Tissue-engineered trachea regeneration using decellularized trachea matrix treated with laser micropore technique

A Contemporary Review of Trachea, Nose, and Ear Cartilage Bioengineering and Additive Manufacturing

The complex structure, chemical composition, and biomechanical properties of craniofacial cartilaginous structures make them challenging to reconstruct. Autologous grafts have limited tissue availability and can cause significant donor-site morbidity, homologous grafts often require immunosuppression, and alloplastic grafts may have high rates of infection or displacement. Furthermore, all these grafting techniques require a high level of surgical skill to ensure that the reconstruction matches the original structure. Current research indicates that additive manufacturing shows promise in overcoming these limitations. Autologous stem cells have been developed into cartilage when exposed to the appropriate growth factors and culture conditions, such as mechanical stress and oxygen deprivation. Additive manufacturing allows for increased precision when engineering scaffolds for stem cell cultures. Fine control over the porosity and structure of a material ensures adequate cell adhesion and fit between the graft and the defect. Several recent tissue engineering studies have focused on the trachea, nose, and ear, as these structures are often damaged by congenital conditions, trauma, and malignancy. This article reviews the limitations of current reconstructive techniques and the new developments in additive manufacturing for tracheal, nasal, and auricular cartilages.

Decellularized laser micro-patterned osteochondral implants exhibit zonal recellularization and self-fixing for osteochondral regeneration in a goat model

Background

Osteochondral regeneration has long been recognized as a complex and challenging project in the field of tissue engineering. In particular, reconstructing the osteochondral interface is crucial for determining the effectiveness of the repair. Although several artificial layered or gradient scaffolds have been developed recently to simulate the natural interface, the functions of this unique structure have still not been fully replicated. In this paper, we utilized laser micro-patterning technology (LMPT) to modify the natural osteochondral "plugs" for use as grafts and aimed to directly apply the functional interface unit to repair osteochondral defects in a goat model.

Methods

For in vitro evaluations, the optimal combination of LMPT parameters was confirmed through mechanical testing, finite element analysis, and comparing decellularization efficiency. The structural and biological properties of the laser micro-patterned osteochondral implants (LMP-OI) were verified by measuring the permeability of the interface and assessing the recellularization processes. In the goat model for osteochondral regeneration, a conical frustum-shaped defect was specifically created in the weight-bearing area of femoral condyles using a customized trephine with a variable diameter. This unreported defect shape enabled the implant to properly self-fix as expected.

Results

The micro-patterning with the suitable pore density and morphology increased the permeability of the LMP-OIs, accelerated decellularization, maintained mechanical stability, and provided two relative independent microenvironments for subsequent recellularization. The LMP-OIs with goat's autologous bone marrow stromal cells in the cartilage layer have securely integrated into the osteochondral defects. At 6 and 12 months after implantation, both imaging and histological assessments showed a significant improvement in the healing of the cartilage and subchondral bone.

Conclusion

With the natural interface unit and zonal recellularization, the LMP-OI is an ideal scaffold to repair osteochondral defects especially in large animals.

The translational potential of this article

These findings suggest that such a modified xenogeneic osteochondral implant could potentially be explored in clinical translation for treatment of osteochondral injuries. Furthermore, trimming a conical frustum shape to the defect region, especially for large-sized defects, may be an effective way to achieve self-fixing for the implant.

Temporal control in shell-core structured nanofilm for tracheal cartilage regeneration: synergistic optimization of anti-inflammation and chondrogenesis

Cartilage tissue engineering offers hope for tracheal cartilage defect repair. Establishing an anti-inflammatory microenvironment stands as a prerequisite for successful tracheal cartilage restoration, especially in immunocompetent animals. Hence, scaffolds inducing an anti-inflammatory response before chondrogenesis are crucial for effectively addressing tracheal cartilage defects. Herein, we develop a shell-core structured PLGA@ICA-GT@KGN nanofilm using poly(lactic-co-glycolic acid) (PLGA) and icariin (ICA, an anti-inflammatory drug) as the shell layer and gelatin (GT) and kartogenin (KGN, a chondrogenic factor) as the core via coaxial electrospinning technology. The resultant PLGA@ICA-GT@KGN nanofilm exhibited a characteristic fibrous structure and demonstrated high biocompatibility. Notably, it showcased sustained release characteristics, releasing ICA within the initial 0 to 15 days and gradually releasing KGN between 11 and 29 days. Subsequent in vitro analysis revealed the potent anti-inflammatory capabilities of the released ICA from the shell layer, while the KGN released from the core layer effectively induced chondrogenic differentiation of bone marrow stem cells (BMSCs). Following this, the synthesized PLGA@ICA-GT@KGN nanofilms were loaded with BMSCs and stacked layer by layer, adhering to a 'sandwich model' to form a composite sandwich construct. This construct was then utilized to repair circular tracheal defects in a rabbit model. The sequential release of ICA and KGN facilitated by the PLGA@ICA-GT@KGN nanofilm established an anti-inflammatory microenvironment before initiating chondrogenic induction, leading to effective tracheal cartilage restoration. This study underscores the significance of shell-core structured nanofilms in temporally regulating anti-inflammation and chondrogenesis. This approach offers a novel perspective for addressing tracheal cartilage defects, potentially revolutionizing their treatment methodologies.

Global Bibliometric and Visualized Analysis of Tracheal Tissue Engineering Research

The development of tracheal tissue engineering (TTE) has seen a rapid growth in recent years. The purpose of this study was to investigate the global status, trends, and hotspots of TTE research based on bibliometrics and visualization analysis. Publications related to TTE were retrieved and included in the Web of Science Core Collection. VOSviewer and CiteSpace were used to generate knowledge maps. Six hundred fifty-five publications were identified, and the quantity of the annual publications worldwide was on the increase. International collaboration is a widespread reality. The United States led the world in the field of trachea tissue engineering, whereas University College London was the institution with the greatest contribution. In addition, Biomaterials had a great influence in this field, attracting the largest number of papers. Moreover, the topics of TTE research largely concentrated on the biomechanical scaffold preparation, the vascularization and epithelialization of scaffold, the tracheal cartilage regeneration, and the tissue-engineered tracheal transplantation. And the research on the application of decellularization and 3D printing for the construction of a tissue-engineered trachea was likely to receive more widespread attention in the future. Impact statement In recent years, tracheal tissue engineering (TTE) has experienced rapid growth. In this study, we investigated the worldwide status and trends of TTE research, and revealed the countries, institutions, journals, and authors that had made significant contributions to the field of TTE. Moreover, the possible research hotspots in the future were predicted. According to our research, researchers can gain a better understanding of the trends in this field, and stay informed of the most current research by tracking key journals, institutions, and authors.

Photothermal-Controllable Microneedles with Antitumor, Antioxidant, Angiogenic, and Chondrogenic Activities to Sequential Eliminate Tracheal Neoplasm and Reconstruct Tracheal Cartilage

The optimal treatment for tracheal tumors necessitates sequential tumor elimination and tracheal cartilage reconstruction. This study introduces an innovative inorganic nanosheet, MnO2 /PDA@Cu, comprising manganese dioxide (MnO2 ) loaded with copper ions (Cu) through in situ polymerization using polydopamine (PDA) as an intermediary. Additionally, a specialized methacrylic anhydride modified decellularized cartilage matrix (MDC) hydrogel with chondrogenic effects is developed by modifying a decellularized cartilage matrix with methacrylic anhydride. The MnO2 /PDA@Cu nanosheet is encapsulated within MDC-derived microneedles, creating a photothermal-controllable MnO2 /PDA@Cu-MDC microneedle. Effectiveness evaluation involved deep insertion of the MnO2 /PDA@Cu-MDC microneedle into tracheal orthotopic tumor in a murine model. Under 808 nm near-infrared irradiation, facilitated by PDA, the microneedle exhibited rapid overheating, efficiently eliminating tumors. PDA's photothermal effects triggered controlled MnO2 and Cu release. The MnO2 nanosheet acted as a potent inorganic nanoenzyme, scavenging reactive oxygen species for an antioxidant effect, while Cu facilitated angiogenesis. This intervention enhanced blood supply at the tumor excision site, promoting stem cell enrichment and nutrient provision. The MDC hydrogel played a pivotal role in creating a chondrogenic niche, fostering stem cells to secrete cartilaginous matrix. In conclusion, the MnO2 /PDA@Cu-MDC microneedle is a versatile platform with photothermal control, sequentially combining antitumor, antioxidant, pro-angiogenic, and chondrogenic activities to orchestrate precise tracheal tumor eradication and cartilage regeneration.

