Blends of natural and synthetic polymers: A new route to novel biomaterials

Blends of natural and synthetic polymers were studied for potential applications in the biomedical field. Collagen and hyaluronic acid were mixed in aqueous solution with poly(vinyl alcohol) and poly(acrylic acid). The properties of the blends were studied by differential scanning calorimetry and dynamic mechanical thermal analysis. Some methods were also investigated to enhance the miscibility of the polymers in these blends.     

Enzymatic erosion of bioartificial membranes to control drug delivery

The preparation of an enzymatic controlled drug release system from blends of PVA/starch/alphaA, in the form of films, is described. It was shown that alphaA hydrolyses the starch within these films, resulting in a time-dependent change of the porosity in the matrix. Films were characterized by calorimetric analysis to study the interactions between the enzyme and the polymeric constituents at the molecular level. The presence of alphaA, in fact, influenced the PVA crystallization in the blends. Release tests and permeability experiments were carried out to evaluate the transport properties of the films. An increase in porosity and permeability was observed by increasing alphaA content (16-28 wt.-%). Films loaded with theophylline and caffeine were also prepared to analyze drug release properties of the matrix. Drug release kinetics were coherent with the measured changes in porosity: at higher alphaA concentrations the amount of released drug increased under the influence of diffusion and erosion processes. The results obtained are promising for the realization of drug delivery devices for a rapid release or for the release of poorly soluble drugs which usually remain entrapped in the matrix.SEM images of a PVA/starch/alphaA film before (A) and after (B) the erosion.     

Segmented Polyurethanes for Medical Applications: Synthesis,Characterization and in vitro Enzymatic Degradation Studies

Degradable segmented poly(ether-ester-urethanes) of variable segment chemistry and content were synthesized and characterized. Polycaprolactone diol, a series of poly(ether-ester) block copolymers, and a diisocyanate giving non toxic degradation products were used to form the prepolymer. Cyclohexane dimethanol and a L–phenylalanine–based diester (Phe diester) were used as chain extenders. The influence of α-chimotrypsin on the degradation was investigated by exposing the polymers to buffer and enzyme solutions for 12 days. The SEM, SEC, and gravimetric results showed that a significant erosion of the Phe diester containing polymer compared with the control polyurethane occurred in the presence of the enzyme but not in a normal buffer solution.     

Acrylonitrile-acrylic acid copolymer membrane imprinted with uric acid for clinical uses

The preparation of new polymeric membranes using molecular imprinting technology for application in blood filtration devices is described. Membranes, based on an acrylic acid-acrylonitrile copolymer, produced through phase inversion, were modified by introducing specific binding sites for uric acid into their structure. The materials prepared are intended for use to selectively remove uric acid from the blood in the case of increased serum uric acid values associated with different pathologies. The interactions at a molecular level between the membrane forming copolymer and the template were investigated by means of calorimetry, infrared spectroscopy and morphological analysis. The presence of interactions between the template and the copolymer, and a good thermal stability of the imprinted membranes were observed. In addition, the results of rebinding tests on the imprinted membranes indicated a good capacity of molecular recognition for the template and satisfactory selectivity properties towards compounds of similar structure such as theophylline. Membrane permeability values suggest their application as (ultra) haemofiltration devices. Poly(acrylonitrile-co-acrylic acid) membrane.     

Hydrophilic Films Based on Blends of Poly(acrylic acid) and Poly(2‐hydroxyethyl vinyl ether): Thermal,Mechanical, and Morphological Characterization

Hydrophilic films based on blends of poly(acrylic acid) and poly(2‐hydroxyethyl vinyl ether) were prepared by casting. The characterization of the films was performed by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM). It was shown that an increase of poly(2‐hydroxyethyl vinyl ether) content in the blends considerably decreases the glass transition temperature of the samples. The films containing 10 and 20 mol‐% of poly(2‐hydroxyethyl vinyl ether) show behavior of polymers in the glassy state, but a further increase of nonionic polymer content in the blend (30–50 mol‐%) provides the mechanical properties typical of a rubbery state. The content of water traces in the films has a significant effect on the mechanical properties of the materials.

Normalized DSC thermograms of PAA:PHEVE films. [PAA]:[PHEVE] = 90:10 (1), 80:20 (2), 70:30 (3), 60:40 (4), 50:50 mol‐% (5).     

Bioartificial materials based on blends of dextran and poly(vinyl alcohol-co-acrylic acid)

Bioartificial polymeric materials based on blends of dextran and poly(vinyl alcohol-co-acrylic acid) P(VA-co-AA) were prepared in the form of films and characterised to evaluate the miscibility of the natural component with the synthetic one. The idea of this work was to compatibilise PVA and dextran by introducing carboxylic groups along the PVA chains.The copolymer was synthesised and characterised in our laboratories. The results evidenced that the copolymer had an appropriate molecular weight and the content of PAA in the copolymer was 45% (weight). Then, films with different composition ratios were prepared by solution casting and analysed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), chemical imaging analysis and mechanical tests. The results obtained indicated that the introduction of carboxylic groups along the PVA chains had a positive effect on the miscibility degree of the synthetic component with the biological one.