that can improve the therapeutic ratio between toxicity and therapeutic efficacy.

Controllable manipulation of alginate-gelatin core-shell microcarriers for HUMSCs expansion

Human umbilical cord mesenchymal stem cells (HUMSCs) are one of the most attractive sources of stem cells, and it is meaningful to design and develop a type of microcarriers with suitable mechanical strength for HUMSCs proliferation in order to acquire enough cells for cell-based therapy. Alginate-gelatin core-shell (AG) soft microcarriers were thus fabricated via a microfluidic device with droplet shearing/gelation facilities and surface coating for in vitro expansion of HUMSCs. The attachment and proliferation of HUMSCs on AG microcarriers with different mechanical strengths modulated by gelatin coating was studied, and the harvested cells were characterized to verity their differentiation potential. The obtained core-shell microcarriers were all uniform in size with a high mono-dispersity (CV < 5 %). An increase in the gelatin surface coating concentration from 0.5 % to 1.5 % would lead to the reduction in both the particle size of the microcarriers and swelling ratio upon the contact of culture medium, but increased elastic modulus. Microcarriers of 245.12 μm with a gelatin coating elastic modulus of 27.5 kPa (AG10) were found to be the optimal substrate for HUMSCs with an initial attachment efficiency of 44.41 % and a 5-day expansion efficiency of 647 %. The cells harvested from AG10 still reserved their outstanding pluripotency. Fresh AG10 could smoothly transfer cells from a running microcarrier-cell system of confluence to serve as a convenient way of scaling-up the existing culture. The current study thus developed suitable microcarriers, AG10, for in vitro HUMSCs expansion with well reserve of cell multipotency, and also provided a manufacturing and surface manipulating strategy of precise production and fine regulation of microcarrier properties.

High-Throughput Production of Microsponges from Platelet Lysate for Tissue Engineering Applications

Cell-based therapies require a large number of cells, as well as appropriate methods to deliver the cells to damaged tissue. Microcarriers provide an optimal platform for large-scale cell culture while also improving cell retention during cell delivery. However, this technology still presents significant challenges due to low-throughput fabrication methods and an inability of the microcarriers to recreate the properties of human tissue. This work proposes, for the first time, the use of methacryloyl platelet lysates (PLMA), a photocrosslinkable material derived from human platelet lysates, to produce porous microcarriers. Initially, high quantities of PLMA/alginate core-shell microcapsules are produced using coaxial electrospray. Subsequently, the microcapsules are collected, irradiated with ultraviolet light, washed, and freeze dried yielding PLMA microsponges. These microsponges are able to support the adhesion and proliferation of human adipose-derived stem cells, while also displaying potential in the assembly of autologous microtissues. Cell-laden microsponges were shown to self-organize into aggregates, suggesting possible applications in bottom-up tissue engineering applications. Impact Statement Microcarriers have increasingly been used as delivery platforms in cell therapy. Herein, the encapsulation of human-derived proteins in alginate microcapsules is proposed as a method to produce microcarriers from photopolymerizable materials. The capsules function as a template structure, which is then processed into spherical microparticles, which can be used in cell culture, cell delivery, and bottom-up assembly. As a proof of concept, this method was combined with lyophilization to process methacryloyl platelet lysates into injectable microsponges for cell delivery.

Hydrogel Microencapsulation Enhances Cryopreservation of Red Blood Cells with Trehalose

Cryopreservation of red blood cells (RBCs) plays a vital role in preserving rare blood and serologic testing, which is essential for clinical transfusion medicine. The main difficulties of the current cryopreservation technique are the high glycerol concentration and the tedious deglycerolization procedure after thawing. In this study, we explored a microencapsulation method for cryopreservation. RBC-hydrogel microcapsules with a diameter of approximately 2.184 ± 0.061 mm were generated by an electrostatic spraying device. Then, 0.7 M trehalose was used as a cryoprotective agent (CPA), and microcapsules were adhered to a stainless steel grid for liquid nitrogen freezing. The results show that compared with the RBCs frozen by cryovials, the recovery of RBCs after microencapsulation is significantly improved, up to a maximum of more than 85%. Additionally, the washing process can be completed using only 0.9% NaCl. After washing, the RBCs maintained their morphology and adenosine 5'-triphosphate (ATP) levels and met clinical transfusion standards. The microencapsulation method provides a promising, referenceable, and more practical strategy for future clinical transfusion medicine.

