Successful creation of tissue-engineered autologous auricular cartilage in an immunocompetent large animal model

Suitability of Ex Vivo-Expanded Microtic Perichondrocytes for Auricular Reconstruction

Tissue engineering (TE) techniques offer solutions for tissue regeneration but require large quantities of cells. For microtia patients, TE methods represent a unique opportunity for therapies with low donor-site morbidity and reliance on the surgeon's individual expertise. Microtia-derived chondrocytes and perichondrocytes are considered a valuable cell source for autologous reconstruction of the pinna. The aim of this study was to investigate the suitability of perichondrocytes from microtia patients for autologous reconstruction in comparison to healthy perichondrocytes and microtia chondrocytes. Perichondrocytes were isolated via two different methods: explant culture and enzymatic digestion. The isolated cells were analyzed in vitro for their chondrogenic cell properties. We examined migration activity, colony-forming ability, expression of mesenchymal stem cell markers, and gene expression profile. We found that microtic perichondrocytes exhibit similar chondrogenic properties compared to chondrocytes in vitro. We investigated the behavior in three-dimensional cell cultures (spheroids and scaffold-based 3D cell cultures) and assessed the expression of cartilage-specific proteins via immunohistochemistry, e.g., collagen II, which was detected in all samples. Our results show that perichondrocytes from microtia patients are comparable to healthy perichondrocytes and chondrocytes in terms of chondrogenic cell properties and could therefore be a promising cell source for auricular reconstruction.

The Promise of Regenerative Medicine in the Reconstruction of Auricular Cartilage Deformities

There are many physiologic and psychologic challenges associated with ear cartilage deformities which are incredibly distasteful to patients, particularly children. The development of regenerative medicine (RM) sciences has opened up a new window for the reconstruction of auricular cartilage because it allows the creation of a structure similar to the auricular in appearance and function. As part of this review, we discuss the role that each RM tool, including tissue engineering, cells, and biomolecules, plays in developing engineered auricular tissue. In previous studies, it was shown that the simultaneous use of natural and synthetic biomaterials as well as three-dimensional printing techniques could improve the biological and mechanical properties of this tissue. Another critical issue is using stem cells and differentiated cartilage cells to produce tissue-specific cellular structures and extracellular matrix. Also, the importance of choosing a suitable animal model in terms of handling and care facilities, physiologic similarities to humans, and breed uniformity in the preclinical assessments have been highlighted. Then, the clinical trials registered on the clinicaltrials.gov website, and the commercialized product, called AuriNovo, have been comprehensively explained. Overall, it is important to provide engineered auricular cartilage structures with acceptable safety and efficacy compared with standard methods, autologous cartilage transplantation, and prosthetic reconstruction in RM.

Cartilage tissue engineering by extrusion bioprinting utilizing porous hyaluronic acid microgel bioinks

3D bioprinting offers an excellent opportunity to provide tissue-engineered cartilage to microtia patients. However, hydrogel-based bioinks are hindered by their dense and cell-restrictive environment, impairing tissue development and ultimately leading to mechanical failure of large scaffoldsin vivo. Granular hydrogels, made of annealed microgels, offer a superior alternative to conventional bioinks, with their improved porosity and modularity. We have evaluated the ability of enzymatically crosslinked hyaluronic acid (HA) microgel bioinks to form mature cartilagein vivo. Microgel bioinks were formed by mechanically sizing bulk HA-tyramine hydrogels through meshes with aperture diameters of 40, 100 or 500µm. Annealing of the microgels was achieved by crosslinking residual tyramines. Secondary crosslinked scaffolds were stable in solution and showed tunable porosity from 9% to 21%. Bioinks showed excellent rheological properties and were used to print different objects. Printing precision was found to be directly correlated to microgel size. As a proof of concept, freeform reversible embedding of suspended hydrogels printing with gelation triggered directly in the bath was performed to demonstrate the versatility of the method. The granular hydrogels support the homogeneous development of mature cartilage-like tissuesin vitrowith mechanical stiffening up to 200 kPa after 63 d. After 6 weeks ofin vivoimplantation, small-diameter microgels formed stable constructs with low immunogenicity and continuous tissue maturation. Conversely, increasing the microgel size resulted in increased inflammatory response, with limited stabilityin vivo. This study reports the development of new microgel bioinks for cartilage tissue biofabrication and offers insights into the foreign body reaction towards porous scaffolds implantation.

