Anson Ma - Academia.edu (original) (raw)

Papers by Anson Ma

Research paper thumbnail of Controlling system components with a sound card: A versatile inkjet fluid testing platform

Review of Scientific Instruments, 2016

In this paper, we demonstrate how to use a personal computer sound card to develop an experimenta... more In this paper, we demonstrate how to use a personal computer sound card to develop an experimental platform for evaluating the jettability and jetting behavior of inkjet fluids. The test fluid is driven out of a nozzle acoustically using a loudspeaker, forming a jet. The subsequent jet breakup process is then captured using a stroboscopic light source and a camera. Instead of using a delay generator as in previous work, the current setup uses a computer sound card and audio amplifier to (i) generate actuation waveforms of arbitrary shapes and (ii) synchronize the jet actuation and imaging with a time precision close to 5 µs. To correct for any signal distortions caused by the built-in high pass filters of the sound card and amplifier, a numerical filter is created and applied before sending the desired signal to the sound card. Such correction method does not require physically modifying the hardware of the sound card or amplifier and is applicable to different waveforms and filters provided that the transfer function is correctly identified. The platform has been tested using 20% (v/v) glycerol in water as a model fluid. Combining this platform with digital image analysis further enables a quantitative assessment of parameters such as the volumes and positions of the jet and drop that are important for quality control and development of new ink formulations.

Research paper thumbnail of The Rheology and Processing of Carbon Nanotubes for Polymer Composite Applications

This presentation first highlights experimental observations on the rheology of: (1) non-function... more This presentation first highlights experimental observations on the rheology of: (1) non-functionalized CNTs that aggregate and (2) functionalized CNTs that do not aggregate in flow. The shear and extensional flow behavior of these two types of CNTs are compared and contrasted. Extensional flow is of particular relevance to fiber spinning and inkjet printing of CNT-containing “fluids”. In the second part of the presentation, two different rheological models are presented and discussed. These models connect the viscosity data with the orientation and the aggregation state of CNTs, offering insights into controlling CNT dispersion, alignment, and the final properties of CNT polymer composites.

Research paper thumbnail of The microstructure and mechanical properties of 3D printed carbon nanotube‐polylactic acid composites

Polymer Composites, 2018

This article reports 3D printing of carbon nanotube-polylactic acid (CNT-PLA) composites using an... more This article reports 3D printing of carbon nanotube-polylactic acid (CNT-PLA) composites using an extrusion-based Fused Deposition Modeling (FDM) method. CNTs with an average diameter of 128 nm and an average length of 2.5 μm were first compounded with PLA and extruded into feedstock filaments at 0.5%, 2.5%, and 5% (w/w) CNT loadings. CNT aggregates were observed, but no clogging occurred during printing with a 500-μm print nozzle. The rheology of the CNT-PLA samples was characterized to understand the printing-induced alignment of CNTs along the road axis. Additionally, the effect of printing flow rate was explored for a fixed printing gap and nozzle diameter. Higher flow rates reduced the void fraction in the FDM parts, but unexpectedly resulted in less degree of CNT alignment, which is attributed to radial flow and fusion between adjacent roads. The mechanical properties of the CNT-PLA tensile test coupons were characterized. Inclusion of CNTs increased the Young's modulus by...

Research paper thumbnail of Carbon nanotube composite reinforcements

Carbon nanotubes (CNTs) belong to a novel class of nanoscale fibers. Their high aspect ratio and ... more Carbon nanotubes (CNTs) belong to a novel class of nanoscale fibers. Their high aspect ratio and superior physical properties make them an appealing candidate to be incorporated into polymeric materials for mechanical reinforcement and conductivity enhancement. This chapter provides an overview of the development of CNT polymer composites. We first discuss the structure and physical properties of CNTs as individual nanoscale entities. We then review different techniques available for processing them into composites and the challenges involved. Two different flow models are introduced, and we conclude this chapter by discussing the performance and potential applications of some CNT polymer composites.

