Prolate and oblate chiral liquid crystal spheroids.

Liquid crystals are known to exhibit intriguing textures and color patterns, with applications in display and optical technologies. This work focuses on chiral materials and examines the palette of morphologies that arises when microdroplets are deformed into nonspherical shapes in a controllable manner. Specifically, geometrical confinement and mechanical strain are used to manipulate orientational order, phase transitions, and topological defects that arise in chiral liquid crystal droplets. Inspired by processes encountered in nature, where insects and animals often rely on strain and temperature to alter the optical appearance of dispersed liquid crystalline elements, chiral droplets are dispersed in polymer films and deformation induced by uniaxial or biaxial stretching. Our measurements are interpreted by resorting to simulations of the corresponding systems, thereby providing an in-depth understanding of the morphologies that arise in these materials. The reported structures and assemblies offer potential for applications in smart coatings, smart fabrics, and wearable sensors.

A pH-Triggered, Self-Assembled, and Bioprintable Hybrid Hydrogel Scaffold for Mesenchymal Stem Cell Based Bone Tissue Engineering.

Effective bone tissue engineering can restore bone and skeletal functions that are impaired by traumas and/or certain medical conditions. Bone is a complex tissue and functions through orchestrated interactions between cells, biomechanical forces, and biofactors. To identify ideal scaffold materials for effective mesenchymal stem cell (MSC)-based bone tissue regeneration, here we develop and characterize a composite nanoparticle hydrogel by combining carboxymethyl chitosan (CMCh) and amorphous calcium phosphate (ACP) (designated as CMCh-ACP hydrogel). We demonstrate that the CMCh-ACP hydrogel is readily prepared by incorporating glucono δ-lactone (GDL) into an aqueous dispersion or rehydrating the acidic freeze-dried nanoparticles in a pH-triggered controlled-assembly fashion. The CMCh-ACP hydrogel exhibits excellent biocompatibility and effectively supports MSC proliferation and cell adhesion. Moreover, while augmenting BMP9-induced osteogenic differentiation, the CMCh-ACP hydrogel itself is osteoinductive and induces the expression of osteoblastic regulators and bone markers in MSCs in vitro. The CMCh-ACP scaffold markedly enhances the efficiency and maturity of BMP9-induced bone formation in vivo, while suppressing bone resorption occurred in long-term ectopic osteogenesis. Thus, these results suggest that the pH-responsive self-assembled CMCh-ACP injectable and bioprintable hydrogel may be further exploited as a novel scaffold for osteoprogenitor-cell-based bone tissue regeneration.

Thermoresponsive Citrate-Based Graphene Oxide Scaffold Enhances Bone Regeneration from BMP9-Stimulated Adipose-Derived Mesenchymal Stem Cells.

Effective bone tissue engineering is important to overcome the unmet clinical challenges as more than 1.6 million bone grafts are done annually in the United States. Successful bone tissue engineering needs minimally three critical constituents: osteoprogenitor cells, osteogenic factors, and osteoinductive/osteoconductive scaffolds. Osteogenic progenitors are derived from multipotent mesenchymal stem cells (MSCs), which can be prepared from numerous tissue sources, including adipose tissue. We previously showed that BMP9 is the most osteogenic BMP and induces robust bone formation of immortalized mouse adipose-derived MSCs entrapped in a citrate-based thermoresponsive hydrogel referred to as PPCNg. As graphene and its derivatives emerge as promising biomaterials, here we develop a novel thermosensitive and injectable hybrid material by combining graphene oxide (GO) with PPCNg (designated as GO-P) and characterize its ability to promote bone formation. We demonstrate that the thermoresponsive behavior of the hybrid material is maintained while effectively supporting MSC survival and proliferation. Furthermore, GO-P induces early bone-forming marker alkaline phosphatase (ALP) and potentiates BMP9-induced expression of osteogenic regulators and bone markers as well as angiogenic factor VEGF in MSCs. In vivo studies show BMP9-transduced MSCs entrapped in the GO-P scaffold form well-mineralized and highly vascularized trabecular bone. Thus, these results indicate that GO-P hybrid material may function as a new biocompatible, injectable scaffold with osteoinductive and osteoconductive activities for bone regeneration.

