The past, present and future of ligament regenerative engineering

[Research progress on early postoperative pain management strategies after arthroscopic anterior cruciate ligament reconstruction]

Objective

To summarize the early postoperative pain management strategies for anterior cruciate ligament reconstruction (ACLR), and to select a reasonable and effective pain management plan to promote functional rehabilitation after ACLR.

Methods

The literature about the early postoperative pain management strategies of ACLR both domestically and internationally in recent years was extensiverly reviewed, and the effects of improving postoperative pain were reviewed.

Results

Currently, physical therapy and oral medication have advantages such as economy and simplicity, but the effect of improving postoperative pain is not satisfactory, often requires a combination of intravenous injection or intravenous pump, which is also a common way to relieve pain. However, in order to meet the analgesic needs of patients, the amount of analgesic drugs used is often large, which increases the incidence of various adverse reactions. Local infiltration analgesia (LIA), including periarticular or intra-articular injection of drugs, can significantly improve the early postoperative pain of ACLR, and achieve similar postoperative effectiveness as nerve block. LIA can be used as an analgesic technique instead of nerve block, and avoid the corresponding weakness of innervated muscles caused by nerve block, which increases the risk of postoperative falls. Many studies have confirmed that LIA can alleviate postoperative early pain in ACLR, especially the analgesic effects of periarticular injection are more satisfactory. It can also avoid the risk of cartilage damage caused by intra-articular injection. However, the postoperative analgesic effect and timeliness still need to be improved. It is possible to consider combining multimodal mixed drug LIA (combined with intra-articular and periarticular) with other pain intervention methods to exert a synergistic effect, in order to avoid the side effects and risks brought by single drugs or single administration route. LIA is expected to become one of the most common methods for relieving postoperative early pain in ACLR.

Conclusion

Early pain after arthroscopic ACLR still affects the further functional activities of patients, and all kinds of analgesic methods can achieve certain effectiveness, but there is no unified standard at present, and the advantages and disadvantages of various analgesic methods need further research.

Advancements in scaffold for treating ligament injuries; in vitro evaluation

Tendon/ligament (T/L) injuries are a worldwide health problem that affects millions of people annually. Due to the characteristics of tendons, the natural rehabilitation of their injuries is a very complex and lengthy process. Surgical treatment of a T/L injury frequently necessitates using autologous or allogeneic grafts or synthetic materials. Nonetheless, these alternatives have limitations in terms of mechanical properties and histocompatibility, and they do not permit the restoration of the original biological function of the tissue, which can negatively impact the patient's quality of life. It is crucial to find biological materials that possess the necessary properties for the successful surgical treatment of tissues and organs. In recent years, the in vitro regeneration of tissues and organs from stem cells has emerged as a promising approach for preparing autologous tissue and organs, and cell culture scaffolds play a critical role in this process. However, the biological traits and serviceability of different materials used for cell culture scaffolds vary significantly, which can impact the properties of the cultured tissues. Therefore, this review aims to analyze the differences in the biological properties and suitability of various materials based on scaffold characteristics such as cell compatibility, degradability, textile technologies, fiber arrangement, pore size, and porosity. This comprehensive analysis provides valuable insights to aid in the selection of appropriate scaffolds for in vitro tissue and organ culture.

[Research progress on bioactive strategies for promoting tendon graft healing after anterior cruciate ligament reconstruction]

Objective

To review the bioactive strategies that enhance tendon graft healing after anterior cruciate ligament reconstruction (ACLR), and to provide insights for improving the therapeutic outcomes of ACLR.

Methods

The domestic and foreign literature related to the bioactive strategies for promoting the healing of tendon grafts after ACLR was extensively reviewed and summarized.

Results

At present, there are several kinds of bioactive materials related to tendon graft healing after ACLR: growth factors, cells, biodegradable implants/tissue derivatives. By constructing a complex interface simulating the matrix, environment, and regulatory factors required for the growth of native anterior cruciate ligament (ACL), the growth of transplanted tendons is regulated at different levels, thus promoting the healing of tendon grafts. Although the effectiveness of ACLR has been significantly improved in most studies, most of them are still limited to the early stage of animal experiments, and there is still a long way to go from the real clinical promotion. In addition, limited by the current preparation technology, the bionics of the interface still stays at the micron and millimeter level, and tends to be morphological bionics, and the research on the signal mechanism pathway is still insufficient.

