RESUMEN
Articular cartilage undergoes structural and biochemical changes during maturation, but the knowledge on how these changes relate to articular cartilage function at different stages of maturation is lacking. Equine articular cartilage samples of four different maturation levels (newborn, 5-month-old, 11-month-old and adult) were collected (N = 25). Biomechanical tensile testing, Fourier transform infrared microspectroscopy (FTIR-MS) and polarized light microscopy were used to study the tensile, biochemical and structural properties of articular cartilage, respectively. The tensile modulus was highest and the breaking energy lowest in the newborn group. The collagen and the proteoglycan contents increased with age. The collagen orientation developed with age into an arcade-like orientation. The collagen content, proteoglycan content, and collagen orientation were important predictors of the tensile modulus (p < 0.05 in multivariable regression) and correlated significantly also with the breaking energy (p < 0.05 in multivariable regression). Partial least squares regression analysis of FTIR-MS data provided accurate predictions for the tensile modulus (r = 0.79) and the breaking energy (r = 0.65). To conclude, the composition and structure of equine articular cartilage undergoes changes with depth that alter functional properties during maturation, with the typical properties of mature tissue reached at the age of 5-11 months.
Asunto(s)
Cartílago Articular/anatomía & histología , Cartílago Articular/crecimiento & desarrollo , Caballos/fisiología , Resistencia a la Tracción/fisiología , Animales , Fenómenos Biomecánicos , Colágeno/metabolismo , Análisis de los Mínimos Cuadrados , Análisis Multivariante , Proteoglicanos/metabolismo , Análisis de RegresiónRESUMEN
OBJECTIVE: The aim of this study was to evaluate the performance of a hand-held indentation device for fast and reliable determination of skin stiffness. METHODS: Device accuracy to indentation depths of 0.6 and 1.3 mm was first evaluated on plastic foam materials with mechanical properties verified by a laboratory material testing device. Subsequently, the device's sensitivity to detect age-related changes in skin stiffness was evaluated among 46 healthy women (18-79 years). Finally, the reproducibility of the method was tested with six healthy subjects. RESULTS: High correlation was detected between indentation stiffness of reference material and Young's modulus determined with mechanical testing device (0.6 mm indenter: r = 0.97, P = 0.05; 1.3 mm indenter: r = 0.98, P = 0.04). Age-related decrease of 38% in skin stiffness was observed in healthy volunteers (P < 0.05). The coefficient of variation for 0.6 and 1.3 mm indenters was 7.4% and 8.5%, respectively. No trend related to hysteresis effect was observed from repeated measurements. CONCLUSIONS: The presented indentation technique was accurate against the laboratory material testing device. Furthermore, skin changes related to ageing could be detected with the indentation technique. The new device was found to be feasible for monitoring skin stiffness in cosmetics and clinical conditions.
Asunto(s)
Elasticidad , Ensayo de Materiales/instrumentación , Fenómenos Fisiológicos de la Piel , Adolescente , Adulto , Anciano , Femenino , Antebrazo/fisiología , Humanos , Persona de Mediana Edad , Reproducibilidad de los Resultados , Adulto JovenRESUMEN
BACKGROUND: Indentation techniques haves been applied to measure stiffness of human soft tissues. Tissue properties and geometry of the indentation instrument control the measured response. METHODS: Mechanical roles of different soft tissues were characterized to understand the performance of the indentation instrument. An optimal instrument design was investigated. Experimental indentations in forearm of human subjects (N = 11) were conducted. Based on peripheral quantitative computed tomography imaging, a finite element (FE) model for indentation was created. The model response was matched with the experimental data. RESULTS: Optimized values for the elastic modulus of skin and adipose tissue were 130.2 and 2.5 kPa, respectively. The simulated indentation response was 3.9 ± 1.2 (mean ± SD) and 4.9 ± 2.0 times more sensitive to changes in the elastic modulus of the skin than to changes in the elastic modulus of adipose tissue and muscle, respectively. Skin thickness affected sensitivity of the instrument to detect changes in stiffness of the underlying tissues. CONCLUSION: Finite element modeling provides a feasible method to quantitatively evaluate the geometrical aspects and the sensitivity of an indentation measurement device. Systematically, the skin predominantly controlled the indentation response regardless of the indenter geometry or variations in the volume of different soft tissues.