Compressive biomechanical properties of human nasal septal cartilage

3D Bioprinting of Hyaline Cartilage Using Nasal Chondrocytes

Due to the limited self-repair capacity of the hyaline cartilage, the repair of cartilage remains an unsolved clinical problem. Tissue engineering strategy with 3D bioprinting technique has emerged a new insight by providing patient's personalized cartilage grafts using autologous cells for hyaline cartilage repair and regeneration. In this review, we first summarized the intrinsic property of hyaline cartilage in both maxillofacial and orthopedic regions to establish the requirement for 3D bioprinting cartilage tissue. We then reviewed the literature and provided opinion pieces on the selection of bioprinters, bioink materials, and cell sources. This review aims to identify the current challenges for hyaline cartilage bioprinting and the directions for future clinical development in bioprinted hyaline cartilage.

Human nasal cartilage: Functional properties and structure-function relationships for the development of tissue engineering design criteria

Nose reconstruction often requires scarce cartilage grafts. Nasal cartilage properties must be determined to serve as design criteria for engineering grafts. Thus, mechanical and biochemical properties were obtained in multiple locations of human nasal septum, upper lateral cartilage (ULC), and lower lateral cartilage (LLC). Within each region, no statistical differences among locations were detected, but anisotropy at some septum locations was noted. In the LLC, the tensile modulus and ultimate tensile strength (UTS) in the inferior-superior direction were statistically greater than in the anterior-posterior direction. Cartilage from all regions exhibited hyperelasticity in tension, but regions varied in degree of hyalinicity (i.e., Col II:Col I ratio). The septum contained the most collagen II and least collagen I and III, making it more hyaline than the ULC and LLC. The septum had a greater aggregate modulus, UTS, and lower total collagen/wet weight (Col/WW) than the ULC and LLC. The ULC had greater tensile modulus, DNA/WW, and lower glycosaminoglycan/WW than the septum and LLC. The ULC had a greater pyridinoline/Col than the septum. Histological staining suggested the presence of chondrons in all regions. In the ULC and LLC, tensile modulus correlated with total collagen content, while aggregate modulus correlated with pyridinoline content and weakly with pentosidine content. However, future studies should be performed to validate these proposed structure-function relationships. This study of human nasal cartilage provides 1) crucial design criteria for nasal cartilage tissue engineering efforts, 2) quantification of major and minor collagen subtypes and crosslinks, and 3) structure-function relationships. Surprisingly, the large mechanical properties found, particularly in the septum, suggests that nasal cartilage may experience higher-than-expected mechanical loads. STATEMENT OF SIGNIFICANCE: While tissue engineering holds promise to generate much-needed cartilage grafts for nasal reconstruction, little is known about nasal cartilage from an engineering perspective. In this study, the mechanical and biochemical properties of the septum, upper lateral cartilage (ULC), and lower lateral cartilage (LLC) were evaluated using cartilage-specific methods. For the first time in this tissue, all major and minor collagens and collagen crosslinks were measured, demonstrating that the septum was more hyaline than the ULC and LLC. Additionally, new structure-function relationships in the ULC and LLC were identified. This study greatly expands upon the quantitative understanding of human nasal cartilage and provides crucial engineering design criteria for much-needed nasal cartilage tissue engineering efforts.

Assessment of a novel patient-specific 3D printed multi-material simulator for endoscopic sinus surgery

Background: Three-dimensional (3D) printing is an emerging tool in the creation of anatomical models for surgical training. Its use in endoscopic sinus surgery (ESS) has been limited because of the difficulty in replicating the anatomical details. Aim: To describe the development of a patient-specific 3D printed multi-material simulator for use in ESS, and to validate it as a training tool among a group of residents and experts in ear-nose-throat (ENT) surgery. Methods: Advanced material jetting 3D printing technology was used to produce both soft tissues and bony structures of the simulator to increase anatomical realism and tactile feedback of the model. A total of 3 ENT residents and 9 ENT specialists were recruited to perform both non-destructive tasks and ESS steps on the model. The anatomical fidelity and the usefulness of the simulator in ESS training were evaluated through specific questionnaires. Results: The tasks were accomplished by 100% of participants and the survey showed overall high scores both for anatomy fidelity and usefulness in training. Dacryocystorhinostomy, medial antrostomy, and turbinectomy were rated as accurately replicable on the simulator by 75% of participants. Positive scores were obtained also for ethmoidectomy and DRAF procedures, while the replication of sphenoidotomy received neutral ratings by half of the participants. Conclusion: This study demonstrates that a 3D printed multi-material model of the sino-nasal anatomy can be generated with a high level of anatomical accuracy and haptic response. This technology has the potential to be useful in surgical training as an alternative or complementary tool to cadaveric dissection.

Properties of the Nasal Cartilage, from Development to Adulthood: A Scoping Review

OBJECTIVE

Nasal septum cartilage is a hyaline cartilage that provides structural support to the nasal cavity and midface. Currently, information on its cellular and mechanical properties is widely dispersed and has often been inferred from studies conducted on other cartilage types such as the knee. A detailed understanding of nasal cartilage properties is important for several biological, clinical, and engineering disciplines. The objectives of this scoping review are to (1) consolidate actual existing knowledge on nasal cartilage properties and (2) identify gaps of knowledge and research questions requiring future investigations.

DESIGN

This scoping review incorporated articles identified using PROSPERO, Cochrane Library (CDSR and Central), WOS BIOSIS, WOS Core Collection, and ProQuest Dissertations and Theses Global databases. Following the screening process, 86 articles were considered. Articles were categorized into three groups: growth, extracellular matrix, and mechanical properties.

RESULTS

Most articles investigated growth properties followed by extracellular matrix and mechanical properties. NSC cartilage is not uniform. Nasal cartilage growth varies with age and location. Similarly, extracellular matrix composition and mechanical properties are location-specific within the NSC. Moreover, most articles included in the review investigate these properties in isolation and only very few articles demonstrate the interrelationship between multiple cartilage properties.

CONCLUSIONS

This scoping review presents a first comprehensive description of research on NSC properties with a focus on NSC growth, extracellular matrix and mechanical properties. It additionally identifies the needs (1) to understand how these various cartilage properties intersect and (2) for more granular, standardized assessment protocols to describe NSC.