Core-Shell Microcapsules: Biofabrication and Potential Applications in Tissue Engineering and Regenerative Medicine

The construction of biomaterial scaffolds that accurately recreate the architecture of living tissues in vitro is a major challenge in the field of tissue engineering and regenerative medicine. Core-shell microcapsules...

Layer-by-Layer Biomimetic Microgels for 3D Cell Culture and Nonviral Gene Delivery

Localized release of nucleic acid therapeutics is essential for many biomedical applications, including gene therapy, tissue engineering, and medical implant coatings. We applied the substrate-mediated transfection and layer-by-layer (LbL) technique to achieve an efficient local gene delivery. In the experiments presented herein, we embeded lipoplexes containing plasmid DNA encoding for enhanced green fluorescent protein (pEGFP) within polyelectrolyte alginate-based microgels composed of poly(allylamine hydrochloride) (PAH), chondroitin sulfate (CS), and poly-l-lysine (PLL) with diameters between 70 and 90 μm. Droplet-based microfluidics was used as the main process to produce the alginate (ALG)-based microgels with discrete size, shape, and low coefficient of variation. The physicochemical and morphological properties of the polyelectrolyte microgels were characterized via optical microscopy, scanning electron microscopy (SEM), and zeta potential analysis. We found that polyelectrolyte microgels provide low cytotoxicity and cell-material interactions (adhesion, spreading, and proliferation). In addition, the microsystem showed the ability to load lipoplexes and a loading efficiency equal to 83%, and it enabled in vitro surface-based transfection of MCF-7 cells. This approach provides a new suitable route for cell adhesion and local gene delivery.

Stem Cells as a Source of Pancreatic Cells for Production of 3D Bioprinted Bionic Pancreas in the Treatment of Type 1 Diabetes

Type 1 diabetes (T1D) is the third most common autoimmune disease which develops due to genetic and environmental risk factors. Often, intensive insulin therapy is insufficient, and patients require a pancreas or pancreatic islets transplant. However, both solutions are associated with many possible complications, including graft rejection. The best approach seems to be a donor-independent T1D treatment strategy based on human stem cells cultured in vitro and differentiated into insulin and glucagon-producing cells (β and α cells, respectively). Both types of cells can then be incorporated into the bio-ink used for 3D printing of the bionic pancreas, which can be transplanted into T1D patients to restore glucose homeostasis. The aim of this review is to summarize current knowledge about stem cells sources and their transformation into key pancreatic cells. Last, but not least, we comment on possible solutions of post-transplant immune response triggered stem cell-derived pancreatic cells and their potential control mechanisms.

Fabrication of monodisperse alginate microgel beads by microfluidic picoinjection: a chelate free approach

Micron-sized alginate hydrogel beads are extensively employed as an encapsulation medium for biochemical and biomedical applications. Here we report on the microfluidic assisted fabrication of calcium alginate (Ca-alginate) beads by on-chip picoinjection of aqueous calcium chloride (CaCl2) in emulsified aqueous sodium alginate (Na-alginate) droplets or by picoinjection of Na-alginate solution in emulsified aqueous CaCl2 droplets. There is no added chelator to reduce the Ca activity in either of the two strategies. The two fabrication strategies are implemented using a flow-focusing and picoinjection modules in a single PDMS chip. Aqueous alginate solution was emulsified and infused with CaCl2 solution as the squeezed droplet pass the picoinjection channel; consequently, monodisperse, spherical, and structurally homogeneous Ca-alginate beads were obtained. Monodisperse alginate microgel populations with a mean diameter in the range of 8 to 28 μm and standard deviation less than 1 μm were successfully generated using microfluidic channels with various dimensions and controlling the flow parameters. Monodisperse but also non-spherical particles with diameters 6 to 15 μm were also fabricated when picoinjecting Na-alginate solution in emulsified aqueous CaCl2 droplets. The Ca-alginate microbeads fabricated with tailormade size in the range from sub-cellular and upwards were in both strategies realized without any use of chelators or change in pH conditions, which is considered a significant advantage for further exploitation as encapsulation process for improved enzymatic activity and cell viability.

