Nanoscale characterization of isolated individual type I collagen fibrils: polarization and piezoelectricity

Abstract Piezoresponse force microscopy was applied to directly study individual type I collagen fibrils with diameters of ∼100 nm isolated from bovine Achilles tendon. It was revealed that single collagen fibrils behave predominantly as shear piezoelectric materials with a piezoelectric coefficient on the order of 1 pm V −1 , and have unipolar axial polarization throughout their entire length. It was estimated that, under reasonable shear load conditions, the fibrils were capable of generating an electric potential up to tens of millivolts. The result substantiates the nanoscale origin of piezoelectricity in bone and tendons, and implies also the potential importance of the shear load-transfer mechanism, which has been the principle basis of the nanoscale mechanics model of collagen, in mechanoelectric transduction in bone

Scalable, Hydrophobic and Highly-Stretchable Poly(isocyanurate-Urethane) Aerogels

Scalable, low-density and flexible aerogels offer a unique combination of excellent mechanical properties and scalable manufacturability. Herein, we report the fabrication of a family of low-density, ambient-dried and hydrophobic poly(isocyanurate-urethane) aerogels derived from a triisocyanate precursor. The bulk densities ranged from 0.28 to 0.37 g cm-3 with porosities above 70% v/v. The aerogels exhibit a highly stretchable behavior with a rapid increase in the Young\u27s modulus with bulk density (slope of log-log plot \u3e 6.0). In addition, the aerogels are very compressible (more than 80% compressive strain) with high shape recovery rate (more than 80% recovery in 30 s). Under tension even at high strains (e.g., more than 100% tensile strain), the aerogels at lower densities do not display a significant lateral contraction and have a Poisson\u27s ratio of only 0.22. Under dynamic conditions, the properties (e.g., complex moduli and dynamic stress-strain curves) are highly frequency- and rate-dependent, particularly in the Hopkinson pressure bar experiment where in comparison with quasi-static compression results, the properties such as mechanical strength were three orders of magnitude stiffer. The attained outcome of this work supports a basis on the understanding of the fundamental mechanical behavior of a scalable organic aerogel with potential in engineering applications including damping, energy absorption, and substrates for flexible devices

The structural origin of second harmonic generation in fascia

Fascia tissue is rich in collagen type I proteins and can be imaged by second harmonic generation (SHG) microscopy. While identifying the overall alignment of the collagen fibrils is evident from those images, the tridimensional structural origin for the observation of SHG signal is more complex than it apparently seems. Those images reveal that the noncentrosymmetric (piezoelectric) structures are distributed heterogeneously on spatial dimensions inferior to the resolution provided by the nonlinear optical microscope (sub-micron). Using piezoresponse force microscopy (PFM), we show that an individual collagen fibril has a noncentrosymmetric structural organization. Fibrils are found to be arranged in nano-domains where the anisotropic axis is preserved along the fibrillar axis, while across the collagen sheets, the phase of the second order nonlinear susceptibility is changing by 180 degrees between adjacent nano-domains. This complex architecture of noncentrosymmetric nano-domains governs the coherent addition of 2ω light within the focal volume and the observed features in the SHG images taken in fascia

Mechanical heterogeneity of dentin at different length scales as determined by AFM phase contrast

In this study we sought to gain insights of the structural and mechanical heterogeneity of dentin at different length scales. We compared four distinct demineralization protocols with respect to their ability to expose the periodic pattern of dentin collagen. Additionally, we analyzed the phase contrast resulting from AFM images obtained in tapping mode to interrogate the viscoelastic behavior and surface adhesion properties of peritubular and intertubular dentin, and partially demineralized dentin collagen fibrils, particularly with respect to their gap and overlap regions. Results demonstrated that all demineralization protocols exposed the gap and overlap zones of dentin collagen fibrils. Phase contrast analyses suggested that the intertubular dentin, where the organic matrix is concentrated, generated a higher phase contrast due a higher contribution of energy dissipation (damping) than the highly mineralized peritubular region. At increasing amplitudes, viscoelasticity appeared to play a more significant contribution to the phase contrast of the images of collagen fibrils. The overlap region yielded a greater phase contrast than the more elastic gap zones. In summary, our results contribute to the perspective that, at different length scales, dentin is constituted of structural features that retain heterogeneous mechanical properties contributing to overall mechanical performance of the tissue. Furthermore, the interpretation of phase contrast from images generated with AFM tapping mode appears to be an effective tool to gain an improved understanding of the structure and property relationship of biological tissues and biomaterials at the micro- and nano-scale

Measuring the dynamic mechanical response of hydrated mouse bone by nanoindentation

This study demonstrates a novel approach to characterizing hydrated bone's viscoelastic behavior at lamellar length scales using dynamic indentation techniques. We studied the submicron-level viscoelastic response of bone tissue from two different inbred mouse strains, A/J and B6, with known differences in whole bone and tissue-level mechanical properties. Our results show that bone having a higher collagen content or a lower mineral-to-matrix ratio demonstrates a trend towards a larger viscoelastic response. When normalized for anatomical location relative to biological growth patterns in the antero-medial (AM) cortex, bone tissue from B6 femora, known to have a lower mineral-to-matrix ratio, is shown to exhibit a significantly higher viscoelastic response compared to A/J tissue. Newer bone regions with a higher collagen content (closer to the endosteal edge of the AM cortex) showed a trend towards a larger viscoelastic response. Our study demonstrates the feasibility of this technique for analyzing local composition-property relationships in bone. Further, this technique of viscoelastic nanoindentation mapping of the bone surface at these submicron length scales is shown to be highly advantageous in studying subsurface features, such as porosity, of wet hydrated biological specimens, which are difficult to identify using other methods

