Impact of alginate type and bead diameter on mass transfers and the metabolic activities of encapsulated C3A cells in bioartificial liver applications

An appropriate selection of a 3D alginate culture model for hepatic Huh-7 cell line encapsulation intended for viral studies

Three-dimensional (3D) culture systems have been introduced to provide cells with a biomimetic environment that is similar to in vivo conditions. Among the polymeric molecules available, sodium-alginate (Na-alg) salt is a material that is currently employed in different areas of drug delivery and tissue engineering, because it offers biocompatibility and optimal chemical properties, and its gelation with calcium chloride provides calcium-alginate (Ca-alg) scaffolds with mechanical stability and relative permeability. In this work, four different preparations of Ca-alg beads with varying Na-alg viscosity and concentration were used for a human hepatoma cell line (Huh-7) encapsulation. The effects of Ca-alg bead preparation on structural cell organization, liver-specific functions, and the expression of specific receptors implicated in hepatotropic virus permissivity were evaluated. Hepatic cells were cultured in 500 μm diameter Ca-alg beads for 7 days under dynamic conditions. For all culture systems, cell viability reached almost 100% at day 7. Cell proliferation was concomitantly followed by hepatocyte organization in aggregates, which adopted two different morphologies (spheroid aggregates or multicellular channel-like structures), depending on Ca-alg bead preparation. These cellular organizations established a real 3D hepatocyte architecture with cell polarity, cell junctions, and abundant bile canaliculi possessing microvillus-lined channels. The functionality of these 3D cultures was confirmed by the production of albumin and the exhibition of CYP1A activity over culture time, which were variable, according to Ca-alg bead condition. The expression of specific receptors of hepatitis C virus by Huh-7 cells suggests encouraging data for the further development of a new viral culture system in Ca-alg beads. In summary, this 3D hepatic cell culture represents a promising physiologically relevant system for further in vitro studies and demonstrates that an adequate encapsulation condition can be selected for each target application in liver tissue engineering, specifically in viral studies.

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.

Encapsulation of Huh-7 cells within alginate-poly(ethylene glycol) hybrid microspheres

Novel calcium alginate poly(ethylene glycol) hybrid microspheres (Ca-alg-PEG) were developed and evaluated as potentially suitable materials for cell microencapsulation. Grafting 5-13% of the backbone units of sodium alginate (Na-alg) with α-amine-ω-thiol PEG maintained the gelling capacity in presence of calcium ions, while thiol end groups allowed for preparing chemically crosslinked hydrogel via spontaneous disulfide bond formation. The combination of these two gelling mechanisms yielded Ca-alg-PEG. Human hepatocellular carcinoma cells (Huh-7) were encapsulated in Ca-alg-PEG and calcium alginate beads (Ca-alg), and cultured for 2 weeks under agitation conditions. Immediately after completion of the microencapsulation, the cell viability was 60% and similar in Ca-alg-PEG and Ca-alg. The proliferation of Huh-7 encapsulated in Ca-alg-PEG was slightly higher than in Ca-alg. Accelerated proliferation after 2 weeks was observed for the encapsulation in Ca-alg-PEG. The production of albumin confirmed the functionality of the encapsulated Huh-7 cells. The study confirms the suitability of Ca-alg-PEG and the one-step technology for cell microencapsulation.

Bioengineering embryonic stem cell microenvironments for the study of breast cancer

Breast cancer is the most prevalent disease amongst women worldwide and metastasis is the main cause of death due to breast cancer. Metastatic breast cancer cells and embryonic stem (ES) cells display similar characteristics. However, unlike metastatic breast cancer cells, ES cells are nonmalignant. Furthermore, embryonic microenvironments have the potential to convert metastatic breast cancer cells into a less invasive phenotype. The creation of in vitro embryonic microenvironments will enable better understanding of ES cell-breast cancer cell interactions, help elucidate tumorigenesis, and lead to the restriction of breast cancer metastasis. In this article, we will present the characteristics of breast cancer cells and ES cells as well as their microenvironments, importance of embryonic microenvironments in inhibiting tumorigenesis, convergence of tumorigenic and embryonic signaling pathways, and state of the art in bioengineering embryonic microenvironments for breast cancer research. Additionally, the potential application of bioengineered embryonic microenvironments for the prevention and treatment of invasive breast cancer will be discussed.

Determination of pore size distribution at the cell-hydrogel interface

Background

Analyses of the pore size distribution in 3D matrices such as the cell-hydrogel interface are very useful when studying changes and modifications produced as a result of cellular growth and proliferation within the matrix, as pore size distribution plays an important role in the signaling and microenvironment stimuli imparted to the cells. However, the majority of the methods for the assessment of the porosity in biomaterials are not suitable to give quantitative information about the textural properties of these nano-interfaces.

Findings

Here, we report a methodology for determining pore size distribution at the cell-hydrogel interface, and the depth of the matrix modified by cell growth by entrapped HepG₂ cells in microcapsules made of 0.8% and 1.4% w/v alginate. The method is based on the estimation of the shortest distance between two points of the fibril-like network hydrogel structures using image analysis of TEM pictures. Values of pore size distribution determined using the presented method and those obtained by nitrogen physisorption measurements were compared, showing good agreement. A combination of these methodologies and a study of the cell-hydrogel interface at various cell culture times showed that after three days of culture, HepG₂ cells growing in hydrogels composed of 0.8% w/v alginate had more coarse of pores at depths up to 40 nm inwards (a phenomenon most notable in the first 20 nm from the interface). This coarsening phenomenon was weakly observed in the case of cells cultured in hydrogels composed of 1.4% w/v alginate.

Conclusions

The method purposed in this paper allows us to obtain information about the radial deformation of the hydrogel matrix due to cell growth, and the consequent modification of the pore size distribution pattern surrounding the cells, which are extremely important for a wide spectrum of biotechnological, pharmaceutical and biomedical applications.