Bioactive cell-hydrogel microcapsules for cell-based drug delivery

Natural Biopolymers as Additional Tools for Cell Microencapsulation Applied to Cellular Therapy

One of the limitations in organ, tissue or cellular transplantations is graft rejection. To minimize or prevent this, recipients must make use of immunosuppressive drugs (IS) throughout their entire lives. However, its continuous use generally causes several side effects. Although some IS dose reductions and withdrawal strategies have been employed, many patients do not adapt to these protocols and must return to conventional IS use. Therefore, many studies have been carried out to offer treatments that may avoid IS administration in the long term. A promising strategy is cellular microencapsulation. The possibility of microencapsulating cells originates from the opportunity to use biomaterials that mimic the extracellular matrix. This matrix acts as a support for cell adhesion and the syntheses of new extracellular matrix self-components followed by cell growth and survival. Furthermore, by involving the cells in a polymeric matrix, the matrix acts as an immunoprotective barrier, protecting cells against the recipient’s immune system while still allowing essential cell survival molecules to diffuse bilaterally through the polymer matrix pores. In addition, this matrix can be associated with IS, thus diminishing systemic side effects. In this context, this review will address the natural biomaterials currently in use and their importance in cell therapy.

An alginate-based encapsulation system for delivery of therapeutic cells to the CNS

Treatment options for neurodegenerative conditions such as Parkinson's disease have included the delivery of cells which release dopamine or neurotrophic factors to the brain. Here, we report the development of a novel approach for protecting cells after implantation into the central nervous system (CNS), by developing dual-layer alginate beads that encapsulate therapeutic cells and release an immunomodulatory compound in a sustained manner. An optimal alginate formulation was selected with a view to providing a sustained physical barrier between engrafted cells and host tissue, enabling exchange of small molecules while blocking components of the host immune response. In addition, a potent immunosuppressant, FK506, was incorporated into the outer layer of alginate beads using electrosprayed poly-ε-caprolactone core–shell nanoparticles with prolonged release profiles. The stiffness, porosity, stability and ability of the alginate beads to support and protect encapsulated SH-SY5Y cells was demonstrated, and the release profile of FK506 and its effect on T-cell proliferation in vitro was characterized. Collectively, our results indicate this multi-layer encapsulation technology has the potential to be suitable for use in CNS cell delivery, to protect implanted cells from host immune responses whilst providing permeability to nutrients and released therapeutic molecules.

Novel composite cell encapsulation system: dual-layer, micro-scale beads maintain cell survival while releasing immunomodulatory FK506 in a sustained manner. This biotechnology platform could be applicable for treatment of CNS and other disorders.

Biomimetic Hydrogels to Promote Wound Healing

Wound healing is a common physiological process which consists of a sequence of molecular and cellular events that occur following the onset of a tissue lesion in order to reconstitute barrier between body and external environment. The inherent properties of hydrogels allow the damaged tissue to heal by supporting a hydrated environment which has long been explored in wound management to aid in autolytic debridement. However, chronic non-healing wounds require added therapeutic features that can be achieved by incorporation of biomolecules and supporting cells to promote faster and better healing outcomes. In recent decades, numerous hydrogels have been developed and modified to match the time scale for distinct stages of wound healing. This review will discuss the effects of various types of hydrogels on wound pathophysiology, as well as the ideal characteristics of hydrogels for wound healing, crosslinking mechanism, fabrication techniques and design considerations of hydrogel engineering. Finally, several challenges related to adopting hydrogels to promote wound healing and future perspectives are discussed.

Biomedical Implants for Regenerative Therapies

Regenerative therapies aim to develop novel treatments to restore tissue function. Several strategies have been investigated including the use of biomedical implants as three-dimensional artificial matrices to fill the defect side, to replace damaged tissues or for drug delivery. Bioactive implants are used to provide growth environments for tissue formation for a variety of applications including nerve, lung, skin and orthopaedic tissues. Implants can either be biodegradable or non-degradable, should be nontoxic and biocompatible, and should not trigger an immunological response. Implants can be designed to provide suitable surface area-to-volume ratios, ranges of porosities, pore interconnectivities and adequate mechanical strengths. Due to their broad range of properties, numerous biomaterials have been used for implant manufacture. To enhance an implant’s bioactivity, materials can be functionalised in several ways, including surface modification using proteins, incorporation of bioactive drugs, growth factors and/or cells. These strategies have been employed to create local bioactive microenvironments to direct cellular responses and to promote tissue regeneration and controlled drug release. This chapter provides an overview of current bioactive biomedical implants, their fabrication and applications, as well as implant materials used in drug delivery and tissue regeneration. Additionally, cell- and drug-based bioactivity, manufacturing considerations and future trends will be discussed.

