G. Pizzirani

Bioartificial materials based on blends of collagen and poly(acrylic acid)

The interactions between soluble collagen (C) from calf skin and poly(acrylic acid) (PAA) were studied. Mixing aqueous solutions of collagen and PAA, at various pH values (2.5-4), leads to the formation of complexes that precipitate in the form of insoluble aggregates. The effects of mixture composition, pH, and ionic strength on C/PAA complex formation were investigated by gravimetric, turbidimetric, and conductometric analysis. The experimental results indicate that the complexes form through electrostatic interactions. Homogeneous solid films with variable C/PAA ratios were obtained by casting from solutions in which the pH was adjusted just over the isoelectric point of collagen, thus avoiding the attractive ionic interactions responsible for the complexation of collagen and PAA molecules. A relevant result obtained is related to the possibility of restoring the ionic interactions between the two polymers inside the solid films. Mixture composition and pH appear to influence the thermal properties of both complexes and films.

Bioartificial materials based on collagen: 1. Collagen cross-linking with gaseous glutaraldehyde

The effect of exposure time of thin films of soluble collagen to glutaraldehyde (GTA) vapour was studied at 37 degrees C, and was evaluated by examining the thermal and biological stability and the swelling ratio. It was found that the collagen films treated with GTA vapour for 18 h showed the highest denaturation temperature, the lowest swelling ratio, and an enhanced proteolytic stability. This study shows that soluble collagen can be effectively cross-linked with GTA vapour and that the degree of cross-linking can be controlled by varying the exposure time.

Bioartificial materials based on collagen: 2. Mixtures of soluble collagen and poly(vinylalcohol) cross-linked with gaseous glutaraldehyde

Thin films of both pure soluble collagen (CLG) and poly(vinylalcohol) (PVA) and mixtures of the two, ranging from 20-80% PVA composition were studied to test the effects of PVA content and of glutaraldehyde vapour cross-linking. Both the thermal and mechanical behavior and, in addition, proteolytic stability were clearly influenced by the ratio of CLG/PVA. The experimental results indicate that no thermodynamic compatibility occurs between the two homopolymers. However, there is evidence that strong interactions, probably due to hydrogen bond formation, occur between the biological and synthetic polymers. The interactions appear stronger in those films with a lower PVA content and which were not cross-linked. Both the thermal and biological stability are increased and there is an improvement of the mechanical properties. The mutual intermolecular influence appears to allow the attainment of a good mechanical compatibility between CLG and PVA.

Physical and biological properties of dehydro-thermally cross-linked collagen-poly(vinyl alcohol) blends

Dehydro-thermal treatments for 3, 24 and 72 h were used to crosslink blends of collagen and poly(vinyl alcohol) with various compositions. This crosslinking method increases the biological stabilityin vitro of collagen, as was established by an enzymatic test. When the poly(vinyl alcohol) content is not more than 20% the resistance of collagen to enzymatic digestion is not affected by the presence of the synthetic component. A higher content of poly(vinyl alcohol) produces a steric hindrance screening that enhances the resistance of collagen to the collagenase. Dehydro-thermal treatment performed for 24 and 72 h increases the crystallinity of poly(vinyl alcohol), thus reducing the solubility of this component of the blend. Calorimetric analysis was carried out by differential scanning calorimetry to investigate the structure and the thermal stability of the blends. Dehydro-thermal treatments carried out for 24 and 72 h induce high degrees of crosslinking in collagen and high crystallinity in poly(vinyl alcohol). The two components of the blend seem to create independent structures and the blend can show interpenetrating-network-like behaviour.

A new process for the production of bone cement by gelled suspension polymerization of MMA

A new suspension polymerization process, utilizing a water-agarose gel as suspending phase, is described. In the early stage of the process, the monomer is dispersed in the water-agarose solution by adequate stirring, then the solution gelifies and polymerization starts. By this technique, PMMA powders adequate for bone cement production were obtained. Several tests were performed on the polymer obtained in order to determine its basic physicochemical properties: viscometric tests, GPC tests, DSC tests, granulometric distribution analysis and SEM analysis. The measured properties show that the material obtained can be satisfactorily compared with the existing commercial powders for bone cements.

Anionic polymerization of styrene in tetrahydropyran under an electric field periodically reversed

Abstract The anionic polymerization of living polystyryl di-sodium salt was investigated in tetrahydropyran (THP) at 25°, under high vacuum either in the absence or in the presence of an electric field with either constant or periodically reversed polarity over a wide range of frequencies. The application of an electric field with constant polarity increased the apparent rate constant of propagation. It increased in fact the term k p(−) K D 1 2 (where k p(−) , is the rate constant of propagation of free ions and K D is the dissociation constant of ion-pairs) whereas it left unaffected the rate constant of propagation of ion-pairs k p(±) . The observed effect of the field did not change appreciably if the polarity of the field was reversed with a frequency up to ca . 0.04 Hz. At frequencies of reversal above ca . 0.16 Hz, the enhancement of the polymerization rate due to the electric field became negligible. The observed field effects are interpreted in terms of electrolytic phenomena and of the possibility of growing macroanions assuming a more extended conformation in which the living ends become more accessible to the monomer.

Some aspects of the n-vinylcarbazole polymerization initiated by iodine

Abstract The polymerization of N-vinylcarbazole initiated by iodine in dichloroethane solution, shows some interesting features, particularly the unusual trend of the conversion-time curves: in all cases a very fast initial reaction is followed by a much slower process. Molecular weights of the polymers decrease noticeably with increasing conversion and with increasing initial monomer concentration. The system is very complex and the data indicate that two different mechanisms are operating.