Analysis of bending behavior of native and engineered auricular and costal cartilage

Laser Ablation Facilitates Implantation of Dynamic Self-Regenerating Cartilage for Articular Cartilage Regeneration

OBJECTIVES

This study investigated a novel strategy for improving regenerative cartilage outcomes. It combines fractional laser treatment with the implantation of neocartilage generated from autologous dynamic Self-Regenerating Cartilage (dSRC).

METHODS

dSRC was generated in vitro from harvested autologous swine chondrocytes. Culture was performed for 2, 4, 8, 10, and 12 weeks to study matrix maturation. Matrix formation and implant integration were also studied in vitro in swine cartilage discs using dSRC or cultured chondrocytes injected into CO2 laser-ablated or mechanically punched holes. Cartilage discs were cultured for up to 8 weeks, harvested, and evaluated histologically and immunohistochemically.

RESULTS

The dSRC matrix was injectable by week 2, and matrices grew larger and more solid with time, generating a contiguous neocartilage matrix by week 8. Hypercellular density in dSRC at week 2 decreased over time and approached that of native cartilage by week 8. All dSRC groups exhibited high glycosaminoglycan (GAG) production, and immunohistochemical staining confirmed that the matrix was typical of normal hyaline cartilage, being rich in collagen type II. After 8 weeks in cartilage lesions in vitro, dSRC constructs generated a contiguous cartilage matrix, while isolated cultured chondrocytes exhibited only a sparse pericellular matrix. dSRC-treated lesions exhibited high GAG production compared to those treated with isolated chondrocytes.

CONCLUSIONS

Isolated dSRC exhibits hyaline cartilage formation, matures over time, and generates contiguous articular cartilage matrix in fractional laser-created microenvironments in vitro, being well integrated with native cartilage.

Efficient engineering of human auricular cartilage through mesenchymal stem cell chaperoning

A major challenge to the clinical translation of tissue-engineered ear scaffolds for ear reconstruction is the limited auricular chondrocyte (hAuC) yield available from patients. Starting with a relatively small number of chondrocytes in culture results in dedifferentiation and loss of phenotype with subsequent expansion. To significantly decrease the number of chondrocytes required for human elastic cartilage engineering, we co-cultured human mesenchymal stem cells (hMSCs) with HAuCs to promote healthy elastic cartilage formation. HAuCs along with human bone marrow-derived hMSCs were encapsulated into 1% Type I collagen at 25 million/mL total cell density with different ratios (HAuCs/hMSCs: 10/90, 25/75, 50/50) and then injected into customized 3D-printed polylactic acid (PLA) ridged external scaffolds, which simulate the shape of the auricular helical rim, and implanted subcutaneously in nude rats for 1, 3 and 6 months. The explanted constructs demonstrated near complete volume preservation and topography maintenance of the ridged "helical" feature after 6 months with all ratios. Cartilaginous appearing tissue formed within scaffolds by 3 months, verified by histologic analysis demonstrating mature elastic cartilage within the constructs with chondrocytes seen in lacunae within a Type II collagen and proteoglycan-enriched matrix, and surrounded by a neoperichondrial external layer. Compressive mechanical properties comparable to human elastic cartilage were achieved after 6 months. Co-implantation of hAuCs and hMSCs in collagen within an external scaffold efficiently produced shaped human elastic cartilage without volume loss even when hAuC comprised only 10% of the implanted cell population, marking a crucial step toward the clinical translation of auricular tissue engineering.

Three-Dimensional-Printed External Scaffolds Mitigate Loss of Volume and Topography in Engineered Elastic Cartilage Constructs

OBJECTIVE

A major obstacle in the clinical translation of engineered auricular scaffolds is the significant contraction and loss of topography that occur during maturation of the soft collagen-chondrocyte matrix into elastic cartilage. We hypothesized that 3-dimensional-printed, biocompatible scaffolds would "protect" maturing hydrogel constructs from contraction and loss of topography.

DESIGN

External disc-shaped and "ridged" scaffolds were designed and 3D-printed using polylactic acid (PLA). Acellular type I collagen constructs were cultured in vitro for up to 3 months. Collagen constructs seeded with bovine auricular chondrocytes (BAuCs) were prepared in 3 groups and implanted subcutaneously in vivo for 3 months: preformed discs with ("Scaffolded/S") or without ("Naked/N") an external scaffold and discs that were formed within an external scaffold via injection molding ("Injection Molded/SInj").

RESULTS

The presence of an external scaffold or use of injection molding methodology did not affect the acellular construct volume or base area loss. In vivo, the presence of an external scaffold significantly improved preservation of volume and base area at 3 months compared to the naked group (P < 0.05). Construct contraction was mitigated even further in the injection molded group, and topography of the ridged constructs was maintained with greater fidelity (P < 0.05). Histology verified the development of mature auricular cartilage in the constructs within external scaffolds after 3 months.

CONCLUSION

Custom-designed, 3D-printed, biocompatible external scaffolds significantly mitigate BAuC-seeded construct contraction and maintain complex topography. Further refinement and scaling of this approach in conjunction with construct fabrication utilizing injection molding may aid in the development of full-scale auricular scaffolds.

Ethanol treatment of nanoPGA/PCL composite scaffolds enhances human chondrocyte development in the cellular microenvironment of tissue-engineered auricle constructs

A major obstacle for tissue engineering ear-shaped cartilage is poorly developed tissue comprising cell-scaffold constructs. To address this issue, bioresorbable scaffolds of poly-ε-caprolactone (PCL) and polyglycolic acid nanofibers (nanoPGA) were evaluated using an ethanol treatment step before auricular chondrocyte scaffold seeding, an approach considered to enhance scaffold hydrophilicity and cartilage regeneration. Auricular chondrocytes were isolated from canine ears and human surgical samples discarded during otoplasty, including microtia reconstruction. Canine chondrocytes were seeded onto PCL and nanoPGA sheets either with or without ethanol treatment to examine cellular adhesion in vitro. Human chondrocytes were seeded onto three-dimensional bioresorbable composite scaffolds (PCL with surface coverage of nanoPGA) either with or without ethanol treatment and then implanted into athymic mice for 10 and 20 weeks. On construct retrieval, scanning electron microscopy showed canine auricular chondrocytes seeded onto ethanol-treated scaffolds in vitro developed extended cell processes contacting scaffold surfaces, a result suggesting cell-scaffold adhesion and a favorable microenvironment compared to the same cells with limited processes over untreated scaffolds. Adhesion of canine chondrocytes was statistically significantly greater (p ≤ 0.05) for ethanol-treated compared to untreated scaffold sheets. After implantation for 10 weeks, constructs of human auricular chondrocytes seeded onto ethanol-treated scaffolds were covered with glossy cartilage while constructs consisting of the same cells seeded onto untreated scaffolds revealed sparse connective tissue and cartilage regeneration. Following 10 weeks of implantation, RT-qPCR analyses of chondrocytes grown on ethanol-treated scaffolds showed greater expression levels for several cartilage-related genes compared to cells developed on untreated scaffolds with statistically significantly increased SRY-box transcription factor 5 (SOX5) and decreased interleukin-1α (inflammation-related) expression levels (p ≤ 0.05). Ethanol treatment of scaffolds led to increased cartilage production for 20- compared to 10-week constructs. While hydrophilicity of scaffolds was not assessed directly in the present findings, a possible factor supporting the summary data is that hydrophilicity may be enhanced for ethanol-treated nanoPGA/PCL scaffolds, an effect leading to improvement of chondrocyte adhesion, the cellular microenvironment and cartilage regeneration in tissue-engineered auricle constructs.

