Maturation State-Dependent Alterations in Meniscus Integration: Implications for Scaffold Design and Tissue Engineering

Abstract

The knee meniscus is a crucial component of the knee that functions to stabilize the joint, distribute load, and maintain congruency. Meniscus tears and degeneration are common, and natural healing is limited. Notably, few children present with meniscus injuries and other related fibrocartilaginous tissues heal regeneratively in immature animals and in the fetus. In this work, we evaluated fetal, juvenile, and adult bovine meniscus properties and repair capacity in vitro. Although no changes in cell behavior (migration and proliferation) were noted with age, drastic alterations in the density and distribution of the major components of meniscus tissue (proteoglycan, collagen, and DNA) occurred with development. Coincident with these marked tissue changes, the in vitro healing capacity of the tissue decreased with age. Fetal and juvenile meniscus formed a robust repair over 8 weeks on both a histological and mechanical basis, despite a lack of vascular supply. In contrast, adult meniscus did not integrate over this period. However, integration was improved significantly with the addition of the growth factor transforming growth factor-beta 3. Finally, to evaluate engineered scaffold integration in the context of aging, we monitored cellular infiltration from native tissue into engineered nanofibrous constructs. Our findings suggest that maturation processes that enable load bearing in the adult limit endogenous healing potential and identify new metrics for the development of tissue-engineered meniscus implants.

Porosity and Cell Preseeding Influence Electrospun Scaffold Maturation and Meniscus IntegrationIn Vitro

“…However, fibrous tissues, especially in the adult, have a low endogenous cellular content, and these cells may be constrained from migrating to the wound interface by the dense extracellular matrix in which they reside. 18 To address this issue, the biomaterial scaffold might be either preseeded with cells immediately before implantation, or matured in vitro until reaching functional equivalence with the native tissue. In this study, preseeding of meniscus cells onto the scaffold before placement in the defect markedly improved integration strength for the low-porosity aligned scaffolds (which showed poor integration when implanted in an acellular format).…”

“…Finally, we used meniscus tissue derived from young (0-3 month) bovine donors; this tissue is hypercellular and has a distinct matrix composition compared to the adult tissue. 18 As meniscus tears occur primarily in the adult human population, additional studies will be required to determine if age-related differences directly impact scaffold maturation and integration capacity.…”

“…A smaller dermal punch (4 mm diameter) was used to remove a central core from the cylinder to form a ring, and an electrospun disc was press-fit into the meniscus ring as depicted in Figure 1A. 18 Before insertion, scaffolds were exposed to the UV light for 10 min per side.…”

“…18 Briefly, an Instron 5848 was outfitted with a 3.5-mm-diameter indenter in series with a 50-N-load cell. This indenter was placed above a plate with a 5-mm-diameter hole.…”

“…Previously, we utilized an in vitro explant defect model to assess the integration potential of the native tissue as a function of age. 18 In this system, the force required to separate apposing pieces of tissue arranged as concentric cylinders (i.e., the integration strength) was determined. This approach has been used in both meniscus and cartilage tissue engineering to assess tissue-tissue and tissue-biomaterial integration.…”