Construction of three-dimensional, homogeneous regenerative cartilage tissue based on the ECG-DBM complex

Introduction: The feasibility of using a steel decalcified bone matrix (DBM)-reinforced concrete engineered cartilage gel (ECG) model concept for in vivo cartilage regeneration has been demonstrated in preliminary experiments. However, the regenerated cartilage tissue contained an immature part in the center. The present study aimed to achieve more homogeneous regenerated cartilage based on the same model concept. Methods: For this, we optimized the culture conditions for the engineered cartilage gel-decalcified bone matrix (ECG-DBM) complex based on the previous model and systematically compared the in vitro chondrogenic abilities of ECG in the cartilage slice and ECG-DBM complex states. We then compared the in vivo cartilage regeneration effects of the ECG-DBM complex with those of an equivalent volume of ECG and an equivalent ECG content. Results and discussion: Significant increases in the DNA content and cartilage-specific matrix content were observed for the ECG-DBM complex compared with the ECG cartilage slice, suggesting that the DBM scaffold significantly improved the quality of ECG-derived cartilage regeneration in vitro. In the in vivo experiments, high-quality cartilage tissue was regenerated in all groups at 8 weeks, and the regenerated cartilage exhibited typical cartilage lacunae and cartilage-specific extracellular matrix deposition. Quantitative analysis revealed a higher chondrogenic efficiency in the ECG-DBM group. Specifically, the ECG-DBM complex achieved more homogeneous and stable regenerated cartilage than an equivalent volume of ECG and more mature regenerated cartilage than an equivalent ECG content. Compared with ECG overall, ECG-DBM had a more controllable shape, good morphology retention, moderate mechanical strength, and high cartilage regeneration efficiency. Further evaluation of the ECG-DBM complex after in vitro culture for 7 and 14 days confirmed that an extended in vitro preculture facilitated more homogeneous cartilage regeneration.

A bioengineered trachea-like structure improves survival in a rabbit tracheal defect model

A practical strategy for engineering a trachea-like structure that could be used to repair or replace a damaged or injured trachea is an unmet need. Here, we fabricated bioengineered cartilage (BC) rings from three-dimensionally printed fibers of poly(ɛ-caprolactone) (PCL) and rabbit chondrocytes. The extracellular matrix (ECM) secreted by the chondrocytes combined with the PCL fibers formed a "concrete-rebar structure," with ECM deposited along the PCL fibers, forming a grid similar to that of native cartilage. PCL fiber-hydrogel rings were then fabricated and alternately stacked with BC rings on silicone tubes. This trachea-like structure underwent vascularization after heterotopic transplantation into rabbits for 4 weeks. The vascularized bioengineered trachea-like structure was then orthotopically transplanted by end-to-end anastomosis to native rabbit trachea after a segment of trachea had been resected. The bioengineered trachea-like structure displayed mechanical properties similar to native rabbit trachea and transmural angiogenesis between the rings. The 8-week survival rate in transplanted rabbits was 83.3%, and the respiratory rate of these animals was similar to preoperative levels. This bioengineered trachea-like structure may have potential for treating tracheal stenosis and other tracheal injuries.

Evolution of biomimetic ECM scaffolds from decellularized tissue matrix for tissue engineering: A comprehensive review

Tissue engineering is essentially a technique for imitating nature. Natural tissues are made up of three parts: extracellular matrix (ECM), signaling systems, and cells. Therefore, biomimetic ECM scaffold is one of the best candidates for tissue engineering scaffolds. Among the many scaffold materials of biomimetic ECM structure, decellularized ECM scaffolds (dECMs) obtained from natural ECM after acellular treatment stand out because of their inherent natural components and microenvironment. First, an overview of the family of dECMs is provided. The principle, mechanism, advances, and shortfalls of various decellularization technologies, including physical, chemical, and biochemical methods are then critically discussed. Subsequently, a comprehensive review is provided on recent advances in the versatile applications of dECMs including but not limited to decellularized small intestinal submucosa, dermal matrix, amniotic matrix, tendon, vessel, bladder, heart valves. And detailed examples are also drawn from scientific research and practical work. Furthermore, we outline the underlying development directions of dECMs from the perspective that tissue engineering scaffolds play an important role as an important foothold and fulcrum at the intersection of materials and medicine. As scaffolds that have already found diverse applications, dECMs will continue to present both challenges and exciting opportunities for regenerative medicine and tissue engineering.

Pre-epithelialized cryopreserved tracheal allograft for neo-trachea flap engineering

Background: Tracheal reconstruction presents a challenge because of the difficulty in maintaining the rigidity of the trachea to ensure an open lumen and in achieving an intact luminal lining that secretes mucus to protect against infection. Methods: On the basis of the finding that tracheal cartilage has immune privilege, researchers recently started subjecting tracheal allografts to "partial decellularization" (in which only the epithelium and its antigenicity are removed), rather than complete decellularization, to maintain the tracheal cartilage as an ideal scaffold for tracheal tissue engineering and reconstruction. In the present study, we combined a bioengineering approach and a cryopreservation technique to fabricate a neo-trachea using pre-epithelialized cryopreserved tracheal allograft (ReCTA). Results: Our findings in rat heterotopic and orthotopic implantation models confirmed that tracheal cartilage has sufficient mechanical properties to bear neck movement and compression; indicated that pre-epithelialization with respiratory epithelial cells can prevent fibrosis obliteration and maintain lumen/airway patency; and showed that a pedicled adipose tissue flap can be easily integrated with a tracheal construct to achieve neovascularization. Conclusion: ReCTA can be pre-epithelialized and pre-vascularized using a 2-stage bioengineering approach and thus provides a promising strategy for tracheal tissue engineering.

The Immunosuppressive Niche Established with a Curcumin-Loaded Electrospun Nanofibrous Membrane Promotes Cartilage Regeneration in Immunocompetent Animals

Inflammatory cells mount an immune response against in vitro engineered cartilage implanted into immunocompetent animals, consequently limiting the usage of tissue-engineered cartilage to repair cartilage defects. In this study, curcumin (Cur)-an anti-inflammatory agent-was mixed with poly(lactic-co-glycolic acid) (PLGA) to develop a Cur/PLGA nanofibrous membrane with nanoscale pore size and anti-inflammatory properties. Fourier-transform infrared spectroscopy and high-performance liquid chromatography analyses confirmed the successful loading of Cur into the Cur/PLGA nanofibrous membrane. The results of the in vitro assay demonstrated the sustained release kinetics and enhanced stability of Cur in the Cur/PLGA nanofibrous membrane. Western blotting and enzyme-linked immunosorbent assay analyses revealed that the Cur/PLGA nanofibrous membrane significantly downregulated the expression of inflammatory cytokines (IL-1β, IL-6, and TNF-α). A chondrocyte suspension was seeded into a porous PLGA scaffold, and the loaded scaffold was cultured for 3 weeks in vitro to engineer cartilage tissues. The cartilage was packed with the in vitro engineered Cur/PLGA nanofibrous membrane and subcutaneously implanted into rats to generate an immunosuppressive niche. Compared with those in the PLGA-implanted and pure cartilage (without nanofibrous membrane package)-implanted groups, the cartilage was well preserved and the inflammatory response was suppressed in the Cur/PLGA-implanted group at weeks 2 and 4 post-implantation. Thus, this study demonstrated that packaging the cartilage with the Cur/PLGA nanofibrous membrane effectively generated an immunosuppressive niche to protect the cartilage against inflammatory invasion. These findings enable the clinical translation of tissue-engineered cartilage to repair cartilage defects.

