Chondrogenic differentiation of human mesenchymal stem cells in three-dimensional alginate gels

Fabrication of core-shell microcapsules using PLGA and alginate for dual growth factor delivery system

To effectively harness the great potential of stem cells, we designed a dual growth factor delivery system for the application toward stem cell differentiation into specific lineages. This system carries a core-shell structure within microcapsules made of poly(L-lactide-co-glycolide) (PLGA) and alginate, which were fabricated using a coaxial electro-dropping method. Both PLGA and alginate were supplied from the inner and outer nozzles, respectively. The size and shape of microcapsules were greatly varying depending on the variables: nozzle size, applied voltage, volumetric feeding ratio (PLGA:alginate), feeding rate, and polymer concentrations. Once proper conditions were met, single or multi PLGA cores were found settled within the microcapsules. From the microscopic images, wrinkled surfaces of microcapsules were observed, along with the PLGA cores inside the alginate domain. When two different microcapsules were made, switching the position of bone morphogenetic protein (BMP)-2 and dexamethasone (Dex) for either core or shell domain, their release profiles were very unique on a temporal basis, based on their location in the microcapsules. An initial burst of biomolecules was highly suppressed when either biomolecule was loaded in the PLGA core. It was clear that the osteogenic biomolecules encapsulated in the microcapsule could be released together and their concentrations were disparate at each time point. Meanwhile as the hydrogel constructs including rat bone marrow stromal cells (BMSCs) and osteogenic factor-loaded microcapsules were cultured for up to 4 weeks, the gene expressions levels of osteopontin, type I collagen, and osteocalcin were significantly upregulated as compared to the control group. The present coaxial system was very effective in manufacturing PLGA core-alginate shell microcapsules and in encapsulating multiple biomolecules essential for stem cell differentiation.

Regulation of Chondrogenesis by Transforming Growth Factor-ß3 and Insulin-like Growth Factor-1 from Human Mesenchymal Umbilical Cord Blood Cells

Objective.

Mature articular cartilage is vulnerable to injuries and disease processes that cause irreversible tissue damage because of its limited capacity for self-repair. Umbilical cord blood is a source of mesenchymal stem cells, which can give rise to cells of different lineages, including cartilage, bone, and fat. Cellular condensation is a required step in the initiation of mesenchymal chondrogenesis. We attempted to differentiate cells from umbilical cord blood into chondrocytes with insulin-like growth factor 1 (IGF-1) and transforming growth factor-ß3 (TGF-ß3).

Methods.

Cells were grown in high density micromass and monolayer culture systems and then evaluated for expression of type II collagen, aggrecan, and Sox9. Umbilical cord blood from 130 patients was harvested.

Results.

Expression of type II collagen, aggrecan, and Sox9 was detected after 14 days in TGF-ß3- and IGF-1-stimulated cells in both types of culture (monolayer and micromass). On Day 21 in the micromass culture, expression levels were greater than they were at 14 days for all genes. TGF-ß3 was found to be more efficient at promoting chondrogenesis than IGF-1. By western blot, we also found that after 3 weeks, the expression of type II collagen was greater in micromass culture with TGF-ß3.

Conclusion.

TGF-ß3 used in micromass culture is the best growth factor for promoting the proliferation and differentiation of mesenchymal cells from umbilical cord blood during chondrogenesis. This approach may provide an alternative to autologous grafting.

Controlling stem cell fate with material design

Advances in our understanding of stem cell interactions with their environment are leading to the development of new materials-based approaches to control stem cell behavior toward cellular culture and tissue regeneration applications. Materials can provide cues based on chemistry, mechanics, structure, and molecule delivery that control stem cell fate decisions and matrix formation. These approaches are helping to advance clinical translation of a range of stem cell types through better expansion techniques and scaffolding for use in tissue engineering approaches for the regeneration of many tissues. With this in mind, this progress report covers basic concepts and recent advances in the use of materials for manipulating stem cells.

