The application of BMP-12-overexpressing mesenchymal stem cells loaded 3D-printed PLGA scaffolds in rabbit rotator cuff repair

Biomimetic gradient scaffolds for the tissue engineering and regeneration of rotator cuff enthesis

Rotator cuff tear is one of the most common musculoskeletal disorders, which often results in recurrent shoulder pain and limited movement. Enthesis is a structurally complex and functionally critical interface connecting tendon and bone that plays an essential role in maintaining integrity of the shoulder joint. Despite the availability of advanced surgical procedures for rotator cuff repair, there is a high rate of failure following surgery due to suboptimal enthesis healing and regeneration. Novel strategies based on tissue engineering are gaining popularity in improving tendon-bone interface (TBI) regeneration. Through incorporating physical and biochemical cues into scaffold design which mimics the structure and composition of native enthesis is advantageous to guide specific differentiation of seeding cells and facilitate the formation of functional tissues. In this review, we summarize the current state of research in enthesis tissue engineering highlighting the development and application of biomimetic scaffolds that replicate the gradient TBI. We also discuss the latest techniques for fabricating potential translatable scaffolds such as 3D bioprinting and microfluidic device. While preclinical studies have demonstrated encouraging results of biomimetic gradient scaffolds, the translation of these findings into clinical applications necessitates a comprehensive understanding of their safety and long-term efficacy.

Dual Growth Factor Delivery Using Photo-Cross-Linkable Gelatin Hydrogels for Effectively Reinforced Regeneration of the Rotator Cuff Tendon

Rotator cuff tears are currently treated with drugs (steroids and nonsteroidal anti-inflammatory drugs) and surgery. However, the damaged rotator cuff requires a considerable amount of time to regenerate, and the regenerated tissue cannot restore the same level of function as that before the damage. Although growth factors can accelerate regeneration, they are difficult to be used alone because of the risk of degradation and the difficulties in ensuring their sustained release. Thus, hydrogels such as gelatin are used, together with growth factors. Gelatin is a biocompatible and biodegradable hydrogel derived from collagen; therefore, it closely resembles the components of native tissues and can retain water and release drugs continuously, while also showing easily tunable mechanical properties by simple modifications. Moreover, gelatin is a natural biopolymer that possesses the ability to form hydrogels of varying compositions, thereby facilitating effective cross-linking. Therefore, gelatin can be considered to be suitable for rotator-to-tendon healing. In this study, we designed photo-cross-linkable gelatin hydrogels to enhance spacing and adhesive effects for rotator cuff repair. We mixed a ruthenium complex (Ru(II)bpy32+) and sodium persulfate into gelatin-based hydrogels and exposed them to blue light to induce gelation. Basic fibroblast growth factor and bone morphogenetic protein-12 were encapsulated in the gelatin hydrogel for localized and sustained release into the wound, thereby enhancing the cell proliferation. The effects of these dual growth factor-loaded hydrogels on cell cytotoxicity and tendon regeneration in rotator cuff tear models were evaluated using mechanical and histological assessments. The findings confirmed that the gelatin hydrogel was biocompatible and that treatment with the dual growth factor-loaded hydrogels in in vivo rotator cuff tear models promoted regeneration and functional restoration in comparison with the findings in the nontreated group. Therefore, growth factor-loaded gelatin-based hydrogels may be suitable for the treatment of rotator cuff tears.

Advancements of 3D bioprinting in regenerative medicine: Exploring cell sources for organ fabrication

3D bioprinting has unlocked new possibilities for generating complex and functional tissues and organs. However, one of the greatest challenges lies in selecting the appropriate seed cells for constructing fully functional 3D artificial organs. Currently, there are no cell sources available that can fulfill all requirements of 3D bioprinting technologies, and each cell source possesses unique characteristics suitable for specific applications. In this review, we explore the impact of different 3D bioprinting technologies and bioink materials on seed cells, providing a comprehensive overview of the current landscape of cell sources that have been used or hold potential in 3D bioprinting. We also summarized key points to guide the selection of seed cells for 3D bioprinting. Moreover, we offer insights into the prospects of seed cell sources in 3D bioprinted organs, highlighting their potential to revolutionize the fields of tissue engineering and regenerative medicine.

