Biomechanical evaluation of human and porcine auricular cartilage

Development and Characterization of Heparin-Containing Hydrogel/3D-Printed Scaffold Composites for Craniofacial Reconstruction

Regeneration of cartilage and bone tissues remains challenging in tissue engineering due to their complex structures, and the need for both mechanical support and delivery of biological repair stimuli. Therefore, the goal of this study was to develop a composite scaffold platform for anatomic chondral and osteochondral repair using heparin-based hydrogels to deliver small molecules within 3D-printed porous scaffolds that provide structure, stiffness, and controlled biologic delivery. We designed a mold-injection system to combine hydrolytically degradable hydrogels and 3D-printed scaffolds that could be employed rapidly (< 30 min) in operating room settings (~23 °C). Micro-CT analysis demonstrated the effectiveness of our injection system through homogeneously distributed hydrogel within the pores of the scaffolds. Hydrogels and composite scaffolds exhibited efficient loading (~94%) of a small positively charged heparin-binding molecule (crystal violet) with sustained release over 14 days and showed high viability of encapsulated porcine chondrocytes over 7 days. Compression testing demonstrated nonlinear viscoelastic behavior where tangent stiffness decreased with scaffold porosity (porous scaffold tangent stiffness: 70%: 4.9 MPa, 80%: 1.5 MPa, and 90%: 0.20 MPa) but relaxation was not affected. Lower-porosity scaffolds (70%) showed stiffness similar to lower ranges of trabecular bone (4-8 MPa) while higher-porosity scaffolds (80% and 90%) showed stiffness similar to auricular cartilage (0.16-2 MPa). Ultimately, this rapid composite scaffold fabrication method may be employed in the operating room and utilized to control biologic delivery within load-bearing scaffolds.

Accessory tympanic plate ossicle: a new osteological entity

The auricular cartilage, which is typically soft and flexible, can calcify or ossify because of diseases such as diabetes mellitus, trauma, radiation therapy for cancer, and more commonly from frostbite. Calcified, ossified, or hardened auricular cartilage is a rare finding in the clinical literature and appears to be absent in the physical and forensic anthropological literature. This study examines the ossified auricular cartilage and tests whether the hypothesis can be identified in postmortem skeletonized tissue and be part of the external auditory meatus. A total of 290 crania were examined for accessory ossicles. A descriptive and interpretative analysis was performed grossly, histologically, and morphometrically to document the morphology and location of the ossicles, investigate their structure, and perform hypothesis testing. Results revealed that seven females and one male crania from a total of 290 crania (2.76%) exhibit semi-ossified auricular cartilage attached to the tympanic plate of the temporal bone. The morphology and location of the ossicles at the junction of the auricle and external auditory meatus indicate they are hardened auricular cartilage that was verified with histological observations. Regression analysis indicates that addition of the ossicle to the depth of the auditory tube significantly changes coefficient of determination (R2) with respect to cranial breadth. In conclusion, results indicate that small cartilaginous structures of the external ear may ossify forming accessory tympanic plate ossicles that potentially could be identified in skeletal remains as a new osteological entity. This report highlights the types of information that can be gained using an approach that integrates forensic anthropology, gross anatomy, and histology.

Hydrogel Based on Chitosan/Gelatin/Poly(Vinyl Alcohol) for In Vitro Human Auricular Chondrocyte Culture

