Multilayered Scaffolds for Osteochondral Tissue Engineering Based on Bioactive Glass and Biodegradable Polymers

Language
en
Document Type
Doctoral Thesis
Issue Date
2014-08-04
Issue Year
2014
Authors
Nooeaid, Patcharakamon
Editor
Abstract

Injuries of the articular cartilage may penetrate to the underlying subchondral bone, forming osteochondral defects which have a limited capacity of self-regeneration. Accompanied with limited surgical treatments and the fact that the causes are not understood well, an approach based in tissue engineering becomes a promising strategy for osteochondral repair. Such tissue engineering approaches are based on the combination of synthetic scaffolds, suitable cell sources and active molecules or growth factors. The suitable osteochondral scaffold should be developed considering appropriate biomaterials and processing techniques in order to fabricate engineered scaffolds as suitable 3D microenvironment with sufficient mechanical integrity for cells growth and tissue regeneration. The combination of biodegradable polymers and bioactive glasses in the form of bi- or multilayered composite scaffolds is a promising approach in osteochondral regeneration, whereby the development of robust fabrication methods is crucial for the success of this strategy. In this investigation, two different structural architectures of scaffolds are comparatively studied for the cartilage phase, including (I) porous foams and (II) electrospun fibers fabricated by using freeze drying and electrospinning techniques, respectively. A biocompatible polysaccharide, namely sodium alginate, processed on the upper surface of 3D highly porous interconnected Bioglass®-based foams by freeze-drying followed by ionically crosslinking to produce a cartilage-engineered substrate. Sodium alginate coated Bioglass®-based scaffolds (fabricated by foam replication technique followed by polymer coating), were manufactured as scaffold for subchondral bone. Both phases were integrated by different methods; including using a sodium alginate adhesive layer to from Alg/Na-Alg coated Bioglass® bilayered scaffolds and formation of a monolithic biphasic scaffold. In the second approach, sodium alginate is fabricated into submicron fibers by electrospinning, and deposited on the alginate coated Bioglass®-based scaffold, forming electrospun Alg/Alg-coated Bioglass® bilayered scaffold. In addition, synthetic biodegradable polymer (PDLLA) was used to fabricate the same structural architectures (by using the same techniques) in order to compare between different scaffold materials. The scaffold architecture, constitutive microstructural features, and mechanical properties were investigated with respect to their requirements for regeneration of both cartilage and subchondral bone.
Alginate freeze-dried foams provide pore sizes in the range of 125 to 225 µm, whereas alginate coated Bioglass®-based scaffolds for bone regeneration show larger pore sizes (100-600 µm), required for bone regeneration. Both scaffolds exhibit high porosity and pore interconnectivity and they were confirmed to be suitable pore sizes for chondrocyte seeding, for synthesis of cartilaginous ECM, and for bone in-growth and vascularization, respectively. The mechanical properties of Alg-foams and Alg-c-BG scaffolds were confirmed to be closer to those of native tissues. In addition, antibiotic drug, i.e. tetracycline, was incorporated into polymer coated Bioglass-based scaffolds in order to enhance functionality of the scaffolds for use as a drug or biomolecule carrier in bone regeneration. The in vitro studies of Alg-foams and Alg-c-BG scaffolds are carried out separately by seeding chondrocytes and MSCs, and osteoblasts-like cells, respectively. MG-63 osteoblast-like cells were seeded on RGD-Alg-c-BG and Alg-c-BG scaffolds to evaluate the biocompatibility, cell viability, proliferation and differentiation in comparison with BG scaffolds. It was found that BG scaffolds promote high cell proliferation and bone mineralization upon 21 days culture, followed by RGD-Alg-c-BG and Alg-c-BG scaffolds, respectively. Therefore, alginate coated Bioglass-based composite scaffolds represent promising candidates for the regeneration of subchondral bone in osteochondral tissue engineering. Simutaneously, in vitro cell culture studies of alginate and alginate/chondroitin sulfate-foams for cartilage regeneration were evaluated by seeding with porcine chondrocytes and mesenchymal stem cells. All tests proved the biocompatibility of the materials to cells and chondrocytes maintained their phenotype over the investigated culture times (14 days). In addition, MSCs promoted the differentiation into chondrocyte-like cells and also provided the expression of collagen type II and proteoglycan after 7 days in culture, which are the specific markers of cartilage regeneration. The results thus confirmed that alginate based scaffolds have a great potential for use as cartilaginous scaffolds.

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