Conclusion

With the further study of ACL anatomy, development, and the improvement of preparation technology, the research of bioactive strategies to promote the healing of tendon grafts after ACLR is expected to be further promoted.

Bioactive Nanostructured Scaffold-Based Approach for Tendon and Ligament Tissue Engineering

An effective therapeutic strategy to treat tendon or ligament injury continues to be a clinical challenge due to the limited natural healing capacity of these tissues. Furthermore, the repaired tendons or ligaments usually possess inferior mechanical properties and impaired functions. Tissue engineering can restore the physiological functions of tissues using biomaterials, cells, and suitable biochemical signals. It has produced encouraging clinical outcomes, forming tendon or ligament-like tissues with similar compositional, structural, and functional attributes to the native tissues. This paper starts by reviewing tendon/ligament structure and healing mechanisms, followed by describing the bioactive nanostructured scaffolds used in tendon and ligament tissue engineering, with emphasis on electrospun fibrous scaffolds. The natural and synthetic polymers for scaffold preparation, as well as the biological and physical cues offered by incorporating growth factors in the scaffolds or by dynamic cyclic stretching of the scaffolds, are also covered. It is expected to present a comprehensive clinical, biological, and biomaterial insight into advanced tissue engineering-based therapeutics for tendon and ligament repair.

Oxygen-Generating Biomaterials for Translational Bone Regenerative Engineering

Successful regeneration of critical-size defects remains one of the significant challenges in regenerative engineering. These large-scale bone defects are difficult to regenerate and are often reconstructed with matrices that do not provide adequate oxygen levels to stem cells involved in the regeneration process. Hypoxia-induced necrosis predominantly occurs in the center of large matrices since the host tissue's local vasculature fails to provide sufficient nutrients and oxygen. Indeed, utilizing oxygen-generating materials can overcome the central hypoxic region, induce tissue in-growth, and increase the quality of life for patients with extensive tissue damage. This article reviews recent advances in oxygen-generating biomaterials for translational bone regenerative engineering. We discussed different oxygen-releasing and delivery methods, fabrication methods for oxygen-releasing matrices, biology, oxygen's role in bone regeneration, and emerging new oxygen delivery methods that could potentially be used for bone regenerative engineering.

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 Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

Nanofiber Scaffold Based on Polylactic Acid-Polycaprolactone for Anterior Cruciate Ligament Injury

Anterior Cruciate Ligament (ACL) injuries are becoming more prevalent in athletes. Anterior Cruciatum Ligament Reconstruction (ACLR) surgery was used to treat ACL injuries and resulted in a recurrence rate of 94% due to the biomechanically repaired tissue being weaker than the original tissue. As a result, biodegradable artificial ligaments must be developed that can withstand mechanical stress during neoligament formation and stabilize the ACL. The purpose of this study is to determine the effect of composition variations in polylactic acid (PLA) and polycaprolactone (PCL) used as ACL nanofiber scaffolds on ultimate tensile strength (UTS) and modulus of elasticity, fiber diameter, cytotoxicity level, and degradation level, as well as the PLA-PCL concentration that provides the best value as an ACL scaffold. Electrospinning was used to fabricate the nanofiber scaffold with the following PLA-PCL compositions: A (100:0), B (85:15), C (80:20), D (70:30), and E (0:100) (wt%). The functional group test revealed no new peaks in any of the samples, and the ester group could be identified in the C-O bond at wave numbers 1300-1100 cm-1 and in the C=O bond at wave numbers 1750-1730 cm-1. The average fiber diameter, as determined by SEM morphology, is between 1000 and 2000 nm. The unbraided sample had a UTS range of 1.578-4.387 MPa and an elastic modulus range of 8.351-141.901 MPa, respectively, whereas the braided sample had a range of 0.879-1.863 MPa and 2.739-4.746 MPa. The higher the PCL composition, the lower the percentage of viable cells and the faster the sample degrades. All samples had a cell viability percentage greater than 60%, and samples C, D, and E had a complete degradation period greater than six months. The ideal scaffold, Sample C, was composed of PLA-PCL 80:20 (wt%), had an average fiber diameter of 827 ± 271 nm, a living cell percentage of 97.416 ± 5.079, and a degradation time of approximately 219 days.

