Peroxidase-Catalyzed Cell Encapsulation in Subsieve-Size Capsules of Alginate with Phenol Moieties in Water-Immiscible Fluid Dissolving H2O2

Effect of cell adhesiveness of Cell Dome shell on enclosed HeLa cells

The Cell Dome is a dome-shaped structure (diameter: 1 mm, height: 270 μm) with cells enclosed within a cavity, covered by a hemispherical hydrogel shell, and immobilized on a glass plate. Given that the cells within Cell Dome are in contact with the inner walls of the hydrogel shell, the properties of the shell are anticipated to influence cell behavior. To date, the impact of the hydrogel shell properties on the enclosed cells has not been investigated. In this study, we explored the effects of the cell adhesiveness of hydrogel shell on the behavior of enclosed cancer cells. Hydrogel shells with varying degrees of cell adhesiveness were fabricated using aqueous solutions containing either an alginate derivative with phenolic hydroxyl moieties exclusively or a mixture of alginate and gelatin derivatives with phenolic hydroxyl moieties. Hydrogel formation was mediated by horseradish peroxidase. We used the HeLa human cervical cancer cell line, which expresses fucci2, a cell cycle marker, to observe cell behavior. Cells cultured in hydrogel shells with cell adhesiveness proliferated along the inner wall of the hydrogel shell. Conversely, cells in hydrogel shells without cell adhesiveness grew uniformly at the bottom of the cavities. Furthermore, cells in non-adhesive hydrogel shells had a higher percentage of cells in the G1/G0 phase compared to those in adhesive shells and exhibited increased resistance to mitomycin hydrochloride when the cavities became filled with cells. These results highlight the need to consider the cell adhesiveness of the hydrogel shell when selecting materials for constructing Cell Dome.

Phenolated alginate hydrogel induced osteogenic properties of mesenchymal stem cells via Wnt signaling pathway

Osteogenic properties of phenolated alginate (1.2 %) hydrogel containing collagen (0.5 %)/nano-hydroxyapatite (1 %) were studied on human mesenchymal stem cells in vitro. The phenolation rate and physical properties of the hydrogel were assessed using nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), swelling ratio, gelation time, mechanical assay, and degradation rate. The viability of encapsulated cells was monitored on days 7, 14, and 21 using an MTT assay. Osteoblast differentiation was studied using western blotting, and real-time PCR. Using PCR array analysis, the role of the Wnt signaling pathway was also investigated. Data showed that the combination of alginate/collagen/nanohydroxyapatite yielded proper mechanical features. The addition of nanohydroxyapatite, and collagen reduced degradation, swelling rate coincided with increased stiffness. Elasticity and pore size were also diminished. NMR and FTIR revealed suitable incorporation of collagen and nanohydroxyapatite in the structure of alginate. Real-time PCR analysis and western blotting indicated the expression of osteoblast-related genes such as Runx2 and osteocalcin. PCR array revealed the induction of numerous genes related to Wnt signaling pathways during the maturation of human stem cells toward osteoblast-like cells. In vivo data indicated that transplantation of phenolated alginate/collagen/nanohydroxyapatite hydrogel led to enhanced de novo bone formation in rats with critical-sized calvarial defects. Phenolated alginate hydrogel can promote the osteogenic capacity of human amniotic membrane mesenchymal stem cells in the presence of nanohydroxyapatite and collagen via engaging the Wnt signaling pathway.

Cell Dome as an Evaluation Platform for Organized HepG2 Cells

Human-hepatoblastoma-derived cell line, HepG2, has been widely used in liver and liver cancer studies. HepG2 spheroids produced in a three-dimensional (3D) culture system provide a better biological model than cells cultured in a two-dimensional (2D) culture system. Since cells at the center of spheroids exhibit specific behaviors attributed to hypoxic conditions, a 3D cell culture system that allows the observation of such cells using conventional optical or fluorescence microscopes would be useful. In this study, HepG2 cells were cultured in "Cell Dome", a micro-dome in which cells are enclosed in a cavity consisting of a hemispherical hydrogel shell. HepG2 cells formed hemispherical cell aggregates which filled the cavity of Cell Domes on 18 days of culture and the cells could continue to be cultured for 29 days. The cells at the center of hemispherical cell aggregates were observed using a fluorescence microscope. The cells grew in Cell Domes for 18 days exhibited higher Pi-class Glutathione S-Transferase enzymatic activity, hypoxia inducible factor-1α gene expression, and higher tolerance to mitomycin C than those cultured in 2D on tissue culture dishes (* p < 0.05). These results indicate that the center of the glass adhesive surface of hemispherical cell aggregates which is expected to have the similar environment as the center of the spheroids can be directly observed through glass plates. In conclusion, Cell Dome would be useful as an evaluation platform for organized HepG2 cells.

