Papers by Author: R. Palazzolo

Abstract: The first generation of synthetic bone substitute materials (BSM) was initially investigated in the mid 1970s using hydroxyapatite (HA) as a biomaterial for remodeling of bone defects. The concepts established by CPC pioneers in the early 1980s were used as a platform to initiate a second generation of BSM for commercialization. Since then, advances have been made in composition, performance and manufacturing. A self-setting and injectable calcium phosphate cement (CPC) based on amorphous calcium phosphate (ACP) with calcium to phosphate (Ca/P) atomic ratio less than 1.5, combined with dicalcium phosphate dihydrate (DCPD or brushite, seeded with apatite), is proposed. Amorphization of raw material was observed following high energy mechano-chemical processing. Upon hydration, the cement hardened in less than 3 minutes at 37°C and reached a maximum compressive strength of about 50 MPa. The final product was a low crystalline calcium deficient carbonated apatite similar to the composition and structure of bone mineral. In vivo performance of this cement in mediating bone healing was compared to α-BSM® in a rabbit femoral defect model. Performance characteristics of some commercially available CPC products are compared. The concerns of CPC designers and the needs of product users (surgeons) are discussed.

Abstract: ACP (amorphous calcium phosphate) and DCPD (dicalcium phosphate dihydrate, or Brushite) powders were high energy dry ball milled at a 1:1 ratio for 1, 2, 3, 4, 10, or 24 hours to produce a variety of powders for use as calcium phosphate cements (CPC). A 1:1 blend of powders not subjected to milling was used as baseline material (control). Physicochemical and mechanical characterization was performed on the powder or cement at each milling time point and compared to control. The following changes were noted after 24 hours of milling: the crystallinity was reduced to a fully amorphous phase, the tap density increased by 89%, the specific surface area decreased by a factor of 7, and the total porosity of hardened cement decreased by 50%. Additionally, the compressive strength of hardened CPC increased from 2.6 MPa to a peak of 50 MPa after 10-h milling. The rate of paste hardening increased throughout the 24-h period. Full conversion of each milled material produced a similar composition low-crystalline calcium deficiency apatite with Ca/P atomic ratio of 1.45 and specific surface area around 195 m2/g. The specific structure of these CPC, with high surface area and reactivity of nano-crystals, is ideal for in vivo remodeling of new bone and controlled release of protein and growth factors.