Characterization of mesoporous calcium phosphates from calcareous marine sediments containing Si, Sr and Zn for bone tissue engineering

3D printing of conch-like scaffolds for guiding cell migration and directional bone growth

Regeneration of severe bone defects remains an enormous challenge in clinic. Developing regenerative scaffolds to directionally guide bone growth is a potential strategy to overcome this hurdle. Conch, an interesting creature widely spreading in ocean, has tough spiral shell that can continuously grow along the spiral direction. Herein, inspired by the physiological features of conches, a conch-like (CL) scaffold based on β-TCP bioceramic material was successfully prepared for guiding directional bone growth via digital light processing (DLP)-based 3D printing. Benefiting from the spiral structure, the CL scaffolds significantly improved cell adhesion, proliferation and osteogenic differentiation in vitro compared to the conventional 3D scaffolds. Particularly, the spiral structure in the scaffolds could efficiently induce cells to migrate from the bottom to the top of the scaffolds, which was like “cells climbing stairs”. Furthermore, the capability of guiding directional bone growth for the CL scaffolds was demonstrated by a special half-embedded femoral defects model in rabbits. The new bone tissue could consecutively grow into the protruded part of the scaffolds along the spiral cavities. This work provides a promising strategy to construct biomimetic biomaterials for guiding directional bone tissue growth, which offers a new treatment concept for severe bone defects, and even limb regeneration.

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A conch-like scaffold was firstly developed for guiding directional bone growth.

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The CL scaffolds efficiently induced cells “climbing stairs”- like-migrating.

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The CL scaffolds showed improved bioactivities benefited from the spiral structure.

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This work provided a new treatment concept for severe bone defects.

Crystallization of carboplatin-loaded onto microporous calcium phosphate using high-vacuum method: Characterization and release study

Drug delivery systems are a new approach to increase therapeutic efficacy and to reduce the side effects of traditional treatments. Calcium phosphates (CaPs) have been studied as drug delivery systems, especially in bone diseases. However, each system has some particularities that depend on the physical and chemical characteristics of the biomaterials and drug interaction. In this work, granulated CaPs were used as a matrix for loading the anticancer drug carboplatin using the high-vacuum method. Five compositions were applied: hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), biphasic HAp 60%/β-TCP 40% (BCP), β-TCP/MgO nanocomposite, and β-TCP/SiO2 nanocomposite. Carboplatin drug in 50, 60, and 70 mg/g was precipitated on the surface of CaPs. Morphological, chemical and surface modifications in the carboplatin-CaPs were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), backscattered electron microscopy (BSE), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared (FT-IR), and Raman spectroscopy. The characterization of the CaP-carboplatin biomaterials showed heterogeneous crystalline precipitation of the drug, and no morphological modifications of the CaPs biomaterials. The in vitro release profile of carboplatin from CaPs was evaluated by the ultraviolet-visible (UV-Vis) method. The curves showed a burst release of upon 60% of carboplatin loaded followed by a slow-release of the drug for the time of the study. The results were typical of a low-interaction system and physisorption mechanism. The high-vacuum method permitted to load the high amount of carboplatin drug on the surface of the biomaterials despite the low interaction between carboplatin and CaPs.

Si, Sr, Ag co-doped hydroxyapatite/TiO2 coating: enhancement of its antibacterial activity and osteoinductivity

A multifaceted coating with favourable cytocompatibility, osteogenic activity and antibacterial properties would be of great significance and value due to its capability for improving osseointegration and alleviating prosthesis loosening. This study marks the first report on the coating of TiO2 nanotubular (TNT) arrays with Sr-and-Si-substituted hydroxyapatite (SSHA) endowed with antibacterial characteristics using silver ions. This TNT layer coated with Ag-substituted SSHA (SSAgHA) formed a composite coating with an interconnected microporous structure and a homogeneous distribution of Sr, Si and Ag; such a coating promoted cell adhesion and osteogenic potential. The anchoring effect of the TNT layer improved the adhesion strength of the SSAgHA/TNT coating to 16.9 ± 3.1 MPa, which was higher than the 15 MPa set in the ISO standard 13 779-4:2002. Moreover, the bio-corrosion resistance of the underlying Ti substrate was greatly enhanced by the composite coating. Hydroxyapatite (HA) and SSAgHA coatings provided a suitable environment for the adhesion, spreading and proliferation of mouse osteoblasts. The SSAgHA coating excellently inhibited bacterial activity and enhanced osteoinductivity with higher osteogenic differentiation compared with the HA coating. Sr and Si dopants increased the expression levels of the genes related to osteogenesis and successfully offset the potential cytotoxicity of Ag ions. Super-osteoinductivity was attributed to the rough and superhydrophilic surface of the composite coating. Therefore, the present study demonstrated the potential of the electrodeposited SSAgHA/TNT composite coating as a promising metallic implant with great intrinsic antibacterial activity and osteointegration ability.