Injectable nanofiber microspheres modified with metal phenolic networks for effective osteoarthritis treatment

Osteoarthritis (OA) is one of the most common chronic musculoskeletal diseases, which accounts for a large proportion of physical disabilities worldwide. Herein, we fabricated injectable gelatin/poly(L-lactide)-based nanofibrous microspheres (MS) via electrospraying technology, which were further modified with tannic acid (TA) named as TMS or metal phenolic networks (MPNs) consisting of TA and strontium ions (Sr²⁺) and named as TSMS to enhance their bioactivity for OA therapy. The TA-modified microspheres exhibited stable porous structure and anti-oxidative activity. Notably, TSMS showed a sustained release of TA as compared to TMS, which exhibited a burst release of TA. While all types of microspheres exhibited good cytocompatibility, TSMS displayed good anti-inflammatory properties with higher cell viability and cartilage-related extracellular matrix (ECM) secretion. The TSMS microspheres also showed less apoptosis of chondrocytes in the hydrogen peroxide (H₂O₂)-induced inflammatory environment. The TSMS also inhibited the degradation of cartilage along with the considerable repair outcome in the papain-induced OA rabbit model in vivo as well as suppressed the expression level of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-1-beta (IL-1β). Taken together, TSMS may provide a highly desirable therapeutic option for intra-articular treatment of OA. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) is a chronic disease, which is caused by the inflammation of joint. Current treatments for OA achieve pain relief but hardly prevent or slow down the disease progression. Microspheres are at the forefront of drug delivery and tissue engineering applications, which can also be minimal-invasively injected into the joint. Polyphenols and therapeutic ions have been shown to be beneficial for the treatment of diseases related to the joints, including OA. Herein, we prepared gelatin/poly(L-lactide)-based nanofibrous microspheres (MS) via electrospinning incorporated electrospraying technology and functionalized them with the metal phenolic networks (MPNs) consisting of TA and strontium ions (Sr²⁺), and assessed their potential for OA therapy both in vitro and in vivo.

Curcumin-loaded nanofilm generating avascular niche to stabilize in vivo ectopic chondrogenesis of BMSC

Bone marrow stem cells (BMSCs) engineered cartilage (BEC) represent a promising substitute for cartilage repairment. However, the in vitro-generated BEC was prone to endochondral ossification after in vivo ectopic implantation, significantly hindering its clinical translation. Increasing evidence suggested that vascularization essentially led to endochondral ossification of BEC in the subcutaneous microenvironment. Herein, a potent antiangiogenic agent of curcumin (Cur) was successfully laden into a polycaprolactone (PCL) to prepare a Cur/PCL nanofilm. The in vitro findings of this study showed that after co-culturing with human umbilical vein endothelial cells, Cur was sustained-released from Cur/PCL and suppressed the formation of tubes. Further, the Cur/PCL nanofilm was cytocompatible when recolonized with BMSCs. BMSCs were seeded into a porous polyglycolic acid scaffold and underwent 4 weeks of in vitro chondrogenic culture to successfully produce BEC. Thereafter, the BEC is encapsulated by the Cur/PCL nanofilm and subcutaneously implanted into nude mice for 4 weeks. The localized and sustained Cur release could inhibit vascular invasion via the antagonization of vascular endothelial growth factor signal, and stabilizes the cartilaginous phenotype. The results confirmed that Cur/PCL nanofilms protected BEC from vascularization and endochondral ossification in vivo, thus, indicating that the encapsulation of BEC using an anti-angiogenic nanofilm could be used as a novel strategy for modulating the in vivo ectopic BEC stability to repair cartilage defects.

Scaffold-based tissue engineering: Supercritical carbon dioxide as an alternative method for decellularization and sterilization of dense materials

Development of ready-to-use biomaterials and scaffolds is vital for further advancement of scaffold-based tissue engineering in clinical practice. Scaffolds need to mimic 3D ultrastructure, have adequate mechanical strength, are biocompatible, non-immunogenic and need to promote tissue regeneration in vivo. Although decellularization of native tissues seems promising to deliver scaffolds that meet these criteria, adequate decellularization of hard, poorly penetrable and poorly diffusible tissues remains challenging whilst being a very time-consuming process. In this study, a method to decellularize hard, dense tissues using supercritical carbon-dioxide preceded by a freeze/thaw cycle and followed by several washing steps is presented, demonstrating decellularisation efficiency and substantially reduced production/handling time. Additionally, supercritical carbon-dioxide treatment was used as sterilization method, further reducing the time required to produce the final scaffold. Histological evaluation showed that, after fine-tuning of the process, a partially acellular scaffold was obtained, with preservation of glycosaminoglycans and collagen fibers, albeit that the amount of residual dsDNA was still higher then chemically decellularized tissue. Biomechanical properties of the scaffold were similar to the native, non-decellularized tissue. After sterilization with supercritical carbon-dioxide the simulated functional outcome was more similar to native trachea, when compared to sterilization using gamma irradiation. Thus, decellularization and sterilization using supercritical carbon-dioxide with washing steps is an effective method for dense cartilaginous materials, and tuneable to meet different demands in other applications, but further optimization may be required. STATEMENT OF SIGNIFICANCE: Further advancement of the use of tissue engineered tracheal constructs is restricted by the lack of the ideal scaffold. Decellularized trachea is considered a promising scaffold, but the hard, poorly diffusible tissue remains challenging while forming a very time consumable process. Decellularization using supercritical carbon dioxide (scCO₂) seems promising, resulting in efficient removal of cellular material while reducing production and handling time. Addition of scCO₂ as a sterilization method resulted in further time reduction while improving functional outcome in comparison with traditional sterilization methods. This study presents an promising alternative method for decellularization and sterilization of dense materials, which can be tuned to meet different demands in other applications.

Preclinical and clinical orthotopic transplantation of decellularized/engineered tracheal scaffolds: A systematic literature review

Severe tracheal injuries that cannot be managed by mobilization and end-to-end anastomosis represent an unmet clinical need and an urgent challenge to face in surgical practice; within this scenario, decellularized scaffolds (eventually bioengineered) are currently a tempting option among tissue engineered substitutes. The success of a decellularized trachea is expression of a balanced approach in cells removal while preserving the extracellular matrix (ECM) architecture/mechanical properties. Revising the literature, many Authors report about different methods for acellular tracheal ECMs development; however, only few of them verified the devices effectiveness by an orthotopic implant in animal models of disease. To support translational medicine in this field, here we provide a systematic review on studies recurring to decellularized/bioengineered tracheas implantation. After describing the specific methodological aspects, orthotopic implant results are verified. Furtherly, the only three clinical cases of compassionate use of tissue engineered tracheas are reported with a focus on outcomes.

Scaffold-Free Tracheal Engineering via a Modular Strategy Based on Cartilage and Epithelium Sheets

Tracheal defects lead to devastating problems, and practical clinical substitutes that have complex functional structures and can avoid adverse influences from exogenous bioscaffolds are lacking. Herein, a modular strategy for scaffold-free tracheal engineering is developed. A cartilage sheet (Cart-S) prepared by high-density culture is laminated and reshaped to construct a cartilage tube as the main load-bearing structure in which the chondrocytes exhibit a stable phenotype and secreted considerable cartilage-specific matrix, presenting a native-like grid arrangement. To further build a tracheal epithelial barrier, a temperature-sensitive technique is used to construct the monolayer epithelium sheet (Epi-S), in which the airway epithelial cells present integrated tight junctions, good transepithelial electrical resistance, and favorable ciliary differentiation capability. Epi-S can be integrally transferred to inner wall of cartilage tube, forming a scaffold-free complex tracheal substitute (SC-trachea). Interestingly, when Epi-S is attached to the cartilage surface, epithelium-specific gene expression is significantly enhanced. SC-trachea establishes abundant blood supply via heterotopic vascularization and then is pedicle transplanted for tracheal reconstruction, achieving 83.3% survival outcomes in rabbit models. Notably, the scaffold-free engineered trachea simultaneously satisfies sufficient mechanical properties and barrier function due to its matrix-rich cartilage structure and well-differentiated ciliated epithelium, demonstrating great clinical potential for long-segmental tracheal reconstruction.