Research paper thumbnail of Additive manufacturing of embedded carbon nanocomposite structures with multi-material digital light processing (MMDLP)

Journal of Materials Research

Additive manufacturing (AM) has become an increasingly powerful technique for fabricating complex... more Additive manufacturing (AM) has become an increasingly powerful technique for fabricating complex three-dimensional micro-architectures for a wide variety of applications. Despite the multitude of AM techniques that support single material printing at progressively higher throughput, larger build size, and finer spatial resolution, multi-material printing of interlaced structures with one of the materials being a filled composite has not been demonstrated. This work aims to demonstrate the technical feasibility of fabricating such heterogeneous structures using a custom-built multi-material digital light processing (MMDLP) 3D printer. The printer was equipped with two resin dispensers and an air-jet that enable fast exchange between the resins-one of which was filled with carbon nanotubes (CNTs) up to 0.25%. The inclusion of CNTs reduced the cure depth of the resins, but significantly lowered the critical exposure required to initiate the photopolymerization. This information was successfully used to select appropriate process parameters for printing complex CNT-filled multi-material structures.

Research paper thumbnail of Development of a Pilot-Scale HuskyJet Binder Jet 3D Printer for Additive Manufacturing of Pharmaceutical Tablets

International Journal of Pharmaceutics

Research paper thumbnail of Impact of powder-binder interactions on 3D printability of pharmaceutical tablets using drop test methodology

European Journal of Pharmaceutical Sciences

Research paper thumbnail of Binder-Jet 3D Printing of Indomethacin-laden Pharmaceutical Dosage Forms

Journal of Pharmaceutical Sciences

Research paper thumbnail of Formulation design for inkjet-based 3D printed tablets

International Journal of Pharmaceutics

Research paper thumbnail of 3D printing of polymer-bonded magnets from highly concentrated, plate-like particle suspensions

Materials & Design

• 3D printing of polymer-bonded magnets using plate-like, melt-spun magnetic particles yields str... more • 3D printing of polymer-bonded magnets using plate-like, melt-spun magnetic particles yields stronger magnets. • Mixing two different sizes of particles lowers the overall viscosity, taking advantage of the rheological Farris effect. • Controlling the rheology enables 3D printing of polymer-bonded magnets with the best magnetic performance reported thus far.

Research paper thumbnail of UV-assisted direct write of polymer-bonded magnets

Journal of Magnetism and Magnetic Materials

This work presents a novel fabrication technique called ''UV-assisted Direct Write (UADW)", which... more This work presents a novel fabrication technique called ''UV-assisted Direct Write (UADW)", which combines extrusion-based direct write (DW) and in situ layer-by-layer UV curing to fabricate polymerbonded permanent magnets of arbitrary shapes at room temperature. The process requires minimal post heat treatment and therefore preserves the magnetic properties of the raw powder in the printed product. Experimentation achieved a maximum solid loading of printable ink of 60% by volume, or 91% by weight. Samples with 60 vol.% nominal particle concentration exhibited remanence of 3.80 kG (52% of raw powder value) and intrinsic coercivity of 9.50 kOe. Magnetized samples showed no reduction in intrinsic coercivity, which proves good curing of the final product and good bonding between particles and binder. Compared to other 3D-printed magnets reported in the literature, UADW magnets possess the highest intrinsic coercivity with one of the highest magnetic remanence values.

Research paper thumbnail of Direct write fabrication of high-density parallel silver interconnects

Additive Manufacturing

This study investigates the suitability of direct write (DW) technology for the fabrication of hi... more This study investigates the suitability of direct write (DW) technology for the fabrication of high-resolution wear sensors. We demonstrate the production of high-density parallel interconnect traces and provide recommendations for processing conditions to minimize line width and line spacing based on DW ink rheology. To create parallel silver lines with 50 μm center-to-center spacing and 15 μm line width on alumina substrates, we used an nScrypt DW system and sintered the lines at 625°C in air. The sintered lines exhibited an electrical resistivity of 5.29 × 10 −8 Ω m (about three times bulk silver resistivity reported in the literature) with a standard deviation of 3.68 × 10-9 Ω m (ca. 7% variation). To determine the conditions needed to consistently create fine conductive lines, we simulated the volumetric flow rate and analyzed the effects on line geometry of several printing parameters including valve opening, dispensing gap, and substrate translation speed. Our results indicate decreasing the valve opening, decreasing the dispensing gap, and/or increasing the translation speed of the substrate reduces the resultant printing flow rate and cross-sectional area of DW lines. For a fixed valve opening and dispensing gap, we also observed broken lines due to overstretching of the inks at exceedingly high substrate translation speeds.