Mechanical properties of whole-body soft human tissues: a review

The mechanical properties of soft tissues play a key role in studying human injuries and their mitigation strategies. While such properties are indispensable for computational modelling of biological systems, they serve as important references in loading and failure experiments, and also for the development of tissue simulants. To date, experimental studies have measured the mechanical properties of peripheral tissues (e.g. skin)in-vivoand limited internal tissuesex-vivoin cadavers (e.g. brain and the heart). The lack of knowledge on a majority of human tissues inhibit their study for applications ranging from surgical planning, ballistic testing, implantable medical device development, and the assessment of traumatic injuries. The purpose of this work is to overcome such challenges through an extensive review of the literature reporting the mechanical properties of whole-body soft tissues from head to toe. Specifically, the available linear mechanical properties of all human tissues were compiled. Non-linear biomechanical models were also introduced, and the soft human tissues characterized using such models were summarized. The literature gaps identified from this work will help future biomechanical studies on soft human tissue characterization and the development of accurate medical models for the study and mitigation of injuries.

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

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

Will Tissue-Engineering Strategies Bring New Hope for the Reconstruction of Nasal Septal Cartilage?

The nasal septal cartilage plays an important role in the growth of midface and as a vertical strut preventing the collapse of the nasal bones. The repair of nasal cartilage defects remains a major challenge in reconstructive surgery. The tissue engineering strategy in the development of tissue has opened a new perspective to generate functional tissue for transplantation. Given the poor regenerative properties of cartilage and a limited amount of autologous cartilage availability, intense interest has evoked for tissue engineering approaches for cartilage development to provide better outcomes for patients who require nasal septal reconstruction. Despite numerous attempts to substitute the shapely hyaline cartilage in the nasal cartilages, many significant challenges remained unanswered. The aim of this research was to carry out a critical review of the literature on research work carried out on the development of septal cartilage using a tissue engineering approach, concerning different cell sources, scaffolds and growth factors, as well as its clinical pathway and trials have already been carried out.

Multicenter Pilot Study to Assess a Biphasic Calcium Phosphate Implant for Functional and Aesthetic Septorhinoplasty

Importance: A validated biomaterial would have several medical advantages in septorhinoplasties requiring a large-volume graft such as avoiding donor site morbidity, making ambulatory surgery possible, and reducing surgical costs. Objective: To assess the safety and efficacy of a ceramic to treat saddle and crooked noses. The main endpoint was the biocompatibility of the implant. The secondary endpoint was its functional and aesthetic efficacy. Design, Setting, and Participants: The nasal septum (NASEPT) study is a pilot multicenter noncomparative prospective phase IIa clinical trial. The biomaterial tested was a biphasic calcium phosphate implant composed of 75% hydroxyapatite and 25% beta tri calcium phosphate. This versatile material can be used to replace septal skeleton when it is absent or nonusable. We included 25 patients with a multifractured osseous and cartilaginous framework after several traumas or surgeries. The implant placement technique was identical to an extracorporeal septoplasty through the external approach. Main Outcomes and Measures: The primary endpoint was the occurrence of expected adverse and severe adverse events. The secondary endpoints were clinical functional and aesthetic results and histological microscopic modifications. Results: Any extrusion, infection, pain, and epistaxis were observed. All implants were placed in a sagittal, straight, and solid position without extralobular depression. Comparisons between pre- and postoperative symptoms showed that nasal comfort (p < 10^-4) and quality of life (p < 10^-4) were dramatically improved in all patients. The nasolabial angle (p = 0.047) and the columellar projection (p = 0.024) were improved after surgery. Histological data showed little submucosal inflammation at 6 months with well-differentiated epithelium. The mean follow-up was 23 months: three patients underwent revision surgery for functional or aesthetic details and four implants were removed (16%) owing to a foreign body reaction between 17 and 74 months. Conclusion and Relevance: The NASEPT implant meets functional and aesthetic requirements in complex septorhinoplasties but its long-term biocompatibility needs to be improved. It could potentially avoid donor site morbidity.

Defining a New Variable That May Impact Long-term Postoperative Nasal Tip Support: The Biomechanical Properties of the Columellar Strut Graft

BACKGROUND

Although columellar strut grafts (CSGs) are considered among the fundamental steps for providing nasal tip support, a downward rotation of the nasal tip in patients with strut grafts can still be encountered. Patient-related factors such as nasal skin thickness can allow the plastic surgeon to anticipate certain drawbacks that can be encountered in the healing phase, but patient-based differences of nasal cartilage and the resulting impact have yet to be investigated. The purpose of this study was to evaluate the effect of the biomechanical properties of CSGs on late postoperative nasal tip position and support.

METHODS

The study was undertaken with the participation of 20 patients undergoing closed-technique primary rhinoplasty with CSGs. Each cartilage specimen was biomechanically analyzed to calculate the modulus of elasticity. Preoperative and postoperative images were obtained to determine nasal tip position and rotation with quantitative measurements. Postoperative 3- and 12-month measurements were evaluated according to their relationship with the elasticity modulus of the utilized cartilages.

RESULTS

The evaluation demonstrated that the elasticity modulus can impact the long-term support of the nasolabial angle in which an increase in the coefficient of elasticity can result in a decrease in long-term nasal tip support.

CONCLUSION

The results of the study reveal a new objective variable that can impact nasal tip dynamics and patient-related differences following rhinoplasty. This study not only brings forth a different perspective in the evaluation of nasal tip dynamics but can also provide data for determining ideal values for cartilage prefabrication.

A 3D-Printed Hybrid Nasal Cartilage with Functional Electronic Olfaction

Advances in biomanufacturing techniques have opened the doors to recapitulate human sensory organs such as the nose and ear in vitro with adequate levels of functionality. Such advancements have enabled simultaneous targeting of two challenges in engineered sensory organs, especially the nose: i) mechanically robust reconstruction of the nasal cartilage with high precision and ii) replication of the nose functionality: odor perception. Hybrid nasal organs can be equipped with remarkable capabilities such as augmented olfactory perception. Herein, a proof-of-concept for an odor-perceptive nose-like hybrid, which is composed of a mechanically robust cartilage-like construct and a biocompatible biosensing platform, is proposed. Specifically, 3D cartilage-like tissue constructs are created by multi-material 3D bioprinting using mechanically tunable chondrocyte-laden bioinks. In addition, by optimizing the composition of stiff and soft bioinks in macro-scale printed constructs, the competence of this system in providing improved viability and recapitulation of chondrocyte cell behavior in mechanically robust 3D constructs is demonstrated. Furthermore, the engineered cartilage-like tissue construct is integrated with an electrochemical biosensing system to bring functional olfactory sensations toward multiple specific airway disease biomarkers, explosives, and toxins under biocompatible conditions. Proposed hybrid constructs can lay the groundwork for functional bionic interfaces and humanoid cyborgs.