Three-dimensional (3D) hydrogels provide tissue-like complexities and allow for the spatial orientation of cells, leading to more realistic cellular responses in pathophysiological environments. There is a growing interest in developing multifunctional hydrogels using ternary mixtures for biomedical applications. This study examined the biocompatibility and suitability of human auricular chondrocytes from microtia cultured onto steam-sterilized 3D Chitosan/Gelatin/Poly(Vinyl Alcohol) (CS/Gel/PVA) hydrogels as scaffolds for tissue engineering applications. Hydrogels were prepared in a polymer ratio (1:1:1) through freezing/thawing and freeze-drying and were sterilized by autoclaving. The macrostructure of the resulting hydrogels was investigated by scanning electron microscopy (SEM), showing a heterogeneous macroporous structure with a pore size between 50 and 500 μm. Fourier-transform infrared (FTIR) spectra showed that the three polymers interacted through hydrogen bonding between the amino and hydroxyl moieties. The profile of amino acids present in the gelatin and the hydrogel was determined by ultra-performance liquid chromatography (UPLC), suggesting that the majority of amino acids interacted during the formation of the hydrogel. The cytocompatibility, viability, cell growth and formation of extracellular matrix (ECM) proteins were evaluated to demonstrate the suitability and functionality of the 3D hydrogels for the culture of auricular chondrocytes. The cytocompatibility of the 3D hydrogels was confirmed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, reaching 100% viability after 72 h. Chondrocyte viability showed a high affinity of chondrocytes for the hydrogel after 14 days, using the Live/Dead assay. The chondrocyte attachment onto the 3D hydrogels and the formation of an ECM were observed using SEM. Immunofluorescence confirmed the expression of elastin, aggrecan and type II collagen, three of the main components found in an elastic cartilage extracellular matrix. These results demonstrate the suitability and functionality of a CS/Gel/PVA hydrogel as a 3D support for the auricular chondrocytes culture, suggesting that these hydrogels are a potential biomaterial for cartilage tissue engineering applications, aimed at the regeneration of elastic cartilage.

Applied use of biomechanical measurements from human tissues for the development of medical skills trainers: a scoping review

OBJECTIVE

The objective of this review was to identify quantitative biomechanical measurements of human tissues, the methods for obtaining these measurements, and the primary motivations for conducting biomechanical research.

INTRODUCTION

Medical skills trainers are a safe and useful tool for clinicians to use when learning or practicing medical procedures. The haptic fidelity of these devices is often poor, which may be because the synthetic materials chosen for these devices do not have the same mechanical properties as human tissues. This review investigates a heterogeneous body of literature to identify which biomechanical properties are available for human tissues, the methods for obtaining these values, and the primary motivations behind conducting biomechanical tests.

INCLUSION CRITERIA

Studies containing quantitative measurements of the biomechanical properties of human tissues were included. Studies that primarily focused on dynamic and fluid mechanical properties were excluded. Additionally, studies only containing animal, in silico , or synthetic materials were excluded from this review.

METHODS

This scoping review followed the JBI methodology for scoping reviews and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sources of evidence were extracted from CINAHL (EBSCO), IEEE Xplore, MEDLINE (PubMed), Scopus, and engineering conference proceedings. The search was limited to the English language. Two independent reviewers screened titles and abstracts as well as full-text reviews. Any conflicts that arose during screening and full-text review were mediated by a third reviewer. Data extraction was conducted by 2 independent reviewers and discrepancies were mediated through discussion. The results are presented in tabular, figure, and narrative formats.

RESULTS

Data were extracted from a total of 186 full-text publications. All of the studies, except for 1, were experimental. Included studies came from 33 countries, with the majority coming from the United States. Ex vivo methods were the predominant approach for extracting human tissue samples, and the most commonly studied tissue type was musculoskeletal. In this study, nearly 200 unique biomechanical values were reported, and the most commonly reported value was Young's (elastic) modulus. The most common type of mechanical test performed was tensile testing, and the most common reason for testing human tissues was to characterize biomechanical properties. Although the number of published studies on biomechanical properties of human tissues has increased over the past 20 years, there are many gaps in the literature. Of the 186 included studies, only 7 used human tissues for the design or validation of medical skills training devices. Furthermore, in studies where biomechanical values for human tissues have been obtained, a lack of standardization in engineering assumptions, methodologies, and tissue preparation may implicate the usefulness of these values.

CONCLUSIONS

This review is the first of its kind to give a broad overview of the biomechanics of human tissues in the published literature. With respect to high-fidelity haptics, there is a large gap in the published literature. Even in instances where biomechanical values are available, comparing or using these values is difficult. This is likely due to the lack of standardization in engineering assumptions, testing methodology, and reporting of the results. It is recommended that journals and experts in engineering fields conduct further research to investigate the feasibility of implementing reporting standards.

REVIEW REGISTRATION

Open Science Framework https://osf.io/fgb34.