Melt-Spun, Cross-Section Modified Polycaprolactone Fibers for Use in Tendon and Ligament Tissue Engineering

Tissue Engineering is considered a promising route to address existing deficits of autografts and permanent synthetic prostheses for tendons and ligaments. However, the requirements placed on the scaffold material are manifold and include mechanical, biological and degradation-related aspects. In addition, scalable processes and FDA-approved materials should be applied to ensure the transfer into clinical practice. To accommodate these aspects, this work focuses on the high-scale fabrication of high-strength and highly oriented polycaprolactone (PCL) fibers with adjustable cross-sectional geometry and degradation kinetics applying melt spinning technology. Four different fiber cross-sections were investigated to account for potential functionalization and cell growth guidance. Mechanical properties and crystallinity were studied for a 24-week exposure to phosphate-buffered saline (PBS) at 37 °C. PCL fibers were further processed into scaffolds using multistage circular braiding with three different hierarchical structures. One structure was selected based on its morphology and scaled up in thickness to match the requirements for a human anterior cruciate ligament (ACL) replacement. Applying a broad range of draw ratios (up to DR9.25), high-strength PCL fibers with excellent tensile strength (up to 69 cN/tex) could be readily fabricated. The strength retention after 24 weeks in PBS at 37 °C was 83–93%. The following braiding procedure did not affect the scaffolds’ mechanical properties as long as the number of filaments and the braiding angle remained constant. Up-scaled PCL scaffolds resisted loads of up to 4353.88 ± 37.30 N, whilst matching the stiffness of the human ACL (111–396 N/mm). In conclusion, this work demonstrates the fabrication of highly oriented PCL fibers with excellent mechanical properties. The created fibers represent a promising building block that can be further processed into versatile textile implants for tissue engineering and regenerative medicine.

Second Generation of Tissue-Engineered Ligament Substitutes for Torn ACL Replacement: Adaptations for Clinical Applications

The anterior cruciate ligament (ACL) of the knee joint is one of the strongest ligaments of the body and is often the target of traumatic injuries. Unfortunately, its healing potential is limited, and the surgical options for its replacement are frequently associated with clinical issues. A bioengineered ACL (bACL) was developed using a collagen matrix, seeded with autologous cells and successfully grafted and integrated into goat knee joints. We hypothesize that, in order to reduce the cost and simplify the model, an acellular bACL can be used as a substitute for a torn ACL, and bone plugs can be replaced by endobuttons to fix the bACL in situ. First, acellular bACLs were successfully grafted in the goat model with 18% recovery of ultimate tensile strength 6 months after implantation (94 N/mm² vs. 520). Second, a bACL with endobuttons was produced and tested in an exvivo bovine knee model. The natural collagen scaffold of the bACL contributes to supporting host cell migration, growth and differentiation in situ post-implantation. Bone plugs were replaced by endobuttons to design a second generation of bACLs that offer more versatility as biocompatible grafts for torn ACL replacement in humans. A robust collagen bACL will allow solving therapeutic issues currently encountered by orthopedic surgeons such as donor-site morbidity, graft failure and post-traumatic osteoarthritis.

Ligament Regenerative Engineering: Braiding Scalable and Tunable Bioengineered Ligaments Using a Bench-Top Braiding Machine

Anterior cruciate ligament (ACL) injuries are common sports injuries that typically require surgical intervention. Autografts and allografts are used to replace damaged ligaments. The drawbacks of autografts and allografts, which include donor site morbidity and variability in quality, have spurred research in the development of bioengineered ligaments. Herein, the design and development of a cost-effective bench-top 3D braiding machine that fabricates scalable and tunable bioengineered ligaments is described. It was demonstrated that braiding angle and picks per inch can be controlled with the bench-top braiding machine. Pore sizes within the reported range needed for vascularization and bone regeneration are demonstrated. By considering a one-to-one linear relationship between cross-sectional area and peak load, the bench-top braiding machine can theoretically fabricate bioengineered ligaments with a peak load that is 9× greater than the human ACL. This bench-top braiding machine is generalizable to all types of yarns and may be used for regenerative engineering applications.