One-Step FRESH Bioprinting of Low-Viscosity Silk Fibroin Inks

Silk fibroin (SF) is an attractive material for composing bioinks suitable for three-dimensional (3D) bioprinting. However, the low viscosity of SF solutions obtained through common dissolution methods limits 3D-bioprinting applications without the addition of thickeners or partial gelation beforehand. Here, we report a method of 3D bioprinting low-viscosity SF solutions without additives. We combined a method of freeform reversible embedding of suspended hydrogels, known as the FRESH method, with horseradish peroxidase-catalyzed cross-linking. Using this method, we successfully fabricated 3D SF hydrogel constructs from low-viscosity SF ink (10% w/w, 50 mPa s at 1 s^-1 shear rate), which does not yield 3D constructs when printed onto a plate in air. Studies using mouse fibroblasts confirmed that the printing process was cell-friendly. Additionally, cells enclosed in printed SF hydrogel constructs maintained > 90% viability for 11 days of culture. These results demonstrate that the 3D bioprinting technique developed in this study enables new 3D bioprinting applications using SF inks and thus has a great potential to contribute to tissue engineering and regenerative medicine.

Crosslinking Strategies for the Microfluidic Production of Microgels

This article provides a systematic review of the crosslinking strategies used to produce microgel particles in microfluidic chips. Various ionic crosslinking methods for the gelation of charged polymers are discussed, including external gelation via crosslinkers dissolved or dispersed in the oil phase; internal gelation methods using crosslinkers added to the dispersed phase in their non-active forms, such as chelating agents, photo-acid generators, sparingly soluble or slowly hydrolyzing compounds, and methods involving competitive ligand exchange; rapid mixing of polymer and crosslinking streams; and merging polymer and crosslinker droplets. Covalent crosslinking methods using enzymatic oxidation of modified biopolymers, photo-polymerization of crosslinkable monomers or polymers, and thiol-ene “click” reactions are also discussed, as well as methods based on the sol−gel transitions of stimuli responsive polymers triggered by pH or temperature change. In addition to homogeneous microgel particles, the production of structurally heterogeneous particles such as composite hydrogel particles entrapping droplet interface bilayers, core−shell particles, organoids, and Janus particles are also discussed. Microfluidics offers the ability to precisely tune the chemical composition, size, shape, surface morphology, and internal structure of microgels by bringing multiple fluid streams in contact in a highly controlled fashion using versatile channel geometries and flow configurations, and allowing for controlled crosslinking.

Phenolated alginate-collagen hydrogel induced chondrogenic capacity of human amniotic mesenchymal stem cells

Horseradish peroxidase (HRP)-catalyzed hydrogels are considered to be an important platform for tissue engineering applications. In this study, we investigated the chondrogenic capacity of phenolated (1.2%) alginate-(0.5%) collagen hydrogel on human amniotic mesenchymal stem cells after 21 days. Using NMR, FTIR analyses, and SEM imaging, we studied the phenolation and structure of alginate-collagen hydrogel. For physicochemical evaluations, gelation time, mechanical properties, swelling, and degradation rate were assessed. The survival rate was monitored using the MTT assay and DAPI staining. Western blotting was performed to measure the chondrogenic differentiation of cells. NMR showed successful phenolation of the alginate-collagen hydrogel. FTIR exhibited the interaction between the functional groups of collagen with phenolated alginate. SEM showed the existence of collagen microfibrils in the alginate-collagen hydrogel. Compared to phenolated alginate, the addition of collagen increased hydrogel elasticity by 10%. Both swelling rate and biodegradability were reduced in the presence of collagen. We noted an increased survival rate in phenolated alginate-collagen compared to the control cells (p < 0.05). Western blotting revealed the increase of chondrocyte-associated proteins such as SOX9 and COL2A1 in phenolated-alginate-collagen hydrogels after 21 days. These data showed that phenolated alginate-collagen hydrogel is an appropriate 3 D substrate to induce chondrogenic capacity of human mesenchymal stem cells.