Nipple Engineering: Maintaining Nipple Geometry with Externally Scaffolded Processed Autologous Costal Cartilage

INTRODUCTION

Nipple reconstruction is the essential last step of breast reconstruction after total mastectomy, resulting in improved general and aesthetic satisfaction. However, most techniques are limited by secondary scar contracture and loss of neo-nipple projection leading to patient dissatisfaction. Approximately, 16,000 patients undergo autologous flap breast reconstruction annually, during which the excised costal cartilage (CC) is discarded. We propose utilizing processed CC placed within biocompatible 3D-printed external scaffolds to generate tissue cylinders that mimic the shape, size and biomechanical properties of native human nipple tissue while mitigating contracture and projection loss.

METHODS

External scaffolds were designed and then 3D-printed using polylactic acid (PLA). Patient-derived CC was processed by mincing or zesting, then packed into the scaffolds, implanted into nude rats and explanted after 3 months for volumetric, histologic and biomechanical analyses. Similar analyses were performed on native human nipple tissue and unprocessed CC.

RESULTS

After 3 months in vivo, gross analysis demonstrated significantly greater preservation of contour, projection and volume of the scaffolded nipples. Mechanical analysis demonstrated that processing of the cartilage resulted in implant equilibrium modulus values closer to that of the human nipple. Histologic analysis showed the presence of healthy and viable cartilage after 3 months in vivo, invested with fibrovascular tissue.

CONCLUSIONS

Autologous CC can be processed intraoperatively and placed within biocompatible external scaffolds to mimic the shape and biomechanical properties of the native human nipple. This allows for custom design and fabrication of individualized engineered autologous implants tailored to patient desire, without the loss of projection seen with traditional approaches.

Application of flexural and membrane stress analysis to distinguish tensile and compressive moduli of biologic materials

Three-point bending is often used during the mechanical determination of tissue material properties. When taken to failure, the test samples often experience high deformations. The objective of this study was to present beam and plate theories as analytical tools for determining tensile and compressive elastic moduli during the transition from flexure to membrane stress states. Samples of cartilage, a highly flexible connective tissue having differing tensile and compressive moduli, were tested. Three-point bending tests were conducted on auricular (ear) and costal (rib) cartilage harvested from pigs. The influence of span length variation and Poisson's ratio assumptions were statistically assessed. Tensile elastic moduli of the ear (3.886 MPa) and rib (6.131 MPa) were derived from high-deformation bending tests. The functional assessment described here can be applied as a design input approach for tissue reconstruction and tissue engineering, considering both hard and soft tissue applications.

Biofabrication of a shape-stable auricular structure for the reconstruction of ear deformities

Bioengineering of the human auricle remains a significant challenge, where the complex and unique shape, the generation of high-quality neocartilage, and shape preservation are key factors. Future regenerative medicine–based approaches for auricular cartilage reconstruction will benefit from a smart combination of various strategies. Our approach to fabrication of an ear-shaped construct uses hybrid bioprinting techniques, a recently identified progenitor cell population, previously validated biomaterials, and a smart scaffold design. Specifically, we generated a 3D-printed polycaprolactone (PCL) scaffold via fused deposition modeling, photocrosslinked a human auricular cartilage progenitor cell–laden gelatin methacryloyl (gelMA) hydrogel within the scaffold, and cultured the bioengineered structure in vitro in chondrogenic media for 30 days. Our results show that the fabrication process maintains the viability and chondrogenic phenotype of the cells, that the compressive properties of the combined PCL and gelMA hybrid auricular constructs are similar to native auricular cartilage, and that biofabricated hybrid auricular structures exhibit excellent shape fidelity compared with the 3D digital model along with deposition of cartilage-like matrix in both peripheral and central areas of the auricular structure. Our strategy affords an anatomically enhanced auricular structure with appropriate mechanical properties, ensures adequate preservation of the auricular shape during a dynamic in vitro culture period, and enables chondrogenically potent progenitor cells to produce abundant cartilage-like matrix throughout the auricular construct. The combination of smart scaffold design with 3D bioprinting and cartilage progenitor cells holds promise for the development of clinically translatable regenerative medicine strategies for auricular reconstruction.

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First application of human auricular cartilage progenitor cells for bioprinting.

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Dual-printing of hybrid ear-shaped constructs with excellent shape fidelity over time.

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Strategy and design ensured adequate deposition of cartilage-like matrix throughout large auricular constructs.

The Morphology and Bending Behavior of Regenerated Costal Cartilage with Kawanabe-Nagata Method in Rabbits - the Short Term Result of an Experimental Study

BACKGROUND

The chest wall deformity is a well-known complication following costal cartilage harvest with the biomechanical factor considered to be a cause of this donor-site morbidity. Kawanabe-Nagata method is a widely-accepted approach to prevent the deformity. However, knowledge about the biomechanical properties of regenerated costal cartilage is limited, and the value of reimplantation of autologous costal cartilage blocks is not clear.

METHODS

The fifth costal cartilage on both sides of six male, 8 weeks of age, New Zealand white rabbits were harvested with the perichondrium preserved intact in situ. The perichondrium was sutured to form a perichondrial pocket and part of the excised costal cartilage was cut into 0.5 mm cartilage blocks and returned to the perichondrial pocket of left side. The animals were sacrificed 16 weeks postoperatively and the regenerated and a piece native costal cartilage was harvested for morphological and three point bending test.