Thermo-Mechanical Behaviour of Human Nasal Cartilage

The aim of this study was to undergo a comprehensive analysis of the thermo-mechanical properties of nasal cartilages for the future design of a composite polymeric material to be used in human nose reconstruction surgery. A thermal and dynamic mechanical analysis (DMA) in tension and compression modes within the ranges 1 to 20 Hz and 30 °C to 250 °C was performed on human nasal cartilage. Differential scanning calorimetry (DSC), as well as characterization of the nasal septum (NS), upper lateral cartilages (ULC), and lower lateral cartilages (LLC) reveals the different nature of the binding water inside the studied specimens. Three peaks at 60–80 °C, 100–130 °C, and 200 °C were attributed to melting of the crystalline region of collagen matrix, water evaporation, and the strongly bound non-interstitial water in the cartilage and composite specimens, respectively. Thermogravimetric analysis (TGA) showed that the degradation of cartilage, composite, and subcutaneous tissue of the NS, ULC, and LLC take place in three thermal events (~37 °C, ~189 °C, and ~290 °C) showing that cartilage releases more water and more rapidly than the subcutaneous tissue. The water content of nasal cartilage was estimated to be 42 wt %. The results of the DMA analyses demonstrated that tensile mode is ruled by flow-independent behaviour produced by the time-dependent deformability of the solid cartilage matrix that is strongly frequency-dependent, showing an unstable crystalline region between 80–180 °C, an amorphous region at around 120 °C, and a clear glass transition point at 200 °C (780 kJ/mol). Instead, the unconfined compressive mode is clearly ruled by a flow-dependent process caused by the frictional force of the interstitial fluid that flows within the cartilage matrix resulting in higher stiffness (from 12 MPa at 1 Hz to 16 MPa at 20 Hz in storage modulus). The outcomes of this study will support the development of an artificial material to mimic the thermo-mechanical behaviour of the natural cartilage of the human nose.

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.

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.

Morphological and biomechanical characterization of immature and mature nasoseptal cartilage

Nasoseptal cartilage has been assumed to be isotropic, unlike the well-defined zonal organization of articular cartilage attributed to postnatal biomechanical loading. We know from clinical experience that malrotation of surgical nasoseptal cartilage grafts can lead to increased graft absorption. Other studies have also suggested directionally dependent compressive stiffness suggesting anisotropy, but morphological investigations are lacking. This study characterizes immature and mature native bovine nasoseptal cartilage using a combination of immunohistochemistry, biomechanical testing and structural imaging. Our findings indicate that there is extensive postnatal synthesis and reorganization of the extracellular matrix in bovine nasoseptal cartilage, independent of joint loading forces responsible for articular cartilage anisotropy. Immature nasoseptal cartilage is more cellular and homogenous compared to the zonal organization of cells and extracellular matrix of mature cartilage. Mature samples also exhibited greater glycosaminoglycan content and type II collagen fibre alignment compared to immature cartilage and this correlates with greater compressive stiffness. Engineered neocartilage often consists of immature, isotropic, homogenous tissue that is unable to meet the functional and mechanical demands when implanted into the native environment. This study demonstrates the importance of anisotropy on biomechanical tissue strength to guide future cartilage tissue engineering strategies for surgical reconstruction.

Differences between human septal and alar cartilage with respect to biomechanical features and biochemical composition

Cartilage grafts have become popular in facial plastic surgery to reconstruct defects or to improve aesthetic outcomes in various applications. But there is a considerable rate of graft failure like resorption or deformation. To improve graft survival and function, accurate understanding of the properties of the recipient site is indispensable. Therefore 10 noses of human cadavers were meticulously dissected and specimens of alar and septal cartilage subjected to confined compression and tensile tests. Furthermore, cell number, glycosaminoglycan and hydroxyproline content were measured. RESULTS: showed a significant difference (p < 0.05) of alar and septal cartilage regarding Equilibrium Modulus, cell number and glycosaminoglycan but not hydroxyproline content. Tensile tests showed a significant difference (p < 0.001) between alar and septal cartilage (vertical vector of force) for E-modulus, maximal force and maximal strain but not for horizontal vector of force. There was a significant difference (p < 0.05) within septal cartilage samples depending on vector of force (vertical vs. horizontal). Finally multifactorial linear regression allowed an estimation of Equilibrium Modulus depending on compression, glycosaminoglycan content and cell number with statistical significance (p < 0.05). In conclusion, nasal cartilage differs in function and composition depending on anatomical location and the prevalent forces. Therefore further research will be necessary to evaluate if graft failure depends on a mismatch of functional properties and if grafts can be adapted to the recipient site.

Toward tissue-engineering of nasal cartilages

Nasal cartilage pathologies are common; for example, up to 80% of people are afflicted by deviated nasal septum conditions. Because cartilage provides the supportive framework of the nose, afflicted patients suffer low quality of life. To correct pathologies, graft cartilage is often required. Grafts are currently sourced from the patient's septum, ear, or rib. However, their use yields donor site morbidity and is limited by tissue quantity and quality. Additionally, rhinoplasty revision rates exceed 15%, exacerbating the shortage of graft cartilage. Alternative grafts, such as irradiated allogeneic rib cartilage, are associated with complications. Tissue-engineered neocartilage holds promise to address the limitations of current grafts. The engineering design process may be used to create suitable graft tissues. This process begins by identifying the surgeon's needs. Second, nasal cartilages' properties must be understood to define engineering design criteria. Limited investigations have examined nasal cartilage properties; numerous additional studies need to be performed to examine topographical variations, for example. Third, tissue-engineering processes must be applied to achieve the engineering design criteria. Within the recent past, strategies have frequently utilized human septal chondrocytes. As autologous and allogeneic rib graft cartilage is used, its suitability as a cell source should also be examined. Fourth, quantitative verification of engineered neocartilage is critical to check for successful achievement of the engineering design criteria. Finally, following the FDA paradigm, engineered neocartilage must be orthotopically validated in animals. Together, these steps delineate a path to engineer functional nasal neocartilages that may, ultimately, be used to treat human patients. STATEMENT OF SIGNIFICANCE: Nasal cartilage pathologies are common and lead to greatly diminished quality of life. The ability to correct pathologies is limited by cartilage graft quality and quantity, as well as donor site morbidity and surgical complications, such as infection and resorption. Despite the significance of nasal cartilage pathologies and high rhinoplasty revision rates (15%), little characterization and tissue-engineering work has been performed compared to other cartilages, such as articular cartilage. Furthermore, most work is published in clinical journals, with little in biomedical engineering. Therefore, this review discusses what nasal cartilage properties are known, summarizes the current state of nasal cartilage tissue-engineering, and makes recommendations via the engineering design process toward engineering functional nasal neocartilage to address current limitations.

