Bone consists of up to 70% mostly nanocrystalline hydroxyapatite (HA), and the rest is mostly collagen. One can suggest that synthetic nanoHA/collagen composites could potentially be the closest materials to resemble the bone microarchitecture and prepare resorbable bone substitutes and scaffolds. However, the data on the mechanical properties and property/structure relationships of HA/collagen composites are still scarce. It can be explained, in part, by the high cost of collagen and substantial amounts of materials needed for many tests. However, gelatin is cheap, has many properties similar to collagen, and can be used as a model material for the mechanical testing of HA-based composites. In this study, we report the results of an investigation of some mechanical properties of HA/gelatin composites with 0 to 80% HA nanoparticle (size 15-60 nm) loading by weight. The HA nanoparticle dispersions were mixed with gelatin in trifluoroethanol or in water in different ratios and placed in Teflon molds to produce the sheets with the thickness in the range of 0.4 – 1.0 mm. Nanoindentation technique was used to determine the Young's modulus and hardness. Bending tests were performed using dynamic mechanical analysis with the amplitudes in the 1 – 50 micron range at 1 Hz. The values of Young's modulus (1 – 20 GPa), hardness (70 – 500 MPa) and bending modulus (0.3 – 2.4 GPa) were obtained. The highest values of the Young's modulus and hardness of these composite materials were achieved for 40% – 60% HA content by weight, which was close to the values for similar HA/collagen composites. However, the maximum bending strength was observed for 20 – 35% HA content. We discuss further the observed trends of the mechanical properties and their dependence on other factors such as the test conditions, sample geometry, and HA particle size.

Calcium phosphate (CaP) materials are commonly used in bone tissue engineering applications since they closely resemble the chemistry of bone and teeth. The inorganic component of mineralized tissue is multiphasic in nature-thus to better replicate those tissues, CaP materials should also be multiphasic. Combustion synthesis is a process that creates multiphasic CaP (HCaP) with low energy input over a relatively short time. The structure and chemistry of HCaP synthesized via auto-ignition combustion synthesis (AICS) varies greatly with respect to structural hydration. Product hydration was accomplished by modifying hydrogen and oxygen content in the combustion reaction by changing the amount of fuel, urea [ ] pre-reaction, and heating or sintering products post-reaction. The reaction equation for this specific system is given below. Calcium nitrate [ ], and ammonium nitrate [ ] are the components that form HCaP. Urea acts as an ignition source and fuel. Changes in the amount of urea dictate the amount of excess hydrogen to form water within the reaction. Excess products formed include water, carbon dioxide, and nitrogen. Salts of the reactants were mixed with 10 milliliters of de-ionized water in a Pyrex beaker, heated on a hot plate for 20 minutes or until the reactants began to foam, and then placed in a muffle furnace at 1000°C until the foam ignited in a combustion reaction. This was noted by the progression of a combustion wave throughout the foam. Post-AICS, products were heated at 105°C for 8 hours and 24 hours and massed to determine water content of the product. Subsequently, the products were sintered at 1000°C for 8 hours and massed again. The primary products formed using AICS are hydroxyapatite (HA), á-tricalcium calcium phosphate (TCP) and hydrated forms of tricalcium phosphate (HTCP). During low temperature heating, 105°C, water content decreases as time increases and the products began to densify. Initial results indicate that surface porosity decreases during the powder densification. XRD shows that peak intensity increases after low temperature heating, indicating an increase in crystallinity and grain orientation. XRD confirms that both crystalline and amorphous phases occur in the hydroxyapatite (HA), á-TCP and HTCP products. The amount of structural hydration has an effect on CaP, and these effects are noted by an increase in density and decrease in porosity as structurally bound water is removed from the system. Future research will be dedicated to determining hydration ratio (amount of urea in the reaction to the amount of water within the products) and a Ca:P ratio that result in optimal powder porosity, ductility and grain size generating a multiphasic HCaP implant biomaterial that accurately replicates natural bony tissue.

Negatively charged poly(lactic-co-glycolic acid) (PLGA) microspheres were prepared by the solid-in-oil-in-water (s/o/w) method using the anionic surfactant, sodium dodecyl sulfate (SDS), and a hydrophilic antibiotic (amoxicillin) was encapsulated with an encapsulation efficiency of 40.6%. A layer of hydroxyapatite (HA) was coated on these negatively charged PLGA microspheres by a dual constant composition method in 3 - 6 hours. The HA-coated PLGA microspheres (HPLG) had a core-shell structure and were characterised by scanning electron microscopy, focused ion beam microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction and Fourier transform infrared spectroscopy. Sustained release of amoxicillin from HPLG for at least 31 days was shown from in-vitro drug release experiments. A typical triphasic drug release profile had been observed for PLGA and HPLG microspheres. This device exhibited two desirable properties: the sustained release from PLGA and osteoconductivity from HA. Hence, it could have potential applications in delivering drugs to treat bone disorders or infections.