Rupture, reconstruction, and rehabilitation: A multi-disciplinary review of mechanisms for central nervous system adaptations following anterior cruciate ligament injury

BACKGROUND

Despite surgical reconstruction and extensive rehabilitation, persistent quadriceps inhibition, gait asymmetry, and functional impairment remain prevalent in patients after anterior cruciate ligament (ACL) injury. A combination of reports have suggested underlying central nervous system adaptations in those after injury govern long-term neuromuscular impairments. The classic assumption has been to attribute neurophysiologic deficits to components of injury, but other factors across the continuum of care (e.g. surgery, perioperative analgesia, and rehabilitative strategies) have been largely overlooked.

OBJECTIVE

This review provides a multidisciplinary perspective to 1) provide a narrative review of studies reporting neuroplasticity following ACL injury in order to inform clinicians of the current state of literature and 2) provide a mechanistic framework of neurophysiologic deficits with potential clinical implications across all phases of injury and recovery (injury, surgery, and rehabilitation) RESULTS: Studies using a variety of neurophysiologic modalities have demonstrated peripheral and central nervous system adaptations in those with prior ACL injury. Longitudinal investigations suggest neurophysiologic changes at spinal-reflexive and corticospinal pathways follow a unique timecourse across injury, surgery, and rehabilitation.

CONCLUSION

Clinicians should consider the unique injury, surgery, anesthesia, and rehabilitation on central nervous system adaptations. Therapeutic strategies across the continuum of care may be beneficial to mitigate maladaptive neuroplasticity in those after ACL injury.

Enhancing the Surface Properties of a Bioengineered Anterior Cruciate Ligament Matrix for Use with Point-of-Care Stem Cell Therapy

We have previously developed a poly(L-lactic) acid (PLLA) bioengineered anterior cruciate ligament (ACL) matrix that has demonstrated enhanced healing when seeded with primary ACL cells prior to implantation in a rabbit model, as compared with the matrix alone. This suggests that improving cell adhesion on the matrix may beneficially affect the healing response and long-term performance of the bioengineered ACL matrix. One regenerative engineering approach involves enhancing the surface properties of the matrix to support cell adhesion and growth in combination with point-of-care stem cell therapy. Herein, we studied the cell adhesion properties of PLLA braided microfiber matrices enhanced through the physical adsorption of fibronectin and air plasma treatment. We evaluated the kinetics and binding efficiency of fibronectin onto matrices at three time points and three fibronectin concentrations. Incubating the matrix for 120 min in a solution of 25 mg mL^-1 fibronectin achieved the greatest binding efficiency to the matrix and cellular adhesion. Exposing the matrices to air plasma treatment for 5 min before fibronectin adsorption significantly enhanced the cell adhesion of rabbit bone marrow-derived mesenchymal stem cells (R-BMMSCs) 24 h post cell seeding. Finally, cellular proliferation was monitored for up to 21 d, the matrices were exposed to air plasma treatment, and fibronectin adsorption was found to result in enhanced cell number. These findings suggest that exposure to air plasma treatment and fibronectin adsorption enhances the cellular adhesion of PLLA braided microfiber matrices and may improve the clinical efficacy of the matrix in combination with point-of-care stem cell therapies.

Mechanically superior matrices promote osteointegration and regeneration of anterior cruciate ligament tissue in rabbits

The gold standard treatment for anterior cruciate ligament (ACL) reconstruction is the use of tendon autografts and allografts. Limiting factors for this treatment include donor site morbidity, potential disease transmission, and variable graft quality. To address these limitations, we previously developed an off-the-shelf alternative, a poly(l-lactic) acid (PLLA) bioengineered ACL matrix, and demonstrated its feasibility to regenerate ACL tissue. This study aims to 1) accelerate the rate of regeneration using the bioengineered ACL matrix by supplementation with bone marrow aspirate concentrate (BMAC) and growth factors (BMP-2, FGF-2, and FGF-8) and 2) increase matrix strength retention. Histological evaluation showed robust tissue regeneration in all groups. The presence of cuboidal cells reminiscent of ACL fibroblasts and chondrocytes surrounded by an extracellular matrix rich in anionic macromolecules was up-regulated in the BMAC group. This was not observed in previous studies and is indicative of enhanced regeneration. Additionally, intraarticular treatment with FGF-2 and FGF-8 was found to suppress joint inflammation. To increase matrix strength retention, we incorporated nondegradable fibers, polyethylene terephthalate (PET), into the PLLA bioengineered ACL matrix to fabricate a "tiger graft." The tiger graft demonstrated the greatest peak loads among the experimental groups and the highest to date in a rabbit model. Moreover, the tiger graft showed superior osteointegration, making it an ideal bioengineered ACL matrix. The results of this study illustrate the beneficial effect bioactive factors and PET incorporation have on ACL regeneration and signal a promising step toward the clinical translation of a functional bioengineered ACL matrix.

