Preparation and characterization of calcium sulfate-biomimetic apatite nanocomposites for controlled release of antibiotics

Design and Manufacture of Bone Cements Based on Calcium Sulfate Hemihydrate and Mg, Sr-Doped Bioactive Glass

In the present study, a novel composite bone cement based on calcium sulfate hemihydrate (CSH) and Mg, Sr-containing bioactive glass (BG) as solid phase, and solution of chitosan as liquid phase were developed. The phase composition, morphology, setting time, injectability, viscosity, and cellular responses of the composites with various contents of BG (0, 10, 20, and 30 wt.%) were investigated. The pure calcium sulfate cement was set at approximately 180 min, whereas the setting time was drastically decreased to 6 min by replacing 30 wt.% glass powder for CSH in the cement solid phase. BG changed the microscopic morphology of the set cement and decreased the size and compaction of the precipitated gypsum phase. Replacing the CSH phase with BG increased injection force of the produced cement; however, all the cements were injected at a nearly constant force, lower than 20 N. The viscosity measurements in oscillatory mode determined the shear-thinning behavior of the pastes. Although the viscosity of the pastes increased with increasing BG content, it was influenced by the frequency extent. Pure calcium sulfate cement exhibited some transient cytotoxicity on human-derived bone mesenchymal stem cells and it was compensated by introducing BG phase. Moreover, BG improved the cell proliferation and mineralization of extracellular matrix as shown by calcein measurements. The results indicate the injectable composite cement comprising 70 wt.% CSH and 30 wt.% Mg, Sr-doped BG has better setting, mechanical and cellular behaviors and hence, is a potential candidate for bone repair, however more animal and human clinical evaluations are essential.

Effect of Platelet-Rich Plasma Addition on the Chemical Properties and Biological Activity of Calcium Sulfate Hemihydrate Bone Cement

Currently, platelet-rich plasma (PRP) is an attractive additive for bone repair materials. PRP could enhance the osteoconductive and osteoinductive of bone cement, as well as modulate the degradation rate of calcium sulfate hemihydrate (CSH). The focus of this study was to investigate the effect of different PRP ratios (P1: 20 vol%, P2: 40 vol%, and P3: 60 vol%) on the chemical properties and biological activity of bone cement. The injectability and compressive strength of the experimental group were significantly higher than those of the control. On the other hand, the addition of PRP decreased the crystal size of CSH and prolonged the degradation time. More importantly, the cell proliferation of L929 and MC3T3-E1 cells was promoted. Furthermore, qRT-PCR, alizarin red staining, and western blot analyses showed that the expressions of osteocalcin (OCN) and Runt-related transcription factor 2 (Runx2) genes and β-catenin protein were up-regulated, and mineralization of extracellular matrix was enhanced. Overall, this study provided insight into how to improve the biological activity of bone cement through PRP incorporation.

Copper-Loaded Biodegradable Bone Wax with Antibacterial and Angiogenic Properties in Early Bone Repair

Traditional bone wax has lots of shortcomings such as the risk of infection and inflammation and the ability to hinder osteogenesis that limit its clinical applications. In this study, we designed a novel biodegradable bone wax with desirable angiogenic and antibacterial ability and low foreign body reaction by mixing calcium sulfate, poloxamer, and cupric ions. To evaluate its biocompatibility and angiogenetic effect in vitro, we cultured human umbilical vein endothelial cells (HUVECs) with the indicated bone wax to observe cell viability and vessel-like tubular formation. The bone wax was then implanted in a critical-sized bone defect rat model for 4 and 8 weeks to successfully stimulate angiogenesis in vivo. Finally, the bone wax extract was incubated with Gram-positive Staphylococcus aureus to confirm its antibacterial ability. The copper-loaded biodegradable bone wax overcomes the drawbacks of traditional bone wax and provides a new approach for the treatment of bone injuries.

Drug-Loaded Biomimetic Ceramics for Tissue Engineering

The mimesis of biological systems has been demonstrated to be an adequate approach to obtain tissue engineering scaffolds able to promote cell attachment, proliferation, and differentiation abilities similar to those of autologous tissues. Bioceramics are commonly used for this purpose due to their similarities to the mineral component of hard tissues as bone. Furthermore, biomimetic scaffolds are frequently loaded with diverse therapeutic molecules to enhance their biological performance, leading to final products with advanced functionalities. In this review, we aim to describe the already developed bioceramic-based biomimetic systems for drug loading and local controlled release. We will discuss the mechanisms used for the inclusion of therapeutic molecules on the designed systems, paying special attention to the identification of critical parameters that modulate drug loading and release kinetics on these scaffolds.

Cytotoxicity of gypsum-based biomaterial for direct pulp capping using stem cells from human exfoliated deciduous teeth

Aim:

The aim of this study was to evaluate the cytotoxicity effects of experimental gypsum-based biomaterial prepared with various concentrations of chitosan (Gyp-CHT).

Materials and Methods:

The study was performed using cell viability assay for mitochondrial dehydrogenase activity in stem cells from human exfoliated deciduous teeth (SHED), after 1, 2, and 3 days of exposure to the biomaterial extracts of varying concentrations. Differences in mean cell viability values were assessed by one-way analysis of variance, followed by Dunnett T3 post hoc test for multiple comparisons (P < 0.05).