Advancements in 3D-printed artificial tendon

Millions of people have been reported with tendon injuries each year. Unfortunately, Tendon injuries are increasing rapidly due to heavy exercise and a highly aging population. In addition, the introduction of 3D-printing technology in the area of tendon repair and replacement has resolved numerous issues and significantly improved the quality of artificial tendons. This advancement has also enabled us to explore and identify the most effective combinations of biomaterials that can be utilized in this field. This review discusses the recent development of the 3D-printed artificial tendon; where recently, some research investigated the most suitable pore sizes, diameter, and strength for scaffolds to have high tendon cells ingrowth and proliferation, giving a better understanding of the effects of densities and structure patterns on tendon's mechanical properties. In addition, it presents the divergence between 3D-printed tendons and other tissue and how the different 3D-printing techniques and models participated in this development.

From materials to clinical use: advances in 3D-printed scaffolds for cartilage tissue engineering

Osteoarthritis caused by articular cartilage defects is a particularly common orthopedic disease that can involve the entire joint, causing great pain to its sufferers. A global patient population of approximately 250 million people has an increasing demand for new therapies with excellent results, and tissue engineering scaffolds have been proposed as a potential strategy for the repair and reconstruction of cartilage defects. The precise control and high flexibility of 3D printing provide a platform for subversive innovation. In this perspective, cartilage tissue engineering (CTE) scaffolds manufactured using different biomaterials are summarized from the perspective of 3D printing strategies, the bionic structure strategies and special functional designs are classified and discussed, and the advantages and limitations of these CTE scaffold preparation strategies are analyzed in detail. Finally, the application prospect and challenges of 3D printed CTE scaffolds are discussed, providing enlightening insights for their current research.

Strategies of immobilizing BMP-2 with 3D-printed scaffolds to improve osteogenesis

The management and definitive treatment of critical-size bone defects in severe trauma, tumor resection and congenital malformation are troublesome for orthopedic surgeons and patients worldwide without recognized good treatment strategies. Researchers and clinicians are working to develop new strategies to treat these problems. This review aims to summarize the techniques used by additive manufacturing scaffolds loaded with BMP-2 to promote osteogenesis and to analyze the current status and trends in relevant clinical translation. Optimize composite scaffold design to enhance bone regeneration through printing technology, material selection, structure design and loading methods of BMP-2 to advance the clinical therapeutic bone repair field.

Strategies for promoting tendon-bone healing: Current status and prospects

Tendon-bone insertion (TBI) injuries are common, primarily involving the rotator cuff (RC) and anterior cruciate ligament (ACL). At present, repair surgery and reconstructive surgery are the main treatments, and the main factor determining the curative effect of surgery is postoperative tendon-bone healing, which requires the stable combination of the transplanted tendon and the bone tunnel to ensure the stability of the joint. Fibrocartilage and bone formation are the main physiological processes in the bone marrow tract. Therefore, therapeutic measures conducive to these processes are likely to be applied clinically to promote tendon-bone healing. In recent years, biomaterials and compounds, stem cells, cell factors, platelet-rich plasma, exosomes, physical therapy, and other technologies have been widely used in the study of promoting tendon-bone healing. This review provides a comprehensive summary of strategies used to promote tendon-bone healing and analyses relevant preclinical and clinical studies. The potential application value of these strategies in promoting tendon-bone healing was also discussed.

