Tissue-Engineered Decellularized Allografts for Anterior Cruciate Ligament Reconstruction

Plastic and elastic biomechanical properties of anterior cruciate ligament autografts

BACKGROUND

Anterior cruciate ligament (ACL) rupture is a common orthopedic injury, occurring in roughly 68.6 per 100,000 persons annually, with the primary treatment option being ACL reconstruction. However, debate remains about the appropriate graft type for restoring the native biomechanical properties of the knee. Furthermore, plastic graft elongation may promote increased knee laxity and instability without rupture. This study aims to investigate the plastic properties of common ACL-R graft options.

METHODS

Patellar tendon (PT), hamstring tendon (HT), and quadriceps tendon (QT) grafts were harvested from 11 cadaveric knees (6 male and 5 female) with a mean age of 71(range 55-81). All grafts were mechanically tested under uniaxial tension until failure to determine each graft's elastic and plastic biomechanical properties.

RESULTS

Mechanically, the QT graft was the weakest, exhibiting the lowest failure force and the lowest failure stress (QT < HT, p = 0.032). The PT was the stiffest of the grafts, having a significantly higher stiffness (PT > QT, p = 0.0002) and Young's modulus (PT > QT, p = 0.001; PT > HT, p = 0.041). The HT graft had the highest plastic elongation at 4.01 ± 1.32 mm (HT > PT, p = 0.002). The post-yield behavior of the HT tendon shows increased energy storage capabilities with the highest plastic energy storage (HT > QT, p = 0.012) and the highest toughness (HT > QT, p = 0.032).

CONCLUSION

Our study agrees with prior studies indicating that the failure load of all grafts is above the requirements for everyday activities. However, grafts may be susceptible to yielding before failure during daily activities. This may result in the eventual loss of functionality for the neo-ACL, resulting in increased knee laxity and instability.

Advances focusing on the application of decellularization methods in tendon-bone healing

BACKGROUND

The tendon or ligament is attached to the bone by a triphasic but continuous area of heterogeneous tissue called the tendon-bone interface (TBI). The rapid and functional regeneration of TBI is challenging owing to its complex composition and difficulty in self-healing. The development of new technologies, such as decellularization, has shown promise in the regeneration of TBI. Several ex vivo and in vivo studies have shown that decellularized grafts and decellularized biomaterial scaffolds achieved better efficacy in enhancing TBI healing. However further information on the type of review that is available is needed.

AIM OF THE REVIEW

In this review, we discuss the current application of decellularization biomaterials in promoting TBI healing and the possible mechanisms involved. With this work, we would like to reveal how tissues or biomaterials that have been decellularized can improve tendon-bone healing and to provide a theoretical basis for future related studies.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

Decellularization is an emerging technology that utilizes various chemical, enzymatic and/or physical strategies to remove cellular components from tissues while retaining the structure and composition of the extracellular matrix (ECM). After decellularization, the cellular components of the tissue that cause an immune response are removed, while various biologically active biofactors are retained. This review further explores how tissues or biomaterials that have been decellularized improve TBI healing.

Exploring polysaccharide and protein-enriched decellularized matrix scaffolds for tendon and ligament repair: A review

Tissue engineering (TE) has become a primary research topic for the treatment of diseased or damaged tendon/ligament (T/L) tissue. T/L injuries pose a severe clinical burden worldwide, necessitating the development of effective strategies for T/L repair and tissue regeneration. TE has emerged as a promising strategy for restoring T/L function using decellularized extracellular matrix (dECM)-based scaffolds. dECM scaffolds have gained significant prominence because of their native structure, relatively high bioactivity, low immunogenicity, and ability to function as scaffolds for cell attachment, proliferation, and differentiation, which are difficult to imitate using synthetic materials. Here, we review the recent advances and possible future prospects for the advancement of dECM scaffolds for T/L tissue regeneration. We focus on crucial scaffold properties and functions, as well as various engineering strategies employed for biomaterial design in T/L regeneration. dECM provides both the physical and mechanical microenvironments required by cells to survive and proliferate. Various decellularization methods and sources of allogeneic and xenogeneic dECM in T/L repair and regeneration are critically discussed. Additionally, dECM hydrogels, bio-inks in 3D bioprinting, and nanofibers are briefly explored. Understanding the opportunities and challenges associated with dECM-based scaffold development is crucial for advancing T/L repairs in tissue engineering and regenerative medicine.

