The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee. Due to its limited intrinsical healing potential and vascularization, injuries of the ACL do not heal satisfactorily, and surgical intervention is usually required. The limitations of existing reconstructive grafts and autologous transplants have prompted interest in tissue-engineered solutions. A tissue engineering scaffold for ACL reconstruction must be able to mimic the mechanical properties of the native ligament, provide sufficient porosity to promote cell growth of the neoligament tissue, and be biodegradable. This study investigates long-term biodegradable poly-ε-caprolactone (PCL)-based scaffolds for ACL replacement using the 3D hexagonal braiding technique. The scaffolds were characterized mechanically as well as morphologically. All scaffolds, regardless of their braid geometry, achieved the maximum tensile load of the native ACL. The diameter of all scaffolds was lower than that of the native ligament, making the scaffolds implantable with established surgical methods. The 3D hexagonal braiding technique offers a high degree of geometrical freedom and, thus, the possibility to develop novel scaffold architectures. Based on the findings of this study, the 3D-braided PCL-based scaffolds studied were found to be a promising construct for tissue engineering of the anterior cruciate ligament.

Mechanophores that translate mechanical force into optical signals are powerful tools for probing damage in polymeric materials, yet regularly suffer from undesired thermal reactivity compromising mechanochemical selectivity and processability of the host polymer. Here, we show that the [4+2] photodimerization of highly emissive 9-π-extended anthracene yields an optical force probe (OFP) which features excellent thermal stability above 200 °C as well as photochemical robustness. We demonstrate mechanochemical activation in thermoplastic polymers using blends of commercial poly(methyl methacrylate) (PMMA), polystyrene (PS), thermoplastic polyurethane (TPU), and polyethylene (PE) at low functional material loadings (≤ 5 wt%). Importantly, we subject OFP-functionalized TPU to melt processing including extrusion and melt spinning, and obtain mechanofluorogenic fibers that retain intact OFPs. Together, our results underscore photodimerization of fluorophores as strategy to tailor the optical readout of OFPs and open an avenue to investigate molecular-level damage in melt-processed thermoplastics.