Thermo-Mechanical Behaviour of Human Nasal Cartilage

Abstract

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.

Keywords: cartilage; nasal soft tissue; rhinoplasty; thermo-mechanical characterization; viscoelasticity.

Figure 1

Sketch of a human nose showing the main anatomical regions (frontal view).

Figure 2

Most common nasal aesthetic defects: (a) Dorsal hump, (b) Crooked nose, (c) Wide dorsum, (d) Droopy nose (with hump), and (e) Rounded tip (the pictures were taken from the Miguel Ferreira’s patients by previous permission to be used in this study).

Figure 3

Harvesting of nasal cartilage samples in different regions of corpse nose: (a) dog-bone- and (b) flat disc-shaped specimens.

Figure 4

Differential scanning calorimetry (DSC) analyses of the (a) CT, (b) CP, (c) SC from NS, ULC, and LLC (donor 1).

Figure 5

Average values and standard deviations of thermal features (Enthalpy and Temperature) of the 1st peak for LLC, ULC, and NS structures (CT: cartilage; SC: subcutaneous; CP: composite).

Figure 6

TG analyses of the LLC: (a) CT, (b) CP, (c) SC (donor 2).

Figure 6

TG analyses of the LLC: (a) CT, (b) CP, (c) SC (donor 2).

Figure 7

Mean values and standard deviations of thermal peaks (T_p1 to T_p3) obtained by TG/DTG analyses for the analysed structures regarding cartilage (CT), subcutaneous tissue (SC), and composite (CP). (^·) Reports a single value.

Figure 8

Mean values and standard deviations of weight-loss obtained by TG/DTG analyses for the analysed structures regarding cartilage (CT), subcutaneous tissue (SC), and composite (CP). (^·) Reports a single value.

Figure 9

Tensile multi-frequency (a) storage and (b) loss moduli, (c) damping of the NS (donor 1).

Figure 10

Compressive multi-frequency (a) storage and (b) loss moduli, (c) damping of the NS (donor 1).

Figure 11

Histology of different nasal regions: of the NS (a–b), LLC (c–d), and ULC (e–f) samples. 1. Cartilage (µm); 2. Distance from the epidermis to the outer layer of cartilage (µm); 3. Distance from the epidermis to the inner layer of cartilage (µm); 4. Distance from the perichondrium to the tension area (µm).

Figure 12

Measurements of different morphological regions (a) and count of different cell types (b) of the histology samples of the NS, LLC, and ULC. 1. Cartilage (µm); 2. Distance from the epidermis to the outer layer of cartilage (µm); 3. Distance from the epidermis to the inner layer of cartilage (µm); 4. Distance from the perichondrium to the tension area (µm). Cell count was evaluated in a sample area of 0.3641 mm² (n = 3; SD < 5%).

Figure 13

Semi-thin sections (1 µm thickness) stained with Toluidine Blue of different nasal regions: (a) NS, (b) LLC, and (c) ULC.