Research paper thumbnail of Direct Write Fabrication of Platinum-Based Thick-Film Resistive Temperature Detectors

IEEE Sensors Journal

This paper investigates the feasibility and performance of platinum thick-film resistance tempera... more This paper investigates the feasibility and performance of platinum thick-film resistance temperature detectors (RTDs) fabricated using extrusion-based direct write (DW). A platinum (Pt) layer of micron-level thickness was directly deposited onto a planar alumina substrate and was physically and electrically characterized. A four-wire electrical configuration was used to eliminate the effects of contact resistance and increase measurement accuracy. The resistance-temperature behavior of printed Pt traces was consistent with that of bulk Pt wire. Durability testing indicated the printed Pt RTD was suitable for temperature measurements from room temperature to at least 350°C, showing no degradation under long-term heating and lower signal noise than was observed in a Nickel-alloy type E thermocouple (TC). At 500°C, the peak temperature variation of the Pt RTD was comparable to that of the type E TCs. To demonstrate the design freedom enabled by DW technology, an additional conformal RTD design was deposited onto a semi-cylinder glass-ceramic substrate and was subsequently characterized. This paper offers an alternative to current thick-film RTD fabrication techniques.

Research paper thumbnail of Influence of Manufacturing Process Variables on the Properties of Ophthalmic Ointments of Tobramycin

Pharmaceutical research, Jan 25, 2018

The main purpose of this study was to evaluate qualitative (Q1) and quantitative (Q2) equivalent ... more The main purpose of this study was to evaluate qualitative (Q1) and quantitative (Q2) equivalent oleaginous ophthalmic ointments of tobramycin (TOB) with different physicochemical properties and identify critical process/quality attributes using various in vitro methods of characterization. Various sources of petrolatum and TOB, and two mixing methods were employed to generate Q1/Q2 equivalent ointments. Characterization studies included content uniformity, microscopy, modulated temperature differential scanning calorimetry (MTDSC), gas chromatography-mass spectrometry (GC/MS), thermogravimetric analysis (TGA) and rheology. The particle size distribution of TOB influenced the content uniformity of ointments. Differences in the MTDSC endothermic and exothermic peaks of TOB suggested the presence of different polymorphic forms. GC/MS revealed variations in the composition and distribution of linear and branched hydrocarbons of petrolatums. Differences were also observed in the TGA der...

Research paper thumbnail of The Margination of Particles in Areas of Constricted Blood Flow

Biophysical journal, Jan 8, 2018

Stroke is a leading cause of death globally and is caused by stenoses, abnormal narrowings of blo... more Stroke is a leading cause of death globally and is caused by stenoses, abnormal narrowings of blood vessels. Recently, there has been an increased interest in shear-activated particle clusters for the treatment of stenosis, but there is a lack of literature investigating the impact of different stenosis geometries on particle margination. Margination refers to the movement of particles toward the blood vessel wall and is desirable for drug delivery. The current study investigated ten different geometries and their effects on margination. Microfluidic devices with a constricted area were fabricated to mimic a stenosed blood vessel with different extent of occlusion, constricted length, and eccentricity (gradualness of the constriction and expansion). Spherical fluorescent particles with a diameter of 2.11 μm were suspended in blood and tracked as they moved into, through, and out of the constricted area. A margination parameter, M, was used to quantify margination based on the partic...

