Abstract
A modified one-step process was used to prepare tetracalcium phosphate/monetite/calcium sulfate hemihydrate powder cement mixtures (CAS). The procedure allowed the formation of monetite and calcium sulfate hemihydrate (CSH) in the form of nanoparticles. It was hypothesized that the presence of nanoCSH in small amounts enhances the in vitro bioactivity of CAS cement in relation to osteogenic gene markers in mesenchymal stem cells (MSCs). The CAS powder mixtures with 15 and 5 wt.% CSH were prepared by milling powder tetracalcium phosphate in an ethanolic solution of both orthophosphoric and sulfuric acids. The CAS cements had short setting times (around 5 min). The fast setting of the cement samples after the addition of the liquid component (water solution of NaH2PO4) was due to the partial formation of calcium sulfate dihydrate and hydroxyapatite before soaking in SBF with a small change in the original phase composition in cement powder samples after milling. Nanocrystalline hydroxyapatite biocement was produced by soaking of cement samples after setting in simulated body fluid (SBF). The fast release of calcium ions from CAS5 cement, as well as a small rise in the pH of SBF during soaking, were demonstrated. After soaking in SBF for 7 days, the final product of the cement transformation was nanocrystalline hydroxyapatite. The compressive strength of the cement samples (up to 30 MPa) after soaking in simulated body fluid (SBF) was comparable to that of bone. Real time polymerase chain reaction (RT-PCR) analysis revealed statistically significant higher gene expressions of alkaline phosphatase (ALP), osteonectin (ON) and osteopontin (OP) in cells cultured for 14 days in CAS5 extract compared to CSH-free cement. The addition of a small amount of nanoCSH (5 wt.%) to the tetracalcium phosphate (TTCP)/monetite cement mixture significantly promoted the over expression of osteogenic markers in MSCs. The prepared CAS powder mixture with its enhanced bioactivity can be used for bone defect treatment and has good potential for bone healing.
Highlights
One group of Calcium phosphate-based cements (CPC) are self-setting cements, based on tetracalciumcalcium phosphate/monetite powder mixtures (TTCPM), which are characterized by rapid setting and a gradual transformation of calcium phosphate components to calcium deficient hydroxyapatite (HAP) after mixing with a liquid component [3,4]
The orthophosphoric acid was added in such an amount to have the Ca/P mole ratio in the cements close to 1.67 and sulfuric acid was added in amounts of 5 and 15 wt.% of calcium sulfate hemihydrate (CSH) designated CAS5 and CAS15, both acids added) in the final cements
From a comparison of the images we found that the calcium deposits were produced in wells with cells cultured in M2 cement extracts, as well as i the negative control, but the content of deposits was clearl higher in wells with cement extracts, and the CAS5 extract significantly supported diffe entiation of mesenchymal stem cells (MSCs) and their ability to perform calcification
Summary
Calcium phosphate-based cements (CPC) are used to treat bone defects because they are similar to bone hydroxyapatite and have excellent biocompatibility and osteoconduction [1,2]. One group of CPCs are self-setting cements, based on tetracalciumcalcium phosphate/monetite powder mixtures (TTCPM), which are characterized by rapid setting and a gradual transformation of calcium phosphate components to calcium deficient hydroxyapatite (HAP) after mixing with a liquid component [3,4]. The drawbacks of TTCPM biocements are a slower rate of resorption in vivo, a relatively rapid change of pH to a strong basic region after the preparation of the cement paste, and, insufficient osteoinduction after defect treatment. The increase in cement solubility or basicity of cement paste can be solved by changing the Ca/P molar ratio in the cement, the acid character of liquid component (e.g., soluble organic substances (carboxylic acids, phytic acid)) and forming porous scaffolds using porogens biodegradable biopolymers [5,6,7]
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