Emerging polymeric material strategies for cartilage repair

Cartilage is found throughout the body, serving an array of essential functions. Owing to the limited healing capacity of cartilage, damage or degeneration is often permanent and so requires clinical intervention. Established surgical techniques generally rely on biological grafting. However, recent advances in polymeric materials provide an encouraging alternative to overcome limits of auto- and allografts. For regenerative engineering of cartilage, a polymeric scaffold ideally supports and instructs tissue regeneration while also providing mechanical integrity. Scaffolds direct regeneration via chemical and mechanical cues, as well as delivery and support of exogenous cells and bioactive factors. Advanced polymeric scaffolds aim to direct regeneration locally, replicating the heterogeneities of native tissues. Alternatively, new cartilage-mimetic hydrogels have potential to serve as synthetic cartilage replacements. Prepared as multi-network or composite hydrogels, the most promising candidates have simultaneously realized the hydration, mechanical, and tribological properties of native cartilage. Collectively, the recent rise in polymers for cartilage regeneration and replacement proposes a changing paradigm, with a new generation of materials paving the way for improved clinical outcomes.

Icariin-loaded hydrogel with concurrent chondrogenesis and anti-inflammatory properties for promoting cartilage regeneration in a large animal model

Currently, an effective repair method that can promote satisfactory cartilage regeneration is unavailable for cartilage damages owing to inevitable inflammatory erosion. Cartilage tissue engineering has revealed considerable treatment options for cartilage damages. Icariin (ICA) is a flavonoid component of Epimedii folium with both chondrogenic and anti-inflammatory properties. In this study, we prepared an ICA/CTS hydrogel by loading ICA into chitosan (CTS) hydrogel to impart chondrogenesis and anti-inflammatory properties to the ICA/CTS hydrogel. In vitro results revealed that ICA showed sustained release kinetics from the ICA/CTS hydrogel. In addition, compared to the CTS hydrogel, the ICA/CTS hydrogel exhibited a favorable in vitro anti-inflammatory effect upon incubation with lipopolysaccharide pre-induced RAW264.7 macrophages, as indicated by the suppression of inflammatory-related cytokines (IL-6 and TNF-α). Additionally, when co-cultured with chondrocytes in vitro, the ICA/CTS hydrogel showed good cytocompatibility, accelerated chondrocyte proliferation, and enhanced chondrogenesis compared to the CTS hydrogel. Moreover, the in vitro engineered cartilage from the chondrocyte-loaded ICA/CTS hydrogel achieved stable cartilage regeneration when subcutaneously implanted in a goat model. Finally, the addition of ICA endowed the ICA/CTS hydrogel with a potent anti-inflammatory effect compared to what was observed in the CTS hydrogel, as confirmed by the attenuated IL-1β, IL-6, TNF-α, and TUNEL expression. The prepared ICA/CTS hydrogel offered an effective method of delivery for chondrogenic and anti-inflammatory agents and served as a useful platform for cartilage regeneration in an immunocompetent large animal model.

Extracellular Matrix Microparticles Improve GelMA Bioink Resolution for 3D Bioprinting at Ambient Temperature

Introduction

Current bioinks for 3D bioprinting, such as gelatin-methacryloyl, are generally low viscosity fluids at room temperature, requiring specialized systems to create complex geometries.

Methods and Results

Adding decellularized extracellular matrix microparticles derived from porcine tracheal cartilage to gelatin-methacryloyl creates a yield stress fluid capable of forming self-supporting structures. This bioink blend performs similarly at 25°C to gelatin-methacryloyl alone at 15°C in linear resolution, print fidelity, and tensile mechanics.

Conclusion

This method lowers barriers to manufacturing complex tissue geometries and removes the need for cooling systems.

Skin-derived epithelial lining facilitates orthotopic tracheal transplantation by protecting the tracheal cartilage and inhibiting granulation hyperplasia

Long-segment tracheal defects caused by tumours, inflammation or trauma can cause serious damage to the quality of life of patients. Although many novel neotracheas have been constructed, the therapeutic effect of orthotopic transplantation was compromised mainly because of the lack of an epithelial lining in those neotracheas. In this study, we aimed to investigate the therapeutic function of skin-derived epithelial lining for orthotopic tracheal transplantation. Strips of auricular cartilage with fixed interval were interrupted sutured on a silicone tube to mimic the cartilage rings of the native trachea. Neotrachea in the with epithelium group retained the unilateral skin as the epithelial lining in the lumen, whereas the neotrachea in the without epithelium group consisted solely of cartilage strips. After revascularized in the sternohyoid muscle, 2-cm-long tracheal defects were made and were reconstructed using these neotracheas. Our results showed that the skin-derived epithelial lining simultaneously protected the engineered tracheal cartilage and inhibited granulation hyperplasia in the tracheal lumen; further, compared with the without epithelium group, the group with epithelium showed a marked improvement in the tracheal lumen patency and the survival rate of rabbits. Our study provides a critical cue for improvements in the repair of tracheal defects via skin-derived epithelial lining and may significantly advance the clinical translation of tissue-engineered trachea.

A defined road to tracheal reconstruction: laser structuring and cell support for rapid clinic translation

One of the severe complications occurring because of the patient's intubation is tracheal stenosis. Its incidence has significantly risen because of the COVID-19 pandemic and tends only to increase. Here, we propose an alternative to the donor trachea and synthetic prostheses-the tracheal equivalent. To form it, we applied the donor trachea samples, which were decellularized, cross-linked, and treated with laser to make wells on their surface, and inoculated them with human gingiva-derived mesenchymal stromal cells. The fabricated construct was assessed in vivo using nude (immunodeficient), immunosuppressed, and normal mice and rabbits. In comparison with the matrix ones, the tracheal equivalent samples demonstrated the thinning of the capsule, the significant vessel ingrowth into surrounding tissues, and the increase in the submucosa resorption. The developed construct was shown to be highly biocompatible and efficient in trachea restoration. These results can facilitate its clinical translation and be a base to design clinical trials.

Research progress in seed cells for cartilage tissue engineering

Cartilage defects trouble millions of patients worldwide and their repair via conventional treatment is difficult. Excitingly, tissue engineering technology provides a promising strategy for efficient cartilage regeneration with structural regeneration and functional reconstruction. Seed cells, as biological prerequisites for cartilage regeneration, determine the quality of regenerated cartilage. The proliferation, differentiation and chondrogenesis of seed cells are greatly affected by their type, origin and generation. Thus, a systematic description of the characteristics of seed cells is necessary. This article reviews in detail the cellular characteristics, research progress, clinical translation challenges and future research directions of seed cells while providing guidelines for selecting appropriate seed cells for cartilage regeneration.

Bevacizumab-Laden Nanofibers Simulating an Antiangiogenic Niche to Improve the Submuscular Stability of Stem Cell Engineered Cartilage

Bone marrow stem cells (BMSCs) engineered cartilage (BEC) is prone to endochondral ossification in a submuscular environment due to the process of vascular infiltration, which limits its application in repairing tracheal cartilage defects. Bevacizumab, an antitumor drug with pronounced antiangiogenic activity, is successfully laden into a poly(L-lactide-co-caprolactone) system to prepare bevacizumab-laden nanofiber (BevNF) characterized by 5% and 10% bevacizumab concentrations. The in vitro results reveal that a sustained release of bevacizumab can be realized from BevNF, exhibiting inhibitive cytotoxicity toward human umbilical vein endothelial cells whereas non-cytotoxicity toward BMSCs-induced chondrocytes. A model is also established by encapsulating BEC within BevNF, aiming to realize an antiangiogenic niche under conditions of sustained and localized release of bevacizumab to inhibit the process of vascular invasion, resulting in the eventual stabilization of the cartilaginous phenotype and promotion of the process of cartilage maturation in the submuscular environment. These results also confirm that the chondrogenesis stability of BEC increases with an increase in the bevacizumab concentration, and 10% BevNF is sufficient to protect BEC from vascularization. This demonstrates that the use of BevNF can potentially help develop an effective strategy for regulating the submuscular stability of BEC to repair the defects formed in tracheal cartilage.