Research paper thumbnail of Dissolution and Characterization of Boron Nitride Nanotubes in Superacid

Langmuir : the ACS journal of surfaces and colloids, Dec 19, 2017

Boron nitride nanotubes (BNNTs) are of interest for their unique combination of high tensile stre... more Boron nitride nanotubes (BNNTs) are of interest for their unique combination of high tensile strength, high electrical resistivity, high neutron cross section, and low reactivity. The fastest route to employing these properties in composites and macroscopic articles is through solution processing. However, dispersing BNNTs without functionalization or use of a surfactant is challenging. We show here by cryogenic transmission electron microscopy that BNNTs spontaneously dissolve in chlorosulfonic acid as disentangled individual molecules. Electron energy loss spectroscopy of BNNTs dried from the solution confirms preservation of the sphybridization for boron and nitrogen, eliminating the possibility of BNNT functionalization or damage. The length and diameter of the BNNTs was statistically calculated to be ∼4.5 μm and ∼4 nm, respectively. Interestingly, bent or otherwise damaged BNNTs are filled by chlorosulfonic acid. Additionally, nanometer-sized synthesis byproducts, including bor...

Research paper thumbnail of Global strain field mapping of a particle-laden interface using digital image correlation

Journal of Colloid and Interface Science

Hypothesis: The ability to identify the stress-strain relations correctly is critical to understa... more Hypothesis: The ability to identify the stress-strain relations correctly is critical to understanding and modeling any rheological responses of an interface. Langmuir-Pockels (LP) trough is one of the most commonly used tools for studying an interface. Most, if not all, existing studies assume a 1D uniaxial compression during a LP-trough compression experiment. It is hypothesized that the deformation field is far more complex than what is typically assumed. Experiments: To examine this hypothesis, we custom-built a glass-bottomed LP trough equipped with a camera to capture a series of optical images as a carbon nanotube (CNT)-laden interface is compressed. A digital image correlation (DIC) technique was then applied to the images to evaluate the global strain field during compression of the CNT laden interface. The DIC-corrected strain data were subsequently analyzed with the surface stress data to quantify the surface shear and dilatational moduli of the CNTladen interface. Findings: Our experimental findings clearly show, for the first time, the development of a non-uniform and complex 2D strain field during compression. The local strains were further quantified and compared with the usual assumption of 1D uniaxial compression. Although the compressive strain averaged over the whole trough area closely resembles the 1D uniaxial compression strain, the 1D compression assumption underestimates the local strain by about 36% at the center of the trough, where the surface stresses are measured. This is the first study in applying the DIC technique to map out the global strain field as a particle-laden interface is compressed. The method may also be applicable to other systems with similar optical texture, allowing the correct identification of stress-strain relationship of an interface.

Research paper thumbnail of Direct Tracking of Particles and Quantification of Margination in Blood Flow

Biophysical journal, Jan 4, 2016

Margination refers to the migration of particles toward blood vessel walls during blood flow. Und... more Margination refers to the migration of particles toward blood vessel walls during blood flow. Understanding the mechanisms that lead to margination will aid in tailoring the attributes of drug-carrying particles for effective drug delivery. Most previous studies evaluated the margination propensity of these particles via an adhesion mechanism, i.e., by measuring the number of particles that adhered to the channel wall. Although particle adhesion and margination are related, adhesion also depends on other factors. In this study, we quantified the margination propensity of particles of varying diameters (0.53, 0.84, and 2.11 μm) and apparent wall shear rates (30, 61, and 121 s(-1)) by directly tracking fluorescent particles flowing through a microfluidic channel. The margination parameter, M, is defined as the total number of particles found within the cell-free layers normalized by the total number of particles that passed through the channel. In this study, an M-value of 0.2 indicat...

Research paper thumbnail of Super acid processing of Single walled carbon nanotube (SWNT): effect of SWNT aspect Ratio on Macroscopic properties

Single walled carbon nanotubes are exceptional building blocks that combine great mechanical, ele... more Single walled carbon nanotubes are exceptional building blocks that combine great mechanical, electrical and thermal properties with low density. A number of processing techniques have been proposed to manufacture macroscopic articles made purely of carbon nanotubes. Superacid processing is the most flexible and promising of all since it allows dissolution of a wide range of carbon nanotube materials, including hundreds

Research paper thumbnail of Self-healing of thermally-induced, biocompatible and biodegradable protein hydrogel

RSC Adv., 2016

Almost 100% self-healing extent recovery performance was observed in thermal-induced bovine serum... more Almost 100% self-healing extent recovery performance was observed in thermal-induced bovine serum albumin hydrogel with external heating. Good biocompatibility and biodegradability of this materials were also demonstrated.