We have used sol-gel methods to immobilize gold-silica nanoshells to create robust SERS based sensors. Using a protocol commonly used to immobilize proteins, biologically friendly SERS sensors for the study of gold binding peptides and proteins have been created. Specifically, by combining tetramethyl orthosilicate (TMOS), methyltrimethoxysilicate (MTMS), phosphate buffer, and gold nanoparticles we have created sol-gels with reduced fluorescence and Raman backgrounds. The resulting substrates have been tested using the Raman scattering response of 4-mercaptonbenzoic acid (4-MBA) to determine porosity and long-term stability of this SERS substrate. Multiple rinse cycles using phosphate buffer showed no significant decline in the SERS response of the substrate up to ten rinse cycles. Future studies will test the feasibility of using such substrates for the detection of biomolecules on the surface of gold.

The mechanics of living cells is largely determined by their cytoskeleton, a dynamic network of microtubules and protein filaments in the cytoplasm. Microtubules are the most rigid cytoskeletal filaments and bear compressive forces in cells. Microtubules in vivo often severely buckle into short wavelengths. By contrast, isolated microtubules in vitro buckle into single long-wavelength arcs. To explain this discrepancy, we describe a mechanics model of microtubule buckling in living cells. The model shows that, while the buckling wavelength is set by the interplay between the microtubules and the elastic surrounding filament network, the buckling growth rate is set by the viscous cytoplasm. The quantitative results from the model shed light on developing new and robust methods to measure various in vivo mechanical properties of subcellular structures, e.g., bending rigidity of microtubules, elastic modulus of filament network, and viscosity of cytoplasm. The model can also be readily generalized to study the deformation of hard engineering materials at soft bio-interfaces.

Despite the recognized success and worldwide acceptance of ultrahigh molecular weight polyethylene (UHMWPE) for total joint arthroplasty, the generation of UHMWPE wear debris from the articulating surface is of major concern and limits the longevity of the artificial joint device. Blends of UHMWPE with an aromatic thermosetting copolyester (ATSP) at 50:50 volume ratio using poly(ethylene-co-acrylic acid) (PEA) as a compatibilizer were developed to address this problem. The amount of PEA was 0, 5, 10, 15 and 20 weight percent of the weight of ATSP, respectively. The wear properties of these blends were evaluated by a pin-on-disk wear test in which an ASTM F-75 cobalt-chromium alloy disk was chosen as a counterface and sterile filtered bovine serum diluted in deionized water to 75% (volume) was used as a lubricant. The wear tests from 0.2 to 3 million cycles showed that UHMWPE/ATSP blend with 10 wt% PEA had average weight loss smaller than UHMWPE and comparable to crosslinked UHMWPE. The wear debris study indicated that UHMWPE/ATSP blend with 10 wt% PEA created a smaller size percentage of the wear debris particles in the biologically active range than UHMWPE and crosslinked UHMWPE. The direct-contact cytotoxicity tests showed that ATSP and UHMWPE/ATSP blend with 10 wt% PEA were not toxic.

Owing to its photoluminescent properties and high surface area, porous silicon (por-Si) has shown great potential toward a myriad of applications including optoelectronics, chemical sensors, biocomposite materials, and medical implants. However, the native hydride-termination is only metastable with respect to surface oxidation under ambient conditions. Por-Si samples oxidize and degrade even more quickly when exposed to saline aqueous environments. Borrowing from solution phase synthetic methods, a selection of hydrosilylation reactions has been recently reported for functionalizing organic groups onto oxide-free, hydride-terminated porous silicon surfaces. Monolayers, bound through direct silicon-carbon bonds, are produced via thermal, microwave, Lewis acid, and carbocation mediated pathways. All of these wet, benchtop methods result in the formation of stable monolayers which protect the underlying silicon surface from ambient oxidation and chemical attack. However, no direct comparison of monolayer stability resulting from these diverse mechanisms has been reported. A variety of alkyl monolayers were prepared on porous silicon using the diverse hydrosilylation routes describe above and then immersed into a sequence of simulated gastric and intestinal fluids to replicate the conditions of potential por-Si biosensors or medicinal delivery systems in the human gastrointestinal tract. Degradation of the organic monolayers and oxidation of the underlying por-Si surfaces were monitored using both qualitative and semiquantitative transmission mode Fourier transform infrared spectroscopy (FTIR). Our initial results indicate that methods employing chemical catalysts often incorporate these species within the monolayer as defects, producing less robust surfaces compared to catalyst-free reactions. Regardless, monolayer protected por-Si samples demonstrated superior durability as opposed to the unfunctionalized controls.

We identified both crystalline and amorphous phase of human spleen particles. The silicon particles in the spleen were 10-30 μm large. Silicon, silicon-aluminium and silicon-calcium particles by EDX were found. We assume that the silicon must enter the organism from the external environment and the presence of silicon in the human spleen is consequence of the cleaning function of human spleen.