A Low-Cost Open Source Device for Cell Microencapsulation

Microencapsulation is a widely studied cell therapy and tissue bioengineering technique, since it is capable of creating an immune-privileged site, protecting encapsulated cells from the host immune system. Several polymers have been tested, but sodium alginate is in widespread use for cell encapsulation applications, due to its low toxicity and easy manipulation. Different cell encapsulation methods have been described in the literature using pressure differences or electrostatic changes with high cost commercial devices (about 30,000 US dollars). Herein, a low-cost device (about 100 US dollars) that can be created by commercial syringes or 3D printer devices has been developed. The capsules, whose diameter is around 500 µm and can decrease or increase according to the pressure applied to the system, is able to maintain cells viable and functional. The hydrogel porosity of the capsule indicates that the immune system is not capable of destroying host cells, demonstrating that new studies can be developed for cell therapy at low cost with microencapsulation production. This device may aid pre-clinical and clinical projects in low- and middle-income countries and is lined up with open source equipment devices.

Encapsulation of Adipose-Derived Mesenchymal Stem Cells in Calcium Alginate Maintains Clonogenicity and Enhances their Secretory Profile

Adipose-derived mesenchymal stem cells (ASCs) are well known for their secretory potential, which confers them useful properties in cell therapy. Nevertheless, this therapeutic potential is reduced after transplantation due to their short survival in the human body and their migration property. This study proposes a method to protect cells during and after injection by encapsulation in microparticles of calcium alginate. Besides, the consequences of encapsulation on ASC proliferation, pluripotential, and secretome were studied. Spherical particles with a mean diameter of 500 µm could be obtained in a reproducible manner with a viability of 70% after 16 days in vitro. Moreover, encapsulation did not alter the proliferative properties of ASCs upon return to culture nor their differentiation potential in adipocytes, chondrocytes, and osteocytes. Concerning their secretome, encapsulated ASCs consistently produced greater amounts of interleukin-6 (IL-6), interleukin-8 (IL-8), and vascular endothelial growth factor (VEGF) compared to monolayer cultures. Encapsulation therefore appears to enrich the secretome with transforming growth factor β1 (TGF-β1) and macrophage inflammatory protein-1β (MIP-1β) not detectable in monolayer cultures. Alginate microparticles seem sufficiently porous to allow diffusion of the cytokines of interest. With all these cytokines playing an important role in wound healing, it appears relevant to investigate the impact of using encapsulated ASCs on the wound healing process.

Coating Materials for Neural Stem/Progenitor Cell Culture and Differentiation

Neural stem/progenitor cells (NSPCs) have a potential to treat various neurological diseases, such as Parkinson's Disease, Alzheimer's Disease, and Spinal Cord Injury. However, the limitation of NSPC sources and the difficulty to maintain their stemness or to differentiate them into specific therapeutic cells are the main hurdles for clinical research and application. Thus, for obtaining a therapeutically relevant number of NSPCs in vitro, it is important to understand factors regulating their behaviors and to establish a protocol for stable NSPC proliferation and differentiation. Coating materials for cell culture, such as Matrigel, laminin, collagen, and other coating materials, can significantly affect NSPC characteristics. This article provides a review of coating materials for NSPC culturing in both two dimensions and three dimensions, and their functions in NSPC proliferation and differentiation, and presents a useful guide to select coating materials for researchers.

The Influence of bFGF on the Fabrication of Microencapsulated Cartilage Cells under Different Shaking Modes