Upregulated desmin/integrin β1/MAPK axis promotes elastic cartilage regeneration with increased ECM mechanical strength

Elastic cartilage tissue engineering is promising for providing available scaffolds for plastic reconstructive surgery. The insufficient mechanical strength of regenerative tissue and scarce resources of reparative cells are two obstacles for the preparation of tissue-engineered elastic cartilage scaffolds. Auricular chondrocytes are important reparative cells for elastic cartilage tissue engineering, but resources are scarce. Identifying auricular chondrocytes with enhanced capability of elastic cartilage formation is conducive to reducing the damage to donor sites by decreasing the demand on native tissue isolation. Based on the biochemical and biomechanical differences in native auricular cartilage, we found that auricular chondrocytes with upregulated desmin expressed more integrin β1, forming a stronger interaction with the substrate. Meanwhile, activated MAPK pathway was found in auricular chondrocytes highly expressing desmin. When desmin was knocked down, the chondrogenesis and mechanical sensitivity of chondrocytes were both impaired, and the MAPK pathway was downregulated. Finally, auricular chondrocytes highly expressing desmin regenerated more elastic cartilage with increased ECM mechanical strength. Therefore, desmin/integrin β1/MAPK signaling can not only serve as a selection standard but also a manipulation target of auricular chondrocytes to promote elastic cartilage regeneration.

Mechanical properties of extensive calcified costal cartilage: An experimental study

Background

Autologous costal cartilage is widely used as nasal augmentation or nasal reconstruction material. However, no study has focused on the mechanical difference between no calcified costal cartilage and extensive calcified costal cartilage at present. Our study aims to study the loading behavior of calcified costal cartilage under tensile and compressive stress.

Method

Human costal cartilage specimen was obtained from five extensive calcified costal cartilage patients and classified into four groups (group A: no calcified costal cartilage; group B: calcified costal cartilage; group C: no calcified costal cartilage after transplantation in BALB/c nude mice for half a year; group D: calcified costal cartilage after transplantation in BALB/c nude mice for half a year). Young's modulus, stress relaxation slope, and relaxation amount were analyzed through tensile and compressive tests using a material testing machine.

Results

We included five female patients with extensive calcified costal cartilage. Group B exhibited significantly higher Young's modulus in both the tensile and compressive tests (p < 0.05 in tensile test, p < 0.01 in compressive test), higher relaxation slope (P < 0.01) and higher relaxation amount (p < 0.05 in compression test). After transplantation, the Young's modulus of calcified and non-calcified costal cartilage decreased, except that the calcified costal cartilage increased slightly in the tensile test. The final relaxation slope and relaxation amount had increased at different degrees, but the changes did not change significantly before and after transplantation (P > 0.05).

Conclusion

Our results showed that the stiffness of calcified cartilage would increase 30.06% under tension and 126.31% under compression. This study may provide new insights to researchers focusing on extensive calcified costal cartilage can be used for autologous graft material.

Contribution of perichondrium to the mechanical properties of auricular cartilage

The poor mechanical strength of tissue-engineered auricular cartilage which is possibly due to the lack of perichondrium limits its application in auricular reconstruction surgery. However, there is insufficient research and no reliable data to support this. This study aims to investigate the contribution of perichondrium to the mechanical strength of auricular cartilage under loading. Rabbit auricular cartilage was harvested and classified into two groups. The perichondrium was removed in Group A and was left intact in Group B. Young's modulus, stress relaxation slope, and relaxation amout were analyzed through tensile and compressive tests using a material testing machine. Group B exhibited significantly higher Young's modulus in both the tensile and compressive tests (p < 0.05), lower relaxation slope (p < 0.05 in tensile test, p = 0.65 in compressive test), and lower relaxation amout (p < 0.05 in tensile test, p < 0.01 in compressive test). Our results showed that the perichondrium has a definite contribution to the mechanical properties of ear cartilage. This study may provide new insights to researchers focusing on improving the mechanical strength of tissue-engineered auricular cartilage.

Hybrid Three-Dimensional-Printed Ear Tissue Scaffold With Autologous Cartilage Mitigates Soft Tissue Complications

OBJECTIVES/HYPOTHESIS

To analyze the use of highly translatable three-dimensional (3D)-printed auricular scaffolds with and without novel cartilage tissue inserts in a rodent model.

STUDY DESIGN

Preclinical rodent animal model.

METHODS

This prospective study assessed a single-stage 3D-printed auricular bioscaffold with or without porcine cartilage tissue inserts in an athymic rodent model. Digital Imaging and Communications in Medicine computed tomography images of a human auricle were segmented to create an external anatomic envelope filled with orthogonally interconnected spherical pores. Scaffolds with and without tissue inset sites were 3D printed by laser sintering bioresorbable polycaprolactone, then implanted subcutaneously in five rats for each group.

