Anti-washout carboxymethyl chitosan modified tricalcium silicate bone cement: preparation, mechanical properties and in vitro bioactivity

Effects of Superfine Tricalcium Silicate Powder on the Physicochemical and Mechanical Properties of Its Premixed Cement as a Root Canal Filling Material

Calcium silicate-based cement is a promising material for filling root canals. However, it has several drawbacks to its clinical application, including difficult operation and low curing strength. In this study, we successfully prepared an ultrafine tricalcium silicate powder and investigated the effects of this ultrafine powder on the performance of the premixed tricalcium silicate cement, including the curing process, setting time, hydration products, microstructure, injectivity, fluidity, and compressive strength. The results demonstrate that the addition of ultrafine tricalcium silicate powder alters the hydration product content and product morphology of the premixed cement. By increasing the content of the ultrafine powder, the injectable property of the cement can be increased to more than 95%, the fluidity can be increased from 18 mm to 35 mm, and the curing time can be shortened from 13 h to 11 h. Notably, the addition of the ultrafine powder greatly enhances the compressive strength of the hardened cement, which increases from 20.6 MPa to 51.0 MPa. These results indicate that altering the particle size distribution of the powder is an effective method for enhancing the physicochemical and mechanical properties of tricalcium silicate cement as a root canal filling material.

Effects of ATP on the Physicochemical Properties and Cytocompatibility of Calcium Sulfate/Calcium Citrate Composite Cement

Adenosine triphosphate (ATP), acting as a source of energy, has effects on cellular activities, such as adhesion, proliferation, and differentiation. In this study, ATP-loaded calcium sulfate hemihydrate/calcium citrate tetrahydrate cement (ATP/CSH/CCT) was successfully prepared for the first time. The effect of different contents of ATP on the structure and physicochemical properties of ATP/CSH/CCT was also studied in detail. The results indicated that incorporating ATP into the cement did not significantly alter their structures. However, the addition ratio of ATP directly impacted the mechanical properties and in vitro degradation properties of the composite bone cement. The compressive strength of ATP/CSH/CCT gradually decreased with an increasing ATP content. The degradation rate of ATP/CSH/CCT did not significantly change at low concentrations of ATP, but it increased with a higher ATP content. The composite cement induced the deposition of a Ca-P layer in a phosphate buffer solution (PBS, pH = 7.4). Additionally, the release of ATP from the composite cement was controlled. The ATP was controlled releasing at the 0.5% and 1% ATP in cement by the diffusion of ATP and the degradation of the cement, whereas it was controlled by the diffusion process merely at the 0.1% ATP in cement. Furthermore, ATP/CSH/CCT demonstrated good cytoactivity with the addition of ATP and is expected to be used for the repair and regeneration of bone tissue.

Biocompatible carboxymethyl chitosan-modified glass ionomer cement with enhanced mechanical and anti-bacterial properties

Due to the potential adverse effects of conventional dental cements, the demand for biocompatible cements have grown tremendously in the field of dentistry. In this respect, Glass ionomer cements (GICs) are being developed by different researchers. However, low mechanical strength of GIC make them unsuitable for application in high-stress areas. Thus, numerous initiatives to improve mechanical performance have been attempted till date including incorporation of reinforcing fillers. Novelty of the study lies in using carboxymethyl chitosan (CMC) to develop a biocompatible dental cement (DC/CMC-m-GP), which would have enhanced mechanical strength due to greater interaction of CMC with the particles of GIC and better cyto-compatibility due to its cell-proliferation activity. The mechanical strength, acid erosion and fluoride release of DC/CMC-m-GP were studied and compared with control dental cement (DC/Control). DC/CMC-m-GP shows compressive strength of 157.45 M Pa and flexural strength of 18.76 M Pa which was higher as compared to DC/Control. The morphology of the GICs were studied through FESEM. Anti-microbial activity of DC/CMC-m-GP was studied by Agar disc-diffusion method and biofilm assay against S. mutans, which shows that DC/CMC-m-GP inhibits bacterial adhesion on its surface. MTT assay infers that DC/CMC-m-GP was non-cytotoxic and did not affect the cell viability significantly.