RESULTS

There was no remarkable chest wall deformity in all animals, and there were no apparent differences in the appearance of the regenerated cartilage with and without reimplantation autologous cartilage blocks. The elastic modulus of native cartilage was significantly higher than the regenerated cartilage. The stiffness of regenerated cartilage without reimplantation was higher than that of with reimplantation, but this difference was not significant.

CONCLUSIONS

The stiffness of regenerated cartilage was significantly lower than the native cartilage. Reimplantation of autologous cartilage blocks was not superior to that without reimplantation in regard to restoring the volume defect and strengthening the regenerated cartilage.

Beyond the L-Strut: Redefining the Biomechanics of Rhinoplasty Using Topographic Optimization Modeling

Rhinoplasty utilizes cartilage harvested from the nasal septum as autologous graft material. Traditional dogma espouses preservation of the "L-strut" of dorsal and caudal septum, which is less resistant to axial loading than virgin septum. Considering the 90° angle between dorsal and caudal limbs, the traditional L-strut also suffers from localized increases in internal stresses leading to premature septal "cracking," structural-scale deformation, or both. Deformation and failure of the L-strut leads to nasal deviation, saddle deformity, loss of tip support, or restriction of the nasal valve. The balance between cartilage yield and structural integrity is a topographical optimization problem. Guided by finite element (FE) modelling, recent efforts have yielded important modifications including the chamfering of right-angled corners to reduce stress concentrations and the preservation of a minimum width along the inferior portion of the caudal strut. However, all existing FE studies offer simplified assumptions to make the construct easier to model. This review article highlights advances in our understanding of septal engineering and identifies areas that require more work to further refine the balance between the competing interests of graft acquisition and the maintenance of nasal structural integrity.

Structural and Mechanical Comparison of Human Ear, Alar, and Septal Cartilage

Supplemental Digital Content is available in the text.

Background:

In the human ear and nose, cartilage plays a key role in establishing its form and function. Interestingly, there is a noticeable paucity on biochemical, structural, and mechanical studies focused on facial cartilage. Such studies are needed to provide elementary knowledge that is fundamental to tissue engineering of cartilage. Therefore, in this study, a comparison is made of the biochemical, structural, and mechanical differences between ear, ala nasi, and septum on the extracellular matrix (ECM) level.

Methods:

Cartilage samples were harvested from 10 cadaveric donors. Each sample was indented 10 times with a nanoindenter to determine the effective Young’s modulus. Structural information of the cartilage was obtained by multiple-photon laser scanning microscopy capable of revealing matrix components at subcellular resolution. Biochemistry was performed to measure glycosaminoglycan (GAG), DNA, elastin, and collagen content.

Results:

Significant differences were seen in stiffness between ear and septal cartilage (P = 0.011) and between ala nasi and septal cartilage (P = 0.005). Elastin content was significantly higher in ear cartilage. Per cartilage subtype, effective Young’s modulus was not significantly correlated with cell density, GAG, or collagen content. However, in septal cartilage, low elastin content was associated with higher stiffness. Laser microscopy showed a distinct difference between ear cartilage and cartilage of nasal origin.

Conclusion:

Proposed methods to investigate cartilage on the ECM level provided good results. Significant differences were seen not only between ear and nasal cartilage but also between the ala nasi and septal cartilage. Albeit its structural similarity to septal cartilage, the ala nasi has a matrix stiffness comparable to ear cartilage.

A pilot study comparing mechanical properties of tissue-engineered cartilages and various endogenous cartilages

BACKGROUND

Mechanical properties of tissue-engineered cartilage and a variety of endogenous cartilage were measured. The main goal was to evaluate if the tissue-engineered cartilage have similar mechanical characteristics to be replaced with rib cartilage in microtia reconstruction. Such study lays the foundation for future human clinical trials for microtia reconstruction.

METHOD

Atomic force microscopy and compression testing were used to measure the viscoelasticity of tissue-engineered cartilage (stem cell seeded on Poly lactic co-glycolytic acid nanofibers and Pellet) and endogenous cartilage: conchal bowl, microtic ears, preauricular remnants, and rib. Atomic force microscopy, calculates biomaterial elasticity through force-deformation measurement and Hertz model. Compression testing determines the stress relaxation by measuring slope of stress reduction at 10% strain.

FINDING

Tissue-engineered cartilage demonstrated elasticity (4.6kPa for pellet and 6.6kPa for PLGA) and stress relaxation properties (7.6 (SD 1.1) kPa/s for pellet) most similar to those of native conchal bowl cartilage (31.8 (SD 18) kPa for the elasticity and 15.1 (SD 2.1) kPa/s for stress relaxation factor). Rib cartilage was most dissimilar from the mechanical characteristics of conchal cartilage and demonstrated the highest elastic modulus (361 (SD 372) kPa). Moreover, except preauricular cartilage samples, the level of elastic modulus increased with age.

INTERPRETATION

The use of tissue-engineered cartilage developed via PLGA and Pellet methods, may be an appropriate substitute for rib cartilage in the reconstruction of microtic ears, however their mechanical characteristics still need to be improved and require further validation in animal studies.

Noninvasive Measurement of Ear Cartilage Elasticity on the Cellular Level: A New Method to Provide Biomechanical Information for Tissue Engineering

Background:

An important feature of auricular cartilage is its stiffness. To tissue engineer new cartilage, we need objective tools to provide us with the essential biomechanical information to mimic optimal conditions for chondrogenesis and extracellular matrix (ECM) development. In this study, we used an optomechanical sensor to investigate the elasticity of auricular cartilage ECM and tested whether sensitivity and measurement reproducibility of the sensor would be sufficient to accurately detect (subtle) differences in matrix compositions in healthy, diseased, or regenerated cartilage.

Methods:

As a surrogate model to different cartilage ECM compositions, goat ears (n = 9) were subjected to different degradation processes to remove the matrix components elastin and glycosaminoglycans. Individual ear samples were cut and divided into 3 groups. Group 1 served as control and was measured within 2 hours after animal death and at 24 and 48 hours, and groups 2 and 3 were measured after 24- and 48-h hyaluronidase or elastase digestion. Per sample, 9 consecutive measurements were taken ±300 μm apart.

Results:

Good reproducibility was seen between consecutive measurements with an overall interclass correlation coefficient average of 0.9 (0.81–0.98). Although degradation led to variable results, overall, a significant difference was seen between treatment groups after 48 hours (control, 4.2 MPa [±0.5] vs hyaluronidase, 2.0 MPa [±0.3], and elastase, 3.0 MPa [±0.4]; both P < 0.001).