RESULTS

Ten athymic rats were studied to a goal of 24 weeks postoperatively. Precise anatomic similarity and scaffold integrity were maintained in both scaffold conditions throughout experimentation with grossly visible tissue ingrowth and angiogenesis upon explantation. Cartilage-seeded scaffolds had relatively lower rates of nonsurgical site complications compared to unseeded scaffolds with relatively increased surgical site ulceration, though neither met statistical significance. Histology revealed robust soft tissue infiltration and vascularization in both seeded and unseeded scaffolds, and demonstrated impressive maintenance of viable cartilage in cartilage-seeded scaffolds. Radiology confirmed soft tissue infiltration in all scaffolds, and biomechanical modeling suggested amelioration of stress in scaffolds implanted with cartilage.

CONCLUSIONS

A hybrid approach incorporating cartilage insets into 3D-printed bioscaffolds suggests enhanced clinical and histological outcomes. These data demonstrate the potential to integrate point-of-care tissue engineering techniques into 3D printing to generate alternatives to current reconstructive surgery techniques and avoid the demands of traditional tissue engineering.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:1008-1015, 2021.

Preclinical assessment of clinically streamlined, 3D-printed, biocompatible single- and two-stage tissue scaffolds for ear reconstruction

Auricular reconstruction is a technically demanding procedure requiring significant surgical expertise, as the current gold standard involves hand carving of the costal cartilage into an auricular framework and re-implantation of the tissue. 3D-printing presents a powerful tool that can reduce technical demands associated with the procedure. Our group compared clinical, radiological, histological, and biomechanical outcomes in single- and two-stage 3D-printed auricular tissue scaffolds in an athymic rodent model. Briefly, an external anatomic envelope of a human auricle was created using DICOM computed tomography (CT) images and modified in design to create a two-stage, lock-in-key base and elevating platform. Single- and two-stage scaffolds were 3D-printed by laser sintering poly-L-caprolactone (PCL) then implanted subcutaneously in five athymic rats each. Rats were monitored for ulcer formation, site infection, and scaffold distortion weekly, and scaffolds were explanted at 8 weeks with analysis using microCT and histologic staining. Nonlinear finite element analysis was performed to determine areas of high strain in relation to ulcer formation. Scaffolds demonstrated precise anatomic appearance and maintenance of integrity of both anterior and posterior auricular surfaces and scaffold projection, with no statistically significant differences in complications noted between the single- and two-staged implantation. While minor superficial ulcers occurred most commonly at the lateral and superior helix coincident with finite element predictions of high skin strains, evidence of robust tissue ingrowth and angiogenesis was visible grossly and histologically. This promising preclinical small animal model supports future initiatives for making clinically viable options for an ear tissue scaffold.

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.

Modulating nonlinear elastic behavior of biodegradable shape memory elastomer and small intestinal submucosa(SIS) composites for soft tissue repair

Structural repair of soft tissue for regenerative therapies can be advanced by developing biocompatible and bioresorbable materials with mechanical properties similar to the tissue targeted for therapy. Developing new materials modeling soft tissue mechanics can mitigate many limitations of material based therapies, specifically concerning the mechanical stress and deformation the material imposes on surrounding tissue structures. However, many elastomeric materials used in soft tissue repair lack the ability to be delivered through minimally invasive surgical (MIS) or transcatheter routes and require open surgical approaches for placement and application. We have developed a biocompatible and fully biodegradable shape memory elastomer, poly-(glycerol dodecanedioate) (PGD), which fulfills the requirements for hyperelasticity and exhibits shape memory behavior to serve as a novel substrate material for regenerative therapy in minimally invasive clinical procedures. Our previous work demonstrated control over the tangent modulus at 12.5% compressive strain between 1 and 3 MPa by increasing the crosslinking density in the polymer. In order to improve control over a broader range of mechanical properties, nonlinear behavior, and toughness, we 1) varied PGD physical crosslink density, 2) incorporated sheets of porcine small intestinal submucosa (SIS, Cook Biotech, Inc.) with varying thickness, and 3) mixed lyophilized SIS particulates into PGD at different weight percentages. Tensile testing (ASTM D412a) revealed PGD containing SIS sheets of were stiffer than controls (p < 0.01). Incorporating lyophilized SIS particulates into PGD increased the strain to failure (p < 0.001) compared to PGD controls. Test specimens with 1 ply sheets had greater tear strength (ASTM D624c) compared to PGD tear specimens prepared control specimens (p < 0.001). However, incorporating SIS particulates decreased tear strength of PGD-SIS 0.5 wt% particulate composites (p < 0.01) compared to PGD controls. Incorporating 2 ply and 4 ply sheets and 0.5 wt% particulates into PGD decreased the fixity and recovery of composite materials compared to controls (p < 0.01). Nonlinear modeling of stress strain curves under uniaxial tension demonstrated tunability of PGD-SIS composite materials to model various nonlinear soft tissues. These findings support the use of shape memory PGD-SIS composite materials towards the design of implantable devices for a variety of soft tissue regeneration applications by minimally invasive surgery.

