Fibrin Gels Exhibit Improved Biological, Structural, and Mechanical Properties Compared with Collagen Gels in Cell-Based Tendon Tissue-Engineered Constructs

Abstract

The prevalence of tendon and ligament injuries and inadequacies of current treatments is driving the need for alternative strategies such as tissue engineering. Fibrin and collagen biopolymers have been popular materials for creating tissue-engineered constructs (TECs), as they exhibit advantages of biocompatibility and flexibility in construct design. Unfortunately, a few studies have directly compared these materials for tendon and ligament applications. Therefore, this study aims at determining how collagen versus fibrin hydrogels affect the biological, structural, and mechanical properties of TECs during formation in vitro. Our findings show that tendon and ligament progenitor cells seeded in fibrin constructs exhibit improved tenogenic gene expression patterns compared with their collagen-based counterparts for approximately 14 days in culture. Fibrin-based constructs also exhibit improved cell-derived collagen alignment, increased linear modulus (2.2-fold greater) compared with collagen-based constructs. Cyclic tensile loading, which promotes the maturation of tendon constructs in a previous work, exhibits a material-dependent effect in this study. Fibrin constructs show trending reductions in mechanical, biological, and structural properties, whereas collagen constructs only show improved tenogenic expression in the presence of mechanical stimulation. These findings highlight that components of the mechanical stimulus (e.g., strain amplitude or time of initiation) need to be tailored to the material and cell type. Given the improvements in tenogenic expression, extracellular matrix organization, and material properties during static culture, in vitro findings presented here suggest that fibrin-based constructs may be a more suitable alternative to collagen-based constructs for tissue-engineered tendon/ligament repair.

Role of Biomaterials and Controlled Architecture on Tendon/Ligament Repair and Regeneration

“…Regardless, hydrogel systems can provide the flexibility to control and manipulate a range of properties such as degradation, injectability, biofunctionalization, release of growth factors and drugs, and structural porosity to facilitate cell proliferation and stiffness, in order to understand and elucidate mechanisms of T/L regeneration, and subsequently work toward achieving tendon‐like and ligament‐like tissue growth in in vitro experiments and in small animal models in vivo. In recent years, studies have extensively explored hydrogel systems developed from natural polymers such as collagen, gelatin, silk, hyaluronic acid, fibrin, alginate, and chitosan, and have successfully demonstrated favorable biological responses in both in vitro and in vivo small animal models, such as through the upregulation of gene expressions for T/L tissue, typically for scleraxis, collagen types I and III, and tenomodulin, and observations for mature tissue formation and deposition of organized collagen. The advantages of these natural polymers for hydrogels over synthetic polymers include biocompatibility and the ability to mimic the features and components in the T/L ECM by presenting cell recognition signals which provide a suitable niche for cellular proliferation and differentiation, which can subsequently augment tissue repair and healing.…”

Tendon stem progenitor cells: Understanding the biology to inform therapeutic strategies for tendon repair

“…Devising an effective therapy for tendon repair/regeneration will likely require a multi‐pronged approach that combines activation/delivery of an appropriate cell type, tailored differentiation (either ex vivo or in vivo), and a microenvironment conducive to regeneration. While this review focused on TSPCs since these tissue‐specific cells may be “primed” toward tenogenic differentiation, pioneering early research in tendon tissue engineering applied bone marrow‐derived mesenchymal stem cells and tested strategies for optimizing their tenogenic potential via 3‐dimensional and mechanical cues . Recent studies also highlight the exciting capacity of neighboring endogenous cells to be activated and recruited toward tendon repair in vivo, given the correct molecular signals .…”

“…While this review focused on TSPCs since these tissue-specific cells may be "primed" toward tenogenic differentiation, pioneering early research in tendon tissue engineering applied bone marrow-derived mesenchymal stem cells and tested strategies for optimizing their tenogenic potential via 3-dimensional and mechanical cues. [106][107][108][109][110][111][112] Recent studies also highlight the exciting capacity of neighboring endogenous cells to be activated and recruited toward tendon repair in vivo, given the correct molecular signals. 58,113 The choice of cell type is an essential consideration which impacts the overall therapeutic strategy.…”

Molecular regulation of tendon cell fate during development

“…During embryogenesis, developing tendons are highly cellular with minimal extracellular matrix, and are anchored under tension between the skeleton and muscle. Using the developmental state as design guidelines, there are now several available methods to engineer linear constructs of cells fixed between two anchors . In most of these protocols, cells are seeded at high densities (either scaffold‐free or embedded within a hydrogel biomaterial) and formed first as a sheet.…”