Conclusions:

The optomechanical sensor system we used provided a fast and reliable method to perform measurements of cartilage ECM in a reverse tissue-engineering model. In future applications, this method seems feasible for the monitoring of changes in stiffness during the development of tissue-engineered auricular cartilage.

Direct electrospinning of 3D auricle-shaped scaffolds for tissue engineering applications

Thirty-two poly(ε)caprolactone (PCL) scaffolds have been produced by electrospinning directly into an auricle-shaped mould and seeded with articular chondrocytes harvested from bovine ankle joints. After seeding, the auricle shaped constructs were cultured in vitro and analysed at days 1, 7, 14 and 21 for regional differences in total DNA, glycosaminoglycan (GAG) and collagen (COL) content as well as the expression of aggrecan (AGG), collagen type I and type II (COL1/2) and matrix metalloproteinase 3 and 13 (MMP3/13). Stress-relaxation indentation testing was performed to investigate regional mechanical properties of the electrospun constructs. Electrospinning into a conductive mould yielded stable 3D constructs both initially and for the whole in vitro culture period, with an equilibrium modulus in the MPa range. Rapid cell proliferation and COL accumulation was observed until week 3. Quantitative real time PCR analysis showed an initial increase in AGG, no change in COL2, a persistent increase in COL1, and only a slight decrease initially for MMP3. Electrospinning of fibrous scaffolds directly into an auricle-shape represents a promising option for auricular tissue engineering, as it can reduce the steps needed to achieve an implantable structure.

A 3D bioprinting system to produce human-scale tissue constructs with structural integrity

A challenge for tissue engineering is producing three-dimensional (3D), vascularized cellular constructs of clinically relevant size, shape and structural integrity. We present an integrated tissue-organ printer (ITOP) that can fabricate stable, human-scale tissue constructs of any shape. Mechanical stability is achieved by printing cell-laden hydrogels together with biodegradable polymers in integrated patterns and anchored on sacrificial hydrogels. The correct shape of the tissue construct is achieved by representing clinical imaging data as a computer model of the anatomical defect and translating the model into a program that controls the motions of the printer nozzles, which dispense cells to discrete locations. The incorporation of microchannels into the tissue constructs facilitates diffusion of nutrients to printed cells, thereby overcoming the diffusion limit of 100-200 μm for cell survival in engineered tissues. We demonstrate capabilities of the ITOP by fabricating mandible and calvarial bone, cartilage and skeletal muscle. Future development of the ITOP is being directed to the production of tissues for human applications and to the building of more complex tissues and solid organs.

High Strength Multifunctional Multiwalled Hydrogel Tubes: Ion-Triggered Shape Memory, Antibacterial, and Anti-inflammatory Efficacies

In this study, ion-responsive hydrogen bonding strengthened hydrogels (termed as PVV) were synthesized by one-pot copolymerization of 2-vinyl-4,6-diamino-1,3,5-triazine (VDT), 1-vinylimidazole (VI), and polyethylene glycol diacrylate. The diaminotriazine-diaminotriazine (DAT-DAT) H-bonding interaction and copolymerization of VI contributed to a notable increase in comprehensive performances including tensile/compressive strength, elasticity, modulus, and fracture energy. In addition, introducing mM levels of zinc ions could further increase the mechanical properties of PVV hydrogels and fix a variety of temporary shapes due to the strong coordination of zinc with imidazole. The release of zinc ions from the hydrogel contributed to an antibacterial effect, without compromising the shape memory effect. Remarkably, a multiwalled hydrogel tube (MWHT) fixed with Zn(2+) demonstrated much higher flexural strengths and a more sustainable release of zinc ions than the solid hydrogel cylinder (SHC). A Zn(2+)-fixed MWHT was implanted subcutaneously in rats, and it was found that the Zn(2+)-fixed MWHT exhibited anti-inflammatory and wound healing efficacies. The reported high strength hydrogel with integrated functions holds potential as a tissue engineering scaffold.

Biomechanical evaluation of human and porcine auricular cartilage

OBJECTIVES/HYPOTHESIS

The mechanical properties of normal auricular cartilage provide a benchmark against which to characterize changes in auricular structure/function due to genetic defects creating phenotypic abnormalities in collagen subtypes. Such properties also provide inputs/targets for auricular reconstruction scaffold design. Several studies report the biomechanical properties for septal, costal, and articular cartilage. However, analogous data for auricular cartilage are lacking. Therefore, our aim in this study was to characterize both whole-ear and auricular cartilage mechanics by mechanically testing specimens and fitting the results to nonlinear constitutive models.

STUDY DESIGN

Mechanical testing of whole ears and auricular cartilage punch biopsies.

METHODS

Whole human cadaveric ear and auricular cartilage punch biopsies from both porcine and human cartilage were subjected to whole-ear helix-down compression and quasistatic unconfined compression tests. Common hyperelastic constitutive laws (widely used to characterize soft tissue mechanics) were evaluated for their ability to represent the stress-strain behavior of auricular cartilage.

RESULTS

Load displacement curves for whole ear testing exhibited compliant linear behavior until after significant displacement where nonlinear stiffening occurred. All five commonly used two-term hyperelastic soft tissue constitutive models successfully fit both human and porcine nonlinear elastic behavior (mean R(2) fit >0.95).

CONCLUSIONS

Auricular cartilage exhibits nonlinear strain-stiffening elastic behavior that is similar to other soft tissues in the body. The whole ear exhibits compliant behavior with strain stiffening at high displacement. The constants from the hyperelastic model fits provide quantitative baselines for both human and porcine (a commonly used animal model for auricular tissue engineering) auricular mechanics.

