Abstract
Scaffolds for bone regeneration have been engineered by a plethora of manufacturing technologies and biomaterials. However, the performance of these systems is often limited by lack of robustness in the process design, that hampers their scalability to clinical application. In the present study, Design of Experiment (DoE) was used as statistical tool to design the biofabrication of hybrid hydroxyapatite (HA)/collagen scaffolds for bone regeneration and optimize their integration in a multilayer osteochondral device. The scaffolds were synthesized via a multi-step bioinspired process consisting in HA nano-crystals nucleation on the collagen self-assembling fibers and ribose glycation was used as collagen cross-linking method to modulate the mechanical and physical properties. The process design was performed by selecting hydrogel concentration, HA/collagen ratio and cross-linker content as key variables and the fabrication was carried out basing on a full factorial design. Scaffold performances were tested by evaluating porosity, swelling ratio, degradation rate and mechanical behavior as model output responses while physicochemical properties of the constructs were evaluated by TGA, ICP, FT-IR spectroscopy, and XRD analysis. Physicochemical characterizations confirmed the nucleation of a biomimetic inorganic phase and the interaction of the HA and collagenic components. The DoE model revealed a significant interaction between HA content and collagen cross-linking in determining porosity, swelling and mechanical properties of the scaffolds. The combined effect of hydrogel concentration and mineral phase played a key role on porosity and swelling while degradation resulted to be mainly affected by the HA loading and ribose content. The model was then used to determine the suitable input parameters for the synthesis of multi-layer scaffolds with graded mineralization rate, that can be used to mimic the whole cartilage-bone interface. This work proved that experimental design applied to complex biofabrication processes represents an effective and reliable way to design hybrid constructs with standardized and tunable properties for osteochondral tissue engineering.
Highlights
In the last decades, scaffolds for bone and osteochondral tissue engineering have been studied by using a wide range of materials and manufacturing technologies (Porter et al, 2009; O’Brien, 2011; Hutmacher et al, 2015).The osteochondral area is a complex multi-layered region composed of articular cartilage and subchondral bone: the articular cartilage is composed of organic and mineralized hybrid layers, separated by an interface called tidemark (Sophia Fox et al, 2009; Simon and Jackson, 2018)
The articular extracellular matrix is mainly composed of water, collagen and proteoglycans while the tidemark and the calcified cartilage are mineralized regions characterized by a graded increase of the inorganic phase content from 25 to 65 wt. % (Hoemann et al, 2012; Zhang et al, 2012)
A scaffold for osteochondral regeneration was 3D bioprinted by combining a gradient of nanoHA and poly(lactic-co-glycolic acid) (PLGA) nanospheres incapsulated with chondrogenic transforming growth-factor, demonstrating good osteochondral differentiation in vitro (Castro et al, 2015)
Summary
Scaffolds for bone and osteochondral tissue engineering have been studied by using a wide range of materials and manufacturing technologies (Porter et al, 2009; O’Brien, 2011; Hutmacher et al, 2015).The osteochondral area is a complex multi-layered region composed of articular cartilage and subchondral bone: the articular cartilage is composed of organic and mineralized hybrid layers, separated by an interface called tidemark (Sophia Fox et al, 2009; Simon and Jackson, 2018). The articular extracellular matrix is mainly composed of water (up to 85% of the total weight), collagen and proteoglycans while the tidemark and the calcified cartilage are mineralized regions characterized by a graded increase of the inorganic phase content from 25 to 65 wt. The regeneration of the whole osteochondral region is conventionally mimicked by combining these scaffolds into bi or trilayer devices, characterized by inorganic phase gradient, graded mechanical properties and different materials, eventually loaded with growth factors for supporting simultaneous cartilage and bone regeneration (Tampieri et al, 2008; Li et al, 2015; Bittner et al, 2019). A scaffold for osteochondral regeneration was 3D bioprinted by combining a gradient of nanoHA and poly(lactic-co-glycolic acid) (PLGA) nanospheres incapsulated with chondrogenic transforming growth-factor, demonstrating good osteochondral differentiation in vitro (Castro et al, 2015)
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