Mechanically Loading Cell/Hydrogel Constructs with Low-Intensity Pulsed Ultrasound for Bone Repair.

Low-intensity pulsed ultrasound (LIPUS) has been shown to be effective for orthopedic fracture repair and nonunion defects, but the specific mechanism behind its efficacy is still unknown. Previously, we have shown a measurable acoustic radiation force at LIPUS intensities traditionally used for clinical treatment and have applied this force to osteoblastic cells encapsulated in type I collagen hydrogels. Our goal in this study is to provide insight and inform the appropriate design of a cell therapy approach to bone repair in which osteoblasts are embedded in collagen hydrogels, implanted into a bony defect, and then transdermally stimulated using LIPUS-derived acoustic radiation force to enhance bone formation at the earliest time points after bone defect repair. To this end, in this study, we demonstrate the ability to measure local hydrogel deformations in response to LIPUS-induced acoustic radiation force and reveal that hydrogel deformation varies with both LIPUS intensity and hydrogel stiffness. Specifically, hydrogel deformation is positively correlated with LIPUS intensity and this deformation is further increased by reducing the stiffness of the hydrogel. We have also shown that encapsulated osteoblastic cells respond to increases in LIPUS intensity by upregulating both cyclooxygenase 2 and prostaglandin E2 (PGE2), both implicated in new bone formation and well-established responses to the application of fluid forces on osteoblast cells. Finally, we demonstrate that combining an increase in LIPUS with a three-dimensional culture environment upregulates both markers beyond their expression noted from either experimental condition alone, suggesting that both LIPUS and hydrogel encapsulation, when combined and modulated appropriately, can enhance osteoblastic response considerably. These studies provide important information toward a clinically relevant cell therapy treatment for bone defects that allows the transdermal application of mechanical loading to bone defects without physically destabilizing the defect site.

Ion-damage-free planarization or shallow angle sectioning of solar cells for mapping grain orientation and nanoscale photovoltaic properties.

Ion beam milling is the most common modern method for preparing specific features for microscopic analysis, even though concomitant ion implantation and amorphization remain persistent challenges, particularly as they often modify materials properties of interest. Atomic force microscopy (AFM), on the other hand, can mechanically mill specific nanoscale regions in plan-view without chemical or high energy ion damage, due to its resolution, directionality, and fine load control. As an example, AFM-nanomilling (AFM-NM) is implemented for top-down planarization of polycrystalline CdTe thin film solar cells, with a resulting decrease in the root mean square (RMS) roughness by an order of magnitude, even better than for a low incidence FIB polished surface. Subsequent AFM-based property maps reveal a substantially stronger contrast, in this case of the short-circuit current or open circuit voltage during light exposure. Electron back scattering diffraction (EBSD) imaging also becomes possible upon AFM-NM, enabling direct correlations between the local materials properties and the polycrystalline microstructure. Smooth shallow-angle cross-sections are demonstrated as well, based on targeted oblique milling. As expected, this reveals a gradual decrease in the average short-circuit current and maximum power as the underlying CdS and electrode layers are approached, but a relatively consistent open-circuit voltage through the diminishing thickness of the CdTe absorber. AFM-based nanomilling is therefore a powerful tool for material characterization, uniquely providing ion-damage free, selective area, planar smoothing or low-angle sectioning of specimens while preserving their functionality. This enables novel, co-located advanced AFM measurements, EBSD analysis, and investigations by related techniques that are otherwise hindered by surface morphology or surface damage.

Mapping the Photoresponse of CH3NH3PbI3 Hybrid Perovskite Thin Films at the Nanoscale.