Acellular cartilage matrix biomimetic scaffold with immediate enrichment of autologous bone marrow mononuclear cells to repair articular cartilage defects

Functional repair of articular cartilage defects is always a great challenge in joint surgery clinically. Tissue engineering strategies that combine autologous cell implantation with three-dimensional scaffolds have proven effective for repairing articular cartilage tissue. However, it faces the problem of cell sources and scaffold materials. Autologous chondrocytes and bone marrow are difficult to popularize clinically due to limited donor sources and low mononuclear cell (MNC) concentrations, respectively. The density gradient centrifugation method can increase the concentration of MNCs in fresh bone marrow by nearly a hundredfold and achieve immediate enrichment. In addition, acellular cartilage matrix (ACM), with good biocompatibility and a cartilage-specific microenvironment, is considered to be an ideal candidate scaffold for cartilage regeneration. In this study, hybrid pigs were used to establish articular cartilage defect models of different sizes to determine the feasibility and maximum scope of application of ACM-based biomimetic scaffolds combined with MNCs for inducing articular cartilage regeneration. Importantly, ACM-based biomimetic scaffolds instantly enriched MNCs could improve the repair effect of articular cartilage defects in situ, which established a new model of articular cartilage regeneration that could be applied immediately and suited for large-scale clinical promotion. The current study significantly improves the repair effect of articular cartilage defects, which provides scientific evidence and detailed insights for future clinical applications of ACM-based biomimetic scaffolds combined with MNCs.

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Explore the maximum scope of repairing articular cartilage defect with ACM scaffold.

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Immediate enrichment of mononuclear cells by density gradient centrifugation.

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ACM scaffold enriched MNCs improve the repair effect of articular cartilage defect.

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Enrichment of MNCs expands the maximum scope of repairing articular cartilage defect.

Engineering of Tracheal Grafts Based on Recellularization of Laser-Engraved Human Airway Cartilage Substrates

OBJECTIVE

Implantation of tissue-engineered tracheal grafts represents a visionary strategy for the reconstruction of tracheal wall defects after resections and may develop into a last chance for a number of patients with severe cicatricial stenosis. The use of a decellularized tracheal substrate would offer an ideally stiff graft, but the matrix density would challenge efficient remodeling into a living cartilage. In this study, we hypothesized that the pores of decellularized laser-perforated tracheal cartilage (LPTC) tissues can be colonized by adult nasal chondrocytes (NCs) to produce new cartilage tissue suitable for the repair of tracheal defects.

DESIGN

Human, native tracheal specimens, isolated from cadaveric donors, were exposed to decellularized and laser engraving-controlled superficial perforation (300 μm depth). Human or rabbit NCs were cultured on the LPTCs for 1 week. The resulting revitalized tissues were implanted ectopically in nude mice or orthotopically in tracheal wall defects in rabbits. Tissues were assayed histologically and by microtomography analyses before and after implantation.

RESULTS

NCs were able to efficiently colonize the pores of the LPTCs. The extent of colonization (i.e., percentage of viable cells spanning >300 μm of tissue depth), cell morphology, and cartilage matrix deposition improved once the revitalized constructs were implanted ectopically in nude mice. LPTCs could be successfully grafted onto the tracheal wall of rabbits without any evidence of dislocation or tracheal stenosis, 8 weeks after implantation. Rabbit NCs, within the LPTCs, actively produced new cartilage matrix.

CONCLUSION

Implantation of NC-revitalized LPTCs represents a feasible strategy for the repair of tracheal wall defects.

In vivo biocompatibility analysis of the recellularized canine tracheal scaffolds with canine epithelial and endothelial progenitor cells

Decellularized extracellular matrix (ECM) has frequently been applied as a biomaterial for tissue engineering purposes. When implanted, their role can be essential for partial trachea replacement in patients that require a viable transplant solution. Acellular canine tracheal scaffolds with preserved ECM structure, flexibility, and proteins were obtained by high pressure vacuum decellularization. Here, we aimed to evaluate the cell adhesion and proliferation of canine tracheal epithelial cells (EpC) and canine yolk sac endothelial progenitor cells (YS) cultivated on canine decellularized tracheal scaffolds and test the in vivo biocompatibility of these recellularized scaffolds implanted in BALB-c nude mice. In order to evaluate the recellularization efficiency, scaffolds were evaluated by scanning electron microscopy (SEM), immunofluorescence, DNA quantification, mycoplasma test, and in vivo biocompatibility. The scaffolds sterility was confirmed, and EpC and YS cells were cultured by 7 and 14 days. We demonstrated by SEM, immunofluorescence, and genomic DNA analyzes cell adhesion to tracheal ECM. Then, recellularized scaffolds were in vivo subcutaneously implanted in mice and after 45 days, the fragments were collected and analyzed by Hematoxylin-Eosin and Gömori Trichrome staining and PCNA, CD4, CD8, and CD68 immunohistochemistry. In vivo results confirmed that the implanted tissue remains preserved and proliferative, and no fibrotic tissue process was observed in animals. Finally, our results showed the recellularization success due the preserved ECM proteins, and that these may be suitable to future preclinical studies applications for partial trachea replacement in tissue engineering.

Biomimetic Trachea Engineering via a Modular Ring Strategy Based on Bone-Marrow Stem Cells and Atelocollagen for Use in Extensive Tracheal Reconstruction

The fabrication of biomimetic tracheas with a architecture of cartilaginous rings alternately interspersed between vascularized fibrous tissue (CRVFT) has the potential to perfectly recapitulate the normal tracheal structure and function. Herein, the development of a customized chondroitin-sulfate-incorporating type-II atelocollagen (COL II/CS) scaffold with excellent chondrogenic capacity and a type-I atelocollagen (COL I) scaffold to facilitate the formation of vascularized fibrous tissue is described. An efficient modular ring strategy is then adopted to develop a CRVFT-based biomimetic trachea. The in vitro engineering of cartilaginous rings is achieved via the recellularization of ring-shaped COL II/CS scaffolds using bone marrow stem cells as a mimetic for native cartilaginous ring tissue. A CRVFT-based trachea with biomimetic mechanical properties, composed of bionic biochemical components, is additionally successfully generated in vivo via the alternating stacking of cartilaginous rings and ring-shaped COL I scaffolds on a silicone pipe. The resultant biomimetic trachea with pedicled muscular flaps is used for extensive tracheal reconstruction and exhibits satisfactory therapeutic outcomes with structural and functional properties similar to those of native trachea. This is the first study to utilize stem cells for long-segmental tracheal cartilaginous regeneration and this represents a promising method for extensive tracheal reconstruction.

Hierarchical porous bacterial cellulose scaffolds with natural biomimetic nanofibrous structure and a cartilage tissue-specific microenvironment for cartilage regeneration and repair

The limited three-dimensional (3D) nano-scale pore structure and lack of biological function hamper the application of bacterial cellulose (BC) in cartilage tissue engineering. To address this challenge, 3D hierarchical porous BC/decellularized cartilage extracellular matrix (DCECM) scaffolds with structurally and biochemically biomimetic cartilage regeneration microenvironment were fabricated by freeze-drying technique after EDC/NHS chemical crosslinking. The BC/DCECM scaffolds exhibited excellent mechanical properties, water superabsorbency and shape-memory properties. Compared with the BC control, the BC/DCECM scaffolds exhibited enhanced cell adhesion and proliferation. Cartilage regeneration in vitro and in vivo indicated that the BC/DCECM scaffolds achieved satisfactory neocartilage tissue regeneration with superior original shape fidelity, exterior natural cartilage-like appearance and histologically cartilage-specific lacuna formation and ECM deposition. Furthermore, the BC/DCECM scaffolds achieved superior repair outcomes, as hyaline cartilage-like tissue formed within the defect sites. The present study constitutes a strong step toward the further application of BC in cartilage tissue engineering.

Development and clinical translation of tubular constructs for tracheal tissue engineering: a review

Effective restoration of extensive tracheal damage arising from cancer, stenosis, infection or congenital abnormalities remains an unmet clinical need in respiratory medicine. The trachea is a 10-11 cm long fibrocartilaginous tube of the lower respiratory tract, with 16-20 tracheal cartilages anterolaterally and a dynamic trachealis muscle posteriorly. Tracheal resection is commonly offered to patients suffering from short-length tracheal defects, but replacement is required when the trauma exceeds 50% of total length of the trachea in adults and 30% in children. Recently, tissue engineering (TE) has shown promise to fabricate biocompatible tissue-engineered tracheal implants for tracheal replacement and regeneration. However, its widespread use is hampered by inadequate re-epithelialisation, poor mechanical properties, insufficient revascularisation and unsatisfactory durability, leading to little success in the clinical use of tissue-engineered tracheal implants to date. Here, we describe in detail the historical attempts and the lessons learned for tracheal TE approaches by contextualising the clinical needs and essential requirements for a functional tracheal graft. TE manufacturing approaches explored to date and the clinical translation of both TE and non-TE strategies for tracheal regeneration are summarised to fully understand the big picture of tracheal TE and its impact on clinical treatment of extensive tracheal defects.

