Bioinspired bimodal micro-nanofibrous scaffolds promote the tenogenic differentiation of tendon stem/progenitor cells for achilles tendon regeneration

Bioactive 3D Electrohydrodynamic Printed Lattice Architectures Augment Tenogenesis of Tendon Stem/Progenitor Cells

Tendon defect repair remains a tough clinical procedure that hinders functional motion in patients. Electrohydrodynamic (EHD) three-dimensional (3D) printing, as a novel strategy, can controllably fabricate biomimetic micro/nanoscale architecture, but the hydrophobic and bioinert nature of polymers might be adverse to cell-material interplay. In this work, 3D EHD printed polycaprolactone (PCL) was immobilized on basic fibroblast growth factor (bFGF) using polydopamine (PDA), and the proliferation and tenogenic differentiation of tendon stem/progenitor cells (TSPCs) in vitro was researched. A subcutaneous model was established to evaluate the effects of tenogenesis and immunomodulation. We then investigated the in situ implantation and immunomodulation effects in an Achilles tendon defect model. After immobilization of bFGF, the scaffolds profoundly facilitated proliferation and tenogenic differentiation; however, PDA had only a proliferative effect. Intriguingly, the bFGF immobilized on EHD printed PCL indicated a synergistic effect on the highest expression of tenogenic gene and protein markers at 14 days, and the tenogenesis may be induced by activating the transforming growth factor-β (TGF-β) signal pathway in vitro. The subcutaneous engraftment study confirmed a tendon-like structure, similar to that of the native tendon, as well as an M2 macrophage polarization effect. Additionally, the bioactive scaffold exhibited superior efficacy in new collagen formation and repair of Achilles tendon defects. Our study revealed that the topographic cues alone were insufficient to trigger tenogenic differentiation, requiring appropriate chemical signals, and that appropriate immunomodulation was conducive to tenogenesis. The tenogenesis of TSPCs on the bioactive scaffold may be correlated with the TGF-β signal pathway and M2 macrophage polarization.

Mesoporous Particle Embedded Nanofibrous Scaffolds Sustain Biological Factors for Tendon Tissue Engineering

In recent years, fiber-based systems have been explored in the frame of tissue engineering due to their robustness in recapitulating the architecture and mechanical properties of native tissues. Such scaffolds offer anisotropic architecture capable of reproducing the native collagen fibers' orientation and distribution. Moreover, fibrous constructs might provide a biomimetic environment for cell encapsulation and proliferation as well as influence their orientation and distribution. In this work, we combine two fiber fabrication techniques, such as electrospinning and wet-spinning, in order to obtain novel cell-laden 3D fibrous layered scaffolds which can simultaneously provide: (i) mechanical support; (ii) suitable microenvironment for 3D cell encapsulation; and (iii) loading and sustained release of growth factors for promoting the differentiation of human bone marrow-derived mesenchymal stem cells (hB-MSCs). The constructs are formed from wet-spun hydrogel fibers loaded with hB-MSCs deposited on a fibrous composite electrospun matrix made of polycaprolactone, polyamide 6, and mesoporous silica nanoparticles enriched with bone morphogenetic protein-12 (BMP-12). Morphological and mechanical characterizations of the structures were carried out, and the growth factor release was assessed. The biological response in terms of cell viability, alignment, differentiation, and extracellular matrix production was investigated. Ex vivo testing of the layered structure was performed to prove the layers' integrity when subjected to mechanical stretching in the physiological range. The results reveal that 3D layered scaffolds can be proposed as valid candidates for tendon tissue engineering.

A facile one-stone-two-birds strategy for fabricating multifunctional 3D nanofibrous scaffolds

Local bacterial infections lead to delayed wound healing and in extreme cases, such as diabetic foot ulcers, to non-healing due to the impaired cellular function in such wounds. Thus, many scientists have focused on developing advanced therapeutic platforms to treat infections and promote cellular proliferation and angiogenesis. This study presents a facile approach for designing nanofibrous scaffolds in three dimensions (3D) with enhanced antibacterial activity to meet the need of treating chronic diabetic wounds. Being a cationic surfactant as well as an antimicrobial agent, octenidine (OCT) makes a 2D membrane hydrophilic, enabling it to be modified into a 3D scaffold in a "one stone, two birds" manner. Aqueous sodium borohydride (NaBH4) solution plays a dual role in the fabrication process, functioning as both a reducing agent for the in situ synthesis of silver nanoparticles (Ag NPs) anchored on the nanofiber surface and a hydrogen gas producer for expanding the 2D membranes into fully formed 3D nanofiber scaffolds, as demonstrated by morphological analyses. Various techniques were used to characterize the developed scaffold (e.g., SEM, XRD, DSC, FTIR, and surface wettability), demonstrating a multilayered porous structure and superhydrophilic properties besides showing sustained and prolonged release of OCT (61% ± 1.97 in 144 h). Thanks to the synergistic effect of OCT and Ag NPs, the antibacterial performance of the 3D scaffold was significantly higher than that of the 2D membrane. Moreover, cell viability was studied in vitro on mouse fibroblasts L929, and the noncytotoxic character of the 3D scaffold was confirmed. Overall, it is shown that the obtained multifunctional 3D scaffold is an excellent candidate for diabetic wound healing and skin repair.