Enhanced chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells in low oxygen environment micropellet cultures

Chondrogenesis of mesenchymal stem cells (MSCs) is typically induced when they are condensed into a single aggregate and exposed to transforming growth factor-beta (TGF-beta). Hypoxia, like aggregation and TGF-beta delivery, may be crucial for complete chondrogenesis. However, the pellet dimensions and associated self-induced oxygen gradients of current chondrogenic methods may limit the effectiveness of in vitro differentiation and subsequent therapeutic uses. Here we describe the use of embryoid body-forming technology to produce microscopic aggregates of human bone marrow MSCs (BM-MSCs) for chondrogenesis. The use of micropellets reduces the formation of gradients within the aggregates, resulting in a more homogeneous and controlled microenvironment. These micropellet cultures (approximately 170 cells/micropellet) as well as conventional pellet cultures (approximately 2 x 10(5) cells/pellet) were chondrogenically induced under 20% and 2% oxygen environments for 14 days. Compared to conventional pellets under both environments, micropellets differentiated under 2% O(2) showed significantly increased sulfated glycosaminoglycan (sGAG) production and more homogeneous distribution of proteoglycans and collagen II. Aggrecan and collagen II gene expressions were increased in pellet cultures differentiated under 2% O(2) relative to 20% O(2) pellets but 2% O(2) micropellets showed even greater increases in these genes, as well as increased SOX9. These results suggest a more advanced stage of chondrogenesis in the micropellets accompanied by more homogeneous differentiation. Thus, we present a new method for enhancing MSC chondrogenesis that reveals a unique relationship between oxygen tension and aggregate size. The inherent advantages of chondrogenic micropellets over a single macroscopic aggregate should allow for easy integration with a variety of cartilage engineering strategies.

Mechanics and mechanobiology of mesenchymal stem cell-based engineered cartilage

In this review, we outline seminal and recent work highlighting the potential of mesenchymal stem cells (MSCs) in producing cartilage-like tissue equivalents. Specific focus is placed on the mechanical properties of engineered MSC-based cartilage and how these properties relate to that of engineered cartilage based on primary chondrocytes and to native tissue properties. We discuss current limitations and/or concerns that must be addressed for the clinical realization of MSC-based cartilage therapeutics, and provide some insight into potential underpinnings for the observed deviations from chondrocyte-based engineered constructs. We posit that these differences reveal specific deficits in terms of our description of chondrogenesis, and suggest that new benchmarks must be developed towards this end. Further, we describe the growing body of literature on the mechanobiology of MSC-based cartilage, highlighting positive findings with regards to the furtherance of the chondrogenic phenotype. We likewise discuss the failure of early molecular changes to translate directly into engineered constructs with improved mechanical properties. Finally, we highlight recent work from our group and others that may point to new strategies for enhancing the formation of engineered cartilage based on MSCs.

The influence of fibrin based hydrogels on the chondrogenic differentiation of human bone marrow stromal cells

Mesenchymal Stem Cells (MSC) are frequently incorporated into osteochondral implants and cell seeding is often facilitated with hydrogels which exert a profound influence on the chondrogenic differentiation of MSC. An attempt was made to elucidate this effect by comparing the chondrogenic differentiation of Bone Marrow Stromal Cells (BMSC) in fibrin and fibrin alginate composites. A biphasic osteochondral model which simulated the native in vivo environment was employed in the study. In the first stage of the experiment, BMSC was encapsulated in fibrin, Fibrin Alginate 0.3% (FA0.3) and 0.6% (FA0.6). Chondrogenic differentiation within these cell-hydrogel pellets was compared against that of standard cell pellets under inductive conditions and the matrices which supported chondrogenesis were used in the cartilage phase of biphasic constructs. Neo-cartilage growth was monitored in these cocultures. It was observed that hydrogel encapsulation influenced mesenchymal condensation which preceded chondrogenic differentiation. Early cell agglomeration was observed in fibrin as compared to fibrin alginate composites. These fibrin encapsulated cells differentiated into chondrocytes which secreted aggrecan and collagen II. When the alginate content rose from 0.3 to 0.6%, chondrogenic differentiation declined with a reduction in the expression of collagen II and aggrecan. Fibrin and FA0.3 were tested in the cartilage phase of the biphasic osteochondral constructs and the former supported superior cartilage growth with higher cellularity, total Glycosaminoglycan (GAG) and collagen II levels. The FA0.3 cartilage phase was found to be fragmented and partially calcified. The use of fibrin for cartilage repair was advocated as it facilitated BMSC chondrogenesis and cartilaginous growth in an osteochondral environment.