Cartilage tissue engineering for laryngotracheal reconstruction: comparison of chondrocytes from three anatomic locations in the rabbit

A Pilot Study of Decellularized Cartilage for Laryngotracheal Reconstruction in a Neonatal Pig Model

OBJECTIVE

Severe subglottic stenosis develops as a response to intubation in 1% of the >200,000 neonatal intensive care unit infants per year and may require laryngotracheal reconstruction (LTR) with autologous hyaline cartilage. Although effective, LTR is limited by comorbidities, severity of stenosis, and graft integration. In children, there is a significant incidence of restenosis requiring revision surgery. Tissue engineering has been proposed to develop alterative grafting options to improve outcomes and eliminate donor-site morbidity. Our objective is to engineer a decellularized, channel-laden xenogeneic cartilage graft, that we deployed in a proof-of-concept, neonatal porcine LTR model.

METHODS

Meniscal porcine cartilage was freeze-thawed and washed with pepsin/elastase to decellularize and create microchannels. A 6 × 10-mm decellularized cartilage graft was then implanted in 4 infant pigs in an anterior cricoid split. Airway patency and host response were monitored endoscopically until sacrifice at 12 weeks, when the construct phenotype, cricoid expansion, mechanics, and histomorphometry were evaluated.

RESULTS

The selective digestion of meniscal components yielded decellularized cartilage with cell-size channels. After LTR with decellularized meniscus, neonatal pigs were monitored via periodic endoscopy observing re-epithelization, integration, and neocartilage formation. At 12 weeks, the graft appeared integrated and exhibited airway expansion of 4 mm in micro-CT and endoscopy. Micro-CT revealed a larger lumen compared with age-matched controls. Finally, histology showed significant neocartilage formation.

CONCLUSION

Our neonatal porcine LTR model with a decellularized cartilage graft is a novel approach to tissue engineered pediatric LTR. This pilot study sets the stage for "off-the-shelf" graft procurement and future optimization of MEND for LTR.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:807-814, 2024.

Nasal Chondrocyte-Based Engineered Grafts for the Repair of Articular Cartilage "Kissing" Lesions: A Pilot Large-Animal Study

BACKGROUND

Bipolar or "kissing" cartilage lesions formed on 2 opposite articular surfaces of the knee joint are commonly listed as exclusion criteria for advanced cartilage therapies.

PURPOSE

To test, in a pilot large-animal study, whether autologous nasal chondrocyte (NC)-based tissue engineering, recently introduced for the treatment of focal cartilage injuries, could provide a solution for challenging kissing lesions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Osteochondral kissing lesions were freshly introduced into the knee joints of 26 sheep and covered with NC-based grafts with a low or high hyaline-like extracellular matrix; a control group was treated with a cell-free scaffold collagen membrane (SCA). The cartilage repair site was assessed at 6 weeks and 6 months after implantation by histology, immunohistochemistry, and magnetic resonance imaging evaluation.

RESULTS

NC-based grafts, independently of their composition, induced partial hyaline cartilage repair with stable integrity in surrounding healthy tissue at 6 months after treatment. The SCA repaired cartilage to a similar degree to that of NC-based grafts.

CONCLUSION

Kissing lesion repair, as evidenced in this sheep study, demonstrated the feasibility of the treatment of complex cartilage injuries with advanced biological methods. However, the potential advantages of an NC-based approach over a cell-free approach warrant further investigations in a more relevant preclinical model.

CLINICAL RELEVANCE

NC-based grafts currently undergoing phase II clinical trials have a high potential to replace existing cartilage therapies that show significant limitations in the quality and reproducibility of the repair method. We have brought this innovative concept to the next level by addressing a new clinical indication.

Injectable Disc-Derived ECM Hydrogel Functionalised with Chondroitin Sulfate for Intervertebral Disc Regeneration

Low back pain resulting from intervertebral disc (IVD) degeneration is a significant socioeconomic burden. The main effect of the degeneration process involves the alteration of the nucleus pulposus (NP) via cell-mediated enzymatic breakdown of key extracellular matrix (ECM) components. Thus, the development of injectable and biomimetic biomaterials that can instruct the regenerative cell component to produce tissue-specific ECM is pivotal for IVD repair. Chondroitin sulfate (CS) and type II collagen are the primary components of NP tissue and together create the ideal environment for cells to deposit de-novo matrix. Given their high matrix synthesis capacity potential post-expansion, nasal chondrocytes (NC) have been proposed as a potential cell source to promote NP repair. The overall goal of this study was to assess the effects of CS incorporation into disc derived self-assembled ECM hydrogels on the matrix deposition of NCs. Results showed an increased sGAG production with higher amounts of CS in the gel composition and that its presence was found to be critical for the synthesis of collagen type II. Taken together, our results demonstrate how the inclusion of CS into the composition of the material aids the preservation of a rounded cell morphology for NCs in 3D culture and enhances their ability to synthesise NP-like matrix.

3D printing for tissue engineering in otolaryngology

Airway and other head and neck disorders affect hundreds of thousands of patients each year and most require surgical intervention. Among these, congenital deformity that affects newborns is particularly serious and can be life-threatening. In these cases, reconstructive surgery is resolutive but bears significant limitations, including the donor site morbidity and limited available tissue. In this context, tissue engineering represents a promising alternative approach for the surgical treatment of otolaryngologic disorders. In particular, 3D printing coupled with advanced imaging technologies offers the unique opportunity to reproduce the complex anatomy of native ear, nose, and throat, with its import in terms of functionality as well as aesthetics and the associated patient well-being. In this review, we provide a general overview of the main ear, nose and throat disorders and focus on the most recent scientific literature on 3D printing and bioprinting for their treatment.

High-Throughput, Temporal and Dose Dependent, Effect of Vitamins and Minerals on Chondrogenesis

Tissue engineered hyaline cartilage is plagued by poor mechanical properties largely due to inadequate type II collagen expression. Of note, commonly used defined chondrogenic media lack 14 vitamins and minerals, some of which are implicated in chondrogenesis. Type II collagen promoter-driven Gaussia luciferase was transfected into ATDC5 cells to create a chondrogenic cell with a secreted-reporter. The reporter cells were used in an aggregate-based chondrogenic culture model to develop a high-throughput analytic platform. This high-throughput platform was used to assess the effect of vitamins and minerals, alone and in combination with TGFβ1, on COL2A1 promoter-driven expression. Significant combinatorial effects between vitamins, minerals, and TGFβ1 in terms of COL2A1 promoter-driven expression and metabolism were discovered. An “optimal” continual supplement of copper and vitamin K in the presence of TGFβ1 gave a 2.5-fold increase in COL2A1 promoter-driven expression over TGFβ1 supplemented media alone in ATDC5 cells.

Dynamic mechanical loading facilitated chondrogenic differentiation of rabbit BMSCs in collagen scaffolds

Mechanical signals have been played close attention to regulate chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). In this study, dynamic mechanical loading simulation with natural frequencies and intensities were applied to the 3D cultured BMSCs-collagen scaffold constructs. We investigated the effects of dynamic mechanical loading on cell adhesion, uniform distribution, proliferation, secretion of extracellular matrix (ECM) and chondrogenic differentiation of BMSCs-collagen scaffold constructs. The results indicated that dynamic mechanical loading facilitated the BMSCs adhesion, uniform distribution, proliferation and secretion of ECM with a slight contraction, which significantly improved the mechanical strength of the BMSCs-collagen scaffold constructs for better mimicking the structure and function of a native cartilage. Gene expression results indicated that dynamic mechanical loading contributed to the chondrogenic differentiation of BMSCs with higher levels of AGG, COL2A1 and SOX9 genes, and prevented of hypertrophic process with lower levels of COL10A1, and reduced the possibility of fibrocartilage formation due to down-regulated COL1A2. In conclusion, this study emphasized the important role of dynamic mechanical loading on promoting BMSCs chondrogenic differentiation and maintaining the cartilage phenotype for in vitro reconstruction of tissue-engineered cartilage, which provided an attractive prospect and a feasibility strategy for cartilage repair.

