Liquid crystal elastomer coatings with programmed response of surface profile

Stimuli-responsive liquid crystal elastomers (LCEs) with a strong coupling of orientational molecular order and rubber-like elasticity, show a great potential as working elements in soft robotics, sensing, transport and propulsion systems. We demonstrate a dynamic thermal control of the surface topography of LCE coatings achieved through pre-designed patterns of in-plane molecular orientation. These patterns determine whether the LCE coating develops elevations, depressions, or in-plane deformations. The deterministic dependence of the out-of-plane dynamic surface profile on the in-plane orientational pattern is explained by activation forces. These forces are caused by two factors: (i) stretching-contraction of the polymer networks driven by temperature; (ii) spatially varying orientation of the LCE. The activation force concept brings the responsive LCEs into the domain of active matter. The demonstrated relationship can be used to design programmable coatings with functionalities that mimic biological tissues such as skin

Sensor technologies for quality control in engineered tissue manufacturing

The use of engineered cells, tissues, and organs has the opportunity to change the way injuries and diseases are treated. Commercialization of these groundbreaking technologies has been limited in part by the complex and costly nature of their manufacture. Process-related variability and even small changes in the manufacturing process of a living product will impact its quality. Without real-time integrated detection, the magnitude and mechanism of that impact are largely unknown. Real-time and non-destructive sensor technologies are key for in-process insight and ensuring a consistent product throughout commercial scale-up and/or scale-out. The application of a measurement technology into a manufacturing process requires cell and tissue developers to understand the best way to apply a sensor to their process, and for sensor manufacturers to understand the design requirements and end-user needs. Furthermore, sensors to monitor component cells’ health and phenotype need to be compatible with novel integrated and automated manufacturing equipment. This review summarizes commercially relevant sensor technologies that can detect meaningful quality attributes during the manufacturing of regenerative medicine products, the gaps within each technology, and sensor considerations for manufacturing

Temperature dependence of bend elastic constant in oblique helicoidal cholesterics

Elastic moduli of liquid crystals, known as Frank constants, are of quintessential importance for understanding fundamental properties of these materials and for the design of their applications. Although there are many methods to measure the Frank constants in the nematic phase, little is known about the elastic constants of the chiral version of the nematic, the so-called cholesteric liquid crystal, since the helicoidal structure of the cholesteric renders these methods inadequate. Here we present a technique to measure the bend modulus K33 of cholesterics that is based on the electrically tunable reflection of light at an oblique helicoidal ChOH cholesteric structure. K33 is typically smaller than 0.6 pN, showing a nonmonotonous temperature dependence with a slight increase near the transition to the twist-bend phase. K33 depends strongly on the molecular composition. In particular, chiral mixtures that contain the flexible dimer 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) heptane (CB7CB) and rodlike molecules such as pentylcyanobiphenyl (5CB) show a K33 value that is 5 times smaller than K33 of pure CB7CB or of mixtures of CB7CB with chiral dopants. Furthermore, K33 in CB11CB doped with a chiral agent is noticeably smaller than K33 in a similarly doped CB7CB which is explained by the longer flexible link in CB11CB. The proposed technique allows a direct in-situ determination of how the molecular composition, molecular structure and molecular chirality affect the elastic properties of chiral liquid crystals

Tuning selective reflection of light by surface anchoring in cholesteric cells with oblique helicoidal structures

Selective reflection of light by oblique helicoidal cholesteric (ChOH) can be tuned in a very broad spectral range by an applied electric field. In this work, we demonstrate that the peak wavelength of the selective reflection can be controlled by surface alignment of the director in sandwich cells. The peak wavelength is blue-shifted when the surface alignment is perpendicular to the bounding plates and red-shifted when it is planar. The effect is explained by the electric field redistribution within the cell caused by spatially varying heliconical ChOH structure. The observed phenomenon can be used in sensing applications

Pretransitional behavior of viscoelastic parameters at the nematic to twist-bend nematic phase transition in flexible: N -mers

© 2019 the Owner Societies. We report dynamic light scattering measurements of the orientational (Frank) elastic constants and associated viscosities among a homologous series of a liquid crystalline dimer, trimer, and tetramer exhibiting a uniaxial nematic (N) to twist-bend nematic (NTB) phase transition. The elastic constants for director splay (K11), twist (K22) and bend (K33) exhibit the relations K11 > K22 > K33 and K11/K22 > 2 over the bulk of the N phase. Their behavior near the N-NTB transition shows dependency on the parity of the number (n) of the rigid mesomorphic units in the flexible n-mers. Namely, the bend constant K33 in the dimer and tetramer turns upward and starts increasing close to the transition, following a monotonic decrease through most of the N phases. In contrast, K33 for the trimer flattens off just above the transition and shows no pretransitional enhancement. The twist constant K22 increases pretransitionally in both even and odd n-mers, but more weakly so in the trimer, while K11 increases steadily on cooling without evidence of pretransitional behavior in any n-mer. The viscosities associated with pure splay, twist-dominated twist-bend, and pure bend fluctuations in the N phase are comparable in magnitude to those of rod-like monomers. All three viscosities increase with decreasing temperature, but the bend viscosity in particular grows sharply near the N-NTB transition. The N-NTB pretransitional behavior is shown to be in qualitative agreement with the predictions of a coarse-grained theory, which models the NTB phase as a "pseudo-layered" structure with the symmetry (but not the mass density wave) of a smectic-A∗ phase

Nondestructive testing of native and tissue-engineered medical products: adding numbers to pictures.

Traditional destructive tests are used for quality assurance and control within manufacturing workflows. Their applicability to biomanufacturing is limited due to inherent constraints of the biomanufacturing process. To address this, photo- and acoustic-based nondestructive testing has risen in prominence to interrogate not only structure and function, but also to integrate quantitative measurements of biochemical composition to cross-correlate structural, compositional, and functional variances. We survey relevant literature related to single-mode and multimodal nondestructive testing of soft tissues, which adds numbers (quantitative measurements) to pictures (qualitative data). Native and tissue-engineered articular cartilage is highlighted because active biomanufacturing processes are being developed. Included are recent efforts and prominent trends focused on technologies for clinical and in-process biomanufacturing applications

Nondestructive testing of native and tissue-engineered medical products: adding numbers to pictures.

Traditional destructive tests are used for quality assurance and control within manufacturing workflows. Their applicability to biomanufacturing is limited due to inherent constraints of the biomanufacturing process. To address this, photo- and acoustic-based nondestructive testing has risen in prominence to interrogate not only structure and function, but also to integrate quantitative measurements of biochemical composition to cross-correlate structural, compositional, and functional variances. We survey relevant literature related to single-mode and multimodal nondestructive testing of soft tissues, which adds numbers (quantitative measurements) to pictures (qualitative data). Native and tissue-engineered articular cartilage is highlighted because active biomanufacturing processes are being developed. Included are recent efforts and prominent trends focused on technologies for clinical and in-process biomanufacturing applications