Gelatin-Derived Graphene-Silicate Hybrid Materials Are Biocompatible and Synergistically Promote BMP9-Induced Osteogenic Differentiation of Mesenchymal Stem Cells.

Graphene-based materials are used in many fields but have found only limited applications in biomedicine, including bone tissue engineering. Here, we demonstrate that novel hybrid materials consisting of gelatin-derived graphene and silicate nanosheets of Laponite (GL) are biocompatible and promote osteogenic differentiation of mesenchymal stem cells (MSCs). Homogeneous cell attachment, long-term proliferation, and osteogenic differentiation of MSCs on a GL-scaffold were confirmed using optical microscopy and scanning electron microscopy. GL-powders made by pulverizing the GL-scaffold were shown to promote bone morphogenetic protein (BMP9)-induced osteogenic differentiation. GL-powders increased the alkaline phosphatase (ALP) activity in immortalized mouse embryonic fibroblasts but decreased the ALP activity in more-differentiated immortalized mouse adipose-derived cells. Note, however, that GL-powders promoted BMP9-induced calcium mineral deposits in both MSC lines, as assessed using qualitative and quantitative alizarin red assays. Furthermore, the expression of chondro-osteogenic regulator markers such as Runx2, Sox9, osteopontin, and osteocalcin was upregulated by the GL-powder, independent of BMP9 stimulation; although the powder synergistically upregulated the BMP9-induced Osterix expression, the adipogenic marker PPARγ was unaffected. Furthermore, in vivo stem cell implantation experiments demonstrated that GL-powder could significantly enhance the BMP9-induced ectopic bone formation from MSCs. Collectively, our results strongly suggest that the GL hybrid materials promote BMP9-induced osteogenic differentiation of MSCs and hold promise for the development of bone tissue engineering platforms.

Self-organization of hydrophobic-capped triblock copolymers with a polyelectrolyte midblock: a coarse-grained molecular dynamics simulation study.

We present the results of a Langevin dynamics simulation study of micellar organization and hydrogel formation in the solutions of coarse-grained ABA copolymer chains. Polymer chains are modeled as bead-spring chains of Lennard-Jones particles by explicit treatment of ionic species in implicit solvent. The studied copolymer is composed of a polyelectrolyte midblock flanked by two hydrophobic endblocks. We explore the self-assembly of copolymer solutions at a fixed polymer concentration and temperature upon systematic variation of the midblock charge fraction, valency of neutralizing counterions, and the stiffness and length of hydrophobic endblocks. Minimization of the surface energy, conformational entropy of the midblock chains, electrostatic repulsion of midblock charges, and the translational entropy of counterions are found to play central roles in controlling the self-organization features of copolymer solutions. Flower-like micelles with A-blocks forming the core of spherical aggregates and B-blocks constituting the micelle corona are established for the neutral midblocks. Increasing the charge content of B chains lowers the fraction of loop conformations and yields a spanning hydrogel network with midblocks bridging the hydrophobic clusters. Counterion valence is shown to exert a strong effect on the micelle size and network structure. The increase in the rigidity of terminal A-blocks increases the fraction of bridging chains and results in the formation of a hydrogel network with bundle-like hydrophobic domains. Longer endblocks are shown to increase the hydrophobic cluster size and enhance the bridged midblock fraction. The qualitative agreement between the experimental and theoretical studies is also discussed. The comprehensive molecular picture provides a framework for the future studies of stimuli-responsive copolymer systems.

Unjamming and cell shape in the asthmatic airway epithelium.

From coffee beans flowing in a chute to cells remodelling in a living tissue, a wide variety of close-packed collective systems-both inert and living-have the potential to jam. The collective can sometimes flow like a fluid or jam and rigidify like a solid. The unjammed-to-jammed transition remains poorly understood, however, and structural properties characterizing these phases remain unknown. Using primary human bronchial epithelial cells, we show that the jamming transition in asthma is linked to cell shape, thus establishing in that system a structural criterion for cell jamming. Surprisingly, the collapse of critical scaling predicts a counter-intuitive relationship between jamming, cell shape and cell-cell adhesive stresses that is borne out by direct experimental observations. Cell shape thus provides a rigorous structural signature for classification and investigation of bronchial epithelial layer jamming in asthma, and potentially in any process in disease or development in which epithelial dynamics play a prominent role.

