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

Engineering Cell Microenvironment Using Nanopattern-Derived Multicellular Spheroids and Photo-Crosslinked Gelatin/Hyaluronan Hydrogels

Cell cultures of dispersed cells within hydrogels depict the interaction of the cell-extracellular matrix (ECM) in 3D, while the coculture of different cells within spheroids combines both the effects of cell-cell and cell-ECM interactions. In this study, the cell co-spheroids of human bone mesenchymal stem cells/human umbilical vein endothelial cells (HBMSC/HUVECs) are prepared with the assistance of a nanopattern, named colloidal self-assembled patterns (cSAPs), which is superior to low-adhesion surfaces. A phenol-modified gelatin/hyaluronan (Gel-Ph/HA-Ph) hydrogel is used to encapsulate the multicellular spheroids and the constructs are photo-crosslinked using blue light. The results show that Gel-Ph/HA-Ph hydrogels with a 5%-to-0.3% ratio have the best properties. Cells in HBMSC/HUVEC co-spheroids are more favorable for osteogenic differentiation (Runx2, ALP, Col1a1 and OPN) and vascular network formation (CD31+ cells) compared to HBMSC spheroids. In a subcutaneous nude mouse model, the HBMSC/HUVEC co-spheroids showed better performance than HBMSC spheroids in angiogenesis and the development of blood vessels. Overall, this study paves a new way for using nanopatterns, cell coculturing and hydrogel technology for the generation and application of multicellular spheroids.

Cell encapsulated and microenvironment modulating microbeads containing alginate hydrogel system for bone tissue engineering

Functional tissue regeneration using synthetic biomaterials requires proliferation and heterotypic differentiation of stem/progenitor cells within a specialized heterogeneous (biophysical-biochemical) microenvironment. The current techniques have limitations to develop synthetic hydrogels, mimicking native extracellular matrix porosity along with heterogeneous microenvironmental cues of matrix mechanics, degradability, microstructure and cell-cell interactions. Here, we have developed a microenvironment modulating system to fabricate in situ porous hydrogel matrix with two or more distinct tailored microenvironmental niches within microbeads and the hydrogel matrix for multicellular tissue regeneration. Electrosprayed pectin-gelatin blended microbeads and crosslinked alginate hydrogel system help to tailor microenvironmental niches of encapsulated cells where two different cells are surrounded by a specific microenvironment. The effect of different microenvironmental parameters associated with the microbead/hydrogel matrix was evaluated using human umbilical-cord mesenchymal stem cells (hUCMSCs). The osteogenic differentiation of hUCMSCs in the hydrogel matrix was evaluated for bone tissue regeneration. This will be the first report on microenvironment modulating microbead-hydrogel system to encapsulate two/more types of cells in a hydrogel, where each cell is surrounded with distinct niches for heterogeneous tissue regeneration.

Silk fibroin nanofibers: a promising ink additive for extrusion three-dimensional bioprinting

Here, we investigated the usefulness of silk fibroin nanofibers obtained via mechanical grinding of degummed silkworm silk fibers as an additive in bioinks for extrusion three-dimensional (3D) bioprinting of cell-laden constructs. The nanofibers could be sterilized by autoclaving, and addition of the nanofibers improved the shear thinning of polymeric aqueous solutions, independent of electric charge and the content of cross-linkable moieties in the polymers. The addition of nanofibers to bioinks resulted in the fabrication of hydrogel constructs with higher fidelity to blueprints. Mammalian cells in the constructs showed >85% viability independent of the presence of nanofibers. The nanofibers did not affect the morphologies of enclosed cells. These results demonstrate the great potential of silk fibroin nanofibers obtained via mechanical grinding of degummed silkworm silk fibers as an additive in bioinks for extrusion 3D bioprinting.

