Effects of Hydrogel Stiffness and Extracellular Compositions on Modulating Cartilage Regeneration by Mixed Populations of Stem Cells and ChondrocytesIn Vivo

Abstract

Cell-based therapies offer great promise for repairing cartilage. Previous strategies often involved using a single cell population such as stem cells or chondrocytes. A mixed cell population may offer an alternative strategy for cartilage regeneration while overcoming donor scarcity. We have recently reported that adipose-derived stem cells (ADSCs) can catalyze neocartilage formation by neonatal chondrocytes (NChons) when mixed co-cultured in 3D hydrogels in vitro. However, it remains unknown how the biochemical and mechanical cues of hydrogels modulate cartilage formation by mixed cell populations in vivo. The present study seeks to answer this question by co-encapsulating ADSCs and NChons in 3D hydrogels with tunable stiffness (*1-33 kPa) and biochemical cues, and evaluating cartilage formation in vivo using a mouse subcutaneous model. Three extracellular matrix molecules were examined, including chondroitin sulfate (CS), hyaluronic acid (HA), and heparan sulfate (HS). Our results showed that the type of biochemical cue played a dominant role in modulating neocartilage deposition. CS and HA enhanced type II collagen deposition, a desirable phenotype for articular cartilage. In contrast, HS promoted fibrocartilage phenotype with the upregulation of type I collagen and failed to retain newly deposited matrix. Hydrogels with stiffnesses of *7-33 kPa led to a comparable degree of neocartilage formation, and a minimal initial stiffness was required to retain hydrogel integrity over time. Results from this study highlight the important role of matrix cues in directing neocartilage formation, and they offer valuable insights in guiding optimal scaffold design for cartilage regeneration by using mixed cell populations.

A Physiology-Inspired Multifactorial Toolbox in Soft-to-Hard Musculoskeletal Interface Tissue Engineering

“…Such gradients can be reproduced as a consequence of mineral content in nanofibrous systems, taking advantage of simple mineral coatings to increase nanofibrous stiffness to direct stem cell differentiation toward the osteogenic lineage [41]. Comparably, hydrogel stiffness has been shown to have a role in modulating cell-based osteochondral formation in 3D, as soft hydrogels have been shown to support the deposition of neocartilage by cells due to their permissiveness [42] and stiffer hydrogels have been shown to support the deposition of osteogenic-like matrix [43]. Complementarily, micro/nanostructured surface architectures have been developed as an easy and smart strategy to induce bi-lineage differentiation in single , exhibiting a smooth gradient in fiber organization, architecture, and therefore mechanical properties.…”

Cellulose-Based Hydrogels in Tissue Engineering Applications

“…In other approaches, the incorporation of bioactive species, such as cells, growth factors, peptides and proteins into the materials, is proposed to improve the properties of hydrogel scaffolds. 141,142 A limitation of using BC hydrogels in tissue engineering lies in the reduced pore size of its scaffolds (~0.02-10 µm), smaller than the mammalian cell size, as a result, the dense network of the hydrogel cannot penetrate mammalian cells. The pore diameter can be increased with monodisperse agarose microparticles, resulting in an interconnected porous network, with pores ranging from 300 to 500 µm.…”

Biomaterials and Stem Cells: Promising Tools in Tissue Engineering and Biomedical Applications

“…Hydrogels are frequently used biomaterials in the biomedical applications and represent systems consisting of two or more compartments comprising a three-dimensional (3D) network of polymer chains and water that fills the spaces between the macromolecules [77,78]. The main characteristics of hydrogels include the biocompatibility and ability to swell in solution until they reach a state of equilibrium.…”

“…The main characteristics of hydrogels include the biocompatibility and ability to swell in solution until they reach a state of equilibrium. These allow them to be injected into the body in a non-invasive manner [77,78].…”

“…Hydrogels demonstrate transparency and bioadhesive properties and they are widely used in the pharmaceutical and dermatological industries by local administration or filling the defects caused by injury [77]. They may also be utilized as an injectable material for bone and cartilage tissue engineering, which may be combined with appropriate cell injection [53,78,79]. It has been shown that in situ implementation of hydrogels promotes osteoblast differentiation [53,79].…”