Research paper thumbnail of Controlling system components with a sound card: A versatile inkjet fluid testing platform

Review of Scientific Instruments, 2016

In this paper, we demonstrate how to use a personal computer sound card to develop an experimenta... more In this paper, we demonstrate how to use a personal computer sound card to develop an experimental platform for evaluating the jettability and jetting behavior of inkjet fluids. The test fluid is driven out of a nozzle acoustically using a loudspeaker, forming a jet. The subsequent jet breakup process is then captured using a stroboscopic light source and a camera. Instead of using a delay generator as in previous work, the current setup uses a computer sound card and audio amplifier to (i) generate actuation waveforms of arbitrary shapes and (ii) synchronize the jet actuation and imaging with a time precision close to 5 µs. To correct for any signal distortions caused by the built-in high pass filters of the sound card and amplifier, a numerical filter is created and applied before sending the desired signal to the sound card. Such correction method does not require physically modifying the hardware of the sound card or amplifier and is applicable to different waveforms and filters provided that the transfer function is correctly identified. The platform has been tested using 20% (v/v) glycerol in water as a model fluid. Combining this platform with digital image analysis further enables a quantitative assessment of parameters such as the volumes and positions of the jet and drop that are important for quality control and development of new ink formulations.

Research paper thumbnail of The Rheology and Processing of Carbon Nanotubes for Polymer Composite Applications

This presentation first highlights experimental observations on the rheology of: (1) non-function... more This presentation first highlights experimental observations on the rheology of: (1) non-functionalized CNTs that aggregate and (2) functionalized CNTs that do not aggregate in flow. The shear and extensional flow behavior of these two types of CNTs are compared and contrasted. Extensional flow is of particular relevance to fiber spinning and inkjet printing of CNT-containing “fluids”. In the second part of the presentation, two different rheological models are presented and discussed. These models connect the viscosity data with the orientation and the aggregation state of CNTs, offering insights into controlling CNT dispersion, alignment, and the final properties of CNT polymer composites.

Research paper thumbnail of The microstructure and mechanical properties of 3D printed carbon nanotube‐polylactic acid composites

Polymer Composites, 2018

This article reports 3D printing of carbon nanotube-polylactic acid (CNT-PLA) composites using an... more This article reports 3D printing of carbon nanotube-polylactic acid (CNT-PLA) composites using an extrusion-based Fused Deposition Modeling (FDM) method. CNTs with an average diameter of 128 nm and an average length of 2.5 μm were first compounded with PLA and extruded into feedstock filaments at 0.5%, 2.5%, and 5% (w/w) CNT loadings. CNT aggregates were observed, but no clogging occurred during printing with a 500-μm print nozzle. The rheology of the CNT-PLA samples was characterized to understand the printing-induced alignment of CNTs along the road axis. Additionally, the effect of printing flow rate was explored for a fixed printing gap and nozzle diameter. Higher flow rates reduced the void fraction in the FDM parts, but unexpectedly resulted in less degree of CNT alignment, which is attributed to radial flow and fusion between adjacent roads. The mechanical properties of the CNT-PLA tensile test coupons were characterized. Inclusion of CNTs increased the Young's modulus by...

Research paper thumbnail of Carbon nanotube composite reinforcements

Carbon nanotubes (CNTs) belong to a novel class of nanoscale fibers. Their high aspect ratio and ... more Carbon nanotubes (CNTs) belong to a novel class of nanoscale fibers. Their high aspect ratio and superior physical properties make them an appealing candidate to be incorporated into polymeric materials for mechanical reinforcement and conductivity enhancement. This chapter provides an overview of the development of CNT polymer composites. We first discuss the structure and physical properties of CNTs as individual nanoscale entities. We then review different techniques available for processing them into composites and the challenges involved. Two different flow models are introduced, and we conclude this chapter by discussing the performance and potential applications of some CNT polymer composites.