The impact of surgical manipulation on lower lateral cartilage stiffness

BACKGROUND

Cephalic trimming of the alar (or lower lateral) cartilage may cause weakening leading to external nasal valve collapse. Numerous methods have been proposed to combat this weakening in order to maintain lateral crural stiffness. The purpose of this study was to quantify the effect of mucosal stripping, cephalic trimming, cephalic turn-in flap, and lateral crural strut grafting on lateral crural stiffness.

METHODS

In situ cyclic compressive loading was performed on eight lateral crura in 4 fresh frozen cadaveric specimens. Testing was performed on the unaltered degloved cartilage (intact) and following each of the following interventions: mucosal stripping, cephalic turn-in flap, cephalic trimming, and lateral crural strut grafting. Linear regression of the generated force-displacement curves was used to calculate stiffness. Each intervention was compared to the intact cartilage.

RESULTS

Alar cartilage of all of the specimens demonstrated a linear response to compressive loading. Intact cartilage had a mean stiffness of 3.53 N/mm. Mucosal stripping and cephalic turn-in flaps yielded similar stiffness values to intact cartilage. Cephalic trimming reduced stiffness in all cases by a mean of 1.09 N/mm (p = 0.003). Lateral crural strut grafting significantly increased stiffness by a mean of 3.67 N/mm (p = 0.0001).

CONCLUSIONS

Cephalic trimming leads to decreased lateral crural stiffness in cadaveric specimens. Cephalic turn-in flaps restore pre-trimmed stiffness, and lateral crural strut grafting increases overall stiffness of the cartilage. These findings should be considered in patients undergoing rhinoplasty, particularly if there are concerns regarding potential external valve collapse.

A novel soft tissue prediction methodology for orthognathic surgery based on probabilistic finite element modelling

Repositioning of the maxilla in orthognathic surgery is carried out for functional and aesthetic purposes. Pre-surgical planning tools can predict 3D facial appearance by computing the response of the soft tissue to the changes to the underlying skeleton. The clinical use of commercial prediction software remains controversial, likely due to the deterministic nature of these computational predictions. A novel probabilistic finite element model (FEM) for the prediction of postoperative facial soft tissues is proposed in this paper. A probabilistic FEM was developed and validated on a cohort of eight patients who underwent maxillary repositioning and had pre- and postoperative cone beam computed tomography (CBCT) scans taken. Firstly, a variables correlation assessed various modelling parameters. Secondly, a design of experiments (DOE) provided a range of potential outcomes based on uniformly distributed input parameters, followed by an optimisation. Lastly, the second DOE iteration provided optimised predictions with a probability range. A range of 3D predictions was obtained using the probabilistic FEM and validated using reconstructed soft tissue surfaces from the postoperative CBCT data. The predictions in the nose and upper lip areas accurately include the true postoperative position, whereas the prediction under-estimates the position of the cheeks and lower lip. A probabilistic FEM has been developed and validated for the prediction of the facial appearance following orthognathic surgery. This method shows how inaccuracies in the modelling and uncertainties in executing surgical planning influence the soft tissue prediction and it provides a range of predictions including a minimum and maximum, which may be helpful for patients in understanding the impact of surgery on the face.

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

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

In Vivo Chondrogenesis in 3D Bioprinted Human Cell-laden Hydrogel Constructs

BACKGROUND

The three-dimensional (3D) bioprinting technology allows creation of 3D constructs in a layer-by-layer fashion utilizing biologically relevant materials such as biopolymers and cells. The aim of this study is to investigate the use of 3D bioprinting in a clinically relevant setting to evaluate the potential of this technique for in vivo chondrogenesis.

METHODS

Thirty-six nude mice (Balb-C, female) received a 5- × 5- × 1-mm piece of bioprinted cell-laden nanofibrillated cellulose/alginate construct in a subcutaneous pocket. Four groups of printed constructs were used: (1) human (male) nasal chondrocytes (hNCs), (2) human (female) bone marrow-derived mesenchymal stem cells (hBMSCs), (3) coculture of hNCs and hBMSCs in a 20/80 ratio, and (4) Cell-free scaffolds (blank). After 14, 30, and 60 days, the scaffolds were harvested for histological, immunohistochemical, and mechanical analysis.

RESULTS

The constructs had good mechanical properties and keep their structural integrity after 60 days of implantation. For both the hNC constructs and the cocultured constructs, a gradual increase of glycosaminoglycan production and hNC proliferation was observed. However, the cocultured group showed a more pronounced cell proliferation and enhanced deposition of human collagen II demonstrated by immunohistochemical analysis.

CONCLUSIONS

In vivo chondrogenesis in a 3D bioprinted human cell-laden hydrogel construct has been demonstrated. The trophic role of the hBMSCs in stimulating hNC proliferation and matrix deposition in the coculture group suggests the potential of 3D bioprinting of human cartilage for future application in reconstructive surgery.

Effect of hyaluronidase on tissue-engineered human septal cartilage

OBJECTIVES

Structural properties of tissue-engineered cartilage can be optimized by altering its collagen to sulfated glycosaminoglycan (sGAG) ratio with hyaluronidase. The objective was to determine if treatment of neocartilage constructs with hyaluronidase leads to increased collagen:sGAG ratios, as seen in native tissue, and improved tensile properties.

STUDY DESIGN

Prospective, basic science.

METHODS

Engineered human septal cartilage from 12 patients was treated with hyaluronidase prior to culture. Control and treated constructs were analyzed at 3, 6, or 9 weeks for their biochemical, biomechanical, and histological properties.

RESULTS

Levels of sGAG were significantly reduced in treated constructs when compared with control constructs at 3, 6, and 9 weeks. Treated constructs had higher collagen:sGAG ratios when compared with control constructs at 3, 6, and 9 weeks. Treated constructs had greater tensile strength, strain at failure, and increased stiffness as measured by the equilibrium and ramp tensile moduli when compared with the untreated control constructs. Continued time in culture improved tensile strength in both treated and control constructs.

CONCLUSION

Hyaluronidase treatment of engineered septal cartilage decreased total sGAG content without inhibiting expansive growth of the constructs. Decreased sGAG in treated constructs resulted in increased collagen to sGAG ratios and was associated with an increase in tensile strength and stiffness. With additional culture time, sGAG increased modestly in depleted constructs, and some initial gains in tensile properties were dampened. Alterations in the dosage of hyalurondiase during neocartilage fabrication can create constructs that have improved biomechanical properties for eventual surgical implantation.