Cruciate ligament healing and injury prevention in the age of regenerative medicine and technostress: homeostasis revisited

PURPOSE

This clinical concepts paper discusses the essential elements of cruciate ligament recuperation, micro-trauma repair, and remodeling.

METHODS

Cruciate ligament mechanobiology and tissue heterogeneity, anatomy and vascularity, and synovial membrane and fluid functions are discussed in relationship to deficiency-induced inflammatory responses, nervous and immune system function, recuperation, repair and remodeling, and modern threats to homeostasis.

RESULTS

Cruciate ligament surgical procedures do not appreciate the vital linked functions of the central, peripheral, and autonomic nervous systems and immune system function on knee ligament injury recuperation, micro-trauma repair, and remodeling. Enhanced knowledge of these systems could provide innovative ways to decrease primary non-contact knee injury rates and improve outcomes following reconstruction or primary repair.

CONCLUSIONS

Restoration of knee joint homeostasis is essential to cruciate ligament recuperation, micro-trauma repair, and remodeling. The nervous and immune systems are intricately involved in this process. Varying combinations of high-intensity training, under-recovery, technostress, and environmental pollutants (including noise) regularly expose many athletically active individuals to factors that abrogate the environment needed for cruciate ligament recuperation, micro-trauma repair, and remodeling. Current sports training practice, lifestyle psychobehaviors, and environmental factors combine to increase both primary non-contact knee injury risk and the nervous and immune system dysregulation that lead to poor sleep, increased anxiety, and poorly regulated hormone and cytokine levels. These factors may create a worst-case scenario leading to poor ligament recuperation, micro-trauma repair, and remodeling. Early recognition and modification of these factors may decrease knee ligament injury rates and improve cruciate ligament repair or reconstruction outcomes.

LEVEL OF EVIDENCE

V.

Biodegradable polymer nanocomposites for ligament/tendon tissue engineering

Ligaments and tendons are fibrous tissues with poor vascularity and limited regeneration capacity. Currently, a ligament/tendon injury often require a surgical procedure using auto- or allografts that present some limitations. These inadequacies combined with the significant economic and health impact have prompted the development of tissue engineering approaches. Several natural and synthetic biodegradable polymers as well as composites, blends and hybrids based on such materials have been used to produce tendon and ligament scaffolds. Given the complex structure of native tissues, the production of fiber-based scaffolds has been the preferred option for tendon/ligament tissue engineering. Electrospinning and several textile methods such as twisting, braiding and knitting have been used to produce these scaffolds. This review focuses on the developments achieved in the preparation of tendon/ligament scaffolds based on different biodegradable polymers. Several examples are overviewed and their processing methodologies, as well as their biological and mechanical performances, are discussed.

Evaluation of a bioengineered ACL matrix's osteointegration with BMP-2 supplementation