Cell encapsulation in hydrogels has been extensively used in cytotherapy, regenerative medicine, 3D cell culture, and tissue engineering. Herein, we fabricated microencapsulated cells through microcapsules loaded with C5.18 chondrocytes alginate/chitosan prepared by a high-voltage electrostatic method. Under optimized conditions, microencapsulated cells presented uniform size distribution, good sphericity, and a smooth surface with different cell densities. The particle size distribution was determined at 150–280 μm, with an average particle diameter of 220 μm. The microencapsulated cells were cultured under static, shaking, and 3D micro-gravity conditions with or without bFGF (basic fibroblast growth factor) treatment. The quantified detection (cell proliferation detection and glycosaminoglycan (GAG)/type II collagen (Col-II)) content was respectively determined by cell counting kit-8 assay (CCK-8) and dimethylmethylene blue (DMB)/Col-II secretion determination) and qualitative detection (acridine orange/ethidium bromide, hematoxylin-eosin, alcian blue, safranin-O, and immunohistochemistry staining) of these microencapsulated cells were evaluated. Results showed that microencapsulated C5.18 cells under three-dimensional microgravity conditions promoted cells to form large cell aggregates within 20 days by using bFGF, which provided the possibility for cartilage tissue constructs in vitro. It could be found from the cell viability (cell proliferation) and synthesis (content of GAG and Col-II) results that microencapsulated cells had a better cell proliferation under 3D micro-gravity conditions using bFGF than under 2D conditions (including static and shaking conditions). We anticipate that these results will be a benefit for the design and construction of cartilage regeneration in future tissue engineering applications.

Atomic force microscopy-indentation demonstrates that alginate beads are mechanically stable under cell culture conditions

Alginate microbeads are extensively used in tissue engineering as microcarriers and cell encapsulation vessels. In this study, we used atomic force microscopy (AFM) based indentation using 20 µm colloidal probes to assess the local reduced elastic modulus (E * ) using a novel method to detect the contact point based on the principle of virtual work, to measure microbead mechanical stability under cell culture conditions for 2 weeks. The bead diameter and swelling were assessed in parallel. Alginate beads swelled up to 150% of their original diameter following addition of cell culture media. The diameter eventually stabilized from day 2 onwards. This behaviour was mirrored in E * where a significant decrease was observed at the start of the culture period before stabilization was observed at ~ 2.1 kPa. Furthermore, the mechanical properties of freeze dried alginate beads after re-swelling them in culture media were measured. These beads displayed vastly different structural and mechanical properties compared those that did not go through the freeze drying process, with around 125% swelling and a significantly higher E * at values over 3 kPa.

Nanotechnology in cell replacement therapies for type 1 diabetes

Islet transplantation is a promising long-term, compliance-free, complication-preventing treatment for type 1 diabetes. However, islet transplantation is currently limited to a narrow set of patients due to the shortage of donor islets and side effects from immunosuppression. Encapsulating cells in an immunoisolating membrane can allow for their transplantation without the need for immunosuppression. Alternatively, "open" systems may improve islet health and function by allowing vascular ingrowth at clinically attractive sites. Many processes that enable graft success in both approaches occur at the nanoscale level-in this review we thus consider nanotechnology in cell replacement therapies for type 1 diabetes. A variety of biomaterial-based strategies at the nanometer range have emerged to promote immune-isolation or modulation, proangiogenic, or insulinotropic effects. Additionally, coating islets with nano-thin polymer films has burgeoned as an islet protection modality. Materials approaches that utilize nanoscale features manipulate biology at the molecular scale, offering unique solutions to the enduring challenges of islet transplantation.

Human Periodontal Ligament- and Gingiva-derived Mesenchymal Stem Cells Promote Nerve Regeneration When Encapsulated in Alginate/Hyaluronic Acid 3D Scaffold

Repair or regeneration of damaged nerves is still a challenging clinical task in reconstructive surgeries and regenerative medicine. Here, it is demonstrated that periodontal ligament stem cells (PDLSCs) and gingival mesenchymal stem cells (GMSCs) isolated from adult human periodontal and gingival tissues assume neuronal phenotype in vitro and in vivo via a subcutaneous transplantation model in nude mice. PDLSCs and GMSCs are encapsulated in a 3D scaffold based on alginate and hyaluronic acid hydrogels capable of sustained release of human nerve growth factor (NGF). The elasticity of the hydrogels affects the proliferation and differentiation of encapsulated MSCs within scaffolds. Moreover, it is observed that PDLSCs and GMSCs are stained positive for βIII-tubulin, while exhibiting high levels of gene expression related to neurogenic differentiation (βIII-tubulin and glial fibrillary acidic protein) via quantitative polymerase chain reaction (qPCR). Western blot analysis shows the importance of elasticity of the matrix and the presence of NGF in the neurogenic differentiation of encapsulated MSCs. In vivo, immunofluorescence staining for neurogenic specific protein markers confirms islands of dense positively stained structures inside transplanted hydrogels. As far as it is known, this study is the first demonstration of the application of PDLSCs and GMSCs as promising cell therapy candidates for nerve regeneration.