3D printing of cell-delivery scaffolds for tissue regeneration

Tissue engineering strategy that combine biomaterials with living cells has shown special advantages in tissue regeneration and promoted the development of regenerative medicine. In particular, the rising of 3D printing technology further enriched the structural design and composition of tissue engineering scaffolds, which also provided convenience for cell loading and cell delivery of living cells. In this review, two types of cell-delivery scaffolds for tissue regeneration, including 3D printed scaffolds with subsequent cell-seeding and 3D cells bioprinted scaffolds, are mainly reviewed. We devote a major part to present and discuss the recent advances of two 3D printed cell-delivery scaffolds in regeneration of various tissues, involving bone, cartilage, skin tissues etc. Although two types of 3D printed cell-delivery scaffolds have some shortcomings, they do have generally facilitated the exploration of tissue engineering scaffolds in multiple tissue regeneration. It is expected that 3D printed cell-delivery scaffolds will be further explored in function mechanism of seeding cells in vivo, precise mimicking of complex tissues and even organ reconstruction under the cooperation of multiple fields in future.

Easily attainable and low immunogenic stem cells from exfoliated deciduous teeth enhanced the in vivo bone regeneration ability of gelatin/bioactive glass microsphere composite scaffolds

Repair of critical-size bone defects remains a considerable challenge in the clinic. The most critical cause for incomplete healing is that osteoprogenitors cannot migrate to the central portion of the defects. Herein, stem cells from exfoliated deciduous teeth (SHED) with the properties of easy attainability and low immunogenicity were loaded into gelatin/bioactive glass (GEL/BGM) scaffolds to construct GEL/BGM + SHED engineering scaffolds. An in vitro study showed that BGM could augment the osteogenic differentiation of SHED by activating the AMPK signaling cascade, as confirmed by the elevated expression of osteogenic-related genes, and enhanced ALP activity and mineralization formation in SHED. After implantation in the critical bone defect model, GEL/BGM + SHED scaffolds exhibited low immunogenicity and significantly enhanced new bone formation in the center of the defect. These results indicated that GEL/BGM + SHED scaffolds present a new promising strategy for critical-size bone healing.

Enhanced In Vitro Biocompatible Polycaprolactone/Nano-Hydroxyapatite Scaffolds with Near-Field Direct-Writing Melt Electrospinning Technology

Polycaprolactone (PCL) scaffold is a common biological material for tissue engineering, owing to its good biocompatibility, biodegradability and plasticity. However, it is not suitable for osteoblast adhesion and regeneration of bone tissue due to its non-biological activity, poor mechanical strength, slow degradation speed, smooth surface and strong hydrophobicity. To improve the mechanical properties and biocompatibility of PCL scaffold, the PCL/nHA scaffolds were prepared by melting and blending different proportions of nano-hydroxyapatite (nHA) with PCL by the near-field direct-writing melt electrospinning technology in this study. The morphology, porosity, mechanical properties and in vitro biocompatibility of the PCL/nHA scaffolds were studied. The results showed that when the proportion of nHA was less than or equal to 25%, PCL/nHA composite scaffolds were easily formed in which bone marrow mesenchymal stem cells proliferated successfully. When the proportion of nHA was 15%, the PCL/nHA composite scaffolds had excellent structural regularity, good fiber uniformity, outstanding mechanical stability and superior biocompatibility. The PCL/nHA composite scaffolds were ideal scaffold materials, which would broaden their applications for bone tissue engineering.

Influences of Process Parameters of Near-Field Direct-Writing Melt Electrospinning on Performances of Polycaprolactone/Nano-Hydroxyapatite Scaffolds

In this paper, near-field direct-writing melt electrospinning technology was employed to fabricate a polycaprolactone/nano-hydroxyapatite (PCL/nHA) scaffold for future applications in tissue engineering. The influences of different fabrication parameters on the structural characteristics, mechanical properties, and thermal stability of the scaffolds were discussed. It was found that the moving speed of the receiving plate had the most significant effect on the scaffold performance, followed by the receiving distance and spinning voltage. The results also showed that these process parameters affected the fiber diameter, corresponding coefficient of variation, porosity of the composite scaffolds, and mechanical properties of the samples, including the tensile strength and fiber peeling strength. Moreover, the process parameters could influence the thermal degradation performance and melting process. Although the mass loss of the composite scaffolds was not obvious after degradation, the mechanical performance degraded severely. It was concluded that the more appropriate process parameters for preparing PCL/nHA scaffolds were a spinning voltage of -4 kV, receiving distance of 4 mm, moving speed of receiving plate of 5 mm/s, and melt temperature of 130 °C. This study proved that near-field direct-writing melt electrospinning technology is a good method to obtain PCL/nHA composite scaffolds with an excellent mechanical properties and desired morphology for future tissue engineering applications.

