F. Tempesti

Surface-grafted heparinizable materials

Abstract Poly(amido-amine) chains have been grafted on the surface of different materials including glass, silastic, PVC, Dacron, and polyurethane. The poly(amido-amine) is able to complex with heparin by electrostatic interaction. The heparin-adsorbing capacity of the materials so obtained has been tested by biological tests. Heparin is only released at pH > 10, confirming the strong interaction between poly(amido-amine) and heparin. Preliminary theoretical studies have been made to construct a tentative model of the arrangement in the space of poly(amido-amine).

Synthesis and physicochemical characterization of a new material (PUPA) based on polyurethane and poly(amido-amine) components capable of strongly adsorbing quantities of heparin.

The synthesis of new materials (PUPAs) based on a commercial polyurethane and a heparin-complexing polymer, poly(amido-amine), was studied. PUPAs are capable of adsorbing heparin because the basic nitrogens of poly(amido-amine), once protonated, interact with the negative charges carried by the heparin molecule. Six different samples of PUPA were synthesized having a varied ratio of the components. The quantity of basic nitrogen on the surface and the bound heparin for each sample was determined. Two different kinds of heparin are present on a PUPA surface: one is strongly bound but can be detached by 0.1 M NaOH solution, the other is physically adsorbed and is slowly released by a stream of saline solution. A relationship between the quantity of strongly bound heparin and basic nitrogen was found. SEM and FTIR-ATR analysis were performed on all the PUPA samples. The mechanical characteristics change according to chemical composition.

Heparinized polyurethane surface through ionic bonding of heparin.

Surface heparinization through an ionic bond is one of the methods used to improve polyurethane blood compatibility. Chains of poly(amido-amine), a tertiary aminic polymer capable of forming stable complexes with heparin, were either surface-grafted on polyurethane or interconnected with polyurethane chains using hexamethylenediisocyanate as cross-linking agent. In the latter case, a new material (PUPA) is formed with a heparin adsorbing capacity higher than poly (amido-amine) surface-grafted polyurethane. By changing the percentages of the components, different series of PUPA materials can be obtained with different physico-chemical properties. The ATR/FT-IR technique was used to characterize the new materials in the native and in the heparinized state. PUPA solution was used to coat commercial biomedical devices and they were also characterized physico-chemically using ATR/FT-IR.

Heparinizable materials (IV). Surface-grafting on poly(ethylene terephthalate) of heparin-complexing poly(amido-amine) chains

By a chemical process poly(amido-amine) chains have been grafted on the surface of poly(ethylene terephthalate) (Dacron) devices. After treatment, it was shown that the devices could adsorb significant amounts of heparin. Most of the adsorbed heparin can be recovered only by eluting at pH greater than 10 with NaOH solution.

Study of haemodialysis materials; physico-chemical and biological characterization of EVALVA, EVAPA and heparinized EVAPA

Partially hydrolyzed ethylene/vinyl acetate copolymers were modified by the covalent binding of a heparin-complexing polymer and further heparinized in order to improve their blood compatibility. These heparinizable polymeric materials (EVAPA) were obtained by a two-step reaction between an ethylene/vinyl alcohol/vinyl acetate (EVALVA) terpolymer, and the heparin complexing polymer N2LL. The physico-chemical characterization of EVALVA, EVAPA and heparinized-EVAPA was carried out through thermal analysis, SEM, contact angle, potentiometric measurements, water uptake and FT-IR spectroscopic measurements. The biocompatibility of the above-mentioned samples was evaluated usingin vitro methods, through the determination of heparin release in phosphate buffer solution (PBS) and in human plasma, and with the investigation of hemostasis activation.

A material (PUPA) presenting both the properties of polyurethanes and the capacity of adsorbing a high quantity of heparin.

Polyurethanes are widely used for biomedical applications, but there is still a constant search for improved blood-compatible materials. We studied a material (PUPA) obtained by the interconnection between a poly(amido-amine), N2LL, capable of forming stable complexes with heparin and a commercial polyurethane, Pellethane 2363-80AE, using hexamethylenediisocyanate as the crosslinking agent. The amount of absorbed heparin (evaluated by biological tests) was generally much higher than that found on the poly(amido-amine) surface-grafted polyurethane.

Heparin Immobilization on Polyurethane Surface; Grafting of Heparin Complexing Poly(Amido-Amine)s

Poly(amido-amine)s (PAA) are a relatively new family of tertiary amino polymers in which amido — and tertiary amino groups are regularly arranged along the macromolecular chain. They may be obtained by polyaddition of primary or secondary amines to bis acrylamides (1–4): Open image in new window The polymerization takes place under very mild conditions, usually in water or alcohols, at room temperature, and without any added catalysts. The number average molecular weights of the polymers usually range between 5.000 and 20.000. They are influenced by the molecular proportions of the monomers and by the nature of the polymerization solvent. As a rule, higher molecular weights are obtained, with the same monomeric mixture, in water followed by water/alcohols mixtures, alcohols, pirydine/alcohols mixtures and pirydine in the order.