LEVEL OF EVIDENCE

NA. Laryngoscope, 126:1984-1989, 2016.

Redefining the Septal L-Strut to Prevent Collapse

During septorhinoplasty, septal cartilage is frequently resected for various purposes but the L-strut is preserved. Numerous materials are inserted into the nasal dorsum during dorsal augmenation rhinoplasty without considering nasal structural safety. This study used a finite element method (FEM) to redefine the septal L-strut, to prevent collapse as pressure moved from the rhinion to the supratip breakpoint on the nasal dorsum and as the contact percentage between the caudal L-strut and the maxillary crest changed. We designed a 1-cm-wide L-strut model based on computed tomography data. At least 45% of the width of the L-strut in the inferior portion of the caudal strut must be preserved during septoplasty to stabilize the septum. In augmentation rhinoplasty, the caudal L-strut must either be preserved perfectly or reinforced to prevent collapse or distortion of the L-strut. The dorsal augmentation material must be fixed in an augmentation pocket to prevent movement of graft material toward the supratip breakpoint, which can disrupt the L-strut. We conducted a numerical analysis using a FEM to predict tissue/organ behavior and to help clinicians understand the reasons for target tissue/organ collapse and deformation.

Model to Estimate Threshold Mechanical Stability of Lower Lateral Cartilage

IMPORTANCE

In rhinoplasty, techniques used to alter the shape of the nasal tip often compromise the structural stability of the cartilage framework in the nose. Determining the minimum threshold level of cartilage stiffness required to maintain long-term structural stability is a critical aspect in performing these surgical maneuvers.

OBJECTIVE

To quantify the minimum threshold mechanical stability (elastic modulus) of lower lateral cartilage (LLC) according to expert opinion.

METHODS

Five anatomically correct LLC phantoms were made from urethane via a 3-dimensional computer modeling and injection molding process. All 5 had identical geometry but varied in stiffness along the intermediate crural region (0.63-30.6 MPa).

DESIGN, SETTING, AND PARTICIPANTS

A focus group of experienced rhinoplasty surgeons (n = 33) was surveyed at a regional professional meeting on October 25, 2013. Each survey participant was presented the 5 phantoms in a random order and asked to arrange the phantoms in order of increasing stiffness based on their sense of touch. Then, they were asked to select a single phantom out of the set that they believed to have the minimum acceptable mechanical stability for LLC to maintain proper form and function.

MAIN OUTCOMES AND MEASURES

A binary logistic regression was performed to calculate the probability of mechanical acceptability as a function of the elastic modulus of the LLC based on survey data. A Hosmer-Lemeshow test was performed to measure the goodness of fit between the logistic regression and survey data. The minimum threshold mechanical stability for LLC was taken at a 50% acceptability rating.

RESULTS

Phantom 4 was selected most frequently by the participants as having the minimum acceptable stiffness for LLC intermediate care. The minimum threshold mechanical stability for LLC was determined to be 3.65 MPa. The Hosmer-Lemeshow test revealed good fit between the logistic regression and survey data (χ23 = 0.92, P = .82).

CONCLUSIONS AND RELEVANCE

This study presents a novel method of modeling anatomical structures and quantifying the mechanical properties of nasal cartilage. Quantifying these parameters is an important step in guiding surgical maneuvers performed in rhinoplasty.

LEVEL OF EVIDENCE

5.

Crosshatching incision technique in septoplasty: Experimental outcomes under actual surgical settings

OBJECTIVE

In previous experiments, the crosshatching incision has been shown to be an effective method for the correction of cartilaginous deviations. Although the settings of the experiments were different from that of septoplasty, the crosshatching incision has been considered a useful method for septoplasty. Therefore, we attempted to determine the efficacy of the crosshatching incision technique under actual septoplasty surgical settings.

METHODS

Commercial pig ear cartilages were used for the following experiments: firstly, the crosshatching incision was performed with the cartilage in a partially fixed state (in order to approximate caudal and dorsal fixation of septal cartilage); secondly, for the purpose of approximating L-strut preservation in septoplasty, the crosshatching incision was performed while excluding a marginal area of 1cm on any two contiguous borders. After the experiments, the change of curvature was assessed.

RESULTS

Under fixation of two contiguous borders, the curvature of the cartilage did not straighten after using the crosshatching incision. Incisions preserving the L-strut were not effective either. Furthermore, unpredicted deviation and splitting of the cartilage developed after the crosshatching incision.

CONCLUSIONS

Under actual surgical settings, the crosshatching incision was ineffective for the correction of septal deviation. Therefore, usefulness of the crosshatching incision needs to be re-evaluated.

Biomechanical characterisation of the human nasal cartilages; implications for tissue engineering

Nasal reconstruction is currently performed using autologous grafts provides but is limited by donor site morbidity, tissue availability and potentially graft failure. Additionally, current alternative alloplastic materials are limited by their high extrusion and infection rates. Matching mechanical properties of synthetic materials to the native tissue they are replacing has shown to be important in the biocompatibility of implants. To date the mechanical properties of the human nasal cartilages has not been studied in depth to be able to create tissue-engineered replacements with similar mechanical properties to native tissue. The young's modulus was characterized in compression on fresh-frozen human cadaveric septal, alar, and lateral cartilage. Due to the functional differences experienced by the various aspects of the septal cartilage, 16 regions were evaluated with an average elastic modulus of 2.72 ± 0.63 MPa. Furthermore, the posterior septum was found to be significantly stiffer than the anterior septum (p < 0.01). The medial and lateral alar cartilages were tested at four points with an elastic modulus ranging from 2.09 ± 0.81 MPa, with no significant difference between the cartilages (p < 0.78). The lateral cartilage was tested once in all cadavers with an average elastic modulus of 0.98 ± 0.29 MPa. In conclusion, this study provides new information on the compressive mechanical properties of the human nasal cartilage, allowing surgeons to have a better understanding of the difference between the mechanical properties of the individual nasal cartilages. This study has provided a reference, by which tissue-engineered should be developed for effective cartilage replacements for nasal reconstruction.

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

OBJECTIVES/HYPOTHESIS

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

STUDY DESIGN

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

LEVEL OF EVIDENCE

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

Tissue-engineered cartilage for facial plastic surgery

PURPOSE OF REVIEW

The reconstruction of cartilaginous craniofacial defects is ideally performed with analogous grafting material, such as autologous tissue. However, the use of autologous cartilage is limited by its finite availability and potentially suboptimal geometry to repair specific defects. Tissue engineering of human cartilage may provide the adequate supply of grafting and implant material for the reconstruction of cartilaginous facial defects. An update of the various cartilage tissue engineering methodologies is provided in this review.

RECENT FINDINGS

The cartilage tissue engineering paradigm begins with the harvest of a small septal cartilage donor specimen. This is followed by the isolation and subsequent proliferation of chondrocytes and the seeding of these cells onto three-dimensional scaffolds. Neocartilage is created as pericellular substrate, is produced by the cells and deposited throughout the scaffold. Theoretically, the mature cartilage construct can be introduced back into the same patient for reconstruction of craniofacial defects. Initial steps of the cartilage tissue engineering protocol have been standardized; however, modifications of subsequent steps have shown the potential to profoundly impact tissue composition and strength, bringing the properties of cartilage constructs closer to those of native human septum.

SUMMARY

The ability to engineer virtually limitless quantities of autologous cartilage could have a profound impact on facial plastic and reconstructive surgery. The strategies used to refine human cartilage culture techniques have successfully produced neocartilage constructs with biochemical and biomechanical properties approaching those of native septal tissue. With the steady progress achieved in recent years, there is great capacity for the proximate realization of surgically implantable tissue-engineered cartilage constructs.

Regenerative medicine and nasal surgery

Nasal surgery is a constellation of operations that are intended to restore form and function to the nose. The amount of augmentation required for a given case is a delicate interplay between patient aesthetic desires and corrective measures taken for optimal nasal airflow. Traditional surgical techniques make use of autologous donor tissue or implanted alloplastic materials to restore nasal deficits. Limited availability of donor tissue and associated harvest site morbidity have pushed surgeons and researchers to investigate methods to bioengineer nasal tissues. For this article, we conducted a review of the literature on regenerative medicine as it pertains to nasal surgery. PubMed was searched for articles dating from January 1, 1994, through August 1, 2014. Journal articles with a focus on regenerative medicine and nasal tissue engineering are included in this review. Our search found that the greatest advancements have been in the fields of mucosal and cartilage regeneration, with a growing body of literature to attest to its promise. With recent advances in bioscaffold fabrication, bioengineered cartilage quality, and mucosal regeneration, the transition from comparative animal models to more expansive human studies is imminent. Each of these advancements has exciting implications for treating patients with increased efficacy, safety, and satisfaction.

Evaluation of Autogenous Engineered Septal Cartilage Grafts in Rabbits- A Minimally Invasive Preclinical Model

OBJECTIVES

Evaluate safety of autogenous engineered septal neocartilage grafts.Compare properties of implanted grafts versus in vitro controls.

STUDY DESIGN

Prospective, basic science.

SETTING

Research laboratory.

METHODS

Constructs were fabricated from septal cartilage and serum harvested from adult rabbits and then cultured in vitro or implanted on the nasal dorsum as autogenous grafts for 30 or 60 days. Rabbits were monitored for local and systemic complications. Histological, biochemical and biomechanical properties of implanted and in vitro constructs were evaluated and compared.

RESULTS

No systemic or serious local complications were observed. After 30 and 60 days, implanted constructs contained more DNA (p<0.01) and less sGAG per DNA (p<0.05) when compared with in vitro controls. Confined compressive aggregate moduli were also higher in implanted constructs when compared with in vitro controls (p<0.05) and increased with longer in vivo incubation time (p<0.01). Implanted constructs displayed resorption rates of 20-45 percent. Calcium deposition in implanted constructs was observed using alizarin red histochemistry and microtomographic analyses.

CONCLUSION

Autogenous engineered septal cartilage grafts were well tolerated. As seen in experiments with athymic mice, implanted constructs accumulated more DNA and less sGAG when compared with in vitro controls. Confined compressive aggregate moduli were also higher in implanted constructs. Implanted constructs displayed resorption rates similar to previously published studies using autogenous implants of native cartilage. The basis for observed calcification in implanted constructs and its effect on long-term graft efficacy is unknown at this time and will be a focus of future studies.

Obtaining maximal stability with a septal extension technique in East asian rhinoplasty

Recently, in Korea, the septal extension graft from the septum or rib has become a common method of correcting a small or short nose. The success rate of this method has led to the blind faith that it provides superior tip projection and definition, and to the failure to notice its weaknesses. Even if there is a sufficient amount of cartilage, improper separation or fixation might waste the cartilage, resulting in an inefficient operation. Appropriate resection and effective fixation are essential factors for economical rhinoplasty. The septal extension graft is a remarkable procedure since it can control the nasal tip bidirectionally and three dimensionally. Nevertheless, it has a serious drawback since resection is responsible for septal weakness. Safe resection and firm reconstruction of the framework should be carried out. Operating on the basis of the principle of "safe harvest" and rebuilding the structures is important. Further, it is important to learn several techniques to manage septal weakness, insufficient cartilage quantity, and failure of the rigid frame during the surgery.

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.

Volume Expansion of Tissue Engineered Human Nasal Septal Cartilage

IMPORTANCE

Cartilaginous craniofacial defects range in size and autologous cartilaginous tissue is preferred for repair of these defects. Therefore, it is important to have the ability to produce large size cartilaginous constructs for repair of cartilaginous abnormalities.

OBJECTIVES

To produce autologous human septal neocartilage constructs substantially larger in size than previously produced constructsTo demonstrate that volume expanded neocartilage constructs possess comparable histological and biochemical properties to standard size constructsTo show that volume expanded neocartilage constructs retain similar biomechanical properties to standard size constructs.

DESIGN

Prospective, basic science.

SETTING

Laboratory.

PARTICIPANTS

The study used remnant human septal specimens removed during routine surgery at the University of California, San Diego Medical Center or San Diego Veterans Affairs Medical Center. Cartilage from a total of 8 donors was collected.

MAIN OUTCOMES MEASURED

Human septal chondrocytes from 8 donors were used to create 12mm and 24mm neocartilage constructs. These were cultured for a total of 10 weeks. Photo documentation, histological, biochemical, and biomechanical properties were measured and compared.

RESULTS

The 24mm diameter constructs were qualitatively similar to the 12mm constructs. They possessed adequate strength and durability to be manually manipulated. Histological analysis of the constructs demonstrated similar staining patterns in standard and volume expanded constructs. Proliferation, as measured by DNA content, was similar in 24mm and 12mm constructs. Additionally, glycosaminoglycan (GAG) and total collagen content did not significantly differ between the two construct sizes. Biomechanical analysis of the 24mm and 12mm constructs demonstrated comparable compressive and tensile properties.

