Phase pure, high hardness, biocompatible calcium silicates with excellent anti-bacterial and biofilm inhibition efficacies for endodontic and orthopaedic applications

Evaluation and optimization of physical, mechanical, and biological characteristics of 3D printed Whitlockite/calcium silicate composite scaffold for bone tissue regeneration using response surface methodology

Calcium phosphate-based bioscaffolds are used for bone tissue regeneration because of their physical and chemical resemblance to human bone. Calcium, phosphate, sodium, potassium, magnesium, and silicon are important components of human bone. The successful biomimicking of human bone characteristics involves incorporating all the human bone elements into the scaffold material. In this work, Mg-Whitlockite (WH) and Calcium Silicate (CS) were selected as matrix and reinforcement respectively, because of their desirable elemental composition and regenerative properties. The magnesium in WH increases mineralization in bone, and the silicon ions in CS support vascularization. The Mg-WH was synthesized using the wet chemical method, and powder characterization tests were performed. Response surface methodology (RSM) is used to design the experiments with a combination of material compositions, infill ratios (IFs), and sintering temperatures (STs). The WH/CS bioceramic composite is 3D printed in three different compositions: 100/0, 75/25, and 50/50 wt%, with IFs of 50%, 75%, and 100%. The physical and mechanical characterization study of printed samples is conducted and the result is optimized using RSM. ANOVA (Analysis of Variance) is used to establish the relationship between input parameters and responses. The optimized input parameters were the WH/CS composition of 50/50 wt%, IF of 50%, and ST of 1150 °C, which bring out the best possible combination of physical and mechanical characteristics. The RSM optimized response was a density of 2.27 g cm-3, porosity of 36.74%, wettability of 45.79%, shrinkage of 25.13%, compressive strength of 12 MPa, and compressive modulus of 208.49 MPa with 92% desirability. The biological characterization studies were conducted for the scaffold samples prepared with optimized input parameters. The biological studies confirmed the capabilities of the WH/CS composite scaffolds in bone regenerative applications.

Recent advances on nanomaterials for antibacterial treatment of oral diseases

An imbalance of bacteria in oral environment can lead to a variety of oral diseases, such as periodontal disease, dental caries, and peri-implant inflammation. In the long term, in view of the increasing bacterial resistance, finding suitable alternatives to traditional antibacterial methods is an important research today. With the development of nanotechnology, antibacterial agents based on nanomaterials have attracted much attention in dental field due to their low cost, stable structures, excellent antibacterial properties and broad antibacterial spectrum. Multifunctional nanomaterials can break through the limitations of single therapy and have the functions of remineralization and osteogenesis on the basis of antibacterial, which has made significant progress in the long-term prevention and treatment of oral diseases. In this review, we have summarized the applications of metal and their oxides, organic and composite nanomaterials in oral field in recent five years. These nanomaterials can not only inactivate oral bacteria, but also achieve more efficient treatment and prevention of oral diseases by improving the properties of the materials themselves, enhancing the precision of targeted delivery of drugs and imparting richer functions. Finally, future challenges and untapped potential are elaborated to demonstrate the future prospects of antibacterial nanomaterials in oral field.

CaSiO3-HAp Metal-Reinforced Biocomposite Ceramics for Bone Tissue Engineering

Reconstructive and regenerative bone surgery is based on the use of high-tech biocompatible implants needed to restore the functions of the musculoskeletal system of patients. Ti6Al4V is one of the most widely used titanium alloys for a variety of applications where low density and excellent corrosion resistance are required, including biomechanical applications (implants and prostheses). Calcium silicate or wollastonite (CaSiO₃) and calcium hydroxyapatite (HAp) is a bioceramic material used in biomedicine due to its bioactive properties, which can potentially be used for bone repair. In this regard, the research investigates the possibility of using spark plasma sintering technology to obtain new CaSiO₃-HAp biocomposite ceramics reinforced with a Ti6Al4V titanium alloy matrix obtained by additive manufacturing. The phase and elemental compositions, structure, and morphology of the initial CaSiO₃-HAp powder and its ceramic metal biocomposite were studied by X-ray fluorescence, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller analysis methods. The spark plasma sintering technology was shown to be efficient for the consolidation of CaSiO₃-HAp powder in volume with a Ti6Al4V reinforcing matrix to obtain a ceramic metal biocomposite of an integral form. Vickers microhardness values were determined for the alloy and bioceramics (~500 and 560 HV, respectively), as well as for their interface area (~640 HV). An assessment of the critical stress intensity factor K_Ic (crack resistance) was performed. The research result is new and represents a prospect for the creation of high-tech implant products for regenerative bone surgery.