Regeneration of Subcutaneous Cartilage in a Swine Model Using Autologous Auricular Chondrocytes and Electrospun Nanofiber Membranes Under Conditions of Varying Gelatin/PCL Ratios

The scarcity of ideal biocompatible scaffolds makes the regeneration of cartilage in the subcutaneous environment of large animals difficult. We have previously reported the successful regeneration of good-quality cartilage in a nude mouse model using the electrospun gelatin/polycaprolactone (GT/PCL) nanofiber membranes. The GT/PCL ratios were varied to generate different sets of membranes to conduct the experiments. However, it is unknown whether these GT/PCL membranes can support the process of cartilage regeneration in an immunocompetent large animal model. We seeded swine auricular chondrocytes onto different GT/PCL nanofiber membranes (GT:PCL = 30:70, 50:50, and 70:30) under the sandwich cell-seeding mode. Prior to subcutaneously implanting the samples into an autologous host, they were cultured in vitro over a period of 2 weeks. The results revealed that the nanofiber membranes with different GT/PCL ratios could support the process of subcutaneous cartilage regeneration in an autologous swine model. The maximum extent of homogeneity in the cartilage tissues was achieved when the G5P5 (GT: PC = 50: 50) group was used for the regeneration of cartilage. The formed homogeneous cartilage tissues were characterized by the maximum cartilage formation ratio. The extents of the ingrowth of the fibrous tissues realized and the extents of infiltration of inflammatory cells achieved were found to be the minimum in this case. Quantitative analyses were conducted to determine the wet weight, cartilage-specific extracellular matrix content, and Young’s modulus. The results indicated that the optimal extent of cartilage formation was observed in the G5P5 group. These results indicated that the GT/PCL nanofiber membranes could serve as a potential scaffold for supporting subcutaneous cartilage regeneration under clinical settings. An optimum GT/PCL ratio can promote cartilage formation.

Chondrocyte-laden GelMA hydrogel combined with 3D printed PLA scaffolds for auricle regeneration

The current gold standard for auricular reconstruction after microtia or ear trauma is the autologous cartilage graft with an autologous skin flap overlay. Harvesting autologous cartilage requires an additional surgery that may result in donor area complications. In addition, autologous cartilage is limited and the auricular reconstruction requires complex sculpting, which requires excellent clinical skill and is very time consuming. This work explores the use of 3D printing technology to fabricate bioactive artificial auricular cartilage using chondrocyte-laden gelatin methacrylate (GelMA) and polylactic acid (PLA) for auricle reconstruction. In this study, chondrocytes were loaded within GelMA hydrogel and combined with the 3D-printed PLA scaffolds to biomimetic the biological mechanical properties and personalized shape. The printing accuracy personalized scaffolds, biomechanics and chondrocyte viability and biofunction of artificial auricle have been studied. It was found that chondrocytes were fixed in the PLA auricle scaffolds via GelMA hydrogels and exhibited good proliferative properties and cellular activity. In addition, new chondrocytes and chondrogenic matrix, as well as type II collagen were observed after 8 weeks of implantation. At the same time, the transplanted auricle complex kept full and delicate auricle shape. This study demonstrates the potential of using 3D printing technology to construct in vitro living auricle tissue. It shows a great prospect in the clinical application of auricle regeneration.

Facial Cartilaginous Reconstruction-A Historical Perspective, State-of-the-Art, and Future Directions

Importance: Reconstruction of facial deformity poses a significant surgical challenge due to the psychological, functional, and aesthetic importance of this anatomical area. There is a need to provide not only an excellent colour and contour match for skin defects, but also a durable cartilaginous structural replacement for nasal or auricular defects. The purpose of this review is to describe the history of, and state-of-the-art techniques within, facial cartilaginous surgery, whilst highlighting recent advances and future directions for this continually advancing specialty. Observations: Limitations of synthetic implants for nasal and auricular reconstruction, such as silicone and porous polyethylene, have meant that autologous cartilage tissue for such cases remains the current gold standard. Similarly, tissue engineering approaches using unrelated cells and synthetic scaffolds have shown limited in vivo success. There is increasing recognition that both the intrinsic and extrinsic microenvironment are important for tissue engineering and synthetic scaffolds fail to provide the necessary cues for cartilage matrix secretion. Conclusions and Relevance: We discuss the first-in-man studies in the context of biomimetic and developmental approaches to engineering durable cartilage for clinical translation. Implementation of engineered autologous tissue into clinical practise could eliminate donor site morbidity and represent the next phase of the facial reconstruction evolution.

