Darryl A. Boyd

Microfluidic strategies for design and assembly of microfibers and nanofibers with tissue engineering and regenerative medicine applications.

Fiber-based materials provide critical capabilities for biomedical applications. Microfluidic fiber fabrication has recently emerged as a very promising route to the synthesis of polymeric fibers at the micro and nanoscale, providing fine control over fiber shape, size, chemical anisotropy, and biological activity. This Progress Report summarizes advanced microfluidic methods for the fabrication of both microscale and nanoscale fibers and illustrates how different methods are enabling new biomedical applications. Microfluidic fabrication methods and resultant materials are explained from the perspective of their microfluidic device principles, including co-flow, cross-flow, and flow-shaping designs. It is then detailed how the microchannel design and flow parameters influence the variety of synthesis chemistries that can be utilized. Finally, the integration of biomaterials and microfluidic strategies is discussed to manufacture unique fiber-based systems, including cell scaffolds, cell encapsulation, and woven tissue matrices.

Sulfur and Its Role In Modern Materials Science.

Although well-known and studied for centuries, sulfur continues to be at the center of an extensive array of scientific research topics. As one of the most abundant elements in the Universe, a major by-product of oil refinery processes, and as a common reaction site within biological systems, research involving sulfur is both broad in scope and incredibly important to our daily lives. Indeed, there has been renewed interest in sulfur-based reactions in just the past ten years. Sulfur research spans the spectrum of topics within the physical sciences including research on improving energy efficiency, environmentally friendly uses for oil refinery waste products, development of polymers with unique optical and mechanical properties, and materials produced for biological applications. This Review focuses on some of the latest exciting ways in which sulfur and sulfur-based reactions are being utilized to produce materials for application in energy, environmental, and other practical areas.

3D hydrodynamic focusing microfluidics for emerging sensing technologies.

While the physics behind laminar flows has been studied for 200 years, understanding of how to use parallel flows to augment the capabilities of microfluidic systems has been a subject of study primarily over the last decade. The use of one flow to focus another within a microfluidic channel has graduated from a two-dimensional to a three-dimensional process and the design principles are only now becoming established. This review explores the underlying principles for hydrodynamic focusing in three dimensions (3D) using miscible fluids and the application of these principles for creation of biosensors, separation of cells and particles for sample manipulation, and fabrication of materials that could be used for biosensors. Where sufficient information is available, the practicality of devices implementing fluid flows directed in 3D is evaluated and the advantages and limitations of 3D hydrodynamic focusing for the particular application are highlighted.

ORMOCHALCs: organically modified chalcogenide polymers for infrared optics

A novel method combining elemental sulfur and selenium was developed, yielding crystalline sulfur-selenium compounds. The compounds were melted, and an organic comonomer added. Once the organic comonomer was consumed, the viscous compound was vitrified and allowed to cool yielding organic-inorganic hybrid polymers that are termed Organically Modified Chalcogenide (ORMOCHALC) polymers.

Small-Molecule Detection in Thiol–Yne Nanocomposites via Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is generally performed on planar surfaces, which can be difficult to prepare and may limit the interaction of the sensing surface with targets in large volume samples. We propose that nanocomposite materials can be configured that both include SERS probes and provide a high surface area-to-volume format, i.e., fibers. Thiol-yne nanocomposite films and fibers were fabricated using exposure to long-wave ultraviolet light after the inclusion of gold nanoparticles (AuNPs) functionalized with thiophenol. A SERS response was observed that was proportional to the aggregation of the AuNPs within the polymers and the amount of thiophenol present. Overall, this proof-of-concept fabrication of SERS active polymers indicated that thiol-yne nanocomposites may be useful as durable film or fiber SERS probes. Properties of the nanocomposites were evaluated using various techniques including UV-vis spectroscopy, μ-Raman spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy.

Periodically patterned germanium surfaces modified to form superhydrophobic, IR-transmissive substrates

Various periodically patterned, infrared (IR) transmissive germanium substrates were surface modified to alter the surface wettability. Goniometric analysis showed that the surface modification rendered the substrates superhydrophobic. Following the surface modification, it was determined that the desirable IR transmission properties were maintained. Both the hydrophobicity and the IR transmission capabilities of the modified, patterned germanium substrates were shown to be significantly enhanced in comparison to a germanium substrate that underwent the same processes, but was devoid of nanostructures on its surface. The results of this work provide an opportunity for the development of enhanced utility infrared transmissive optics in wet or humid conditions.

Fabrication of Photoluminescent Quantum Dot Thiol–yne Nanocomposites via Thermal Curing or Photopolymerization

Strong, flexible, and transparent materials have garnered tremendous interest in recent years as materials and electronics manufacturers pursue devices that are bright, flexible, durable, tailorable, and lightweight. Depending on the starting components, polymers fabricated using thiol–yne chemistry have been shown to be exceptionally strong and/or flexible, while also being amenable to modification by the incorporation of nanoparticles. In the present work, novel ligands were synthesized and used to functionalize quantum dots (QDs) of various diameters. The functionalized QDs were then incorporated into thiol–yne prepolymer matrices. These matrices were subsequently polymerized to form QD thiol–yne nanocomposite polymers. To demonstrate the versatility of the fabrication process, the prepolymers were either thermally cured or photopolymerized. The resulting transparent nanocomposites expressed the size-specific color of the QDs within them when exposed to ultraviolet irradiation, demonstrating that QDs can be incorporated into thiol–yne polymers without significantly altering QD expression. With the inclusion of QDs, thiol–yne nanocomposite polymers are promising candidates for use in numerous applications including as device display materials, optical lens materials, and/or sensor materials.

Superhydrophobic, infrared transmissive moth eye-like substrates for use in wet conditions

Infrared (IR) transmissive moth eye-like substrates, including randomly patterned fused silica and various periodically patterned germanium substrates, were surface modified using a simple process. Goniometric analysis showed that the surface modification altered the surface wettability of each substrate, rendering them superhydrophobic. Following the surface modification, it was determined that the desirable IR transmission and antireflective properties of each substrate type were maintained. Furthermore, the hydrophobicity, IR transmission and antireflective capabilities of the substrates were shown to be significantly enhanced in comparison to native, non-patterned fused silica and germanium substrates that underwent the same processes. The results of this work provide an opportunity for the development of enhanced utility for infrared transmissive optics in wet or humid conditions.

Laser damage testing of silica windows with hydrophobic antireflective surfaces (Conference Presentation)

Antireflective surface structures (ARSS) are nano-patterned structures etched into the optical surface that simulate behavior like that of a moth’s eye, which has cone-like structures that reduce reflections in the visible. We have previously reported record high laser induced damage thresholds (LIDT) up to 100 J/cm2 at 1 µm (10 nsec pulsewidth) for silica glass windows with random ARSS. However, these windows with ARSS are hydrophilic, leading to practical problems for their use in fielded laser systems. Recently, we developed and reported a new process for treating the surface of silica windows with ARSS such that it becomes hydrophobic. In this paper we will report results for the LIDT for samples with these antireflective, hydrophobic surfaces, and compare to results for samples that are untreated but have ARSS, samples with hydrophobic treatment but no ARSS, and finally those having neither ARSS or hydrophobic treatment. The morphology of the laser damage observed and potential mechanisms will be discussed.