Renato P. Camata

Osteogenic differentiation of human mesenchymal stem cells directed by extracellular matrix-mimicking ligands in a biomimetic self-assembled peptide amphiphile nanomatrix

This study investigated the ability of nanoscale, biomimetic peptide amphiphile (PA) scaffolds inscribed with specific cellular adhesive ligands to direct the osteogenic differentiation of human mesenchymal stem cells (hMSCs) without osteogenic supplements. PA sequences were synthesized to mimic the native bone extracellular matrix (ECM), expressing different isolated ligands (i.e., RGDS, DGEA, KRSR). All PAs were presented as self-assembled two-dimensional coatings for the seeded hMSCs. Initial attachment results demonstrated that the different PAs could be individually recognized based on the incorporated adhesive ligands. Long-term studies assessed osteogenic differentiation up to 35 days. The RGDS-containing PA nanomatrix expressed significantly greater alkaline phosphatase activity, indicating the early promotion of osteogenic differentiation. A progressive shift toward osteogenic morphology and positive staining for mineral deposition provided further confirmation of the RGDS-containing PA nanomatrix. Overall, the PA nanomatrix clearly has great promise for directing the osteogenic differentiation of hMSCs without the aid of supplements by mimicking the native ECM, providing an adaptable environment that allows for different adhesive ligands to control cellular behaviors. This research model establishes the beginnings of a new versatile approach to regenerate bone tissues by closely following the principles of natural tissue formation.

Size classification of silicon nanocrystals

We report on the synthesis of size-classified silicon nanocrystals by differential mobility classification of a polydisperse ultrafine silicon aerosol. Using the described technique, the average nanocrystal size can be tuned by simply adjusting an electric field. Samples of nonagglomerated silicon nanocrystals have been obtained and size control has been achieved within 15%–20% in the 2–10 nm size regime.

In vitro dissolution and mechanical behavior of c-axis preferentially oriented hydroxyapatite thin films fabricated by pulsed laser deposition

Owing to its resemblance to the major inorganic constituent of bone and tooth, hydroxyapatite is recognized as one of the most biocompatible materials and is widely used in systems for bone replacement and regeneration. In this study the pulsed laser deposition technique was chosen to produce hydroxyapatite with different crystallographic orientations in order to investigate some of the material properties, including its in vitro dissolution behavior, as well as mechanical properties. The crystallographic orientations of hydroxyapatite coatings can be carefully controlled, mainly by varying the energy density of the KrF excimer laser (248 nm) used for deposition. Nanoindentation results showed that highly c-axis oriented hydroxyapatite coatings have higher hardness and Youngs modulus values compared with the values of randomly oriented coatings. After 24h immersion in simulated physiological solution the overall surface morphology of the highly oriented coatings was dramatically altered. The porosity was drastically increased and sub-micron pores were formed throughout the coatings, whereas the average size of the grains in the coatings was not significantly changed. The composition of the textured hydroxyapatite coatings remained essentially unchanged. Their c-axis texture, on the other hand, was rather enhanced with an increase in immersion time. The c-axis oriented hydroxyapatite surfaces are likely to promote preferentially oriented growth through a cyclic process of dissolution and reprecipitation, followed by homoepitaxial growth. The remarkable morphological and microstructural changes after dissolution suggest a capability of highly textured hydroxyapatite as a tissue engineering scaffold with an interconnecting porous network that may be beneficial for cellular activity.

Photoelectric emission measurements on the analogs of individual cosmic dust grains

The photoelectric emission process is considered to be the dominant mechanism for charging of cosmic dust grains in many astrophysical environments. The grain charge and equilibrium potentials play an important role in the dynamical and physical processes that include heating of the neutral gas in the interstellar medium, coagulation processes in the dust clouds, and levitation and dynamical processes in the interplanetary medium and planetary surfaces and rings. An accurate evaluation of photoelectric emission processes requires knowledge of the photoelectric yields of individual dust grains of astrophysical composition as opposed to the values obtained from measurements on flat surfaces of bulk materials, as it is generally assumed on theoretical considerations that the yields for the small grains are much different from the bulk values. We present laboratory measurements of the photoelectric yields of individual dust grains of silica, olivine, and graphite of ~0.09-5 μm radii levitated in an electrodynamic balance and illuminated with UV radiation at 120-160 nm wavelengths. The measured yields are found to be substantially higher than the bulk values given in the literature and indicate a size dependence with larger particles having order-of-magnitude higher values than for submicron-size grains.