State of the art of clinical applications of Tissue Engineering in 2021

Tissue engineering (TE) was introduced almost 30 years ago as a potential technique for regenerating human tissues. However, despite promising laboratory findings, the complexity of the human body, scientific hurdles, and lack of persistent long-term funding still hamper its translation towards clinical applications. In this report, we compile an inventory of clinically applied TE medical products relevant to surgery. A review of the literature, including articles published within the period from 1991 to 2020, was performed according to the PRISMA protocol, using databanks PubMed, Cochrane Library, Web of Science, and Clinicaltrials.gov. We identified 1039 full-length articles as eligible; due to the scarcity of clinical, randomised, controlled trials and case studies, we extended our search towards a broad surgical spectrum. Forty papers involved clinical TE studies. Amongst these, 7 were related to TE protocols for cartilage applied in the reconstruction of nose, ear, and trachea. Nine papers reported TE protocols for articular cartilage, 9 for urological purposes, 7 described TE strategies for cardiovascular aims, and 8 for dermal applications. However, only two clinical studies reported on three-dimensional (3D) and functional long-lasting TE constructs. The concept of generating 3D TE constructs and organs based on autologous molecules and cells is intriguing and promising. The first translational tissue-engineered products and techniques have been clinically implemented. However, despite the 30 years of research and development in this field, TE is still in its clinical infancy. Multiple experimental, ethical, budgetary, and regulatory difficulties hinder its rapid translation. Nevertheless, the first clinical applications show great promise and indicate that the translation towards clinical medical implementation has finally started.

Auricular reconstruction: where are we now? A critical literature review

PURPOSE

Deformities of the external ear can affect psychosocial well-being and hearing. Current gold-standard reconstructive treatment is autologous costal cartilage grafting despite the vast morbidity profile. Tissue engineering using stem cells and 3D printing can create patient-specific reconstructed auricles with superior cosmetic outcomes and reduced morbidity. This review critically analyses recent and breakthrough research in the field of regenerative medicine for the pinna, considering gaps in current literature and suggesting further steps to identify whether this could be the new gold-standard.

METHODS

A literature review was conducted. PubMed (MEDLINE) and Cochrane databases were searched using key terms regenerative medicine, tissue engineering, 3D printing, biofabrication, auricular reconstruction, auricular cartilage, chondrocyte, outer ear and pinna. Studies in which tissue-engineered auricles were implanted into animal or human subjects were included. Exclusion criteria included articles not in English and not published within the last ten years. Titles, abstracts and full texts were screened. Reference searching was conducted and significant breakthrough studies included.

RESULTS

8 studies, 6 animal and 2 human, were selected for inclusion. Strengths and weaknesses of each are discussed. Common limitations include a lack of human studies, small sample sizes and short follow-up times.

CONCLUSION

Regenerative medicine holds significant potential to improve auricular reconstruction. To date there are no large multi-centred human studies in which tissue-engineered auricles have been implanted. However, recent human studies suggest promising results, raising the ever-growing possibility that tissue engineering is the future of auricular reconstruction. We aim to continue developing knowledge in this field.

Proliferation medium in three-dimensional culture of auricular chondrocytes promotes effective cartilage regeneration in vivo

Introduction

Cartilage regeneration have been attracted attentions because of the poor ability of cartilage tissues to regenerate. Three-dimensional (3D) culture of chondrocytes is considered to be advantageous for cartilage regeneration. Although it is plausible that maturation of the constructs before transplantation positively affects the chondrogenesis, matured constructs after cultures for longer periods do not necessarily result in effective cartilage regeneration. In this study, we compared different types of culture media including growth factors which are clinically available. We prepared differentiation medium containing insulin-like growth factor-1 (IGF-1), proliferation medium containing fibroblast growth factor-2 (FGF-2) and insulin, and combination of them, and compared their efficacies on chondrogenesis when used in 3D culture of engineered cartilage constructs.

Methods

Cartilage constructs were fabricated by auricular chondrocytes and atelocollagen, and they were 3D-cultured with four types of media: control medium, differentiation medium, proliferation medium, and combination medium. After 3 weeks of culture, the constructs were analyzed for cell number, gene and protein expressions and mechanical properties. The constructs were also transplanted into nude mice. After 8 weeks, the degree of cartilage regeneration was evaluated. Constructs manufactured with canine auricular chondrocytes were subjected to autologous transplantation into beagles and examined for cartilage regeneration.