Bioinspired Protein/Peptide Loaded 3D Printed PLGA Scaffold Promotes Bone Regeneration

Background: This study was aimed to investigate the effect of three dimensional (3D)printed poly lactide-co-glycolide (PLGA) scaffolds combined with Gly-Phe-Hyp-Gly-Arg (GFOGER) and bone morphogenetic protein 9 (BMP-9) on the repair of large bone defects.

Methods: 3D printing method was used to produce PLGA scaffolds, and the sample was viewed by both optical microscopy and SEM, XRD analysis, water absorption and compressive strength analysis, etc. The rabbits were divided into six groups randomly and bone defect models were constructed (6 mm in diameter and 9 mm in depth): control group (n = 2), sham group (n = 4), model group (n = 4) and model + scaffold group (n = 4 rabbits for each group, 0%,2% and 4%). The rabbits were sacrificed at the 4th and 12th weeks after surgery, and the samples were collected for quantitative analysis of new bone mineral density by micro-CT, histopathological observation, immunohistochemistry and Western blot to detect the protein expression of osteoblast-related genes.

Results: This scaffold presented acceptable mechanical properties and slower degradation rates. After surface modification with GFOGER peptide and BMP-9, the scaffold demonstrated enhanced new bone mineral deposition and density over the course of a 12 week in vivo study. Histological analysis and WB confirmed that this scaffold up-regulated the expression of Runx7, OCN, COL-1 and SP7, contributing to the noted uniform trabeculae formation and new bone regeneration.

Conclusions: The application of this strategy in the manufacture of composite scaffolds provided extensive guidance for the application of bone tissue engineering.

Advances in Stem Cell Therapies for Rotator Cuff Injuries

Rotator cuff injury is a common upper extremity musculoskeletal disease that may lead to persistent pain and functional impairment. Despite the clinical outcomes of the surgical procedures being satisfactory, the repair of the rotator cuff remains problematic, such as through failure of healing, adhesion formation, and fatty infiltration. Stem cells have high proliferation, strong paracrine action, and multiple differentiation potential, which promote tendon remodeling and fibrocartilage formation and increase biomechanical strength. Additionally, stem cell-derived extracellular vesicles (EVs) can increase collagen synthesis and inhibit inflammation and adhesion formation by carrying regulatory proteins and microRNAs. Therefore, stem cell-based therapy is a promising therapeutic strategy that has great potential for rotator cuff healing. In this review, we summarize the advances of stem cells and stem cell-derived EVs in rotator cuff repair and highlight the underlying mechanism of stem cells and stem cell-derived EVs and biomaterial delivery systems. Future studies need to explore stem cell therapy in combination with cellular factors, gene therapy, and novel biomaterial delivery systems.

Application of 3D-Printed, PLGA-Based Scaffolds in Bone Tissue Engineering

Polylactic acid–glycolic acid (PLGA) has been widely used in bone tissue engineering due to its favorable biocompatibility and adjustable biodegradation. 3D printing technology can prepare scaffolds with rich structure and function, and is one of the best methods to obtain scaffolds for bone tissue repair. This review systematically summarizes the research progress of 3D-printed, PLGA-based scaffolds. The properties of the modified components of scaffolds are introduced in detail. The influence of structure and printing method change in printing process is analyzed. The advantages and disadvantages of their applications are illustrated by several examples. Finally, we briefly discuss the limitations and future development direction of current 3D-printed, PLGA-based materials for bone tissue repair.

Narrative review of gene modification: applications in three-dimensional (3D) bioprinting

Objective

This article focused on the application scenarios of three-dimensional (3D) bioprinting and gene-editing technology in various medical fields, including gene therapy, tissue engineering, tumor microenvironment simulation, tumor model construction, cancer regulation and expression, osteogenesis, and skin and vascular regeneration, and summarizing its development prospects and shortcomings.