BSA- and Elastin-Coated GO, but Not Collagen-Coated GO, Enhance the Biological Performance of Alginate Hydrogels

The use of embedded cells within alginate matrices is a developing technique with great clinical applications in cell-based therapies. However, one feature that needs additional investigation is the improvement of alginate-cells viability, which could be achieved by integrating other materials with alginate to improve its surface properties. In recent years, the field of nanotechnology has shown the many properties of a huge number of materials. Graphene oxide (GO), for instance, seems to be a good choice for improving alginate cell viability and functionality. We previously observed that GO, coated with fetal bovine serum (FBS) within alginate hydrogels, improves the viability of embedded myoblasts. In the current research, we aim to study several proteins, specifically bovine serum albumin (BSA), type I collagen and elastin, to discern their impact on the previously observed improvement on embedded myoblasts within alginate hydrogels containing GO coated with FBS. Thus, we describe the mechanisms of the formation of BSA, collagen and elastin protein layers on the GO surface, showing a high adsorption by BSA and elastin, and a decreasing GO impedance and capacitance. Moreover, we described a better cell viability and protein release from embedded cells within hydrogels containing protein-coated GO. We conclude that these hybrid hydrogels could provide a step forward in regenerative medicine.

Microcapsules with Distinct Dual-Layer Shells and Their Applications for the Encapsulation, Preservation, and Slow Release of Hydrophilic Small Molecules

Microcapsules with two distinct layers of shells were fabricated using an approach combining microfluidics and photopolymerization. Unlike conventional microcapsules with a single shell, a fluorinated oil layer was introduced between the lumen and the outer polymer shell. The fluorinated oil layer significantly suppresses the leakage of the encapsulated ingredients in the lumen and consequently gives the microcapsules remarkable slow release capability for hydrophilic small molecule-based payloads, such as Rhodamine 6G. The release period of Rhodamine 6G can be up to 4 months when using a photocurable resin as the shell material, and the release of Rhodamine 6G can be regulated via the osmolality of the incubation solution for porous hydrogel microcapsules. Even under maximum hypotonic conditions, the release period of Rhodamine 6G in the hydrogel microcapsules is at least 10 days. The slow release capability can be significantly enhanced (6 weeks or longer) by increasing the thicknesses of the hydrogel shell and fluorinated oil layer.

Graphene oxide enhances alginate encapsulated cells viability and functionality while not affecting the foreign body response

The combination of protein-coated graphene oxide (GO) and microencapsulation technology has moved a step forward in the challenge of improving long-term alginate encapsulated cell survival and sustainable therapeutic protein release, bringing closer its translation from bench to the clinic. Although this new approach in cell microencapsulation represents a great promise for long-term drug delivery, previous studies have been performed only with encapsulated murine C2C12 myoblasts genetically engineered to secrete murine erythropoietin (C2C12-EPO) within 160 µm diameter hybrid alginate protein-coated GO microcapsules implanted into syngeneic mice. Here, we show that encapsulated C2C12-EPO myoblasts survive longer and release more therapeutic protein by doubling the micron diameter of hybrid alginate-protein-coated GO microcapsules to 380 µm range. Encapsulated mesenchymal stem cells (MSC) genetically modified to secrete erythropoietin (D1-MSCs-EPO) within 380 µm-diameter hybrid alginate-protein-coated GO microcapsules confirmed this improvement in survival and sustained protein release in vitro. This improved behavior is reflected in the hematocrit increase of allogeneic mice implanted with both encapsulated cell types within 380 µm diameter hybrid alginate-protein-coated GO microcapsules, showing lower immune response with encapsulated MSCs. These results provide a new relevant step for the future clinical application of protein-coated GO on cell microencapsulation.

