Maurizio Palla

Hydrogels of poly(vinyl alcohol) and collagen as new bioartificial materials Part I Physical and morphological characterization

Poly(vinyl alcohol) was used to make hydrogels containing various amounts of collagen. These “bioartificial materials”, made of synthetic and biological polymers, were studied to investigate the effect of the presence of the collagen on the structural properties of the hydrogels. A comparison between thermal and morphological properties of collagen-containing hydrogels and hydrogels of pure poly(vinyl alcohol) was made.

The activation of human plasma prekallikrein as a hemocompatibility test for biomaterials. II. Contact activation by EVAL and EVAL-SMA copolymers

The activation of human plasma prekallikrein (PKK) to kallikrein (KK), induced by the contact of blood with foreign materials, is a useful in vitro hemocompatibility test. Kallikrein is easily detected by its reaction with the chromogenic substrate H-D-Pro-Phe-Arg-pNA, which releases p-nitroaniline, revealed by its absorption at 405 nm. This test, which was already carried out by evaluating PKK activation by the end-point method, has been carried out in this work by the more accurate initial velocity method, i.e. by evaluating the activation from the initial rates of the KK-substrate reaction. The tests were carried out on the following materials: borosilicate glass (as a high-activation reference material), silicone (as a low-activation reference material), the commercial biomaterial Cardiothane 51, three graft copolymers synthesized in our laboratory by reacting ethylene-vinyl alcohol copolymer (EVAL) with styrene-maleic anhydride copolymer (SMA), and EVAL itself. A mathematical treatment based on a simple kinetic model has been used for a first-approximation evaluation of the PKK-activating power of the materials tested. The quite low activating power of the EVAL-SMA copolymers, which are easily processable into water-permeable hollow fibers, suggests the possibility of their use in blood dialyzers.

Blends of hyaluronic acid derivatives with ethylene-vinyl alcohol copolymers as potential biomaterials

Films were prepared by solution casting from blends of hyaluronic acid derivatives and ethylene-vinyl alcohol copolymers. A chemico-physical and biological characterization was carried out on these “bioartificial materials” made of synthetic and biological polymers. The morphological and chemical properties of the films were investigated by scanning electron microscopy and differential scanning calorimetry. The transport properties of these films were tested in liquid systems to evaluate their possible use in dialysis and/or haemodialysis. The biocompatibility was investigated by a haemocompatibility test based on the contact activation of plasma prekallikrein. No particular interaction between the two components was observed. The results of the permeation tests were compared with those obtained using commercial products such as Cuprophane and poly(acrylonitrile) membranes. These tests indicate that the permeability of the blends decreases as the content of the synthetic polymer increases. The good haemocompatibility of these materials suggests their possible use as biomaterials.

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.

Composites Between Alumina and an Ester‐Ether‐Ester Bioresorbable Copolymer

Composites between alumina and the biore-sorbable (poly(e-caprolactone)-block-poly(oxyethylene)-block-poly(e-caprolactone) copolymer were obtained by reacting e-caprolactone with preformed poly(ethylene glycol), in the presence of ceramic alumina powder, at 185°C under vacuum. The mechanical properties, tested by compression and flexural strengths and Youngs modulus, show that the copolymer interacts poorly with the alumina grains. Both scanning electron and atomic force microscopy show a scare wettability between alumina and copolymer, as well as the aggregation of alumina micro-particles into clusters of big size. Both mechanical and morphological tests seem to indicate a stronger interaction between the alumina micro-particles than between the alumina surface and the reaction mixture during the polymerization, as well as a compacting effet by alumina on the forming copolymer. The FT-IR spectra of the composites show both copolymer and alumina absorption bands. The FT-IR analysis on the fractions of an extraction which CHCl 3 indicates the presence of traces of poly(e-caprolactone), stably linked to alumina. The polymerization of e-caprolactone with alumina alone in the same conditions gives poly(e-caprolactone), mainly free and in minor part linked to the alumina surface. Two polymerization mechanisms, simultaneously occuring, are proposed. The most relevant result of this work is the lack of chemical inertness of alumina towards e-caprolactone, which leads to reconsider also the use of alumina as a biochemically inert material.