Results

During 3D culture, remarkably high gene expression of type II collagen was detected in the construct cultured with the differentiation medium whereas cell apoptosis were suppressed in the proliferation medium. When transplanted into nude mice, the constructs 3D-cultured in the proliferation medium produced abundant cartilage matrices. In autologous implantation model, the construct cultured in the proliferation medium again showed better chondrogenesis than those in other media.

Conclusions

The present study indicates that 3D culture with the proliferation medium maintains the cell viability to potentiate the subsequent cartilage regeneration. Here, we propose that not only differentiation but also high cell viability accompanied by proliferation factors should be taken into account to improve cartilage regeneration.

Bioactive factors for cartilage repair and regeneration: Improving delivery, retention, and activity

Articular cartilage is a remarkable tissue whose sophisticated composition and architecture allow it to withstand complex stresses within the joint. Once injured, cartilage lacks the capacity to self-repair, and injuries often progress to joint wide osteoarthritis (OA) resulting in debilitating pain and loss of mobility. Current palliative and surgical management provides short-term symptom relief, but almost always progresses to further deterioration in the long term. A number of bioactive factors, including drugs, corticosteroids, and growth factors, have been utilized in the clinic, in clinical trials, or in emerging research studies to alleviate the inflamed joint environment or to promote new cartilage tissue formation. However, these therapies remain limited in their duration and effectiveness. For this reason, current efforts are focused on improving the localization, retention, and activity of these bioactive factors. The purpose of this review is to highlight recent advances in drug delivery for the treatment of damaged or degenerated cartilage. First, we summarize material and modification techniques to improve the delivery of these factors to damaged tissue and enhance their retention and action within the joint environment. Second, we discuss recent studies using novel methods to promote new cartilage formation via biofactor delivery, that have potential for improving future long-term clinical outcomes. Lastly, we review the emerging field of orthobiologics, using delivered and endogenous cells as drug-delivering "factories" to preserve and restore joint health. Enhancing drug delivery systems can improve both restorative and regenerative treatments for damaged cartilage. STATEMENT OF SIGNIFICANCE: Articular cartilage is a remarkable and sophisticated tissue that tolerates complex stresses within the joint. When injured, cartilage cannot self-repair, and these injuries often progress to joint-wide osteoarthritis, causing patients debilitating pain and loss of mobility. Current palliative and surgical treatments only provide short-term symptomatic relief and are limited with regards to efficiency and efficacy. Bioactive factors, such as drugs and growth factors, can improve outcomes to either stabilize the degenerated environment or regenerate replacement tissue. This review highlights recent advances and novel techniques to enhance the delivery, localization, retention, and activity of these factors, providing an overview of the cartilage drug delivery field that can guide future research in restorative and regenerative treatments for damaged cartilage.

The effectiveness of allogeneic mesenchymal stem cells therapy for knee osteoarthritis in pigs

Background

Intraarticular injection of the mesenchymal stem cells (MSCs) has shown to be successful for treating osteoarthritis (OA). Nevertheless, many studies have been focusing on autologous MSCs. The following study investigates the safety and effectiveness of intraarticular injection of allogenic MSCs in a pig OA model.

Methods

Superparamagnetic iron oxide (SPIO) nanoparticles were labelled with bone marrow-derived mesenchymal stem cells (BM-MSCs) to allow cells tracking using magnetic resonance imaging (MRI). A pig OA model was established by bilateral medial meniscectomy. Next, SPIO-BM-MSCs were injected into the right knee, while the left knee was left untreated. MRI and radiography were used to assess the degree of OA and to evaluate the effectiveness of allogenic MSCs. Hematoxylin and eosin (H&E), safranin-o fast green staining, toluidine blue, and immunohistochemical staining were used to evaluate the therapeutic effect of the injections.

Results

At concentration of ≤20 µg/mL, SPIO caused no toxicity to BM-MSCs. Four weeks after surgery, OA changes were observed on MRI scan. The SPIO labeled BM-MSCs were found moving towards the impaired part of the cartilage 8 to 24 h after injections. In addition, no significant differences between the right side (therapeutic side) and the left side (untreated side) were observed following histological and immunohistochemistry analysis.

Conclusions

The suitable concentration of SPIO for labelling BMSCs was 20 µg/mL, while the allogenic MSCs could move towards and accumulate around the impaired cartilage. No significant difference was found between treatment and control group.