LEVEL OF EVIDENCE

NA

Increased adipogenesis of human adipose-derived stem cells on polycaprolactone fiber matrices

With accelerating rates of obesity and type 2 diabetes world-wide, interest in studying the adipocyte and adipose tissue is increasing. Human adipose derived stem cells--differentiated to adipocytes in vitro--are frequently used as a model system for white adipocytes, as most of their pathways and functions resemble mature adipocytes in vivo. However, these cells are not completely like in vivo mature adipocytes. Hosting the cells in a more physiologically relevant environment compared to conventional two-dimensional cell culturing on plastic surfaces, can produce spatial cues that drive the cells towards a more mature state. We investigated the adipogenesis of adipose derived stem cells on electro spun polycaprolactone matrices and compared functionality to conventional two-dimensional cultures as well as to human primary mature adipocytes. To assess the degree of adipogenesis we measured cellular glucose-uptake and lipolysis and used a range of different methods to evaluate lipid accumulation. We compared the averaged results from a whole population with the single cell characteristics--studied by coherent anti-Stokes Raman scattering microscopy--to gain a comprehensive picture of the cell phenotypes. In adipose derived stem cells differentiated on a polycaprolactone-fiber matrix; an increased sensitivity in insulin-stimulated glucose uptake was detected when cells were grown on either aligned or random matrices. Furthermore, comparing differentiation of adipose derived stem cells on aligned polycaprolactone-fiber matrixes, to those differentiated in two-dimensional cultures showed, an increase in the cellular lipid accumulation, and hormone sensitive lipase content. In conclusion, we propose an adipocyte cell model created by differentiation of adipose derived stem cells on aligned polycaprolactone-fiber matrices which demonstrates increased maturity, compared to 2D cultured cells.

Evaluation of nanofiber-based polyglycolic acid scaffolds for improved chondrocyte retention and in vivo bioengineered cartilage regeneration

BACKGROUND

In conventional studies on the regeneration of auricle-shaped cartilage in autogenous models using large animals, there were problems with the cartilage regeneration induction capacity and long-term retention of geometric shape. In this study, the authors sought to improve on outcome in these regards: a nonwoven fabric of polyglycolic acid was developed through nanotechnology, and the effect of nanofiber diameter on in vitro cell-seeding efficiency and the in vivo response after implantation in an autogenous large-animal model were evaluated.

METHODS

Canine chondrocytes were isolated and seeded onto polyglycolic acid fabric ranging from 0.5 to 20 μm in average diameter. Cell seeding efficiency was highest for mid-range polyglycolic acid fibers (average diameter, 0.8, 3.0, and 7.0 μm). Flat and auricle-shaped scaffolds were constructed using polypropylene structural support, sandwiching a nonwoven polyglycolic acid fabric that contained autogenous chondrocytes together with basic fibroblast growth factor-laden particles and an exterior fibrin sealant. Scaffolds were then implanted autogenously and evaluated at 5 and 20 weeks.

RESULTS

Biomechanical strength was optimal for polyglycolic acid fiber diameters of 0.8 to 3.0 μm. Optimal cell maintenance and neocartilage response were seen with polyglycolic acid fiber diameters in the same mid-range for nanofiber constructs.

CONCLUSION

These findings demonstrate the potential for nanoscale modulation of auricle-shaped cartilage regeneration in a large-animal model.

Compressive and tensile mechanical properties of the porcine nasal septum

The expanding nasal septal cartilage is believed to create a force that powers midfacial growth. In addition, the nasal septum is postulated to act as a mechanical strut that prevents the structural collapse of the face under masticatory loads. Both roles imply that the septum is subject to complex biomechanical loads during growth and mastication. The purpose of this study was to measure the mechanical properties of the nasal septum to determine (1) whether the cartilage is mechanically capable of playing an active role in midfacial growth and in maintaining facial structural integrity and (2) if regional variation in mechanical properties is present that could support any of the postulated loading regimens. Porcine septal samples were loaded along the horizontal or vertical axes in compression and tension, using different loading rates that approximate the in vivo situation. Samples were loaded in random order to predefined strain points (2-10%) and strain was held for 30 or 120 seconds while relaxation stress was measured. Subsequently, samples were loaded until failure. Stiffness, relaxation stress and ultimate stress and strain were recorded. Results showed that the septum was stiffer, stronger and displayed a greater drop in relaxation stress in compression compared to tension. Under compression, the septum displayed non-linear behavior with greater stiffness and stress relaxation under faster loading rates and higher strain levels. Under tension, stiffness was not affected by strain level. Although regional variation was present, it did not strongly support any of the suggested loading patterns. Overall, results suggest that the septum might be mechanically capable of playing an active role in midfacial growth as evidenced by increased compressive residual stress with decreased loading rates. However, the low stiffness of the septum compared to surrounding bone does not support a strut role. The relatively low stiffness combined with high stress relaxation under fast loading rates suggests that the nasal septum is a stress dampener, helping to absorb and dissipate loads generated during mastication.

Effect of intercostal muscle and costovertebral joint material properties on human ribcage stiffness and kinematics

Current finite element (FE) models of the human thorax are limited by the lack of local-level validation, especially in the ribcage. This study exercised an existing FE ribcage model for a 50th percentile male under quasi-static point loading and dynamic sternal loading. Both force-displacement and kinematic responses of the ribcage were compared against experimental data. The sensitivity of the model response to changes in the material properties of the costovertebral (CV) joints and intercostal muscles was assessed. The simulations found that adjustments to the CV joints tended to change the amount of rib rotation in the sagittal plane, while changes to the elastic modulus and thickness of the intercostal muscles tended to alter both the stiffness and the direction and magnitude of rib motions. This study can lend insight into the role that the material properties of these two thoracic structures play in the dynamics of the ribcage during a frontal loading condition.

Design of composite scaffolds and three-dimensional shape analysis for tissue-engineered ear

Engineered cartilage is a promising option for auricular reconstruction. We have previously demonstrated that a titanium wire framework within a composite collagen ear-shaped scaffold helped to maintain the gross dimensions of the engineered ear after implantation, resisting the deformation forces encountered during neocartilage maturation and wound healing. The ear geometry was redesigned to achieve a more accurate aesthetic result when implanted subcutaneously in a nude rat model. A non-invasive method was developed to assess size and shape changes of the engineered ear in three dimensions. Computer models of the titanium framework were obtained from CT scans before and after implantation. Several parameters were measured including the overall length, width and depth, the minimum intrahelical distance and overall curvature values for each beam section within the framework. Local curvature values were measured to gain understanding of the bending forces experienced by the framework structure in situ. Length and width changed by less than 2%, whereas the depth decreased by approximately 8% and the minimum intrahelical distance changed by approximately 12%. Overall curvature changes identified regions most susceptible to deformation. Eighty-nine per cent of local curvature measurements experienced a bending moment less than 50 µN-m owing to deformation forces during implantation. These quantitative shape analysis results have identified opportunities to improve shape fidelity of engineered ear constructs.