Tuning the mechanical properties of alginate-peptide hydrogels

Alginate, a polysaccharide that gels in the presence of divalent ions, has been used in the field of regenerative medicine to facilitate cell growth in impaired tissues by providing an artificial bio-surrounding similar to the natural extra cellular matrix (ECM). Here, we present a systematic investigation of the effect of three arginine-glycine-aspartic acid (RGD)-containing peptides, G6KRGDY, A6KRGDY and V6KRGDY, on the physical properties of alginate-peptide hydrogels. Rheology measurements showed that the storage modulus of the alginate-A6KRGDY and alginate-V6KRGDY gels is an order of magnitude higher than that of the alginate-G6KRGDY gel. Small angle X-ray scattering (SAXS) measurements suggest that the difference in the mechanical properties of the gels is due to the formation of larger peptide junction zones in addition to the ones formed by calcium ions. These findings indicate that the peptides' ability to self-assemble in aqueous solution is a significant factor in tuning the stiffness of the alginate/peptide hybrid hydrogels.

Bone regeneration in osteoporosis by delivery BMP-2 and PRGF from tetronic-alginate composite thermogel

As the life expectancy of the world population increases, osteoporotic (OP) fracture risk increase. Therefore in the present study a novel injectable thermo-responsive hydrogel loaded with microspheres of 17β-estradiol, microspheres of bone morphogenetic protein-2 (BMP-2) and plasma rich in growth factors (PRGF) was applied locally to regenerate a calvaria critical bone defect in OP female rats. Three systems were characterized: Tetronic® 1307 (T-1307) reinforced with alginate (T-A), T-A with PRGF and T-A-PRGF with microspheres. The addition of the microspheres increased the viscosity but the temperature for the maximum viscosity did not change (22-24 °C). The drugs were released during 6 weeks in one fast phase (three days) followed by a long slow phase. In vivo evaluation was made in non-OP and OP rats treated with T-A, T-A with microspheres of 17β-estradiol (T-A-βE), T-A-βE prepared with PRGF (T-A-PRGF-βE), T-A-βE with microspheres of BMP-2 (T-A-βE-BMP-2) and the combination of the three (T-A-PRGF-βE-BMP). After 12 weeks, histological and histomorphometric analyzes showed a synergic effect due to the addition of BMP-2 to the T-A-βE formulation. The PRGF did not increased the bone repair. The new bone filling the OP defect was less mineralized than in the non-OP groups.

Preparation of Novel Nano-Sized Hydrogel Microcapsules via Layer-By-Layer Assembly as Delivery Vehicles for Drugs onto Hygiene Paper

Hydrogel microcapsules are improved transplantation delivery vehicles for pharmaceuticals by effectively segregating the active ingredients from the surroundings and delivering them to a certain target site. Layer-by-layer (LbL) assembly is an attractive process to fabricate the nano-sized hydrogel microcapsules. In this study, nano-sized hydrogel microcapsules were prepared through LbL assembly using calcium carbonate nanoparticles (CaCO₃ NPs) as the sacrificial inorganic template, sodium alginate (SA) and polyethyleneimine (PEI) as the shell materials. Ciprofloxacin was used to study the encapsulation and release properties of the hydrogel microcapsules. The hydrogel microcapsules were further adsorbed onto the paper to render antimicrobial properties. The results showed that the mean size of the CaCO₃ template was reduced after dispersing into sodium n-dodecyl sulfate (SDS) solution under sonication. Transmission electron microscope (TEM) and atomic force microscope (AFM) revealed that some hydrogel microcapsules had a diameter under 200 nm, typical creases and collapses were found on the surface. The nano-sized PEI/SA hydrogel microcapsules showed high loading capacity of ciprofloxacin and a sustained release. PEI/SA hydrogel microcapsules rendered good antimicrobial properties onto the paper by the adsorption of hydrogel microcapsules, however, the mechanical properties of the hygiene paper were decreased.