A poly (l-lactic) acid bioengineered anterior cruciate ligament (ACL) matrix has previously demonstrated the ability to support tissue regeneration in a rabbit ACL reconstruction model. The matrix was designed for optimal bone and ligament regeneration by developing a matrix with differential pore sizes in its bone and ligament compartments. Building upon past success, we designed a new bioengineered ACL matrix that is easier to install and can be used with endobutton fixation during ACL reconstruction. To achieve this, a new braiding procedure was developed to allow the matrix to be folded in half, making two-limbs, while maintaining its bone and ligament compartments. The osteointegration of the matrix with and without bone morphogenetic protein 2 (BMP-2) supplementation was evaluated in a rabbit ACL reconstruction model. Two doses of BMP-2 were evaluated, 1 and 10 μg, and delivered by saline injection into the bone tunnel at the end of surgery. A fibrous matrix-to-bone interface with occasional Sharpey’s fibers was the primary mode of osteointegration observed. The matrix was also found to support a fibrocartilage matrix-to-bone interface. In some cases, the presence of chondrocyte-like cells was observed at the aperture of the bone tunnel and the center of the matrix within the bone tunnel. Treatment with BMP-2 was associated with a trend towards smaller bone tunnel cross-sectional areas, and 1 μg of BMP-2 was found to significantly enhance osteoid seam width in comparison with no BMP-2 or 10 μg of BMP-2 treatment. Regenerated tissue was well organized within the bioengineered ACL matrix and aligned with the poly (l-lactic) acid fibers. Disorganized tissue was found between the two-limbs of the bioengineered ACL matrix and hypothesized to be due to a lack of structural scaffolding. This study suggests that the bioengineered ACL matrix can undergo similar modes of osteointegration as current autografts and allografts, and that BMP-2 treatment may enhance osteoblastic activity within the bone tunnels.

Advances in Tendon and Ligament Tissue Engineering: Materials Perspective

Introduction. Tendons are specialised, heterogeneous connective tissues, which represent a significant healthcare challenge after injury. Primary surgical repair is the gold standard modality of care; however, it is highly dependent on the extent of injuries. Tissue engineering represents an alternative solution for good tissue integration and regeneration. In this review, we look at the advanced biomaterial composites employed to improve cellular growth while providing appropriate mechanical properties for tendon and ligament repair. Methodology. Comprehensive literature searches focused on advanced composite biomaterials for tendon and ligament tissue engineering. Studies were categorised depending on the application. Results. In the literature, a range of natural and/or synthetic materials have been combined to produce composite scaffolds tendon and ligament tissue engineering. In vitro and in vivo assessment demonstrate promising cellular integration with sufficient mechanical strength. The biological properties were improved with the addition of growth factors within the composite materials. Most in vivo studies were completed in small-scale animal models. Conclusions. Advanced composite materials represent a promising solution to the challenges associated with tendon and ligament tissue engineering. Nevertheless, these approaches still demonstrate limitations, including the necessity of larger-scale animal models to ease future clinical translation and comprehensive assessment of tissue response after implantation.

Orthopaedic regenerative tissue engineering en route to the holy grail: disequilibrium between the demand and the supply in the operating room

Orthopaedic disorders are very frequent, globally found and often partially unresolved despite the substantial advances in science and medicine. Their surgical intervention is multifarious and the most favourable treatment is chosen by the orthopaedic surgeon on a case-by-case basis depending on a number of factors related with the patient and the lesion. Numerous regenerative tissue engineering strategies have been developed and studied extensively in laboratory through in vitro experiments and preclinical in vivo trials with various established animal models, while a small proportion of them reached the operating room. However, based on the available literature, the current strategies have not yet achieved to fully solve the clinical problems. Thus, the gold standards, if existing, remain unchanged in the clinics, notwithstanding the known limitations and drawbacks. Herein, the involvement of regenerative tissue engineering in the clinical orthopaedics is reviewed. The current challenges are indicated and discussed in order to describe the current disequilibrium between the needs and solutions made available in the operating room. Regenerative tissue engineering is a very dynamic field that has a high growth rate and a great openness and ability to incorporate new technologies with passion to edge towards the Holy Grail that is functional tissue regeneration. Thus, the future of clinical solutions making use of regenerative tissue engineering principles for the management of orthopaedic disorders is firmly supported by the clinical need.

A cell-laden hybrid fiber/hydrogel composite for ligament regeneration with improved cell delivery and infiltration

Ligament, a fibrous connective tissue between bones, is a unique tissue in human anatomy because it has complex viscoelastic properties and is very tough. Moreover, it is an important tissue for regeneration because frequent injuries occur, but there are limited types of substitutes that can be used as a tissue replacement. In this study, we present a stem cell-laden fiber/hydrogel composite structure with a layered fibrous structure, which can enhance cell infiltration, topographical cue and mechanical properties. It can promote cell viability, proliferation, and differentiation of the ligament phenotype with the help of a growth factor. The mechanical properties of the developed structure were experimentally identified using tensile tests, while cell viability and various functionalities were verified through culture tests using mesenchymal stem cells.