|
|
NANOSTRUCTURED BIOCOMPATIBLE SYSTEMS BASED ON MAGNETIC NANOPARTICLES AND STIMULI RESPONSIVE POLYMERS |
|
Contract nr: 71-068 / 2007
Contact: Dr. Rodica Turcu |
Results
Stage I StageII StageIII StageIV Stage III
I. Synthesis of smart materials with core-shell structure, based on magnetic nanoparticles and biocompatible polymers. In this stage at first magnetite was obtained. Later, without separating the magnetic nanoparticles from the aqueous solution, the absorption reaction was made to cover the nanoparticles with glycolic acid, serine, 2-bromopropionic acid and acrylic acid. In this way stabilized magnetic nanoparticles were obtained, with their surface consisting in different functionalized groups. Further on, these groups can be directly polymerized with different monomers. In this way core-shell magnetic nanoparticles were obtained, based on polycaprolactone (PCL), and polylactic acid (PLA) , and polymerizing the nanoparticles having on their surface hydroxyl groups. The hydroxyl group is the initiator of polymerizing reaction of lactones. Magnetic nanoparticles with core-shell structure based on poly(hydroxyethyl metacril) (PHEMA) were obtained. The HEMA polymerization took place in the presence of the nanoparticles stabilized with 2-bromoprpionic acid. Magnetic nanoparticles with core-shell structure based on poly(N- isopropyl acrylamide) (PNIPA) were obtained. NIPA polymerization took place in the presence of the nanoparticles stabilized with a double layer of shell. In innovative application of the polymer synthesis is the polymerization of caprolactone in microwave field, in the presence of the magnetic nanoparticle and catalyst and without solvents. By using the microwave field the polymerization time is considerably reduced from 5 hours to a few minutes. The magnetic core are not affected by the microwave field.
II. Characterization of the smart materials with core-shell structure, based on magnetic nanoparticles and biocompatible polymers. FTIR measurements confirmed the formation of magnetic nanostructures, due to the presence in all spectra of the absorption band specific to magnetite and the investigated polymers. DSC measurements confirmed that PCL is a biodegradable polymer with response to temperature. The PCL melting point was found to be around 480C. XRD measurements on magnetic nanoparticles stabilized with glycol acid and serina, respectively confirmed the presence of magnetite spinel structure. By line profile analysis it was determined the crystallite mean size (Deff). For the magnetite nanoparticles stabilized with glycol acid , the mean crystallite size is Deff=9.4 nm. For the magnetite nanoparticles stabilized with serine, the mean crystallite size is Deff=16.3 nm. TEM images showed that the nature of molecules used for in situ functionalization influence the morphology of the nanoparticles. In case of serine the nanoparticles are polyhedral, and in case of glycol acid the nanoparticles are spherical. The nanoparticle diameter observed by TEM is 10-15 nm for the functionalized nanoparticles, and it increases with polymer covering to 20-25 nm. XPS spectroscopy measurements proved that thermal treatment on magnetite nanoparticles does not imply a transition phase, by the absence in the spectra of the iron oxides satellites. Mossbauer spectroscopy shows a relatively similar magnetic phase in case of nanoparticles with serine, glycol acid and caprolactone. A different magnetic phase composition was found at nanoparticles with lactic acid. EPR measurements showed at all samples the increase of the resonance field and a decrease of line width by increasing the temperature. It should be noticed that the line width are large, this is correlated with strong dipolar interactions and the possibility of nanoparticles clusterization. DLS measurements showed an accentuated variability of the agglomeration sizes. All samples, in particular at successive measurements present relatively constant sizes. Magnetic measurements taken at room temperature evidenced the superparamagnetic behavior of the nanocomposites.
|