Horseradish peroxidase-catalyzed hydrogelation consuming enzyme-produced hydrogen peroxide in the presence of reducing sugars

In the present work, three kinds of reducing sugars: glucose, galactose, and mannose, are applied to horseradish peroxidase (HRP)-catalyzed hydrogelation of an aqueous solution containing natural polymers modified with phenolic hydroxyl moieties. In this system, HRP consumes hydrogen peroxide that was generated from the oxidation of thiol groups in HRP in the presence of reducing sugars. Herein, we highlight the versatility of applicable sugar types and the controllable hydrogel properties. The mechanical properties and microstructures of the resultant hydrogels can be well controlled by varying the concentration and the reducing power of sugars. Moreover, reducing sugar-independent cytocompatibility of the hydrogels was confirmed by the growth of cells on them. The wide selection of sugar types provides a better understanding of the reaction mechanism and enables the characterization of hydrogels with well-controlled properties.

Combinatory approach for developing silk fibroin scaffolds for cartilage regeneration

Several processing technologies and engineering strategies have been combined to create scaffolds with superior performance for efficient tissue regeneration. Cartilage tissue is a good example of that, presenting limited self-healing capacity together with a high elasticity and load-bearing properties. In this work, novel porous silk fibroin (SF) scaffolds derived from horseradish peroxidase (HRP)-mediated crosslinking of highly concentrated aqueous SF solution (16 wt%) in combination with salt-leaching and freeze-drying methodologies were developed for articular cartilage tissue engineering (TE) applications. The HRP-crosslinked SF scaffolds presented high porosity (89.3 ± 0.6%), wide pore distribution and high interconnectivity (95.9 ± 0.8%). Moreover, a large swelling capacity and favorable degradation rate were observed up to 30 days, maintaining the porous-like structure and β-sheet conformational integrity obtained with salt-leaching and freeze-drying processing. The in vitro studies supported human adipose-derived stem cells (hASCs) adhesion, proliferation, and high glycosaminoglycans (GAGs) synthesis under chondrogenic culture conditions. Furthermore, the chondrogenic differentiation of hASCs was assessed by the expression of chondrogenic-related markers (collagen type II, Sox-9 and Aggrecan) and deposition of cartilage-specific extracellular matrix for up to 28 days. The cartilage engineered constructs also presented structural integrity as their mechanical properties were improved after chondrogenic culturing. Subcutaneous implantation of the scaffolds in CD-1 mice demonstrated no necrosis or calcification, and deeply tissue ingrowth. Collectively, the structural properties and biological performance of these porous HRP-crosslinked SF scaffolds make them promising candidates for cartilage regeneration.

STATEMENT OF SIGNIFICANCE

In cartilage tissue engineering (TE), several processing technologies have been combined to create scaffolds for efficient tissue repair. In our study, we propose novel silk fibroin (SF) scaffolds derived from enzymatically crosslinked SF hydrogels processed by salt-leaching and freeze-drying technologies, for articular cartilage applications. Though these scaffolds, we were able to combine the elastic properties of hydrogel-based systems, with the stability, resilience and controlled porosity of scaffolds processed via salt-leaching and freeze-drying technologies. SF protein has been extensively explored for TE applications, as a result of its mechanical strength, elasticity, biocompatibility, and biodegradability. Thus, the structural, mechanical and biological performance of the proposed scaffolds potentiates their use as three-dimensional matrices for cartilage regeneration.