Structure and mechanical properties of high-weight-bearing and low-weight-bearing areas of hip cartilage at the micro- and nano-levels

BACKGROUND

Articular cartilage has a high-weight-bearing area and a low-weight-bearing area, the macroscopic elastic moduli of the two regions are different. Chondrocytes are affected by the applied force at the microscopic level. Currently, the modulus of the two areas at the micro and nano levels is unknown, and studies on the relationship between macro-, micro- and nano-scale elastic moduli are limited. Such information may be important for further understanding of cartilage mechanics. Moreover, the surface morphology, proteoglycan content, and micro and nano structure of the two areas, which influences the mechanical properties of cartilage should be discussed.

METHODS

Safranin-O/Fast Green staining was used to evaluate the surface morphology and semi-quantify proteoglycan content of porcine femoral head cartilage between the two weight-bearing areas. The unconfined compression test was used to determine the macro elastic modulus. Atomic force microscope was used to measure the micro and nano compressive elastic modulus as well as the nano structure. Scanning electron microscope was employed to evaluate the micro structure.

RESULTS

No significant differences in the fibrillation index were observed between two areas (P = 0.5512). The Safranin-O index of the high-weight-bearing area was significantly higher than that of the low-weight-bearing area (P = 0.0387). The compressive elastic modulus of the high-weight-bearing area at the macro and micro level was significantly higher than that of the low-weight-bearing area (P = 0.0411 for macro-scale, and P = 0.0001 for micro-scale), while no statistically significant differences were observed in the elastic modulus of collagen fibrils at the nano level (P = 0.8544). The density of the collagen fibers was significantly lower in the high-weight-bearing area (P = 0.0177). No significant differences were observed in the structure and diameter of the collagen fibers between the two areas (P = 0.7361).

CONCLUSIONS

A higher proteoglycan content correlated with a higher compressive elastic modulus of the high-weight-bearing area at the micro level than that of the low-weight-bearing area, which was consistent with the trend observed from the macroscopic compressive elastic modulus. The weight-bearing level was not associated with the elastic modulus of individual collagen fibers and the diameter at the nano level. The micro structure of cartilage may influence the macro- and micro-scale elastic modulus.

Cartilage and collagen mechanics under large-strain shear within in vivo and at supraphysiogical temperatures

Human joints, particularly those of extremities, experience a significant range of temperatures in vivo. Joint temperature influences the mechanics of both joint and cartilage, and the mechanics of cartilage can affect the temperature of both joint and cartilage. Thermal treatments and tissue repairs, such as thermal chondroplasty, and ex vivo tissue engineering may also expose cartilage to supraphysiological temperatures. Furthermore, although cartilage undergoes principally compressive loads in vivo, shear strain plays a significant role at larger compressive strains. Thus, we aimed to determine whether and how the bulk mechanical responses of cartilage undergoing large-strain shear change (1) within the range of temperatures relevant in vivo, and (2) both during and after supraphysiological thermal treatments. We completed large-strain shear tests (10 and 15%) at four thermal conditions: 24^∘C and 40^∘C to span the in vivo range, and 70^∘C and 24^∘C repeated after 70^∘C to explore mechanics during and after potential treatments. We calculated the bulk mechanical responses (strain-energy dissipation densities, peak-to-peak shear stresses, and peak-effective shear moduli) as of function of temperature and used statistical methods to probe significant differences. To probe the mechanisms underlying differences we assessed specimens, principally the type II collagen, with imaging (second harmonic generation and transmission electron microscopies, and histology) and assessed the temperature-dependent mechanics of type II collagen molecules within cartilage using steered molecular dynamics simulations. Our results suggest that the bulk mechanical responses of cartilage depend significantly on temperature both within the in vivo range and at supraphysiological temperatures, showing significant reductions in all mechanical measures with increasing temperature. Using imaging and simulations we determined that one underlying mechanism explaining our results may be changes in the molecular deformation profiles of collagen molecules versus temperature, likely compounded at larger length scales. These new insights into the mechanics of cartilage and collagen may suggest new treatment targets for damaged or osteoarthritic cartilage.

