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Habelitz, S.
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Habelitz, S.
Official Name
Habelitz, S.
Research Output
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Publication
Visualizing molecular polar order in tissues via electromechanical coupling
2012-12, Denning, Denise, Alilat, Sofiane, Habelitz, S., Fertala, A., Rodriguez, Brian J.
Electron microscopy (EM) and atomic force microscopy
(AFM) techniques have long been used to characterize collagen fibril
ordering and alignment in connective tissues. These techniques, however,
are unable to map collagen fibril polarity, i.e., the polar orientation
that is directed from the amine to the carboxyl termini. Using a
voltage modulated AFM-based technique called piezoresponse force
microscopy (PFM), we show it is possible to visualize both the alignment
of collagen fibrils within a tissue and the polar orientation of the
fibrils with minimal sample preparation. We demonstrate the technique on
rat tail tendon and porcine eye tissues in ambient conditions. In each
sample, fibrils are arranged into domains whereby neighboring domains
exhibit opposite polarizations, which in some cases extend to the
individual fibrillar level. Uniform polarity has not been observed in
any of the tissues studied. Evidence of anti-parallel ordering of the
amine to carboxyl polarity in bundles of fibrils or in individual
fibrils is found in all tissues, which has relevance for understanding
mechanical and biofunctional properties and the formation of connective
tissues. The technique can be applied to any biological material
containing piezoelectric biopolymers or polysaccharides.
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Publication
Piezoelectric properties of aligned collagen membranes
2014-02, Denning, Denise, Paukshto, Michael V., Habelitz, S., Rodriguez, Brian J.
Electromechanical coupling, a phenomenon present in collagenous materials, may influence cell–extracellular matrix interactions. Here, electromechanical coupling has been investigated via piezoresponse force microscopy in transparent and opaque membranes consisting of helical-like arrays of aligned type I collagen fibrils self-assembled from acidic solution. Using atomic force microscopy, the transparent membrane was determined to contain fibrils having an average diameter of 76 ± 14 nm, whereas the opaque membrane comprised fibrils with an average diameter of 391 ± 99 nm. As the acidity of the membranes must be neutralized before they can serve as cell culture substrates, the structure and piezoelectric properties of the membranes were measured under ambient conditions before and after the neutralization process. A crimp structure (1.59 ± 0.37 µm in width) perpendicular to the fibril alignment became apparent in the transparent membrane when the pH was adjusted from acidic (pH = 2.5) to neutral (pH = 7) conditions. In addition, a 1.35-fold increase was observed in the amplitude of the shear piezoelectricity of the transparent membrane. The structure and piezoelectric properties of the opaque membrane were not significantly affected by the neutralization process. The results highlight the presence of an additional translational order in the transparent membrane in the direction perpendicular to the fibril alignment. The piezoelectric response of both membrane types was found to be an order of magnitude lower than that of collagen fibrils in rat tail tendon. This reduced response is attributed to less-ordered molecular assembly than is present in D-periodic collagen fibrils, as evidenced by the absence of D-periodicity in the membranes. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.
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Publication
Electromechanical properties of dried tendon and iso-electrically focused collagen hydrogels
2012-08, Denning, Denise, Abu-Rub, M. T., Zeugolis, Dimitrios I., Habelitz, S., Pandit, A., Fertala, A., Rodriguez, Brian J.
Assembling artificial collagenous tissues with
structural, functional, and mechanical properties which mimic natural
tissues is of vital importance for many tissue engineering applications.
While the electro-mechanical properties of collagen are thought to play
a role in, for example, bone formation and remodeling, this functional
property has not been adequately addressed in engineered tissues. Here
the electro-mechanical properties of rat tail tendon are compared with
those of dried isoelectrically focused collagen hydrogels using
piezoresponse force microscopy under ambient conditions. In both the
natural tissue and the engineered hydrogel D-periodic type I collagen
fibrils are observed, which exhibit shear piezoelectricity. While both
tissues also exhibit fibrils with parallel orientations, Fourier
transform analysis has revealed that the degree of parallel alignment of
the fibrils in the tendon is three times that of the dried hydrogel.
The results obtained demonstrate that isoelectrically focused collagen
has similar structural and electro-mechanical properties to that of
tendon, which is relevant for tissue engineering applications.