9 research outputs found
Microfabrication of Custom Collagen Structures Capable of Guiding Cell Morphology and Alignment
The patterning of biological components
into structural analogues
of native tissues to simulate an environment for directing cell growth
is one important strategy in biomaterials fabrication. It is widely
accepted that chemical, mechanical, and topological cues from the
extracellular matrix (ECM) provide important signals for guiding cells
to exhibit characteristic polarity, orientation, and morphology. To
fully understand the delicate relationship between cell behavior and
ECM features, biomaterials fabrication requires improved techniques
for tailoring nano/microstructured patterns from relevant biological
building blocks rather than using nonbiological materials. Here we
reveal a unique approach for the nano/microfabrication of custom patterned
biomaterials using collagen as the sole building material. With this
new fabrication technique, we further revealed that custom collagen
patterns could direct the orientation and morphology of fibroblast
growth as a function of vertex density and pattern spacing. Our findings
suggest that this technique may be readily adopted for the free form
fabrication of custom cell scaffolds purely from natural biological
molecules including collagen, among other relevant ECM components
Controlling and Assessing the Surface Display of Cell-Binding Domains on Magnetite Conjugated Fluorescent Liposomes
Biological systems provide us with
a diverse source of peptide-based
ligands for cellular adhesion. Controlling and assessing the ligand
surface density as well as tailoring the surface chemistry to have
specific cellular adhesion properties are important in biomaterials
design. In the following work, we provide a means for displaying peptide-based
ligands on magnetic liposomes in which the surface density and chemistry
may be controlled. Simultaneously, the conjugated vesicles provide
a fluorescent signal for examining steric hindrance among surface
ligands. In addition, the inherent magnetic and fluorescence features
of this system revealed potential for magnet-based cell isolation
and fluorescent labeling of adhered cells, respectively. Adhered cells
were found to remain viable and proliferative, thereby allowing them
to be used for subsequent evaluation. In a specific demonstration,
we control the density of fibronectin-mimetic ligands on the polydiacetylene
liposome surfaces. We find that steric limitation occurring at over
20% surface density result in decreased cell adhesion, in accord with
related techniques. The magnetic-liposome system offers the means
for not only separating cells adhered to the biomaterial, but also
providing the ability to control and assess the biomaterial surface.
This may prove particularly useful for examining combinations of peptide-based
ligands or for evaluating the molecular-level ligand accessibility
and its effect on cell attachment to a biomaterial surface
Controlled Supramolecular Assembly of Helical Silica Nanotube–Graphene Hybrids for Chiral Transcription and Separation
Chiral templating and enantioselective separations are demonstrated on graphene surfaces as directed by encapsulated silica nanotubes. Electrostatic assembly of helical silica nanotubes within graphene sheets results in a hybrid material with the electrochemical properties of graphene and the capability for chiral recognition. Control of the silica nanotube helicity within the graphene hybrid provides a means for directed chiral templating of guest molecules on the outer graphene surface as revealed in the chiral transcription of <i>N</i><sup>1</sup>,<i>N</i><sup>3</sup>,<i>N</i><sup>5</sup>-tri(4-pyridinyl)cyclohexane-1,3,5-tricarboxamide as well as polyallylamine into supramolecular templated assemblies. Changing the helicity of the internal nanotube also provides control over enantiomer selectivity as demonstrated by the chiral separation of racemic mixtures of phenylalanine, tryptophan, and alanine derivatives
Reinforcement of a Sugar-Based Bolaamphiphile/Functionalized Graphene Oxide Composite Gel: Rheological and Electrochemical Properties
A sugar-based bolaamphiphile/graphene
oxide composite hydrogel
has been prepared using simple mixing. Unlike the corresponding sugar-based
native gel, the composite gel exhibits a fibrillar structure with
a 10–20 nm fiber diameter. The composite gel forms an interdigitated
bilayer structure incorporating intermolecular hydrogen-bonding interactions.
The composite gel formation did not change the beneficial electrical
properties of graphene offering the potential for integration of this
new material into electronic systems. Interestingly, the mechanical
and electrochemical properties of the composite gel are both dramatically
enhanced when compared to the native gel, thereby reflecting that
the functionalized graphene oxide layers are efficiently intercalated
within the composite gel structure
Chiral Arrangement of Achiral Au Nanoparticles by Supramolecular Assembly of Helical Nanofiber Templates
Chiral
materials composed of organized nanoparticle superstructures
have promising applications to photonics and sensing. Reliable customization
of the chiroptical properties of these materials remains an important
goal; hence, we report a customizable scheme making use of modular
gelator components for controlling the helicity and formation of nanofibers
over long length scales resulting in hydrogel templates. Controlled
growth of gold nanoparticles at spatially arranged locations along
the nanofiber is achieved by UV reduction of AuÂ(I) ions on the supramolecular
templates. The resulting materials were found to have significant
interparticle interactions and well-defined helicity to provide high
quality, chiroptically active materials. With this novel approach,
the tailored assembly of nanoparticle superstructures with predictable
chiroptical properties can be realized in high yield, which we expect
to allow rapid advancement of chiral nanomaterials research
Luminescent Calix[4]arene-Based Metallogel Formed at Different Solvent Composition
We
have synthesized a calix[4]Âarene derivative (<b>1</b>)
containing terpyridine and showed that gelation occurred in the presence
of Pt<sup>2+</sup> in DMSO/H<sub>2</sub>O of varying compositions.