Background

3D bioprinting is a process based on additive manufacturing that uses biological materials as the microenvironment living cells. The scaffolds and carriers manufactured by 3D bioprinting technology provide a safe, efficient, and economical platform for genes, cells, and biomolecules. Gene modification refers to replacing, splicing, silencing, editing, controlling or inactivating genes and delivering new genes. The combination of this technology that changes cell function or cell fate or corrects endogenous mutations and 3D bioprinting technology has been widely used in various medical field.

Methods

We conducted a literature search for papers published up to March 2021 on the gene modification combined with 3D bioprinting in various medical fields via PubMed, Web of Science, China National Knowledge Infrastructure (CNKI). The following medical subject heading terms were included for a MEDLINE search: “3D printing/gene editing”, “3D printing/genetic modification”, “3D printing/seed cell”, “bioprinting/gene editing”, “bioprinting/genetic modification”, “bioprinting/seed cell”, “scaffold/gene editing”, “scaffold/genetic modification”, “scaffold/seed cell”, “gene/scaffold”, “gene/bioprinting”, “gene/3D printing”. Quantitative and qualitative data was extracted through interpretation of each article.

Conclusions

We have reviewed the application scenarios of 3D bioprinting and gene-editing technology in various medical fields, it provides an efficient and accurate delivery system for personalized tumor therapy, enhancing the targeting effect while maintaining the integrity of the fabricated structure. It exhibits significant application potential in developing tumor drugs. In addition, scaffolds obtained via 3D bioprinting provide gene therapy applications for skin and bone healing and repair and inducing stem cell differentiation. It also considers the future development direction in this field, such as the emergence and development of gene printing, 4D printing. The combination of nanotechnology and gene printing may provide a new way for future disease research and treatment.

Unsupervised Machine Learning-Based Analysis of Clinical Features, Bone Mineral Density Features and Medical Care Costs of Rotator Cuff Tears

Purpose

We aim to present unsupervised machine learning-based analysis of clinical features, bone mineral density (BMD) features, and medical care costs of Rotator cuff tears (RCT).

Patients and Methods

Fifty-three patients with RCT were reviewed, the clinical features, BMD features, and medical care costs were collected and analyzed by descriptive statistics. Furtherly, unsupervised machine learning (UML) algorithm was used for dimensionality reduction and cluster analysis of the RCT data.

Results

There were 26 males and 27 females. The patients were divided into four subgroups using the UML algorithm. There were significant differences among four subgroups regarding trauma exposure, full-thickness supraspinatus tendon tears, infraspinatus tendon tear, subscapularis tendon tear, BMD distribution, medial row anchors, lateral row anchors, total medical care costs, and consumables costs. We observed the highest frequency of trauma exposure, infraspinatus tendon tear, subscapularis tendon tear, osteoporosis, the highest number of medial row anchors, lateral row anchors, total medical care costs, and consumables costs in subgroup II.

Conclusion

The unsupervised machine learning-based analysis of RCT can provide clinically meaningful classification, which shows good interpretability and contribute to a better understanding of RCT. The significance of the results is limited due to the small number of samples, a larger follow-up study is needed to confirm the encouraging results.

SOD2 overexpression in bone marrow‑derived mesenchymal stem cells ameliorates hepatic ischemia/reperfusion injury