Usefulness of polyglycolic acid-polypropylene composite scaffolds for three-dimensional cartilage regeneration in a large-animal autograft model

BACKGROUND

Approaches to auricular reconstruction have shown improved outcome when a basic fibroblast growth factor (bFGF) slow-release system and fibrin spraying are combined with biodegradable polymers. More complex, three-dimensional structures, such as those that replicate the human auricle, are often lost because of biodegradation of the synthetic scaffold.

METHODS

To improve the mechanical strength of regenerated cartilage, the authors grafted canine autologous chondrocytes after seeding onto scaffolds made of a complex of polyglycolic acid and polypropylene, incorporating a slow-release bFGF system with a fibrin spray coating.

RESULTS

Five weeks after grafting, thicker cartilage with increased bending stress was obtained with the slow-release bFGF. In a three-polyglycolic acid-layer construct sandwiched around polypropylene, simulating a three-dimensional auricular structure, greater cartilage regeneration and angiogenesis were found around the implant. Sox5-positive cells were identified, indicative of maturation of neocartilage with chondroblast proliferation.

CONCLUSION

These results support the usefulness of combining absorbable and nonabsorbable materials (polyglycolic acid and polypropylene) in composite scaffolds for autologous cartilage regeneration in a large-animal autograft model.

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.

Flexural properties of native and tissue-engineered human septal cartilage

OBJECTIVE

To determine and compare the bending moduli of native and engineered human septal cartilage.

STUDY DESIGN

Prospective, basic science.

SETTING

Research laboratory.

SUBJECTS AND METHODS

Neocartilage constructs were fabricated from expanded human septal chondrocytes cultured in differentiation medium for 10 weeks. Constructs (n = 10) and native septal cartilage (n = 5) were tested in a 3-point bending apparatus, and the bending moduli were calculated using Euler-Bernoulli beam theory.

RESULTS

All samples were tested successfully and returned to their initial shape after unloading. The bending modulus of engineered constructs (0.32 ± 0.25 MPa, mean ± SD) was 16% of that of native septal cartilage (1.97 ± 1.25 MPa).

CONCLUSION

Human septal constructs, fabricated from cultured human septal chondrocytes, are more compliant in bending than native human septal tissue. The bending modulus of engineered septal cartilage can be measured, and this modulus provides a useful measure of construct rigidity while undergoing maturation relative to native tissue.

Microstructural manipulation of electrospun scaffolds for specific bending stiffness for heart valve tissue engineering

Biodegradable thermoplastic elastomers are attractive for application in cardiovascular tissue construct development due to their amenability to a wide range of physical property tuning. For heart valve leaflets, while low flexural stiffness is a key design feature, control of this parameter has been largely neglected in the scaffold literature where electrospinning is being utilized. This study evaluated the effect of processing variables and secondary fiber populations on the microstructure, tensile and bending mechanics of electrospun biodegradable polyurethane scaffolds for heart valve tissue engineering. Scaffolds were fabricated from poly(ester urethane) urea (PEUU) and the deposition mandrel was translated at varying rates in order to modify fiber intersection density. Scaffolds were also fabricated in conjunction with secondary fiber populations designed either for mechanical reinforcement or to be selectively removed following fabrication. It was determined that increasing fiber intersection densities within PEUU scaffolds was associated with lower bending moduli. Further, constructs fabricated with stiff secondary fiber populations had higher bending moduli whereas constructs with secondary fiber populations which were selectively removed had noticeably lower bending moduli. Insights gained from this work will be directly applicable to the fabrication of soft tissue constructs, specifically in the development of cardiac valve tissue constructs.

The tissue-engineered auricle: past, present, and future

The reconstruction, repair, and regeneration of the external auricular framework continue to be one of the greatest challenges in the field of tissue engineering. To replace like with like, we should emulate the native structure and composition of auricular cartilage by combining a suitable chondrogenic cell source with an appropriate scaffold under optimal in vitro and in vivo conditions. Due to the fact that a suitable and reliable substitute for auricular cartilage has yet to be engineered, hand-carved autologous costal cartilage grafts and ear-shaped porous polyethylene implants are the current treatment modalities for auricular reconstruction. However, over the last decade, significant advances have been made in the field of regenerative medicine and tissue engineering. A variety of scaffolds and innovative approaches have been investigated as alternatives to using autologous carved costal cartilage or porous polyethylene implants. A review of recent developments and the current state of the art and science is presented, focusing on scaffolds, cell sources, seeding densities, and mechanical characteristics of tissue-engineered auricular cartilage.

Reconstruction of human elastic cartilage by a CD44+ CD90+ stem cell in the ear perichondrium

Despite the great demands for treating craniofacial injuries or abnormalities, effective treatments are currently lacking. One promising approach involves human elastic cartilage reconstruction using autologous stem/progenitor populations. Nevertheless, definitive evidence of the presence of stem cells in human auricular cartilage remains to be established. Here, we demonstrate that human auricular perichondrium, which can be obtained via a minimally invasive approach, harbors a unique cell population, termed as cartilage stem/progenitor cells (CSPCs). The clonogenic progeny of a single CD44(+) CD90(+) CSPC displays a number of features characteristic of stem cells. Highly chondrogenic CSPCs were shown to reconstruct large (>2 cm) elastic cartilage after extended expansion and differentiation. CSPC-derived cartilage was encapsulated by a perichondrium layer, which contains a CD44(+) CD90(+) self-renewing stem/progenitor population and was maintained without calcification or tumor formation even after 10 mo. This is a unique report demonstrating the presence of stem cells in auricular cartilage. Utilization of CSPCs will provide a promising reconstructive material for treating craniofacial defects with successful long-term tissue restoration.

An evaluation of applied biomechanics as an adjunct to systematic specific causation in forensic medicine

Biomechanical tests of post hoc probability have been proposed by prior authors as reliable tests of causation in forensic settings. Biomechanical assessment of injury kinetics and kinematics is a potentially important tool in forensic medicine, but there is also the potential for misapplication. The most reliable application is when biomechanical analysis is used to explain injury mechanisms, such as how an injury may have occurred. When a biomechanical analysis is used as a means of determining whether, rather than how an injury has resulted from a traumatic exposure, then a lack of reliability of the methodology limits its application in forensic medicine. Herein, we describe a systematic assessment of causation by adapting established general causation principles to specific causation scenarios, and how biomechanical analysis of injury mechanics is properly used to augment such an approach in conjunction with the principles of forensic epidemiology. An example calculation of relative risk associated with cervical spine injury is provided as a representative probabilistic metric for assessing causation. The statistical benefits and limitations of biomechanical analysis are discussed as an adjunct to forensic medicine.