Decellularized tracheal scaffolds in tracheal reconstruction: An evaluation of different techniques

In humans, the trachea is a conduit for ventilation connecting the throat and lungs. However, certain congenital or acquired diseases may cause long-term tracheal defects that require replacement. Tissue engineering is considered a promising method to reconstruct long-segment tracheal lesions and restore the structure and function of the trachea. Decellularization technology retains the natural structure of the trachea, has good biocompatibility and mechanical properties, and is currently a hotspot in tissue engineering studies. This article lists various recent representative protocols for the generation of decellularized tracheal scaffolds (DTSs), as well as their validity and limitations. Based on the advancements in decellularization methods, we discussed the impact and importance of mechanical properties, revascularization, recellularization, and biocompatibility in the production and implantation of DTS. This review provides a basis for future research on DTS and its application in clinical therapy.

The characterization, cytotoxicity, macrophage response and tissue regeneration of decellularized cartilage in costal cartilage defects

After harvesting multiple costal cartilages, the local defect disrupts the integrity of the chest wall and may lead to obvious thoracic complications, such as local depression and asymmetry of the bilateral thoracic height. Decellularized materials have been used for tissue reconstruction in clinical surgeries. To apply xenogenic decellularized cartilage in costal cartilage defects, porcine-derived auricular and costal cartilage was tested for characterization, cytotoxicity, macrophage response, and tissue regeneration. Most of the DNA and α-Gal were effectively removed, and the collagen was well preserved after the decellularization process. The glycosaminoglycan (GAG) content decreased significantly compared to that in untreated cartilage. The decellularized auricular cartilage had a larger pore size, more pores, and a higher degradation rate than the decellularized costal cartilage. No apparent nuclei or structural damage was observed in the extracellular matrix. The decellularized auricular cartilage had a higher cell proliferation rate and more prominent immunomodulatory effect than the other groups. Two types of decellularized cartilage, particularly decellularized auricular cartilage, promoted the tissue regeneration in the cartilage defect area, combined with noticeable cartilage morphology and increased chondrogenic gene expression. In our research, the functional components and structure of the extracellular matrix were well preserved after the decellularization process. The decellularized cartilage had better biocompatibility and suitable microenvironment for tissue regeneration in the defect area, suggesting its potential application in cartilage repair during the surgery. STATEMENT OF SIGNIFICANCE: Autologous costal cartilage has been widely used in various surgeries, while the cartilage defects after the harvesting of multiple costal cartilages may cause localized chest wall deformities. Decellularized cartilage is an ideal material that could be produced in the factory and applied in surgeries. In this study, both decellularized costal cartilage and auricular cartilage preserved original structure, functional biocompatibility, immunosuppressive effects, and promoted tissue regeneration in the cartilage defect area.

Optimization of a decellularization protocol of porcine tracheas. Long-term effects of cryopreservation. A histological study

OBJECTIVE

The aim of this study was to optimize a decellularization protocol in the trachea of Sus scrofa domestica (pig) as well as to study the effects of long-term cryopreservation on the extracellular matrix of decellularized tracheas.

METHODS

Porcine tracheas were decellularized using Triton X-100, SDC, and SDS alone or in combination. The effect of these detergents on the extracellular matrix characteristics of decellularized porcine tracheas was evaluated at the histological, biomechanical, and biocompatibility level. Morphometric approaches were used to estimate the effect of detergents on the collagen and elastic fibers content as well as on the removal of chondrocytes from decellularized organs. Moreover, the long-term structural, ultrastructural, and biomechanical effect of cryopreservation of decellularized tracheas were also estimated.

RESULTS

Two percent SDS was the most effective detergent tested concerning cell removal and preservation of the histological and biomechanical properties of the tracheal wall. However, long-term cryopreservation had no an appreciable effect on the structure, ultrastructure, and biomechanics of decellularized tracheal rings.

CONCLUSION

The results presented here reinforce the use of SDS as a valuable decellularizing agent for porcine tracheas. Furthermore, a cryogenic preservation protocol is described, which has minimal impact on the histological and biomechanical properties of decellularized porcine tracheas.

3D bioprinting of a trachea-mimetic cellular construct of a clinically relevant size

Despite notable advances in extrusion-based 3D bioprinting, it remains a challenge to create a clinically-sized cellular construct using extrusion-based 3D printing due to long printing times adversely affecting cell viability and functionality. Here, we present an advanced extrusion-based 3D bioprinting strategy composed of a two-step printing process to facilitate creation of a trachea-mimetic cellular construct of clinically relevant size. A porous bellows framework is first printed using typical extrusion-based 3D printing. Selective printing of cellular components, such as cartilage rings and epithelium lining, is then performed on the outer grooves and inner surface of the bellows framework by a rotational printing process. With this strategy, 3D bioprinting of a trachea-mimetic cellular construct of clinically relevant size is achieved in significantly less total printing time compared to a typical extrusion-based 3D bioprinting strategy which requires printing of an additional sacrificial material. Tracheal cartilage formation was successfully demonstrated in a nude mouse model through a subcutaneous implantation study of trachea-mimetic cellular constructs wrapped with a sinusoidal-patterned tubular mesh preventing rapid resorption of cartilage rings in vivo. This two-step 3D bioprinting for a trachea-mimetic cellular construct of clinically relevant size can provide a fundamental step towards clinical translation of 3D bioprinting based tracheal reconstruction.

Accelerated tissue regeneration in decellularized vascular grafts with a patterned pore structure

Decellularized tissue is expected to be utilized as a regenerative scaffold. However, the migration of host cells into the central region of the decellularized tissues is minimal because the tissues are mainly formed with dense collagen and elastin fibers. This results in insufficient tissue regeneration. Herein, it is demonstrated that host cell migration can be accelerated by using decellularized tissue with a patterned pore structure. Patterned pores with inner diameters of 24.5 ± 0.4 μm were fabricated at 100, 250, and 500 μm intervals in the decellularized vascular grafts via laser ablation. The grafts were transplanted into rat subcutaneous tissue for 1, 2, and 4 weeks. All the microporous grafts underwent faster recellularization with macrophages and fibroblast cells than the non-porous control tissue. In the case of non-porous tissue, the cells infiltrated approximately 50% of the area four weeks after transplantation. However, almost the entire area was occupied by the cells after two weeks when the micropores were aligned at a distance of less than 250 μm. These results suggest that host cell infiltration depends on the micropore interval, and a distance shorter than 250 μm can accelerate cell migration into decellularized tissues.

Exosomes from 3T3-J2 promote expansion of tracheal basal cells to facilitate rapid epithelization of 3D-printed double-layer tissue engineered trachea

Functional epithelization plays a pivotal role in maintaining long-term lumen patency of tissue-engineered trachea (TET). Due to the slow migration of autologous epithelium, spontaneous epithelization process of transplanted TET is always tardive. Seeding tracheal basal cells (TBCs) on TET before transplantation might be favorable for accelerating epithelization, but rapid expansion of TBCs in vitro is still relatively intractable. In this study, we proposed a promising expansion strategy which enables the TBCs to proliferate rapidly in vitro. TBCs were isolated from the autologous tracheal mucosae of rabbit, and co-cultured with exosomes derived from 3T3-J2 cells. After co-culture with exosomal component, TBCs could vigorously proliferate in vitro and retained their multi-potency. It was in stark contrast to that the single-cultured TBCs could only be expand to passage 2 in about 30 days, moreover, the most majority of single-cultured cells entered late apoptotic stage. On the other hand, a bionic tubular double-layer scaffold with good mechanical property and bio-compatibility was designed and fabricated by 3D printing technology. Then TET with bi-lineage cell-type was constructed in vitro by implanting autologous chondrocytes on the outer-layer of scaffold, and TBCs on the inner-layer, respectively. And then TET was pre-vascularized in vivo, and pedicled transplanted to restore long-segmental defect in recipient rabbits. It was found that the chondrocytes and TBCs seeded on double-layer scaffolds developed well as expected. And almost complete coverage with ciliated epitheliums was observed on the lumen surface of TET 2-week after operation, in comparison with that the epithelization of TET without pre-seeding of TBCs accomplished nearly 2-month after operation. In conclusion, the promising expansion strategy of TBCs together with 3D-printed double-layer scaffolds facilitate the rapid epithelization process of transplanted TET, which might be of vital significance for clinical and translational medicine.