Evaluation of human nasal cartilage nonlinear and rate dependent mechanical properties

Nasal reconstruction frequently requires donor cartilage and tissue, and ideally, donor tissue will closely emulate native nasal cartilage mechanics. Tissue engineering scaffolds, especially 3D printed scaffolds, have been proposed for nasal reconstruction, and the success of these constructs may depend on how well scaffolds reflect native nasal cartilage mechanical properties. Therefore, consistent and comprehensive characterization of native nasal cartilage mechanical properties is a foundation for nasal cartilage tissue engineering and reconstruction in general by providing design targets for reconstructive materials. Our group has previously shown the feasibility of producing scaffolds with porous architecture permitting chondrocyte growth and cartilage production. In this study, we determined the nonlinear and stress relaxation behavior of human nasal cartilage under unconfined compression. We then fit this experimental data to nonlinear elastic, nonlinear viscoelastic and nonlinear biphasic constitutive models. The resulting coefficients will provide design targets for nasal reconstruction and scaffold design as well as outcome measures for assessment of tissue engineered nasal cartilage.

[Mechanical study of polyurethane elastomer and Medpor as the material of artificial auricular scaffold]

Objective

By comparing the mechanics of human auricular cartilage, polyurethane elastic material, and high density polyethylene material (Medpor), to produce theoretical proof on choosing optimal artificial auricular scaffold materials.

Methods

The experimental materials were divided into 3 groups with 6 samples in each: the auricular cartilage group (group A), the polyurethane elastic material group (group B), and the Medpor group (group C). With an Instron5967 mechanical testing machine, compression and tensile testing were performed to respectively measure values of compression parameters (including yield stress, yield load, elastic modulus, yield compressibility, compressibility within 2 MPa, and compression stress within 10% strain) and values of tensile parameters (including yield stress, yield load, elastic modulus, yield elongation, elongation within 2 MPa, tensile stress within 1% strain) for comparison.

Results

Compression testing: no obvious yield points were observed in the whole process in samples of group B, while obvious yield points were observed in samples of groups A and C. There was no significant difference between groups A and C with respect to yield stress and yield load ( P>0.05); while the yield compressibility in group C was significantly lower than that in group A ( P<0.05) and the elastic modulus in group C was significantly higher than that in group A ( P<0.05). There was a significant difference with respect to compressibility within 2 MPa of materials among the 3 groups ( P<0.05), the high, medium, and low values go to groups B, A, and C respectively. The compression stress within 10% strain in group C was significantly higher than that in groups A and B ( P<0.05), and there was no significant difference between that in groups A and B ( P>0.05). Tensile testing: the materials in group B had extremely high tensile strength. The yield stress in groups A and B was significantly higher than that in group C ( P<0.05), and the elastic modulus and tensile stress within 1% strain were significantly lower than those in group C ( P<0.05); but no significant difference was found between those in groups A and B ( P>0.05). There was no significant difference with respect to yield load among the 3 groups ( P>0.05); but there was significant difference with respect to yield elongation among the 3 groups ( P<0.05), and the high, medium, and low values go to groups B, A, and C respectively. The elongation within 2 MPa in group B was significantly higher than that in groups A and C ( P<0.05), and there was no significant difference between that in groups A and C ( P>0.05).

Conclusion

Compared with the Medpor, the polyurethane elastic material is a more ideal artificial auricular scaffold material.

Auricle shaping using 3D printing and autologous diced cartilage

OBJECTIVE

To reconstruct the auricle using a porous, hollow, three-dimensional (3D)-printed mold and autologous diced cartilage mixed with platelet-rich plasma (PRP).

