Polymeric additives to enhance the functional properties of calcium phosphate cements

Abstract

The vast majority of materials used in bone tissue engineering and regenerative medicine are based on calcium phosphates due to their similarity with the mineral phase of natural bone. Among them, calcium phosphate cements, which are composed of a powder and a liquid that are mixed to obtain a moldable paste, are widely used. These calcium phosphate cement pastes can be injected using minimally invasive surgery and adapt to the shape of the defect, resulting in an entangled network of calcium phosphate crystals. Adding an organic phase to the calcium phosphate cement formulation is a very powerful strategy to enhance some of the properties of these materials. Adding some water-soluble biocompatible polymers in the calcium phosphate cement liquid or powder phase improves physicochemical and mechanical properties, such as injectability, cohesion, and toughness. Moreover, adding specific polymers can enhance the biological response and the resorption rate of the material. The goal of this study is to overview the most relevant advances in this field, focusing on the different types of polymers that have been used to enhance specific calcium phosphate cement properties.

Keywords: calcium phosphate cement; hydroxyapatite; polymer.

Figure 1.

Different strategies for incorporating polymers in CPCs. The polymer can be incorporated either in the liquid phases (A, B, and C) or in the powder phases (D and E). A represents the mixing of a polymeric solution with the CPC powder to obtain a set CPC, which has the polymer homogeneously distributed in the structure. B represents foaming of the liquid solution, which is then combined with the powder to obtain a set macroporous CPC. C represents the incorporation of a small amount of CPC powder in a big volume of polymer solution, upon which a slurry is formed and is then freeze–dried, resulting in a macroporous polymer–CPC scaffold. D represents the combination of the powder phase with polymer fibers to obtain a fiber-reinforced CPC. Moreover, the fibers may act as pore generators when degraded. E represents the combination of the powder phase with polymer MSs, which can act as controlled drug eluting systems and simultaneously generate macropores in the CPC. CPC: calcium phosphate cement.