Engineering a Cell Home for Stem Cell Homing and Accommodation

Distilling complexity to advance regenerative medicine from laboratory animals to humans, in situ regeneration will continue to evolve using biomaterial strategies to drive endogenous cells within the human body for therapeutic purposes; this approach avoids the need for delivering ex vivo-expanded cellular materials. Ensuring the recruitment of a significant number of reparative cells from an endogenous source to the site of interest is the first step toward achieving success. Subsequently, making the "cell home" cell-friendly by recapitulating the natural extracellular matrix (ECM) in terms of its chemistry, structure, dynamics, and function, and targeting specific aspects of the native stem cell niche (e.g., cell-ECM and cell-cell interactions) to program and steer the fates of those recruited stem cells play equally crucial roles in yielding a therapeutically regenerative solution. This review addresses the key aspects of material-guided cell homing and the engineering of novel biomaterials with desirable ECM composition, surface topography, biochemistry, and mechanical properties that can present both biochemical and physical cues required for in situ tissue regeneration. This growing body of knowledge will likely become a design basis for the development of regenerative biomaterials for, but not limited to, future in situ tissue engineering and regeneration.

Biomimetics in drug delivery systems: A critical review

Today, the advanced drug delivery systems have been focused on targeted drug delivery fields. The novel drug delivery is involved with the improvement of the capacity of drug loading in drug carriers, cellular uptake of drug carriers, and the sustained release of drugs within target cells. In this review, six groups of therapeutic drug carriers including biomimetic hydrogels, biomimetic micelles, biomimetic liposomes, biomimetic dendrimers, biomimetic polymeric carriers and biomimetic nanostructures, are studied. The subject takes advantage of the biomimetic methods of productions or the biomimetic techniques for the surface modifications, similar to what accrues in natural cells. Moreover, the effects of these biomimetic approaches for promoting the drug efficiency in targeted drug delivery are visible. The study demonstrates that the fabrication of biomimetic nanocomposite drug carriers could noticeably promote the efficiency of drugs in targeted drug delivery systems.

The structural, morphological and thermal properties of grafted pH-sensitive interpenetrating highly porous polymeric composites of sodium alginate/acrylic acid copolymers for controlled delivery of diclofenac potassium

In present investigation new formulations of Sodium Alginate/Acrylic acid hydrogels with high porous structure were synthesized by free radical polymerization technique for the controlled drug delivery of analgesic agent to colon. Many structural parameters like molecular weight between crosslinks (M_c), crosslink density (M_r), volume interaction parameter (v_2,s), Flory Huggins water interaction parameter and diffusion coefficient (Q) were calculated. Water uptake studies was conducted in different USP phosphate buffer solutions. All samples showed higher swelling ratio with increasing pH values because of ionization of carboxylic groups at higher pH values. Porosity and gel fraction of all the samples were calculated. New selected samples were loaded with the model drug (diclofenac potassium).The amount of drug loaded and released was determined and it was found that all the samples showed higher release of drug at higher pH values. Release of diclofenac potassium was found to be dependent on the ratio of sodium alginate/acrylic acid, EGDMA and pH of the medium. Experimental data was fitted to various model equations and corresponding parameters were calculated to study the release mechanism. The Structural, Morphological and Thermal Properties of interpenetrating hydrogels were studied by FTIR, XRD, DSC, and SEM.

Fibronectin-Alginate microcapsules improve cell viability and protein secretion of encapsulated Factor IX-engineered human mesenchymal stromal cells

Continuous delivery of proteins by engineered cells encapsu-lated in biocompatible polymeric microcapsules is of considerable therapeutic potential. However, this technology has not lived up to expectations due to inadequate cell--matrix interactions and subsequent cell death. In this study we hypoth-esize that the presence of fibronectin in an alginate matrix may enhance the viability and functionality of encapsulated human cord blood-derived mesenchymal stromal cells (MSCs) expressing the human Factor IX (FIX) gene. MSCs were encapsulated in alginate-PLL microcapsules containing 10, 100, or 500 μg/ml fibronectin to ameliorate cell survival. MSCs in microcapsules with 100 and 500 μg/ml fibronectin demonstrated improved cell viability and proliferation and higher FIX secretion compared to MSCs in non-supplemented microcapsules. In contrast, 10 μg/ml fibronectin did not significantly affect the viability and protein secretion from the encapsulated cells. Differentiation studies demonstrated osteogenic (but not chondrogenic or adipogenic) differentiation capability and efficient FIX secretion of the enclosed MSCs in the fibronectin-alginate suspension culture. Thus, the use of recombinant MSCs encapsulated in fibronectin-alginate microcapsules in basal or osteogenic cultures may be of practical use in the treatment of hemophilia B.

