Scanning holographic optical tweezers.

The aim of this Letter is to introduce a new optical tweezers approach, called scanning holographic optical tweezers (SHOT), which drastically increases the working area (WA) of the holographic-optical tweezers (HOT) approach, while maintaining tightly focused laser traps. A 12-fold increase in the WA is demonstrated. The SHOT approach achieves its utility by combining the large WA of the scanning optical tweezers (SOT) approach with the flexibility of the HOT approach for simultaneously moving differently structured optical traps in and out of the focal plane. This Letter also demonstrates a new heuristic control algorithm for combining the functionality of the SOT and HOT approaches to efficiently allocate the available laser power among a large number of traps. The proposed approach shows promise for substantially increasing the number of particles that can be handled simultaneously, which would enable optical tweezers additive fabrication technologies to rapidly assemble microgranular materials and structures in reasonable build times.

Holographic optical assembly and photopolymerized joining of planar microspheres.

The aim of this research is to demonstrate a holographically driven photopolymerization process for joining colloidal particles to create planar microstructures fixed to a substrate, which can be monitored with real-time measurement. Holographic optical tweezers (HOT) have been used to arrange arrays of microparticles prior to this work; here we introduce a new photopolymerization process for rapidly joining simultaneously handled microspheres in a plane. Additionally, we demonstrate a new process control technique for efficiently identifying when particles have been successfully joined by measuring a sufficient reduction in the particles' Brownian motion. This technique and our demonstrated joining approach enable HOT technology to take critical steps toward automated additive fabrication of microstructures.

3D printed cellular solid outperforms traditional stochastic foam in long-term mechanical response.

3D printing of polymeric foams by direct-ink-write is a recent technological breakthrough that enables the creation of versatile compressible solids with programmable microstructure, customizable shapes, and tunable mechanical response including negative elastic modulus. However, in many applications the success of these 3D printed materials as a viable replacement for traditional stochastic foams critically depends on their mechanical performance and micro-architectural stability while deployed under long-term mechanical strain. To predict the long-term performance of the two types of foams we employed multi-year-long accelerated aging studies under compressive strain followed by a time-temperature-superposition analysis using a minimum-arc-length-based algorithm. The resulting master curves predict superior long-term performance of the 3D printed foam in terms of two different metrics, i.e., compression set and load retention. To gain deeper understanding, we imaged the microstructure of both foams using X-ray computed tomography, and performed finite-element analysis of the mechanical response within these microstructures. This indicates a wider stress variation in the stochastic foam with points of more extreme local stress as compared to the 3D printed material, which might explain the latter's improved long-term stability and mechanical performance.

Under-three minute PCR: probing the limits of fast amplification.

Nucleic acid amplification is enormously useful to the biotechnology and clinical diagnostic communities; however, to date point-of-use PCR has been hindered by thermal cycling architectures and protocols that do not allow for near-instantaneous results. In this work we demonstrate PCR amplification of synthetic SARS respiratory pathogenic targets and bacterial genomic DNA in less than three minutes in a hardware configuration utilizing convenient sample loading and disposal. Instead of sample miniaturization techniques, near-instantaneous heating and cooling of 5 µL reaction volumes is enabled by convective heat transfer of a thermal fluid through porous media combined with an integrated electrical heater. This method of rapid heat transfer has enabled 30 cycles of PCR amplification to be completed in as little as two minutes and eighteen seconds. Surprisingly, multiple enzymes have been shown to work at these breakthrough speeds on our system. A tool for measuring enzyme kinetics now exists and can allow polymerase optimization through directed evolution studies. Pairing this instrument technology with modified polymerases should result in a new paradigm for high-throughput, ultra-fast PCR and will hopefully improve our ability to quickly respond to the next viral pandemic.

Neutron production from feedback controlled thermal cycling of a pyroelectric crystal.

The LLNL Crystal Driven Neutron Source is operational and has produced record ion currents of approximately 10 nA and neutron output of 1.9(+/-0.3)x10(5) per thermal cycle using a crystal heating rate of 0.2 degrees C/s from 10 to 110 degrees C. A 3 cm diameter by 1 cm thick LiTaO(3) crystal with a socket secured field emitter tip is thermally cycled with feedback control for ionization and acceleration of deuterons onto a deuterated target to produce D-D fusion neutrons. The entire crystal and temperature system is mounted on a bellows which allows movement of the crystal along the beam axis and is completely contained on a single small vacuum flange. The modular crystal assembly permitted experimental flexibility. Operationally, flashover breakdowns along the side of the crystal and poor emitter tip characteristics can limit the neutron source. The experimental neutron results extend earlier published work by increasing the ion current and pulse length significantly to achieve a factor-of-two higher neutron output per thermal cycle. These findings are reviewed along with details of the instrument.

Simultaneous ulcerative colitis and Crohn's disease. Report of a case.

This report describes a patient with simultaneous Crohn's disease of the terminal ileum and ulcerative colitis of the left colon and rectum. Well documented cases of "mixed" ileocolitis are quite rare.

The use of the bristle brush for transcatheter embolization.

Small nylon brushes with a stainless steel core have been found safe and effective for transcatheter arterial occlusion. Studies performed in 14 dogs demonstrate the brushes result in rapid occlusion of the renal artery. Follow-up studies for periods up to ten months document the safety and permanence of the occlusion. The animal studies reported herein suggest that these devices can be safely used in humans in cases where large artery occlusion is desired.