Differentiation potential of human adipose stem cells bioprinted with hyaluronic acid/gelatin-based bioink through microextrusion and visible light-initiated crosslinking

Bioprinting has a great potential to fabricate three-dimensional (3D) functional tissues and organs. In particular, the technique enables fabrication of 3D constructs containing stem cells while maintaining cell proliferation and differentiation abilities, which is believed to be promising in the fields of tissue engineering and regenerative medicine. We aimed to demonstrate the utility of the bioprinting technique to create hydrogel constructs consisting of hyaluronic acid (HA) and gelatin derivatives through irradiation by visible light to fabricate 3D constructs containing human adipose stem cells (hADSCs). The hydrogel was obtained from a solution of HA and gelatin derivatives possessing phenolic hydroxyl moieties in the presence of ruthenium(II) tris-bipyridyl dication and sodium ammonium persulfate. hADSCs enclosed in the bioprinted hydrogel construct elongated and proliferated in the hydrogel. In addition, their differentiation potential was confirmed by examining the expression of pluripotency marker genes and cell surface marker proteins, and differentiation to adipocytes in adipogenic differentiation medium. Our results demonstrate the great potential of the bioprinting method and the resultant hADSC-laden HA/gelatin constructs for applications in tissue engineering and regenerative medicine.

Hydrolytic Activity of Esterase-Antibody Complexes Retained Within Gel Capsules After Complex Isolation

Delipidation in biological samples is important for some diagnostic tests and protein analyses. Lipids in the samples can be hydrolyzed by native esterases (ESs) within gel capsules after ES, and ES-antibody complexes are specifically trapped, extracted, and separated. Acrylamide and agarose gel capsules containing complexes of ES antibody were produced after the complexes were extracted using protein A-immobilized membranes, separated by non-denaturing electrophoresis, and stained by colloidal silver using glucose as a reductant. ES activity of ES-antibody complexes within the gel capsule was significantly higher than that in the complexes with the control antibodies upon isolation, separation, and detection of the complex. In addition, lipids bound to human serum albumin decreased after human plasma was treated with gel capsules containing ES-antibody complexes. We demonstrate that the gel capsule containing ES-antibody complexes can be successfully isolated using techniques described in this study. Furthermore, delipidation of human plasma is obtained by incubation with the gel capsule. These results indicate that surplus materials such as lipids in biological samples can be removed or reduced by gel capsule containing enzymes.

Fabrication of cell-laden macroporous biodegradable hydrogels with tunable porosities and pore sizes

In this work, we investigated a cytocompatible particulate leaching method for the fabrication of cell-laden macroporous hydrogels. We used dehydrated and uncrosslinked gelatin microspheres as leachable porogens to create macroporous oligo(poly(ethylene glycol) fumarate) hydrogels. Varying gelatin content and size resulted in a wide range of porosities and pore sizes, respectively. Encapsulated mesenchymal stem cells (MSCs) exhibited high viability immediately following the fabrication process, and culture of cell-laden hydrogels revealed improved cell viability with increasing porosity. Additionally, the osteogenic potential of the encapsulated MSCs was evaluated over 16 days. Overall, this study presents a robust method for the preparation of cell-laden macroporous hydrogels with desired porosity and pore size for tissue engineering applications.

Impact of the composition of alginate and gelatin derivatives in bioconjugated hydrogels on the fabrication of cell sheets and spherical tissues with living cell sheaths

