Background: Tendon and ligamentous injuries are incredibly common worldwide, and there have been advancements for treatments through the use of biological and synthetic scaffolds to recapitulate the properties of a native enthesis. Hydrogel matrix stiffness and composition has been shown to promote the differentiation of mesenchymal stem cells (MSCs) to various cell lines, demonstrated by the expression of genes corresponding to specific tissues. There still remains a gap in knowledge in comparing how different alterations of the content of hydrogels can induce MSC differentiation in the context of a synthetic scaffold aimed to model that of a native enthesis. 

Objective: Develop biomimetic scaffolds that correspond with the biomechanical properties of each layer at the transition point between tendon and bone, incorporating components such as HAP and sodium alginate to form a microenvironment that is biochemically optimal for the differentiation of tendon, cartilage, and bone within each respective scaffold.  

Methods: Fish Gelma was made as previously discussed (Yoon, 2016). Three hydrogels were composed of Fish GelMA at different concentrations corresponding to each layer of the enthesis: bone (30%), tendon (20%), cartilage (10%). HAP (8%) was added to the bone hydrogel preparation, and sodium alginate (4%) was added to the tendon hydrogel preparation. Hydrogels were crosslinked via the photoinitiator Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) (0.5% in solution). The nano-mechanical properties of biomimetic scaffolds were tested at the Pico and Nano Characterization Core Facility at UCLA through an atomic force microscopy (AFM) machine called the JPK Nanowizard 4A which measures elasticity, adhesion, and dissipation using both closed-loop atomic resolution and fast scanning capabilities (3sec/image). 

Results: Young’s modulus (kPa) was acquired for bone, tendon and cartilage tissues respectively (exact numbers are still in progress). Several different bio-ink formulations were tested to best replicate the modulus values of the native enthesis. The trials are currently ongoing. 

Conclusions: The layers of a native enthesis (bone, cartilage, and tendon) were replicated by using a biomimetic scaffold through the use of varying concentrations of Gelma, alongside extra components (HAP, Sodium Alginate) with the goals of inducing MSC differentiation. Young’s modulus (kPa) was acquired through AFM in order to determine relative stiffnesses of each layer. Due to multiple roadblocks in the creation of Gelma, alongside significant AFM outages that prevented analysis, future work will be aimed at optimizing the hydrogels to analyze expression of tissue specific genes.