Hybrid Microwave Solid-Phase Synthesis of Wollastonite Based on Natural Renewable Raw Materials

Abstract

A method was tested to perform the solid-phase synthesis of ceramic wollastonite under hybrid microwave heating using such natural renewable raw materials as sea shells as a source of CaCO3 with the addition of commercial SiO2 powder. The XRD, SEM, TGA, and EDS methods were used to explore the effect of the mechanical homogenization time and the conditions for the chemical interaction of raw materials, provided that the required phase composition is reached. It was studied how temperature (800–1150°C) and time (15–60 min) of sintering affect the composition and structure of the ceramic wollastonite samples, including those in the presence of the strengthening additive sodium tetraborate. The formation of an apatite (Ca10(PO4)6(OH)2) layer on the surface of the obtained samples under conditions of their contact with artificial human blood plasma was assessed to confirm the biocompatible properties of these materials. The proposed method of synthesis is promising for obtaining a chemically pure valuable biomaterial in the form of synthetic wollastonite with the possibility of rational use of biogenic raw materials.

In vitro comparisons of microscale and nanoscale calcium silicate particles

Calcium silicate (CaSi) materials have been used for bone repair and generation due to their osteogenic properties. Tailoring the surface chemistry and structure of CaSi can enhance its clinical performance. There is no direct comparison between microscale and nanoscale CaSi particles. Therefore, this article aimed to compare and evaluate the surface chemistry, structure, and in vitro properties of microscale CaSi (μCaSi) and nanoscale CaSi (nCaSi) particles synthesized by the sol-gel method and precipitation method, respectively. As a result, the semi-crystalline μCaSi powders were assemblies of irregular microparticles containing a major β-dicalcium silicate phase, while the amorphous nCaSi powders consisted of spherical particles with a size of 100 nm. After soaking in a Tris-HCl solution, the amount of Si ions released from nCaSi was higher than that released from μCaSi, but there was no significant difference in Ca ion release between the two CaSi particles. Compared to microscale CaSi (μCaSi), nanoscale CaSi (nCaSi) significantly enhanced the growth and differentiation of human mesenchymal stem cells (hMSC) and inhibited the function of RAW 264.7 macrophages. In the case of antibacterial activity against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), nanoscale nCaSi displayed a higher bacteriostatic ratio, a greater growth inhibition zone and more reactive oxygen species (ROS) production than microscale μCaSi. The conclusion is that nanoscale CaSi had greater antibacterial and osteogenic activity compared to microscale CaSi. Next generation CaSi-based materials with unique properties are emerging to meet specific clinical needs.

Electrosprayed calcium silicate nanoparticle-coated titanium implant with improved antibacterial activity and osteogenesis

