Tailoring the Mechanical Properties of Tissue Engineering Scaffolds made from Decellularized Cartilage
Due to its limited regeneration capacity, articular cartilage defects are considered a frequent
clinical problem. Initial cartilage defects, if left untreated, will progress in severity over
time and can eventually lead to degenerative joint diseases such as osteoarthritis. Hence,
orthopedic surgeons would like to aim to treat cartilage defects early on to prevent further
damage. Healthy articular cartilage consists of hyaline cartilage which assures its proper
function. However, the major drawback of current treatments such as Autologous Chondrocyte
Implantation or Microfracture is that they cannot guide the formation of a pure
hyaline cartilage. Following current treatments a fibrocartilage or a mixture of fibro- and
hyaline cartilage fills the defect in the place of hyaline cartilage. Fibrocartilage has the
disadvantage that it degrades over time due to its inferior mechanical properties compared to
hyaline cartilage. To solve this issue, future treatments should focus on creating pure hyaline
cartilage. Recently, it was hypothesized that one possibility to engineer pure hyaline cartilage
is the production of scaffolds which mimic the mechanical properties and zonal structure of
native cartilage.
The overall goal with my Ph.D. project is the development of a scaffold based on decellularised
articular cartilage, which has zone-specific mechanical properties to induce zonal
lineage commitment in chondro-progenitors. The Ph.D. project was divided into three major
sections. In the first section, the zonal mechanical properties of human articular cartilage
were measured by instrumented indentation which was information crucial to targeting the
appropriate properties in scaffolds. This resulted in finding a depth-dependent mechanical
property gradient. In the second section, a decellularisation method involving supercritical
carbon dioxide in combination with a CO2-philic detergent was developed that could
overcome the limitations of existing complex and time-consuming protocols to decellularise
articular cartilage. Using this method, bovine articular cartilage was successfully decellularised
while important cell adhesion molecules were maintained. The high matrix density of
articular cartilage makes cell infiltration challenging. For that reason, the articular cartilage
was processed into a porous scaffold, in the third section of this thesis. The porous scaffold
was produced by pepsin-digestion of the decellularised cartilage, lyophilization and covalent
crosslinking. It was demonstrated that the mechanical properties of these scaffolds could be
tailored by changing the digest concentration prior to lyophilization. However, the developed
scaffold fabrication procedure only enabled the achievement of the mechanical properties of
the superficial zone, whereas the mechanical properties were too low to target the middle,
deep and calcified zone. Further analysis was therefore only focused on superficial cartilage.
The superficial zone-specific protein lubricin was evident on the surface of the scaffolds
after 14 and 28 days of cell culture when seeded with human chondro-progenitors. This
confirms that mimicking the zone-specific mechanical properties in these prepared scaffolds
can produce zonal lineage commitment.
These results show a promising concept to induce zonal lineage commitment in chondro-progenitors, a valuable
feature to engineer pure hyaline cartilage with natural structure in future cartilage treatments.
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