Purpose

Articular cartilage is the physiological bearing of mammalian joints; any material that attempts to repair or replace this tissue must ultimately bear this role (load-bearing and lubrication). The functional performance of healthy articular cartilage is driven by the pressurization of interstitial fluid that occurs in response to load-induced deformation of the solid matrix and the consequential exudation of interstitial fluid. The goal of this work is to recapitulate these fluid-solid interactions to create functional cartilage repair materials.

Methods and Materials

Fiber reinforced hydrated networks were produced using a combined approach of electrospinning and electrospraying, Figure 1. Electrospun poly(caprolactone) (PCL) provided a high tensile stiffness fibrous matrix, while electrosprayed gelatin (Gel) yielded a hydrated network responsible for swelling and resistance to fluid flux. Scaffolds were evaluated for their functional performance (effective modulus) and material properties (tensile modulus, equilibrium modulus, permeability, fluid fraction).

Results

As Figure 1D demonstrates, neat structures of fibrous PCL and Gel produced negligible compressive resistance (~0.1 MPa contact modulus) with very little to no time dependence. However, the combination of the two materials through electrospinning and electrospraying yielded a dramatically different response with an effective modulus, tensile modulus, equilibrium modulus, permeability, and fluid fraction of: 3.6 MPa, 2.77 MPa, 0.68 MPa, 0.0004 mm⁴/Ns, and 75%, values which start to approach that of native articular cartilage.

Figure 1. (A) Scanning electron microscopy image of electrospun network (left) and collagen (right). Image adapted from (Vanden Berg-Foels WS, et al. J Microscopy. 2012). (B) Generalized microstructure of collagen fibers and proteoglycans. (C) Scaffold fabrication. (D) Functional mechanics of fiber reinforced hydrated networks compared to neat phases and bovine cartilage.

Conclusion

We have developed a system to embed a hydrated network within a fibrous matrix and produce a cartilage-like response through interstitial fluid pressurization.