Research paper thumbnail of Additive manufacturing of embedded carbon nanocomposite structures with multi-material digital light processing (MMDLP)

Journal of Materials Research

Additive manufacturing (AM) has become an increasingly powerful technique for fabricating complex... more Additive manufacturing (AM) has become an increasingly powerful technique for fabricating complex three-dimensional micro-architectures for a wide variety of applications. Despite the multitude of AM techniques that support single material printing at progressively higher throughput, larger build size, and finer spatial resolution, multi-material printing of interlaced structures with one of the materials being a filled composite has not been demonstrated. This work aims to demonstrate the technical feasibility of fabricating such heterogeneous structures using a custom-built multi-material digital light processing (MMDLP) 3D printer. The printer was equipped with two resin dispensers and an air-jet that enable fast exchange between the resins-one of which was filled with carbon nanotubes (CNTs) up to 0.25%. The inclusion of CNTs reduced the cure depth of the resins, but significantly lowered the critical exposure required to initiate the photopolymerization. This information was successfully used to select appropriate process parameters for printing complex CNT-filled multi-material structures.

Research paper thumbnail of Development of a Pilot-Scale HuskyJet Binder Jet 3D Printer for Additive Manufacturing of Pharmaceutical Tablets

International Journal of Pharmaceutics

Research paper thumbnail of Impact of powder-binder interactions on 3D printability of pharmaceutical tablets using drop test methodology

European Journal of Pharmaceutical Sciences

Research paper thumbnail of Binder-Jet 3D Printing of Indomethacin-laden Pharmaceutical Dosage Forms

Journal of Pharmaceutical Sciences

Research paper thumbnail of Formulation design for inkjet-based 3D printed tablets

International Journal of Pharmaceutics

Research paper thumbnail of 3D printing of polymer-bonded magnets from highly concentrated, plate-like particle suspensions

Materials & Design

• 3D printing of polymer-bonded magnets using plate-like, melt-spun magnetic particles yields str... more • 3D printing of polymer-bonded magnets using plate-like, melt-spun magnetic particles yields stronger magnets. • Mixing two different sizes of particles lowers the overall viscosity, taking advantage of the rheological Farris effect. • Controlling the rheology enables 3D printing of polymer-bonded magnets with the best magnetic performance reported thus far.

Research paper thumbnail of UV-assisted direct write of polymer-bonded magnets

Journal of Magnetism and Magnetic Materials

This work presents a novel fabrication technique called ''UV-assisted Direct Write (UADW)", which... more This work presents a novel fabrication technique called ''UV-assisted Direct Write (UADW)", which combines extrusion-based direct write (DW) and in situ layer-by-layer UV curing to fabricate polymerbonded permanent magnets of arbitrary shapes at room temperature. The process requires minimal post heat treatment and therefore preserves the magnetic properties of the raw powder in the printed product. Experimentation achieved a maximum solid loading of printable ink of 60% by volume, or 91% by weight. Samples with 60 vol.% nominal particle concentration exhibited remanence of 3.80 kG (52% of raw powder value) and intrinsic coercivity of 9.50 kOe. Magnetized samples showed no reduction in intrinsic coercivity, which proves good curing of the final product and good bonding between particles and binder. Compared to other 3D-printed magnets reported in the literature, UADW magnets possess the highest intrinsic coercivity with one of the highest magnetic remanence values.

Research paper thumbnail of Direct write fabrication of high-density parallel silver interconnects

Additive Manufacturing

This study investigates the suitability of direct write (DW) technology for the fabrication of hi... more This study investigates the suitability of direct write (DW) technology for the fabrication of high-resolution wear sensors. We demonstrate the production of high-density parallel interconnect traces and provide recommendations for processing conditions to minimize line width and line spacing based on DW ink rheology. To create parallel silver lines with 50 μm center-to-center spacing and 15 μm line width on alumina substrates, we used an nScrypt DW system and sintered the lines at 625°C in air. The sintered lines exhibited an electrical resistivity of 5.29 × 10 −8 Ω m (about three times bulk silver resistivity reported in the literature) with a standard deviation of 3.68 × 10-9 Ω m (ca. 7% variation). To determine the conditions needed to consistently create fine conductive lines, we simulated the volumetric flow rate and analyzed the effects on line geometry of several printing parameters including valve opening, dispensing gap, and substrate translation speed. Our results indicate decreasing the valve opening, decreasing the dispensing gap, and/or increasing the translation speed of the substrate reduces the resultant printing flow rate and cross-sectional area of DW lines. For a fixed valve opening and dispensing gap, we also observed broken lines due to overstretching of the inks at exceedingly high substrate translation speeds.