A scaffold-filter model for studying the chondrogenic differentiation of stem cells in vitro

This study was undertaken to explore the synergistic effect of scaffold materials and a cartilage-like environment on the chondrogenic differentiation of stem cells. Because stem cells encapsulated in a cartilage scaffold will be induced by scaffold molecules as well as permeable molecules from the surroundings, it is impossible to optimize a chondro-inducible scaffold without considering environmental sensitivity. How do we know if a designed scaffold will be sufficient prior to implantation? In this study, bone marrow mesenchymal stem cells (bMSCs) were seeded in various scaffolds, including collagen hydrogel, collage/sodium alginate hydrogel, collagen sponge and silk fibroin sponge. The cell-scaffold complex was encapsulated in a filter pocket to avoid direct contact with co-cultured chondrocytes. Scaffolds differed in the ability to adsorb inducible molecules expressed by chondrocytes, as evidenced by various expressions of cartilage specific proteins and genes. Collagen hydrogel unexpectedly supported chondrogenic differentiation in an environment filled with chondrocytes secretion better than other reinforced scaffolds, which is consistent with the previous experiment in vivo. This result indicated that the environmental sensitivity of a scaffold is important for in vivo chondro-induction. This in vitro scaffold-filter model may be useful as a precursor to investigate the chondro-inducing potential of various scaffolds for cartilage repair.

A UV-sensitive hydrogel based combinatory drug delivery chip (UV gel-Drug Chip) for cancer cocktail drug screening

Photosensitive PEGDA hydrogel based platform for high dynamic range testing of combinatorial cocktail drug screening by using FSC method for colon cancer.

Assessment of the Behavior of Mesenchymal Stem Cells Immobilized in Biomimetic Alginate Microcapsules

The combination of mesenchymal stem cells (MSCs) and biomimetic matrices for cell-based therapies has led to enormous advances, including the field of cell microencapsulation technology. In the present work, we have evaluated the potential of genetically modified MSCs from mice bone marrow, D1-MSCs, immobilized in alginate microcapsules with different RGD (Arg-Gly-Asp) densities. Results demonstrated that the microcapsules represent a suitable platform for D1-MSC encapsulation since cell immobilization into alginate matrices does not affect their main characteristics. The in vitro study showed a higher activity of D1-MSCs when they are immobilized in RGD-modified alginate microcapsules, obtaining the highest therapeutic factor secretion with low and intermediate densities of the bioactive molecule. In addition, the inclusion of RGD increased the differentiation potential of immobilized cells upon specific induction. However, subcutaneous implantation did not induce differentiation of D1-MSCs toward any lineage remaining at an undifferentiated state in vivo.

Biotransformation of lysine into cadaverine using barium alginate-immobilized Escherichia coli overexpressing CadA

In this study, Escherichia coli cells overexpressing lysine decarboxylase (CadA) were used for cadaverine production. Barium alginate was selected as a matrix for immobilization of E. coli YH91. Free cells and immobilized cells (IC) were characterized for their physiochemical properties, and the optimum pH and temperature were determined as 6 and 37 °C, respectively. Immobilized cells were three times more thermally stable compared to free cells at the optimum temperature and had a half-life (t 1/2) of 131 h. The free cells lost most of lysine decarboxylase activity after nine cycles, but in contrast immobilized cells retained 56% of their residual activity even after the 18th cycle. The immobilized cells gave a maximum production of cadaverine (75.8 g/L) with 84% conversion.

Controlled Delivery of Human Cells by Temperature Responsive Microcapsules

Cell therapy is one of the most promising areas within regenerative medicine. However, its full potential is limited by the rapid loss of introduced therapeutic cells before their full effects can be exploited, due in part to anoikis, and in part to the adverse environments often found within the pathologic tissues that the cells have been grafted into. Encapsulation of individual cells has been proposed as a means of increasing cell viability. In this study, we developed a facile, high throughput method for creating temperature responsive microcapsules comprising agarose, gelatin and fibrinogen for delivery and subsequent controlled release of cells. We verified the hypothesis that composite capsules combining agarose and gelatin, which possess different phase transition temperatures from solid to liquid, facilitated the destabilization of the capsules for cell release. Cell encapsulation and controlled release was demonstrated using human fibroblasts as model cells, as well as a therapeutically relevant cell line-human umbilical vein endothelial cells (HUVECs). While such temperature responsive cell microcapsules promise effective, controlled release of potential therapeutic cells at physiological temperatures, further work will be needed to augment the composition of the microcapsules and optimize the numbers of cells per capsule prior to clinical evaluation.

