3D Bundle Research Articles

Spatially Confined Assembly and Immobilization of Hierarchical Nanoparticle Architectures inside Microdroplets in Magnetic Fields.

Magnetic field-directed colloidal interactions offer facile tools for assembly of structures that range from linear chains to multidimensional hierarchical architectures. While the field-driven assembly of colloidal particles has commonly been investigated in unbounded media, a knowledge gap remains concerning such assembly in confined microenvironments. Here, we investigate how confinement of ferromagnetic nanoparticles in microspheres directs their magnetic assembly into hierarchical architectures. Microdroplets from polydimethylsiloxane (PDMS) liquid precursor containing dispersed iron oxide magnetic nanoparticles (MNPs) were placed in a static magnetic field leading to the formation of organized assemblies inside the host droplets. By changing the MNP concentrations, we revealed a sequence of microstructures inside the droplets, ranging from linear chains at a low MNP loading, transitioning to a combination of chains and networked bundles, to solely 3D bundles at high MNP loading. These experimental results were analyzed with the aid of COMSOL simulations where we calculated the potential energy to identify the preferred assembly conformations. The chains at high MNP loading minimized their energy by aggregating laterally to form bundles with their MNP dipoles being out-of-registry. We cured these PDMS droplets to immobilize the assemblies by forming soft microbeads. These microbeads constitute an "interaction toolbox" with different magnetic macroscale responses, which are governed by the structuring of the MNPs and their magnetic polarizability. We show that thanks to their ability to rotate by field-induced torque under a rotating field, these microbeads can be employed in applications such as optical modulators and microrollers.

Bioinspired scaffolds based on aligned polyurethane nanofibers mimic tendon and ligament fascicles.

Topographical factors of scaffolds play an important role in regulating cell functions. Although the effects of alignment topography and three-dimensional (3D) configuration of nanofibers as well as surface stiffness on cell behavior have been investigated, there are relatively few reports that attempt to understand the relationship between synergistic effects of these parameters and cell responses. Herein, the influence of biophysical and biomechanical cues of electrospun polyurethane (PU) scaffolds on mesenchymal stem cells (MSCs) activities was evaluated. To this aim, multiscale bundles were developed by rolling up the aligned electrospun mats mimicking the fascicles of tendons/ligaments and other similar tissues. Compared to mats, the 3D bundles not only maintained the desirable topographical features (i.e., fiber diameter, fiber orientation, and pore size), but also boosted tensile strength (∼40MPa), tensile strain (∼260%), and surface stiffness (∼1.75MPa). Alignment topography of nanofibers noticeably dictated cell elongation and a uniaxial orientation, resulting in tenogenic commitment of MSCs. MSCs seeded on the bundles expressed higher levels of tenogenic markers compared to mats. Moreover, the biomimetic bundle scaffolds improved synthesis of extracellular matrix components compared to mats. These results suggest that biophysical and biomechanical cues modulate cell-scaffold interactions, providing new insights into hierarchical scaffold design for further studies.

Self-Adaptive Weighted Rank-Defect 3D Bundle Adjustment of Laser Tracker

Self-Adaptive Weighted Rank-Defect 3D Bundle Adjustment of Laser Tracker

Oriented Attachment of Calcite Nanocrystals: Formation of Single-Crystalline Configurations as 3D Bundles via Lateral Stacking of 1D Chains.

The formation of single-crystalline configurations by the oriented attachment of calcite was experimentally demonstrated as 3D bundles in a nonaqueous system. In the initial stage, 1D short chains elongated in the c direction were formed through the primary oriented attachment of calcite nanoblocks ∼30 nm in diameter. The 3D bundles were then produced through subsequent side-by-side oriented attachment of the 1D chains in the progressive stage. Finally, micrometer-sized single-crystalline architectures were constructed via large-scale oriented attachment of the nanoscale building blocks with a decrease in repulsion force due to the surface charge.

Model simulation of the SPOC wave in a bundle of striated myofibrils.

SPOC (spontaneous oscillatory contraction) is a phenomenon observed in striated muscle under intermediate activation conditions. Recently, we constructed a theoretical model of SPOC for a sarcomere, a unit sarcomere model, which explains the behavior of SPOC at each sarcomere level. We also constructed a single myofibril model, which visco-elastically connects the unit model in series, and explains the behaviors of SPOC at the myofibril level. In the present study, to understand the SPOC properties in a bundle of myofibrils, we extended the single myofibril model to a two-dimensional (2D) model and a three-dimensional (3D) model, in which myofibrils were elastically connected side-by-side through cross-linkers between the Z-lines and M-lines. These 2D and 3D myofibril models could reproduce various patterns of SPOC waves experimentally observed in a 2D sheet and a 3D bundle of myofibrils only by choosing different values of elastic constants of the cross-linkers and the external spring. The results of these 2D and 3D myofibril models provide insight into the SPOC properties of the higher-ordered assembly of myofibrils.

Investigation of 2D and 3D electrospun scaffolds intended for tendon repair

Two-dimensional (2D) electrospun fibre mats have been investigated as fibrous sheets intended as biomaterials scaffolds for tissue repair. It is recognised that tissues are three-dimensional (3D) structures and that optimisation of the fabrication process should include both 2D and 3D scaffolds. Understanding the relative merits of the architecture of 2D and 3D scaffolds for tendon repair is required. This study investigated three different electrospun scaffolds based on poly(ε-caprolactone) fibres intended for repair of injured tendons, referred to as; 2D random sheet, 2D aligned sheet and 3D bundles. 2D aligned fibres and 3D bundles mimicked the parallel arrangement of collagen fibres in natural tendon and 3D bundles further replicated the tertiary layer of a tendon's hierarchical configuration. 3D bundles demonstrated greatest tensile properties, being significantly stronger and stiffer than 2D aligned and 2D random fibres. All scaffolds supported adhesion and proliferation of tendon fibroblasts. Furthermore, 2D aligned sheets and 3D bundles allowed guidance of the cells into a parallel, longitudinal arrangement, which is similar to tendon cells in the native tissue. With their superior physical properties and ability to better replicate tendon tissue, the 3D electrospun scaffolds warrant greater investigation as synthetic grafts in tendon repair.

Ion specific effects in bundling and depolymerization of taxol-stabilized microtubules

Microtubules (MTs) are nanometer scale hollow cylindrical biological polyelectrolytes. They are assembled from alpha/beta-tubulin dimers, which stack to form protofilaments (PFs) with lateral interactions between PFs resulting in the curved MT. In cells, MTs and their assemblies are critical components in a range of functions from providing tracks for the transport of cargo to forming the spindle structure during mitosis. Previous studies have, shown that while cations with valence equal to or larger than 3+ tend to assemble tight 3D bundles of taxol-stabilized MTs, certain divalent cations induce relatively loose 2D bundles of different symmetry (D. J. Needleman et al., Proc. Natl. Acad. Sci. U. S. A., 2004, 101, 16099). Similarly, divalent cations form 2D bundles of DNA adsorbed on cationic membranes (I. Koltover et al., Proc. Natl. Acad. Sci. U. S. A., 2000, 97, 14046). The bundling behavior for these biological polyelectrolyte systems is qualitatively in agreement with current theory. Here, we present results which show that, unlike the case for DNA adsorbed on cationic membranes, bundling of taxol-stabilized MTs occurs only for certain divalent cations above a critical ion concentration (e.g. Ca2+, Sr2+, Ba2+). Instead, many divalent cations pre-empt the bundling transition and depolymerize taxol-stabilized MTs at a lower counterion concentration. Although previous cryogenic TEM has shown that, in the absence of taxol, Ca2+ depolymerizes MTs assembling in buffers containing GTP (guanosine triphosphate), our finding is surprising given the know stabilizing effects of taxol on GDP (guanosine diphosphate)-MTs. The ion concentration required for MT depolymerization decreases with increasing atomic number for the divalents Mg2+, Mn2+, Co2+, and Zn2+. GdCl3 (3+) is found to be extremely efficient at MT depolymerization requiring ion concentrations of about 1 mM, while oligolysine(2+), is observed not to depolymerize MTs at concentrations as high as 144 mM. The surprising MT depolymerization results are discussed in the context of divalents either disrupting lateral interactions between PFs (which are strengthened for taxol containing beta-tubulin) or interfering with taxol's ability to induce flexibility at the interface between two tubulin dimers in the same PF (which has been recently suggested as a mechanism by which taxol stabilizes MTs post-hydrolysis with the induced flexibility counteracting the kink between GDP-tublin dimers in a PF).

Superresolution Investigation of In Vivo Structure and Dynamics of E. coli FtsZ Structures during Cytokinesis

Control of E. coli cell division is achieved by a network of proteins that organize cytokinesis in space and time. FtsZ, a tubulin-like GTPase that forms head-to-tail protofilaments, localizes to the midcell and assembles into a ring-like structure known as the Z-ring. The Z-ring serves as an essential scaffold to recruit all other division proteins and generates contractile force for cytokinesis, but its supramolecular structure and contraction mechanism remain unknown. We have used photoactivated localization microscopy (PALM) to characterize the in vivo structural dynamics of the Z-ring in E. coli at a spatial resolution of ∼35 nm.Superresolution imaging revealed that the Z-ring is ∼110nm wide and is composed of a loose 3D bundle of FtsZ protofilaments that overlap with each other in both the longitudinal and radial directions in the cell. These 110nm rings were observed in either a single-ring conformation at midcell or in a multiple-ring conformation reminiscent of a tight helix. The tight helix conformation was very rarely observed in cells with a visible septation, suggesting that the Z-ring fluctuates between the single-ring and tight helix conformation before cytokinesis begins, but then adopts only the single-ring conformation during constriction. We also observed non-ringlike FtsZ structures emanating from the midcell in cells at later stages of constriction, indicating Z-ring disassembly. These disassembling structures were observed in cells with 200-600nm septum diameters, suggesting that Z-ring disassembly occurs gradually throughout the constriction process. We also observed that the bandwidth distribution of the Z-ring did not change with varying expression levels, cell size, or during the progression of cytokinesis, suggesting that the factors that regulate Z-ring thickness are not affected by FtsZ concentration or changes in cell shape.

Physicochemical characterisation of degrading polycaprolactone scaffolds

A degradation study investigating the hydrolysis of different scaffolds of polycaprolactone suspended in phosphate buffer solution at 37 °C was performed over a three month period. Structures included electrospun fibres, held as 2D mats and 3D bundles, and solvent cast films. These structures and their surrounding solutions were physiochemically characterised using a range of techniques. Changes in scaffold physicochemical properties were observed over the course of the study, including significant loss in molecular mass, increases in thermal properties and crystallinity, and increases in tensile properties. The presence of degradation products, such as capronic acid containing compounds was also identified in the surrounding solution. 3D electrospun bundles - as a consequence of being the least crystalline scaffold and hence most susceptible to hydrolysis – demonstrated greatest reduction in molecular mass over the three months, followed by 2D electrospun mats, and the lowest mass loss was observed for solvent cast films.

3D bundles of self-assembled lanthanum hydroxide nanorods via a rapid microwave-assisted route

Three-dimensional (3D) bundles of self-assembled lanthanum hydroxide nanorods with average crystallite size of about 20 nm were fabricated via a facile and rapid microwave-assisted chemical route. The obtained material was characterized with X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. The obtained nanorods have average diameter of about 115 nm and average length of about 730 nm. Self-assembly of primary La(OH) 3 nanoparticles and their subsequent anisotropic growth along 〈2 0 0〉 direction, was proposed to be the mechanism for the formation of 3D bundles of nanorods, using TEM images. The thermal behavior of the obtained La(OH) 3 powder was also investigated by differential thermal analysis and thermal gravimetric (DTA/TG) method.

Surface Tension Driven Self-Assembly of Bundles and Networks of 200 nm Diameter Rods Using a Polymerizable Adhesive

This letter demonstrates the first utilization of surface tension based self-assembly on the 200 nm scale to form mechanically stable aggregates comprised of metallic rods. The self-assembly occurs as a result of the minimization of interfacial tension of liquid layers of a hydrophobic polymerizable adhesive that is precipitated on the rods. After the assembly, the adhesive is polymerized to form permanently bonded aggregates. Depending on the patterning of the rods and the chemical functionalization used, either closed 3D bundles or open 2D networks can be formed.