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Browsing by Subject "Scanning probe microscopy"
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Item Applications of atomic force microscopy for the assessment of nanoscale morphological and mechanical properties of bone(2012-01) Wallace, Joseph M.Scanning probe microscopy (SPM) has been in use for 30 years, and the form of SPM known as atomic force microscopy (AFM) has been around for 25 of those years. AFM has been used to produce high resolution images of a variety of samples ranging from DNA to carbon nanotubes. Type I collagen and many collagen-based tissues (including dentin, tendon, cartilage, skin, fascia, vocal cords, and cornea) have been studied with AFM, but comparatively few studies of bone have been undertaken. The purpose of this review is to introduce the general principles of AFM operation, demonstrate what AFM has been used for in bone research, and discuss the new directions that this technique can take the study of bone at the nanoscale.Item Near-Field Investigations of the Anisotropic Properties of Supported Lipid Bilayers(2012-07-24) Johnson, Merrell A.; Decca, Ricardo; Rader, Andrew J.; Ritchie, Ken; Petrache, Horia; Wassall, StephenThe details of Polarization Modulation Near-Field Scanning Optical Microscopy (PM-NSOM) are presented. How to properly calibrate and align the system is also introduced. A measurement of Muscovite crystal is used to display the capabilities of the setup. Measurements of supported Lβʹ 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers are presented, emphasizing how it was tooled in exploiting the anisotropic nature of the acyl chains. A discussion of how the effective retardance (ΔS = 2π( n_e-n_o )t/λ) and the direction of the projection of the acyl chains (θ) are measured simultaneously is given, (where t is the thickness of the bilayer and λ is the wavelength of light used). It is shown from ΔS the birefringence (ne-no) of the bilayer is determined, by assuming the acyl chain tilt with respect to the membrane's normal to be ϕ ≈ 32. Time varying experiments show lateral diffusions of ~ 2 x 10-12 cm2/s. Temperature controlled PM-NSOM is shown to be a viable way to determine the main phase transition temperature (Tm) for going from the gel Lβʹ to liquid disorder Lα state of supported DPPC bilayers. A change of ΔS ~ (3.8 +/- 0.3 mrad) at the main phase transition temperature Tm (≈41^o C) is observed. This agrees well with previous values of (ne-no) and translates to an assumed <ϕ> ~ 32^o when T < Tm and 0^o when T > Tm. Evidence of supper heating and supper cooling will be presented, along with a discussion of the fluctuations that occur around Tm. Finally it is shown how physical parameters such as the polarizability are extracted from the data. Values of the transverse (αt) and longitudinal (αl) polarizabilites of the acyl chains are shown to be, αt = 44.2 Å3 and αl = 94.4 Å3, which correspond well with the theoretical values of a single palmitic acid (C16) αt = 25.14 Å3 and αl = 45.8 Å3.