Visible Light-Induced Hydrogelation of an Alginate Derivative and Application to Stereolithographic Bioprinting Using a Visible Light Projector and Acid Red

Visible light-induced hydrogelation is attractive for various biomedical applications. In this study, hydrogels of alginate with phenolic hydroxyl groups (Alg-Ph) were obtained by irradiating a solution containing the polymer, ruthenium II trisbipyridyl chloride ([Ru(bpy)₃]²⁺) and sodium persulfate (SPS), with visible light. The hydrogelation kinetics and the mechanical properties of the resultant hydrogels were tunable by controlling the intensity of the light and the concentrations of [Ru(bpy)₃]²⁺ and SPS. With appropriate concentrations of [Ru(bpy)₃]²⁺ and SPS, the hydrogel could be obtained following approximately 10 s of irradiation using a normal desktop lamp. The hydrogelation process and the resultant hydrogel were cytocompatible; mouse fibroblast cells enclosed in the Alg-Ph hydrogel maintained more than 90% viability for 1 week. The solution containing Alg-Ph, [Ru(bpy)₃]²⁺ and SPS was useful as a bioink for stereolithographic bioprinting. Cell-laden hydrogel constructs could be printed using the bioprinting system equipped with a visible light projector without a significant decrease in cell viability in the presence of photoabsorbent Acid Red 18. The hydrogel construct including a perfusable helical lumen of 1 mm in diameter could be fabricated using the printing system. These results demonstrate the significant potential of this visible light-induced hydrogelation system and the stereolithographic bioprinting using the hydrogelation system for tissue engineering and regenerative medicine.

Horseradish peroxidase-catalyzed hydrogelation for biomedical applications

Hydrogels catalyzed by horseradish peroxidase (HRP) serve as an efficient and effective platform for biomedical applications due to their mild reaction conditions for cells, fast and adjustable gelation rate in physiological conditions, and an abundance of substrates as water-soluble biocompatible polymers.

Nanoemulsion-induced enzymatic crosslinking of tyramine-functionalized polymer droplets

In situ gelation of water-in-oil polymer emulsions is a key method to produce hydrogel particles. Although this approach is in principle ideal for encapsulating bioactive components such as cells, the oil phase can interfere with straightforward presentation of crosslinker molecules. Several approaches have been developed to induce in-emulsion gelation by exploiting the triggered generation or release of crosslinker molecules. However, these methods typically rely on photo- or acid-based reactions that are detrimental to cell survival and functioning. In this work, we demonstrate the diffusion-based supplementation of small molecules for the in-emulsion gelation of multiple tyramine-functionalized polymers via enzymatic crosslinking using a H₂O₂/oil nanoemulsion. This strategy is compatible with various emulsification techniques, thereby readily supporting the formation of monodisperse hydrogel particles spanning multiple length scales ranging from the nano- to the millimeter. As proof of principle, we leveraged droplet microfluidics in combination with the cytocompatible nature of enzymatic crosslinking to engineer hollow cell-laden hydrogel microcapsules that support the formation of viable and functional 3D microtissues. The straightforward, universal, and cytocompatible nature of nanoemulsion-induced enzymatic crosslinking facilitates its rapid and widespread use in numerous food, pharma, and life science applications.

Inkjetting Plus Peroxidase-Mediated Hydrogelation Produces Cell-Laden, Cell-Sized Particles with Suitable Characters for Individual Applications

The authors report a method to prepare cell-laden, cell-sized microparticles from various materials suitable for individual applications. The method includes a piezoelectric inkjetting technology and a horseradish peroxidase (HRP)-catalyzed crosslinking reaction. The piezoelectric inkjetting technology enables production of cell-laden, cell-sized (20-60 μm) droplets from a polymer aqueous solution. The HRP-catalyzed crosslinking of the polymer in the ejected solution enables production of spherical microparticles from various materials. Superior cytocompatibility of the microencapsulation method is confirmed from the viability and growth profiles of normal murine mammary gland epithelial cells.

