Chromophore-Free Sealing and Repair of Soft Tissues Using Mid-Infrared Light-Activated Biosealants

Poor strength, infection, leakage, long procedure times, and inflammation limit the efficacy of common tissue sealing devices in surgeries and trauma. Light-activated sealing is attractive for tissue sealing and repair, and can be facilitated by the generation of local heat following absorption of nonionizing laser energy by chromophores. Here, the inherent ability of biomaterials is exploited to absorb nonionizing, mid-infrared (midIR) light in order to engender rapid photothermal sealing and repair of soft tissue wounds. In this approach, the biomaterial simultaneously acts as a photothermal convertor as well as a biosealant, which dispenses the need for exogeneous light-absorbing nanoparticles or dyes. Biomechanical recovery, mathematical modeling, histopathology analyses, tissue strain mapping using digital imaging correlation, and visualization of the biosealant-tissue interface using hyperspectral imaging indicate superior performance of midIR sealing in live mice compared to conventional sutures and glue. The midIR-biosealant approach demonstrates rapid sealing of soft tissues, improves cosmesis, lowers potential for scarring, obviates safety concerns because of the nonionizing light used, and allows adoption of a wide diversity of biomaterials. Taken together, the studies demonstrate a novel advance both in biomaterials for surgical sealing along with the use of nonionizing midIR light, with high potential for clinical translation.     

Electromigration Damage Characterization in Sn-3.9Ag-0.7Cu and Sn-3.9Ag-0.7Cu-0.5Ce Solder Joints by Three-Dimensional X-ray Tomography and Scanning Electron Microscopy

Cerium (Ce)-containing Sn-3.9Ag-0.7Cu alloy exhibits desirable attributes of microstructural refinement, increased ductility, and mechanical shock performance, while possessing better oxidation resistance than other rare-earth-containing solders. In addition to the beneficial mechanical properties, it is imperative to study the reliability performance of novel solder alloys in the form of electromigration experiments, in comparison with Sn-3.9Ag-0.7Cu. In this study, electromigration tests were conducted on solder joints at elevated temperature with a constant current using a V-groove testing methodology. The microstructural change of solder joints during electromigration was investigated by scanning electron microscopy, and the void growth was monitored utilizing the three-dimensional (3D) x-ray microtomography imaging technique. The current density inside the solder matrix was determined by 3D microstructure-based finite-element modeling. Finally, the product of diffusivity and effective charge number of solder joints during electromigration was calculated from both marker displacement and 3D void growth. It was found that electromigration-induced Cu diffusion in Sn-3.9Ag-0.7Cu-0.5Ce alloy was greatly accelerated, and void formation at the cathode side was retarded as a result of finer microstructure and existence of CeSn₃ intermetallic particles.     

On the Nature of the Interface between Ag<Subscript>3</Subscript>Sn Intermetallics and Sn in Sn-3.5Ag Solder Alloys

We report on the nature of the orientation of Ag₃Sn and the Ag₃Sn/Sn interface in Sn-3.5Ag solder. Orientation imaging microscopy (OIM) and transmission electron microscopy (TEM) were used to characterize the orientation and nature of the interface, respectively. OIM and TEM showed that Sn-3.5Ag containing spherical Ag₃Sn particles does not have a preferred orientation with respect to the Sn matrix. However, needle-like Ag₃Sn formed during slower cooling appeared to have a preferred orientation within individual Sn colonies. The interface between Sn and Ag₃Sn appeared to be incoherent, as confirmed by high-resolution TEM analysis.     

Localization of fringes produced by rotation of the recording plate in focused-image holography

The equations determining the localization of interference fringes produced by rotation of the photographic plate in ‘focused-image holography’ are derived for an arbitrary cylindrical surface. The important properties of fringe localization are discussed and are experimentally verified.     

Tensile Behavior of Single-Crystal Tin Whiskers

The growth of metallic (predominantly Sn) whiskers from pure metallic platings has been studied for over 50 years. While the phenomenon of Sn whiskering has been studied for decades, very little is known about the mechanical properties of these materials. This can be attributed to the difficulty in handling, gripping, and testing such fine-diameter and high-aspect-ratio whiskers. We report on the stress–strain behavior of Sn whiskers inside a dual-beam focused ion beam (FIB) with a scanning electron microscope (SEM). Lift-out of the whiskers was conducted in situ in the FIB, and the whiskers were tested using a microelectromechanical system tensile testing stage. Using this technique, the whiskers had minimum exposure to ambient air and were not handled by hand. SEM images after fracture enabled reliable calculation of the whisker cross-sectional area. Tests on two different whiskers revealed relatively high tensile strengths of 720 MPa and 880 MPa, respectively, and a limited strain to failure of ～2% to 3%. For both whiskers, the Young’s modulus was between 42 GPa and 45 GPa. It is interesting to note that the whiskers were quite strong and had limited ductility. These findings are intriguing and provide a basis for further work to understand the effect of Sn whisker mechanical properties on short circuits in electronics.     

