RESUMO
The enthesis is an extremely specific region, localized at the tendon-bone interface (TBI) and made of a hybrid connection of fibrocartilage with minerals. The direct type of enthesis tissue is commonly subjected to full laceration, due to the stiffness gradient between the soft tissues and hard bone, and this often reoccurs after surgical reconstruction. For this purpose, the present work aimed to design and develop a tubular scaffold based on pullulan (PU) and chitosan (CH) and intended to enhance enthesis repair. The scaffold was designed with a topographical gradient of nanofibers, from random to aligned, and hydroxyapatite (HAP) nanoparticles along the tubular length. In particular, one part of the tubular scaffold was characterized by a structure similar to bone hard tissue, with a random mineralized fiber arrangement; while the other part was characterized by aligned fibers, without HAP doping. The tubular shape of the scaffold was also designed to be extemporarily loaded with chondroitin sulfate (CS), a glycosaminoglycan effective in wound healing, before the surgery. Micro CT analysis revealed that the scaffold was characterized by a continuous gradient, without interruptions from one end to the other. The gradient of the fiber arrangement was observed using SEM analysis, and it was still possible to observe the gradient when the scaffold had been hydrated for 6 days. In vitro studies demonstrated that human adipose stem cells (hASC) were able to grow and differentiate onto the scaffold, expressing the typical ECM production for tendon in the aligned zone, or bone tissue in the random mineralized part. CS resulted in a synergistic effect, favoring cell adhesion/proliferation on the scaffold surface. These results suggest that this tubular scaffold loaded with CS could be a powerful tool to support enthesis repair upon surgery.
RESUMO
The spontaneous healing of a tendon laceration results in the formation of scar tissue, which has lower functionality than the original tissue. Moreover, chronic non-healing tendon injuries frequently require surgical treatment. Several types of scaffolds have been developed using the tissue engineering approach, to complement surgical procedures and to enhance the healing process at the injured site. In this work, an electrospun hybrid tubular scaffold was designed to mimic tissue fibrous arrangement and extracellular matrix (ECM) composition, and to be extemporaneously loaded into the inner cavity with human platelet lysate (PL), with the aim of leading to complete post-surgery functional regeneration of the tissue for functional regeneration of the osteo-tendon interface. For this purpose, pullulan (P)/chitosan (CH) based polymer solutions were enriched with hydroxyapatite nanoparticles (HP) and electrospun. The nanofibers were collected vertically along the length of the scaffold to mimic the fascicle direction of the tendon tissue. The scaffold obtained showed tendon-like mechanical performance, depending on HP content and tube size. The PL proteins were able to cross the scaffold wall, and in vitro studies have demonstrated that tenocytes and osteoblasts are able to adhere to and proliferate onto the scaffold in the presence of PL; moreover, they were also able to produce either collagen or sialoproteins, respectively-important components of ECM. These results suggest that HP and PL have a synergic effect, endorsing PL-loaded HP-doped aligned tubular scaffolds as an effective strategy to support new tissue formation in tendon-to-bone interface regeneration.