Perovskite solar cells (PSCs) based on thin films of organolead trihalide perovskites (OTPs) hold unprecedented promise for low-cost, high-efficiency photovoltaics (PVs) of the future. While PV performance parameters of PSCs, such as short circuit current, open circuit voltage, and maximum power, are always measured at the macroscopic scale, it is necessary to probe such photoresponses at the nanoscale to gain key insights into the fundamental PV mechanisms and their localized dependence on the OTP thin-film microstructure. Here we use photoconductive atomic force microscopy spectroscopy to map for the first time variations of PV performance at the nanoscale for planar PSCs based on hole-transport-layer free methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) thin films. These results reveal substantial variations in the photoresponse that correlate with thin-film microstructural features such as intragrain planar defects, grains, grain boundaries, and notably also grain-aggregates. The insights gained into such microstructure-localized PV mechanisms are essential for guiding microstructural tailoring of OTP films for improved PV performance in future PSCs.

Direct Observation of Ferroelectric Domains in Solution-Processed CH3NH3PbI3 Perovskite Thin Films.

A new generation of solid-state photovoltaics is being made possible by the use of organometal-trihalide perovskite materials. While some of these materials are expected to be ferroelectric, almost nothing is known about their ferroelectric properties experimentally. Using piezoforce microscopy (PFM), here we show unambiguously, for the first time, the presence of ferroelectric domains in high-quality ß-CH3NH3PbI3 perovskite thin films that have been synthesized using a new solution-processing method. The size of the ferroelectric domains is found to be about the size of the grains (∼100 nm). We also present evidence for the reversible switching of the ferroelectric domains by poling with DC biases. This suggests the importance of further PFM investigations into the local ferroelectric behavior of hybrid perovskites, in particular in situ photoeffects. Such investigations could contribute toward the basic understanding of photovoltaic mechanisms in perovskite-based solar cells, which is essential for the further enhancement of the performance of these promising photovoltaics.

Mode of action studies of a new desensitizing mouthwash containing 0.8% arginine, PVM/MA copolymer, pyrophosphates, and 0.05% sodium fluoride.

OBJECTIVE: The mode of action of an arginine mouthwash using the Pro-Argin™ Mouthwash Technology, containing 0.8% arginine, PVM/MA copolymer, pyrophosphates and 0.05% sodium fluoride, has been proposed and confirmed as occlusion using a variety of in vitro techniques. METHODS: Quantitative and qualitative laboratory techniques were employed to investigate the mode of action of the new arginine mouthwash. Confocal laser scanning microscopy (CSLM) and atomic force microscopy (AFM) investigated a hydrated layer on dentine surface. Electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectroscopy (SIMS) and near-infrared spectroscopy (NIR) provided information about its chemical nature. RESULTS: CLSM was used to observe the formation of a hydrated layer on exposed dentine tubules upon application of the arginine mouthwash. Fluorescence studies confirmed penetration of the hydrated layer in the inner walls of the dentinal tubules. The AFM investigation confirmed the affinity of the arginine mouthwash for the dentine surface, supporting its adhesive nature. NIR showed the deposition of arginine after several mouthwash applications, and ESCA/SIMS detected the presence of phosphate groups and organic acid groups, indicating the deposition of copolymer and pyrophosphates along with arginine. CONCLUSION: The studies presented in this paper support occlusion of the dentine surface upon the deposition of an arginine-rich layer together with copolymer and phosphate ions from an alcohol-free mouthwash containing 0.8% arginine, PVM/MA copolymer, pyrophosphates and 0.05% sodium fluoride.

Long Distance Electron Transfer Across >100 nm Thick Au Nanoparticle/Polyion Films to a Surface Redox Protein.

Glutathione-decorated 5 nm gold nanoparticles (AuNPs) and oppositely charged poly(allylamine hydrochloride) (PAH) were assembled into {PAH/AuNP} n films fabricated layer-by-layer (LbL) on pyrolytic graphite (PG) electrodes. These AuNP/polyion films utilized the AuNPs as electron hopping relays to achieve direct electron transfer between underlying electrodes and redox proteins on the outer film surface across unprecedented distances >100 nm for the first time. As film thickness increased, voltammetric peak currents for surface myoglobin (Mb) on these films decreased but the electron transfer rate was relatively constant, consistent with a AuNP-mediated electron hopping mechanism.