A systematic review of simulated laryngotracheal reconstruction animal models

OBJECTIVES

Review of the literature to identify practical, high-fidelity, commercially available animal models for simulation training and surgical skills maintenance in laryngotracheal reconstruction (LTR).

METHODS

A systematic review of PubMed and Embase databases was conducted independently by two authors, according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Search terms included "laryngotracheal reconstruction," "laryngotracheoplasty," "pig and larynx," "sheep and larynx," and "rabbit and larynx." Articles were then assessed, identifying model cost and availability, model validation, feasibility as a training tool, and verisimilitude to pediatric LTR.

RESULTS

In total, 79 articles were considered suitable for inclusion in the study, incorporating both in vitro and in vivo models. Models utilized included rabbit (n = 69), pig (n = 7), sheep (n = 1), and goat (n = 2). The rabbit model was similar in size to the neonate, but differences in laryngeal anatomy and cartilage texture made graft insertion difficult. The anatomy of the pig, sheep, and goat larynges more closely resembled the pediatric patient, allowing improved grafting, but corresponded more in size to that of an older child. Commercial availability of the pig and sheep was considered greatest, and was reflected in cost. None of the animal models identified in the literature have been validated as a simulation tool.

CONCLUSIONS

The rabbit, sheep and pig models seemed to demonstrate the greatest potential for use as advanced pediatric airway surgery simulation models, with the rabbit model being most utilized in the literature. However, as yet there have been no models formally validated as a simulation training tool. Laryngoscope, 129:235-243, 2019.

Study of Mechanical Properties of Engineered Cartilage in an in Vivo Culture for Design of a Biodegradable Scaffold

Introduction

An engineered trachea with an absorbable scaffold should be used to augment the repair of a stenotic tracheal section in infants and children because this type of engineered airway structure can grow as the child grows. Our strategy for relief of tracheal stenosis is tracheoplasty by engineered cartilage implantation in accordance with the concept of costal cartilage grafting to enlarge the lumen. This study investigated the mechanical properties of regenerative cartilage with a biodegradable scaffold, Neoveil®, to aid in design of a composite scaffold that maintained semi-rigid properties until cartilage could be generated.

Materials and methods

New Zealand White rabbit (n=3) chondrocytes were isolated from auricular cartilage with collagenase type 2 digestion. Then 10×106/cm3 chondrocytes in atelocollagen solution were seeded onto polyglycolic acid (PGA) mesh. A total of 36 constructs, 12 from each rabbit, were implanted into athymic mice (3 constructs/mouse). Constructs were retrieved after 8 weeks and evaluated by measurements of mechanical and biochemical properties as well as histological examination. Thirty-six PGA mesh sheets of the same size but without cells were implanted in control mice.

Results

After 6 weeks of implantation, staining of sections with Safranin O revealed cartilage accumulation. Glycosaminoglycan was gradually produced from chondrocytes in the engineered constructs, correlating with the duration of implantation. Mechanical parameters had the same values as those for rabbit tracheal cartilage 8 weeks after implantation.

Conclusions

Biodegradable Neoveil® had good biocompatibility and was able to support extracellular matrix formation in engineered cartilage in an animal model.

Trophic effects of adipose-tissue-derived and bone-marrow-derived mesenchymal stem cells enhance cartilage generation by chondrocytes in co-culture

AIMS

Combining mesenchymal stem cells (MSCs) and chondrocytes has great potential for cell-based cartilage repair. However, there is much debate regarding the mechanisms behind this concept. We aimed to clarify the mechanisms that lead to chondrogenesis (chondrocyte driven MSC-differentiation versus MSC driven chondroinduction) and whether their effect was dependent on MSC-origin. Therefore, chondrogenesis of human adipose-tissue-derived MSCs (hAMSCs) and bone-marrow-derived MSCs (hBMSCs) combined with bovine articular chondrocytes (bACs) was compared.

METHODS

hAMSCs or hBMSCs were combined with bACs in alginate and cultured in vitro or implanted subcutaneously in mice. Cartilage formation was evaluated with biochemical, histological and biomechanical analyses. To further investigate the interactions between bACs and hMSCs, (1) co-culture, (2) pellet, (3) Transwell® and (4) conditioned media studies were conducted.

RESULTS

The presence of hMSCs-either hAMSCs or hBMSCs-increased chondrogenesis in culture; deposition of GAG was most evidently enhanced in hBMSC/bACs. This effect was similar when hMSCs and bAC were combined in pellet culture, in alginate culture or when conditioned media of hMSCs were used on bAC. Species-specific gene-expression analyses demonstrated that aggrecan was expressed by bACs only, indicating a predominantly trophic role for hMSCs. Collagen-10-gene expression of bACs was not affected by hBMSCs, but slightly enhanced by hAMSCs. After in-vivo implantation, hAMSC/bACs and hBMSC/bACs had similar cartilage matrix production, both appeared stable and did not calcify.

CONCLUSIONS

This study demonstrates that replacing 80% of bACs by either hAMSCs or hBMSCs does not influence cartilage matrix production or stability. The remaining chondrocytes produce more matrix due to trophic factors produced by hMSCs.

Use of autologous adipose-derived mesenchymal stem cells for creation of laryngeal cartilage

OBJECTIVES/HYPOTHESIS

Adipose-derived mesenchymal stem cells (ASCs) are an exciting potential cell source for tissue engineering because cells can be derived from the simple excision of autologous fat. This study introduces a novel approach for tissue-engineering cartilage from ASCs and a customized collagen oligomer solution, and demonstrates that the resultant cartilage can be used for laryngeal cartilage reconstruction in an animal model.

STUDY DESIGN

Basic science experimental design.

METHODS

ASCs were isolated from F344 rats, seeded in a customized collagen matrix, and cultured in chondrogenic differentiation medium for 1, 2, and 4 weeks until demonstrating cartilage-like characteristics in vitro. Large laryngeal cartilage defects were created in the F344 rat model, with the engineered cartilage used to replace the cartilage defects, and the rats followed for 1 to 3 months. Staining examined cellular morphology and cartilage-specific features.

RESULTS

In vitro histological staining revealed rounded chondrocyte-appearing cells evenly residing throughout the customized collagen scaffold, with positive staining for cartilage-specific markers. The cartilage was used to successfully repair large cartilaginous defects in the rat model, with excellent functional results.

CONCLUSIONS

This study is the first study to demonstrate, in an animal model, that ASCs cultured in a unique form of collagen oligomer can create functional cartilage-like grafts that can be successfully used for partial laryngeal cartilage replacement.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:E123-E129, 2018.