Gelatin and alginate derivatives possessing phenolic hydroxyl moieties (gelatin-Ph and Alg-Ph) were dissolved in aqueous solution and conjugated via horseradish peroxidase-catalyzed crosslinking, resulting in hydrogelation. The objective of creating the hydrogels was to prepare cell sheets and spherical tissues wrapped in living cell sheaths. An increase in the gelatin-Ph content in the hydrogel improved cellular adhesion on the hydrogel surface but hindered degradability by alginate lyase. A hydrogel with the desired characteristics was obtained from a solution containing 0.5% (w/v) gelatin-Ph and 1.5% (w/v) Alg-Ph. Human aortic endothelial (HAE) cells and mouse embryo fibroblast 10T1/2 cells grew on the hydrogels and could be harvested as cell sheets by treatment with alginate lyase. 10T1/2 cells enclosed in Alg-Ph/gelatin-Ph microcapsules composed of the conjugate hydrogel elongated on the inner surface of the microcapsules and grew three times faster than those enclosed in Alg-Ph microcapsules. Alg-Ph/gelatin-Ph microcapsules not only supported growth of the enclosed cells into spherical tissues, but also provided a cell adhesive outer surface for the fabrication of an HAE cell layer. Finally, spherical tissues of 10T1/2 cells wrapped in living HAE cell sheaths were obtained by treatment with alginate lyase.

Fabrication of three-dimensional porous cell-laden hydrogel for tissue engineering

For tissue engineering applications, scaffolds should be porous to enable rapid nutrient and oxygen transfer while providing a three-dimensional (3D) microenvironment for the encapsulated cells. This dual characteristic can be achieved by fabrication of porous hydrogels that contain encapsulated cells. In this work, we developed a simple method that allows cell encapsulation and pore generation inside alginate hydrogels simultaneously. Gelatin beads of 150-300 microm diameter were used as a sacrificial porogen for generating pores within cell-laden hydrogels. Gelation of gelatin at low temperature (4 degrees C) was used to form beads without chemical crosslinking and their subsequent dissolution after cell encapsulation led to generation of pores within cell-laden hydrogels. The pore size and porosity of the scaffolds were controlled by the gelatin bead size and their volume ratio, respectively. Fabricated hydrogels were characterized for their internal microarchitecture, mechanical properties and permeability. Hydrogels exhibited a high degree of porosity with increasing gelatin bead content in contrast to nonporous alginate hydrogel. Furthermore, permeability increased by two to three orders while compressive modulus decreased with increasing porosity of the scaffolds. Application of these scaffolds for tissue engineering was tested by encapsulation of hepatocarcinoma cell line (HepG2). All the scaffolds showed similar cell viability; however, cell proliferation was enhanced under porous conditions. Furthermore, porous alginate hydrogels resulted in formation of larger spheroids and higher albumin secretion compared to nonporous conditions. These data suggest that porous alginate hydrogels may have provided a better environment for cell proliferation and albumin production. This may be due to the enhanced mass transfer of nutrients, oxygen and waste removal, which is potentially beneficial for tissue engineering and regenerative medicine applications.

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.

Small Agarose Microcapsules with Cell-Enclosing Hollow Core for Cell Therapy: Transplantation of Ifosfamide-Activating Cells to the Mice with Preestablished Subcutaneous Tumor

Cell transplantation after enclosing in microcapsules has been studied as an alternative approach for treatment of wide variety of diseases. In the present study, we examined the feasibility of using agarose microcapsules, having a cell-enclosing hollow core of 100–150 μm in diameter and agarose gel membrane of about 20 μm in thickness, as a device for the methodology. We enclosed cells that had been genetically engineered to express cytochrome P450 2B1, an enzyme that activates the anticancer prodrug ifosfamide. The enclosed cells were shown to express the enzymatic function in the microcapsules in that they suppressed the growth of tumor cells in medium containing ifosfamide. In addition, a more significant regression of preformed tumors was observed in the nude mice implanted with the cell-enclosing microcapsules compared with those implanted with empty capsules after administration of ifosfamide. Preformed tumors shrank by less than 40% in volume in 6 of the 10 recipients implanted with cell-enclosing microcapsules. In contrast, only 1 in 10 of the preformed tumors in the recipient implanted with empty microcapsules shrank by this amount. These results suggest that agarose microcapsules containing cytochrome P450 2B1 enzyme-expressing cells are feasible devices for improving the chemotherapy of tumors. Thus, agarose microcapsule having hollow cores are generally a good candidate as vehicles for cell-encapsulation approaches to cell therapy.