Research paper thumbnail of Direct Write Fabrication of Platinum-Based Thick-Film Resistive Temperature Detectors

IEEE Sensors Journal

This paper investigates the feasibility and performance of platinum thick-film resistance tempera... more This paper investigates the feasibility and performance of platinum thick-film resistance temperature detectors (RTDs) fabricated using extrusion-based direct write (DW). A platinum (Pt) layer of micron-level thickness was directly deposited onto a planar alumina substrate and was physically and electrically characterized. A four-wire electrical configuration was used to eliminate the effects of contact resistance and increase measurement accuracy. The resistance-temperature behavior of printed Pt traces was consistent with that of bulk Pt wire. Durability testing indicated the printed Pt RTD was suitable for temperature measurements from room temperature to at least 350°C, showing no degradation under long-term heating and lower signal noise than was observed in a Nickel-alloy type E thermocouple (TC). At 500°C, the peak temperature variation of the Pt RTD was comparable to that of the type E TCs. To demonstrate the design freedom enabled by DW technology, an additional conformal RTD design was deposited onto a semi-cylinder glass-ceramic substrate and was subsequently characterized. This paper offers an alternative to current thick-film RTD fabrication techniques.

Research paper thumbnail of Influence of Manufacturing Process Variables on the Properties of Ophthalmic Ointments of Tobramycin

Pharmaceutical research, Jan 25, 2018

The main purpose of this study was to evaluate qualitative (Q1) and quantitative (Q2) equivalent ... more The main purpose of this study was to evaluate qualitative (Q1) and quantitative (Q2) equivalent oleaginous ophthalmic ointments of tobramycin (TOB) with different physicochemical properties and identify critical process/quality attributes using various in vitro methods of characterization. Various sources of petrolatum and TOB, and two mixing methods were employed to generate Q1/Q2 equivalent ointments. Characterization studies included content uniformity, microscopy, modulated temperature differential scanning calorimetry (MTDSC), gas chromatography-mass spectrometry (GC/MS), thermogravimetric analysis (TGA) and rheology. The particle size distribution of TOB influenced the content uniformity of ointments. Differences in the MTDSC endothermic and exothermic peaks of TOB suggested the presence of different polymorphic forms. GC/MS revealed variations in the composition and distribution of linear and branched hydrocarbons of petrolatums. Differences were also observed in the TGA der...

Research paper thumbnail of The Margination of Particles in Areas of Constricted Blood Flow

Biophysical journal, Jan 8, 2018

Stroke is a leading cause of death globally and is caused by stenoses, abnormal narrowings of blo... more Stroke is a leading cause of death globally and is caused by stenoses, abnormal narrowings of blood vessels. Recently, there has been an increased interest in shear-activated particle clusters for the treatment of stenosis, but there is a lack of literature investigating the impact of different stenosis geometries on particle margination. Margination refers to the movement of particles toward the blood vessel wall and is desirable for drug delivery. The current study investigated ten different geometries and their effects on margination. Microfluidic devices with a constricted area were fabricated to mimic a stenosed blood vessel with different extent of occlusion, constricted length, and eccentricity (gradualness of the constriction and expansion). Spherical fluorescent particles with a diameter of 2.11 μm were suspended in blood and tracked as they moved into, through, and out of the constricted area. A margination parameter, M, was used to quantify margination based on the partic...

