Buceo con escafandra autónoma

Although TGF! has been shown to also stimulate migration, other biomolecules may be helpful to increase cell infiltration, and thus matrix deposition, within the acellular scaffold implanted after microfracture. Stromal derived factor-1 (SDF-1) is a potent chemoattracting chemokine that plays a critical role in regulating the migration of progenitor cells to remodeling tissue. Chapter 9 describes the incorporation of sulfated HA macromers to control release of heparin-binding cytokines such as SDF-1. Release of SDF-1 in partial chondral and

osteochondral defects has been shown to improve histological outcomes in vivo [14, 15]. However, SDF-1 has also been associated with osteoarthritis and can cause significant

degeneration of human osteoarthritic cartilage explants in vitro [16-18]. Thus, it is still unclear

whether SDF-1 release would improve outcomes by recruiting cells that deposit more matrix or if SDF-1 would increase MMP expression of neighboring chondrocytes to then cause cartilage degeneration.

It is also possible that the release of TGF!3 could overcome of the possible negative

effects of SDF-1, and that the release of both growth factors would cause significant infiltration and then increased cartilaginous matrix deposition. Moreover, we have recently found that the addition of SDF-1 to juvenile porcine cartilage explants did not cause significant cartilage

Figure 10.1 (A) Histology and (B) GAG quantification of juvenile, porcine cartilage explants incubated for 4 days in vitro with biomolecules (i.e. SDF-1 or both SDF-1 and TGF!) either added exogenously or released from fibrous HA hydrogels.

degeneration, unlike with human osteoarthritic cartilage explants [16], as seen by histology and quantification of GAG within the tissue (i.e. digested) and in the media (i.e. soluble) (Figure 10.1). As described previously, ongoing and future work is now focused on the investigation of SDF-1- releasing fibrous HA hydrogels in vivo, using the same animal model as in Specific Aim 3. Thus far, we have found that the mechanical properties of both MeHA/HH+SDF and MeHA/HH+SDF/TGF!3 were not significantly different than any of the other previously tested HA- only groups (Figure 10.2). However, as before, histology may be necessary to discover differences between conditions, with possible improvements in cellularity, matrix deposition, and matrix morphology, and these analyses are still ongoing.

10.3 Conclusions

Although research into clinical and tissue engineering approaches for cartilage repair are numerous, clinical treatments are still limited. To date, there is no reproducible, long-term strategy to completely restore and regenerate cartilage, and millions of Americans suffer from osteoarthritis and acute cartilage lesions every year. This thesis focused on developing,

Figure 10.2 Young’s moduli from microindentation testing of normal, empty, microfracture, and

characterizing, and applying a novel fibrous HA-based hydrogel to further our knowledge of biomaterial-based cartilage repair strategies. Specifically, after the development of the HA electrospinning system, the fibrous HA hydrogels were applied using both in vitro and in vivo

approaches towards cartilage repair. Although in vitro studies with MSCs showed that softer and less adhesive fibers generally enhanced MSC chondrogenesis, the lack of cell infiltration into such scaffolds even with extensive cell-seeding and post-fabrication methods reduced their potential as in vitro cultured, cell scaffolds.

The remainder of the thesis exploited the tunability of fibrous HA hydrogels towards translation and application with microfracture in a porcine cartilage defect model. Importantly, although these scaffolds were difficult to infiltrate with cells in vitro, cellularity was high in vivo

even after 2 weeks, confirming the decision to directly implant the scaffolds in vivo without prior in vitro culture. Through these in vivo studies, material choice (i.e. HA or PCL) and the inclusion of TGF!3 were found to be the most influential parameters, and other important findings were the heterogeneity of samples over all outcome measures and the extensive subchondral bone remodeling (especially with PCL scaffolds) in juvenile mini-pigs. Finally, the incorporation of sulfated HA macromers allowed for specific control over release of SDF-1 and TGF!3 due to differences in electrostatic interactions, and ongoing and future work includes the investigation of SDF-1-releasing fibrous HA hydrogels through in vivo studies for improved cellularity and matrix production. Overall, the work described in this thesis represents a significant advancement in the development of novel biomaterials for cartilage repair.

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