A thermodynamic model of short-term cell adhesion in vitro

Biomimetic microbeads containing a chondroitin sulfate/chitosan polyelectrolyte complex for cell-based cartilage therapy

Articular cartilage has a limited healing capacity that complicates the treatment of joint injuries and osteoarthritis. Newer repair strategies have focused on the use of cells and biomaterials to promote cartilage regeneration. In the present study, we developed and characterized bioinspired materials designed to mimic the composition of the cartilage extracellular matrix. Chondroitin sulfate (CS) and chitosan (CH) were used to form physically cross-linked macromolecular polyelectrolyte complexes (PEC) without the use of additional crosslinkers. A single-step water-in-oil emulsification process was used to either directly embed mesenchymal stem cells (MSC) in PEC particles created with a various concentrations of CS and CH, or to co-embed MSC with PEC in agarose-based microbeads. Direct embedding of MSC in PEC resulted in high cell viability but irregular and large particles. Co-embedding of PEC particles with MSC in agarose (Ag) resulted in uniform microbeads 80-90 μm in diameter that maintained high cell viability over three weeks in culture. Increased serum content resulted in more uniform PEC distribution within the microbead matrix, and both high and low CS:CH ratios resulted in more homogeneous microbeads than 1:1 formulations. Under chondrogenic conditions, expression of sulfated GAG and collagen type II was increased in 10:1 CS:CH PEC-Ag microbeads compared to pure Ag beads, indicating a chondrogenic influence of the PEC component. Such PEC-Ag microbeads may have utility in the directed differentiation and delivery of progenitor cell populations for cartilage repair.

Role of trapped air in the formation of cell-and-protein micropatterns on superhydrophobic/superhydrophilic microtemplated surfaces

Air trapped within the interstices of TiO(2) nanotube surfaces bearing superhydrophobic/superhydrophilic microtemplated domains controls formation of protein micropatterns but not cell micropatterns. Protein binding from either bovine-serum albumin (BSA) or fetal-bovine serum (FBS) solutions to superhydrophobic domains is blocked in the presence of trapped air, leading to clear protein binding contrast between superhydrophilic and superhydrophobic domains. Protein binds to superhydrophobic domains when air is displaced by sonication, leading to more protein binding to superhydrophobic domains than to superhydrophilic, with concomitantly blurred protein binding contrast. The overall contrast obtained in formation of cell (hFOB1.19, MG63, and HeLa) micropatterns depends on the cell type and protein composition of the fluid phase. All cell types preferentially attach to superhydrophilic domains from each fluid phase tested (FBS, BSA, and basal media containing no protein). All cell types do not attach to superhydrophobic domains from FBS solutions, with-or-without trapped air, creating a visually-obvious cell attachment pattern. However, cells attached to superhydrophobic domains from basal media suspensions, with-or-without trapped air, creating a blurred cell attachment pattern. Cell attachment from BSA-containing solutions gave mixed results depending on cell type. Thus, trapped air does not necessarily block cell attachment as has been suggested in the literature. Rather, cell attachment is controlled by interfacial tensions between cells, surfaces, and fluid phases in a manner that can be understood in terms of the Dupré work-of-adhesion formulation. Cell attachment patterns developed within the initial attachment phase persist for up to two days of continuous culture but overgrow thereafter, with-or-without trapped air, showing that trapped air does not block cell overgrowth over time of continuous culture.

Extended-Term Culture of Bone Cells in a Compartmentalized Bioreactor

A specialized bioreactor is used to grow mineralizing, collagenous tissue up to 150 microm thick from an inoculum of isolated murine (mouse calvaria MC3T3-E1, American Type Culture Collection (ATCC) CRL-2593) or human (hFOB 1.19 ATCC CRL-11372) fetal osteoblasts over uninterrupted culture periods longer than 120 days (4 months). Proliferation and phenotypic progression of an osteogenic-cell monolayer into a tissue consisting of 6 or more cell layers of mature osteoblasts in the bioreactor was compared with cell performance in conventional tissue-culture polystyrene (TCPS) controls. Cells in the bioreactor basically matched results obtained in TCPS over a 15-day culture interval, but loss of insoluble extracellular matrix and an approximate doubling of apoptosis rates in TCPS after 30 days indicated that progressive instability of cultures maintained in TCPS with periodic refeeding but without subculture. In contrast, stable cultures were maintained in the bioreactor for more than 120 days, suggesting that extended-term tissue maintenance is feasible with little or no special technique. Transmission electron microscopy ultramorphology of tissue derived from hFOB 1.19 recovered from the bioreactor after only 15 days of culture showed evidence of osteocytic-like processes and gap junctions between cells like those observed in vivo, in addition to elaboration of the usual osteoblastic markers such as alkaline phosphatase activity and mineralization (alizarin red). Thus, the bioreactor design based on the principle of simultaneous growth and dialysis was shown to create an extraordinarily stable peri-cellular environment that better simulates the in vivo condition than conventional tissue culture. The bioreactor shows promise as a tool for the in vitro study of osteogenesis and osteopathology.