Induction of fiber alignment and mechanical anisotropy in tissue engineered menisci with mechanical anchoring

Abstract

This study investigated the effect of mechanical anchoring on the development of fiber organization and anisotropy in anatomically shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were mixed with collagen and injected into molds designed to produce meniscus implants with 12 mm extensions at each horn. After a day of static culture, 10 and 20mg/ml collagen menisci were either clamped or unclamped and cultured for up to 8 weeks. Clamped menisci were anchored in culture trays throughout culture to mimic the native meniscus horn attachment sites, restrict contraction circumferentially, and encourage circumferential alignment. Clamped menisci retained their size and shape, and by 8 weeks developed circumferential and radial fiber organization that resembled native meniscus. Clamping also increased collagen accumulation and improved mechanical properties compared to unclamped menisci. Enhanced organization in clamped menisci was further reflected in the development of anisotropic tensile properties, with 2-3 fold higher circumferential moduli compared to radial moduli, a similar ratio to native meniscus. Ten and 20mg/ml clamped menisci had similar levels of organization, with 20mg/ml menisci producing larger diameter fibers and significantly better mechanical properties. Collectively, these data demonstrate the benefit of using bio-inspired mechanical boundary conditions to drive the formation of a highly organized collagen fiber network.

Fiber development and matrix production in tissue-engineered menisci using bovine mesenchymal stem cells and fibrochondrocytes

“…Previously, we developed an anatomically accurate tissue engineered meniscus using fibrochondrocytes (FCCs) in a high density collagen gel (26). FCCs, embedded in the meniscal construct, developed large fibers under static mechanical boundary conditions with mechanical properties approaching native values (27). …”

“…However, there is little data on MSCs produce a functionally organized fibers from a disorganized matrix. Anchoring at the attachments provides critical mechanical signals for collagen organization and matrix secretion (27,40,41). However there is little data on how mechanical anchoring affects MSCs in the context of producing a functionally organized meniscus.…”

Meniscus mechanics and mechanobiology

“…A complete understanding of tissue level mechanics is also important as it sets design criteria for the next generation of replacement devices. Abdelgaied et al (2015) describe the impact of decellularization on the biomechanical properties of a potential xenogeneic replacement tissue, while Fisher et al (2015) and Puetzer et al (2015) focus on the mechanical behavior of newly developed tissue engineered constructs. Fisher et al assess the impact of mimicking the structural complexities of the meniscus within multi-lamellar mesenchymal stem cell-seeded nanofibrous constructs while Puetzer et al highlight the important of mechanical anchoring on the development of anisotropic behavior in collagen gels seeded with meniscal fibrochondrocytes.…”

Next generation tissue engineering of orthopedic soft tissue-to-bone interfaces

“…For example, cells rearranged collagen gels into large, oriented fibers during culture of a meniscus construct, indicating the value of incorporating cellular remodeling capability into a scaffold. [71] Implementation of continuity, integration of structure, and support for cellular remodeling in scaffolds allows for control of mechanical properties, strengthening of interfacial regions, and ability of the scaffold to integrate with native tissue upon in vivo implantation.…”

“…[87–89,171] Mimicking this static mechanical boundary condition has shown organized fiber remodeling from several cell types including fibroblasts, [172–175] MSCs, [176–178] cardiomyocytes, [175] annulus fibrosis chondrocytes, [179] and meniscal fibrochondrocytes. [59,71,83] Mechanical anchoring at the bony ends of a soft tissue-to-bone model system directed longitudinal fiber formation as well as formed interdigitated fibers at the collagen-bone interface (Fig. 7C).…”