A new injectable quick hardening anti-collapse bone cement allows for improving biodegradation and bone repair

The development of injectable cement-like biomaterials via a minimally invasive approach has always attracted considerable clinical interest for modern bone regeneration and repair. Although α-tricalcium phosphate (α-TCP) powders may readily react with water to form hydraulic calcium-deficient hydroxyapatite (CDHA) cement, its long setting time, poor anti-collapse properties, and low biodegradability are suboptimal for a variety of clinical applications. This study aimed to develop new injectable α-TCP-based bone cements via strontium doping, α-calcium sulfate hemihydrate (CSH) addition and liquid phase optimization. A combination of citric acid and chitosan was identified to facilitate the injectable and anti-washout properties, enabling higher resistance to structure collapse. Furthermore, CSH addition (5 %-15 %) was favorable for shortening the setting time (5-20 min) and maintaining the compressive strength (10-14 MPa) during incubation in an aqueous buffer medium. These α-TCP-based composites could also accelerate the biodegradation rate and new bone regeneration in rabbit lateral femoral bone defect models in vivo. Our studies demonstrate that foreign ion doping, secondary phase addition and liquid medium optimization could synergistically improve the physicochemical properties and biological performance of α-TCP-based bone cements, which will be promising biomaterials for repairing bone defects in situations of trauma and diseased bone.

The in vivo dissolution of tricalcium silicate bone cement

This study aimed to investigate the in vivo dissolution of tricalcium silicate (Ca₃ SiO₅ , C₃ S) bone cement in the rabbit femoral defect. Results indicated that C₃ S paste directly integrated with the bone tissue without the protection of the bone-like apatite. Calcium silicate hydrate gel (C-S-H gel) and Ca(OH)₂ were the main components of C₃ S paste. The dissolution model of C₃ S paste was a mass loss rather than a decrease in volume. The initial dissolution of C₃ S paste (0 ~ 6 weeks) was greatly attributed to the release of Ca(OH)₂ , and the later dissolution (>6 weeks) was attributed to the decalcification of C-S-H gel. Although the mass of C₃ S paste could decrease by more than 19 wt % after 6 weeks of implantation, the created pores (<1 μm) were not large enough for the bone tissue to migrate into C₃ S paste. The loss of Ca ions also resulted in the transformation of SiO₄ tetrahedrons from Q¹ and Q² to Q⁰ , Q³ , and Q⁴ in C-S-H gel. Because only isolated SiO₄ tetrahedrons (Q⁰ ) and Ca ions could be absorbed by the bone tissue, C₃ S paste gradually transformed into a silica-rich gel. The fundamental reason for no decrease in volume of C₃ S paste was that the SiO₄ tetrahedron network still maintained the frame structure of C₃ S paste during the implantation.

Investigation of characteristics as endodontic sealer of novel experimental elastin-like polypeptide-based mineral trioxide aggregate

Although mineral trioxide aggregates (MTA) have been adopted as an endodontic sealer because of excellent sealing effect and bioactive property and been modified with improvement of its characteristics, the developed MTA sealers have not yet satisfied all the ideal requirements of endodontic sealers. The aim of this study was to assess the characteristics of elastin-like polypeptide (ELP)-incorporated MTA for use as an endodontic sealer and compare them with those of commercial MTA sealers. Two commercial MTA sealers and three experimental ELP-incorporated MTA sealers with 0.3, 0.4, and 0.5 liquid/powder (L/P) ratio for 10 wt% ELP liquid were evaluated. The push-out bond strength, flow rate, sealer penetrability and wash-out resistance were tested and the sealer-dentin interface was observed using a scanning electron microscope (SEM). Our study revealed the ELP-incorporated MTA sealer, especially in 0.4 L/P ratio, exhibited the higher push-out bond strength and flow rate (P < 0.05), and equal or superior sealer penetration and remarkable wash-out resistance compared to commercial MTA sealers. The groups of ELP-based experimental sealers also exhibited more intimate contact with dentin compared to the commercial MTA sealers. Our research will suggest the possible adoption of the ELP-incorporated MTA as endodontic sealer for clinical use.