Biomimetic Extracellular Scaffolds by Microfluidic Superstructuring of Nanofibers

The extracellular matrix is a dynamic framework bearing chemical and morphological cues that support many cellular functions, and artificial analogs with well-defined chemistry are of great interest for biomedical applications. Herein, we describe hierarchical, extracellular-matrix-mimetic microgels, termed "superbundles" (SBs) composed of peptide amphiphile (PA) supramolecular nanofiber networks created using flow-focusing microfluidic devices. We explore the effects of altered flow rate ratio and PA concentration on the ability to create SBs and develop design rules for producing SBs with both cationic and anionic PA nanofibers and gelators. We demonstrate the morphological similarities of SBs to decellularized extracellular matrices and showcase their ability to encapsulate and retain proteinaceous cargos with a wide variety of isoelectric points. Finally, we demonstrate that the novel SB morphology does not affect the well-established biocompatibility of PA gels.

Feasibility study of oxidized naringin as a novel crosslinking agent for crosslinking decellularized porcine Achilles tendon and its potential application for anterior cruciate ligament repair

Naringin (Nar), a natural flavanone glycoside, has been shown to possess a variety of biological activities, including anti-inflammatory, anti-apoptotic, bone formation, and so forth. In this study, Nar was oxidized by sodium periodate and the oxidized naringin (ONar) was used as a novel biological crosslinking agent. In addition, ONar-fixed porcine decellularized Achilles tendon (DAT) was developed to substitute anterior cruciate ligament (ACL) for researching a novel ACL replacement material. The ONar with a 24 h oxidation time had appropriate aldehyde group content, almost no cytotoxicity, and a good crosslinking effect. The critical characteristics and cytocompatibility of ONar-fixed DAT were also investigated. The results demonstrated that 1% ONar-fixed DAT exhibited good resistance to enzymatic degradation and thermal stability as well as suitable mechanical strength. Moreover, 1% ONar-fixed specimens exhibited excellent L929 fibroblasts-cytocompatibility and MC3T3-E1-cytocompatibility. They also promoted the secretion of hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF) from fibroblasts and bone morphogenetic protein-2 (BMP-2) from osteoblasts. And they also showed the good anti-inflammatory properties in vivo experiments. Our data provided an experimental basis for ONar as a new cross-linking reagent in chemical modification of DAT and ONar-fixed DAT for ACL repair.

Injectable FHE+BP composites hydrogel with enhanced regenerative capacity of tendon-bone interface for anterior cruciate ligament reconstruction

Features of black phosphorous (BP) nano sheets such as enhancing mineralization and reducing cytotoxicity in bone regeneration field have been reported. Thermo-responsive FHE hydrogel (mainly composed of oxidized hyaluronic acid (OHA), poly-ε-L-lysine (ε-EPL) and F127) also showed a desired outcome in skin regeneration due to its stability and antibacterial benefits. This study investigated the application of BP-FHE hydrogel in anterior cruciate ligament reconstruction (ACLR) both in in vitro and in vivo, and addressed its effects on tendon and bone healing. This BP-FHE hydrogel is expected to bring the benefits of both components (thermo-sensitivity, induced osteogenesis and easy delivery) to optimize the clinical application of ACLR and enhance the recovery. Our in vitro results confirmed the potential role of BP-FHE via significantly increased rBMSC attachment, proliferation and osteogenic differentiation with ARS and PCR analysis. Moreover, In vivo results indicated that BP-FHE hydrogels can successfully optimize the recovery of ACLR through enhancing osteogenesis and improving the integration of tendon and bone interface. Further results of Biomechanical testing and Micro-CT analysis [bone tunnel area (mm2) and bone volume/total volume (%)] demonstrated that BP can indeed accelerate bone ingrowth. Additionally, histological staining (H&E, Masson and Safranin O/fast green) and immunohistochemical analysis (COL I, COL III and BMP-2) strongly supported the ability of BP to promote tendon-bone healing after ACLR in murine animal models.