Tumor Growth Suppression Induced by Biomimetic Silk Fibroin Hydrogels

Protein-based hydrogels with distinct conformations which enable encapsulation or differentiation of cells are of great interest in 3D cancer research models. Conformational changes may cause macroscopic shifts in the hydrogels, allowing for its use as biosensors and drug carriers. In depth knowledge on how 3D conformational changes in proteins may affect cell fate and tumor formation is required. Thus, this study reports an enzymatically crosslinked silk fibroin (SF) hydrogel system that can undergo intrinsic conformation changes from random coil to β-sheet conformation. In random coil status, the SF hydrogels are transparent, elastic, and present ionic strength and pH stimuli-responses. The random coil hydrogels become β-sheet conformation after 10 days in vitro incubation and 14 days in vivo subcutaneous implantation in rat. When encapsulated with ATDC-5 cells, the random coil SF hydrogel promotes cell survival up to 7 days, whereas the subsequent β-sheet transition induces cell apoptosis in vitro. HeLa cells are further incorporated in SF hydrogels and the constructs are investigated in vitro and in an in vivo chick chorioallantoic membrane model for tumor formation. In vivo, Angiogenesis and tumor formation are suppressed in SF hydrogels. Therefore, these hydrogels provide new insights for cancer research and uses of biomaterials.

Cryopreservation of a small number of human sperm using enzymatically fabricated, hollow hyaluronan microcapsules handled by conventional ICSI procedures

PURPOSE

We investigated whether enzymatically fabricated hyaluronan (HA) microcapsules were feasible for use in the cryopreservation of a small number of sperm.

METHODS

HA microcapsules were fabricated using a system of water-immiscible fluid under laminar flow. Three sperm were injected into a hollow HA microcapsule using a micromanipulator. Capsules containing injected sperm were incubated in a freezing medium composed of sucrose as the cryoprotectant and then placed in a Cryotop® device and plunged into liquid nitrogen. After thawing, the capsule was degraded by hyaluronidase, and the recovery rate of sperm and their motility were investigated.

RESULTS

The HA microcapsule measuring 200 μm in diameter and with a 30-μm thick membrane was handled using a conventional intracytoplasmic sperm injection (ICSI) system, and the procedure involved the injection of sperm into the capsule. The HA microcapsules containing sperm were cryopreserved in a Cryotop® device and decomposed by the addition of hyaluronidase. The recovery rate of sperm after cryopreservation and degradation of HA microcapsules was sufficient for use in clinical practice (90 %).

CONCLUSIONS

Hollow HA microcapsules can be used for the cryopreservation of a small number of sperm without producing adverse effects on sperm quality.

Structured microparticles with tailored properties produced by membrane emulsification

This paper provides an overview of membrane emulsification routes for fabrication of structured microparticles with tailored properties for specific applications. Direct (bottom-up) and premix (top-down) membrane emulsification processes are discussed including operational, formulation and membrane factors that control the droplet size and droplet generation regimes. A special emphasis was put on different methods of controlled shear generation on membrane surface, such as cross flow on the membrane surface, swirl flow, forward and backward flow pulsations in the continuous phase and membrane oscillations and rotations. Droplets produced by membrane emulsification can be used for synthesis of particles with versatile morphology (solid and hollow, matrix and core/shell, spherical and non-spherical, porous and coherent, composite and homogeneous), which can be surface functionalised and coated or loaded with macromolecules, nanoparticles, quantum dots, drugs, phase change materials and high molecular weight gases to achieve controlled/targeted drug release and impart special optical, chemical, electrical, acoustic, thermal and magnetic properties. The template emulsions including metal-in-oil, solid-in-oil-in-water, oil-in-oil, multilayer, and Pickering emulsions can be produced with high encapsulation efficiency of encapsulated materials and narrow size distribution and transformed into structured particles using a variety of solidification processes, such as polymerisation (suspension, mini-emulsion, interfacial and in-situ), ionic gelation, chemical crosslinking, melt solidification, internal phase separation, layer-by-layer electrostatic deposition, particle self-assembly, complex coacervation, spray drying, sol-gel processing, and molecular imprinting. Particles fabricated from droplets produced by membrane emulsification include nanoclusters, colloidosomes, carbon aerogel particles, nanoshells, polymeric (molecularly imprinted, hypercrosslinked, Janus and core/shell) particles, solder metal powders and inorganic particles. Membrane emulsification devices operate under constant temperature due to low shear rates on the membrane surface, which range from (1-10)×10(3) s(-1) in a direct process to (1-10)×10(4) s(-1) in a premix process.