Applications of Chondrocyte-Based Cartilage Engineering: An Overview

Chondrocytes are the exclusive cells residing in cartilage and maintain the functionality of cartilage tissue. Series of biocomponents such as different growth factors, cytokines, and transcriptional factors regulate the mesenchymal stem cells (MSCs) differentiation to chondrocytes. The number of chondrocytes and dedifferentiation are the key limitations in subsequent clinical application of the chondrocytes. Different culture methods are being developed to overcome such issues. Using tissue engineering and cell based approaches, chondrocytes offer prominent therapeutic option specifically in orthopedics for cartilage repair and to treat ailments such as tracheal defects, facial reconstruction, and urinary incontinence. Matrix-assisted autologous chondrocyte transplantation/implantation is an improved version of traditional autologous chondrocyte transplantation (ACT) method. An increasing number of studies show the clinical significance of this technique for the chondral lesions treatment. Literature survey was carried out to address clinical and functional findings by using various ACT procedures. The current study was conducted to study the pharmacological significance and biomedical application of chondrocytes. Furthermore, it is inferred from the present study that long term follow-up studies are required to evaluate the potential of these methods and specific positive outcomes.

Disparate response of articular- and auricular-derived chondrocytes to oxygen tension

PURPOSE/AIM

To determine the effect of reduced (5%) oxygen tension on chondrogenesis of auricular-derived chondrocytes. Currently, many cell and tissue culture experiments are performed at 20% oxygen with 5% carbon dioxide. Few cells in the body are subjected to this supra-physiological oxygen tension. Chondrocytes and their mesenchymal progenitors are widely reported to have greater chondrogenic expression when cultured at low, more physiological, oxygen tension (1-7%). Although generally accepted, there is still some controversy, and different culture methods, species, and outcome metrics cloud the field. These results are, however, articular chondrocyte biased and have not been reported for auricular-derived chondrocytes.

MATERIALS AND METHODS

Auricular and articular chondrocytes were isolated from skeletally mature New Zealand White rabbits, expanded in culture and differentiated in high density cultures with serum-free chondrogenic media. Cartilage tissue derived from aggregate cultures or from the tissue engineered sheets were assessed for biomechanical, glycosaminoglycan, collagen, collagen cross-links, and lysyl oxidase activity and expression.

RESULTS

Our studies show increased proliferation rates for both auricular and articular chondrocytes at low (5%) O2 versus standard (20%) O2. In our scaffold-free chondrogenic cultures, low O2 was found to increase articular chondrocyte accumulation of glycosaminoglycan, but not cross-linked type II collagen, or total collagen. Conversely, auricular chondrocytes accumulated less glycosaminoglycan, cross-linked type II collagen and total collagen under low oxygen tension.

CONCLUSIONS

This study highlights the dramatic difference in response to low O2 of chondrocytes isolated from different anatomical sites. Low O2 is beneficial for articular-derived chondrogenesis but detrimental for auricular-derived chondrogenesis.

Pediatric laryngotracheal reconstruction with tissue-engineered cartilage in a rabbit model

OBJECTIVES/HYPOTHESIS

To develop an effective rabbit model of in vitro- and in vivo-derived tissue-engineered cartilage for laryngotracheal reconstruction (LTR).

STUDY DESIGN

1) Determination of the optimal scaffold 1% hyaluronic acid (HA), 2% HA, and polyglycolic acid (PGA) and in vitro culture time course using a pilot study of 4 by 4-mm in vitro-derived constructs analyzed on a static culture versus zero-gravity bioreactor for 4, 8, and 12 weeks, with determination of compressive modulus and histology as outcome measures. 2) Three-stage survival rabbit experiment utilizing autologous auricular chondrocytes seeded in scaffolds, either 1% HA or PGA. The constructs were cultured for the determined in vitro time period and then cultured in vivo for 12 weeks. Fifteen LTRs were performed using HA cartilage constructs, and one was performed with a PGA construct. All remaining specimens and the final reconstructed larynx underwent mechanical testing, histology, and glycosaminoglycan (GAG) content determination, and then were compared to cricoid control specimens (n = 13) and control LTR using autologous thyroid cartilage (n = 18).

METHODS

1) One rabbit underwent an auricular punch biopsy, and its chondrocytes were isolated and expanded and then encapsulated in eight 4 by 4-mm discs of 1% HA, 2% HA, PGA either in rotary bioreactor or static culture for 4, 8, and 12 weeks, respectively, with determination of compressive modulus, GAG content, and histology. 2) Sixteen rabbits underwent ear punch biopsy; chondrocytes were isolated and expanded. The cells were seeded in 13 by 5 by 2.25-mm UV photopolymerized 1% HA (w/w) or calcium alginate encapsulated synthetic PGA (13 × 5 × 2 mm); the constructs were then incubated in vitro for 12 weeks (the optimal time period determined above in paragraph 1) on a shaker. One HA and one PGA construct from each animal was tested mechanically and histologically, and the remaining eight (4 HA and 4 PGA) were implanted in the neck. After 12 weeks in vivo, the most optimal-appearing HA construct was used as a graft for LTR in 15 rabbits and PGA in one rabbit. The seven remaining specimens underwent hematoxylin and eosin, Safranin O, GAG content determination, and flexural modulus testing. At 12 weeks postoperative, the animals were euthanized and underwent endoscopy. The larynges underwent mechanical and histological testing. All animals that died underwent postmortem examination, including gross and microhistological analysis of the reconstructed airway.

RESULTS

Thirteen of the 15 rabbits that underwent LTR with HA in vitro- and in vivo-derived tissue-engineered cartilage constructs survived. The 1% HA specimens had the highest modulus and GAG after 12 weeks in vitro. The HA constructs became well integrated in the airway, supported respiration for the 12 weeks, and were histologically and mechanically similar to autologous cartilage.

CONCLUSIONS

The engineering of in vitro- and in vivo-derived cartilage with HA is a novel approach for laryngotracheal reconstruction. The data suggests that the in vitro- and in vivo-derived tissue-engineered approaches may offer a promising alternative to current strategies used in pediatric airway reconstruction, as well as other head and neck applications.

LEVEL OF EVIDENCE

NA. Laryngoscope, 126:S5-S21, 2016.

Introducing a 3-dimensionally Printed, Tissue-Engineered Graft for Airway Reconstruction

Objective:

To use 3-dimensional (3D) printing and tissue engineering to create a graft for laryngotracheal reconstruction (LTR).

Study Design:

In vitro and in vivo pilot animal study.

Setting:

Large tertiary care academic medical center.

Subjects and Methods:

A 3D computer model of an anterior LTR graft was designed. That design was printed with polylactic acid on a commercially available 3D printer. The scaffolds were seeded with mature chondrocytes and collagen gel and cultured in vitro for up to 3 weeks. Scaffolds were evaluated in vitro for cell viability and proliferation. Anterior graft LTR was performed on 9 New Zealand white rabbits with the newly created scaffolds. Three animals were sacrificed at each time point (4, 8, and 12 weeks). The in vivo graft sites were assessed via bronchoscopy and histology.

Results:

The in vitro cell proliferation assay demonstrated initial viability of 87.5%. The cells proliferated during the study period, doubling over the first 7 days. Histology revealed that the cells retained their cartilaginous properties during the 21-day study period. In vivo testing showed that all animals survived for the duration of the study. Bronchoscopy revealed a well-mucosalized tracheal lumen with no evidence of scarring or granulation tissue. Histology indicated the presence of newly formed cartilage in the region where the graft was present.

Conclusions:

Our results indicate that it is possible to produce a custom-designed, 3D-printed, tissue-engineered graft for airway reconstruction.

