Simonida Lj. Tomić

The polymerisation kinetics of lower dialkyl itaconates

SUMMARY: The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (DnBI), and dihexyl itaconate (DHI) in the bulk were studied in the temperature range from 50 to 70 C. The concentration of the initiator, 2,2 -azoisobutyronitrile (AIBN), was varied between 0.02 and 0.085 mol/dm 3 . The rate of polymerisation (Rp), degree of polymerisation (DP), overall polymerization rate constant (K), the ratio of the propagation and termination rate constants (kp/kt 1/2 ), as well as the chain transfer constant to monomer (CM) were determined. The values of Rp, K, and kp/kt 1/2 of the investigated monomers all increase with increasing size of the alkyl group in the ester substituent, whereas CM decreases when going from the dimethyl to the dihexyl ester. The values of CM are larger than the corresponding values for the alkyl esters of methacrylic acid.

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.

pH-sensitive hydrogels based on (meth)acrylates and itaconic acid

Novel hydrogels based on 2-hydroxyethyl methacrylate (HEMA), itaconic acid (IA) and different poly (alkylene glycol) (meth)acrylates (PAGM) (P(HEMA/IA/PAGM)) were synthesized. We investigated the influence of different PAGM components, with acrylic or methacrylic acid residues in the main chain and ethylene glycol (EG) and/or propylene glycol (PG) units in pendant chains of varying length, on the nature and inherent properties of P(HEMA/IA/PAGM) copolymeric hydrogels. Swelling studies revealed pH sensitive behavior of P(HEMA/IA/PAGM) samples. Hydrogel structure and morphology were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), which confirmed their chemical structure and differences in pore size. The shear modulus values for P(HEMA/IA/PAGM) hydrogels were close to that of PHEMA, but slightly lower than the value for P(HEMA/IA). Cephalexin (CEX) drug release profiles from P(HEMA/IA/PAGM) samples showed a marked dependence on the PAGM component. The presence of IA also influenced the release rate of CEX, leading to a faster release when IA was combined with the more hydrophilic PAGM component. An in vitro assay of P(HEMA/IA/PAGM) cytotoxicity showed good cell viability. The results obtained indicate that P(HEMA/IA/PAGM) hydrogel properties were significantly dependent on the PAGM component, meaning that the type of side chains can be used to tune the characteristics of such biomaterials. These properties make P(HEMA/IA/PAGM) copolymeric hydrogels applicable in biomedical and biotechnological fields and controlled drug delivery.

Synthesis, Swelling Properties and Evaluation of Genotoxicity of Hydrogels Based on (Meth)acrylates and Itaconic Acid

In this study we prepared hydrogels based on 2-hydroxyethyl methacrylate (HEMA): PHEMA homopolymer and two terpolymers of HEMA, itaconic acid (IA) and two poly(alkylene glycol) (meth) acrylates (PAGM): poly(ethylene glycol)6 acrylate (P(HEMA/IA/PAGM1)) and poly(propylene glycol)5 methacrylate (P(HEMA/IA/PAGM2)). Hydrogels were synthesized by gamma-irradiated radical polymerization and subjected to swelling measurements and genotoxicity evaluation. Swelling studies confirmed that these hydrogels deserve consideration as biomaterials due to their ability to swell in phosphate buffer but maintaining physical integrity for a prolonged contact time after equilibrium state has been reached. Comet assay showed certain genotoxic effect following cell exposure to extracts of hydrogels, which was dependent on the concentration of extracts, chemical composition of hydrogels and the degree of crosslinking. The influence of concentration on genotoxicity was the most pronounced. The synthesis of these novel HEMA-based hydrogels should be optimized so as to reduce their toxicity and enable the use in clinical practice.

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.

2-hydroxyethyl metahcrylate/gelatin based superporous hydrogels for tissue regeneration

In this study, superporous hydrogels were synthesized by free radical polymerization of 2-hydroxyethyl methacrylate without and in the presence of gelatin. Highly porous hydrogel structures were obtained by two different techniques: using a gas blowing agent, sodium bicarbonate, and a cryogenic treatment followed by freeze-drying. After the gel synthesis, gelatin molecules were covalently immobilised onto PHEMA via glytaraldehyde activation. All samples were characterized for morphological, mechanical, swelling and antibacterial properties. The results obtained show that samples with gelatin show better properties in comparison with PHEMA samples, which make these materials highly attractive for developing hydrogel scaffolds for tissue regeneration.

Controlled Release and Antimicrobial Study of zinc(II)-Ion from zinc/poly(2-Hydroxyethyl Acrylate/Itaconic Acid) Hybrid Hydrogels

A novel zinc/poly(2-hydroxyethyl acrylate/itaconic acid) (Zn/P(HEA/IA)) hybrid hydrogels were successfully prepared by free radical crosslinking copolymerization of 2- hydroxyethyl acrylate (HEA) and itaconic acid (IA) monomers. Zn(II)-ions were subsequently embeded by swelling dry gels in zinc salt solution. Zinc ions are of biomedical importance due to their essential role for sustaining living organisms as well as for their anti-inflammatory and antimicrobial properties. Swelling studies were performed in vitro, in order to evaluate zinc ion effect on fluid diffusion into hydrogels. Observations from swelling studies indicate that intermolecular interactions, such as coordinate bonding between Zn(II) and carboxyl and hydroxyl groups further stabilize the hybrid structure to a certain extent. Values of equilibrium degrees of swelling (qe) of Zn/P(HEA/IA) hybrid hydrogels depend on itaconic acid content. The release of the Zn(II)-ions from the hybrids was investigated in vitro, for a time period of seven days. The release profiles of Zn(II)-ions from the Zn/P(HEA/IA) hybrid hydrogels have shown a two-phase exponential profile with fast initial phase followed by a slower rate of release, reaching a plateau. The antimicrobial activity of the samples tested using E. coli pathogen showed satisfactory antimicrobial potential of Zn-loaded hybrid hydrogels. The obtained results have shown that such a new type of Zn/P(HEA/IA) hybrid hydrogels Therefore, hydrogels enriched with zinc ions system holds wide potential for application in clinic as an antibacterial biomaterial.