Dual cross-linked COL1/HAp bionic gradient scaffolds containing human amniotic mesenchymal stem cells promote rotator cuff tendon-bone interface healing

The tendon-bone interface heals through scar tissue, while the lack of a natural interface gradient structure and collagen fibre alignment leads to the occurrence of retearing. Therefore, the promotion of tendon healing has become the focus of regenerative medicine. The purpose of this study was to develop a gradient COL1/ hydroxyapatite (HAp) biomaterial loaded with human amniotic mesenchymal stem cells (hAMSCs). The performance of common cross-linking agents, Genipin, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS), and dual cross-linked materials were compared to select the best cross-linking mechanism to optimize the biological and mechanical properties of the scaffold. The optimal COL1/HAp-loaded with hAMSCs were implanted into the tendon-bone rotator cuff interfaces in rats and the effect on the tendon-bone healing was assessed by micro-CT, histological analysis, and biomechanical properties. The results showed that Genipin and EDC/NHS dual cross-linked COL1/HAp had good biological activity and mechanical properties and promoted the proliferation and differentiation of hAMSCs. Animal experiments showed that the group using a scaffold loaded with hAMSCs had excellent continuity and orientation of collagen fibers, increased fibrocartilage and bone formation, and significantly higher biomechanical functions than the control group at the interface at 12 weeks post operation. This study demonstrated that dual cross-linked gradient COL1/HAp-loaded hAMSCs could promote interface healing, thereby providing a feasible strategy for tendon-bone interface regeneration.

Mechanical properties and failure mechanisms of polyamide 12 gradient scaffolds developed with selective laser sintering

Developing a functional gradient scaffold compatible with the fantastic biological and mechanical properties of natural bone tissue is imperative in bone tissue engineering. In this work, the stretch-dominated (cubical and circular) and bending-dominant (diamond and gyroid) pore styles were employed to design custom-graded scaffolds based on the curve interference method and then were fabricated by selective laser sintering (SLS) using polyamide 12 (PA12) powder. Subsequently, the mechanical behavior, failure mechanism, and energy absorption performance of porous structures were investigated via compression experiments and finite element (FE) simulation. The results indicated that the stretch-dominated radial gradient structures entire exhibited transverse shear failure and the bending-dominant radial gradient structures whole exhibited progressive destruction, while all of the axial gradient scaffolds suffered a predictable layer-by-layer fracture. Among them, the bending-dominated radial gradient structure of gyroid had been proven to sustain stronger deformability and energy absorption capacity. Meanwhile, the FE method powerfully predicted the mechanical behavior of the scaffold, and this research thereby possessed significant implications for the development of bone tissue engineering.

Multimaterial and multiscale scaffold for engineering enthesis organ

Tendon and ligament injuries are relevant clinical problems in modern society, and the current medical approaches do not guarantee complete recovery of the physiological functionalities. Moreover, they present a non-negligible failure rate after surgery. Failures often occur at the enthesis, which is the area of tendons and ligaments insertion to bones. This area is highly anisotropic and composed of four distinct zones: tendon or ligament, non-mineralized fibrocartilage, mineralized fibrocartilage, and bone. The organization of these regions provides a gradient in mechanical properties, biochemical composition, cellular phenotype, and extracellular matrix organization. Tissue engineering represents an alternative to traditional medical approaches. This work presents a novel biofabrication approach for engineering the enthesis. Gradient-based scaffolds were fabricated by exploiting the combination of electrospinning and three-dimensional (3D) bioprinting technologies. Studies were conducted to evaluate scaffold biocompatibility by seeding bone marrow-derived mesenchymal stem cells (BM-MSCs). Then, the scaffold's ability to promote cellular adhesion, growth, proliferation, and differentiation in both tenogenic and osteogenic phenotypes was evaluated. Fabricated scaffolds were also morphologically and mechanically characterized, showing optimal properties comparable to literature data. The versatility and potentiality of this novel biofabrication approach were demonstrated by fabricating clinical-size 3D enthesis scaffolds. The mechanical characterization highlighted their behavior during a tensile test was comparable to tendons and ligaments in vivo.

Articular cartilage and osteochondral tissue engineering techniques: Recent advances and challenges

In spite of the considerable achievements in the field of regenerative medicine in the past several decades, osteochondral defect regeneration remains a challenging issue among diseases in the musculoskeletal system because of the spatial complexity of osteochondral units in composition, structure and functions. In order to repair the hierarchical tissue involving different layers of articular cartilage, cartilage-bone interface and subchondral bone, traditional clinical treatments including palliative and reparative methods have showed certain improvement in pain relief and defect filling. It is the development of tissue engineering that has provided more promising results in regenerating neo-tissues with comparable compositional, structural and functional characteristics to the native osteochondral tissues. Here in this review, some basic knowledge of the osteochondral units including the anatomical structure and composition, the defect classification and clinical treatments will be first introduced. Then we will highlight the recent progress in osteochondral tissue engineering from perspectives of scaffold design, cell encapsulation and signaling factor incorporation including bioreactor application. Clinical products for osteochondral defect repair will be analyzed and summarized later. Moreover, we will discuss the current obstacles and future directions to regenerate the damaged osteochondral tissues.