Generation and characterization of osteochondral grafts with human nasal chondrocytes

We investigated whether nasal chondrocytes (NC) can be used to generate composite constructs with properties necessary for the repair of osteochondral (OC) lesions, namely maturation, integration and capacity to recover from inflammatory burst. OC grafts were fabricated by combining engineered cartilage tissues (generated by culturing NC or articular chondrocytes - AC - onto Chondro-Gide® matrices) with devitalized spongiosa cylinders (Tutobone®). OC tissues were then exposed to IL-1β for three days and cultured for additional 2 weeks in the absence of IL-1β. Cartilage maturation extent was assessed (immune) histologically, biochemically and by delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) while cartilage/bone integration was assessed using a peel-off mechanical test. The use of NC as compared to AC allowed for more efficient cartilage matrix accumulation and superior integration of the cartilage/bone layers. dGEMRIC and biochemical analyzes of the OC constructs showed a reduced glycosaminoglycan (GAG) contents upon IL-1β administration. Cartilaginous matrix contents and integration forces returned to baseline up on withdrawal of IL-1β. By having a cartilage layer well developed and strongly integrated to the subchondral layer, OC tissues generated with NC may successfully engraft in an inflammatory post-surgery joint environment.

Coefficient of Friction Patterns Can Identify Damage in Native and Engineered Cartilage Subjected to Frictional-Shear Stress

The mechanical loading environment encountered by articular cartilage in situ makes frictional-shear testing an invaluable technique for assessing engineered cartilage. Despite the important information that is gained from this testing, it remains under-utilized, especially for determining damage behavior. Currently, extensive visual inspection is required to assess damage; this is cumbersome and subjective. Tools to simplify, automate, and remove subjectivity from the analysis may increase the accessibility and usefulness of frictional-shear testing as an evaluation method. The objective of this study was to determine if the friction signal could be used to detect damage that occurred during the testing. This study proceeded in two phases: first, a simplified model of biphasic lubrication that does not require knowledge of interstitial fluid pressure was developed. In the second phase, frictional-shear tests were performed on 74 cartilage samples, and the simplified model was used to extract characteristic features from the friction signals. Using support vector machine classifiers, the extracted features were able to detect damage with a median accuracy of approximately 90%. The accuracy remained high even in samples with minimal damage. In conclusion, the friction signal acquired during frictional-shear testing can be used to detect resultant damage to a high level of accuracy.

Xiphoid process-derived chondrocytes: a novel cell source for elastic cartilage regeneration

Reconstruction of elastic cartilage requires a source of chondrocytes that display a reliable differentiation tendency. Predetermined tissue progenitor cells are ideal candidates for meeting this need; however, it is difficult to obtain donor elastic cartilage tissue because most elastic cartilage serves important functions or forms external structures, making these tissues indispensable. We found vestigial cartilage tissue in xiphoid processes and characterized it as hyaline cartilage in the proximal region and elastic cartilage in the distal region. Xiphoid process-derived chondrocytes (XCs) showed superb in vitro expansion ability based on colony-forming unit fibroblast assays, cell yield, and cumulative cell growth. On induction of differentiation into mesenchymal lineages, XCs showed a strong tendency toward chondrogenic differentiation. An examination of the tissue-specific regeneration capacity of XCs in a subcutaneous-transplantation model and autologous chondrocyte implantation model confirmed reliable regeneration of elastic cartilage regardless of the implantation environment. On the basis of these observations, we conclude that xiphoid process cartilage, the only elastic cartilage tissue source that can be obtained without destroying external shape or function, is a source of elastic chondrocytes that show superb in vitro expansion and reliable differentiation capacity. These findings indicate that XCs could be a valuable cell source for reconstruction of elastic cartilage.

Scaffold-free cartilage subjected to frictional shear stress demonstrates damage by cracking and surface peeling

Scaffold-free engineered cartilage is being explored as a treatment for osteoarthritis. In this study, frictional shear stress was applied to determine the friction and damage behaviour of scaffold-free engineered cartilage, and tissue composition was investigated as it related to damage. Scaffold-free engineered cartilage frictional shear stress was found to exhibit a time-varying response similar to that of native cartilage. However, damage occurred that was not seen in native cartilage, manifesting primarily as tearing through the central plane of the constructs. In engineered cartilage, cells occupied a significantly larger portion of the tissue in the central region where damage was most prominent (18 ± 3% of tissue was comprised of cells in the central region vs 5 ± 1% in the peripheral region; p < 0.0001). In native cartilage, cells comprised 1-4% of tissue for all regions. Average bulk cellularity of engineered cartilage was also greater (68 × 10³  ± 4 × 10³ vs 52 × 10³  ± 22 × 10³ cells/mg), although this difference was not significant. Bulk tissue comparisons showed significant differences between engineered and native cartilage in hydroxyproline content (8 ± 2 vs 45 ± 3 µg HYP/mg dry weight), solid content (12.5 ± 0.4% vs 17.9 ± 1.2%), shear modulus (0.06 ± 0.02 vs 0.15 ± 0.07 MPa) and aggregate modulus (0.12 ± 0.03 vs 0.32 ± 0.14 MPa), respectively. These data indicate that enhanced collagen content and more uniform extracellular matrix distribution are necessary to reduce damage susceptibility. Copyright © 2014 John Wiley & Sons, Ltd.

The role of physiological mechanical cues on mesenchymal stem cell differentiation in an airway tract-like dense collagen-silk fibroin construct

Airway tracts serve as a conduit of transport in the respiratory system. Architecturally, these are composed of cartilage rings that offer flexibility and prevent collapse during normal breathing. To this end, the successful regeneration of an airway tract requires the presence of differentiated chondrocytes and airway smooth muscle cells. This study investigated the role of physiological dynamic mechanical stimulation, in vitro, on the differentiation of mesenchymal stem cells (MSCs), three-dimensionally seeded within a tubular dense collagen matrix construct-reinforced with rings of electrospun silk fibroin mat (TDC-SFC). In particular, the role of either shear stress supplied by laminar fluid flow or cyclic shear stress in combination with circumferential strain, provided by pulsatile flow, on the chondrogenic differentiation, and contractile lineage of MSCs, and their effects on TDC-SFC morphology and mechanical properties were analysed. Chondrogenic differentiation of MSCs was observed in the presence of chondrogenic supplements under both static and laminar flow cultures. In contrast, physiological pulsatile flow resulted in preferential cellular orientation within TDC-SFC, as dictated by dynamic circumferential strain, and induced MSC contractile phenotype expression. In addition, pulsatile flow decreased MSC-mediated collagen matrix remodelling and increased construct circumferential strength. Therefore, TDC-SFC demonstrated the central role of a matrix in the delivery of mechanical stimuli over chemical factors, by providing an in vitro niche to control MSC differentiation, alignment and its capacity to remodel the matrix.

Osteochondral articular defect repair using auricle-derived autologous chondrocytes in a rabbit model

Hypothesizing that the implantation of non-articular (heterotopic) chondrocytes might be an alternative approach to support articular cartilage repair, we analyzed joint cartilage defect healing in the rabbit model after implantation of autologous auricle-derived (auricular) chondrocytes. Autologous lapine articular and auricular chondrocytes were cultured for 3 weeks in polyglycolic acid (PGA) scaffolds before being implanted into critical sized osteochondral defects of the rabbit knee femoropatellar groove. Cell-free PGA scaffolds and empty defects served as controls. Construct quality was determined before implantation and defect healing was monitored after 6 and 12 weeks using vitality assays, macroscopical and histological score systems. Neo-cartilage was formed in the PGA constructs seeded with both articular and auricular chondrocytes in vitro and in vivo. At the histological level, cartilage repair was slightly improved when using autologous articular chondrocyte seeded constructs compared to empty defects and was significantly superior compared to defects treated with auricular chondrocytes 6 weeks after implantation. Although only the immunohistological differences were significant, auricular chondrocyte implantation induced an inferior healing response compared with the empty defects. Elastic auricular chondrocytes might maintain some tissue-specific characteristics when implanted into joint cartilage defects which limit its repair capacity.