Research paper thumbnail of Dissolution and Characterization of Boron Nitride Nanotubes in Superacid

Langmuir : the ACS journal of surfaces and colloids, Dec 19, 2017

Boron nitride nanotubes (BNNTs) are of interest for their unique combination of high tensile stre... more Boron nitride nanotubes (BNNTs) are of interest for their unique combination of high tensile strength, high electrical resistivity, high neutron cross section, and low reactivity. The fastest route to employing these properties in composites and macroscopic articles is through solution processing. However, dispersing BNNTs without functionalization or use of a surfactant is challenging. We show here by cryogenic transmission electron microscopy that BNNTs spontaneously dissolve in chlorosulfonic acid as disentangled individual molecules. Electron energy loss spectroscopy of BNNTs dried from the solution confirms preservation of the sphybridization for boron and nitrogen, eliminating the possibility of BNNT functionalization or damage. The length and diameter of the BNNTs was statistically calculated to be ∼4.5 μm and ∼4 nm, respectively. Interestingly, bent or otherwise damaged BNNTs are filled by chlorosulfonic acid. Additionally, nanometer-sized synthesis byproducts, including bor...

Research paper thumbnail of Global strain field mapping of a particle-laden interface using digital image correlation

Journal of Colloid and Interface Science

Hypothesis: The ability to identify the stress-strain relations correctly is critical to understa... more Hypothesis: The ability to identify the stress-strain relations correctly is critical to understanding and modeling any rheological responses of an interface. Langmuir-Pockels (LP) trough is one of the most commonly used tools for studying an interface. Most, if not all, existing studies assume a 1D uniaxial compression during a LP-trough compression experiment. It is hypothesized that the deformation field is far more complex than what is typically assumed. Experiments: To examine this hypothesis, we custom-built a glass-bottomed LP trough equipped with a camera to capture a series of optical images as a carbon nanotube (CNT)-laden interface is compressed. A digital image correlation (DIC) technique was then applied to the images to evaluate the global strain field during compression of the CNT laden interface. The DIC-corrected strain data were subsequently analyzed with the surface stress data to quantify the surface shear and dilatational moduli of the CNTladen interface. Findings: Our experimental findings clearly show, for the first time, the development of a non-uniform and complex 2D strain field during compression. The local strains were further quantified and compared with the usual assumption of 1D uniaxial compression. Although the compressive strain averaged over the whole trough area closely resembles the 1D uniaxial compression strain, the 1D compression assumption underestimates the local strain by about 36% at the center of the trough, where the surface stresses are measured. This is the first study in applying the DIC technique to map out the global strain field as a particle-laden interface is compressed. The method may also be applicable to other systems with similar optical texture, allowing the correct identification of stress-strain relationship of an interface.

Research paper thumbnail of Direct Tracking of Particles and Quantification of Margination in Blood Flow

Biophysical journal, Jan 4, 2016

Margination refers to the migration of particles toward blood vessel walls during blood flow. Und... more Margination refers to the migration of particles toward blood vessel walls during blood flow. Understanding the mechanisms that lead to margination will aid in tailoring the attributes of drug-carrying particles for effective drug delivery. Most previous studies evaluated the margination propensity of these particles via an adhesion mechanism, i.e., by measuring the number of particles that adhered to the channel wall. Although particle adhesion and margination are related, adhesion also depends on other factors. In this study, we quantified the margination propensity of particles of varying diameters (0.53, 0.84, and 2.11 μm) and apparent wall shear rates (30, 61, and 121 s(-1)) by directly tracking fluorescent particles flowing through a microfluidic channel. The margination parameter, M, is defined as the total number of particles found within the cell-free layers normalized by the total number of particles that passed through the channel. In this study, an M-value of 0.2 indicat...

Research paper thumbnail of Super acid processing of Single walled carbon nanotube (SWNT): effect of SWNT aspect Ratio on Macroscopic properties

Single walled carbon nanotubes are exceptional building blocks that combine great mechanical, ele... more Single walled carbon nanotubes are exceptional building blocks that combine great mechanical, electrical and thermal properties with low density. A number of processing techniques have been proposed to manufacture macroscopic articles made purely of carbon nanotubes. Superacid processing is the most flexible and promising of all since it allows dissolution of a wide range of carbon nanotube materials, including hundreds

Research paper thumbnail of Self-healing of thermally-induced, biocompatible and biodegradable protein hydrogel

RSC Adv., 2016

Almost 100% self-healing extent recovery performance was observed in thermal-induced bovine serum... more Almost 100% self-healing extent recovery performance was observed in thermal-induced bovine serum albumin hydrogel with external heating. Good biocompatibility and biodegradability of this materials were also demonstrated.