Biomechanical characterisation of equine laryngeal cartilage

REASONS FOR PERFORMING THE STUDY

Upper airway obstruction is a common problem in the performance horse as the soft tissues of the larynx collapse into the airway, yet there is a paucity of information on biomechanical properties for the structural cartilage components.

OBJECTIVE

To measure the geometry and compressive mechanical properties of the hyaline cartilage to improve understanding of laryngeal function and morphology.

METHODS

A total of 11 larynges were harvested from Thoroughbred and Standardbred racehorses. During gross dissection, linear dimensions of the cricoid were obtained. From both the cricoid and arytenoid, specimens were cored to obtain 6 mm disc samples from 3 sites within the dorsal cricoid (caudal, middle and rostral) and 2 central sites in the arytenoids (inner, outer). The specimens were mechanically tested using radial confined compression to calculate the aggregate modulus and permeability of the tissue. The biomechanical data were analysed using a nested mixed effects model.

RESULTS

Geometrically, the cricoid has relatively straight walls compared to the morphology of human, ovine and canine larynges. There were significant observations of higher modulus with increasing age (0.13 MPa per year; P = 0.007) and stiffer cricoid cartilage (2.29 MPa) than the arytenoid cartilage (0.42 MPa; P<0.001), but no difference was observed between the left and right sides. Linear contrasts showed that the rostral aspect (2.51 MPa) of the cricoid was 20% stiffer than the caudal aspect (2.09 MPa; P = 0.025), with no difference between the arytenoid sites.

CONCLUSIONS

The equine larynx is a well supported structure due to both the geometry and material properties of the cricoid cartilage. The hyaline structure is an order of magnitude higher in compressive modulus compared to the arytenoids and other hyaline-composed tissues.

POTENTIAL RELEVANCE

These characterisations are important to understand the biomechanics of laryngeal function and the mechanisms involved with surgical interventions.

A pseudo-elastic effective material property representation of the costal cartilage for use in finite element models of the whole human body

OBJECTIVE

Injury-predictive finite element (FE) models of the chest must reproduce the structural coupling behavior of the costal cartilage accurately. Gross heterogeneities (the perichondrium and calcifications) may cause models developed based on local material properties to erroneously predict the structural behavior of cartilage segments. This study sought to determine the pseudo-elastic effective material properties required to reproduce the structural behavior of the costal cartilage under loading similar to what might occur in a frontal automobile collision.

METHODS

Twenty-eight segments of cadaveric costal cartilage were subjected to cantilever-like, dynamic loading. Three limited-mesh FE models were then developed for each specimen, having element sizes of 10 mm (typical of current whole-body FE models), 3 mm, and 2 mm. The cartilage was represented as a homogeneous, isotropic, linear elastic material. The elastic moduli of the cartilage models were optimized to fit the anterior-posterior (x-axis) force versus displacement responses observed in the experiments. For a subset of specimens, additional model validation tests were performed under a second boundary condition.

RESULTS

The pseudo-elastic effective moduli ranged from 4.8 to 49 MPa, with an average and standard deviation of 22 ± 13.6 MPa. The models were limited in their ability to reproduce the lateral (y-axis) force responses observed in the experiments. The prediction of the x-axis and y-axis forces in the second boundary condition varied. Neither the effective moduli nor the model fit were significantly affected (Student's t-test, p < 0.05) by the model mesh density. The average pseudo-elastic effective moduli were significantly (p < 0.05) greater than local costal cartilage modulus values reported in the literature.

CONCLUSIONS

These results are consistent with the presence of stiffening heterogeneities within the costal cartilage structure. These effective modulus values may provide guidance for the representation of the costal cartilage in whole-body FE models where these heterogeneities cannot be modeled distinctly.

The Contribution of the Perichondrium to the Structural Mechanical Behavior of the Costal-Cartilage

The costal-cartilage in the human ribcage is a composite structure consisting of a cartilage substance surrounded by a fibrous, tendonlike perichondrium. Current computational models of the human ribcage represent the costal-cartilage as a homogeneous material, with no consideration for the mechanical contributions of the perichondrium. This study sought to investigate the role of the perichondrium in the structural mechanical behavior of the costal-cartilage. Twenty-two specimens of postmortem human costal-cartilage were subjected to cantileveredlike loading both with the perichondrium intact and with the perichondrium removed. The test method was chosen to approximate the cartilage loading that occurs when a concentrated, posteriorly directed load is applied to the midsternum. The removal of the perichondrium resulted in a statistically significant (two-tailed Student’s t-test, p≤0.05) decrease of approximately 47% (95% C.I. of 35–58%) in the peak anterior-posterior reaction forces generated during the tests. When tested with the perichondrium removed, the specimens also exhibited failure in the cartilage substance in the regions that experienced tension from bending. These results suggest that the perichondrium does contribute significantly to the stiffness and strength of the costal-cartilage structure under this type loading, and should be accounted for in computational models of the thorax and ribcage.

Asymmetrical strain distributions and neutral axis location of cartilage in flexure

Flexural deformation has been used for the biomechanical characterization of native and engineered cartilage and as a mechanical stimulus to induce alteration of cartilage shape during in vitro culture. Flexure is also a physiologically relevant mode of deformation for various cartilaginous structures such as the ears and nose, but a kinematic description of cartilage in flexure is lacking even for simple deformations. The hypothesis of this study was that tension-compression (T-C) nonlinearity of cartilage will result in asymmetrical strain distributions during bending, while a material with similar behavior in tension and compression, such as alginate, will have a more symmetrical distribution of strains. Strips of calf articular cartilage and alginate were tested under uniform circular bending, and strains were determined by a micromechanical analysis of images acquired by epifluorescence microscopy. This experimental analysis was interpreted in the context of a model of small-deflection, pure bending of thin, homogeneous beams of a bimodular elastic material. The results supported the hypothesis and showed that marked asymmetry existed in cartilage flexural strains where the location of the neutral axis was significantly different than the midline and closer to the tensile surface. In contrast, alginate samples had a centrally located neutral axis. These experimental results were supported by the model indicating that the bimodular simplification of cartilage properties is a useful first approximation of T-C nonlinearity in these tests. The neutral axis location in cartilage samples was not influenced by the testing orientation (towards or away from the superficial-most tissue) or magnitude of flexure. These findings characterize the kinematics of cartilage at equilibrium during simple bending and indicate that T-C nonlinearity is an important determinant of the flexural strain distributions in the tested tissue.