Gelation was presumably mediated by the Pt–Pt and π–π
stacking interactions. The scanning electron microscopy image of the
xerogel showed a spherical structure with diameter of 1.8–2.1
μm. Interestingly, the metallogel showed strong luminescence
enhancement, which was dependent on the DMSO/H<sub>2</sub>O ratio
of the solvent. We examined the effects of concentration, temperature,
and time resolution on the luminescence emission of both the gel <b>1</b>-Pt<sup>2+</sup> and the sol <b>1</b>-Pt<sup>2+</sup>. The luminescence lifetimes of the metallogel were particularly
long, on the order of several microseconds. The luminescence lifetimes
were also strongly dependent on the solvent composition. We also determined
the thermodynamic parameters for the self-assembly of the gel by the
Birks kinetic scheme. Furthermore, the rheological properties of the
metallogels in the presence of more than 4.0 equiv of Pt<sup>2+</sup> were independent of the concentration of Pt<sup>2+</sup> applied
Determining Chiral Configuration of Diamines via Contact Angle Measurements on Enantioselective Alanine-Appended Benzene-Tricarboxamide Gelators
Spectroscopic
techniques exist that may discern between enantiomers
and assess chiral purity. A nonspectroscopic approach that may be
directly observed could provide numerous benefits. Using chiral alanine-appended
benzene-tricarboxamide gelators, we reveal a methanol gel system that
is capable of providing visual discrimination between enantiomers
of various diamines. Specifically, gelation is induced by supramolecular
nanofiber assembly resulting from interaction between a chiral gelator
and a diamine of opposing chirality (i.e., a heterochiral system).
Upon further implementing the chiral gelator in electrospun fibers
as solid state films, we revealed enantioselective surface wetting
properties that allowed for determining chirality through contact
angle measurements. While these two approaches of observable gelation
and surface wetting offer nonspectroscopic approaches, we also find
that the supramolecular nanofiber assembly was able to enhance the
induced circular dichroism signal resulting from addition of chiral
diamines, allowing precise quantification of their enantiomeric purity
Ultraviolet Patterned Calixarene-Derived Supramolecular Gels and Films with Spatially Resolved Mechanical and Fluorescent Properties
Supramolecular
assemblies have in the past been considered mechanically
weak and in most cases unable to withstand their own weight. Calixarene-derived
networks can, however, provide robust supramolecular gels. Incorporating
a photoreactive stilbene moiety, we show that the aggregation state
of the material can be tuned by heating and UV exposure in order to
control the mechanical as well as the fluorescent properties. Regulating
the extent of heating to control the proportion of H-aggregates and
J-aggregates and further cross-linking of H-aggregates by control
over UV exposure allows for adjustable photopatterning of the fluorescence
as well as the material stiffness in the range from ∼100 to
450 kPa. We expect this straightforward supramolecular system will
be suitable for advanced prototyping in applications where modulus
and shape are important design criteria
Self-Assembled Tb<sup>3+</sup> Complex Probe for Quantitative Analysis of ATP during Its Enzymatic Hydrolysis via Time-Resolved Luminescence in Vitro and in Vivo
To
more accurately assess the pathways of biological systems, a probe
is needed that may respond selectively to adenosine triphosphate (ATP)
for both in vitro and in vivo detection modes. We have developed a
luminescence probe that can provide real-time information on the extent
of ATP, ADP, and AMP by virtue of the luminescence and luminescence
lifetime observed from a supramolecular polymer based on a <i>C</i><sub>3</sub> symmetrical terpyridine complex with Tb<sup>3+</sup> (<b>S1-Tb</b>). The probe shows remarkable selective
luminescence enhancement in the presence of ATP compared to other
phosphate-displaying nucleotides including adenosine diphosphate (ADP),
adenosine monophosphate (AMP), guanosine triphosphate (GTP), thymidine
triphosphate (TTP), H<sub>2</sub>PO<sub>4</sub><sup>–</sup> (Pi), and pyrophosphate (PPi). In addition, the time-resolved luminescence
lifetime and luminescence spectrum of <b>S1-Tb</b> could facilitate
the quantitative measurement of the exact amount of ATP and similarly
ADP and AMP within living cells. The time-resolved luminescence lifetime
of <b>S1-Tb</b> could also be used to quantitatively monitor
the amount of ATP, ADP, and AMP in vitro following the enzymatic hydrolysis
of ATP. The long luminescence lifetime, which was observed into the
millisecond range, makes this <b>S1-Tb</b>-based probe particularly
attractive for monitoring biological ATP levels in vivo, because any
short lifetime background fluorescence arising from the complex molecular
environment may be easily eliminated