Heterotopic and orthotopic autologous chondrocyte implantation using a minipig chondral defect model

Implantation of non-articular (heterotopic) chondrocyte-based implants might be an alternative approach to articular cartilage repair. This strategy could be helpful in cases in which there are no or too few articular chondrocytes available. Therefore, this study was undertaken to compare joint cartilage defect healing in the minipig model after implantation of heterotopic auricular and orthotopic articular chondrocytes. Poly-glycolic acid (PGA) associated three-dimensional (3D) constructs were prepared culturing autologous minipig-derived articular and auricular chondrocytes for 7 days in a dynamic culture system. Chondrocyte PGA constructs were implanted into 8mm diameter and ∼1.1mm deep chondral defects within the medial and lateral condyles of the minipig knee joints. Empty defects served as controls for assessment of the intrinsic healing response. Defect healing was monitored 6 months post implantation using a macroscopic and microscopic score system and biomechanical analysis. Neo-cartilage formation could be observed in the PGA constructs seeded with articular and auricular chondrocytes in vivo. The defect healing did not significantly differ at the macroscopic and histological level in response to implantation of either autologous articular or auricular chondrocytes seeded constructs compared with the empty defects. Although the differences were not significant, the auricular chondrocytes-based implants led to a slightly inferior repair quality at the macroscopic level, but a histologically superior healing response when compared with the empty defect group. However, biomechanical analysis revealed a higher stiffness in repair tissues produced by auricular chondrocyte implantation compared with the other groups. Deduced from these results, articular chondrocytes represent the preferable cell source for implantation.

Cell sources for trachea tissue engineering: past, present and future

Trachea tissue engineering has been one of the most promising approaches to providing a potential clinical application for the treatment of long-segment tracheal stenosis. The sources of the cells are particularly important as the primary factor for tissue engineering. The use of appropriate cells seeded onto scaffolds holds huge promise as a means of engineering the trachea. Furthermore, appropriate cells would accelerate the regeneration of the tissue even without scaffolds. Besides autologous mature cells, various stem cells, including bone marrow-derived mesenchymal stem cells, adipose tissue-derived stem cells, umbilical cord blood-derived mesenchymal stem cells, amniotic fluid stem cells, embryonic stem cells and induced pluripotent stem cells, have received extensive attention in the field of trachea tissue engineering. Therefore, this article reviews the progress on different cell sources for engineering tracheal cartilage and epithelium, which can lead to a better selection and strategy for engineering the trachea.

Methods for producing scaffold-free engineered cartilage sheets from auricular and articular chondrocyte cell sources and attachment to porous tantalum

Scaffold-free cartilage engineering techniques may provide a simple alternative to traditional methods employing scaffolds. We previously reported auricular chondrocyte-derived constructs for use in an engineered trachea model; however, the construct generation methods were not reported in detail. In this study, methods for cartilage construct generation from auricular and articular cell sources are described in detail, and the resulting constructs are compared for use in a joint resurfacing model. Attachment of cartilage sheets to porous tantalum is also investigated as a potential vehicle for future attachment to subchondral bone. Large scaffold-free cartilage constructs were produced from culture-expanded chondrocytes from skeletally mature rabbits, and redifferentiated in a chemically-defined culture medium. Auricular constructs contained more glycosaminoglycan (39.6±12.7 vs. 9.7±1.9 μg/mg wet weight, mean and standard deviation) and collagen (2.7±0.45 vs. 1.1±0.2 μg/mg wet weight, mean and standard deviation) than articular constructs. Aggregate modulus was also higher for auricular constructs vs. articular constructs (0.23±0.07 vs. 0.12±0.03 MPa, mean and standard deviation). Attachment of constructs to porous tantalum was achieved by neocartilage ingrowth into tantalum pores. These results demonstrate that large scaffold-free neocartilage constructs can be produced from mature culture-expanded chondrocytes in a chemically-defined medium, and that these constructs can be attached to porous tantalum.

Optimization of a chondrogenic medium through the use of factorial design of experiments

The standard culture system for in vitro cartilage research is based on cells in a three-dimensional micromass culture and a defined medium containing the chondrogenic key growth factor, transforming growth factor (TGF)-β1. The aim of this study was to optimize the medium for chondrocyte micromass culture. Human chondrocytes were cultured in different media formulations, designed with a factorial design of experiments (DoE) approach and based on the standard medium for redifferentiation. The significant factors for the redifferentiation of the chondrocytes were determined and optimized in a two-step process through the use of response surface methodology. TGF-β1, dexamethasone, and glucose were significant factors for differentiating the chondrocytes. Compared to the standard medium, TGF-β1 was increased 30%, dexamethasone reduced 50%, and glucose increased 22%. The potency of the optimized medium was validated in a comparative study against the standard medium. The optimized medium resulted in micromass cultures with increased expression of genes important for the articular chondrocyte phenotype and in cultures with increased glycosaminoglycan/DNA content. Optimizing the standard medium with the efficient DoE method, a new medium that gave better redifferentiation for articular chondrocytes was determined.

High-fidelity tissue engineering of patient-specific auricles for reconstruction of pediatric microtia and other auricular deformities

Introduction

Autologous techniques for the reconstruction of pediatric microtia often result in suboptimal aesthetic outcomes and morbidity at the costal cartilage donor site. We therefore sought to combine digital photogrammetry with CAD/CAM techniques to develop collagen type I hydrogel scaffolds and their respective molds that would precisely mimic the normal anatomy of the patient-specific external ear as well as recapitulate the complex biomechanical properties of native auricular elastic cartilage while avoiding the morbidity of traditional autologous reconstructions.

Methods

Three-dimensional structures of normal pediatric ears were digitized and converted to virtual solids for mold design. Image-based synthetic reconstructions of these ears were fabricated from collagen type I hydrogels. Half were seeded with bovine auricular chondrocytes. Cellular and acellular constructs were implanted subcutaneously in the dorsa of nude rats and harvested after 1 and 3 months.

Results

Gross inspection revealed that acellular implants had significantly decreased in size by 1 month. Cellular constructs retained their contour/projection from the animals' dorsa, even after 3 months. Post-harvest weight of cellular constructs was significantly greater than that of acellular constructs after 1 and 3 months. Safranin O-staining revealed that cellular constructs demonstrated evidence of a self-assembled perichondrial layer and copious neocartilage deposition. Verhoeff staining of 1 month cellular constructs revealed de novo elastic cartilage deposition, which was even more extensive and robust after 3 months. The equilibrium modulus and hydraulic permeability of cellular constructs were not significantly different from native bovine auricular cartilage after 3 months.

Conclusions

We have developed high-fidelity, biocompatible, patient-specific tissue-engineered constructs for auricular reconstruction which largely mimic the native auricle both biomechanically and histologically, even after an extended period of implantation. This strategy holds immense potential for durable patient-specific tissue-engineered anatomically proper auricular reconstructions in the future.