Indentation stiffness of aging human costal cartilage

Costal cartilage, connecting the ribs and sternum, serves a mechanical function in the body. It undergoes structural changes with aging but it is unclear if its material properties are affected by these changes. To investigate this question, experimental indentation load-relaxation tests were performed on human costal cartilage as a function of specimen age and sex. The experimental data were fit to spherical indentation ramp-relaxation solutions generated previously by elastic-viscoelastic correspondence [Mattice JM, Lau AG, Oyen ML and Kent RW. Spherical indentation load-relaxation of soft biological tissues. J Mater Res 2006;8:2003-10]. Numerical values of short- and long-time shear modulus and of material time-constants were examined as a function of age. Costal cartilage calcification was assessed with blinded scoring of computed tomography reconstructions of the ribcage and mechanical properties were correlated with calcification score. Overall, the costal cartilage midsubstance was slightly stiffer than articular cartilage, and did not show significant variation in stiffness with age or specimen calcification. Increased age did result in increased local variability of the indentation stiffness results. Future studies will be required to address the findings of the current study that although calcification did increase with age, the calcification was primarily found on the costal cartilage periphery, thus insignificantly affecting the midsubstance stiffness.

A mechanical composite spheres analysis of engineered cartilage dynamics

In the preparation of bioengineered reparative strategies for damaged or diseased tissues, the processes of biomaterial degradation and neotissue synthesis combine to affect the developing mechanical state of multiphase, composite engineered tissues. Here, cell-polymer constructs for engineered cartilage have been fabricated by seeding chondrocytes within three-dimensional scaffolds of biodegradable polymers. During culture, synthetic scaffolds degraded passively as the cells assembled an extracellular matrix (ECM) composed primarily of glycosaminoglycan and collagen. Biochemical and biomechanical assessment of the composite (cells, ECM, and polymer scaffold) were modeled at a unit-cell level to mathematically solve stress-strain relationships and thus construct elastic properties (n=4 samples per seven time points). This approach employed a composite spheres, micromechanical analysis to determine bulk moduli of: (1) the cellular-ECM inclusion within the supporting scaffold structure; and (2) the cellular inclusion within its ECM. Results indicate a dependence of constituent volume fractions with culture time (p<0.05). Overall mean bulk moduli were variably influenced by culture, as noted for the cell-ECM inclusion (K(c-m)=29.7 kPa, p=0.1439), the cellular inclusion (K(c)=5.5 kPa, p=0.0067), and its surrounding ECM (K(m)=373.9 kPa, p=0.0748), as well as the overall engineered construct (K=165.0 kPa, p=0.6899). This analytical technique provides a framework to describe the time-dependent contribution of cells, accumulating ECM, and a degrading scaffold affecting bioengineered construct mechanical properties.

Defining nasal cartilage elasticity: biomechanical testing of the tripod theory based on a cantilevered model

OBJECTIVE

To define the modulus of elasticity for nasal septum, auricular, upper lateral, and lower lateral cartilages.

METHODS

Prospective enrollment of sequential patients undergoing septorhinoplasty. Test samples were obtained through routine surgical interventions using atraumatic harvesting techniques. The modulus of elasticity was determined using a customized biomechanical testing device. A clinical analysis of nasal tip strength and "ethnic" nasal categorization was performed.

RESULTS

Five sequential patients were enrolled; 4 underwent biomechanical testing of harvested cartilage. All 4 patients were classified as having a leptor-rhine nasal architecture. The modulus of elasticity for the lower lateral cartilages was 1.82 to 15.28 MPa. Values for auricular, nasal septum, and upper lateral cartilages (medial and caudal) were also determined.

CONCLUSIONS

This is the first biomechanical study performed on human auricular, lower lateral, and upper lateral cartilages. The elastic modulus can be determined from samples obtained during routine septorhinoplasty. The modulus of elasticity for all areas was significantly higher than values previously demonstrated for bioengineered elastic cartilage and carved human nasal septal specimens. Shaving the lateral portions of the nasal septum may significantly reduce tensile strength, which may affect graft performance in vivo. Further refinement of testing methods and an increase in the number of analyzed samples are required for formal statistical analysis and further determination of clinical relevance in different nasal subtypes.

Producing a Flexible Tissue-Engineered Cartilage Framework Using Expanded Polytetrafluoroethylene Membrane as a Pseudoperichondrium

BACKGROUND

Both native and engineered cartilage is brittle and fractures easily without perichondrium. The aim of this study was to understand the role of the perichondrium and try to enhance the flexible properties of tissue-engineered cartilage using expanded polytetrafluoroethylene (ePTFE) membrane as a pseudoperichondrium.

METHODS

The study was conducted in two phases. In phase I, native swine auricular cartilage of different thicknesses was studied by histologic evaluation and failure testing. Next, isolated perichondrium was bonded to native cartilage slices using fibrin glue or Dermabond and tested to failure. In phase II, swine auricular chondrocytes were suspended in fibrin glue. The chondrocyte-fibrin glue composites were then bound to expanded polytetrafluoroethylene membrane in two trilaminar configurations: In group EC-1, the membrane was in the center, whereas it was on the surfaces in group EC-2. Specimens were implanted into nude mice for 4 weeks, 8 weeks, 12 weeks, and 8 months and subjected to histologic evaluation and failure testing.

RESULTS

In phase I, the results demonstrated that perichondrium securely bonded to the cartilage plays an important role in maintaining the flexible nature of elastic cartilage. In phase II, failure testing revealed that specimens in group EC-1 (expanded polytetrafluoroethylene core) were fractured during bending and destroyed after torsion, whereas those in group EC-2 (cartilage core) returned to their original shape without fracturing even after rigorous torsion. Histologic analysis demonstrated that transplanted chondrocytes penetrated into the microporous structure of expanded polytetrafluoroethylene and created a bond to it.

CONCLUSION

It is possible to engineer flexible cartilage using expanded polytetrafluoroethylene as a pseudoperichondrium.

Cell-based therapies and tissue engineering

Tissue engineering is a rapidly evolving discipline that may some-day afford surgeons a limitless supply of autologous tissue for transplantation or allow in situ tissue regeneration. A number of biologic, engineering, and clinical challenges continue to face tissue engineers and surgeons alike. One important example is the choice of an appropriate cell scaffold that promotes growth and is eventually resorbed by the body. Although the application of bioengineered tissue is specific to the anatomic areas of interest,continued advances bring tissue engineering closer to reality in all areas of otolaryngology.