Dual-bioactive molecules loaded aligned core-shell microfibers for tendon tissue engineering

Development of a controlled delivery ultrafine fibrous system with two bioactive molecules is required to stimulate tendon healing in different phase. In this study, we used emulsion stable jet electrospinning to fabricate aligned poly(L-lactic acid) (PLLA) based ultrafine fibers with two small bioactive molecules of L-Arginine (Arg) and low molecular weight hyaluronic acid (HA). The results demonstrated that the aligned Arg/HA/PLLA microfibrous scaffold showed core-shell structure and allowed sequential release of Arg and HA due to their different electric charge. The scaffold also showed enhanced hydrophilicity, cell migration, spread and proliferation. Using an Achilles tendon repair model in rats, we demonstrated that this novel fibrous scaffold can prevent adhesion and promote tendon regeneration. Additionally, two p53 and ER-α-mediated signalling pathways were described as the probable main path of synergistic effects of the novel scaffold on tendon generation. Thus, this study may provide an important strategy for developing biofunctional and biomimetic tendon scaffolds.

Constructing high-strength nano-micro fibrous woven scaffolds with native-like anisotropic structure and immunoregulatory function for tendon repair and regeneration

Tendon injuries are common debilitating musculoskeletal diseases with high treatment expenditure in sports medicine. The development of tendon-biomimetic scaffolds may be promising for improving the unsatisfactory clinical outcomes of traditional therapies. In this study, we combined an advanced electrospun nanofiber yarn-generating technique with a traditional textile manufacturing strategy to fabricate innovative nano-micro fibrous woven scaffolds with tendon-like anisotropic structure and high-strength mechanical properties for the treatment of large-size tendon injury. Electrospun nanofiber yarns made from pure poly L-lactic acid (PLLA) or silk fibroin (SF)/PLLA blend were fabricated, and their mechanical properties matched and even exceeded those of commercial PLLA microfiber yarns. The PLLA or SF/PLLA nanofiber yarns were then employed as weft yarns interlaced with commercial PLLA microfiber yarns as warp yarns to generate two new types of nanofibrous scaffolds (nmPLLA and nmSF/PLLA) with a plain-weaving structure. Woven scaffolds made from pure PLLA microfiber yarns (both weft and warp directions) (mmPLLA) were used as controls.In vitroexperiments showed that the nmSF/PLLA woven scaffold with aligned fibrous topography significantly promoted cell adhesion, elongation, proliferation, and phenotypic maintenance of tenocytes compared with mmPLLA and nmPLLA woven scaffolds. Moreover, the nmSF/PLLA woven scaffold exhibited the strongest immunoregulatory functions and effectively modulated macrophages towards the M2 phenotype.In vivoexperiments revealed that the nmSF/PLLA woven scaffold notably facilitated Achilles tendon regeneration with improved structure by macroscopic, histological, and ultrastructural observations six months after surgery, compared with the other two groups. More importantly, the regenerated tissue in the nmSF/PLLA group had excellent biomechanical properties comparable to those of the native tendon. Overall, our study provides an innovative biological-free strategy with ready-to-use features, which presents great potential for clinical translation for damaged tendon repair.

Advanced Nanofiber-Based Scaffolds for Achilles Tendon Regenerative Engineering

The Achilles tendon (AT) is responsible for running, jumping, and standing. The AT injuries are very common in the population. In the adult population (21–60 years), the incidence of AT injuries is approximately 2.35 per 1,000 people. It negatively impacts people’s quality of life and increases the medical burden. Due to its low cellularity and vascular deficiency, AT has a poor healing ability. Therefore, AT injury healing has attracted a lot of attention from researchers. Current AT injury treatment options cannot effectively restore the mechanical structure and function of AT, which promotes the development of AT regenerative tissue engineering. Various nanofiber-based scaffolds are currently being explored due to their structural similarity to natural tendon and their ability to promote tissue regeneration. This review discusses current methods of AT regeneration, recent advances in the fabrication and enhancement of nanofiber-based scaffolds, and the development and use of multiscale nanofiber-based scaffolds for AT regeneration.