To ensure clinical success, the implant and the surrounding bone tissue must not only be integrated, but also must not be suspected of infection. In this work, an antibacterial and bioactive nanostructured calcium silicate (CaSi) layer on titanium substrate by an electrospray deposition method was prepared, followed by annealing at 700, 750 and 800 °C to improve the bonding strength of the CaSi coating. The phase composition, microstructure and bonding strength of the CaSi coatings were examined. Human mesenchymal stem cells (hMSCs), Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) species were used to analyze the osteogenic and antibacterial activity of the coatings, respectively. Experimental results showed that the as-prepared CaSi coating was mainly composted of β-dicalcium silicate phase with a particle size of about 300 nm. After annealing, the thickness of the oxidation reaction layer increased obviously from 0.3 μm to 1 μm with increase in temperature, which was confirmed by the cross-sectional morphology and element depth profile. The bonding strength of the coating annealed at 750 °C (19.0 MPa) was significantly higher (p < 0.05) than that of the as-prepared coating (4.4 MPa) and the ISO 13,779 standard (15 MPa). The results of antibacterial efficacy and stem cell osteogenesis consistently elaborated that the 750 °C-annealed coating had higher activity than the as-prepared coating and the Ti control. It is concluded that after annealing at 750 °C, the CaSi nanoparticle-coated Ti implant had good bond strength, osteogenic and antibacterial activity.

Ca-Si mesoporous nanoparticles with the optimal Ag-Zn ratio inhibit the Enterococcus faecalis infection of teeth through dentinal tubule infiltration: an in vitro and in vivo study

Enterococcus faecalis is the main cause of refractory root canal infections in human teeth. The control of root canal infection is one of the conditions necessary for the successful treatment of refractory root canal infections. In the present study, nano-scale silver-zinc-calcium-silica particles loaded with different ratios of silver-zinc were successfully prepared (Ag0.5Zn3-MCSNs and Ag0.5Zn10-MCSNs). The release profiles, antibacterial activity against E. faecalis, infiltration depth into dentinal tubules, biocompatibility and effects on dentin microhardness in vitro were investigated. In addition, the antimicrobial effects of the particles against Enterococcus faecalis reinfection were evaluated in vivo in the teeth of beagle dogs. Ag, Zn, Ca and Si were released from Ag-Zn-MCSNs, and the atomic ratio of silver and zinc released can reach the optimal value of 1 : 12 (Ag0.5Zn10-MCSNs). The particles also showed good biocompatibility and antibacterial activity against Enterococcus faecalis and did not reduce the hardness of dentin. The nanoparticles could be driven into the dentinal tubules of dentin slices by ultrasonic activation. In the root canals of beagle dogs, both Ag0.5Zn3-MCSNs and Ag0.5Zn10-MCSNs demonstrated strong preventive effects against E. faecalis infection. The Ag-Zn-Ca-Si mesoporous nanoparticles may develop into a new effective root canal disinfectant or root canal sealer.

CaSiO3-HAp Structural Bioceramic by Sol-Gel and SPS-RS Techniques: Bacteria Test Assessment

The article presents an original way of getting porous and mechanically strong CaSiO₃-HAp ceramics, which is highly desirable for bone-ceramic implants in bone restoration surgery. The method combines wet and solid-phase approaches of inorganic synthesis: sol-gel (template) technology to produce the amorphous xonotlite (Ca₆Si₆O₁₇·2OH) as the raw material, followed by its spark plasma sintering–reactive synthesis (SPS-RS) into ceramics. Formation of both crystalline wollastonite (CaSiO₃) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) occurs “in situ” under SPS conditions, which is the main novelty of the method, due to combining the solid-phase transitions of the amorphous xonotlite with the chemical reaction within the powder mixture between CaO and CaHPO₄. Formation of pristine HAp and its composite derivative with wollastonite was studied by means of TGA and XRD with the temperatures of the “in situ” interactions also determined. A facile route to tailor a macroporous structure is suggested, with polymer (siloxane-acrylate latex) and carbon (fibers and powder) fillers being used as the pore-forming templates. Microbial tests were carried out to reveal the morphological features of the bacterial film Pseudomonas aeruginosa that formed on the surface of the ceramics, depending on the content of HAp (0, 20, and 50 wt%).

The Antibiofilm Activity and Mechanism of Nanosilver- and Nanozinc-Incorporated Mesoporous Calcium-Silicate Nanoparticles

Background

Mesoporous calcium-silicate nanoparticles (MCSNs) have good prospects in the medical field due to their great physicochemical characteristics, antibacterial activity and drug delivery capacity. This study was to analyze the antibiofilm activity and mechanisms of silver (Ag) and zinc (Zn) incorporated MCSNs (Ag/Zn-MCSNs) with different percentages of Ag and Zn.

