Klara Castkova

Direct synthesis of nanocrystalline hydroxyapatite by hydrothermal hydrolysis of alkylphosphates

The influence of reaction conditions (temperature, type of catalyst, time) on the base-catalyzed reaction of mono-, di-, and trialkylphosphates (alkyl = methyl, ethyl, i-propyl, n-butyl) with Ca2+ ions and on the structure and composition of the reaction products was studied. The composition of the calcium phosphates depends mainly on the reaction temperature. At temperatures below 100°C, a nanocrystalline solid product transforming into dicalcium phosphate by heating (calcination) was found. Pure nanocrystalline hydroxyapatite was prepared by hydrothermal synthesis at 160°C from mono- and dialkylphosphates. The size of hydroxyapatite crystallites was about 1 nm, the particle size about 150 nm. Agglomerated particles of hydroxyapatite larger than 2 μm were prepared at 200°C. Hydrothermal reaction of trialkylphosphates with Ca2+ ions at 200°C produced CaHPO4. The experimental results were used to propose a reaction mechanism for base-catalyzed hydrothermal reactions of alkylphosphates with Ca2+ ions.

Case study: Reinforcement of 45S5 bioglass robocast scaffolds by HA/PCL nanocomposite coatings

The purpose of this study is to analyze the mechanical enhancement provided by nanocomposite coatings deposited on robocast 45S5 bioglass (BG) scaffolds for bone tissue regeneration. In particular, a nanocomposite layer consisting of hydroxyapatite (HA) nanoparticles, as reinforcing phase, in a polycaprolactone (PCL) matrix was deposited onto the surface of the BG struts conforming the scaffold. Three different HA nanopowders were used in this study. The effect of particle size and morphology of these HA nanopowders on the mechanical performance of 45S5 BG scaffolds is evaluated.

The effect of hydroxyapatite particle size on viscoelastic properties and calcium release from a thermosensitive triblock copolymer

Well-defined “smart” injectable hydrogel based on hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(lactic acid-co-glycolic acid) (PLA/PGA) copolymer (PLGA-PEG-PLGA) gelling at the body temperature was modified by bioactive hydroxyapatite (HAp) in the form of micro-, nano-, and core-shell particles (μ-HAp, n-HAp, and CS-x, respectively) to be applicable as calcium delivery system in bone regeneration. Viscoelastic moduli increased with HAp content as expected. Whereas systems containing μ-HAp or CS-x particles maintained two sol-gel and gel-sol phase transitions, the n-HAp containing system showed only one sol-gel phase transition due to the strong interactions between polymer chain and the n-HAp surface. In vitro, studies proved the controlled uniform release of calcium cations from both CS-x and n-HAp over the 9-day period without any initial burst release.