فصلنامه مهندسی پزشکی زیستی
سال سوم شماره 2 (تابستان 1388)

A great deal of attention has been drawn to the colloidal chemistry based semiconductor nanocrysallites, also known as quantum dots (QDs). Because of the strong quantum confinement, quantum dots have unique size-dependent optical properties, which are much more superior to the conventional organic fluorescence materials. In addition, strong chemical resistant makes inorganic semiconductor QDs an ideal candidate for next-generation of bio-labels and other biomedical applications. This study presents a synthesize method of high quality biocompatible CdSe QDs in aqueous solution by using gelatin as inhibitor. A thin ZnS layer was grown on CdSe QDs, forming a CdSe/ZnS core/shell structure, to improve the photoluminescence. The optical properties of the QDs were characterized by photoluminescence spectra. The stability of CdSe/ZnS QDs in aqueous solution has been improved with capping in mercaptosuccinic acid (MSA) groups. PAGE test results show that carboxylic groups of MSA have interacted with NH2 agent of CD20 antibodies. We evaluate the in vitro efficiency of the luminescence of the bioconjugated QDs to kill Raji cells. Raji cells have anti-CD20 which can especially connect to CD20-QDs. In conclusion, we found that CD20-CdSe/ZnS bioconjugated QDs with different concentration 50-250 µg/mL which have been exited at 400nm in 2h intervals can result in Raji cells death. This study shows the potential of CdSe/ZnS for cancer treatment.

The aim of the present paper is to investigate the effect of incorporating various amounts of strontium ions (0.19 - 2.23 wt%) into calcium sulfate bio ceramics on the physical, structural properties and in vitro bioactivity and compare these properties with those of a pure calcium sulfate dehydrate (gypsum) as control. Strontium-doped gypsum (Sr-gypsum) was obtained by mixing calcium sulfate hemihydrates powder and solutions of strontium nitrate followed by washing the specimens with distilled water for the removal of residual salts. Gypsum was the only phase found in the composition of both pure and Sr-gypsum meanwhile a shift into lower diffraction angles was observed in the x-ray diffraction patterns of doped specimens. The Sr-doped sampled exhibited higher compressive strength and lower solubility than pure gypsum. Microstructure of all gypsum specimens had been composed of many rod-like small crystals entangled to each others with more elongation and higher thickness in the cases of Sr-gypsum. EDXA pattern of Sr-gypsum showed the presence of calcium and sulfur ions as the main elements of gypsum as well as slight amount of strontium ion. A continuous release of strontium was observed from the Sr-gypsum after soaking in simulated body fluid for 14 days. Proliferation rate of cultured osteoblasts and higher alkaline phosphatase activity on doped samples was better compared to pure gypsum.

Ni-Ti shape memory alloys display unique properties such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior. They also are suitable materials for medical applications. In spite of high Ni content (above 50%) of Ni-Ti shape memory alloys, these materials represent good biocompatibility due to formation of Titanium oxide (TiO2) passive layer. Although TiO2 passive layer in these alloys can prevent releasing nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a Ni-Ti shape memory alloy with nominal composition of 50.7 atom% Ni was produced by vacuum induction melting (VIM) process. Homogenization treatments of samples were performed at 1050C for 24 hours. Microstructure and chemical composition of specimens were analyzed. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. In order to determine the amount of released Ni, the solution after potentiostatic tests was analyzed by atomic absorption spectroscopy. The samples after corrosion tests were investigated using Scanning Electron Microscopy (SEM). Furthermore corrosion products were analyzed by X-Ray Diffraction (XRD). Results indicate that the breakdown potential of the Ni-Ti alloy in NaCl 0.9% solution is higher than that in ringer solution. Topographical evaluations show that corrosion products are nearly the same in all samples.

Layered double hydroxides (LDHs) are layered solid materials having positively charged layers. A variety of negatively charged biomolecules can be hybridized with LDHs to evolve into bio-LDH Nano hybrids, including vitamins, drugs and DNA strands as well as simple organic acids. In this research, Mg-Al-LDH containing drug was synthesized by coprecipitation and anion exchange methods. The LDH structure was characterized by X-Ray Diffraction XRD, FTIR, SEM and STA techniques. The in vitro release profile of nano hybrids was analyzed by UV spectrophotometer. It was concluded that the present biocompatible hydrotalcite-like compound can be an excellent host material for encapsulating Ibuprofen and can play a role as a delivery vehicle for a controlled release.