Multimodal evaluation of tissue-engineered cartilage

Tissue engineering (TE) has promise as a biological solution and a disease modifying treatment for arthritis. Although cartilage can be generated by TE, substantial inter- and intra-donor variability makes it impossible to guarantee optimal, reproducible results. TE cartilage must be able to perform the functions of native tissue, thus mechanical and biological properties approaching those of native cartilage are likely a pre-requisite for successful implantation. A quality-control assessment of these properties should be part of the implantation release criteria for TE cartilage. Release criteria should certify that selected tissue properties have reached certain target ranges, and should be predictive of the likelihood of success of an implant in vivo. Unfortunately, it is not currently known which properties are needed to establish release criteria, nor how close one has to be to the properties of native cartilage to achieve success. Achieving properties approaching those of native cartilage requires a clear understanding of the target properties and reproducible assessment methodology. Here, we review several main aspects of quality control as it applies to TE cartilage. This includes a look at known mechanical and biological properties of native cartilage, which should be the target in engineered tissues. We also present an overview of the state of the art of tissue assessment, focusing on native articular and TE cartilage. Finally, we review the arguments for developing and validating non-destructive testing methods for assessing TE products.

High-density cell systems incorporating polymer microspheres as microenvironmental regulators in engineered cartilage tissues

To address the significant clinical need for tissue-engineered therapies for the repair and regeneration of articular cartilage, many systems have recently been developed using bioactive polymer microspheres as regulators of the chondrogenic microenvironment within high-density cell cultures. In this review, we highlight various densely cellular systems utilizing polymer microspheres as three-dimensional (3D) structural elements within developing engineered cartilage tissue, carriers for cell expansion and delivery, vehicles for spatiotemporally controlled growth factor delivery, and directors of cell behavior via regulation of cell-biomaterial interactions. The diverse systems described herein represent a shift from the more traditional tissue engineering approach of combining cells and growth factors within a biomaterial scaffold, to the design of modular systems that rely on the assembly of cells and bioactive polymer microspheres as building blocks to guide the creation of articular cartilage. Cell-based assembly of 3D microsphere-incorporated structures represents a promising avenue for the future of tissue engineering.

Optimization of the Expansion and Differentiation of Rabbit Chondrocytes In Vitro

OBJECTIVE

To develop a tissue culture expansion method for rabbit chondrocytes that promotes robust expansion while preserving chondrogenic potential.

DESIGN

Rabbit chondrocytes isolated from articular or auricular chondrocytes were assessed for chondrogenic differentiation potential versus population doubling using different expansion and differentiation conditions. Expansion conditions included serum alone, serum plus basic fibroblast growth factor 2 (FGF-2), and serum plus insulin-like growth factor 1 (IGF-1) and FGF-2. Differentiation conditions consisted of defined medium with and without bone morphogenetic protein 2 (BMP-2).

RESULTS

Nonsupplemented chondrocytes showed limited expandability, whereas supplementation with FGF-2 allowed articular chondrocytes to be expanded past 10 population doublings (PDs) and allowed auricular chondrocytes to expand past 15 population doublings. Differentiation, as measured by glycosaminoglycan production in aggregate cultures, was minimal in articular chondrocytes without BMP-2 supplementation and diminished to less than 50% maximal in auricular chondrocytes by PD 20. However, when FGF-2 was used during expansion and BMP-2 used during differentiation, both articular and auricular chondrocytes retained greater than 50% maximal differentiation for more than 25 PDs. The addition of IGF-1 to FGF-2 during expansion decreased chondrogenicity of auricular chondrocytes exposed to BMP-2, whereas for articular chondrocytes, chondrogenic expression increased.

CONCLUSION

These results demonstrate that FGF-2, for expansion, and BMP-2, for differentiation, dramatically increase the functional expansion of auricular and articular chondrocytes and provide a methodology to expand sufficient numbers of chondrocytes for tissue engineering applications.

PGA-associated heterotopic chondrocyte cocultures: implications of nasoseptal and auricular chondrocytes in articular cartilage repair

The availability of autologous articular chondrocytes remains a limiting issue in matrix assisted autologous chondrocyte transplantation. Non-articular heterotopic chondrocytes could be an alternative autologous cell source. The aims of this study were to establish heterotopic chondrocyte cocultures to analyze cell-cell compatibilities and to characterize the chondrogenic potential of nasoseptal chondrocytes compared to articular chondrocytes. Primary porcine and human nasoseptal and articular chondrocytes were investigated for extracellular cartilage matrix (ECM) expression in a monolayer culture. 3D polyglycolic acid- (PGA) associated porcine heterotopic mono- and cocultures were assessed for cell vitality, types II, I, and total collagen-, and proteoglycan content. The type II collagen, lubricin, and Sox9 gene expressions were significantly higher in articular compared with nasoseptal monolayer chondrocytes, while type IX collagen expression was lower in articular chondrocytes. Only β1-integrin gene expression was significantly inferior in humans but not in porcine nasoseptal compared with articular chondrocytes, indicating species-dependent differences. Heterotopic chondrocytes in PGA cultures revealed high vitality with proteoglycan-rich hyaline-like ECM production. Similar amounts of type II collagen deposition and type II/I collagen ratios were found in heterotopic chondrocytes cultured on PGA compared to articular chondrocytes. Quantitative analyses revealed a time-dependent increase in total collagen and proteoglycan content, whereby the differences between heterotopic and articular chondrocyte cultures were not significant. Nasoseptal and auricular chondrocytes monocultured in PGA or cocultured with articular chondrocytes revealed a comparable high chondrogenic potential in a tissue engineering setting, which created the opportunity to test them in vivo for articular cartilage repair.

Engineered cartilage via self-assembled hMSC sheets with incorporated biodegradable gelatin microspheres releasing transforming growth factor-β1

Self-assembling cell sheets have shown great potential for use in cartilage tissue engineering applications, as they provide an advantageous environment for the chondrogenic induction of human mesenchymal stem cells (hMSCs). We have engineered a system of self-assembled, microsphere-incorporated hMSC sheets capable of forming cartilage in the presence of exogenous transforming growth factor β1 (TGF-β1) or with TGF-β1 released from incorporated microspheres. Gelatin microspheres with two different degrees of crosslinking were used to enable different cell-mediated microsphere degradation rates. Biochemical assays, histological and immunohistochemical analyses, and biomechanical testing were performed to determine biochemical composition, structure, and equilibrium modulus in unconfined compression after 3 weeks of culture. The inclusion of microspheres with or without loaded TGF-β1 significantly increased sheet thickness and compressive equilibrium modulus, and enabled more uniform matrix deposition by comparison to control sheets without microspheres. Sheets incorporated with fast-degrading microspheres containing TGF-β1 produced significantly more GAG and GAG per DNA than all other groups tested and stained more intensely for type II collagen. These findings demonstrate improved cartilage formation in microsphere-incorporated cell sheets, and describe a tailorable system for the chondrogenic induction of hMSCs without necessitating culture in growth factor-containing medium.

Perichondrium directed cartilage formation in silk fibroin and chitosan blend scaffolds for tracheal transplantation

The purpose of this study was to investigate the potential of silk fibroin and chitosan blend (SFCS) biological scaffolds for the purpose of cartilage tissue engineering with applications in tracheal tissue reconstruction. The capability of these scaffolds as cell carrier systems for chondrocytes was determined in vitro and cartilage generation in vivo on engineered chondrocyte-scaffold constructs with and without a perichondrium wrapping was tested in an in vivo nude mouse model. SFCS scaffolds supported chondrocyte adhesion, proliferation, and differentiation, determined as features of the cells based on the spherical cell morphology, increased accumulation of glycosaminoglycans, and increased collagen type II deposition with time within the scaffold framework. Perichondrium wrapping significantly (P<0.001) improved chondrogenesis within the cell-scaffold constructs in vivo. In vivo implantation for 6weeks did not generate cartilage structures resembling native trachea, although cartilage-like structures were present. The mechanical properties of the regenerated tissue increased due to the deposition of chondrogenic matrix within the SFCS scaffold structural framework of the trachea. The support of chondrogenesis by the SFCS tubular scaffold construct resulted in a mechanically sound structure and thus is a step towards an engineered trachea that could potentially support the growth of an epithelial lining resulting in a tracheal transplant with properties resembling those of the fully functional native trachea.

