Elliot P. Douglas

Scanning electron microscopic analysis of the mineralization of type I collagen via a polymer-induced liquid-precursor (PILP) process.

We have put forth the hypothesis that collagen is mineralized during bone formation by means of a polymer-induced liquid-precursor (PILP) process, in which a liquid-phase mineral precursor could be drawn into the gaps and grooves of the collagen fibrils by capillary action, and upon solidification, leave the collagenous matrix embedded with nanoscopic crystallites of hydroxyapatite. This hypothesis is based upon our observations of capillarity seen for liquid-phase mineral precursors generated with calcium carbonate. Here, we demonstrate proof-of-concept of this mechanism by mineralizing Cellagen™ sponges (type I reconstituted bovine collagen) in the presence of a liquid-precursor phase to calcium carbonate. Scanning electron microscopy (SEM) was used to examine the mineralized collagen, which in combination with selective etching studies, revealed the extent to which the mineral phase infiltrated the collagenous matrix. A roughly periodic array of disk-like crystals was found to be embedded within the collagen fibers, demonstrating that the mineral phase spans across the diameter of the fibers. Some of the morphological features of the mineralized fibers in our in vitro model system are similar to those seen in natural bone (albeit of a different mineral phase), lending support to our hypothesis that these non-equilibrium morphologies might be generated by a PILP process. SEM provides a different perspective on the morphology of bone, and has been useful here for examining the extent of mineralization in composite structures generated via the PILP process. However, further investigation is needed to examine the nanostructural arrangement of the crystallites embedded within the collagenous matrix.

Optical limiting of semiconductor nanoparticles for nanosecond laser pulses

Optical limiting of nanosecond laser pulses at 532 nm has been observed in CdxAg1−xS semiconductor nanoparticles within organic solution of polymeric ionic aggregates. Both free-carrier absorption (FCA) and nonlinear scattering contribute to the optical limiting performance. The optical limiting response of CdS nanoparticles, in the diameter range of 2–9 nm, increases with the increase of particle size. It can be further increased by surface coating of the CdS particle with a thin layer of Ag2S or forming ternary CdxAg1−xS particle. The FCA cross sections of CdxAg1−xS solutions were estimated to be between 10−19 and 10−18cm2, which are comparable with those of bulk semiconductors.

Biomimetic Mineralization of Woven Bone-Like Nanocomposites: Role of Collagen Cross-Links

Ideal biomaterials for bone grafts must be biocompatible, osteoconductive, osteoinductive and have appropriate mechanical properties. For this, the development of synthetic bone substitutes mimicking natural bone is desirable, but this requires controllable mineralization of the collagen matrix. In this study, densified collagen films (up to 100 μm thick) were fabricated by a plastic compression technique and cross-linked using carbodiimide. Then, collagen-hydroxyapatite composites were prepared by using a polymer-induced liquid-precursor (PILP) mineralization process. Compared to traditional methods that produce only extrafibrillar hydroxyapatite (HA) clusters on the surface of collagen scaffolds, by using the PILP mineralization process, homogeneous intra- and extrafibrillar minerals were achieved on densified collagen films, leading to a similar nanostructure as bone, and a woven microstructure analogous to woven bone. The role of collagen cross-links on mineralization was examined and it was found that the cross-linked collagen films stimulated the mineralization reaction, which in turn enhanced the mechanical properties (hardness and modulus). The highest value of hardness and elastic modulus was 0.7 ± 0.1 and 9.1 ± 1.4 GPa in the dry state, respectively, which is comparable to that of woven bone. In the wet state, the values were much lower (177 ± 31 and 8 ± 3 MPa) due to inherent microporosity in the films, but still comparable to those of woven bone in the same conditions. Mineralization of collagen films with controllable mineral content and good mechanical properties provide a biomimetic route toward the development of bone substitutes for the next generation of biomaterials. This work also provides insight into understanding the role of collagen fibrils on mineralization.

Enhancing Light Extraction in Top‐Emitting Organic Light‐Emitting Devices Using Molded Transparent Polymer Microlens Arrays

The light extraction efficiency in organic light-emitting devices (OLEDs) is enhanced by up to 2.6 times when a close-packed, hemispherical transparent polymer microlens array (MLA) is molded on the light-emitting surface of a top-emitting device. The microlens array helps to extract the waveguided optical emission in the organic layers and the transparent top electrode, and can be manufactured in large area with low cost.

Progress in semiconducting oxide-based thin-film transistors for displays

Recent progress in the development of transparent thin-film transistors for integration with flexible displays is discussed. Specifically, the fabrication and properties of ZnO-based thin-film transistors on glass are described. Top-gate-type thin-film transistors with transparent n-type ZnO as the active channel layer have been fabricated via wet photolithography processing. The ZnO layers were deposited using pulsed laser deposition. A low leakage current of 10−7 A cm−2 was realized with amorphous HfO2 or (Ce, Tb)MgA11O19 as the gate dielectric. N-channel depletion-mode operation was shown for the undoped ZnO thin-film transistors. Phosphorus-doped ZnO and (Zn, Mg)O were also utilized as channel materials in order to realize a reduction in carrier density. The current–voltage measurements demonstrate an enhancement-mode device operation for the thin-film transistors with P-doped (Zn, Mg)O as the active channel layer and HfO2 serving as the gate dielectric.