In Vitro Regeneration of Patient-specific Ear-shaped Cartilage and Its First Clinical Application for Auricular Reconstruction

Microtia is a congenital external ear malformation that can seriously influence the psychological and physiological well-being of affected children. The successful regeneration of human ear-shaped cartilage using a tissue engineering approach in a nude mouse represents a promising approach for auricular reconstruction. However, owing to technical issues in cell source, shape control, mechanical strength, biosafety, and long-term stability of the regenerated cartilage, human tissue engineered ear-shaped cartilage is yet to be applied clinically. Using expanded microtia chondrocytes, compound biodegradable scaffold, and in vitro culture technique, we engineered patient-specific ear-shaped cartilage in vitro. Moreover, the cartilage was used for auricle reconstruction of five microtia patients and achieved satisfactory aesthetical outcome with mature cartilage formation during 2.5years follow-up in the first conducted case. Different surgical procedures were also employed to find the optimal approach for handling tissue engineered grafts. In conclusion, the results represent a significant breakthrough in clinical translation of tissue engineered human ear-shaped cartilage given the established in vitro engineering technique and suitable surgical procedure. This study was registered in Chinese Clinical Trial Registry (ChiCTR-ICN-14005469).

In Vitro Regeneration of Patient-specific Ear-shaped Cartilage and Its First Clinical Application for Auricular Reconstruction

Microtia is a congenital external ear malformation that can seriously influence the psychological and physiological well-being of affected children. The successful regeneration of human ear-shaped cartilage using a tissue engineering approach in a nude mouse represents a promising approach for auricular reconstruction. However, owing to technical issues in cell source, shape control, mechanical strength, biosafety, and long-term stability of the regenerated cartilage, human tissue engineered ear-shaped cartilage is yet to be applied clinically. Using expanded microtia chondrocytes, compound biodegradable scaffold, and in vitro culture technique, we engineered patient-specific ear-shaped cartilage in vitro. Moreover, the cartilage was used for auricle reconstruction of five microtia patients and achieved satisfactory aesthetical outcome with mature cartilage formation during 2.5 years follow-up in the first conducted case. Different surgical procedures were also employed to find the optimal approach for handling tissue engineered grafts. In conclusion, the results represent a significant breakthrough in clinical translation of tissue engineered human ear-shaped cartilage given the established in vitro engineering technique and suitable surgical procedure.

This study was registered in Chinese Clinical Trial Registry (ChiCTR-ICN-14005469).

•

Patient-specific ear-shaped cartilage was engineered in vitro using expanded MCs and compound biodegradable scaffold.

•

The first microtia case treated with the tissue engineered ear-shaped cartilage was follow-up for 2.5 years.

•

Other four cases with similar and different surgical procedures were also presented.

Microtia is a congenital external ear malformation that can seriously influence the psychological and physiological well-being of affected children. Using expanded microtia chondrocytes, compound biodegradable scaffold, and in vitro culture technique, we engineered patient-specific ear-shaped cartilage in vitro, and performed a pilot clinical trial of auricle reconstruction using the engineered ear cartilage on five patients. Satisfactory aesthetical outcome with mature cartilage formation was achieved with the longest follow-up of 2.5 years.

Cartilage engineering in reconstructive surgery: auricular, nasal and tracheal engineering from a surgical perspective

This review provides an update on cartilage tissue engineering with particular focus on the head and neck. It is aimed at scientists and clinicians who are interested in tissue engineering and its clinical applicability. Principal tissue engineering strategies are summarized in the first part of this review. In the second part, current clinical approaches to auricular, nasal and tracheal reconstruction are discussed from a surgical perspective. By this approach, the requirements for clinical applicability are outlined and new insight into relevant aims of research is given to accelerate the transfer from bench to bedside.

Accurate Measurements of the Skin Surface Area of the Healthy Auricle and Skin Deficiency in Microtia Patients

Background:

The limited cranial skin covering auricular implants is an important yet underrated factor in auricular reconstruction for both reconstruction surgery and tissue engineering strategies. We report exact measurements on skin deficiency in microtia patients and propose an accessible preoperative method for these measurements.

Methods:

Plaster ear models (n = 11; male:female = 2:1) of lobular-type microtia patients admitted to the University Medical Center Utrecht in The Netherlands were scanned using a micro-computed tomographic scanner or a cone-beam computed tomographic scanner. The resulting images were converted into mesh models from which the surface area could be calculated.

Results:

The mean total skin area of an adult-size healthy ear was 47.3 cm², with 49.0 cm² in men and 44.3 cm² in women. Microtia ears averaged 14.5 cm², with 15.6 cm² in men and 12.6 cm² in women. The amount of skin deficiency was 25.4 cm², with 26.7 cm² in men and 23.1 cm² in women.