Horseradish peroxidase-catalyzed formation of hydrogels from chitosan and poly(vinyl alcohol) derivatives both possessing phenolic hydroxyl groups

Horseradish peroxidase-catalyzed cross-linking was applied to prepare hydrogels from aqueous solutions containing chitosan and poly(vinyl alcohol) derivatives both possessing phenolic hydroxyl groups (denoted as Ph-chitosan and Ph-PVA, respectively). Comparing the hydrogels prepared from the solution of 1.0% (w/v) Ph-chitosan and 3.0% (w/v) Ph-PVA and that of 3.0% (w/v) Ph-chitosan and 1.0% (w/v) Ph-PVA, the gelation time of the former hydrogel was 47 s, while was 10s longer than that of the latter one. The breaking point for the former hydrogel under stretching (114% strain) was approximately twice larger than that for the latter one. The swelling ratio of the former hydrogel in saline was about half of the latter one. Fibroblastic cells did not adhere on the former hydrogel but adhered and spread on the latter one. The growth of Escherichia coli cells was fully suppressed on the latter hydrogel during 48 h cultivation.

Polymers in cell encapsulation from an enveloped cell perspective

In the past two decades, many polymers have been proposed for producing immunoprotective capsules. Examples include the natural polymers alginate, agarose, chitosan, cellulose, collagen, and xanthan and synthetic polymers poly(ethylene glycol), polyvinyl alcohol, polyurethane, poly(ether-sulfone), polypropylene, sodium polystyrene sulfate, and polyacrylate poly(acrylonitrile-sodium methallylsulfonate). The biocompatibility of these polymers is discussed in terms of tissue responses in both the host and matrix to accommodate the functional survival of the cells. Cells should grow and function in the polymer network as adequately as in their natural environment. This is critical when therapeutic cells from scarce cadaveric donors are considered, such as pancreatic islets. Additionally, the cell mass in capsules is discussed from the perspective of emerging new insights into the release of so-called danger-associated molecular pattern molecules by clumps of necrotic therapeutic cells. We conclude that despite two decades of intensive research, drawing conclusions about which polymer is most adequate for clinical application is still difficult. This is because of the lack of documentation on critical information, such as the composition of the polymer, the presence or absence of confounding factors that induce immune responses, toxicity to enveloped cells, and the permeability of the polymer network. Only alginate has been studied extensively and currently qualifies for application. This review also discusses critical issues that are not directly related to polymers and are not discussed in the other reviews in this issue, such as the functional performance of encapsulated cells in vivo. Physiological endocrine responses may indeed not be expected because of the many barriers that the metabolites encounter when traveling from the blood stream to the enveloped cells and back to circulation. However, despite these diffusion barriers, many studies have shown optimal regulation, allowing us to conclude that encapsulated grafts do not always follow nature's course but are still a possible solution for many endocrine disorders for which the minute-to-minute regulation of metabolites is mandatory.

Bio-Encapsulation for the Immune-Protection of Therapeutic Cells

The design of new technologies for treatment of human disorders is a complex and difficult task. The aim of this article is to explore state of art discussion of various techniques and materials involve in cell encapsulations. Encapsulation of cells within semi-permeable polymer shells or beads is a potentially powerful tool, and has long been explored as a promising approach for the treatment of several human diseases such as lysosomal storage disease (LSD), neurological disorders, Parkinsons disease, dwarfism, hemophilia, cancer and diabetes using immune-isolation gene therapy.

Microenvironment of alginate-based microcapsules for cell culture and tissue engineering

As a type of 3D model, the technology of microencapsulation holds significant promise for tissue engineering and cell therapy due to its unique performance. The microenvironmental factors within microcapsules play an important role in influencing the behaviors of encapsulated cells. The aim of this review article is to give an overview on the construction of the microenvironmental factors, which include 3D space, physicochemical properties of alginate matrix, cell spheroids, nutritional status, and so on. Furthermore, we clarified the effect of microenvironmental factors on the behaviors of encapsulated cells and the methods about improving the microenvironment of microcapsules. This review will help to understand the interaction of the microenvironment and the encapsulated cells and lay a solid foundation for microcapsule-based cell therapy and tissue engineering.