Small Beam Bond Test Method for CFRP Composites Applied to Concrete

This paper presents the development of a test method that can be used to test the bond capacity of carbon fiber-reinforced polymer (CFRP) composites bonded to concrete. The rationale for the selection of the test method is described along with the results of the experimental work used to refine the test configuration and procedures. The research objectives were to develop a test method that (1) can be used to evaluate the durability of the FRP-concrete bond (adhesion failure mode); (2) facilitate multiple replicate for statistical validation; (3) is simple to conduct; and (4) provides comparative results that are easy to interpret. The method utilizes a small concrete beam modeled after the modulus of rupture test, which is typically used to measure concrete tensile strength. A number of small beam sizes and loading configurations were considered during the investigation. The final recommended specimen configuration is 4×4×14 in. ( 100 mm×100 mm×356 mm ) beam with a half-depth saw cut at midspan. A 1 in. ...

Challenges and promises of overcoming epistemological and methodological partiality: Advancing engineering education through acceptance of diverse ways of knowing

The purpose of this paper is to explore some challenges and promises when the epistemological diversity embedded in qualitative research traditions is introduced to research communities with one dominant research paradigm, such as engineering education. Literature is used from other fields and empirical data are used from engineering education, including the practices of the European Journal of Engineering Education and the Journal of Engineering Education, with the expectation that the ideas that are presented are relevant to a broad range of education disciplines. A number of challenges are identified as the epistemological diversity of qualitative research is introduced to the primarily positivist field of engineering education. Ultimately, embracing epistemological diversity holds the promise of researchers being able to ask: ‘What questions and answers become possible from these newly created positions and what can be learned from these alternative approaches?’.

Moving beyond Formulas and Fixations: Solving Open-Ended Engineering Problems.

Open-ended problem solving is a central skill in engineering practice; consequently, it is imperative for engineering students to develop expertise in solving these types of problems. The complexity of open-ended problems requires a unique set of skills. The purpose of this qualitative study was to investigate the approaches used by engineering students when solving an open-ended engineering problem. A think-aloud method was used to collect data about the problem-solving approaches of eight materials engineering students. Through the use of script analysis three approaches to solving the problem were identified, which were consistent with the Reflective Judgment Model of epistemic development. Students who used a linear, systematic approach were most successful at solving the problem. Less successful students were overwhelmed by its open-endedness and/or became fixated on a single aspect of the problem. These results point to a need to develop open-ended problem-solving skills throughout the engineering curriculum.

Complex Hygrothermal Effects on the Glass Transition of an Epoxy-Amine Thermoset

Anomalous hygrothermal behavior in an epoxy-amine thermoset was observed in terms of increases in glass-transition temperatures (T(g)) after immersion in water at different temperatures. Fourier transform near-infrared (FT-NIR) spectroscopic measurements showed that an increase in conversion was responsible for the increase in glass transition, while plasticization occurred simultaneously, rendering the hygrothermal behavior to be complex. To consider other factors affecting this complex hygrothermal behavior, a relationship between T(g) and conversion was constructed for the unexposed system and compared to the corresponding T(g) values for the exposed system at the same point of each conversion value. With this method, the conversion was successfully excluded to compare the T(g) values directly between the unexposed and exposed systems. This indicates the effects of other factors are negligible compared with the large plasticization effect. The plasticization effect was also evaluated quantitatively by observing T(g) differences between the unexposed and the exposed system as a function of absorbed water amount estimated by a characteristic water peak in the NIR spectra. The result indicates that there is additional anomalous behavior in which DeltaT(g) changes independently of the water amount at higher exposure temperatures.

Surface Modification of Cured Cement Pastes by Silane Coupling Agents

X-ray photoelectron spectroscopy (XPS) and static contact angle measurements were used to study the interaction between silane coupling agents and cured cement paste. Three different silane coupling agents were investigated: aminopropyltriethoxy silane (APTES), 3-glycidyloxypropyltrimethoxy silane (GPTMS), and methoxy-terminated polydimethxyl siloxane (PDMS). These silanes have different end groups, so the change in surface energy after undergoing a successful reaction between the silane and hydroxyls on the surface of the cement paste was demonstrated by a change in contact angle. Relative to untreated samples, APTES samples decreased the contact angle, PDMS samples increased the contact angle, and GPTMS did not show a significant change in contact angle. Samples with a water-to-cement ratio (w/c) of 0.5 showed a larger change in contact angle than 0.4 w/c ratio samples, because of a greater number of hydroxyl groups at the surface. Deconvolution of the O 1s and Si 2p XPS peaks were performed to determine contributions from bridging and nonbridging atoms. An increase in bridging silicon and oxygen atoms relative to untreated samples indicated successful silane condensation and that a covalent bond was formed between the cement paste and silanes.