Functionalizing Soft Matter for Molecular Communication

The information age was enabled by advances in microfabrication and communication theory that allowed information to be processed by electrons and transmitted by electromagnetic radiation. Despite immense capabilities, microelectronics has limited abilities to access and participate in the molecular-based communication that characterizes our biological world. Here, we use biological materials and methods to create components and fabricate devices to perform simple molecular communication functions based on bacterial quorum sensing (QS). Components were created by protein engineering to generate a multidomain fusion protein capable of sending a molecular QS signal, and by synthetic biology to engineer E. coli to receive and report this QS signal. The device matrix was formed using stimuli-responsive hydrogel-forming biopolymers (alginate and gelatin). Assembly of the components within the device matrix was achieved by physically entrapping the cell-based components, and covalently conjugating the protein-based components using the enzyme microbial transglutaminase. We demonstrate simple devices that can send or receive a molecular QS signal to/from the surrounding medium, and a two-component device in which one component generates the signal (i.e., issues a command) that is acted upon by the second component. These studies illustrate the broad potential of biofabrication to generate molecular communication devices.

Advances in cell encapsulation technology and its application in drug delivery

INTRODUCTION

Cell encapsulation technology has improved enormously since it was proposed 50 years ago. The advantages offered over other alternative systems, such as the prevention of repetitive drug administration, have triggered the use of this technology in multiple therapeutic applications.

AREAS COVERED

In this article, improvements in cell encapsulation technology and strategies to overcome the drawbacks that prevent its use in the clinic have been summarized and discussed. Different studies and clinical trials that have been performed in several therapeutic applications have also been described.

EXPERT OPINION

The authors believe that the future translation of this technology from bench to bedside requires the optimization of diverse aspects: i) biosafety, controlling and monitoring cell viability; ii) biocompatibility, reducing pericapsular fibrotic growth and hypoxia suffered by the graft; iii) control over drug delivery; iv) and the final scale up. On the other hand, an area that deserves more attention is the cryopreservation of encapsulated cells as this will facilitate the arrival of these biosystems to the clinic.

Developing robust, hydrogel-based, nanofiber-enabled encapsulation devices (NEEDs) for cell therapies

Cell encapsulation holds enormous potential to treat a number of hormone deficient diseases and endocrine disorders. We report a simple and universal approach to fabricate robust, hydrogel-based, nanofiber-enabled encapsulation devices (NEEDs) with macroscopic dimensions. In this design, we take advantage of the well-known capillary action that holds wetting liquid in porous media. By impregnating the highly porous electrospun nanofiber membranes of pre-made tubular or planar devices with hydrogel precursor solutions and subsequent crosslinking, we obtained various nanofiber-enabled hydrogel devices. This approach is broadly applicable and does not alter the water content or the intrinsic chemistry of the hydrogels. The devices retained the properties of both the hydrogel (e.g. the biocompatibility) and the nanofibers (e.g. the mechanical robustness). The facile mass transfer was confirmed by encapsulation and culture of different types of cells. Additional compartmentalization of the devices enabled paracrine cell co-cultures in single implantable devices. Lastly, we provided a proof-of-concept study on potential therapeutic applications of the devices by encapsulating and delivering rat pancreatic islets into chemically-induced diabetic mice. The diabetes was corrected for the duration of the experiment (8 weeks) before the implants were retrieved. The retrieved devices showed minimal fibrosis and as expected, live and functional islets were observed within the devices. This study suggests that the design concept of NEEDs may potentially help to overcome some of the challenges in the cell encapsulation field and therefore contribute to the development of cell therapies in future.

Enhancing effect of glucose microspheres in the viability of human mesenchymal stem cell suspensions for clinical administration

PURPOSE

A critical limiting factor of cell therapy is the short life of the stem cells. In this study, glucose containing alginate microspheres were developed and characterized to provide a sustained release system prolonging the viability of human mesenchymal stem cells (hMSCs) in a suspension for clinical application.

