Aleksandra N. Krklješ

On the Use of Radiation Technology for Nanoscale Engineering of Silver/Hydrogel Based Nanocomposites for Potential Biomedical Application

For nanoscience to become true nanotechnology, there is a need for breakthroughs in the engineering science of processing and manufacturing at the nanoscale. The radiation technology may offer a novel approaches to solving the problems of placement, high throughput, as well as integration across multiple length scales. Furthermore, there are critical needs for advanced materials in the area of biomaterial engineering, primarily in generating biomaterials of enhanced specific functionalities, which can be achieved by introduction of proper functionalities at the nanoscale dimensions. The radiation techniques are uniquely suited for such task, due to their favorable characteristics and in most cases not possible by other methods of synthesis. Therefore, we are systematically developing novel synthetic strategies for incorporation of noble metal nanoparticles in hydrogel networks by gamma irradiation, for possible biomedical application, using liquid filled cavities in hydrogels as nanoreactors (template synthesis). The radiation process has various advantages, such as easy process control, the possibility of joining synthesis and sterilization in one technological step. The radiation technique does not require any extra substances, and does not need any further purification. On the other hand, in recent years nanoscale antibacterial materials, such as nanocrystalline silver, as novel antimicrobial species have been seen as promising candidates for application owing to their high surface to volume ratio and their novel physical and chemical properties on the nanoscale level. Silver can be safely used even for patients who have diseases like Diabetes Mellitus that interfere with wound healing. The recent emergence of nanotechnology has provided a new therapeutic modality in silver nanoparticles for healing wounds.

Properties of Ag/PVP Hydrogel Nanocomposite Synthesized In Situ by Gamma Irradiation

Metal nanoparticles embedded in crosslinking polymer matrices i.e. hydrogels are novel class of materials which have attracted great attention due to applications in catalysis, photonics, optic, pharmaceutics and biomedicine. This work describes novel, simple and facile radiolytic synthesis of silver nanoparticles (AgNPs) within the poly(N-vinyl-2-pyrrolidone) (PVP) hydrogel. The hydrogel matrix was previously obtained by gamma irradiation induced crosslinking, while the in situ reduction of \(\mathrm{Ag}^{+}\) ions was performed using strongly reducing species formed under the radiolysis of water. Absorption spectrum of Ag/PVP hydrogel shows the presence of surface plasmon band with maxima at 400 nm, which confirms formation of AgNPs (diameter less than 10 nm). Swelling properties of synthesized hydrogels, neat PVP and Ag/PVP nanocomposite, were investigated in the SBF (simulated body fluid) solution at \(37^{\circ}\mathrm{C}\). Obtained results show that Ag/PVP hydrogel nanocomposite has higher equilibrium swelling compared with neat PVP hydrogel. Moreover, kinetics parameters were calculated from the swelling curves. The fluid transport mechanism is non-Fickian for both PVP and Ag/PVP hydrogels, meaning that both diffusion and polymer relaxation control the fluid transport.

Thermal properties of radiolytically synthesized PVA/Ag nanocomposites

The radiolytic method was used to synthesize two types of nanocomposites with silver, PVA/Ag by film casting and PVA hydrogel/Ag nanocomposites. This method is particularly suitable for generating metal nanoparticles in solution. The radiolytic species (solvated electrons and secondary radicals) exhibit strong reducing properties such that metal ions are reduced at each encounter. Metal atoms then tend to grow into larger clusters. It was found that solid or swollen polymers are able to stabilize small crystallites against spontaneous growth via aggregation. Using differential scanning calorimetry (DSC), the melting behavior and kinetics of the PVA/Ag nanocomposites were investigated and compared to those of pure PVA. The melting as well as crystallization behavior of polymers is crucial because it governs the thermal properties, impact resistance and stress strain properties. Understanding the melting behavior is significant not only to tailor the properties of nanocomposites but to investigate the interactions between the constituents. The DSC curves of pure PVA and prepared nanocomposites show only one melting peak between 175 and 230 °C, indicating that the melting behavior of these two systems are analogous. In both cases, with increasing heating rate, the melting peak shifts to a higher temperature, but with increasing Ag content the peak melting temperature is lower. When specimens are heated at high heating rate, the motion of PVA molecular chains cannot follow the heating temperature on time due to the influence of heat hysteresis, which leads to a higher peak melting temperature. When Ag nanoparticles are added they increase the heat transfer among the PVA molecular chains decreasing the melting temperature. The Ag content is a major factor affecting the degree of crystallinity. It was observed that at low nanofiller content, up to the 0.5 wt%, the degree of crystallinity of the nanocomposites increased, while at a higher content the crystallization was retarded. The half time of melting is non-linearly dependent on the amount of nanofiller. In the range from 0.25 to 1 wt% Ag it slightly increases, because at a low Ag content the nanoparticles act as a heterogeneous nucleation agent during the crystallization process. For large amounts of nanofiller, the half time of melting is markedly higher than for pure PVA. At a higher Ag content, the nanoparticles act as a barrier that restricts the thermal motion of PVA molecular chains and the half time of complete melting increases. The significantly lower melting activation energy of the nanocomposites with high amount of nanofiller compared to pure PVA, calculated by the Kissinger method, indicated that nanoparticles reduced the heat barrier for the melting process. .