Self-healing fish gelatin/sodium montmorillonite biohybrid coacervates: structural and rheological characterization.

Complex coacervation driven by associative electrostatic interactions was studied in mixtures of exfoliated sodium-montmorillonite (Na(+)-MMT) nanoplatelets and fish gelatin, at a specific mixing ratio and room temperature. Structural and viscoelastic properties of the coacervate phase were investigated as a function of pH by means of different complementary techniques. Independent of the technique used, the results consistently showed that there is an optimum pH value at which the coacervate phase shows the tightest structure with highest elasticity. The solid-like coacervates showed an obvious shear-thinning behavior and network fracture but immediately recovered back into their original elastic character upon removal of the shear strain. The nonlinear mechanical response characterized by single step stress relaxation experiments revealed the same trend for the yield stress and isochronal shear modulus of the coacervates as a function of pH with a maximum at pH 3.0 and lower values at 2.5 and 3.5 pHs, followed by a very sharp drop at pH 4.0. Finally, small-angle X-ray scattering (SAXS) data confirmed that at pHs lower than 4.0 the coacervate phases were dense and structured with a characteristic length scale (ξ(SAXS)) of ~7-9 nm. Comparing the ξ(SAXS) with rheological characteristic length (ξ(rheol)) estimated from low-frequency linear viscoelastic data and network theory, it was concluded that both the strength of the electrostatic interactions and the conformation of the gelatin chains before and during of the coacervation process are responsible for the structure and rigidity of the coacervates.

Synthesis and characterization of gelatin nanoparticles using CDI/NHS as a non-toxic cross-linking system.

Gelatin nanoparticles, cross-linked by a mixture of a water soluble carbodiimide (CDI) and N-hydroxysuccinimide (NHS) as a non-toxic cross-linking system, was prepared. The conventional two step desolvation method with acetone as the non-solvent was used. The mean size and size distribution as well as the morphology of the formed nanoparticles were evaluated and compared with those of nanoparticles cross-linked by glutaraldehyde (GA) as the most commonly used cross-linking agent. Furthermore, intrinsic viscosities of the nanoparticles cross-linked by CDI/NHS and GA were measured and compared under various conditions. The results showed the formation of smoother and more homogeneous nanoparticles with smaller size when CDI/NHS used as cross-linking agent under the same synthesis condition. Moreover, nanoparticles encapsulating paracetamol as a model drug were produced by the two different cross-linking agents and were characterized for drug entrapment and loading efficiencies and in vitro drug release. Both drug entrapment and loading efficiencies was higher in the CDI/NHS cross-linked nanoparticles; however, the release kinetics was comparable to that of nanoparticles cross-linked with GA. The differences in the characteristics of CDI/NHS and GA cross-linked nanoparticles were attributed to the different nature of network structures formed by the two cross-linking agents. On the whole, these results suggested that CDI/NHS cross-linked nanoparticles have high potential to be used for drug delivery application in preference to the nanoparticles synthesized by toxic cross-linking agents.

Preparation of nylon 6-organoclay nanocomposites via in-situ polymerization and investigation of the crystalline and thermal properties.

In this study, organoclay nanocomposites based on two types of organoclay: montmorillonite intercalated with dimethyle, dehydrogenated tallow quaternary ammonium cation (Cloisite 20A) and dimethyl, 2-ethyl hexyl hydrogenated tallow alkyl ammonium cation (Cloisite 30B) with nylon 6 were prepared through in-situ polymerization. In this experiment, no solvents were used during the synthesis, a method which is employed in green chemistry approach. The organoclay was dispersed in molten monomer (caprolactam) and polymerization took place. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermogravimetry analysis (TGA), Fourier Transform Infrared (FT-IR) and Ultra Violet (UV) absorbance techniques were used to characterize the two types of nanocomposites. The full exfoliation morphology of the two nanocomposites was shown by XRD. DSC analysis showed that crystalline structures of PA 6 were predominantly alpha form, with traces of the gamma and beta forms. While the addition of Cloisite 20A increased the amount of gamma and beta forms, Cloisite 30B eliminated crystalline beta form and increased the gamma form, so that gamma form became predominant crystalline form. FT-IR spectroscopy indicated some of the PA chains grafted on to montmorillonite surface modified by ammonium cations bearing hydroxyl groups.