Tridimensional configurations of human mesenchymal stem/stromal cells to enhance cell paracrine potential towards wound healing processes

This study proposes to use alginate encapsulation as a strategy to assess the paracrine activity of 3D- and 2D-cultured human bone marrow mesenchymal stem/stromal cells (BM MSC) in the setting of wound repair and regeneration processes. A side-by-side comparison of MSC culture in three different 3D configurations (spheroids, encapsulated spheroids and encapsulated single cells) versus 2D monolayer cell culture is presented. The results reveal enhanced resistance to oxidative stress and paracrine potential of 3D spheroid-organized BM MSC. MSC spheroids (148±2μm diameter) encapsulated in alginate microbeads evidence increased angiogenic and chemotactic potential relatively to encapsulated single cells, as supported by higher secreted levels of angiogenic factors and by functional assays showing the capability of encapsulated MSC to promote formation of tubelike structures and migration of fibroblasts into a wounded area. In addition, a higher expression of the anti-inflammatory factor tumor necrosis factor alpha-induced protein 6 (TSG-6) was demonstrated by RT-PCR for encapsulated and non-encapsulated spheroids. Culture of spheroids within an alginate matrix maintains low aggregation levels below 5% and favors resistance to oxidative stress. These are important factors towards the establishment of more standardized and controlled systems, crucial to explore the paracrine effects of 3D-cultured MSC in therapeutic settings.

Dental and orofacial mesenchymal stem cells in craniofacial regeneration: The prosthodontist's point of view

Of the available regenerative treatment options, craniofacial tissue regeneration using mesenchymal stem cells (MSCs) shows promise. The ability of stem cells to produce multiple specialized cell types along with their extensive distribution in many adult tissues have made them an attractive target for applications in tissue engineering. MSCs reside in a wide spectrum of postnatal tissue types and have been successfully isolated from orofacial tissues. These dental- or orofacial-derived MSCs possess self-renewal and multilineage differentiation capacities. The craniofacial system is composed of complex hard and soft tissues derived from sophisticated processes starting with embryonic development. Because of the complexity of the craniofacial tissues, the application of stem cells presents challenges in terms of the size, shape, and form of the engineered structures, the specialized final developed cells, and the modulation of timely blood supply while limiting inflammatory and immunological responses. The cell delivery vehicle has an important role in the in vivo performance of stem cells and could dictate the success of the regenerative therapy. Among the available hydrogel biomaterials for cell encapsulation, alginate-based hydrogels have shown promising results in biomedical applications. Alginate scaffolds encapsulating MSCs can provide a suitable microenvironment for cell viability and differentiation for tissue regeneration applications. This review aims to summarize current applications of dental-derived stem cell therapy and highlight the use of alginate-based hydrogels for applications in craniofacial tissue engineering.

Alginate gel particles-A review of production techniques and physical properties

The application of hydrocolloid gel particles is potentially useful in food, chemical, and pharmaceutical industries. Alginate gel particles are one of the more commonly used hydrocolloid gel particles due to them being biocompatible, nontoxic, biodegradable, cheap, and simple to produce. They are particularly valued for their application in encapsulation. Encapsulation in alginate gel particles confers protective benefits to cells, DNA, nutrients, and microbes. Slow release of flavors, minerals, and drugs can also be achieved by encapsulation in gel particles. The particle size and shape of the gel particles are crucial for specific applications. In this review, current methods of producing alginate gel particles will be discussed, taking into account their advantages, disadvantages, scalability, and impact on particle size. The physical properties of alginate gel particles will determine the effectiveness in different application conditions. This review will cover the current understanding of the alginate biopolymer, gelation mechanisms and factors affecting release properties, gel strength, and rheology of the alginate gel particle systems.

