Clinical Application of Scaffolds for Partial Meniscus Replacement

3D printing of mechanically functional meniscal tissue equivalents using high concentration extracellular matrix inks

Decellularized extracellular matrix (dECM) has emerged as a promising biomaterial in the fields of tissue engineering and regenerative medicine due to its ability to provide specific biochemical and biophysical cues supportive of the regeneration of diverse tissue types. Such biomaterials have also been used to produce tissue-specific inks and bioinks for 3D printing applications. However, a major limitation associated with the use of such dECM materials is their poor mechanical properties, which limits their use in load-bearing applications such as meniscus regeneration. In this study, native porcine menisci were solubilized and decellularized using different methods to produce highly concentrated dECM inks of differing biochemical content and printability. All dECM inks displayed shear thinning and thixotropic properties, with increased viscosity and improved printability observed at higher pH levels, enabling the 3D printing of anatomically defined meniscal implants. With additional crosslinking of the dECM inks following thermal gelation at pH 11, it was possible to fabricate highly elastic meniscal tissue equivalents with compressive mechanical properties similar to the native tissue. These improved mechanical properties at higher pH correlated with the development of a denser network of smaller diameter collagen fibers. These constructs also displayed repeatable loading and unloading curves when subjected to long-term cyclic compression tests. Moreover, the printing of dECM inks at the appropriate pH promoted a preferential alignment of the collagen fibers. Altogether, these findings demonstrate the potential of 3D printing of highly concentrated meniscus dECM inks to produce mechanically functional and biocompatible implants for meniscal tissue regeneration. This approach could be applied to a wide variety of different biological tissues, enabling the 3D printing of tissue mimics with diverse applications from tissue engineering to surgical planning.

Regenerative Medicine for Equine Musculoskeletal Diseases

Simple Summary

Lameness due to musculoskeletal disease is the most common diagnosis in equine veterinary practice. Many of these orthopaedic disorders are chronic problems, for which no clinically satisfactory treatment exists. Thus, high hopes are pinned on regenerative medicine, which aims to replace or regenerate cells, tissues, or organs to restore or establish normal function. Some regenerative medicine therapies have already made their way into equine clinical practice mainly to treat tendon injures, tendinopathies, cartilage injuries and degenerative joint disorders with promising but diverse results. This review summarises the current knowledge of commonly used regenerative medicine treatments and critically discusses their use.

Abstract

Musculoskeletal injuries and chronic degenerative diseases commonly affect both athletic and sedentary horses and can entail the end of their athletic careers. The ensuing repair processes frequently do not yield fully functional regeneration of the injured tissues but biomechanically inferior scar or replacement tissue, causing high reinjury rates, degenerative disease progression and chronic morbidity. Regenerative medicine is an emerging, rapidly evolving branch of translational medicine that aims to replace or regenerate cells, tissues, or organs to restore or establish normal function. It includes tissue engineering but also cell-based and cell-free stimulation of endogenous self-repair mechanisms. Some regenerative medicine therapies have made their way into equine clinical practice mainly to treat tendon injures, tendinopathies, cartilage injuries and degenerative joint disorders with promising results. However, the qualitative and quantitative spatiotemporal requirements for specific bioactive factors to trigger tissue regeneration in the injury response are still unknown, and consequently, therapeutic approaches and treatment results are diverse. To exploit the full potential of this burgeoning field of medicine, further research will be required and is ongoing. This review summarises the current knowledge of commonly used regenerative medicine treatments in equine patients and critically discusses their use.

Muscle strength but not balance improves after arthroscopic biodegradable polyurethane meniscus scaffold application

PURPOSE

This study aimed to assess the impact of biodegradable polyurethane meniscus scaffold implantation (BPMSI) on muscle strength and balance in comparison with the healthy contralateral knee in patients with irreparable medial meniscus defect.

METHODS

This observational and prospective case-cohort study was conducted with patients who had irreparable meniscal defects and underwent arthroscopic meniscus scaffold implantation. Surgeries were carried out on the medial meniscus of 16 right and 4 left knees. Visual analog scale (VAS) was used to assess the degree of pain relief. Knee Injury and Osteoarthritis Outcome Score (KOOS) and Lysholm (LYS) score were used to evaluate the functional improvement at weeks 12, 24 and 36. Concentric and eccentric quadriceps and hamstring peak torque (PT) as well as the peak torque-to-body weight (PTB) ratio, anterior-posterior, mediolateral and overall stability indexes were assessed at the same time points.