Conclusions:

This study proposes a novel method to provide quantitative data on the skin surface area of the healthy adult auricle and the amount of skin deficiency in microtia patients. We demonstrate that the microtia ear has less than 50% of skin available compared with healthy ears. Limited skin availability in microtia patients can lead to healing problems after auricular reconstruction and poses a significant challenge in the development of tissue-engineered cartilage implants. The results of this study could be used to evaluate outcomes and investigate new techniques with regard to tissue-engineered auricular constructs.

Prolonged in vitro precultivation alleviates post-implantation inflammation and promotes stable subcutaneous cartilage formation in a goat model

Synthetic biodegradable scaffolds such as polylactic acid coated polyglycolic acid (PLA-PGA) are especially suitable for engineering shaped cartilage such as auricle, but they induce a serious inflammatory reaction particularly in the immunologically aggressive subcutaneous site, leading to resorption of the engineered autologous cartilage. Our previous study in a rabbit model has demonstrated 2 weeks of in vitro precultivation could significantly alleviate the post-implantation inflammation induced by PLA-PGA engineered cartilaginous grafts, but reproduction of this result failed in a preclinical goat model. The aims of the current study were to investigate whether prolonged in vitro precultivation could form a mature cartilaginous graft to resist the acute host response and promote stable subcutaneous cartilage formation in a preclinical goat model. Goat chondrocytes were seeded onto PLA-PGA scaffolds, in vitro precultivated for 2, 4, 8, and 12 weeks, and then implanted subcutaneously in autologous goats for 1 and 8 weeks. The in vitro engineered cartilage (vitro-EC) was examined histologically (hematoxylin and eosin, safranin-O, collagen II). The 1 week explants were examined histologically and stained for CD3, CD68, collagen I, and apoptosis. The 8 week explants were evaluated by histology, wet weight, volume, glycosaminoglycan (GAG) quantification and Young's modulus. With prolonged in vitro time, the quality of vitro-EC improved and the amount of scaffold residue decreased; more pronounced cartilage formation with fewer immune cells (CD3 and CD68 positive), apoptotic cells, and less collagen I expression were observed in explants that had been in vitro precultivated for a longer period. The subcutaneously regenerated neocartilage became more mature after prolonged implantation. These results suggested that prolonged in vitro precultivation allowed formation of a mature cartilaginous graft to resist the acute host response and promoted stable subcutaneous cartilage formation in autologous goats. These findings may provide useful reference for engineering auricle, trachea, nose, and eyelid shaped cartilage, for example.

Bone Marrow Mesenchymal Stem Cell-Based Engineered Cartilage Ameliorates Polyglycolic Acid/Polylactic Acid Scaffold-Induced Inflammation Through M2 Polarization of Macrophages in a Pig Model

: The regeneration of tissue-engineered cartilage in an immunocompetent environment usually fails due to severe inflammation induced by the scaffold and their degradation products. In the present study, we compared the tissue remodeling and the inflammatory responses of engineered cartilage constructed with bone marrow mesenchymal stem cells (BMSCs), chondrocytes, or both and scaffold group in pigs. The cartilage-forming capacity of the constructs in vitro and in vivo was evaluated by histological, biochemical, and biomechanical analyses, and the inflammatory response was investigated by quantitative analysis of foreign body giant cells and macrophages. Our data revealed that BMSC-based engineered cartilage suppressed in vivo inflammation through the alteration of macrophage phenotype, resulting in better tissue survival compared with those regenerated with chondrocytes alone or in combination with BMSCs. To further confirm the macrophage phenotype, an in vitro coculture system established by engineered cartilage and macrophages was studied using immunofluorescence, enzyme-linked immunosorbent assay, and gene expression analysis. The results demonstrated that BMSC-based engineered cartilage promoted M2 polarization of macrophages with anti-inflammatory phenotypes including the upregulation of CD206, increased IL-10 synthesis, decreased IL-1β secretion, and alterations in gene expression indicative of M1 to M2 transition. It was suggested that BMSC-seeded constructs have the potential to ameliorate scaffold-induced inflammation and improve cartilaginous tissue regeneration through M2 polarization of macrophages.