METHODS

Materialise Magics v20.03 was used to design a 3D, porous, hollow auricle mold. Ten molds were printed by selective laser sintering with polyamide. Cartilage grafts were harvested from one ear of a New Zealand rabbit, and PRP was prepared using 10 mL of auricular blood from the same animal. Ear cartilage was diced into 0.5- to 2.0-mm pieces, weighed, mixed with PRP, and then placed inside the hollow mold. Composite grafts were then implanted into the backs of respective rabbits (n = 10) for 4 months. The shape and composition of the diced cartilage were assessed histologically, and biomechanical testing was used to determine stiffness.

RESULTS

The 3D-printed auricle molds were 0.6-mm thick and showed connectivity between the internal and external surfaces, with round pores of 0.1 to 0.3 cm. After 4 months, the diced cartilage pieces had fused into an auricular shape with high fidelity to the anthropotomy. The weight of the diced cartilage was 5.157 ± 0.230 g (P > 0.05, compared with preoperative). Histological staining showed high chondrocyte viability and the production of collagen II, glycosaminoglycans, and other cartilaginous matrix components. In unrestricted compression tests, auricle stiffness was 0.158 ± 0.187 N/mm, similar to that in humans.

CONCLUSION

Auricle grafts were constructed successfully through packing a 3D-printed, porous, hollow auricle mold with diced cartilage mixed with PRP. The auricle cartilage contained viable chondrocytes, appropriate extracellular matrix components, and good mechanical properties.

LEVELS OF EVIDENCE

NA. Laryngoscope, 129:2467-2474, 2019.

Tissue Engineering and 3-Dimensional Modeling for Facial Reconstruction

Three-dimensional (3D) printing has transformed craniofacial reconstruction over the last 2 decades. For cutaneous oncologic surgeons, several 3D printed technologies are available to assist with craniofacial bony reconstruction and preliminary soft tissue reconstructive efforts. With improved accessibility and simplified design software, 3D printing has opened the door for new techniques in anaplastology. Tissue engineering has more recently emerged as a promising concept for complex auricular and nasal reconstruction. Combined with 3D printing, several groups have demonstrated promising preclinical results with cartilage growth. This article highlights the applications and current state of 3D printing and tissue engineering in craniofacial reconstruction.

Stiff micelle-crosslinked hyaluronate hydrogels with low swelling for potential cartilage repair

Pluronic F127 diacrylate (F127DA) micelle-crosslinked methacrylated hyaluronic acid (MeHA) hydrogel with low-swelling and strong compressive properties was successfully synthesized for the regeneration of cartilages in vivo.

Auricular reconstruction from rib to 3D printing

The human ear imparts critical form and function and remains one of the most challenging facial features to reconstruct. Over the past century, surgeons have developed numerous techniques and materials for total auricular reconstruction. Refined costal cartilage techniques have remained the gold standard for the past half-century. Recent advancements with novel materials, tissue engineering and 3D printing provide immense potential; however, prohibitive costs and regulatory steps remain as barriers to clinical translation.

Influence of backside loading on the floating mass transducer: An in vitro experimental study

HYPOTHESIS

The vibration of the floating mass transducer (FMT) of a single active middle-ear implant (AMEI) is distinctly influenced by the properties of the material coupled to its back side.

BACKGROUND

In round window vibroplasty, the FMT needs to be padded against the surrounding bone opposite from the round window membrane. This represents one factor influencing its performance as a round window driver. Therefore, we examined the effects of different materials linked to the back side of an FMT on its vibration range.

METHODS

The back side of an FMT was glued to a silicone cylinder 1.0 mm in diameter and 1.0 mm - 1.5 mm in length and of 40A, 50A or 70A Shore hardness; to cartilage of equivalent size; or to a round window soft coupler (RWSC), all firmly fixed on a steel plate. The vibrations were determined by a laser Doppler vibrometer (LDV) measuring the velocity of the centre point on the front side of the FMT.

RESULTS

The materials on the back side of the FMT significantly influenced the vibration range of the FMT. The RWSC and silicone of 40A Shore hardness allowed for the highest detected velocities, while cartilage led to a distinct reduction similarly to 70A silicone.

CONCLUSION

The coupling on the back side of an FMT distinctly affects its vibration range. In this regard, the RWSC and silicone of 40A Shore hardness yield the least impairment of vibration. Thus, the RWSC may be a feasible option in round window vibroplasty when additionally connected to the FMT opposite from the round window membrane.