Field Effect Microparticle Generation for Cell Microencapsulation

The diameter and sphericity of alginate-poly-L-lysine-alginate microcapsules, determined by the size and the shape of calcium alginate microspheres, affect their in vivo durability and biocompatibility and the results of transplantation. The commonly used air-jet spray method generates microspheres with a wider variation in diameter, larger sphere morphology, and evenly distributed encapsulated cells. In order to overcome these drawbacks, we designed a field effect microparticle generator to create a stable electric field to prepare microparticles with a smaller diameter and more uniform morphology. Using this electric field microparticle generator the encapsulated cells will be located at the periphery of the microspheres, and thus the supply of oxygen and nutrients for the encapsulated cells will be improved compared with the centrally located encapsulated cells in the air-jet spray method.

Poly-L-ornithine enhances migration of neural stem/progenitor cells via promoting α-Actinin 4 binding to actin filaments

The recruitment of neural stem/progenitor cells (NSPCs) for brain restoration after injury is a promising regenerative therapeutic strategy. This strategy involves enhancing proliferation, migration and neuronal differentation of NSPCs. To date, the lack of biomaterials, which facilitate these processes to enhance neural regeneration, is an obstacle for the cell replacement therapies. Our previous study has shown that NSPCs grown on poly-L-ornithine (PO) could proliferate more vigorously and differentiate into more neurons than that on Poly-L-Lysine (PLL) and Fibronectin (FN). Here, we demonstrate that PO could promote migration of NSPCs in vitro, and the underlying mechanism is PO activates α-Actinins 4 (ACTN4), which is firstly certified to be expessed in NSPCs, to promote filopodia formation and therefore enhances NSPCs migration. Taken together, PO might serve as a better candidate for transplanted biomaterials in the regenerative therapeutic strategy, compared with PLL and FN.

Bioencapsulation technologies in tissue engineering

Bioencapsulation technologies have played an important role in the developing successes of tissue engineering. Besides offering immunoisolation, they also show promise for cell/tissue banking and the directed differentiation of stem cells, by providing a unique microenvironment. This review describes bioencapsulation technologies and summarizes their recent progress in research into tissue engineering. The review concludes with a brief outlook regarding future research directions in this field.

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

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

STATEMENT OF SIGNIFICANCE

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

Diffusion of Oligonucleotides from within Iron-Cross-Linked, Polyelectrolyte-Modified Alginate Beads: A Model System for Drug Release

An analytical model to describe diffusion of oligonucleotides from stable hydrogel beads is developed and experimentally verified. The synthesized alginate beads are Fe(3+) -cross-linked and polyelectrolyte-doped for uniformity and stability at physiological pH. Data on diffusion of oligonucleotides from inside the beads provide physical insights into the volume nature of the immobilization of a fraction of oligonucleotides due to polyelectrolyte cross-linking, that is, the absence of a surface-layer barrier in this case. Furthermore, the results suggest a new simple approach to measuring the diffusion coefficient of mobile oligonucleotide molecules inside hydrogels. The considered alginate beads provide a model for a well-defined component in drug-release systems and for the oligonucleotide-release transduction steps in drug-delivering and biocomputing applications. This is illustrated by destabilizing the beads with citrate, which induces full oligonucleotide release with nondiffusional kinetics.

An understanding of potential and limitations of alginate/PLL microcapsules as a cell retention system for perfusion cultures

Microcapsules for high cell density culture of mammalian cells have found an increasing interest, however, the poor stability of the microcapsules and the lack of characterisation methods led to few quantitative results. Alginate-poly-L-lysine (PLL) microcapsules have been studied in detail in order to form a basis for comparison of capsules made from different polymers. Since the microcapsules can be easily retained in the bioreactor without the need for a cell separation device, high cell densities were achieved with a maximum of 4 × 10(7) cell/ml(microcapsules), corresponding to a colonisation of 5% of the internal capsule volume. Measurement of microcapsule integrity and mechanical resistance showed that alginate-PLL microcapsules are not suitable for perfusion cultures since they are very sensitive to media composition, mainly the presence of non-gelling ions that have a higher affinity for alginate than PLL and Ca(2+), leading to the leakage of PLL and Ca(2+), and to microcapsule rupture.

