Hypotrochoidal scaffolds for cartilage regeneration

Abstract

The main function of articular cartilage is to provide a low friction surface and protect the underlying subchondral bone. The extracellular matrix composition of articular cartilage mainly consists of glycosaminoglycans and collagen type II. Specifically the collagen type II organization has a characteristic organization in three distinct zones; (1) the superficial zone which has collagen fibers oriented parallel to the surface, (2) the intermediate zone where there is no predominant orientation, and (3) the deep zone which shows a high orientation with fibers perpendicular to the underlying bone. Collagen type II fibers in these 3 zones take an arch-like organization that can be mimicked with segments of a hypotrochoidal curve. In this study, a script was developed that allowed the fabrication of scaffolds with a hypotrochoidal design. This design was investigated and compared to a regular 0-90 woodpile design. The results showed that the hypotrochoidal design was successfully fabricated. Micro-CT analyses divided the areas of the scaffold in their distinct zones. In addition, the mechanical analyses revealed that the hypotrochoidal design had a lower component Young's modulus while the toughness and strain at yield were higher compared to the woodpile design. Fatigue tests showed that the hypotrochoidal design lost more energy per cycle due to the damping effect of the unique microarchitecture . Finite element analyses revealed that the hypotrochoidal design had an improved stress distribution compared to the 0-90 woodpile design due to the lower component stiffness. In addition, data from cell culture under dynamic stimulation demonstrated that the collagen type II deposition was improved in the hypotrochoidal design. Finally, Alcian blue staining revealed that the areas where the stress was higher during the stimulation produced more glycosaminoglycans. Our results highlight a new and simple scaffold design based on hypotrochoidal curves that could be used for cartilage tissue engineering.

Development of a biomimetic arch-like 3D bioprinted construct for cartilage regeneration using gelatin methacryloyl and silk fibroin-gelatin bioinks

“…As described before [5], a custom-written Python code (Python Software Foundation, Version 3.7.0) was produced to design the bioprinting pathway. The X and Y coordinates were determined using a hypotrochoidal function (equations (1) and ( 2)) where R = the radius of the large circle, r = the radius of the rolling process, and d = the distance between the center of the rolling circle and the point which is traced.…”

“…Therefore, instead of following a classical wood-pile pattern, we hypothesized that an arch-like pattern of the cell-laden bioprinted construct might aid in producing an anatomically relevant structure, approaching the collagen II architecture in articular cartilage. In past studies, we have shown the significance of scaffold architecture [4,5] as it directs and impacts the development of cartilaginous tissue [28]. Moreover, our previous study [5] has established the significance of arch-like design in improving mechanical strength and chondrogenesis compared to the traditional wood-pile pattern.…”

“…In past studies, we have shown the significance of scaffold architecture [4,5] as it directs and impacts the development of cartilaginous tissue [28]. Moreover, our previous study [5] has established the significance of arch-like design in improving mechanical strength and chondrogenesis compared to the traditional wood-pile pattern. Hence, it would be important to decipher the effect of using such architecture and study the role of the bioink formulation in bioprinting approaches.…”

“…For example, there are numerous studies on bioprinted cartilage [1][2][3], where the bioink-containing cells have been deposited layer-by-layer in a wood-pile pattern (0 • -90 • alignment). These bioprinted structures have been mainly used to study the gene expression or the histological alignment of cells; nevertheless, limited studies have tried to replicate the architecture of collagen II in articular cartilage [4,5]. Hence, it becomes essential to understand how selecting a suitable bioink to simulate the specific geometry/architecture of collagen II will help to impart distinct functionality toward better chondrogenesis.…”