Differences in cartilage-forming capacity of expanded human chondrocytes from ear and nose and their gene expression profiles

The aim of this study was to evaluate the potential of culture-expanded human auricular and nasoseptal chondrocytes as cell source for regeneration of stable cartilage and to analyze the differences in gene expression profile of expanded chondrocytes from these specific locations. Auricular chondrocytes in monolayer proliferated less and more slowly (two passages took 26.7 ± 2.1 days and were reached in 4.37 ± 0.30 population doublings) than nasoseptal chondrocytes (19.3 ± 2.5 days; 5.45 ± 0.20 population doublings). However, auricular chondrocytes produced larger pellets with more cartilage-like matrix than nasoseptal chondrocytes (2.2 ± 0.71 vs. 1.7 ± 0.13 mm in diameter after 35 days of culture). Although the matrix formed by auricular and nasoseptal chondrocytes contained collagen X, it did not mineralize in an in vitro model or after in vivo subcutaneous implantation. A DNA microarray study on expanded auricular and nasoseptal chondrocytes from the same donors revealed 1,090 differentially expressed genes. No difference was observed in the expression of known markers of chondrogenic capacity (e.g., collagen II, FGFR3, BMP2, and ALK1). The most striking differences were that the auricular chondrocytes had a higher expression of anabolic growth factors BMP5 and IGF1, while matrix-degrading enzymes MMP13 and ADAMTS5 were higher expressed in nasoseptal chondrocytes. This might offer a possible explanation for the observed higher matrix production by auricular chondrocytes. Moreover, chondrocytes isolated from auricular or nasoseptal cartilage had specific gene expression profiles even after expansion. These differently expressed genes were not restricted to known characterization of donor site subtype (e.g., elastic), but were also related to developmental processes.

Low oxygen tension during incubation periods of chondrocyte expansion is sufficient to enhance postexpansion chondrogenesis

To determine whether low oxygen (O(2)) tension during expansion affects the matrix density, as well as quantity, of cartilage formed, and to determine whether application of low O(2) tension during incubation periods alone is sufficient to modulate chondrogenic expression, rabbit chondrocytes expanded at either 21% O(2) or 5% O(2) were analyzed for glycosaminoglycan (GAG) and DNA content, total collagen, and gene expression during expansion and postexpansion aggregate cultures. When cultured as aggregates at 21% O(2), chondrocytes expanded at 5% O(2) produced cartilage aggregates that contained more total GAG, GAG per wet weight, GAG per DNA, and total collagen than chondrocytes expanded at 21% O(2). Less of an effect on GAG and collagen content was observed when aggregate culture was performed at 5% O(2). Real-time polymerase chain reaction analysis of COL2A1 expression showed upregulated levels of type IIA (an early marker) and IIB (a late marker) during expansion and elevated levels of type IIB during aggregate culture in chondrocytes expanded in low O(2). The application of low O(2) tension during incubation periods of chondrocyte expansion enhances the ultimate cartilage matrix density and quantity, and this enhancement can be achieved through the use of an O(2) control incubator.

Scaffold-free tissue-engineered cartilage implants for laryngotracheal reconstruction

OBJECTIVES/HYPOTHESIS

Donor site morbidity, including pneumothorax, can be a considerable problem when harvesting cartilage grafts for laryngotracheal reconstruction (LTR). Tissue engineered cartilage may offer a solution to this problem. This study investigated the feasibility of using autologous chondrocytes to tissue-engineer scaffold-free cartilage grafts for LTR in rabbits to avoid degradation that often arises from an inflammatory reaction to scaffold carrier matrix.

STUDY DESIGN

Animal study.

METHODS

Auricular cartilage was harvested from seven New Zealand white rabbits, the chondrocytes expanded and loaded onto a custom-made bioreactor for 7 to 8 weeks to fabricate autologous scaffold-free cartilage sheets. The sheets were cut to size and used for LTR, and the rabbits were sacrificed 4, 8, and 12 weeks after the LTR and prepared for histology.

RESULTS

None of the seven rabbits showed signs of respiratory distress. A smooth, noninflammatory scar was visible intraluminally; the remainder of the tracheal lumen was unremarkable. Histologically, the grafts showed no signs of degradation or inflammatory reaction, were covered with mucosal epithelium, but did show signs of mechanical failure at the implantation site.

CONCLUSIONS

These results show that autologous chondrocytes can be used to fabricate an implantable sheet of cartilage that retains a cartilage phenotype, becomes integrated, and does not produce a significant inflammatory reaction. These findings suggest that with the design of stronger implants, these implants can be successfully used as a graft for LTR.

Use of titanium mesh in laryngotracheal reconstruction: an experimental study on rabbits

Titanium mesh may be an alternative material to be used in laryngotracheal reconstruction. Twenty New Zealand rabbits were divided into two groups. Group A underwent laryngotracheoplasty with titanium mesh-buccal mucosa-muscle complex, and Group B received auricular cartilage grafts. All animals survived without complications. The animals were killed at 60 days, and laryngotracheal regions were evaluated. There was no subglottic collapse at physiologic and supraphysiologic negative airway pressures in Group A and mild-moderate collapse in Group B. Macroscopically the average antero-posterior and lateral diameters were not statistically different among two groups. Light microscopic examination revealed no fibrosis, necrosis or new cartilage formation in both groups. Inflammation and granulation were more pronounced in Group A. The lumens in both groups were moderately obstructed. Reconstruction of the upper airway with titanium mesh may be used in very selected cases where autologous grafting materials are inadequate and unsatisfactory.

Cartilage repair: past and future--lessons for regenerative medicine

Since the first cell therapeutic study to repair articular cartilage defects in the knee in 1994, several clinical studies have been reported. An overview of the results of clinical studies did not conclusively show improvement over conventional methods, mainly because few studies reach level I of evidence for effects on middle or long term. However, these explorative trials have provided valuable information about study design, mechanisms of repair and clinical outcome and have revealed that much is still unknown and further improvements are required. Furthermore, cellular and molecular studies using new technologies such as cell tracking, gene arrays and proteomics have provided more insight in the cell biology and mechanisms of joint surface regeneration. Besides articular cartilage, cartilage of other anatomical locations as well as progenitor cells are now considered as alternative cell sources. Growth Factor research has revealed some information on optimal conditions to support cartilage repair. Thus, there is hope for improvement. In order to obtain more robust and reproducible results, more detailed information is needed on many aspects including the fate of the cells, choice of cell type and culture parameters. As for the clinical aspects, it becomes clear that careful selection of patient groups is an important input parameter that should be optimized for each application. In addition, the study outcome parameters should be improved. Although reduced pain and improved function are, from the patient's perspective, the most important outcomes, there is a need for more structure/tissue-related outcome measures. Ideally, criteria and/or markers to identify patients at risk and responders to treatment are the ultimate goal for these more sophisticated regenerative approaches in joint surface repair in particular, and regenerative medicine in general.