CONCLUSION AND RELEVANCE

Volume expanded human septal neocartilage constructs are qualitatively and histologically similar to standard 12mm constructs. Biochemical and biomechanical analysis of the constructs demonstrated equivalent properties. This study shows that modification of existing protocols is not required to successfully produce neocartilage constructs in larger sizes for reconstruction of more substantial craniofacial defects.

LEVEL OF EVIDENCE

NA.

Mechanical behavior of bovine nasal cartilage under static and dynamic loading

Abnormal mechanical loading may trigger cartilage degeneration associated with osteoarthritis. Tissue response to load has been the subject of several in vitro studies. However, simple stimuli were often applied, not fully mimicking the complex in vivo conditions. Therefore, a rolling/plowing explant test system (RPETS) was developed to replicate the combined in vivo loading patterns. In this work we investigated the mechanical behavior of bovine nasal septum (BNS) cartilage, selected as tissue approximation for experiments with RPETS, under static and dynamic loading. Biphasic material properties were determined and compared with those of other cartilaginous tissues. Furthermore, dynamic loading in plowing modality was performed to determine dynamic response and experimental results were compared with analytical models and Finite Elements (FE) computations. Results showed that BNS cartilage can be modeled as a biphasic material with Young's modulus E=2.03 ± 0.7 MPa, aggregate modulus HA=2.35 ± 0.7 MPa, Poisson's ratio ν=0.24 ± 0.07, and constant hydraulic permeability k0=3.0 ± 1.3 × 10(-15)m(4)(Ns)(-1). Furthermore, dynamic analysis showed that plowing induces macroscopic reactions in the tissue, proportionally to the applied loading force. The comparison among analytical, FE analysis and experimental results showed that predicted tangential forces and sample deformation lay in the range of variation of experimental results for one specific experimental condition. In conclusion, mechanical properties of BNS cartilage under both static and dynamic compression were assessed, showing that this tissue behave as a biphasic material and has a viscoelastic response to dynamic forces.

Shape fidelity of native and engineered human nasal septal cartilage

OBJECTIVE

To test engineered and native septal cartilage for resistance to deformation and remodeling under sustained bending loads and to determine the effect of bending loads on the biochemical properties of constructs.

STUDY DESIGN

Prospective, basic science.

SETTING

Laboratory.

SUBJECTS AND METHODS

Human septal chondrocytes from 6 donors were used to create 12-mm constructs. These were cultured for 10 weeks and subjected to bending for 6 days. Free-swelling controls and native tissue from 6 donors were used for comparison. Shape retention, photo documentation, live-dead staining, and biochemical properties were measured.

RESULTS

Live-dead staining showed no difference in cell survival between loaded constructs and free-swelling controls. The immediate shape retention of the constructs was 39.0% versus 24.4% for native tissue (P = .13). After 2 and 24 hours of relaxation, the constructs possessed similar shape retention to native tissue (26.9% and 16.4%; P = .126; 21.7% and 14.4%; P = .153). There was no significant change in construct shape retention from immediately after release to 2 hours of relaxation (39.0% and 26.9%, respectively; P = .238). In addition, the retention did not change significantly between 2 and 24 hours of relaxation (26.9% and 21.7%; P = .48). There was no significant difference in biochemical properties between loaded constructs and controls.

CONCLUSION

The shape retention properties of human septal neocartilage constructs are comparable to human native septal cartilage. In addition, mechanical loading of neocartilage constructs does not adversely affect cell viability or biochemical properties. This study demonstrates that neocartilage constructs possess adequate shape fidelity for use as septal cartilage graft material.

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.

Orientational dependent sensitivities of T2 and T1ρ towards trypsin degradation and Gd-DTPA2- presence in bovine nasal cartilage

OBJECTIVE

To study the orientational dependencies of T(2) and T(1ρ) in native and trypsin-degraded bovine nasal cartilage, with and without the presence of 1 mM Gd-DTPA(2-).

MATERIALS AND METHODS

Sixteen specimens were prepared in two orthogonal fibril directions (parallel and perpendicular), treated using different protocols (native, Gd treated, trypsin-treated, and combination), and imaged using μMRI at 0° and 55° (the magic angle) fibril orientations with respect to the magnetic field B(0). Two-dimensional (2D) T(2) and T(1ρ) images were then calculated quantitatively.

RESULTS

Without Gd, native perpendicular tissues demonstrated significant T(1ρ) dispersion (including T(2) at the zero spin-lock field) at 0° and less dispersion at 55°, while native parallel specimens exhibited smaller T(1ρ) dispersion at both 0° and 55°. Trypsin degradation caused a minimum 50% increase in T(1ρ). With Gd, trypsin degradation caused significant reduction in T(1ρ) values up to 60%.

CONCLUSION

The collagen orientation in nasal cartilage can influence T(2) and T(1ρ) MRI of cartilage. Without Gd, T(1ρ) was sensitive to the proteoglycan content and its sensitivity was nearly constant regardless of fibril orientation. In comparison, the T(2) sensitivity to proteoglycan was dependant upon fibril orientation, i.e., more sensitive at 55° than 0°. When Gd ions were present, both T(2) and T(1ρ) became insensitive to the proteoglycan content.

Dependencies of multi-component T2 and T1ρ relaxation on the anisotropy of collagen fibrils in bovine nasal cartilage

Both NMR spectroscopy and MRI were used to investigate the dependencies of multi-component T2 and T1ρ relaxation on the anisotropy of bovine nasal cartilage (BNC). The non-negative least square (NNLS) method and the multi-exponential fitting method were used to analyze all experimental data. When the collagen fibrils in nasal cartilage were oriented at the magic angle (55°) to the magnetic field B0, both T2 and T1ρ were single component, regardless of the spin-lock field strength or the echo spacing time in the pulse sequences. When the collagen fibrils in nasal cartilage were oriented at 0° to B0, both T2 and T1ρ at a spin-lock field of 500 Hz had two components. When the spin-lock field was increased to 1000 Hz or higher, T1ρ relaxation in nasal cartilage became a single component, even when the specimen orientation was 0°. These results demonstrate that the specimen orientation must be considered for any multi-component analysis, even for nasal cartilage that is commonly considered homogenously structured. Since the rapidly and slowly relaxing components can be attributed to different portions of the water population in tissue, the ability to resolve different relaxation components could be used to quantitatively examine individual molecular components in connective tissues.