Shear deformations of human articular cartilage: Certain mechanical anisotropies apparent at large but not small shear strains

Articular cartilage has pronounced through-the-thickness heterogeneity in both ultrastructure and mechanical function. The tissue undergoes a combination of large deformations in vivo, where shear is critical in both failure and chondrocyte death. Yet the microstructure mechanical response of cartilage to multi-axial large shear deformations is unknown. We harvested a total of 42 cartilage specimens from seven matched locations across the lateral femoral condyles and patellofemoral grooves of six human male donors (30.2±8.8yrs old, M±SD). With each specimen we applied a range of quasi-static, multi-axial large (simple) shear displacements both parallel and perpendicular to the local split-line direction (SLD). Shear stresses in cartilage specimens from the patellofemoral grooves were higher, and more energy was dissipated, at all applied strains under loading parallel to the local SLD versus perpendicular, while specimens from the lateral condyles were mechanically anisotropic only under larger strains of 20% and 25%. Cartilage also showed significant intra-donor variability at larger shear strains but no significant inter-donor variability. Overall, shear strain-energy dissipation was almost constant at 5% applied shear strain and increased nonlinearly with increasing shear magnitude. Our results suggest that full understanding of cartilage mechanics requires large-strain analyses to account for nonlinear, anisotropic and location-dependent effects not fully realized at small strains.

Biomechanical Characterisation of the Human Auricular Cartilages; Implications for Tissue Engineering

Currently, autologous cartilage provides the gold standard for auricular reconstruction. However, synthetic biomaterials offer a number of advantages for ear reconstruction including decreased donor site morbidity and earlier surgery. Critical to implant success is the material’s mechanical properties as this affects biocompatibility and extrusion. The aim of this study was to determine the biomechanical properties of human auricular cartilage. Auricular cartilage from fifteen cadavers was indented with displacement of 1 mm/s and load of 300 g to obtain a Young’s modulus in compression. Histological analysis of the auricle was conducted according to glycoprotein, collagen, and elastin content. The compression modulus was calculated for each part of the auricle with the tragus at 1.67 ± 0.61 MPa, antitragus 1.79 ± 0.56 MPa, concha 2.08 ± 0.70 MPa, antihelix 1.71 ± 0.63 MPa, and helix 1.41 ± 0.67 MPa. The concha showed to have a significantly greater Young’s Elastic Modulus than the helix in compression (p < 0.05). The histological analysis demonstrated that the auricle has a homogenous structure in terms of chondrocyte morphology, extracellular matrix and elastin content. This study provides new information on the compressive mechanical properties and histological analysis of the human auricular cartilage, allowing surgeons to have a better understanding of suitable replacements. This study has provided a reference, by which cartilage replacements should be developed for auricular reconstruction.

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

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

Mechanical and biochemical mapping of human auricular cartilage for reliable assessment of tissue-engineered constructs

It is key for successful auricular (AUR) cartilage tissue-engineering (TE) to ensure that the engineered cartilage mimics the mechanics of the native tissue. This study provides a spatial map of the mechanical and biochemical properties of human auricular cartilage, thus establishing a benchmark for the evaluation of functional competency in AUR cartilage TE. Stress-relaxation indentation (instantaneous modulus, Ein; maximum stress, σmax; equilibrium modulus, Eeq; relaxation half-life time, t1/2; thickness, h) and biochemical parameters (content of DNA; sulfated-glycosaminoglycan, sGAG; hydroxyproline, HYP; elastin, ELN) of fresh human AUR cartilage were evaluated. Samples were categorized into age groups and according to their harvesting region in the human auricle (for AUR cartilage only). AUR cartilage displayed significantly lower Ein, σmax, Eeq, sGAG content; and significantly higher t1/2, and DNA content than NAS cartilage. Large amounts of ELN were measured in AUR cartilage (>15% ELN content per sample wet mass). No effect of gender was observed for either auricular or nasoseptal samples. For auricular samples, significant differences between age groups for h, sGAG and HYP, and significant regional variations for Ein, σmax, Eeq, t1/2, h, DNA and sGAG were measured. However, only low correlations between mechanical and biochemical parameters were seen (R<0.44). In conclusion, this study established the first comprehensive mechanical and biochemical map of human auricular cartilage. Regional variations in mechanical and biochemical properties were demonstrated in the auricle. This finding highlights the importance of focusing future research on efforts to produce cartilage grafts with spatially tunable mechanics.