SIGNIFICANCE

Finding a strategy that can prevent scaffold-induced inflammation is of utmost importance for the regeneration of tissue-engineered cartilage in an immunocompetent environment. This study demonstrated that bone marrow mesenchymal stem cell (BMSC)-based engineered cartilage could suppress inflammation by increasing M2 polarization of macrophages, resulting in better tissue survival in a pig model. Additionally, the effect of BMSC-based cartilage on the phenotype conversion of macrophages was further studied through an in vitro coculture system. This study could provide further support for the regeneration of cartilage engineering in immunocompetent animal models and provide new insight into the interaction of tissue-engineered cartilage and macrophages.

Combining regenerative medicine strategies to provide durable reconstructive options: auricular cartilage tissue engineering

Recent advances in regenerative medicine place us in a unique position to improve the quality of engineered tissue. We use auricular cartilage as an exemplar to illustrate how the use of tissue-specific adult stem cells, assembly through additive manufacturing and improved understanding of postnatal tissue maturation will allow us to more accurately replicate native tissue anisotropy. This review highlights the limitations of autologous auricular reconstruction, including donor site morbidity, technical considerations and long-term complications. Current tissue-engineered auricular constructs implanted into immune-competent animal models have been observed to undergo inflammation, fibrosis, foreign body reaction, calcification and degradation. Combining biomimetic regenerative medicine strategies will allow us to improve tissue-engineered auricular cartilage with respect to biochemical composition and functionality, as well as microstructural organization and overall shape. Creating functional and durable tissue has the potential to shift the paradigm in reconstructive surgery by obviating the need for donor sites.

Ear-Shaped Stable Auricular Cartilage Engineered from Extensively Expanded Chondrocytes in an Immunocompetent Experimental Animal Model

Advancement of engineered ear in clinical practice is limited by several challenges. The complex, largely unsupported, three-dimensional auricular neocartilage structure is difficult to maintain. Neocartilage formation is challenging in an immunocompetent host due to active inflammatory and immunological responses. The large number of autologous chondrogenic cells required for engineering an adult human-sized ear presents an additional challenge because primary chondrocytes rapidly dedifferentiate during in vitro culture. The objective of this study was to engineer a stable, human ear-shaped cartilage in an immunocompetent animal model using expanded chondrocytes. The impact of basic fibroblast growth factor (bFGF) supplementation on achieving clinically relevant expansion of primary sheep chondrocytes by in vitro culture was determined. Chondrocytes expanded in standard medium were either combined with cryopreserved, primary passage 0 chondrocytes at the time of scaffold seeding or used alone as control. Disk and human ear-shaped scaffolds were made from porous collagen; ear scaffolds had an embedded, supporting titanium wire framework. Autologous chondrocyte-seeded scaffolds were implanted subcutaneously in sheep after 2 weeks of in vitro incubation. The quality of the resulting neocartilage and its stability and retention of the original ear size and shape were evaluated at 6, 12, and 20 weeks postimplantation. Neocartilage produced from chondrocytes that were expanded in the presence of bFGF was superior, and its quality improved with increased implantation time. In addition to characteristic morphological cartilage features, its glycosaminoglycan content was high and marked elastin fiber formation was present. The overall shape of engineered ears was preserved at 20 weeks postimplantation, and the dimensional changes did not exceed 10%. The wire frame within the engineered ear was able to withstand mechanical forces during wound healing and neocartilage maturation and prevented shrinkage and distortion. This is the first demonstration of a stable, ear-shaped elastic cartilage engineered from auricular chondrocytes that underwent clinical-scale expansion in an immunocompetent animal over an extended period of time.

MR elastography for evaluating regeneration of tissue-engineered cartilage in an ectopic mouse model

PURPOSE

The purpose of the present study was to apply noninvasive methods for monitoring regeneration and mechanical properties of tissue-engineered cartilage in vivo at different growth stages using MR elastography (MRE).

METHODS

Three types of scaffolds, including silk, collagen, and gelatin seeded by human mesenchymal stem cells, were implanted subcutaneously in mice and imaged at 9.4T where the shear stiffness and transverse MR relaxation time (T2 ) were measured for the regenerating constructs for 8 wk. An MRE phase contrast spin echo-based sequence was used for collecting MRE images. At the conclusion of the in vivo study, constructs were excised and transcript levels of cartilage-specific genes were quantitated using reverse-transcription polymerase chain reaction.

RESULTS

Tissue-engineered constructs showed a cartilage-like construct with progressive tissue formation characterized by increase in shear stiffness and decrease in T2 that can be correlated with increased cartilage transcript levels including aggrecan, type II collagen, and cartilage oligomeric matrix protein after 8 wk of in vivo culture.

