Susan A. Visser

Classes of Materials Used in Medicine

Publisher Summary There is a diverse range of materials and methods available for the immobilization of biomolecules and cells on or within biomaterial supports. This chapter explains various classes of materials used in medicine. Metallic implant materials have a significant economic and clinical impact on the biomaterials field. Apart from orthopedics, there are other markets for metallic implants and devices including (1) oral and maxillofacial surgery, for example, dental implants, craniofacial plates, and screws and (2) cardiovascular surgery, for example, the parts of artificial hearts, pacemakers, balloon catheters, valve replacements, and aneurysm clips. The chapter also introduces the concepts of polymer characterization and property testing as they are applied to the selection of biomaterials. It provides a table that compares some of the biomolecule immobilization techniques—physical and electrostatic adsorption, cross linking, entrapment, and covalent binding.

Effect of neutralizing cation type on the morphology and properties of model polyurethane ionomers

Abstract The influence of cation type on the morphology and properties of model polyurethane ionomers is investigated in ionomers with different backbone types, pendant anion types and ionic group concentrations. A correlation between the degree of ordering in the local environment of the neutralizing cation and the tensile properties of the ionomers is observed. The geometrical packing constraints of the pendant anion are also seen to be a critical factor in determining the physical properties of ionomers. Differential scanning calorimetry results indicate no significant differences in the extent of phase separation of ionomers neutralized with different cations; however, anion type is shown to have a large influence on the degree of phase separation. Small-angle X-ray scattering analysis of the morphology of the ionomers reveals a correlation between the number of ionic groups per aggregate and the low-temperature storage modulus measured by dynamic mechanical analysis. The importance of the electronic structure and geometrical packing constraints of the ionic groups is emphasized.

Morphology and properties of mixed anion ionomers

Abstract A series of model polyurethane ionomers containing varying concentrations of both sulphonate and carboxylate anions is examined. Tensile testing results demonstrate that the greater acid strength of the sulphonate anions causes the ultimate tensile properties of the ionomer to regularly increase as sulphonate content increases. However, the small-strain moduli of two mixed carboxylate/sulphonate ionomers were shown to vary from the trends predicted from strict acid strength arguments; the two mixed-anion ionomers have higher Youngs moduli than the fully sulphonated ionomer. D.s.c., d.m.t.a. and SAXS analysis indicates that the modulus enhancement in the mixed-anion ionomer arises from a combination of factors, including aggregate packing, ability to immobilize non-ionic chain segments (ionic anchoring) and degree of phase separation. The onset of flow temperature in d.m.t.a. is seen to decrease in parallel with increasing carboxylate content, unlike the tensile properties. Thus, the concept of mixed anion derivatization is shown to fulfil a primary goal in the ionomer field: development of a method to increase ease of processability while retaining strong tensile properties.

Small-angle X-ray scattering investigation of ionomer deformation: effect of neutralizing cation

Abstract The influence of the neutralizing cation on the response of model polyurethane ionomers to uniaxial extension is investigated by small-angle X-ray scattering. Anisotropic scattering patterns are observed for ionomers neutralized with Na+, Sr2+ and Ca2+ upon elongation, with the precise nature of the response depending on the neutralizing cation. Scattering patterns of elongated ionomers neutralized with Ni2+ and Cd2+ display little or no anisotropy up to extension ratios of λ = 5.0 and 3.0, respectively. A model invoking ionic aggregate spatial rearrangement within the polymer matrix and removal of ionic groups from the aggregates to the polymer matrix or to other aggregates is postulated to explain the results.

Extended X-ray absorption fine structure spectroscopic analysis of cation local environment in model polyurethane ionomers

Abstract The local environment of the neutralizing cation was examined by extended X-ray absorption fine structure spectroscopy in a series of model polyurethane ionomers. Polyol type, polyol molecular weight and pendant anion type had small effects on cation local environment. Sample preparation conditions had a noticeable effect in one case. The type of cation was the dominant factor in determining local ordering. The degree of local order decreased with cation type in the order Ni 2+ > Sr 2+ > Cd 2+ , in agreement with the trend of decreasing tensile properties with cation type. Hydration of Ni 2+ -neutralized ionomers induced no change in the Ni 2+ local environment for a sulphonated ionomer, but hydration caused a rapid change in the local structure of the analogous carboxylated ionomer. The changes were in accord with water molecules coordinating to the Ni 2+ cation.

Small-angle neutron scattering investigation of the response of model polyurethane ionomers to uniaxial deformation

Abstract The deformation behaviour of the poly (tetramethylene oxide) subchains of two sodium sulphonated model polyurethane ionomers is examined by small-angle neutron scattering (SANS). Surprisingly, the scattering patterns from both ionomers remained isotropic at low elongations. At higher elongations, visible anisotropy appeared in the SANS patterns, but the change in the radii of gyration in the directions parallel and perpendicular to the stretching direction was small. Three models of network deformation—the junction affine, the phantom network and the affine deformation model—failed to reproduce the experimental results. A two-stage deformation model comprising an initial stage of aggregate rearrangement and subchain relaxation at low elongations, followed by subchain stretching at higher elongations, is postulated to explain the observed results.