Tissue engineering a model for the human ear: assessment of size, shape, morphology, and gene expression following seeding of different chondrocytes

This study examines the tissue engineering of a human ear model through use of bovine chondrocytes isolated from four different cartilaginous sites (nasoseptal, articular, costal, and auricular) and seeded onto biodegradable poly(l-lactic acid) and poly(L-lactide-epsilon-caprolactone) (50 : 50) polymer ear-shaped scaffolds. After implantation in athymic mice for up to 40 weeks, cell/scaffold constructs were harvested and analyzed in terms of size, shape, histology, and gene expression. Gross morphology revealed that all the tissue-engineered cartilages retained the initial human auricular shape through 40 weeks of implantation. Scaffolds alone lost significant size and shape over the same period. Quantitative reverse transcription-polymerase chain reaction demonstrated that the engineered chondrocyte/scaffolds yielded unique expression patterns for type II collagen, aggrecan, and bone sialoprotein mRNA. Histological analysis showed type II collagen and proteoglycan to be the predominant extracellular matrix components of the various constructs sampled at different implantation times. Elastin was also present but it was found only in constructs seeded with auricular chondrocytes. By 40 weeks of implantation, tissue-engineered cartilage of costal origin became calcified, marked by a notably high relative gene expression level of bone sialoprotein and the presence of rigid, nodular protrusions formed by mineralizing rudimentary cartilaginous growth plates. The collective data suggest that nasoseptal, articular, and auricular cartilages represent harvest sites suitable for development of tissue-engineered human ear models with retention over time of three-dimensional construct architecture, gene expression, and extracellular matrix composition comparable to normal, nonmineralizing cartilages. Calcification of constructs of costal chondrocyte origin clearly shows that chondrocytes from different tissue sources are not identical and retain distinct characteristics and that these specific cells are inappropriate for use in engineering a flexible ear model.

Dexamethasone inhibition of confluence-induced apoptosis in human mesenchymal stem cells

Human mesenchymal stem cells (MSCs) have been extensively characterized with respect to their in vitro expansion and differentiation potential, especially with respect to osteogenesis. Dexamethasone (Dex) is a well-known inducer of osteogenic differentiation of MSCs, but little is known about the effect of Dex treatment on apoptosis in MSCs. In this study, apoptosis in MSCs was examined with respect to cell density and Dex supplementation, using DAPI staining and DNA fragmentation ELISA Assay. In MSC cultures initiated at 1.0, 3.0, and 9.0 x 10(3) cells per cm(2), it was found that higher MSC density correlated with increased apoptosis and that this apoptotic effect was diminished in cultures containing 100 nM Dex. MSCs and fibroblasts were co-cultured, along with empty insert controls, and assayed for apoptosis by ELISA and DAPI counts to determine if soluble factors accounted for the cell density-related apoptosis. No difference was seen between MSCs cultured with inserts containing either MSCs, fibroblasts, or empty control. To determine cell contact effects, BrdU-labeled MSCs were cultured alone or with unlabeled chondrocytes at 2x and 8x the number of MSCs, with and without Dex, and apoptosis levels quantified. The results showed increased apoptosis at greater cell densities, and that the amount of apoptosis was greatly diminished in cultures containing Dex. These results show that apoptosis in MSCs is cell density-related, requires direct cell contact, and that Dex treatment reduces or eliminates this density-related apoptosis. These results may impact how MSCs should be cultured for clinical applications.

Fabrication of a neotrachea using engineered cartilage

OBJECTIVES

Surgical management of long-segment tracheal stenosis is an ongoing problem. Many types of tracheal prostheses have been tried but with limited success because of immune rejection, graft ischemia, or restenosis. Tissue engineered cartilage may offer a solution to this problem, although scaffolds, which are currently often used for support, can lead to biocompatibility problems. This study investigated the feasibility of scaffold-free cartilage to tissue engineer a vascularized neotrachea in rabbits.

STUDY DESIGN

Animal study.

METHODS

Autologous neotracheal constructs were implanted in the abdomen of six New Zealand white rabbits. Auricular chondrocytes were used to engineer scaffold-free cartilage sheets. A muscle flap raised from the external abdominal oblique muscle and the engineered cartilage were wrapped around a silicone stent to fabricate a vascularized neotrachea in vivo. In two of the six rabbits, a full thickness skin graft was used to create an epithelial lining. The constructs were harvested after either 6 or 10 weeks.

RESULTS

All neotracheal constructs were healthy with well-vascularized and integrated layers. The implanted engineered cartilage underwent a remodeling process, forming a solid tracheal framework. Constructs harvested after 10 weeks proved to have significantly better mechanical properties than after 6 weeks and were comparable with the rabbit's native trachea.

CONCLUSION

Scaffold-free engineered cartilage can successfully fabricate a well-vascularized, autologous neotrachea with excellent mechanical properties. The results suggest that this approach can be used to reconstruct tracheal defects in rabbits.

Proliferation of chondrocytes on porous poly(DL-lactide)/chitosan scaffolds

Porous poly(DL-lactide)(PDLLA)/chitosan scaffolds with well-controlled pore structures and desirable mechanical characteristics were fabricated via a combination of solvent extraction, phase separation and freeze-drying. These scaffolds were further evaluated for the proliferation of isolated rabbit chondrocytes in vitro for various incubation periods up to 4 weeks in order to finally use them for the cartilage tissue engineering. MTT assay data revealed that the number of cells grown on PDLLA/chitosan scaffolds measurably increased with the weight ratio of the chitosan component and was significantly higher than those collected from pure PDLLA scaffolds for the entire incubation period. Scanning electron microscopy examinations, histological observations and proteoglycan measurements indicated that the resulting PDLLA/chitosan scaffolds exhibited increasing ability to promote the attachment and proliferation of chondrocytes, and also helped seeded chondrocytes spread through the scaffolds and distribute homogeneously inside compared to pure PDLLA scaffolds. Immunohistochemical staining verified that these PDLLA/chitosan scaffolds could preserve the phenotype of chondrocyte and effectively support the production of type II collagen.

Hyaluronan-based scaffolds to tissue-engineer cartilage implants for laryngotracheal reconstruction

OBJECTIVES

Donor site morbidity, including pneumothorax, can be a considerable problem when harvesting cartilage grafts for laryngotracheal reconstruction (LTR). Tissue-engineered cartilage may offer a solution to this problem. This study investigated the feasibility of using Hyalograft C combined with autologous chondrocytes to tissue engineer cartilage grafts for LTR in rabbits.

STUDY DESIGN

Animal study.

METHODS

Eighteen New Zealand white rabbits underwent LTR: 12 rabbits received autologous tissue-engineered cartilage grafts and 6 animals, serving as a positive control group, native auricular cartilage. To determine any differences in response to the site of implantation and any potential immune response to the scaffold, a second piece of engineered neocartilage and a non-cell-loaded scaffold were inserted paralaryngeally into a subset of the rabbits. The rabbits were sacrificed 3, 6, 8, 10, and 12 weeks after the LTR and their larynx examined.

RESULTS

None of the 18 rabbits showed signs of respiratory distress. A smooth, noninflammatory scar was visible intraluminally. Histologically, the native auricular cartilage implants showed excellent integration without any signs of inflammation or cartilage degradation. In contrast, all tissue-engineered grafts and empty scaffolds revealed marked signs of an unspecific foreign body reaction, leading to a complete degradation of the neocartilage, whether implanted para- or intralaryngeally.

CONCLUSION

In contrast to the success with which Hyalograft C has been applied in articular defect repair, our results indicate that, in rabbits, Hyalograft C initiates a foreign body reaction if implanted intra- or paralaryngeally, leading to cartilage degradation and possible graft failure. These findings suggest limitations on the environment in which Hyalograft C can be applied.