Reflection and transmission of electromagnetic waves normally incident on a plasma slab moving uniformly along a magnetostatic field

Power reflection and transmission coefficients are found for linearly and circularly polarized plane electromagnetic waves, normally incident on a plasma slab, moving uniformly along a magnetostatic field, normal to the slab boundaries. The solution is found by applying the boundary conditions in the rest frame, and then using relativistic transformations for the fields and the plasma parameters to find the reflection and transmission coefficients observed in the laboratory frame. The results for the circularly polarized incident waves are found in closed form. Numerical results are presented for linearly polarized incident waves. It is found that with an increase in the magnetostatic field, the absolute maximum of the reflection coefficient increases at different velocities. An increase in the magnetostatic field makes the slab more transparent at velocities for which the transmission coefficient with no magnetostatic field is very small. A dielectric-like behavior is observed for large magnetostatic fields. The sum of the power reflection and power transmission coefficients is found to be no longer equal to unity for velocity different from zero.     

Effects of cooling rate on creep behavior of a Sn-3.5Ag alloy

The effect of cooling rate on microstructure and creep behavior of bulk, eutectic Sn-3.5Ag solders was studied. The cooling rate is an important processing variable that significantly affects the microstructure of the solder and therefore determines its mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace, which resulted in cooling rates of 24°C/s, 0.5°C/s, and 0.08°C/s, respectively. The cooling rate decreased the secondary dendrite arm size and the spacing of the Sn-rich phase, as well as the morphology of Ag₃Sn. The Sn-dendrite arm size and spacing were smaller at fast cooling rates, while slower cooling rates yielded a nearly eutectic microstructure. The morphology of Ag₃Sn also changed from relatively spherical, at faster cooling rates, to needlelike for slower cooling. The effect of cooling rate on creep behavior was studied at 25°C, 60°C, 95°C, and 120°C. Faster cooling rates were found to increase the creep strength of the solder due to the refinement of the solder microstructure. Stress exponents, n, indicated that dislocation climb was the controlling mechanism. Activation energies, for all cooling rates, indicated that the dominant diffusional mechanism corresponded to dislocation pipe diffusion of Sn. Grain boundary sliding (GBS) measurements were conducted, using both scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was observed that GBS had a very small contribution to the total creep strain.     

Effects of cooling rate on the microstructure and tensile behavior of a Sn-3.5wt.%Ag solder

The tensile behavior and microstructure of bulk, Sn-3.5Ag solders as a function of cooling rate were studied. Cooling rate is an important processing parameter that affects the microstructure of the solder and, therefore, significantly influences mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace. Cooling rate significantly affected secondary dendrite-arm size and spacing of the Sn-rich phase, as well as the aspect ratio of Ag₃Sn. The Sn-rich dendrite-arm size and spacing were smaller for water-cooled specimens than for air-cooled specimens. Furnace cooling yielded a nearly eutectic microstructure because the cooling rate approached equilibrium cooling. The morphology of Ag₃Sn also changed from spherical, at a fast cooling rate, to a needlelike morphology for slower cooling. The changes in the microstructure induced by the cooling rate significantly affected the mechanical behavior of the solder. Yield strength was found to increase with increasing cooling rate, although ultimate tensile strength and strain-to-failure seemed unaffected by cooling rate. Cooling rate did not seem to affect Young’s modulus, although a clear coorelation between modulus and porosity was obtained. The mechanical behavior was correlated with the observed microstructure, and fractographic analysis was employed to elucidate the underlying damage mechanisms.     

A novel method for functionalization of C-4 methyl in triterpenoids. A synthesis of cycloeucalanone

Functionalization of 4-methyl group in cycloartane-type triterpenoids has been accomplished utilizing, in the key step, photolytic decomposition of an hypoiodite derived from a 3β-hydroxymethyl-4,4-dimethyl precursor. The synthesis of cycloeucalanone from cyclolaudanone is reported.