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1.  The effects of fixed electrical charge on chondrocyte behavior 
Acta biomaterialia  2011;7(5):2080-2090.
In this study, we have compared the effects of negative and positive fixed charge on chondrocyte behavior in vitro. Electrical charges have been incorporated into oligo(poly(ethylene glycol) fumarate) (OPF) using small charged monomers such as sodium methacrylate (SMA) and (2-(methacryloyloxy) ethyl)-trimethyl ammonium chloride (MAETAC) to produce negatively and positively charged hydrogels, respectively. The hydrogel physical and electrical properties were characterized through measuring and calculating the swelling ratio and zeta potential, respectively. Our results revealed that the properties of these OPF modified hydrogels varied according to the concentration of charged monomers. Zeta potential measurements demonstrated that the electrical property of the OPF hydrogel surfaces changed due to incorporation of SMA and MAETAC and that this change in electrical property was dose-dependent. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy was used to determine the hydrogel surface composition. To assess the effects of surface properties on chondrocyte behavior, primary chondrocytes isolated from rabbit ears were seeded as a monolayer on top of the hydrogels. We demonstrated that the cells remained viable over 7 days and began to proliferate while seeded on top of the hydrogels. Collagen type II staining was positive in all samples; however, the intensity of the stain was higher on negatively charged hydrogels. Similarly, GAG production was significantly higher on negatively charged hydrogels compared to neutral hydrogel. Reverse transcription polymerase chain reaction showed up-regulation of collagen type II and down-regulation of collagen type I on the negatively charged hydrogels. These findings indicate that charge plays an important role in establishing an appropriate environment for chondrocytes and hence in the engineering of cartilage. Thus, further investigation into charged hydrogels for cartilage tissue engineering is merited.
PMCID: PMC3103083  PMID: 21262395
hydrogel; cartilage tissue engineering; OPF; scaffold
2.  Directional fluid flow enhances in vitro periosteal tissue growth and chondrogenesis on poly-ε-caprolactone scaffolds 
The purpose of this study was to investigate the effect of directional fluid flow on periosteal chondrogenesis. Periosteal explants were harvested from two-month-old rabbits and sutured onto poly-ε-caprolactone (PCL) scaffolds with the cambium layer facing away from the scaffolds. The periosteum/PCL composites were cultured in suspension in spinner flask bioreactors and exposed to various fluid flow velocities: 0, 20, 60, 150 rpm for 4 hours each day for 6 weeks. The application of fluid flow significantly increased percent cartilage yield in periosteal explants from 17% in the static controls to 65-75% under fluid flow (there was no significant difference between 20, 60, or 150 rpm). The size of the neocartilage was also significantly greater in explants exposed to fluid flow compared to static culture. The development of zonal organization within the engineered cartilage was observed predominantly in the tissue exposed to flow conditions. The Young's modulus of the engineered cartilage exposed to 60 rpm was significantly greater than the samples exposed to 150 rpm and 20 rpm. These results demonstrate that application of directional fluid flow to periosteal explants secured onto PCL scaffolds enhances cell proliferation, chondrogenic differentiation, cell organization, and alters the biomechanical properties of the engineered cartilage.
PMCID: PMC2928853  PMID: 20540101
periosteum; cartilage; tissue engineering; polycaprolactone; bioreactors; Youngs's modulus
3.  Histone Deacetylase 3 Depletion in Osteo/Chondroprogenitor Cells Decreases Bone Density and Increases Marrow Fat 
PLoS ONE  2010;5(7):e11492.
Histone deacetylase (Hdac)3 is a nuclear enzyme that contributes to epigenetic programming and is required for embryonic development. To determine the role of Hdac3 in bone formation, we crossed mice harboring loxP sites around exon 7 of Hdac3 with mice expressing Cre recombinase under the control of the osterix promoter. The resulting Hdac3 conditional knockout (CKO) mice were runted and had severe deficits in intramembranous and endochondral bone formation. Calvarial bones were significantly thinner and trabecular bone volume in the distal femur was decreased 75% in the Hdac3 CKO mice due to a substantial reduction in trabecular number. Hdac3-CKO mice had fewer osteoblasts and more bone marrow adipocytes as a proportion of tissue area than their wildtype or heterozygous littermates. Bone formation rates were depressed in both the cortical and trabecular regions of Hdac3 CKO femurs. Microarray analyses revealed that numerous developmental signaling pathways were affected by Hdac3-deficiency. Thus, Hdac3 depletion in osterix-expressing progenitor cells interferes with bone formation and promotes bone marrow adipocyte differentiation. These results demonstrate that Hdac3 inhibition is detrimental to skeletal health.
PMCID: PMC2901996  PMID: 20628553

Results 1-3 (3)