Reinforcing interpenetrating network hydrogels with 3D printed polymer networks to engineer cartilage mimetic composites

Abstract

Engineering constructs that mimic the complex structure, composition and biomechanics of the articular cartilage represents a promising route to joint regeneration. Such tissue engineering strategies require the development of biomaterials that mimic the mechanical properties of articular cartilage whilst simultaneously providing an environment supportive of chondrogenesis. Here three-dimensional (3D) bioprinting is used to develop polycaprolactone (PCL) fibre networks to mechanically reinforce interpenetrating network (IPN) hydrogels consisting of alginate and gelatin methacryloyl (GelMA). Inspired by the significant tension-compression nonlinearity of the collagen network in articular cartilage, we printed reinforcing PCL networks with different ratios of tensile to compressive modulus. Synergistic increases in compressive modulus were observed when IPN hydrogels were reinforced with PCL networks that were relatively soft in compression and stiff in tension. The resulting composites possessed equilibrium and dynamic mechanical properties that matched or approached that of native articular cartilage. Finite Element (FE) modelling revealed that the reinforcement of IPN hydrogels with specific PCL networks limited radial expansion and increased the hydrostatic pressure generated within the IPN upon the application of compressive loading. Next, multiple-tool biofabrication techniques were used to 3D bioprint PCL reinforced IPN hydrogels laden with a co-culture of bone marrow-derived stromal cells (BMSCs) and chondrocytes (CCs). The bioprinted biomimetic composites were found to support robust chondrogenesis, with encapsulated cells producing hyaline-like cartilage that stained strongly for sGAG and type II collagen deposition, and negatively for type X collagen and calcium deposition. Taken together, these results demonstrate how 3D bioprinting can be used to engineer constructs that are both pro-chondrogenic and biomimetic of the mechanical properties of articular cartilage.

Bioprinting of a Zonal-Specific Cell Density Scaffold: A Biomimetic Approach for Cartilage Tissue Engineering

“…Despite the presence of the tissue deposition gradients, low amounts of glycosaminoglycan and collagen were seen in all the groups. This may be due to the alginate-based bioinks that offer good printability [25,30,35,[37][38][39][40][41] but do not offer enzymatic-derived tissue remodeling [42], which have been suggested to potentially act as a physical barrier for tissue secretion in vitro, as also observed by others [43][44][45]. On the other hand, alginate-based biomaterials have been shown to be capable of generating cartilage when implanted in vivo [46,47], suggesting that other factors may also be playing a role in this regard.…”

“…This approach was able to significantly increase the bulk mechanical properties compared to the bioink alone, as others have demonstrated [29][30][31]. Other studies also explored the pre-printing of PCL structures and then either cast or z-printed the bioink in the channels of the PCL mesh [35]. Despite this option giving more freedom, as it decouples the fabrication process of the outer frame and the bioprinting of the bioink, z-print is not yet an option available in all 3D printing systems.…”

Design and Synthesis of Chitosan—Gelatin Hybrid Hydrogels for 3D Printable in vitro Models

“…The 3D bioprinting process includes cells and polymers in the same “environment.” As a consequence, the properties of the polymers and the crosslinking methodologies employed during the bioprinting process must be biocompatible and easy to tailor. Examples to date include the use of “ionic crosslinkers” (i.e., calcium or divalent salts) or UV and photo-initiator-assisted reactions (i.e., methacrylation, acrylation; Derakhshanfar et al, 2018 ; Gungor-Ozkerim et al, 2018 ; Anil Kumar et al, 2019 ; Ding et al, 2019 ; Petta et al, 2020 ; Schipani et al, 2020 ; Sun et al, 2020 ). Click reactions can be conducted without the presence of catalyzers or components that can have a detrimental effect; this is advantageous for bioprinting protocols but can be challenging when heterogeneous polymers are employed.…”

Tuning the Phenotype of Cartilage Tissue Mimics by Varying Spheroid Maturation and Methacrylamide‐Modified Gelatin Hydrogel Characteristics

“…[18] Schipani et al first printed porous PCL scaffolds and cell-laden alginate, gelMA, or alginate-gelMA interpenetrating network bioinks were deposited within the pores of these previously printed PCL networks. [62] In this regard, applying a multitool or multitechnology biofabrication approach, where several complementary manufacturing technologies are used simultaneously, is promising. [63] An example hereof is combining extrusion-based bioprinting with melt electrowriting which allows the biofabrication of tissue constructs with improved mechanical properties.…”