RESULTS

Twenty male patients with a mean age and body mass index of 32.2 ± 8.8 years and 26.2 ± 4.2 kg/m², respectively, were included in the study. The amount of pain decreased from 7.6 ± 1.5% to 2.9 ± 1.5% at postoperative week 36. Range of motion, Lysholm score and KOOS increased from 87.0^ο ± 9.5^ο to 115.0^ο ± 15.1^ο, 30.8 ± 4.3 to 81.5 ± 5.3 and 37.4 ± 5.3 to 74.1 ± 7.2, respectively. Concentric quadriceps and hamstring peak torque values and peak torque/body weight ratios were improved in the knees that received a meniscus scaffold implant. Anterior/posterior, medial/lateral, and overall stability indexes with or without biofeedback exhibited a slight improvement, which was not statistically significant.

CONCLUSION

BPMSI led to decreased pain and improved function at postoperative week 36. Although muscle strength almost returned to normal, balance parameters did not recover within 36 weeks after the procedure.

Engineering Anisotropic Meniscus: Zonal Functionality and Spatiotemporal Drug Delivery

Human meniscus is a fibrocartilaginous structure that is crucial for an adequate performance of the human knee joint. Degeneration of the meniscus is often followed by partial or total meniscectomy, which enhances the risk of developing knee osteoarthritis. The lack of a satisfactory treatment for this condition has triggered a major interest in drug delivery (DD) and tissue engineering (TE) strategies intended to restore a bioactive and fully functional meniscal tissue. The aim of this review is to critically discuss the most relevant studies on spatiotemporal DD and TE, aiming for a multizonal meniscal reconstruction. Indeed, the development of meniscal tissue implants should involve a provision for adequate active molecules and scaffold features that take into account the anisotropic ultrastructure of human meniscus. This zonal differentiation is reflected in the meniscus biochemical composition, collagen fiber arrangement, and cell distribution. In this sense, it is expected that a proper combination of advanced DD and zonal TE strategies will play a key role in the future trends in meniscus regeneration. Impact statement Meniscus degeneration is one of the main causes of knee pain, inflammation, and reduced mobility. Currently used suturing procedures and meniscectomy are far from being ideal solutions to the loss of meniscal function. Therefore, drug delivery (DD) and tissue engineering (TE) strategies are currently under investigation. DD systems aim at an in situ controlled release of growth factors, whereas TE strategies aim at mimicking the anisotropy of native meniscus. The goal of this review is to discuss these two main approaches, as well as synergies between them that are expected to lead to a real breakthrough in the field.

Arthroscopic repair of the meniscus: Surgical management and clinical outcomes

From the biomechanical and biological points of view, an arthroscopic meniscal repair (AMR) should always be considered as an option. However, AMR has a higher reoperation rate compared with arthroscopic partial meniscectomy, so it should be carefully indicated.

Compared with meniscectomy, AMR outcomes are better and the incidence of osteoarthritis is lower when it is well indicated.

Factors influencing healing and satisfactory results must be carefully evaluated before indicating an AMR.

Tears in the peripheral third are more likely to heal than those in the inner thirds.

Vertical peripheral longitudinal tears are the best scenario in terms of success when facing an AMR.

‘Inside-out’ techniques were considered as the gold standard for large repairs on mid-body and posterior parts of the meniscus. However, recent studies do not demonstrate differences regarding failure rate, functional outcomes and complications, when compared with the ‘all-inside’ techniques.

Some biological therapies try to enhance meniscal repair success but their efficacy needs further research. These are: mechanical stimulation, supplemental bone marrow stimulation, platelet rich plasma, stem cell therapy, and scaffolds and membranes.

Meniscal root tear/avulsion dramatically compromises meniscal stability, accelerating cartilage degeneration. Several options for reattachment have been proposed, but no differences between them have been established. However, repair of these lesions is actually the reference of the treatment.

Meniscal ramp lesions consist of disruption of the peripheral attachment of the meniscus. In contrast, with meniscal root tears, the treatment of reference has not yet been well established.