Strontium ranelate simultaneously improves the radiopacity and osteogenesis of calcium phosphate cement

In a minimally invasive surgery of osteoporotic fractures, high radiopacity is necessary to monitor the delivery and positioning of injectable cements and good osteogenesis is indispensable. In this work, strontium ranelate (SrR), an agent for treating osteoporosis, is firstly used as a radiopaque agent for calcium phosphate cement (CPC). The addition of SrR does not affect the hydration products of CPC, but prolonged the setting time and decreased the compressive strength. The injectability of the cement was higher than 85% when SrR content is more than 10 wt%. The radiopacity of CPC is significantly improved by SrR and higher than cortical bone when the content of SrR is more than 5 wt%. The concentration of Sr ions released from CPC is increased by the increasing content of SrR, which is among 17-1329 μM. Moreover, CPCs with SrR significantly promote the osteogenic differentiation of mouse bone marrow mesenchymal stem cells and inhibit the osteoclastogenic differentiation of RAW264.7 cells. Based on its good radiopacity and osteogenesis, suppressed osteoclastogenesis and appropriate physicochemical properties, the radiopaque CPC with more than 10 wt% SrR is prospective to be a promising biomaterial for osteoporotic fracture repairing in minimal invasive surgery.

Effects of MgO, ZnO, SrO, and SiO2 in tricalcium phosphate scaffolds on in vitro gene expression and in vivo osteogenesis

β‑tricalcium phosphate (β‑TCP) is a versatile bioceramic for its use in many orthopedic and dental applications due to its excellent biocompatibility and biodegradability. Recently, the addition of additives to β‑TCP has been proven to improve bone repair and regeneration, however, the underlying mechanism of enhanced bone regeneration is still unknown. In this study, strontium oxide (SrO), silica (SiO2), magnesia (MgO), and zinc oxide (ZnO) were added to β‑TCP for dense discs fabrication followed by in vitro evaluation using a preosteoblast cell line. Cell viability and gene expression were analyzed at day 3 and day 9 during the cell culture. MgO and SiO2 were found to significantly enhance and expedite osteoblastic differentiation. A potential mechanism was introduced to explain the additive induced osteoblastic differentiation. In addition, in vivo characterizations showed that porous 3D printed MgO-SiO2-TCP scaffolds significantly improved new bone formation after 16 weeks of implantation. This study shows beneficial effects of additives on osteoblastic viability and differentiation in vitro as well as osteogenesis in vivo, which is crucial towards the development of bone tissue engineering scaffolds.

Osteogenic and angiogenic potentials of the cell-laden hydrogel/mussel-inspired calcium silicate complex hierarchical porous scaffold fabricated by 3D bioprinting

3D printing has been popularly used in the bone tissue engineering, as many of the biomaterials for this field of study can be prepared for and produced from this additive manufacturing technique. In this study, we strategized a solvent-free processing to fabricate the polydopamine-modified calcium silicate (PDACS)/poly-caprolactone (PCL) scaffold with Wharton's jelly mesenchymal stem cells (WJMSCs) incorporated with human umbilical vein endothelial cells (HUVEC)-laden hydrogel. The PDACS/PCL/hydrogel 3D scaffold yielded a Young's modulus of the 3D scaffolds as high as 75 MPa. In addition, the vascular morphogenesis and cellular behaviors regulated by our hybrid scaffolds were also intricately evaluated. Furthermore, the HUVEC in the bioink exhibited higher levels of angiogenic biomarkers and showed potential for the formation of complex vascular networks. Higher levels of bone formation proteins were also observed in our composites. Such a hybrid of synthetic materials with cell constituents not only enhances osteogenesis but also stimulates vessel network development in angiogenesis, presenting the fact that 3D printing can be further applied in improving bone tissue regeneration in numerous aspects. We believe that this method may serve as a useful and effective approach for the regeneration of defective complex hard tissues in deep bone structures.

Effect of reaction solvent on hydroxyapatite synthesis in sol-gel process

Synthesis of hydroxyapatite (HA) through sol-gel process in different solvent systems is reported. Calcium nitrate tetrahydrate (CNTH) and diammonium hydrogen phosphate (DAHP) were used as calcium and phosphorus precursors, respectively. Three different synthesis reactions were carried out by changing the solvent media, while keeping all other process parameters constant. A measure of 0.5 M aqueous DAHP solution was used in all reactions while CNTH was dissolved in distilled water, tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) at a concentration of 0.5 M. Ammonia solution (28-30%) was used to maintain the pH of the reaction mixtures in the 10-12 range. All reactions were carried out at 40 ± 2°C for 4 h. Upon completion of the reactions, products were filtered, washed and calcined at 500°C for 2 h. It was clearly demonstrated through various techniques that the dielectric constant and polarity of the solvent mixture strongly influence the chemical structure and morphological properties of calcium phosphate synthesized. Water-based reaction medium, with highest dielectric constant, mainly produced β-calcium pyrophosphate (β-CPF) with a minor amount of HA. DMF/water system yielded HA as the major phase with a very minor amount of β-CPF. THF/water solvent system with the lowest dielectric constant resulted in the formation of pure HA.