Movement of interstitial water through loaded articular cartilage

The superficial tangential zone (STZ) plays a significant role in normal articular cartilage's ability to support loads and retain fluids. To date, tissue engineering efforts have not replicated normal STZ function in cartilage repairs. This finite element study examined the STZ's role in normal and repaired articular surfaces under different contact conditions. Contact area and pressure distributions were allowed to change with time, tension-compression nonlinearity modeled collagen behavior in the STZ, and nonlinear geometry was incorporated to accommodate finite deformation. Responses to loading via impermeable and permeable rigid surfaces were compared to loading via normal cartilage, a more physiologic condition, anticipating the two rigid loading surfaces would bracket that of normal. For models loaded by normal cartilage, an STZ placed over the inferior repair region reduced the short-term axial compression of the articular surface by 15%, when compared to a repair without an STZ. Covering the repair with a normal STZ shifted the flow patterns and strain levels back toward that of normal cartilage. Additionally, reductions in von Mises stress (21%) and an increase in fluid pressure (13%) occurred in repair tissue under the STZ. This continues to show that STZ properties of sufficient quality are likely critical for the survival of transplanted constructs in vivo. However, response to loading via normal cartilage did not always fall within ranges predicted by the rigid surfaces. Use of more physiologic contact models is recommended for more accurate investigations into properties critical to the success of repair tissues.

Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Contact models of repaired articular surfaces: influence of loading conditions and the superficial tangential zone

Owen

Wayne

2010

“…Previous experimental studies have emphasized the importance of the STZ in normal cartilage function (Glaser and Putz 2002;Torzilli et al 1983;Torzilli 1993). Removal of the STZ resulted in greater deformations when tissue samples were subjected to axial compressive loads.…”

Section: Discussionmentioning

confidence: 99%

“…For articular cartilage, the STZ has been shown to be key for the function of normal tissue. Experimentally, removal of the STZ from normal cartilage negatively affects the remaining cartilage's ability to support axial loads and retain fluids (Glaser and Putz 2002;Torzilli et al 1983;Torzilli 1993). Also, finite element models have predicted excessive axial deformation of repair cartilage without the STZ (Smith et al 2001;Wayne et al 1991).…”

Section: Introductionmentioning

confidence: 99%

Influence of a Superficial Tangential Zone Over Repairing Cartilage Defects: Implications for Tissue Engineering

Owen

Wayne

2006

The superficial tangential zone (STZ) plays a critical role in normal cartilage function but is not yet a focus for designing tissue-engineered constructs for cartilage repair. Without material properties of sufficient quality in this zone, transplanted constructs in vivo may have little chance of survival. This finite element study investigates the impact of the superficial tangential zone on the mechanical function of normal articular surfaces as well as those with transplanted constructs. The zone is modeled as a thin transversely isotropic material with strain dependent permeability. The analyses predict that a normal transversely isotropic STZ placed over a repair region reduces the axial compression (55-68%) of, and the rate of fluid loss (45-82%) from the articular surface. A reduction was also found in von Mises stress (26-57%), axial strain (22-56%), and radial strain (69-73%), and an increase in fluid pressure (19-45%) in repair tissue under the STZ. Incorporating a quality superficial tangential zone in tissue-engineered constructs may be a critical factor in achieving mechanical environments conducive for successful cartilage repairs.

“…The superficial zone plays a crucial role in resisting elevated tensile stresses parallel to the articular surface (Owen and Wayne 2006). Experimental and numerical studies have demonstrated that the removal of the superficial zone from normal cartilage reduces the ability of the tissue to support axial loads and retain fluids (Glaser and Putz 2002;Torzilli et al 1983;Torzilli 1993;Owen and Wayne 2006). Given these important roles of ultrastructure in load-bearing capabilities of native tissue, one of the main challenges for tissue engineering of mechanically stable cartilage is to find the cues to create an engineered tissue with the ultrastructure components and organizations similar to those of native tissue.…”

Section: Introductionmentioning

confidence: 99%

The effect of tissue-engineered cartilage biomechanical and biochemical properties on its post-implantation mechanical behavior

Khoshgoftar

Wilson

Ito

et al. 2012

The insufficient load-bearing capacity of today's tissue-engineered (TE) cartilage limits its clinical application. Focus has been on engineering cartilage with enhanced mechanical stiffness by reproducing native biochemical compositions. More recently, depth dependency of the biochemical content and the collagen network architecture has gained interest. However, it is unknown whether the mechanical performance of TE cartilage would benefit more from higher content of biochemical compositions or from achieving an appropriate collagen organization. Furthermore, the relative synthesis rate of collagen and proteoglycans during the TE process may affect implant performance. Such insights would assist tissue engineers to focus on those aspects that are most important. The aim of the present study is therefore to elucidate the relative importance of implant ground substance stiffness, collagen content, and collagen architecture of the implant, as well as the synthesis rate of the biochemical constituents for the post-implantation mechanical behavior of the implant. We approach this by computing the post-implantation mechanical conditions using a composition-based fibril-reinforced poro-viscoelastic swelling model of the medial tibia plateau. Results show that adverse implant composition and ultrastructure may lead to post-implantation excessive mechanical loads, with collagen orientation being