Culture of hESC-derived pancreatic progenitors in alginate-based scaffolds

The effect of alginate-based scaffolds with added basement membrane proteins on the in vitro development of hESC-derived pancreatic progenitors was investigated. Cell clusters were encapsulated in scaffolds containing the basement membrane proteins collagen IV, laminin, fibronectin, or extracellular matrix-derived peptides, and maintained in culture for up to 46 days. The cells remained viable throughout the experiment with no signs of central necrosis. Whereas nonencapsulated cells aggregated into larger clusters, some of which showed signs of morphological changes and tissue organization, the alginate matrix stabilized the cluster size and displayed more homogeneous cell morphologies, allowing culture for long periods of time. For all conditions tested, a stable or declining expression of insulin and PDX1 and an increase in glucagon and somatostatin over time indicated a progressive reduction in beta cell-related gene expression. Alginate scaffolds can provide a chemically defined, xeno-free and easily scalable alternative for culture of pancreatic progenitors. Although no increase in insulin and PDX1 gene expression after alginate-immobilized cell culture was seen in this study, further optimization of the matrix physicochemical and biological properties and of the medium composition may still be a relevant strategy to promote the stabilization or maturation of stem cell-derived beta cells.

Poly-L-ornithine promotes preferred differentiation of neural stem/progenitor cells via ERK signalling pathway

Neural stem/progenitor cells (NSPCs) replacement therapies are the most attractive strategies to restore an injured brain. Key challenges of such therapies are enriching NSPCs and directing them differentiation into specific neural cell types. Here, three biomaterial substrates Poly-L-ornithine (PO), Poly-L-lysine (PLL) and fibronectin (FN) were investigated for their effects on proliferation and differentiation of rat NSPCs, and the underlying mechanisms were also explored. The results showed PO significantly increased NSPCs proliferation and induced preferred differentiation, compared with PLL and FN. Checking protein markers of several neural cell subtypes, it is showed PO significantly induced NSPCs expressing Doublecortin (DCX) and Olig2, one for neuroblasts and young neurons and the other for young oligodendrocytes. It is suggested the ERK signaling pathway was involving in this process because an ERK antagonist U0126 could inhibit PO’s effects mentioned above, as well as an ERK pathway agonist Ceramide C6 could enhance them. Given that both neurons and oligodendrocytes are the most vulnerable cells in many neurological diseases, PO-induced preferred differentiation into neurons and oligodendrocytes is a potential paradigm for NSPCs-based therapies.

Muscle weakness during aging: a deficiency state involving declining angiogenesis

This essay begins by proposing that muscle weakness of old age from sarcopenia is due in large part to reduced capillary density in the muscles, as documented in 9 reports of aged persons and animals. Capillary density (CD) is determined by local levels of various angiogenic factors, which also decline in muscles with aging, as reported in 7 studies of old persons and animals. There are also numerous reports of reduced CD in the aged brain and other studies showing reduced CD in the kidney and heart of aged animals. Thus a waning angiogenesis throughout the body may be a natural occurrence in later years and may account significantly for the lesser ailments (physical and cognitive) of elderly people. Old age is regarded here as a deficiency state which may be corrected by therapeutic angiogenesis, much as a hormonal deficiency can be relieved by the appropriate hormone therapy. Such therapy could employ recombinant angiogenic factors which are now commercially available.

Size- and shape-dependent foreign body immune response to materials implanted in rodents and non-human primates

The efficacy of implanted biomedical devices is often compromised by host recognition and subsequent foreign body responses. Here, we demonstrate the role of the geometry of implanted materials on their biocompatibility in vivo. In rodent and non-human primate animal models, implanted spheres 1.5 mm and above in diameter across a broad spectrum of materials, including hydrogels, ceramics, metals and plastics, significantly abrogated foreign body reactions and fibrosis when compared with smaller spheres. We also show that for encapsulated rat pancreatic islet cells transplanted into streptozotocin-treated diabetic C57BL/6 mice, islets prepared in 1.5-mm alginate capsules were able to restore blood-glucose control for up to 180 days, a period more than five times longer than for transplanted grafts encapsulated within conventionally sized 0.5-mm alginate capsules. Our findings suggest that the in vivo biocompatibility of biomedical devices can be significantly improved simply by tuning their spherical dimensions.