Calcium alginate microcapsules with spherical liquid cores templated by gelatin microparticles for mass production of multicellular spheroids

Multicellular spheroids are important in biomedical applications, such as drug research and regenerative medicine. We developed microcapsules from sodium alginate and gelatin for mass production of size-controlled spheroids with diameters <200 microm. The microcapsules were composed of calcium alginate gels with spherical liquid cores (diameter approximately 150 microm) for formation of spheroids. The spherical liquid cores were prepared by incubating calcium alginate microcapsules containing thermally gelled, cell-enclosing gelatin microparticles about 150 microm in diameter, at 37 degrees C. The gelatin microparticles were encapsulated within the microcapsules by dropping a sodium alginate solution containing suspended gelatin microparticles into 100 mM CaCl(2). The enclosed feline renal fibroblast cell line, CRFK, cells showed 93.8% viability immediately after encapsulation, then grew and completely filled the spherical cores. Multicellular spheroids were collected within 1 min by soaking microcapsules in a medium containing alginate lyase.

Enzyme-mediated redox initiation for hydrogel generation and cellular encapsulation

A rapid, water-soluble enzyme-mediated radical chain initiation system involving glucose oxidase and Fe(2+) generated hydrogels within minutes at 25 degrees C and in ambient oxygen. The initiation components were evaluated for their effect on polymerization rates of hydroxyethyl acrylate-poly(ethylene glycol)(575) diacrylate comonomer solutions using near-infrared spectroscopy. Increasing glucose concentration increased polymerization rates until reaching a rate plateau above 1 x 10(-3) M of glucose. A square root dependence of the initial polymerization rate on Fe(2+) concentration was observed between 1.0 x 10(-4) M and 5.0 x 10(-4) M of Fe(2+), whereupon excess Fe(2+) reduced final acrylate conversions. The glucose oxidase-mediated initiation system was employed for encapsulation of fibroblasts (NIH3T3s) into a poly(ethylene glycol) tetra-acrylate (M(n) approximately 20000) hydrogel scaffold demonstrating 96% (+/-3%) viability at 24 h postencapsulation. This first use of enzyme-mediated redox radical chain initiation for cellular encapsulation demonstrates polymerization of hydrogels in situ with kinetic control, minimal oxygen inhibition issues, and utilization of low initiator concentrations.

Progress technology in microencapsulation methods for cell therapy

Cell encapsulation in microcapsules allows the in situ delivery of secreted proteins to treat different pathological conditions. Spherical microcapsules offer optimal surface-to-volume ratio for protein and nutrient diffusion, and thus, cell viability. This technology permits cell survival along with protein secretion activity upon appropriate host stimuli without the deleterious effects of immunosuppressant drugs. Microcapsules can be classified in 3 categories: matrix-core/shell microcapsules, liquid-core/shell microcapsules, and cells-core/shell microcapsules (or conformal coating). Many preparation techniques using natural or synthetic polymers as well as inorganic compounds have been reported. Matrix-core/shell microcapsules in which cells are hydrogel-embedded, exemplified by alginates capsule, is by far the most studied method. Numerous refinement of the technique have been proposed over the years such as better material characterization and purification, improvements in microbead generation methods, and new microbeads coating techniques. Other approaches, based on liquid-core capsules showed improved protein production and increased cell survival. But aside those more traditional techniques, new techniques are emerging in response to shortcomings of existing methods. More recently, direct cell aggregate coating have been proposed to minimize membrane thickness and implants size. Microcapsule performances are largely dictated by the physicochemical properties of the materials and the preparation techniques employed. Despite numerous promising pre-clinical results, at the present time each methods proposed need further improvements before reaching the clinical phase.