Decellularized Extracellular Matrix-Based Bioinks for Tendon Regeneration in Three-Dimensional Bioprinting

In the last few years, attempts to improve the regeneration of damaged tendons have been rising due to the growing demand. However, current treatments to restore the original performance of the tissue focus on the usage of grafts; although, actual grafts are deficient because they often cannot provide enough support for tissue regeneration, leading to additional complications. The beneficial effect of combining 3D bioprinting and dECM as a novel bioink biomaterial has recently been described. Tendon dECMs have been obtained by using either chemical, biological, or/and physical treatments. Although decellularization protocols are not yet standardized, recently, different protocols have been published. New therapeutic approaches embrace the use of dECM in bioinks for 3D bioprinting, as it has shown promising results in mimicking the composition and the structure of the tissue. However, major obstacles include the poor structural integrity and slow gelation properties of dECM bioinks. Moreover, printing parameters such as speed and temperature have to be optimized for each dECM bioink. Here, we show that dECM bioink for 3D bioprinting provides a promising approach for tendon regeneration for future clinical applications.

An off-the-shelf decellularized and sterilized human bone-ACL-bone allograft for anterior cruciate ligament reconstruction

Approximately 1% of active individuals participating in sports rupture their anterior cruciate ligaments (ACL) every year, which is currently reconstructed using tendon autografts. Upon reconstruction, clinical issues of concern are ACL graft rupture, persistent knee instability, limited return to sports, and early onset of osteoarthritis (OA). This happens because tendon autografts do not have the same compositional, structural, and mechanical properties as a native ACL. To overcome these problems, we propose to use decellularized bone-ACL-bone allografts in ACL reconstruction (ACLR) as a mechanically robust, biocompatible, and immunologically safe alternative to autografts. Here, a decellularization protocol combined with sterilization using supercritical carbon dioxide (scCO₂) was used to thoroughly decellularize porcine and human ACLs attached to tibial and femoral bone blocks. The specimens were named ultrACLean and their compositional, structural, and mechanical properties were determined. Our results indicate that: 1) decellularization of ultrACLean allografts leads to the removal of nearly 97% of donor cells, 2) ultrACLean has mechanical properties which are not different to native ACL, 3) ultrACLean maintained similar collagen content and decreased GAG content compared to native ACL, and 4) ultrACLean is not cytotoxic to seeded tendon-derived cells in vitro. Results from an in vivo pilot experiment showed that ultrACLean is biocompatible and elicits a moderate immunological response. In summary, ultrACLean has proven to be a mechanically competent and biocompatible graft with the potential to be used in ACLR surgery.

Tissue Engineering the Pinna: Comparison and Characterization of Human Decellularized Auricular Biological Scaffolds

Decellularization is one of the promising techniques in tissue engineering used to create a biological scaffold for subsequent repopulation with the patient's own cells. This study aims to compare two different decellularization protocols to optimize the process of auricle decellularization by assessing and characterizing the decellularization effects on human auricular cartilage. Herein, 12 pairs (8 females, 4 males) of freshly frozen adult human cadaveric auricles were de-epithelialized and defatted leaving only the cartilaginous framework. An auricle from each pair was randomly assigned to either protocol A (latrunculin B-based decellularization) or protocol B (trypsin-based decellularization). Gross examination of the generated scaffolds demonstrated preservation of the auricles' contours and a change in color from pinkish-white to yellowish-white. Hematoxylin and eosin staining demonstrated empty cartilaginous lacunae in both study groups, which confirms the depletion of cells. However, there was greater preservation of the extracellular matrix in auricles decellularized with protocol A as compared to protocol B. Comparing protocol A to protocol B, Masson's trichrome and Safranin-O stains also demonstrated noticeable preservation of collagen and proteoglycans, respectively. Additionally, scanning electron micrographs demonstrated preservation of the cartilaginous microtopography in both study groups. Biomechanical testing demonstrated a substantial decrease in Young's modulus after decellularization using protocol B (1.3 MPa), albeit not significant (P-value > 0.05) when compared to Young's modulus prior to decellularization (2.6 MPa) or after decellularization with protocol A (2.7 MPa). A DNA quantification assay demonstrated a significant drop (P-value < 0.05) in the DNA content after decellularization with protocol A (111.0 ng/mg) and protocol B (127.6 ng/mg) in comparison to before decellularization (865.3 ng/mg). Overall, this study demonstrated effective decellularization of human auricular cartilage, and it is concluded that protocol A provided greater preservation of the extracellular matrix and biomechanical characteristics. These findings warrant proceeding with the assessment of inflammation and cell migration in a decellularized scaffold using an animal model.

