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Persistent corneal wounds result from numerous eye disorders, and to date, available treatments often fail to accelerate reepithelialization, the key initial step in wound healing. To speed reepithelialization, we explored a cell-transfer transplant method utilizing polydimethylsiloxane (PDMS) contact lenses to deliver epithelial cells derived from limbal explants directly within a corneal wound. Human primary epithelial cells and an immortalized corneal epithelial cell line (HCE-SV40) grew well on PDMS contact lenses and their morphology and growth rates where similar to cells grown on tissue culture polystyrene. To initially study cell transfer from PDMS, HCE-SV40 cells were seeded onto PDMS with or without micropatterned posts. After a day in culture, HCE-SV40 cells attached to the unpatterned PDMS uniformly, whereas on micropatterned PDMS they appeared to attach primarily between posts. The cell-covered PDMS contacts were then placed cell-side down onto tissue culture plastic and, after 1, 2, or 3 days, the PDMS contact was removed and the transferred cells were trypsinized and counted. Micropatterned PDMS contact lenses with 100-microm-diameter posts and a post height of 40 microm transferred three times as many cells as unpatterned PDMS. Cell transfer to a wounded cornea was tested in a pig cornea organ culture model de-epithelialized by alkali treatment. Post micropatterned PDMS contact lenses were seeded with labeled HCE-SV40 cells at a density 50,000 cells/cm2 and applied to the wounded pig corneas. After 24, 48, or 96 h of application, PDMS contact lenses were removed, corneas fixed with formaldehyde, and sectioned. After 48 h, epithelial cells transferred from post micropatterned contact lenses to provide 35% epithelial coverage of denuded pig corneas; after 96 h coverage was 65%. We conclude that cell transfer from epithelial-coated PDMS contact lenses micropatterned with posts provides a promising approach to reepithelialize corneal surfaces.
The ideal bone graft substitute requires osteoconductive, osteoinductive, and osteogenic components. This study introduces an "in vivo bioreactor," a model in which pluripotent cells are recruited from circulating blood to a vascularized coralline scaffold supplemented with bone morphogenetic protein-2 (BMP-2). The bioreactor generates new, ectopic host bone with the capability of vascularized tissue transfer. More importantly, bone is reproducibly formed in a closed and malleable environment. In a rat model, the superficial inferior epigastric vessels were isolated, ligated, and then threaded through a prefabricated coral cylinder (hydroxyapatite, ProOsteon 500). Experimental groups were characterized by the following variables: (1) with/without incorporation of vascular pedicle; (2) with/without addition of BMP-2 (0.02 mg/cm3). Scaffolds were harvested 6 weeks after implantation, embedded and sectioned. Tissue samples were decalcified, fixed, and stained with H&E, trichrome green, and CD31/PECAM-1 (a marker of endothelial cells). Vascularized coral scaffolds supplemented with BMP-2 presumably recruited circulating mesenchymal stem cells to generate bone. Bone formation was quantified through histological analysis, and reported as a percentage, area bone/area cross section scaffold x 100. Mean bone formation was 11.30%+/-1.19. All scaffolds supplied by the vascular pedicle, regardless of BMP-2 supplementation, demonstrated neo-vascular ingrowth. Scaffolds lacking a pedicle showed no evidence of vascular ingrowth or bone formation. This paper introduces a model of a novel "in vivo bioreactor" that has future clinical and research applications. The tissue engineering applications of the "bioreactor" include treatment of skeletal defects (nonunion, tumor post-resection reconstruction). The bioreactor also may serve as a unique model in which to study primary and metastatic cancers of bone.
There is a need for microminiaturized cell-culture environments, i.e. NanoLiter BioReactors (NBRs), for growing and maintaining populations of up to several hundred cultured mammalian cells in volumes three orders of magnitude smaller than those contained in standard multi-well screening plates. These devices would enable the development of a new class of miniature, automated cell-based bioanalysis arrays for monitoring the immediate environment of multiple cell lines and assessing the effects of drug or toxin exposure. We fabricated NBR prototypes, each of which incorporates a culture chamber, inlet and outlet ports, and connecting microfluidic conduits. The fluidic components were molded in polydimethylsiloxane (PDMS) using soft-lithography techniques, and sealed via plasma activation against a glass slide, which served as the primary culture substrate in the NBR. The input and outlet ports were punched into the PDMS block, and enabled the supply and withdrawal of culture medium into/from the culture chamber (10-100 nL volume), as well as cell seeding. Because of the intrinsically high oxygen permeability of the PDMS material, no additional CO(2)/air supply was necessary. The developmental process for the NBR typically employed several iterations of the following steps: Conceptual design, mask generation, photolithography, soft lithography, and proof-of-concept culture assay. We have arrived at several intermediate designs. One is termed "circular NBR with a central post (CP-NBR)," another, "perfusion (grid) NBR (PG-NBR)," and a third version, "multitrap (cage) NBR (MT-NBR)," the last two providing total cell retention. Three cells lines were tested in detail: a fibroblast cell line, CHO cells, and hepatocytes. Prior to the culturing trials, extensive biocompatibility tests were performed on all materials to be employed in the NBR design. To delineate the effect of cell seeding density on cell viability and survival, we conducted separate plating experiments using standard culture protocols in well-plate dishes. In both experiments, PicoGreen assays were used to evaluate the extent of cell growth achieved in 1-5 days following the seeding. Low seeding densities resulted in the absence of cell proliferation for some cell lines because of the deficiency of cell-cell and extracellular matrix (ECM)-cell contacts. High viabilities were achieved in all designs. We conclude that an instrumented microfluidics-based NanoBioReactor (NBR) will represent a dramatic departure from the standard culture environment. The employment of NBRs for mammalian cell culture opens a new paradigm of cell biology, so far largely neglected in the literature.