Cite this article: EFORT Open Rev 2018;3:584-594. DOI: 10.1302/2058-5241.3.170059

An electrospun fiber reinforced scaffold promotes total meniscus regeneration in rabbit meniscectomy model

Low vascularization in meniscus limits its regeneration ability after injury, and tissue engineering is the most promising method to achieve meniscus regeneration. In this study, we fabricated a kind of composite scaffold by decellularized meniscus extracellular matrix/polycaprolactone (DMECM/PCL) electrospinning fibers and porous DMECM, in which DMECM/PCL fibers were used as reinforcing component. The tensile modulus of the composite scaffold in longitudinal and crosswise directions were 8.5 ± 1.9 and 2.3 ± 0.3 MPa, respectively. Besides that, the DMECM/PCL electrospinning fibers enhanced suture resistance of the composite scaffold more than 5 times than DMECM scaffold effectively. In vitro cytocompatibility showed that the porous structure provided by DMECM component facilitated meniscus cells' proliferation. DMECM was also the main component to regulate cell behaviors, which promoted meniscus cells expressing extracellular matrix related genes such as COL I, COL II, SOX9 and AGG. Rabbits with total meniscectomy were used as animal model to evaluated the composited scaffolds performance in vivo at 3 and 6 months. Results showed that rabbits with scaffold implanting could regenerate neo-menisci in both time points. The neo-menisci had similar histology structure and biochemical content with native menisci. Although neo-menisci had inferior tensile modulus than native ones, its modulus was improved with implanting time prolonging. MRI imaging showed the signal of neo-meniscus in the body is clear, and X-ray imaging of knee joints demonstrated the implantation of scaffolds could relief joint space narrowing. Moreover, rabbits with neo-menisci had better cartilage condition in femoral condyle and tibial plateau compared than meniscectomy group.

STATEMENT OF SIGNIFICANCE

We fabricated the meniscus scaffold by combining porous decellularized meniscus extracellular matrix (DMECM) and DMECM/PCL electrospinning fibers together, which used the porous structure of DMECM, and the good tensile property of electrospinning fibers. We believe single material cannot satisfy increasing needs of scaffold. Therefore, we combined not only materials but also fabrication methods together to develop scaffold to make good use of each part. DMECM in electrospinning fibers also made these two components possible to be integrated through crosslinking. Compared to existing meniscus scaffold, the composite scaffold had (1) soft structure and extrusion would not happen after implantation, (2) ability to be trimmed to suitable shape during surgery, and (3) good resistance to suture.

A model system for developing a tissue engineered meniscal enthesis

The meniscus acts as a stabilizer, lubricator, and load distributer in the knee joint. The mechanical stability of the meniscus depends on its connection to the underlying bone by a fibrocartilage to bone transition zone called the meniscal enthesis. Tissue engineered menisci hold great promise as a treatment alternative however lack a means of integrated fixation to the underlying bone needed in order for a tissue engineered meniscal replacement to be successful. Tissue engineering the meniscal enthesis is a difficult task given the complex gradients of cell type, mineral, and extracellular matrix molecules. Therefore, there is a need for a simplified and high throughput enthesis model to test experimental parameters. The goal of this study was to develop a simplified enthesis model to test collagen integration with decellularized bone. We found that injection molding collagen into tubing loaded with decellularized bone plugs resulted in a scaffold with three regions: bone, bone-collagen, and collagen. Furthermore, collagen formation was directed in the axial direction by using mechanical fixation at the bony ends. The results of this study showed that this technique can be used to mimic the native enthesis morphology and serves as ideal test platform to generate a model tissue engineered enthesis.

STATEMENT OF SIGNIFICANCE

The meniscal enthesis is a complex structure that is essential to mechanical stability of the meniscus and the knee joint. Several studies document the development of anatomically shaped tissue engineered meniscus constructs, but none have focused on how to integrate such tissues with underlying bone. This study establishes a simplified construct to model the meniscal enthesis composed of a collagen gel seeded with meniscal fibrochondrocytes integrated with decellularized cancellous bone. Mechanical fixation at the bony ends induced tissue integration of fibers into the bony tissue, which is critical for mechanical performance and has yet to be shown in enthesis literature. Our test platform is amenable to targeted experiments investigating mineralization gradients, collagen fiber alignment, cell population phenotype, and media conditioning with experimental impact on enthesis studies for meniscus, tendon, and ligament.

The role of meniscal tissue in joint protection in early osteoarthritis

It is widely accepted that partial meniscectomy leads to early onset of osteoarthritis (OA). A strong correlation exists between the amount and location of the resected meniscus and the development of degenerative changes in the knee. On the other hand, osteoarthritic changes of the joint alter the structural and functional integrity of meniscal tissue. These alterations might additionally compromise the limited healing capacity of the meniscus. In young, active patients without cartilage damage, meniscus therapy including partial meniscectomy, meniscus suture, and meniscus replacement has proven beneficial effects in long-term studies. Even in an early osteoarthritic milieu, there is a relevant regenerative potential of the meniscus and the surrounding cartilage. This potential should be taken into account, and meniscal surgery can be performed with the correct timing and the proper indication even in the presence of early OA.