CONCLUSION

Altogether, the outcome of this research demonstrates the feasibility of MRE and MRI for noninvasive monitoring of engineered cartilage construct's growth after implantation and provides noninvasive biomarkers for regeneration, which may be translated into treatment of tissue defects.

Extensively Expanded Auricular Chondrocytes Form Neocartilage In Vivo

OBJECTIVE

Our goal was to engineer cartilage in vivo using auricular chondrocytes that underwent clinically relevant expansion and using methodologies that could be easily translated into health care practice.

DESIGN

Sheep and human chondrocytes were isolated from auricular cartilage biopsies and expanded in vitro. To reverse dedifferentiation, expanded cells were either mixed with cryopreserved P0 chondrocytes at the time of seeding onto porous collagen scaffolds or proliferated with basic fibroblast growth factor (bFGF). After 2-week in vitro incubation, seeded scaffolds were implanted subcutaneously in nude mice for 6 weeks. The neocartilage quality was evaluated histologically; DNA and glycosaminoglycans were quantified. Cell proliferation rates and collagen gene expression profiles were assessed.

RESULTS

Clinically sufficient over 500-fold chondrocyte expansion was achieved at passage 3 (P3); cell dedifferentiation was confirmed by the simultaneous COL1A1/3A1 gene upregulation and COL2A1 downregulation. The chondrogenic phenotype of sheep but not human P3 cells was rescued by addition of cryopreserved P0 chondrocytes. With bFGF supplementation, chondrocytes achieved clinically sufficient expansion at P2; COL2A1 expression was not rescued but COL1A1/3A1genes were downregulated. Although bFGF failed to rescue COL2A1 expression during chondrocyte expansion in vitro, elastic neocartilage with obvious collagen II expression was observed on porous collagen scaffolds after implantation in mice for 6 weeks.

CONCLUSIONS

Both animal and human auricular chondrocytes expanded with low-concentration bFGF supplementation formed high-quality elastic neocartilage on porous collagen scaffolds in vivo.

Suitability of porcine chondrocyte micromass culture to model osteoarthritis in vitro

In vitro tissue models are useful tools for the development of novel therapy strategies in cartilage repair and care. The limited availability of human primary tissue and high costs of animal models hamper preclinical tests of innovative substances and techniques. In this study we tested the potential of porcine chondrocyte micromass cultures to mimic human articular cartilage and essential aspects of osteoarthritis (OA) in vitro. Primary chondrocytes were enzymatically isolated from porcine femoral condyles and were maintained in 96-multiwell format to establish micromass cultures in a high-throughput scale. Recombinant porcine tumor necrosis factor alpha (TNF-α) was used to induce OA-like changes documented on histological (Safranin O, collagen type II staining), biochemical (hydroxyproline assay, dimethylmethylene blue method), and gene expression level (Affymetrix porcine microarray, real time PCR) and were compared with published data from human articular cartilage and human micromass cultures. After 14 days in micromass culture, porcine primary chondrocytes produced ECM rich in proteoglycans and collagens. On gene expression level, significant correlations of detected genes with porcine cartilage (r = 0.90), human cartilage (r = 0.71), and human micromass culture (r = 0.75) were observed including 34 cartilage markers such as COL2A1, COMP, and aggrecan. TNF-α stimulation led to significant proteoglycan (-75%) and collagen depletion (-50%). Comparative expression pattern analysis revealed the involvement of catabolic enzymes (MMP1, -2, -13, ADAM10), chemokines (IL8, CCL2, CXCL2, CXCL12, CCXL14), and genes associated with cell death (TNFSF10, PMAIPI, AHR) and skeletal development (GPNMB, FRZB) including transcription factors (WIF1, DLX5, TWIST1) and growth factors (IGFBP1, -3, TGFB1) consistent with published data from human OA cartilage. Expression of genes related to cartilage ECM formation (COL2A1, COL9A1, COMP, aggrecan) as well as hypertrophic bone formation (COL1A1, COL10A1) was predominantly found decreased. These findings indicating significant parallels between human articular cartilage and the presented porcine micromass model and vice versa confirm the applicability of known cartilage marker and their characteristics in the porcine micromass model. TNF-α treatment enabled the initiation of typical OA reaction patterns in terms of extensive ECM loss, cell death, formation of an inflammatory environment through the induction of genes coding for chemokines and enzymes, and the modulation of genes involved in skeletal development such as growth factors, transcription factors, and cartilage ECM-forming genes. In conclusion, the porcine micromass model represents an alternative tissue platform for the evaluation of innovative substances and techniques for the treatment of OA.