The optimization of pepsin processing time to balance the mechanical and biological properties of xenogeneic bone

Xenogeneic bone showed great prospects to treat large bone defects due to its bionic composition and structure, but the immunogenicity limited its wide applications. Previously, we developed a pepsin treating method to eliminate the immunogenicity of xenogeneic bone. In this study, we further investigated the effect of pepsin processing time on the biological and mechanical properties. The results indicated that increased pepsin treating time impaired the mechanical properties of xenogeneic bone. And MC3T3-E1 cells showed enhanced adhesion ability, as well as increased production of alkaline phosphatase and calcium nodulus production on the xenogeneic bone processed by pepsin for 24 hr (P24), as compared with xenogeneic bone processed by pepsin for 30 hr (P30) and 36 hr (P36). In addition, we found no significant inflammatory responses after implanting different xenogeneic bone into the intermuscular site of rats. These results suggested that xenogeneic bone processed by pepsin for 24 hr may be a preferable choice when using the xenogeneic bone as biomaterials for further researches.

Tissue Engineering for Mimics and Modulations of Immune Functions

In the field of regenerative medicine, advances in tissue engineering have surpassed the reconstruction of individual tissues or organs and begun to work towards engineering systemic factors such as immune objects and functions. The immune system plays a crucial role in protecting and regulating systemic functions in the human body. Engineered immune tissues and organs have shown potential in recovering dysfunctions and aplasia of the immune system and the evasion from immune-mediated inflammatory responses and rejection elicited by engineered implants from allogeneic or xenogeneic sources are also being pursued to facilitate clinical transplantation of tissue engineered grafts. Here, current progress in tissue engineering to mimic or modulate immune functions is reviewed and elaborated from two perspectives: 1) engineering of immune tissues and organs per se and 2) immune evasion of host immunoinflammatory rejection by tissue-engineered implants.

3D printing of tissue engineering scaffolds: a focus on vascular regeneration

Tissue engineering is an emerging means for resolving the problems of tissue repair and organ replacement in regenerative medicine. Insufficient supply of nutrients and oxygen to cells in large-scale tissues has led to the demand to prepare blood vessels. Scaffold-based tissue engineering approaches are effective methods to form new blood vessel tissues. The demand for blood vessels prompts systematic research on fabrication strategies of vascular scaffolds for tissue engineering. Recent advances in 3D printing have facilitated fabrication of vascular scaffolds, contributing to broad prospects for tissue vascularization. This review presents state of the art on modeling methods, print materials and preparation processes for fabrication of vascular scaffolds, and discusses the advantages and application fields of each method. Specially, significance and importance of scaffold-based tissue engineering for vascular regeneration are emphasized. Print materials and preparation processes are discussed in detail. And a focus is placed on preparation processes based on 3D printing technologies and traditional manufacturing technologies including casting, electrospinning, and Lego-like construction. And related studies are exemplified. Transformation of vascular scaffolds to clinical application is discussed. Also, four trends of 3D printing of tissue engineering vascular scaffolds are presented, including machine learning, near-infrared photopolymerization, 4D printing, and combination of self-assembly and 3D printing-based methods.