Agarose-gelatin conjugate membrane enhances proliferation of adherent cells enclosed in hollow-core microcapsules

Controlling growth of cells enclosed in hollow-core microcapsules is an important issue for the practical use of the device in biomedical and biopharmaceutical fields. In this study, we developed hollow-core microcapsules with a cell-adhesive agarose-gelatin conjugate (Aga-Ge) gel membrane for enhancement of adherent cell growth. We enclosed adherent feline kidney cells in these microcapsules and compared their growth profile and behavior with cells in microcapsules with an unmodified agarose membrane. The cells grew approx. 2-fold faster in microcapsules with the Aga-Ge membrane than in those with the unmodified agarose membrane. Fluorescence observation of the cellular skeleton clearly revealed that the enclosed cells adhered and spread on the inner surface of the Aga-Ge membrane but not on the unmodified agarose membrane. The maximum cell densities estimated on the basis of the cellular mitochondrial activities were independent of the cellular adhesiveness of the membrane. The mitochondrial activities per vehicle were similar for the two types of microcapsules. These results demonstrate that construction of microcapsule membranes from cell-adhesive materials is effective for enhancing cellular growth in these devices.

Enzymatically crosslinked carboxymethylcellulose-tyramine conjugate hydrogel: cellular adhesiveness and feasibility for cell sheet technology

An aqueous solution of carboxylmethylcellulose with phenolic hydroxyl groups (CMC-Ph) is gellable within 1 min via a peroxidase-catalyzed oxidative reaction under mild conditions suitable for mammalian cells. In this research, we evaluated cellular adhesion and proliferation on the resultant hydrogel, and the feasibility of the hydrogel as a substrate for cell sheet technology. Within 4 h of seeding, 76.9% of L929 fibroblast cells adhered to the gel and showed similar morphology of spreading to that on cell culture dish. Subsequently, the adherent cells proliferated on the gel and formed a confluent monolayer after 168 h of culture. From the confluent monolayer we could harvest a cell sheet after about 5 min of digestion of the gel using cellulase dissolved in medium at 5 U ml(-1). The cells in the cell sheet showed well-preserved morphology similar to that shown before they were detached from the gel. In addition, the harvested cell sheet readhered and proliferated after being transferred to another culture dish. These results demonstrate that CMC-Ph gel is a good candidate material for obtaining cell sheets.

Cell microencapsulation technology: towards clinical application

The pharmacokinetic properties of a drug can be significantly improved by the delivery process. Scientists have understood that developing suitable drug delivery systems that release the therapeutically active molecule at the level and dose it is needed and during the optimal time represents a major advance in the field. Cell microencapsulation is an alternative approach for the sustained delivery of therapeutic agents. This technology is based on the immobilization of different types of cells within a polymeric matrix surrounded by a semipermeable membrane for the long-term release of therapeutics. As a result, encapsulated cells are isolated from the host immune system while allowing exchange of nutrients and waste and release of the therapeutic agents. The versatility of this approach has stimulated its use in the treatment of numerous medical diseases including diabetes, cancer, central nervous system diseases and endocrinological disorders among others. The aim of this review article is to give an overview on the current state of the art of the use of cell encapsulation technology as a controlled drug delivery system. The most important advantages of this type of "living" drug release strategy are highlighted, but also its limitations pointed out, and the major challenges to be addressed in the forthcoming years are described.

Production of cell-enclosing hollow-core agarose microcapsules via jetting in water-immiscible liquid paraffin and formation of embryoid body-like spherical tissues from mouse ES cells enclosed within these microcapsules

We developed agarose microcapsules with a single hollow core templated by alginate microparticles using a jet-technique. We extruded an agarose aqueous solution containing suspended alginate microparticles into a coflowing stream of liquid paraffin and controlled the diameter of the agarose microparticles by changing the flow rate of the liquid paraffin. Subsequent degradation of the inner alginate microparticles using alginate lyase resulted in the hollow-core structure. We successfully obtained agarose microcapsules with 20-50 microm of agarose gel layer thickness and hollow cores ranging in diameter from ca. 50 to 450 microm. Using alginate microparticles of ca. 150 microm in diameter and enclosing feline kidney cells, we were able to create cell-enclosing agarose microcapsules with a hollow core of ca. 150 microm in diameter. The cells in these microcapsules grew much faster than those in alginate microparticles. In addition, we enclosed mouse embryonic stem cells in agarose microcapsules. The embryonic stem cells began to self-aggregate in the core just after encapsulation, and subsequently grew and formed embryoid body-like spherical tissues in the hollow core of the microcapsules. These results show that our novel microcapsule production technique and the resultant microcapsules have potential for tissue engineering, cell therapy and biopharmaceutical applications.