Abstract
Traditional methods of treating degenerative skeletal diseases and wounds are to use allografts, autografts, or artificial implants. However, these techniques are not ideal because of possible additional medical complications or limited tissue availability. The use of the patient?s own mesenchymal stem cells for treatment, on the other hand, do not induce any immunogenic response and utilize cells that are in greater supply. Because of these advantages, doctors and researchers are investigating applications where mesenchymal stem cells (MSCs) can be used in tissue regeneration, often for bone restoration. Two important components to consider in tissue engineering transplants are: 1) tissue-specific cells; and, 2) a biocompatible scaffold which these cells can adhere to that provides short-term mechanical stability until the cells develop and produce an extracellular matrix in the implant site. The purpose of this research is two fold: 1) investigate a more effective method of inducing osteogenic differentiation of human adipose-derived adult stem (hADAS) cells through mechanical loading; and, 2) improve hADAS cell adhesion to a novel three-dimensional poly(L-lactic acid) scaffold using oxygen plasma treatment.
Mechanical stimulation of bone marrow-derived mesenchymal stem cells has been shown to enhance osteogenesis. However, more recent studies have shown that continuous loading of these cells results in desensitization and eventual loss of responsiveness to mechanical loading. To investigate this phenomenon in hADAS cells, cells from two donors with distinct and disparate osteogenic differentiation capabilities (i.e. high calcium deposition and low calcium deposition) were subjected to continuous loading via cyclic tensile strain, rest insertion loading (10 seconds of rest inserted between each loading cycle), or maintained in static culture. Results revealed that rest insertion and continuous loading did not significantly alter calcium deposition in hADAS of both donors when cells were maintained in complete growth medium. However, when cells were cultured in osteogenic differentiation medium, both regimens of mechanical loading accelerated the induction of osteogenesis, as well as increased the total calcium deposition in hADAS cells of both donors compared to unstrained controls in osteogenic differentiation medium. The donor cells which innately deposited higher amounts of calcium appeared to respond more favorably to mechanical stimulation compared to the donor cells which deposited lower amounts of calcium, suggesting that perhaps cell lines that are more prone to osteogenic differentiation will respond better to mechanical stimulation compared to cell lines that are not.
The second key component of tissue engineered bone constructs are the scaffolds to which the cells adhere. Cell adherence has been linked to future proliferation and differentiation. Therefore, optimizing cell adherence to scaffolds is fundamental in perfecting a bone construct for implantation. In order to investigate the cellular adherence of hADAS cells on poly(L-lactic acid) (PLLA), hADAS cells were seeded on either oxygen plasma treated or untreated scaffolds. Over a 48 hour time period, hADAS cells were evaluated for 1) number of cells adhered to the scaffold; 2) viability; and, 3) morphology and distribution of cells throughout the three-dimensional PLLA matrix. Results from three age- and gender-matched donors showed a trend of increased number of cells adhered to oxygen plasma treated scaffolds compared to hADAS cells seeded on untreated scaffolds. In addition, morphology and distribution was accelerated in hADAS cells seeded on oxygen plasma treated scaffolds at earlier time points than those on untreated scaffolds. This enhanced early cell spreading and distribution due to oxygen plasma treatment of scaffolds suggest that this methodology might provide a more optimal procedure of creating tissue engineered bone grafts.
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