Hepatic ischemia/reperfusion injury (HIRI) is a complex pathophysiological process that may develop after liver transplantation and resection surgery, as well as in uncontrolled clinical conditions. Bone marrow‑derived mesenchymal stem cells (BM‑MSCs) are potential targets for liver diseases. Thus, the present study aimed to investigate the effects of superoxide dismutase 2 (SOD2) overexpression in BM‑MSCs on HIRI by constructing a HIRI rat model. The adenoviral vector containing SOD2 and the corresponding control vector were designed and constructed, and SOD2‑overexpressing BM‑MSCs were injected into the tail vein of the rats. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, as well as pathological changes and the remnant liver regeneration rate were determined. The activities of SOD and glutathione peroxidase (GSH‑Px), and malondialdehyde (MDA) content were measured. Reactive oxygen species (ROS) were determined with 2',7'‑-dichlorofluorescein diacetate and measured via fluorescence microscopy. Cell apoptosis was assessed using TUNEL staining. Moreover, the expression levels of Bax, Bcl‑2 and caspase‑3 were detected via western blotting. SOD2‑overexpressing BM‑MSCs significantly reduced the elevation of serum AST and ALT levels. Furthermore, SOD2‑overexpressing BM‑MSCs enhanced SOD and GSH‑Px activities, and suppressed the production of MDA and ROS. Histopathological findings revealed that SOD2‑overexpressing BM‑MSCs decreased the number of TUNEL‑positive cells in the liver. It was also found that SOD2‑overexpressing BM‑MSCs promoted Bcl‑2 expression, but inhibited Bax and caspase‑3 expression in HIRI. Collectively, these findings suggest that SOD2‑overexpressing BM‑MSCs may provide therapeutic support in HIRI by inhibiting oxidative stress and hepatocyte apoptosis.

Biomaterials strategies to balance inflammation and tenogenesis for tendon repair

Adult tendon tissue demonstrates a limited regenerative capacity, and the natural repair process leaves fibrotic scar tissue with inferior mechanical properties. Surgical treatment is insufficient to provide the mechanical, structural, and biochemical environment necessary to restore functional tissue. While numerous strategies including biodegradable scaffolds, bioactive factor delivery, and cell-based therapies have been investigated, most studies have focused exclusively on either suppressing inflammation or promoting tenogenesis, which includes tenocyte proliferation, ECM production, and tissue formation. New biomaterials-based approaches represent an opportunity to more effectively balance the two processes and improve regenerative outcomes from tendon injuries. Biomaterials applications that have been explored for tendon regeneration include formation of biodegradable scaffolds presenting topographical, mechanical, and/or immunomodulatory cues conducive to tendon repair; delivery of immunomodulatory or tenogenic biomolecules; and delivery of therapeutic cells such as tenocytes and stem cells. In this review, we provide the biological context for the challenges in tendon repair, discuss biomaterials approaches to modulate the immune and regenerative environment during the healing process, and consider the future development of comprehensive biomaterials-based strategies that can better restore the function of injured tendon. STATEMENT OF SIGNIFICANCE: Current strategies for tendon repair focus on suppressing inflammation or enhancing tenogenesis. Evidence indicates that regulated inflammation is beneficial to tendon healing and that excessive tissue remodeling can cause fibrosis. Thus, it is necessary to adopt an approach that balances the benefits of regulated inflammation and tenogenesis. By reviewing potential treatments involving biodegradable scaffolds, biological cues, and therapeutic cells, we contrast how each strategy promotes or suppresses specific repair steps to improve the healing outcome, and highlight the advantages of a comprehensive approach that facilitates the clearance of necrotic tissue and recruitment of cells during the inflammatory stage, followed by ECM synthesis and organization in the proliferative and remodeling stages with the goal of restoring function to the tendon.

Recent advances in PLGA-based biomaterials for bone tissue regeneration

Bone regeneration is an interdisciplinary complex lesson, including but not limited to materials science, biomechanics, immunology, and biology. Having witnessed impressive progress in the past decades in the development of bone substitutes; however, it must be said that the most suitable biomaterial for bone regeneration remains an area of intense debate. Since its discovery, poly (lactic-co-glycolic acid) (PLGA) has been widely used in bone tissue engineering due to its good biocompatibility and adjustable biodegradability. This review systematically covers the past and the most recent advances in developing PLGA-based bone regeneration materials. Taking the different application forms of PLGA-based materials as the starting point, we describe each form's specific application and its corresponding advantages and disadvantages with many examples. We focus on the progress of electrospun nanofibrous scaffolds, three-dimensional (3D) printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds, and stents prepared by other traditional and emerging methods. Finally, we briefly discuss the current limitations and future directions of PLGA-based bone repair materials. STATEMENT OF SIGNIFICANCE: As a key synthetic biopolymer in bone tissue engineering application, the progress of PLGA-based bone substitute is impressive. In this review, we summarized the past and the most recent advances in the development of PLGA-based bone regeneration materials. According to the typical application forms and corresponding crafts of PLGA-based substitutes, we described the development of electrospinning nanofibrous scaffolds, 3D printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds and scaffolds fabricated by other manufacturing process. Finally, we briefly discussed the current limitations and proposed the newly strategy for the design and fabrication of PLGA-based bone materials or devices.

