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Regulation of mesenchymal stromal cell culture in 3D collagen and NiTi scaffolds by inflammatory and biomechanical factors

Hoffmann, Waldemar. Regulation of mesenchymal stromal cell culture in 3D collagen and NiTi scaffolds by inflammatory and biomechanical factors. 2014, PhD Thesis, University of Basel, Faculty of Medicine.

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Official URL: http://edoc.unibas.ch/diss/DissB_11835

Abstract

The processes of bone fracture healing and bone development share certain similarities and are affected by mechanical loads, the local microenvironment and other factors. In this thesis, an established in vitro fracture callus model was further developed through the introduction of mechanical loading. This system allows for the investigation of the effects of physiological mechanical loads on fracture calluses (engineered endochondral constructs), NiTi-reinforced endochondral constructs and native tissues. Exploring the benefits of rapid-prototyping, shape-memory-alloys and mechanical loading the introduction of a novel, in vitro model for mechanically modulated endochondral ossification is intended.
Inflammatory cytokines, which are present in the environment of the fracture site, are important modulators of fracture healing. Thus, the effect of IL-1β on glycosaminoglycan (GAG) production and BMP-2 expression during chondrogenesis and ECM calcification during the hypertrophic phase of in vitro cultures was investigated. These constructs depict an in vitro model for fracture calluses and are therefore used to investigate the effect of IL-1β on the remodeling process, which occurs upon in vivo implantation. It has been demonstrated that IL-1β finely modulates early and late events of the endochondral bone formation by MSC. Controlling the inflammatory environment could enhance the success of therapeutic approaches for the treatment of fractures by resident MSC as well as improve the engineering of implantable tissues.
Secondary bone fracture healing is a physiological process, which leads to functional tissue regeneration recapitulating endochondral bone formation. Besides other factors, mechanical loading is known to modulate the process of fracture healing. Therefore, a novel perfused compression bioreactor system (PCB) is demonstrated for the investigation of the effect of dynamic mechanical loading on the mineralization process of engineered, hypertrophic constructs. The results obtained demonstrate that dynamic mechanical loading enhances the maturation process of MSC towards late hypertrophic chondrocytes and the mineralization of the extracellular matrix. Moreover, the system possibly allows for the identification of suitable loading regimes to accelerate the process of fracture healing.
In order to improve primary implant stability and to upscale endochondral constructs, selective laser melting (SLM)-based NiTi constructs are foreseen to be utilized as a backbone for hypertrophic cartilage templates. NiTi alloys possess a unique combination of mechanical properties including a relatively low elastic modulus, pseudoelasticity, and high damping capacity, matching the properties of bone. Hence, we demonstrated biocompatibility of NiTi-based constructs. Moreover, MSC adhesion, proliferation and differentiation along the osteogenic lineage were similar to MSC cultured on clinically used Ti. When seeded and cultured on porous 3D SLM-NiTi scaffolds, MSC homogeneously colonized the scaffold, and following osteogenic induction, filled the scaffold’s pore volume with extracellular matrix. The combination of bone-related mechanical properties of SLM-NiTi with its cytocompatibility and support of osteogenic properties by MSC highlights its potential as a superior bone substitute as compared to Ti.
In conclusion, MSC based chondrogenic and hypertrophic constructs depict in vitro models for soft and hard fracture calluses, respectively. This constructs are responsive to both inflammatory cytokines (IL-1β modulating early and late events of the endochondral bone formation) and dynamic mechanical loading (increased degree of maturation of both MSC and ECM). Moreover, it has been shown that the PCB serves as a promising tool for further systematic studies in an in vitro setting leading to a reduction of animal experiments within the field. Nevertheless, the established models (including mechanically loaded constructs) are not capable of supporting load-bearing fracture sites. Therefore, to overcome the lack of mechanical stability a NiTi-based approach is intended. SLM-NiTi was shown to be biocompatible and MSC do colonize these constructs and differentiate along the osteogenic lineage. Using SLM-NiTi scaffolds as a backbone supporting initial load-bearing, MSC could be used to colonize it and fill the scaffolds pores with a chondrogenic and/or hypertrophic ECM. This construct depicts a NiTi-reinforced, mechanically stable endochondral implant intended for orthotopic implantation.
Advisors:Müller, Bert and Martin, Ivan and de Wild, Michael and Zenobi-Wong, Marcy
Faculties and Departments:03 Faculty of Medicine > Bereich Medizinische Fächer (Klinik) > Allgemeine innere Medizin AG > Argovia Professur für Medizin (Müller)
Item Type:Thesis
Thesis no:11835
Bibsysno:Link to catalogue
Number of Pages:1 Online-Ressource (120 Seiten)
Language:English
Identification Number:
Last Modified:07 Dec 2016 11:07
Deposited On:07 Dec 2016 11:07

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