Enhanced antibacterial activity of calcium silicate-based hybrid cements for bone repair

Calcium silicate cement has attracted much attention for bone defect repair and regeneration due to its osteogenic properties. Biomaterial-associated infections and washout have become a common clinical problem. In order to enhance the antibacterial and washout performance of calcium silicate cement to meet clinical needs, different types of chitosan, including chitosan polysaccharide (CTS), quaternary ammonium chitosan (QTS), and chitosan oligosaccharide (COS), as a liquid phase were added to the calcium silicate powder. The physicochemical properties, in vitro bioactivity, antibacterial efficacy, and osteogenic effects (MG63 cells) of the cement were evaluated. Antibacterial activity was conducted with Gram-negative Escherichia coli (E. coli) and a Gram-positive Staphylococcus aureus (S. aureus) bacteria. The amount of intracellular reactive oxygen species (ROS) produced in the bacteria cultured with the chitosan solution was also detected. The experimental results showed that the chitosan additive did not affect the crystalline phase of calcium silicate cement, but increased the setting time and strength of the cement in a concentration-dependent manner. Within the scope of this study, CTS and QTS solutions with a concentration of not <1 wt% improved the washout resistance of the control cement, while the COS solutions failed to strengthen the cement. When soaked in simulated body fluid (SBF) for 1 day, all cement samples formed apatite spherules. As the soaking time increased, the diametral tensile strength of all cements decreased and the porosity increased. The assays of MG63 cell function showed lower osteogenic activity of osteoblastic cells grown on the surfaces of the chitosan-incorporated cements in comparison with the control cement without chitosan. At the same 1% concentration, compared with QTS and COS cement, CTS cement had lower cell attachment, proliferation, differentiation, and mineralization. Conversely, the CTS cement resulted in the highest bacteriostasis ratio among the three hybrid cements against two bacteria. The ROS production followed the order of CTS > QTS > COS at the same 1% concentration. In conclusion, calcium silicate cement with 1% QTS may be a viable candidate for bone defect repair in view of anti-washout performance, setting time, antibacterial activity, and osteogenic activity shown in this study.

A novel injectable calcium phosphate cement-bioactive glass composite for bone regeneration

Background

Calcium phosphate cement (CPC) can be molded or injected to form a scaffold in situ, which intimately conforms to complex bone defects. Bioactive glass (BG) is known for its unique ability to bond to living bone and promote bone growth. However, it was not until recently that literature was available regarding CPC-BG applied as an injectable graft. In this paper, we reported a novel injectable CPC-BG composite with improved properties caused by the incorporation of BG into CPC.

Materials and Methods

The novel injectable bioactive cement was evaluated to determine its composition, microstructure, setting time, injectability, compressive strength and behavior in a simulated body fluid (SBF). The in vitro cellular responses of osteoblasts and in vivo tissue responses after the implantation of CPC-BG in femoral condyle defects of rabbits were also investigated.

Results

CPC-BG possessed a retarded setting time and markedly better injectability and mechanical properties than CPC. Moreover, a new Ca-deficient apatite layer was deposited on the composite surface after immersing immersion in SBF for 7 days. CPC-BG samples showed significantly improved degradability and bioactivity compared to CPC in simulated body fluid (SBF). In addition, the degrees of cell attachment, proliferation and differentiation on CPC-BG were higher than those on CPC. Macroscopic evaluation, histological evaluation, and micro-computed tomography (micro-CT) analysis showed that CPC-BG enhanced the efficiency of new bone formation in comparison with CPC.

Conclusions

A novel CPC-BG composite has been synthesized with improved properties exhibiting promising prospects for bone regeneration.

A novel injectable chitosan/polyglutamate polyelectrolyte complex hydrogel with hydroxyapatite for soft-tissue augmentation

This study demonstrated a chitosan (CS)/polyglutamate (PG) polyelectrolyte complex (PEC) hydrogel combined with spherical hydroxyapatite (HAp) particles as an injectable dermal filler for soft-tissue augmentation. The CS/PG PEC hydrogel with oppositely charged ionic cross-linking, a high gel content, and low degradation rate was introduced as a carrier to achieve high shape and volume stability. An MTT assay indicated that the CS/PG PEC had satisfactory cell biocompatibility. This PEC/HAp hydrogel showed good structural integrity in a PBS solution for up to 60 days. Clinical manageability was indexed by an injection force measurement through sterile 27-gauge needles using a texture analyzer. In an animal study, 0.2 mL of the PEC and PEC/hydroxyapatite (HAp) were implanted within the dorsal dermis of a swine ear. Injected tissue areas were biopsied 2 weeks, and 2 and 6 months after the injection. According to the histomorphometric results, the PEC and PEC/HAp groups showed percentages of retention of the maximum height of the cross-section of about 44% and 73% at 6 months. New collagen was observed in the central position indicating a possible collagenesis effect. These results suggest that this PEC/HAp system can be used as an alternative for soft-tissue augmentation.