Magnesium-contained Hydroxyapatite Nano powder was synthesized by wet chemical method using calcium nitrate tetra hydrate, magnesium nitrate hexa hydrate and di ammonium hydrogen phosphate in the presence of Glutamic acid. According to thermal analysis (STA) findings the samples were calcinated at specific temperatures and characterized by XRD, FTIR and TEM analysis. XRD results showed the that b-TCP ((Ca1-xMgx)3(PO4)2) was the dominant phase at 920°C. No characteristic peaks of hydroxyapatite were observed at that temperature. In contrast, the sample which was synthesized in the absence of Glutamic acid, contained both hydroxyapatite and b-TCP phase. The Findings showed a rapid decline in degree of crystallinity at 90°C with presence of Glutamic acid in reaction media. Transmission electron microscopy (TEM) observations on heat treated samples at 480°C revealed that using Glutamic acid has noticeable effect on crystallite size instead of its growth orientation. Dimensions of biomimetic nanoparticles as observed by TEM were 150x60nm and in the witness sample was 500x150nm. According to Scherrer formula for crystallite size, the size of the witness sample was calculated about 40nm. However, because of low degree of crystallinity it was impossible to calculate the size of Glutamic contained samples.

In this paper, dissolution kinetics of Amorphous Calcium Phosphate as well as cements in the Simulated Osteoclastic Medium (SOM) was evaluated based on the Shrinking Core models considering the liquid-solid reactions. Based on this model, three steps may be considered as controlling steps in the system: diffusion of component A through the surrounding films, reaction of component A with solid on the surface and diffusion through the interface. Two cases were considered here: 1. Shrinking Core model with formation of the intermediate phase 2. Shrinking Core model without formation of the intermediate phase Then, experimental data were used for the evaluation of the controlling steps and its mechanism (s). The results showed that enough amounts of calcium were entered into the solution in the initial stage of the process. This in turn causes to form a film on the particles, and the potential of calcium carbonate complex, resulted in the reduction of calcium saturation in the system. The amounts of entered calcium into the solution were higher in the amorphous system. In other words, a longer time is required in the crystalline system for more entrance of calcium into the solution (as in the sample H1T). Based on these observations, it was concluded that the approximately crystalline cements with carbonate falls between the crystalline cements without carbonate and amorphous system (The amounts of entered calcium into the solution). Dissolution rate of ACCPs in the Simulated Osteoclastic Medium (SOM) was dependent on the contents of carbonate and remaining water. Dissolution behavior in the SOM showed that the behavior of ACCP (high carbonate)–DCPD–PHA–Gelatin system was comparable to the ACCP (low carbonate)-DCPD. The presence of PHA and gelatin in cement system decreased the dissolution rate. The dissolution kinetics of the cements and ACCPs in the SOM was likely controlled by the formation of an acid-resisting ACP and/or DCPD as product layer.

In this study hydroxyapatite (HA), flour-hydroxyapatite (FHA) and fluorapatite (FA) nanopowders synthesized by sol-gel route. Theses powders are used as biocompatible materials for bone replacement and teeth restoration. Ammonium fluoride (NH4F MERK), calcium nitrate [Ca(NO3)2,4H2O MERK] and triethyl phosphite [TEP, (C2H5O) 3P MERK)] were used as F, Ca and P precursors respectively. Triethyl phosphite was first hydrolyzed in ethanol with a small amount of distilled water. To prepare FHA and FA, an appropriate amount of the NH4F powder was added directly to TEP solution. The appropriate amounts of TEP solution was added dropwise to the calcium nitrate solution to yield a stoichiometric ratio of Ca/P=1.67. The resulted solution stirred for 1 h and aged at 25°C for 24 h and 40°C for 72h afterward. After oven drying at 80°C, the powder samples were heat-treated at 550°C for 1 h in air. Microstructural characteristics, powder morphology, chemical structure and phase analysis and in vitro study were performed by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR), Zetasizer instrument and cell culture method. Fluoride-substituted hydroxyapatite powders (FHA) and Fluor apatite (FA) were successfully fabricated via a sol–gel technique with the incorporation of different levels of fluoride ions. Nearly complete substitution of the OH¯ by F¯ occurred with heat treatment, which was confirmed by FTIR analysis. The particle size distribution of powders evaluated by a zeta-sizer instrument was 100-160nm. The XRD results showed that the crystal size of powders is 20-50nm. The phase stability and crystallinity were different depending on the level of fluoride substitution. Moreover, the crystallinity and crystallite size of the powders increased with fluoride substitution. These improvements in the crystallization and phase stability of the apatite structure, resulting from the fluoride substitution via the sol– gel process, suggest enhanced performance of the FHA powders. The cellular response to the HA, FHA and FA powder was assessed by an in vitro culture method using fibroblastic L929 cells. After culturing for 3 days, the results showed that the number of cells increased with increasing fluoride substitution.