Mössbauer spectroscopy of studied tissues revealed different phase of iron oxide in the human spleen. On the ground of this consideration we can claim all samples of investigated tissues exhibit presence of two different paramagnetic iron phases, both based on three-valent (Fe3+) atoms. Consequently only 4 different iron-oxides correspond with experimental results. Multielemental composition of iron particles was found by EDX analysis. We suppose that pH and time are significant factors influence biomineralization of iron in the human spleen.

An analytical model is developed for the effect of surface gradient in ligand density on the adhesion kinetics of a curved elastic membrane with mobile receptors. The displacement and speed of spreading at the edge of the adhesion zone as well as the density profile of receptors along the membrane are predicted as a function of time. According to results, in the diffusion-controlled regime, the front edge displacement of adhesion zone and the rate of membrane spreading decreased with increasing ligand density in a certain direction. Furthermore, the displacement of the edge of the adhesion zone did not scale with the square root of time, as observed on substrates with uniform ligand density.

The sheer number of bacteria living on solid surfaces makes a compelling argument for the existence of surface sensing mechanisms. However, surface sensing abilities have not been widely studied in bacteria, because such abilities are not macroscopically observable in attached organisms with limited mobility. We report experimental evidence that attached Staphylococcus aureus cells recognize the steep gradient near their substrate interface and localize substrate-specific biomolecules toward that region. We present Atomic Force Microscopy-based affinity maps which reflect the cells' biochemical sensory response to the substrate and provide a unique view of regions indicating specific binding activity and bond resilience.

Certain diseases have been associated with the administration of heavy elements as contrast agents to patients undergoing medical imaging procedures. Recently, the presence of gadolinium (Gd) administered as a paramagnetic contrast agent for MRI contrast studies was associated with the incidence of Nephrogenic Fibrosing Dermopathy (NFD), also called Nephrogenic Systemic Fibrosis (NSF). To determine specific causation, Gd and other metallic nanoparticles in various tissues must be detected directly and characterized in-situ. This is done to develop specific mechanisms for the chemical modification of the metal elements as the result of a biologic response. Fixed biopsies embedded in paraffin were sectioned at 3-5 μm thick, deparaffinized by hand (xylene and 100% ethyl alcohol), placed on carbon planchettes, and allowed to air dry. Deparaffinized tissues were examined using a field emission SEM (FE-SEM) to directly detect and image the presence of Gd as well as other metals. Backscatter electron (BSE) imaging (20kV) was used to discern metal particles within tissues. Energy dispersive spectroscopy (EDS) (15kV) was used to verify the specific elements present. This allowed for the spatial characterization of the nanoparticles within the tissues but due to the physical limitations of SEM/EDS, quantification of the amount of metal was not possible. Mass concentration of the metal elements was determined using inductively coupled plasma mass spectrometry (ICP-MS) on digested tissues. Thick tissue sections, >30 μm, were used for ICP-MS to provide enough mass for detection. These sections were taken from the histology blocks adjacent to the thin sections used in the FE-SEM. Gadolinium was detected in skin, heart, lung and liver tissues. The highest concentrations were found in heart and skin; both had average tissue concentrations greater than 200μg/g (100-450μg/g range). In skin, gadolinium nano-particulates were readily seen near cell body locations in autopsy samples and within the cells in biopsy samples. The cells where gadolinium was most easily found were along blood vessels. In the cells the agglomerates appear granular with a size of less than 100 nm. They are diffused throughout the cell but as of this time not associated with any particular cell structure. Subsequent work using TEM will examine that aspect as well as the specific ultrastructure and chemistry of the nanoparticles. In this investigation, gadolinium was detected in the tissues of a number of patients with NSF. Although neither dispositive of a pathophysiologic mechanism, nor proof of causation, the detection and quantification of gadolinium within tissues of NSF patients is supportive of the epidemiologic association between exposure to gadolinium containing contrast material and development of the disease.

Amperometric urea sensor is more suitable than optical and potentiometric urea sensor to diagnose hyperammonemia. However, because sensitivity in low concentration decreases remarkably, despite amperometric urea sensor has been studied for a long time it has not been applied for clinical diagnosis. In this paper, a new structure for an amperometric urea sensor was fabricated by MEMS, electrochemical etching, and electrostatic covalent binding techniques. Until now most amperometric urea sensors have had a membrane fixed on top of the transducer. That method often leads to malfunction of the sensor, arising from problems such as inadequate membrane adhesion, insufficient mechanical stability, and low sensitivity. To solve these kinds of problems, urease (Urs) was immobilized by electrostatic covalent binding method on the porous silicon (PSi) substrate coated self-assembled monolayer (SAM). Electrostatic covalent binding method was used to keep anisotropic orientation of urease on SAM.