Mid-IR laser oscillation in Cr 2+ :ZnSe planar waveguide

We demonstrate 2.6 µm mid-infrared lasing at room temperature in a planar waveguide structure. Planar waveguides were fabricated using pulsed laser deposition (PLD) by depositing chromium doped zinc selenide thin films on sapphire substrate (Cr2+:ZnSe/sapphire). Highly doped Cr2+:ZnSe/Sapphire thin film sample was also used to demonstrate passive Q-switching of Er:YAG laser operating at 1.645 µm.

A Differential Mobility Analyzer and a Faraday Cup Electrometer for Operation at 200-930 Pa Pressure

Abstract We have developed a differential mobility analyzer (DMA) based on the DMA devised by Seto et al. (1997) and a Faraday cup electrometer for measurement of nanometer-sized particles at a few hundred Pa and examined the operating characteristics of the DMA using the tandem DMA technique. The tandem DMA calibration establishes that the DMA successfully classifies particles in the 200–930 Pa pressure range. It was also found that the transfer function of the DMA follows the triangular transfer function and the resolution of the DMA is close to that given for an ideal case. As a standard of a minimum pressure that may be probed with the present DMA system, 400 Pa is estimated when the DMA operates with a 3 nl min −1 sheath flow and a 1 nl min −1 aerosol flow rate.

Space-charge effects in nanoparticle processing using the differential mobility analyzer

We report the observation of mobility classification breakdown due to strong space-charge effects during nanoparticle processing in a radial differential mobility analyzer (DMA). A simple dimensionless group, the space-charge number, is introduced to help identify the conditions for which this phenomenon becomes important. Our analysis suggests a few DMA design features and operation conditions that should enable the accurate classification of ultrafine aerosols with high concentrations of charged particles.

Crystal field engineering of transition metal doped II-VI ternary and quaternary semiconductors for mid-IR tunable laser applications

We report on crystal-field engineering of solid-state laser gain media based on new transition metal (TM) (iron) doped II-VI ternary and quaternary semiconductor materials for middle-infrared (mid-IR) tunable laser applications. Novel ternary and quaternary TM:II-VI materials were fabricated in powder form using thermal annealing of mixtures of commercially available binary powders sealed in evacuated quartz ampoules. These resultant powders were characterized using XRD, micro-Raman spectroscopy, photoluminescence (PL) and PL kinetics. We demonstrate: 1) that this synthesis method enables laser active powder media and is an effective means to fabricate and prototype novel laser active materials, 2) by introducing heavier or lighter ions into the host crystal lattice, it is possible to independently engineer the spectral positions of the absorption and PL band of TM ions in II-VI crystals, and 3) the first time to our knowledge room temperature, mirrorless, random lasing of iron doped Zn0.5Cd0.5Te powders at 5.9 μm.

Calcium Phosphate Bioceramics with Tailored Crystallographic Texture for Controlling Cell Adhesion

The orientation distribution of crystalline grains in calcium phosphate coatings produced by pulsed laser deposition was investigated using an X-ray pole-figure diffractometer. Increased laser energy density of a KrF excimer laser in the 4–7 J/cm 2 range leads to the formation of hydroxyapatite grains with the c-axis preferentially aligned perpendicularly to the substrates. This preferred orientation is most pronounced when the plume direction of incidence is normal to the substrate. This crystallographic texture of hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups, and dehydroxylation effects during deposition all seem to play important roles in texture development. Studies of mesenchymal stem cell/biomaterial interactions show that the surfaces with an oriented distribution of hydroxyapatite grains promote significantly better cell adhesion than surfaces with random grain distribution.

Biphasic and Preferentially Oriented Microcrystalline Calcium Phosphate Coatings: In Vitro and In Vivo Studies

We report results of in-vitro and in-vivo studies on biphasic thin film coatings of hydroxyapatite/tetracalcium phosphate produced by pulsed laser deposition using ablation targets of crystalline hydroxyapatite. Changes in coating phase composition during in-vitro dissolution experiments were monitored by x-ray diffraction. Scanning electron microscopy was used to assess variations in surface morphology. In-vivo experiments involving the insertion of coated metallic implants in the proximal tibia and distal femur of New Zealand White Rabbits were carried out. Histomorphometric studies on implant samples after surgical extraction show that biphasic coatings produced may lead to enhanced osteointegration compared to pure hydroxyapatite coatings.