Hollow fibers: from fabrication to applications

Hollow fibers have attracted more and more attention due to their broad range of applications in numerous fields. We review the latest advance and summarize the fabrication methods, types and applications of hollow fibers. We mainly introduce the fabrication methods of hollow fibers, including co-extrusion/co-axial spinning methods, template methods, 3D printing methods, electrospinning methods, self-crimping methods and gas foaming process. Meanwhile, we summarize four types of hollow fibers: one-layered hollow fibers, multi-layered hollow fibers, multi-hollow fibers and branched hollow fibers. Next, we focus on the main applications of hollow fibers, such as gas separation, cell culture, microfluidic channels, artificial tubular tissues, etc. Finally, we present the prospects of the future trend of development. The review would promote the further development of hollow fibers and benefit their advance in sensing, bioreactors, electrochemical catalysis, energy conversion, microfluidics, gas separation, air purification, drug delivery, functional materials, cell culture and tissue engineering. This review has great significance for the design of new functional materials and development of devices and systems in the related fields.

Three-dimensional porous gas-foamed electrospun nanofiber scaffold for cartilage regeneration

To achieve optimal functional recovery of articular cartilage, scaffolds with nanofibrous structure and biological function have been widely pursued. In this study, two-dimensional electrospun poly(l-lactide-co-ε-caprolactone)/silk fibroin (PLCL/SF) scaffolds (2DS) were fabricated by dynamic liquid support (DLS) electrospinning system, and then cross-linked with hyaluronic acid (HA) to further mimic the microarchitecture of native cartilage. Subsequently, three-dimensional PLCL/SF scaffolds (3DS) and HA-crosslinked three-dimensional scaffolds (3DHAS) were successfully fabricated by in situ gas foaming and freeze-drying. 3DHAS exhibited better mechanical properties than that of the 3DS. Moreover, all scaffolds exhibited excellent biocompatibility in vitro. 3DHAS showed better proliferation and phenotypic maintenance of chondrocytes as compared to the other scaffolds. Histological analysis of cell-scaffold constructs explanted 8 weeks after implantation demonstrated that both 3DS and 3DHAS scaffolds formed cartilage-like tissues, and the cartilage lacuna formed in 3DHAS scaffolds was more mature. Moreover, the reparative capacity of scaffolds was discerned after implantation in the full-thickness articular cartilage model in rabbits for up to 12 weeks. The macroscopic and histological results exhibited typical cartilage-like character and well-integrated boundary between 3DHAS scaffolds and the host tissues. Collectively, biomimetic 3DHAS scaffolds may be promising candidates for cartilage tissue regeneration applications.

Vascularization strategies for tissue engineering for tracheal reconstruction

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. Although several tracheal replacement therapy strategies have been developed in the past, the critical significance of the formation of microvascular networks in 3D scaffolds has not attracted sufficient attention. Here, we review key technologies and related factors of microvascular network construction in tissue-engineered trachea and explore optimized preparation processes of vascularized functional tissues for clinical applications.

Engineering a Highly Biomimetic Chitosan-Based Cartilage Scaffold by Using Short Fibers and a Cartilage-Decellularized Matrix

Engineering scaffolds with structurally and biochemically biomimicking cues is essential for the success of tissue-engineered cartilage. Chitosan (CS)-based scaffolds have been widely used for cartilage regeneration due to its chemostructural similarity to the glycosaminoglycans (GAGs) found in the extracellular matrix of cartilage. However, the weak mechanical properties and inadequate chondroinduction capacity of CS give rise to compromised efficacy of cartilage regeneration. In this study, we incorporated short fiber segments, processed from electrospun aligned poly(lactic-co-glycolic acid) (PLGA) fiber arrays, into a citric acid-modified chitosan (CC) hydrogel scaffold for mechanical strengthening and structural biomimicking and meanwhile introduced cartilage-decellularized matrix (CDM) for biochemical signaling to promote the chondroinduction activity. We found that the incorporation of PLGA short fibers and CDM remarkably strengthened the mechanical properties of the CC hydrogel (+349% in compressive strength and +153% in Young's modulus), which also exhibited a large pore size, appropriate porosity, and fast water absorption ability. Biologically, the engineered CDM-Fib/CC scaffold significantly promoted the adhesion and proliferation of chondrocytes and supported the formation of matured cartilage tissue with a cartilagelike structure and deposition of abundant cartilage ECM-specific GAGs and type II collagen (+42% in GAGs content and +295% in type II collagen content). The enhanced mechanical competency and chondroinduction capacity with the engineered CDM-Fib/CC scaffold eventually fulfilled successful in situ osteochondral regeneration in a rabbit model. This study thereby demonstrated a great potential of the engineered highly biomimetic chitosan-based scaffold in cartilage tissue repair and regeneration.

SP600125, a JNK-Specific Inhibitor, Regulates in vitro Auricular Cartilage Regeneration by Promoting Cell Proliferation and Inhibiting Extracellular Matrix Metabolism

In vitro construction is a major trend involved in cartilage regeneration and repair. Satisfactory in vitro cartilage regeneration depends on a suitable culture system. Current chondrogenic culture systems with a high content of transforming growth factor beta-1 effectively promote cartilaginous extracellular matrix (ECM) production but inhibit chondrocyte survival. As is known, inhibition of the c-Jun N-terminal kinase (JNK) signaling pathway acts in blocking the progression of osteoarthritis by reducing chondrocyte apoptosis and cartilage destruction. However, whether inhibiting JNK signaling resists the inhibitory effect of current chondrogenic medium (CM) on cell survival and affects in vitro auricular cartilage regeneration (including cell proliferation, ECM synthesis, and degradation) has not been investigated. In order to address these issues and optimize the chondrogenic culture system, we generated a three-dimensional in vitro auricular cartilage regeneration model to investigate the effects of SP600125 (a JNK-specific inhibitor) on chondrocyte proliferation and ECM metabolism. SP600125 supplementation efficiently promoted cell proliferation at both cellular and tissue levels and canceled the negative effect of our chondrogenic culture system on cell survival. Moreover, it significantly inhibited ECM degradation by reducing the expressions of tumor necrosis factor-alpha, interleukin-1-beta, and matrix metalloproteinase 13. In addition, SP600125 inhibited ECM synthesis at both cellular and tissue levels, but this could be canceled and even reversed by adding chondrogenic factors; yet this enabled a sufficient number of chondrocytes to be retained at the same time. Thus, SP600125 had a positive effect on in vitro auricular cartilage regeneration in terms of cell proliferation and ECM degradation but a negative effect on ECM synthesis, which could be reversed by adding CM. Therefore, a combination of SP600125 and CM might help in optimizing current chondrogenic culture systems and achieve satisfactory in vitro cartilage regeneration by promoting cell proliferation, reducing ECM degradation, and enhancing ECM synthesis.

Nanostructured Biomaterials for In Vitro Models of Bone Metastasis Cancer

In recent years, tissue engineering approaches have attracted substantial attention owing to their ability to create physiologically relevant in vitro disease models that closely mimic in vivo conditions. Here, we review nanocomposite materials and scaffolds used for the design of in vitro models of cancer, including metastatic sites. We discuss the role of material properties in modulating cellular phenotype in 3D disease models. Also, we highlight the application of tissue-engineered bone as a tool for faithful recapitulation of the microenvironment of metastatic prostate and breast cancer, since these two types of cancer have the propensity to metastasize to bone. Overall, we summarize recent efforts on developing 3D in vitro models of bone metastatic cancers that provide a platform to study tumor progression and facilitate high-throughput drug screening.

