Strong and tough mineralized PLGA nanofibers for tendon-to-bone scaffolds

Abstract

Engineering complex tissues such as the tendon-to-bone insertion sites require a strong and tough biomimetic material system that incorporates both mineralized and unmineralized tissues with different strengths and stiffnesses. However, increasing strength without degrading toughness is a fundamental challenge in materials science. Here, we demonstrate a promising nanofibrous polymer-hydroxyapatite system in which, a continuous fibrous network must function as a scaffold for both mineralized and unmineralized tissues. It is shown that the high toughness of this material system could be maintained without compromising on the strength with the addition of hydroxyapatite mineral. Individual electrospun poly(lactide-co-glycolide) (PLGA) nanofibers demonstrated outstanding strain-hardening behavior and ductility when stretched uniaxially, even in the presence of surface mineralization. This highly desirable hardening behavior which results in simultaneous nanofiber strengthening and toughening was shown to depend on the initial cross-sectional morphology of the PLGA nanofibers. For pristine PLGA nanofibers, it was shown that ellipsoidal cross-sections provide the largest increase in fiber strength by almost 200% compared to bulk PLGA. This exceptional strength accompanied by 100% elongation was shown to be retained for thin and strongly bonded conformal mineral coatings, which were preserved on the nanofiber surface even for such very large extensions.

Nanoengineered biomaterials for repair and regeneration of orthopedic tissue interfaces

“…Similar studies have been conducted using nanohydroxyapatite (nHAp). [47,106] A combinatorial approach of controlling mineral density, chemical factors, and fiber organization could prove influential in the search of an improved design. Yet another innovative study employed natural collagen fibers complexed with nHAp to echo the natural bone-tendon interface.…”

“…[46][47][48][49][50] Specifically, for interface tissue engineering, many of the aforementioned nanomaterials have not been investigated and only a few of the conventional nanomaterials are engineered for interface tissue engineering. For example, a range of nanofabrication techniques are used to obtain nanoengineered scaffolds from synthetic and natural polymers including PLGA, PLLA, PCL, collagen, hyaluronic acid, silk, alginate and fibrin.…”

“…Nanocomposite biomaterials for bone-tendon interfaces.Fiber structure and mineralization are necessary to mimic native tissue [47]. Scaffolds were not investigated in vitro or in vivo [47].…”

Current Approaches and Future Trends to Promote Tendon Repair

“…These fibres revealed outstanding strain-hardening behaviour and ductility when stretched uniaxially, even in the presence of surface mineralization. 21 In order to combine the bio-functionality of the natural polymers with the mechanical performance of the synthetic polymers researchers have also studied hybrid scaffolds composed by both types. Xu et al, for instance, have recently worked with a PLLA/PCL-collagen scaffold seeded with tendon-derived stem cells for the regeneration of a patellar tendon defect in a rabbit model and the results were very promising.…”

“…The fibrous crimp acts as a shock absorber along the tissue length and prevents the fibres damage when a slight longitudinal elongation occurs. 21,22,29 Tendons present a complex mechanical behaviour due to the complex hierarchical collagen fibrous structures, having as primary function the transmission of tensile forces from a muscle to a bone and acting as a buffer by absorbing external excessive forces to prevent muscle damage. 22,29 Tendons response to load is non-linear and anisotropic, presenting high mechanical strength, good flexibility and a viscoelastic behaviour, due to the viscous properties of the collagen fibres and ground substance, exhibiting force-relaxation, creep and mechanical hysteresis.…”