Osteogenic differentiation of human mesenchymal stem cells in mineralized alginate matrices

Mineralized biomaterials are promising for use in bone tissue engineering. Culturing osteogenic cells in such materials will potentially generate biological bone grafts that may even further augment bone healing. Here, we studied osteogenic differentiation of human mesenchymal stem cells (MSC) in an alginate hydrogel system where the cells were co-immobilized with alkaline phosphatase (ALP) for gradual mineralization of the microenvironment. MSC were embedded in unmodified alginate beads and alginate beads mineralized with ALP to generate a polymer/hydroxyapatite scaffold mimicking the composition of bone. The initial scaffold mineralization induced further mineralization of the beads with nanosized particles, and scanning electron micrographs demonstrated presence of collagen in the mineralized and unmineralized alginate beads cultured in osteogenic medium. Cells in both types of beads sustained high viability and metabolic activity for the duration of the study (21 days) as evaluated by live/dead staining and alamar blue assay. MSC in beads induced to differentiate in osteogenic direction expressed higher mRNA levels of osteoblast-specific genes (RUNX2, COL1AI, SP7, BGLAP) than MSC in traditional cell cultures. Furthermore, cells differentiated in beads expressed both sclerostin (SOST) and dental matrix protein-1 (DMP1), markers for late osteoblasts/osteocytes. In conclusion, Both ALP-modified and unmodified alginate beads provide an environment that enhance osteogenic differentiation compared with traditional 2D culture. Also, the ALP-modified alginate beads showed profound mineralization and thus have the potential to serve as a bone substitute in tissue engineering.

Dissolution of copper mineral phases in biological fluids and the controlled release of copper ions from mineralized alginate hydrogels

Here we investigate the dissolution behaviour of copper minerals contained within biocompatible alginate hydrogels. Copper has a number of biological effects and has most recently been evaluated as an alternative to expensive and controversial growth factors for applications in tissue engineering. Precise control and sustained release of copper ions are important due to a narrow therapeutic window of this potentially toxic ion, and alginate would appear to be a good material of choice for this purpose. We found that aqueously insoluble copper minerals could be precipitated during gelling within or mixed into alginate hydrogels in the form of microbeads prior to gelling to serve as depots of copper. These minerals were found to be soluble in a variety of biological fluids relevant to in vitro and in vivo investigations, and the alginate carrier served as a barrier to diffusion of these ions and therefore offered control over the rate and duration of release (Cu(2+) release rates observed between 10-750 µMol g(-1) h(-1) and duration for up to 32 d). Copper mineral and copper mineralized alginate microbeads were characterized using powder x-ray diffraction, FTIR, thermogravimetric analysis and scanning electron microscopy. Dissolution kinetics were studied based on measurements of copper ion concentrations using colourimetric methods. In addition we characterized the complexes formed between released copper ions and biological fluids by electron paramagnetic spectroscopy which offers an insight into the behaviour of these materials in the body.

A novel multilayer immunoisolating encapsulation system overcoming protrusion of cells

Application of alginate-microencapsulated therapeutic cells is a promising approach for diseases that require a local and constant supply of therapeutic molecules. However most conventional alginate microencapsulation systems are associated with low mechanical stability and protrusion of cells which is associated with higher surface roughness and limits their clinical application. Here we have developed a novel multilayer encapsulation system that prevents cells from protruding from capsules. The system was tested using a therapeutic protein with anti-tumor activity overexpressed in mammalian cells. The cell containing core of the multilayer capsule was formed by flexible alginate, creating a cell sustaining environment. Surrounded by a poly-L-lysine layer the flexible core was enveloped in a high-G alginate matrix that is less flexible and has higher mechanical stability, which does not support cell survival. The cells in the core of the multilayer capsule did not show growth impairment and protein production was normal for periods up to 70 days in vitro. The additional alginate layer also lowered the surface roughness compared to conventional cell containing alginate-PLL capsules. Our system provides a solution for two important, often overlooked phenomena in cell encapsulation: preventing cell protrusion and improving surface roughness.