Tendon tissue engineering: Cells, growth factors, scaffolds and production techniques

Tendon injuries are a global health problem that affects millions of people annually. The properties of tendons make their natural rehabilitation a very complex and long-lasting process. Thanks to the development of the fields of biomaterials, bioengineering and cell biology, a new discipline has emerged, tissue engineering. Within this discipline, diverse approaches have been proposed. The obtained results turn out to be promising, as increasingly more complex and natural tendon-like structures are obtained. In this review, the nature of the tendon and the conventional treatments that have been applied so far are underlined. Then, a comparison between the different tendon tissue engineering approaches that have been proposed to date is made, focusing on each of the elements necessary to obtain the structures that allow adequate regeneration of the tendon: growth factors, cells, scaffolds and techniques for scaffold development. The analysis of all these aspects allows understanding, in a global way, the effect that each element used in the regeneration of the tendon has and, thus, clarify the possible future approaches by making new combinations of materials, designs, cells and bioactive molecules to achieve a personalized regeneration of a functional tendon.

A Systematic Review of Tissue Engineering Scaffold in Tendon Bone Healing in vivo

Background: Tendon-bone healing is an important factor in determining the success of ligament reconstruction. With the development of biomaterials science, the tissue engineering scaffold plays an extremely important role in tendon-bone healing and bone tissue engineering. Materials and Methods: Electronic databases (PubMed, Embase, and the Web of Science) were systematically searched for relevant and qualitative studies published from 1 January 1990 to 31 December 2019. Only original articles that met eligibility criteria and evaluated the use of issue engineering scaffold especially biomaterials in tendon bone healing in vivo were selected for analysis. Results: The search strategy identified 506 articles, and 27 studies were included for full review including two human trials and 25 animal studies. Fifteen studies only used biomaterials like PLGA, collage, PCL, PLA, and PET as scaffolds to repair the tendon-bone defect, on this basis, the rest of the 11 studies using biological interventions like cells or cell factors to enhance the healing. The adverse events hardly ever occurred, and the tendon bone healing with tissue engineering scaffold was effective and superior, which could be enhanced by biological interventions. Conclusion: Although a number of tissue engineering scaffolds have been developed and applied in tendon bone healing, the researches are mainly focused on animal models which are with limitations in clinical application. Since the efficacy and safety of tissue engineering scaffold has been proved, and can be enhanced by biological interventions, substantial clinical trials remain to be done, continued progress in overcoming current tissue engineering challenges should allow for successful clinical practice.

Biomimetic strategies for tendon/ligament-to-bone interface regeneration

Tendon/ligament-to-bone healing poses a formidable clinical challenge due to the complex structure, composition, cell population and mechanics of the interface. With rapid advances in tissue engineering, a variety of strategies including advanced biomaterials, bioactive growth factors and multiple stem cell lineages have been developed to facilitate the healing of this tissue interface. Given the important role of structure-function relationship, the review begins with a brief description of enthesis structure and composition. Next, the biomimetic biomaterials including decellularized extracellular matrix scaffolds and synthetic-/natural-origin scaffolds are critically examined. Then, the key roles of the combination, concentration and location of various growth factors in biomimetic application are emphasized. After that, the various stem cell sources and culture systems are described. At last, we discuss unmet needs and existing challenges in the ideal strategies for tendon/ligament-to-bone regeneration and highlight emerging strategies in the field.

