RESUMEN
We describe the use of atomic force microscopy (AFM) to investigate the nanomechanical properties of annulus fibrosus (AF)-the outer fibrous layer of an intervertebral disc (IVD) encapsulating the inner jelly-like mass known as the nucleus pulposus (NP). Disk disease, degenerated discs, slipped discs, and herniated discs are common terms often linked to back pain and are caused due to degeneration of IVD. Due to the variations in the structure and biochemical composition of the IVD, studies of macromechanical properties in the motion segment or AF may lack all significant nanomechanical responses or behaviors. Existing studies do not report the micro or nano level of mechanics of IVD components and whether the nanomechanics of this tissue mimic its macromechanical behavior is not known. Our studies used AFM to investigate the regional micromechanical properties of the AF that have been otherwise difficult due to small sample size of the tissue. Five different zones including peripheral and central were tested mechanically as well as biochemically. Qualitative biochemical staining and quantitative values of nanomechanical properties of different zones are compared and discussed in detail. The results of nanomechanical investigations described in this study not only reveal its mimic at macroscopic level, they represent an important step towards establishing a framework for testing and comparing tissue engineered IVD replacements with native tissues.
Asunto(s)
Disco Intervertebral/fisiología , Fenómenos Mecánicos/fisiología , Microscopía de Fuerza Atómica/métodos , Conejos/anatomía & histología , Animales , Fenómenos Biomecánicos , Disco Intervertebral/citología , Microscopía de Fuerza Atómica/instrumentaciónRESUMEN
Craniosynostosis represents a heterogeneous cluster of congenital disorders and manifests as premature ossification of one or more cranial sutures. Cranial sutures serve to enable calvarial growth and function as joints between skull bones. The mechanical properties of synostosed cranial sutures are of vital importance to their function and yet are poorly understood. The present study was designed to characterize the nanostructural and nanomechanical properties of synostosed postnatal sagittal and metopic sutures. Synostosed postnatal sagittal sutures (n = 5) and metopic sutures (n = 5) were obtained from craniosynostosis patients (aged 9.1 +/- 2.8 months). The synostosed sutural samples were prepared for imaging and indentation on both the endocranial and ectocranial surfaces with the cantilever probe of an atomic force microscopy. Analysis of the nanotopographic images indicated robust variations in sutural surface characteristics with localized peaks and valleys. In 5 x 5 mum scan sizes, the surface roughness of the synostosed metopic suture was significantly greater (223.6 +/- 93.3 nm) than the synostosed sagittal suture (142.9 +/- 80.3 nm) (P < 0.01). The Young's modulus of the synostosed sagittal suture at 0.7 +/- 0.2 MPa was significantly higher than the synostosed metopic suture at 0.5 +/- 0.1 MPa (P < 0.01). These data suggest that various synostosed cranial sutures may have different structural and mechanical characteristics.
Asunto(s)
Suturas Craneales/ultraestructura , Craneosinostosis/patología , Nanoestructuras , Nanotecnología , Fenómenos Biomecánicos , Suturas Craneales/fisiopatología , Craneosinostosis/fisiopatología , Elasticidad , Hueso Frontal/fisiopatología , Hueso Frontal/ultraestructura , Humanos , Lactante , Microscopía de Fuerza Atómica , Hueso Parietal/fisiopatología , Hueso Parietal/ultraestructura , Estrés MecánicoRESUMEN
Growth plate cartilage demonstrates a unique capacity for cell proliferation and matrix synthesis while sustaining mechanical stresses. To test the hypothesis that the extracellular matrices along various depth of growth plate cartilage have different elastic properties, microindentation by atomic force microscopy was applied to en bloc dissected rabbit cranial base growth plate samples from the reserve zone to mineralizing zone in 50-microm increments. The average elastic modulus upon transverse indentation orthogonal to the long axis of the growth plate showed a gradient distribution, increasing significantly from the reserve zone (0.57 +/- 0.05 MPa) to mineralizing zone (1.41 +/- 0.19 MPa). Longitudinal indentation of the reserve zone along the long axis of the growth plate revealed an average elastic modulus of 0.77 +/- 0.12 MPa, significantly different from the same zone upon transverse indentation. Thus, the extracellular matrix of growth plate cartilage seems to be inhomogenous in its capacity to withstand mechanical stresses.