3D Cartilage Regeneration With Certain Shape and Mechanical Strength Based on Engineered Cartilage Gel and Decalcified Bone Matrix

Scaffold-free cartilage-sheet technology can stably regenerate high-quality cartilage tissue in vivo. However, uncontrolled shape maintenance and mechanical strength greatly hinder its clinical translation. Decalcified bone matrix (DBM) has high porosity, a suitable pore structure, and good biocompatibility, as well as controlled shape and mechanical strength. In this study, cartilage sheet was prepared into engineered cartilage gel (ECG) and combined with DBM to explore the feasibility of regenerating 3D cartilage with controlled shape and mechanical strength. The results indicated that ECG cultured in vitro for 3 days (3 d) and 15 days (15 d) showed good biocompatibility with DBM, and the ECG–DBM constructs successfully regenerated viable 3D cartilage with typical mature cartilage features in both nude mice and autologous goats. Additionally, the regenerated cartilage had comparable mechanical properties to native cartilage and maintained its original shape. To further determine the optimal seeding parameters for ECG, the 3 d ECG regenerated using human chondrocytes was diluted in different concentrations (1:3, 1:2, and 1:1) for seeding and in vivo implantation. The results showed that the regenerated cartilage in the 1:2 group exhibited better shape maintenance and homogeneity than the other groups. The current study established a novel mode of 3D cartilage regeneration based on the design concept of steel (DBM)-reinforced concrete (ECG) and successfully regenerated homogenous and mature 3D cartilage with controlled shape and mechanical strength, which hopefully provides an ideal cartilage graft for the repair of various cartilage defects.

A Biomimetic Biphasic Scaffold Consisting of Decellularized Cartilage and Decalcified Bone Matrixes for Osteochondral Defect Repair

It is challenging to develop a biphasic scaffold with biomimetic compositional, structural, and functional properties to achieve concomitant repair of both superficial cartilage and subchondral bone in osteochondral defects (OCDs). This study developed a biomimsubchondraletic biphasic scaffold for OCD repair via an iterative layered lyophilization technique that controlled the composition, substrate stiffness, and pore size in each phase of the scaffold. The biphasic scaffold consisted of a superficial decellularized cartilage matrix (DCM) and underlying decalcified bone matrix (DBM) with distinct but seamlessly integrated phases that mimicked the composition and structure of osteochondral tissue, in which the DCM phase had relative low stiffness and small pores (approximately 134 μm) and the DBM phase had relative higher stiffness and larger pores (approximately 336 μm). In vitro results indicated that the biphasic scaffold was biocompatible for bone morrow stem cells (BMSCs) adhesion and proliferation, and the superficial DCM phase promoted chondrogenic differentiation of BMSCs, as indicated by the up-regulation of cartilage-specific gene expression (ACAN, Collagen II, and SOX9) and sGAG secretion; whereas the DBM phase was inducive for osteogenic differentiation of BMSCs, as indicated by the up-regulation of bone-specific gene expression (Collagen I, OCN, and RUNX2) and ALP deposition. Furthermore, compared with the untreated control group, the biphasic scaffold significantly enhanced concomitant repair of superficial cartilage and underlying subchondral bone in a rabbit OCD model, as evidenced by the ICRS macroscopic and O’Driscoll histological assessments. Our results demonstrate that the biomimetic biphasic scaffold has a good osteochondral repair effect.

Repopulation of decellularised articular cartilage by laser-based matrix engraving

BACKGROUND

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

METHODS

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

FINDINGS

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

INTERPRETATION

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

FUNDING

Austrian Research Promotion Agency FFG ("CartiScaff" #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08).

3D Printed Biomimetic PCL Scaffold as Framework Interspersed With Collagen for Long Segment Tracheal Replacement

The rapid development of tissue engineering technology has provided new methods for tracheal replacement. However, none of the previously developed biomimetic tracheas exhibit both the anatomy (separated-ring structure) and mechanical behavior (radial rigidity and longitudinal flexibility) mimicking those of native trachea, which greatly restricts their clinical application. Herein, we proposed a biomimetic scaffold with a separated-ring structure: a polycaprolactone (PCL) scaffold with a ring-hollow alternating structure was three-dimensionally printed as a framework, and collagen sponge was embedded in the hollows amid the PCL rings by pouring followed by lyophilization. The biomimetic scaffold exhibited bionic radial rigidity based on compressive tests and longitudinal flexibility based on three-point bending tests. Furthermore, the biomimetic scaffold was recolonized by chondrocytes and developed tracheal cartilage in vitro. In vivo experiments showed substantial deposition of tracheal cartilage and formation of a biomimetic trachea mimicking the native trachea both structurally and mechanically. Finally, a long-segment tracheal replacement experiment in a rabbit model showed that the engineered biomimetic trachea elicited a satisfactory repair outcome. These results highlight the advantage of a biomimetic trachea with a separated-ring structure that mimics the native trachea both structurally and mechanically and demonstrates its promise in repairing long-segment tracheal defects.

Repopulation of decellularised articular cartilage by laser-based matrix engraving

Background

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

Methods

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

Findings

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

Interpretation

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

Funding

Austrian Research Promotion Agency FFG (“CartiScaff” #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08)

Biological Evaluation of Acellular Cartilaginous and Dermal Matrixes as Tissue Engineering Scaffolds for Cartilage Regeneration

An acellular matrix (AM) as a kind of natural biomaterial is gaining increasing attention in tissue engineering applications. An acellular cartilaginous matrix (ACM) and acellular dermal matrix (ADM) are two kinds of the most widely used AMs in cartilage tissue engineering. However, there is still debate over which of these AMs achieves optimal cartilage regeneration, especially in immunocompetent large animals. In the current study, we fabricated porous ADM and ACM scaffolds by a freeze-drying method and confirmed that ADM had a larger pore size than ACM. By recolonization with goat auricular chondrocytes and in vitro culture, ADM scaffolds exhibited a higher cell adhesion rate, more homogeneous chondrocyte distribution, and neocartilage formation compared with ACM. Additionally, quantitative polymerase chain reaction (qPCR) indicated that expression of cartilage-related genes, including ACAN, COLIIA1, and SOX9, was significantly higher in the ADM group than the ACM group. Furthermore, after subcutaneous implantation in a goat, histological evaluation showed that ADM achieved more stable and matured cartilage compared with ACM, which was confirmed by quantitative data including the wet weight, volume, and contents of DNA, GAG, total collagen, and collagen II. Additionally, immunological assessment suggested that ADM evoked a low immune response compared with ACM as evidenced by qPCR and immunohistochemical analyses of CD3 and CD68, and TUNEL. Collectively, our results indicate that ADM is a more suitable AM for cartilage regeneration, which can be used for cartilage regeneration in immunocompetent large animals.

Building a Functional Salivary Gland for Cell-Based Therapy: More than Secretory Epithelial Acini

A few treatment options exist for patients experiencing xerostomia due to hyposalivation that occurs as a result of disease or injury to the gland. An opportunity for a permanent solution lies in the field of salivary gland replacement through tissue engineering. Recent success emboldens in the vision of producing a tissue-engineered salivary gland composed of differentiated salivary epithelial cells that are able to differentiate to form functional units that produce and deliver saliva to the oral cavity. This vision is augmented by advances in understanding cellular mechanisms that guide branching morphogenesis and salivary epithelial cell polarization in both acinar and ductal structures. Growth factors and other guidance cues introduced into engineered constructs help to develop a more complex glandular structure that seeks to mimic native salivary gland tissue. This review describes the separate epithelial phenotypes that make up the gland, and it describes their relationship with the other cell types such as nerve and vasculature that surround them. The review is organized around the links between the native components that form and contribute to various aspects of salivary gland development, structure, and function and how this information can drive the design of functional tissue-engineered constructs. In addition, we discuss the attributes of various biomaterials commonly used to drive function and form in engineered constructs. The review also contains a current description of the state-of-the-art of the field, including successes and challenges in creating materials for preclinical testing in animal models. The ability to integrate biomolecular cues in combination with a range of materials opens the door to the design of increasingly complex salivary gland structures that, once accomplished, can lead to breakthroughs in other fields of tissue engineering of epithelial-based exocrine glands or oral tissues.