METHODS

The glucose microspheres were satisfactorily elaborated with alginate by emulsification/internal gelation method. Particle size was evaluated by light diffraction and optical microscopy. Shape and surface texture by scanning electron microscopy (SEM). Zeta potential, infrared spectra and release studies were also conducted. Also, rheological properties and stability of hMSCs suspensions with microspheres were tested. The viability of hMSCs was determined by trypan blue dye exclusion staining.

RESULTS

Microspheres of 86.62 μm, spherical shaped and -32.54 mV zeta potential with excellent stability, good encapsulation efficiency and providing an exponential release of glucose were obtained. hMSCs had better survival rate when they were packed with glucose microspheres. Microspheres maintained the aseptic conditions of the cell suspension without rheological, morphological or immunophenotypic disturbances on hMSCs.

CONCLUSIONS

Developed microspheres were able to enhance the functionality of hMSC suspension. This strategy could be broadly applied to various therapeutic approaches in which prolonged viability of cells is necessary.

Application of cell encapsulation for controlled delivery of biological therapeutics

Cell microencapsulation technology is likely to have an increasingly important role in new approaches rather than the classical and pioneering organ replacement. Apart from becoming a tool for protein and morphogen release and long-term drug delivery, it is becoming a new three-dimensional platform for stem cell research. Recent progress in the field has resulted in biodegradable scaffolds that are able to retain and release the cell content in different anatomical locations. Additional advances include the use biomimetic scaffolds that provide greater control over material-cell interactions and the development of more precise encapsulated cell-tracking systems. This review summarises the state of the art of cell microencapsulation and discusses the main directions and challenges of this field towards the controlled delivery of biological therapeutics.

Alginate-based strategies for therapeutic vascularization

Therapeutic stimulation of vessel growth to improve tissue perfusion has shown promise in many regenerative medicine and tissue engineering applications. Alginate-based biomaterial systems have been investigated for growth factor and/or cell delivery as tools for modulating vessel assembly. Growth factor encapsulation allows for a sustained release of protein and protection from degradation. Implantation of growth factor-loaded alginate constructs typically shows an increase in capillary density but without vascular stabilization. Delivery of multiple factors may improve these outcomes. Cell delivery approaches focus on stimulating vascularization either via cell release of soluble factors, cell proliferation and incorporation into new vessels or alginate prevascularization prior to implantation. These methods have shown some promise but routine clinical application has not been achieved. In this review, current research on the application of alginate for therapeutic neovascularization is presented, shortcomings are addressed and the future direction of these systems discussed.

Microcarriers designed for cell culture and tissue engineering of bone

Microspherical particulates have been an attractive form of biomaterials that find usefulness in cell delivery and tissue engineering. A variety of compositions, including bioactive ceramics, degradable polymers, and their composites, have been developed into a microsphere form and have demonstrated the potential to fill defective bone and to populate tissue cells on curved matrices. To enhance the capacity of cell delivery, the conventional solid form of spheres is engineered to have either a porous structure to hold cells or a thin shell to in-situ encapsulate cells within the structure. Microcarriers can also be a potential reservoir system of bioactive molecules that have therapeutic effects in regulating cell behaviors. Due to their specific form, advanced technologies to culture cell-loaded microcarriers are required, such as simple agitation or shaking, spinner flask, and rotating chamber system. Here, we review systematically, from material design to culture technology, the microspherical carriers used for the delivery of cells and tissue engineering, particularly of bone.

Encapsulation of cells in alginate gels

Cell microencapsulation is based on the immobilization of cells for continuous release of therapeutics. This approach has been tested in the treatment of many diseases and several clinical trials have been performed. Factors such as the choice of cells to be encapsulated, the biomaterial used, and the procedure for carrying out the capsules are important issues when implementing this technology.This book chapter makes a comprehensive description of alginate, the most frequently employed biomaterial, passing by its structure, the extraction and treatment, and finishing with the process of gelation. It also describes the various modifications that can be carried out to allow the interaction between the alginate and the integrin receptors of encapsulated cells. The main microencapsulation technologies are presented as well as how 100 μm alginate-Poly-L-Lysine-alginate microcapsules can be fabricated with Flow-focusing technology.