Dispersant and Protective Roles of Amphiphilic Poly(ethylene phosphate) Block Copolymers in Polyester/Bone Mineral Composites

Abstract

Composites of synthetic bone mineral substitutes (BMS) and biodegradable polyesters are of particular interest for bone surgery and orthopedics. Manufacturing of composite scaffolds commonly uses mixing of the BMS with polymer melts. Melt processing requires a high homogeneity of the mixing, and is complicated by BMS-promoted thermal degradation of polymers. In our work, poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) composites reinforced by commercial β-tricalcium phosphate (βTCP) or synthesized carbonated hydroxyapatite with hexagonal and plate-like crystallite shapes (hCAp and pCAp, respectively) were fabricated using injection molding. pCAp-based composites showed advanced mechanical and thermal characteristics, and the best set of mechanical characteristics was observed for the PLLA-based composite containing 25 wt% of pCAp. To achieve compatibility of polyesters and pCAp, reactive block copolymers of PLLA or PCL with poly(tert-butyl ethylene phosphate) (C1 and C2, respectively) were introduced to the composite. The formation of a polyester-b-poly(ethylene phosphoric acid) (PEPA) compatibilizer during composite preparation, followed by chemical binding of PEPA with pCAp, have been proved experimentally. The presence of 5 wt% of the compatibilizer provided deeper homogenization of the composite, resulting in a marked increase in strength and moduli as well as a more pronounced nucleation effect during isothermal crystallization. The use of C1 increased the thermal stability of the PLLA-based composite, containing 25 wt% of pCAp. In view of positive impacts of polyester-b-PEPA on composite homogeneity, mechanical characteristics, and thermal stability, polyester-b-PEPA will find application in the further development of composite materials for bone surgery and orthopedics.

Crystalline Micro-Sized Carbonated Apatites: Chemical Anisotropy of the Crystallite Surfaces, Biocompatibility, Osteoconductivity, and Osteoinductive Effect Enhanced by Poly(ethylene phosphoric acid)

“…42 Subsequent studies demonstrated that even minimal changes in the reaction conditions and component ratios precluded obtaining crystallites of reproducible size and morphology; a method with reliable reproducibility could only be developed for two types of CAp, namely, (a) hexagonal prismatic CAp with an aspect ratio of 0.8−1 and width of 4−8 μm (hCAp) and (b) aggregates of platelike crystallites (pCAp). 43 It is noteworthy that the size and shape of hCAp and pCAp samples prepared and characterized in the present work (Figure 1a,b, see also Figures S1 and S2 in the SI) were close to those of their counterparts synthesized previously (Figure S5 in the SI). 43 XRD studies of the samples confirmed B-type CAp identity, and TGA and FT-IR data showed that incorporation of CO 3 2− anions was higher for hCAp as compared to pCAp (for details, see Section S1 in the SI).…”

“…43 It is noteworthy that the size and shape of hCAp and pCAp samples prepared and characterized in the present work (Figure 1a,b, see also Figures S1 and S2 in the SI) were close to those of their counterparts synthesized previously (Figure S5 in the SI). 43 XRD studies of the samples confirmed B-type CAp identity, and TGA and FT-IR data showed that incorporation of CO 3 2− anions was higher for hCAp as compared to pCAp (for details, see Section S1 in the SI).…”

“…hCAp and pCAp, [(BHT)­Mg­(μ-OBn)­(THF)] 2 , 2-chloro-1,3,2-dioxaphospholane, 2- tert -butoxy-2-oxo-1,3,2-dioxaphospholane ( t BuOEP), poly­( t BuOEP), and PEPA were synthesized as described previously (for details see Sections S1 and S2 in the Supporting Information, SI). To obtain the desired target concentration of PEPA in aqueous solution (10%), a precisely weighed poly­( t BuOEP) was subjected to thermolysis in the calculated volume of water (see Section S1.3 in the SI).…”

“…49,56 As applied to crystalline pCAp, the high binding strength of PEPA has been proven in our recent study. 43 In the present work, we synthesized a homopolymer of tertbutyl ethylene phosphate ( t BuOEP) of the approximate composition BnO( t BuOEP) 27 H (NMR and SEC data) and converted it to PEPA (>22 ethylene phosphate units, NMR and SEC data; the synthesis of t BuOEP, 58,59 its homopolymerization using aryloxy-Mg catalyst, 57 and preparation of PEPA 60 are described in Section S1.3 in the SI). The sample of pCAp containing 2 wt % of PEPA was prepared by evaporation of the mixture containing pCAp particles and PEPA aqueous solution (see Section S2.4 in the SI).…”

“…41 Two years ago, we succeeded in the hydrothermal synthesis of a wide spectrum of microsized platelike, rodlike, and prismlike crystalline CAp species with different aspect ratios. 42 This approach was optimized in our recent work 43 as applied to the preparation of hexagonal (hCAp) and platelike (pCAp) crystalline species. However, biomedical applications of microsized crystalline CAp of a given composition and uniform shape/size distribution remain virtually unexplored.…”