A hydrogel/particle composite with a gradient of oxygen releasing microparticle for concurrent osteogenic and chondrogenic differentiation in a single scaffold

In the present study, a hydrogel/particle scaffold with a gradient of the oxygen releasing microparticles was developed. Hydrogel component was composed of the oxidized pectin and silk fibroin, whereas the microparticles were constituted from polylactic acid (PLA) and calcium peroxide (CPO). A controlled mixing of the suspensions with different content of the PLA/CPO microparticles conferred a gradient of microparticles in scaffold thickness in a manner that the microparticle content increased with moving from lower to upper face of the composite. Measurement of the scaffold mechanical properties corroborated that with moving from lower to upper face, the compressive modulus increased by 78 %. The measurement of the oxygen and calcium release from the successive sections of the composite revealed that the gradient of microparticle concentration resulted in the gradient of the released oxygen and calcium. MTT analysis proved that the gradient oxygen releasing composite did not induce any toxic effect on human adipose-derived mesenchymal stem cells (hAd-MSCs). Moreover, the cell culture on successive sections of the gradient composite confirmed that oxygen releasing composite substantially improved the cell viability and density comparing the pristine hydrogel and the non-oxygen releasing counterpart. The increase in microparticle content conferred a positive impact on the number of viable cells. The study of osteogenic (ALP, OCN and OPN) and chondrogenic (SOX9, AGG and COL ⅠⅠ) gene expression proved that the gradient composite parts with high microparticle content promoted osteogenesis, whereas the parts with low microparticle content encouraged chondrogenesis of mesenchymal stem cells.

Regeneration of the rotator cuff tendon-to-bone interface using umbilical cord-derived mesenchymal stem cells and gradient extracellular matrix scaffolds from adipose tissue in a rat model

Regeneration of the gradient structure of the tendon-to-bone interface (TBI) is a crucial goal after rotator cuff repair. The purpose of this study was to investigate the efficacy of a biomimetic hydroxyapatite-gradient scaffold (HA-G scaffold) isolated from adipose tissue (AD) with umbilical cord derived mesenchymal stem cells (UC MSCs) on the regeneration of the structure of the TBI by analyzing the histological and biomechanical changes in a rat repair model. As a result, the HA-G scaffold had progressively increased numbers of hydroxyapatite (HA) particles from the tendon to the bone phase. After seeding UC MSCs to the scaffold, specific matrices, such as collagen, glycoaminoglycan, and calcium, were synthesized with respect to the HA density. In a rat repair model, compared to the repair group, the UC MSCs seeded HA-G scaffold group had improved collagen organization and cartilage formation by 52% at 8 weeks and 262.96% at 4 weeks respectively. Moreover, ultimate failure load also increased by 30.71% at 4 weeks in the UC MSCs seeded HA-G scaffold group compared to the repair group. Especially, the improved values were comparable to values in normal tissue. This study demonstrated that HA-G scaffold isolated from AD induced UC MSCs to form tendon, cartilage and bone matrices similar to the TBI structure according to the HA density. Furthermore, UC MSC-seeded HA-G scaffold regenerated the TBI of the rotator cuff in a rat repair model in terms of histological and biomechanical properties similar to the normal TBI. Statement of Significance We found specific extracellular matrix (ECM) formation in the biomimetic-hydroxyapatite-gradient-scaffold (HA-G-scaffold) in vitro as well as improved histological and biomechanical results of repaired rotator cuff after the scaffold implantation in a rat model. This study has four strengths; An ECM scaffold derived from human adipose tissue; only one-layer used for a gradient scaffold not a multilayer used to mimic the unique structure of the gradient tendon-to-bone-interface (TBI) of the rotator cuff; UC-MSCs as a new cell source for TBI regeneration; and the UC-MSCs synthesized specific matrices with respect to the HA density without any other stimuli. This study suggested that the UC-MSC seeded HA-G-scaffold could be used as a promising strategy for the regeneration of rotator cuff tears.

Gradient nanocomposite hydrogels for interface tissue engineering

Two-dimensional (2D) nanomaterials are an emerging class of materials with unique physical and chemical properties due to their high surface area and disc-like shape. Recently, these 2D nanomaterials have been investigated for a range of biomedical applications including tissue engineering, therapeutic delivery and bioimaging, due to their ability to physically reinforce polymeric networks. Here, we present a facile fabrication of a gradient scaffold with two natural polymers (gelatin methacryloyl (GelMA) and methacrylated kappa carrageenan (MκCA)) reinforced with 2D nanosilicates to mimic the native tissue interface. The addition of nanosilicates results in shear-thinning characteristics of prepolymer solution and increases the mechanical stiffness of crosslinked gradient structure. A gradient in mechanical properties, microstructures and cell adhesion characteristics was obtained using a microengineered flow channel. The gradient structure can be used to understand cell-matrix interactions and to design gradient scaffolds for mimicking tissue interfaces.