Scanning Probe Microscopy of Biomaterials and Nanoscale Biomechanics

Atomic force microscope (AFM) has emerged as a powerful tool in the last two decades to study biological materials at the nanoscale. The high resolution imaging capability and high precision force sensitivity of AFM makes it a unique tool for the assessment of characteristic properties of extremely small and soft biological materials. In this dissertation, AFM was utilized to systematically study individual collagen fibrils and cortical bone samples at the nanoscale with the focus on their mechanical and electromechanical properties. Furthermore, a new nanoneedle-based AFM technique was demonstrated to image soft materials such as membrane of living cells in physiological conditions. As the most abundant protein in mammals, type I collagen is a fibrous protein (with in diameter) functioning as one of the main components of bone, tendon, skin, and cornea. In the structural organization of collagen molecules within a collagen fibril there exist alternating zones of gap and overlap in the axial direction of a collagen fibril with a periodicity. This special microstructure has been shown to be of significant importance in multi-functionality of collagen fibrils in tissues with different mechanical requirements. In this dissertation, using high resolution nanoindentation with AFM, nanomechanical heterogeneity along the axial direction of a collagen fibril was revealed; it was shown that the gap and overlap regions have significantly different elastic and energy dissipation properties, correlating the significantly different molecular structures in these two regions. It was further shown that such subfibrillar heterogeneity holds in collagen fibrils inside bone and might be intrinsically related to the excellent energy dissipation performance of bone. Using piezoresposne force microscopy (PFM), the electromechanical properties of a collagen fibril was probed and it was revealed that a single collagen fibril behaves predominantly as a shear piezoelectric material, and has unipolar axial polarization throughout its entire length. Furthermore, it was revealed that there existed an intrinsic piezoelectric heterogeneity within a collagen fibril coinciding with the periodic variation of its gap and overlap regions. This piezoelectric heterogeneity persisted for the collagen fibrils embedded in bone, bringing about new implications for its possible roles in structural formation and remodeling of bone. Since its invention, operation of AFM in liquid for imaging soft biomaterials has been hindered by a low quality factor caused by large drag forces on the cantilever. Utilizing the small dimensions of a nanoneedle, the new method presented in this dissertation resolves the complications by keeping the cantilever outside of the liquid and using a nanoneedle attached to the AFM probe as the sensing element in liquid. It was shown that this method in liquid maintained the harmonic dynamic characteristics of the cantilever similar to that in air and had an intrinsic high quality factor. The performance of the new method is demonstrated through imaging single collagen fibrils in liquid as well as the extremely soft membrane of living cells under physiological conditions

Formidable Challenges in Additive Manufacturing of Solid Oxide Electrolyzers (SOECs) and Solid Oxide Fuel Cells (SOFCs) for Electrolytic Hydrogen Economy toward Global Decarbonization

Solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs) are the leading high-temperature devices to realize the global “Hydrogen Economy”. These devices are inherently multi-material (ceramic and cermets). They have multi-scale, multilayer configurations (a few microns to hundreds of microns) and different morphology (porosity and densification) requirements for each layer. Adjacent layers should exhibit chemical and thermal compatibility and high-temperature mechanical stability. Added to that is the need to stack many cells to produce reasonable power. The most critical barriers to widespread global adoption of these devices have been their high cost and issues with their reliability and durability. Given their complex structure and stringent requirements, additive manufacturing (AM) has been proposed as a possible technological path to enable the low-cost production of durable devices to achieve economies of scale. However, currently, there is no single AM technology capable of 3D printing these devices at the complete cell level or, even more difficult, at the stack level. This article provides an overview of challenges that must be overcome for AM to be a viable path for the manufacturing of SOECs and SOFCs. A list of recommendations is provided to facilitate such efforts

Scanning Probe Microscopy of Biomaterials and Nanoscale Biomechanics

126 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2010.Since its invention, operation of AFM in liquid for imaging soft biomaterials has been hindered by a low quality factor caused by large drag forces on the cantilever. Utilizing the small dimensions of a nanoneedle, the new method presented in this dissertation resolves the complications by keeping the cantilever outside of the liquid and using a nanoneedle attached to the AFM probe as the sensing element in liquid. It was shown that this method in liquid maintained the harmonic dynamic characteristics of the cantilever similar to that in air and had an intrinsic high quality factor. The performance of the new method is demonstrated through imaging single collagen fibrils in liquid as well as the extremely soft membrane of living cells under physiological conditions.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Scanning Probe Microscopy of Biomaterials and Nanoscale Biomechanics

126 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2010.Since its invention, operation of AFM in liquid for imaging soft biomaterials has been hindered by a low quality factor caused by large drag forces on the cantilever. Utilizing the small dimensions of a nanoneedle, the new method presented in this dissertation resolves the complications by keeping the cantilever outside of the liquid and using a nanoneedle attached to the AFM probe as the sensing element in liquid. It was shown that this method in liquid maintained the harmonic dynamic characteristics of the cantilever similar to that in air and had an intrinsic high quality factor. The performance of the new method is demonstrated through imaging single collagen fibrils in liquid as well as the extremely soft membrane of living cells under physiological conditions.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD