No abstract

Blood loss is the major cause of death in both civilian and battlefield traumas. Methods to staunch bleeding include pressure dressings and absorbent materials. For example, Quik-clot effectively halts bleeding by absorbing large quantities of fluid and concentrating platelets to augment clotting, but these treatments are limited to compressible and exposed wounds. An ideal treatment would halt bleeding only at the injury site, be stable at room temperature, be administered easily, and work effectively for internal injuries. We have developed synthetic platelets, based on ArgGly-Asp functionalized nanoparticles, that halve bleeding time after intravenous administration in a rat model of major trauma. The effects of these synthetic platelets surpass other treatments including recombinant factor VIIa, which is used clinically for uncontrolled bleeding. Synthetic platelets were cleared within 24 hours at a dose of 20 mg/ml, and no complications were seen out to 7 days after infusion, the longest time point studied. These synthetic platelets may be useful for early intervention in trauma and demonstrate the role that nanotechnology can have in addressing unmet medical needs.

Nanocomposite materials consisting of colloidal metal nanoparticles embedded in synthetic polymer hydrogels have attracted attention due to potential applications in catalysis, photonics, electronics, optics, and biomedicine.[1] Here we describe a method for synthesizing nanocomposite materials consisting of colloidal gold (Au) nanoparticles embedded in thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) hydrogels. By incorporating thiol groups that have affinity to both Au 3+ ions and colloidal Au into the PNIPAm hydrogels, we demonstrate specific control over the size, morphology, and long-term stability of the Au nanoparticles by adjusting the concentration of thiols in the hydrogel side chains. Compared with the non-Au-containing PNIPAm hydrogels, the Au±PNIPAm nanocomposite hydrogels display remarkably different bulk properties of equilibrium swelling and thermoresponsive phase transition, which are related to the size and morphology, and possibly the surface charge, of the Au nanoparticles. One approach to synthesizing inorganic nanoparticles with potentially well-defined size and morphology is by using polymeric templates such as porous silica, [2a,b] block copolymers, [2c] dendrimers, [2d] lyotropic liquid crystals, [2e] and nonaqueous polymer resins [2f,g] and gels.

Undecanethiol (C11H23SH) and tri(ethylene glycol)-terminated undecanethiol (HO(C2H4O)3C11H22SH) self-assembled monolayers (SAMs) on clean gold surfaces were prepared and characterized. The SAMs were then immersed into either phosphate-buffered saline or calf serum. The SAM samples were investigated using several analytical techniques at numerous points over the next 35 days. Contact angles and current densities in voltammetry changed dramatically for the PBS samples over the time period, particularly after 21 days. Results indicate substantial loss of the integrity of the SAM. Similar alterations with time were observed for the calf serum samples in both contact angle and voltammetry measurements. X-ray photoelectron spectroscopy indicates that the likely origin is desorption of the alkanethiol moiety as evidenced by appreciable loss of the S 2p signal after 35 days.

The coiled‐coil‐based assembly of gold nanoparticles (see Figure and cover) is demonstrated. Control over the assembly and disassembly of nanostructures is achieved under mild conditions (near‐neutral pH and ambient temperature). The flexibility in design afforded by varying the peptide sequence to produce coiled coils with different stabilities is also highlighted by the generation of more stable binary nanoparticle systems with controlled spacing and architecture.

Electrochemical reactions depending on pH are ideal for illustrating the Nernst equation for undergraduate laboratories. An experiment utilizing the hydroquinone/quinone redox was developed which follows the potentials of the anodic and cathodic cyclic voltammetric waves as a function of solution pH. The 1mM hydroquinone solutions are prepared in phosphate/acetate mixed buffers with pH between 1-6. Cyclic voltammograms were obtained for each solution. As solution pH increases, the anodic and cathodic potentials shift cathodically as predicted by the Nernst equation. Plots of peak potential vs. pH were linear and showed that the hydroquinone/quinone redox reaction involves two electrons.

We report the changes in the structure and thermoresponsive behavior of poly(N-isopropylacrylamide) (PNIPAm) hydrogels when gold nanostructures are synthesized in situ within the hydrogel matrix. Cross-linked PNIPAm hydrogels were synthesized using NIPAm and 0.00-3.50% (w/w versus NIPAm) of N,N'-methylenebisacrylamide (MBAm) and/or N,N'-cystaminebisacrylamide (CBAm) as cross-linking agents. The hydrogels were soaked in potassium tetrachloroaurate to introduce gold ions. The hydrogels containing Au3+ were then immersed in a sodium borohydride solution to reduce the gold ions. Infrared spectroscopy, UV-visible spectroscopy, and equilibrium swelling were used to examine the structural/physical differences between gels of different compositions; UV-visible spectroscopy and mass measurements were used to observe the kinetics and thermodynamics of the hydrogel volume phase transition. These studies revealed several differences in the physical characteristics and thermoresponsive behavior of hydrogels based on cross-linker identity and the presence or absence of gold nanostructures. Hydrogels with gold nanostructures and high CBAm and low MBAm content have equilibrium swelling masses 3-20 times their native analogues. In comparison, gold-containing hydrogels with high MBAm and low CBAm content have swelling masses that are equal to their native analogues. Additionally, the gold-containing PNIPAm hydrogels cross-linked with only CBAm have a deswelling temperature of approximately 40 degrees C, approximately 8 degrees C above the samples cross-linked with only MBAm. Varying the CBAm content and introducing gold enables tuning of the deswelling temperature.

We construct colloidal "sticky" rods from the semi-flexible filamentous fd virus and temperature-sensitive polymers poly(N-isopropylacrylamide) (PNIPAM). The phase diagram of fd-PNIPAM system becomes independent of ionic strength at high salt concentration and low temperature, i.e. the rods are sterically stabilized by the polymer. However, the network of sticky rods undergoes a sol-gel transition as the temperature is raised. The viscoelastic moduli of fd and fd-PNIPAM suspensions are compared as a function of temperature, and the effect of ionic strength on the gelling behavior of fd-PNIPAM solution is measured. For all fluidlike and solidlike samples, the frequency-dependant linear viscoelastic moduli can be scaled onto universal master curves.