Anisotropic properties of bovine nasal cartilage

To investigate the structural anisotropy in bovine septal cartilage, quantitative procedures in microscopic magnetic resonance imaging (μMRI), polarized light microscopy (PLM), and mechanical indentation were used to measure the tissue in three orthogonal planes: vertical, medial, and caudocephalic. The quantitative T2 imaging experiments in μMRI found strong anisotropy in the images of both vertical and caudocephalic planes but little anisotropy in the images from the medial plane. The PLM birefringent experiments found that the retardation values in the medial section were only about 10% of these in the vertical and caudocephalic sections and that the angle values in all three sections followed the rotation of the tissue section in the microscope stage. The stress relaxation experiments in mechanical indentation showed reduced stiffness in the medial plane compared to stiffness in either the vertical or caudocephalic planes. Collectively, the results in this project coherently indicate a marked structural anisotropy in cartilage from the nasal septum, where the long axis of the collagen fibrils is oriented in parallel with the medial axis.

Insulin-like growth factor-I and growth differentiation factor-5 promote the formation of tissue-engineered human nasal septal cartilage

INTRODUCTION

Tissue engineering of human nasal septal chondrocytes offers the potential to create large quantities of autologous material for use in reconstructive surgery of the head and neck. Culture with recombinant human growth factors may improve the biochemical and biomechanical properties of engineered tissue. The objectives of this study were to (1) perform a high-throughput screen to assess multiple combinations of growth factors and (2) perform more detailed testing of candidates identified in part I.

METHODS

In part I, human nasal septal chondrocytes from three donors were expanded in monolayer with pooled human serum (HS). Cells were then embedded in alginate beads for 2 weeks of culture in medium supplemented with 2% or 10% HS and 1 of 90 different growth factor combinations. Combinations of insulin-like growth factor-I (IGF-1), bone morphogenetic protein (BMP)-2, BMP-7, BMP-13, growth differentiation factor-5 (GDF-5), transforming growth factor β (TGFβ)-2, insulin, and dexamethasone were evaluated. Glycosaminoglycan (GAG) accumulation was measured. A combination of IGF-1 and GDF-5 was selected for further testing based on the results of part I. Chondrocytes from four donors underwent expansion followed by three-dimensional alginate culture for 2 weeks in medium supplemented with 2% or 10% HS with or without IGF-1 and GDF-5. Chondrocytes and their associated matrix were then recovered and cultured for 4 weeks in 12 mm transwells in medium supplemented with 2% or 10% HS with or without IGF-1 and GDF-5 (the same medium used for alginate culture). Biochemical and biomechanical properties of the neocartilage were measured.

RESULTS

In part I, GAG accumulation was highest for growth factor combinations including both IGF-1 and GDF-5. In part II, the addition of IGF-1 and GDF-5 to 2% HS resulted in a 12-fold increase in construct thickness compared with 2% HS alone (p < 0.0001). GAG and type II collagen accumulation was significantly higher with IGF-1 and GDF-5. Confined compression modulus was greatest with 2% HS, IGF-1, and GDF-5.

CONCLUSION

Supplementation of medium with IGF-1 and GDF-5 during creation of neocartilage constructs results in increased accumulation of GAG and type II collagen and improved biomechanical properties compared with constructs created without the growth factors.

Biomechanics of the deformity of septal L-Struts

OBJECTIVES/HYPOTHESIS

A septal L-strut is often preserved or created during septoplasty. The main intention is to provide structural stability and to straighten the nasal septum. Deformity or excessive deformation of the L-strut might cause functional or aesthetic complications. The objectives were to examine the effects of material properties, the boundary conditions, the nasal tip support, and the geometry of the L-struts on the deformity of septal L-struts.

STUDY DESIGN

Computer-aided modeling was used to create a spring-supported nasal tip and free nasal tip L strut septal cartilage models upon which simulation was performed to analyse the deformation patterns.

METHODS

A five-sided septum model was first created from the computed tomography scan of a human subject. Several models with various combinations of wider or narrower dorsal struts as well as arc of cartilage were then constructed from this septum model. The edges connected to bony supports were assumed to be fixed, and the nasal tip was assumed to be spring supported. Finite element analyses were carried out to determine the deformation and stress distribution in the septal strut for different combinations of material properties and nasal tip spring support.

RESULTS

The spring-supported nasal tip model provides a more accurate representation of the boundary conditions in the nose. In both the free and spring-supported nasal tips-the BC junction and the nasal spine are found to be the consistent points of maximum stress regardless of material properties. The preservation of an arc of cartilage and a wider dorsal strut increase the stability of the structure.

CONCLUSIONS

The introduction of a spring-supported nasal tip model provided a more accurate representation of the boundary conditions in the nose. The bony-cartilaginous junction and the nasal spine were found to be the consistent points of maximum stress, regardless of material properties. The preservation of an arc of cartilage and a wider dorsal strut increased the stability of the structure.

Mold-shaped, nanofiber scaffold-based cartilage engineering using human mesenchymal stem cells and bioreactor

BACKGROUND

Mesenchymal stem cell (MSC)-based tissue engineering is a promising future alternative to autologous cartilage grafting. This study evaluates the potential of using MSCs, seeded into electrospun, biodegradable polymeric nanofibrous scaffolds, to engineer cartilage with defined dimensions and shape, similar to grafts used for subcutaneous implantation in plastic and reconstructive surgery.

MATERIALS AND METHODS

Human bone marrow derived MSCs seeded onto nanofibrous scaffolds and placed in custom-designed molds were cultured for up to 42 days in bioreactors. Chondrogenesis was induced with either transforming growth factor-beta1 (TGF-beta1) alone or in combination with insulin-like growth factor-I (IGF-I).

RESULTS

Constructs exhibited hyaline cartilage histology with desired thickness and shape as well as favorable tissue integrity and shape retention, suggesting the presence of elastic tissue. Time-dependent increase in cartilage matrix gene expression was seen in both types of culture: at Day 42, TGF-beta1/IGF-I treated cultures showed higher collagen Type 2 and aggrecan expression. Both culture conditions showed significant time-dependent increase in sulfated glycosaminoglycan and hydroxyproline contents. TGF-beta1/IGF-I-treated samples were significantly stiffer; with equilibrium compressive Young's modulus values reaching 17 kPa by Day 42.

CONCLUSIONS

The successful ex vivo development of geometrically defined cartilaginous construct using customized molding suggests the potential of cell-based cartilage tissue for reconstructive surgery.