The 3D-Printed PLGA Scaffolds Loaded with Bone Marrow-Derived Mesenchymal Stem Cells Augment the Healing of Rotator Cuff Repair in the Rabbits

The healing of tendon-bone in the rotator cuff is featured by the formation of the scar tissues in the interface after repair. This study aimed to determine if the 3D-printed poly lactic-co-glycolic acid (PLGA) scaffolds loaded with bone marrow-derived mesenchymal stem cells (BMSCs) could augment the rotator cuff repair in the rabbits. PLGA scaffolds were generated by the 3D-printed technology; Cell Counting Kit-8 assay evaluated the proliferation of BMSCs; the mRNA and protein expression levels were assessed by quantitative real-time polymerase chain reaction and western blot, respectively; immunohistology evaluated the rotator cuff repair; biomechanical characteristics of the repaired tissues were also assessed. 3D-printed PLGA scaffolds showed good biocompatibility without affecting the proliferative ability of BMSCs. BMSCs-PLGA scaffolds implantation enhanced the cell infiltration into the tendon-bone injunction at 4 weeks after implantation and improved the histology score in the tendon tissues after implantation. The mRNA expression levels of collagen I, III, tenascin, and biglycan were significantly higher in the scaffolds + BMSCs group at 4 weeks post-implantation than that in the scaffolds group. At 8 and 12 weeks after implantation, the biglycan mRNA expression level in the BMSCs-PLGA scaffolds group was significantly lower than that in the scaffolds group. BMSCs-PLGA scaffolds implantation enhanced collagen formation and increased collagen dimeter in the tendon-bone interface. The biomechanical analysis showed that BMSCs-PLGA scaffolds implantation improved the biomechanical properties of the regenerated tendon. The combination of 3D-printed PLGA scaffolds with BMSCs can augment the tendon-bone healing in the rabbit rotator cuff repair model.

Recent Developments of Biomaterials for Additive Manufacturing of Bone Scaffolds

Recent years have witnessed surging demand for bone repair/regeneration implants due to the increasing number of bone defects caused by trauma, cancer, infection, and arthritis worldwide. In addition to bone autografts and allografts, biomaterial substitutes have been widely used in clinical practice. Personalized implants with precise and personalized control of shape, porosity, composition, surface chemistry, and mechanical properties will greatly facilitate the regeneration of bone tissue and satiate the clinical needs. Additive manufacturing (AM) techniques, also known as 3D printing, are drawing fast growing attention in the fabrication of implants or scaffolding materials due to their capability of manufacturing complex and irregularly shaped scaffolds in repairing bone defects in clinical practice. This review aims to provide a comprehensive overview of recent progress in the development of materials and techniques used in the additive manufacturing of bone scaffolds. In addition, clinical application, pre-clinical trials and future prospects of AM based bone implants are also summarized and discussed.

3D printing of multilayered scaffolds for rotator cuff tendon regeneration

Repairing massive rotator cuff tendon defects remains a challenge due to the high retear rate after surgical intervention. 3D printing has emerged as a promising technique that enables the fabrication of engineered tissues with heterogeneous structures and mechanical properties, as well as controllable microenvironments for tendon regeneration. In this study, we developed a new strategy for rotator cuff tendon repair by combining a 3D printed scaffold of polylactic-co-glycolic acid (PLGA) with cell-laden collagen-fibrin hydrogels. We designed and fabricated two types of scaffolds: one featuring a separate layer-by-layer structure and another with a tri-layered structure as a whole. Uniaxial tensile tests showed that both types of scaffolds had improved mechanical properties compared to single-layered PLGA scaffolds. The printed scaffold with collagen-fibrin hydrogels effectively supported the growth, proliferation, and tenogenic differentiation of human adipose-derived mesenchymal stem cells. Subcutaneous implantation of the multilayered scaffolds demonstrated their excellent in vivo biocompatibility. This study demonstrates the feasibility of 3D printing multilayered scaffolds for application in rotator cuff tendon regeneration.