Methods

Ag/Zn(1:9, molar ratio)-MCSNs and Ag/Zn(9:1, molar ratio)-MCSNs were prepared and characterized. Endocytosis of nanoparticles by Enterococcus faecalis (E. faecalis) treated with Ag/Zn-MCSNs was observed using TEM to explore the antibacterial mechanisms. The antibiofilm activity of Ag/Zn-MCSNs with different ratios of Ag and Zn was tested by E. faecalis biofilm model in human roots. The human roots pretreated by different Ag/Zn-MCSNs were cultured with E. faecalis. Then, SEM and CLSM were used to observe the survival of E. faecalis on the root canal wall. Cytotoxicity of the nanoparticles was tested by CCK8 kits.

Results

The Ag/Zn-MCSNs release Ag⁺ and destroy the cell membranes to kill bacteria. The MCSNs containing Ag showed antibacterial activity against E. faecalis biofilms in different degrees, and they can adhere to dentin surfaces to get a continuous antibacterial effect. However, MTA, MCSNs and Zn-MCSNs could not disrupt the bacterial biofilms obviously. MCSNs, Ag/Zn(1:1, molar ratio)-MCSNs and Ag/Zn(1:9)-MCSNs showed no obvious cytotoxicity, while Ag-MCSNs and Ag/Zn(9:1)-MCSNs showed cytotoxicity. Zn-MCSNs can slightly promote cell proliferation.

Conclusion

Ag/Zn-MCSNs have good antibiofilm activity. They might achieve an appropriate balance between the antibacterial activity and cytotoxicity by adjusting the ratio of Ag and Zn. Ag/Zn-MCSNs are expected to be a new type of root canal disinfectant or sealer for root canal treatment.

Risk factors associated with recurrence of extremity osteomyelitis treated with the induced membrane technique

INTRODUCTION

Our aim was to observe the efficacy of the induced membrane technique in the treatment of extremity osteomyelitis and to analyse the causes of infection recurrence and its risk factors.

METHODS

We retrospectively analysed 424 cases of extremity osteomyelitis treated with the induced membrane technique in our department between May 2013 and June 2017. Infection recurrence time, recurrence sites and other relevant information were collected, summarized, and analysed.

RESULTS

A total of 424 patients were considered as "cured" of osteomyelitis after the first stage and the induced membrane technique was performed to rebuild the bone defects. After a mean follow-up of 31.6 (16-63) months, 52 patients had recurrence of infection, including 42 tibias and 10 femurs. The recurrence rate was 12.26%. Symptoms were relieved in 16 patients after intravenous antibiotic treatment. In the remaining 36 cases (8.49%), the infection was uncontrolled by intravenous antibiotics and surgical debridement was performed. The recurrence rate of infection of the tibia (16.22%) was higher than that of the femur (8.70%). The recurrence rate of post-traumatic osteomyelitis (14.66%) was significantly higher than that of hematogenous osteomyelitis (2.41%). Patients in whom Pseudomonas aeruginosa was isolated at the first stage had a recurrence rate of 28% (7/25), which was higher than that with the other isolated bacteria. Logistic regression analysis showed that repeated operations (≥3), post-traumatic osteomyelitis, and internal fixation at the first stage were risk factors for recurrence of infection, with odds ratios (ORs) of 2.30, 5.53 and 5.28 respectively.

CONCLUSIONS

The induced membrane technique is an effective method in the treatment of extremity osteomyelitis, although infection recurs in some cases. Repeated operations, post-traumatic osteomyelitis, and internal fixation at the first stage were risk factors for recurrence of infection. P. aeruginosa isolated at the first stage, tibia osteomyelitis, the presence of sinus, or flaps may also be associated with recurrence of infection.