Results:

The cell viability to Gyp-CHT in low extract concentrations was statistically similar to that of the control and different from that of high extract concentrations. Gyp-5% CHT showed the highest percentage of cell viability with 110.92%, 108.56%, and 109.11%. The cell viability showed a tendency toward increment with low extract concentration and no constant effect of CHT on cell viability toward higher or lower.

Conclusions:

Gyp-CHT biomaterial has no cytotoxic effects on the cultured SHED.

Insights into water-mediated ion clustering in aqueous CaSO4 solutions: pre-nucleation cluster characteristics studied by ab initio calculations and molecular dynamics simulations

The molecular structure of growth units building crystals is a fundamental issue in the crystallization processes from aqueous solutions. In this work, a systematic investigation of pre-nucleation clusters and their hydration characteristics in aqueous CaSO₄ solutions was performed using ab initio calculations and molecular dynamics (MD) simulations. The results of ab initio calculations and MD simulations indicate that the dominant species in aqueous CaSO₄ solutions are monodentate ion-associated structures. Compared with charged ion clusters, neutral clusters are more likely to be present in an aqueous CaSO₄ solution. Neutral (CaSO₄)_m clusters are probably the growth units involved in the pre-nucleation or crystallization processes. Meanwhile, hydration behavior around ion associated species in aqueous CaSO₄ solutions plays an important role in related phase/polymorphism selections. Upon ion clustering, the residence of some water molecules around Ca²⁺ in ion-associated species is weakened while that of some bridging waters is enhanced due to dual interaction by Ca²⁺ and SO₄^2-. Some phase/polymorphism selections can be achieved in aqueous CaSO₄ solutions by controlling the hydration around pre-nucleation clusters. Moreover, the association trend between calcium and sulfate is found to be relatively strong, which hints at the low solubility of calcium sulfate in water.

Nanocrystalline calcium sulfate/hydroxyapatite biphasic compound as a TGF-β1/VEGF reservoir for vital pulp therapy

OBJECTIVES

Vital pulp therapy aims to treat reversible pulpal injuries via protective dentinogenesis and to preserve more tooth structure. Mineral trioxide aggregate (MTA)-based capping materials demonstrate prolonged setting time increases the risk of pulpal infection during multi-visit treatment. Their non-degradable property occupies pulp space and limits dentin-pulp regeneration. This study reports an inorganic degradable biomaterial that presents a short initial setting time and acts as a growth factor reservoir to promote reparative dentinogenesis.

METHODS

We synthesize nanocrystalline calcium sulfate hemihydrate (nCS), hydroxyapatite (HAp) and calcium sulfate hemihydrate (CS) as a reservoir to which transforming growth factor-beta 1 (TGF-β1) and vascular endothelial growth factor (VEGF) are added (denoted as nCS/HAp/CS/TGF-β1/VEGF). In vitro biocompatibility and mineralization (the activity and expression of alkaline phosphatase, ALP) were evaluated. Rat animal model was created to test in vivo efficacy.

RESULTS

Cultured human dental pulp cells (HDPCs) showed that nCS/HAp/CS/TGF-β1/VEGF cement has excellent biocompatibility and the potential to elevate the activity and expression of ALP. The in vivo efficacy (rat animal model) indicates protective dentin by micro-computed tomography (μ-CT) measurements and histological analyses. The 3D μ-CT non-destructive analysis also determines volume changes during pulpotomy, suggesting that the degraded space of the nCS/HAp/CS/TGF-β1/VEGF cement is repaired by the formation of dentin-pulp tissue.

SIGNIFICANCE

These findings demonstrate that nCS/HAp/CS cement acts as a potent reservoir for the sustained release of growth factors, and that nCS/HAp/CS/TGF-β1/VEGF cement has a high potential to form the reparative dentinogenesis in vivo.

Nanotechnology for treating osteoporotic vertebral fractures

Osteoporosis is a serious public health problem affecting hundreds of millions of aged people worldwide, with severe consequences including vertebral fractures that are associated with significant morbidity and mortality. To augment or treat osteoporotic vertebral fractures, a number of surgical approaches including minimally invasive vertebroplasty and kyphoplasty have been developed. However, these approaches face problems and difficulties with efficacy and long-term stability. Recent advances and progress in nanotechnology are opening up new opportunities to improve the surgical procedures for treating osteoporotic vertebral fractures. This article reviews the improvements enabled by new nanomaterials and focuses on new injectable biomaterials like bone cements and surgical instruments for treating vertebral fractures. This article also provides an introduction to osteoporotic vertebral fractures and current clinical treatments, along with the rationale and efficacy of utilizing nanomaterials to modify and improve biomaterials or instruments. In addition, perspectives on future trends with injectable bone cements and surgical instruments enhanced by nanotechnology are provided.

Gypsum-based biomaterials: Evaluation of physical and mechanical properties, cellular effects and its potential as a pulp liner

This in vitro study aimed to evaluate setting time and compressive strength of gypsum-based chitosan biomaterials and its effect on proliferation of stem cells from human exfoliated deciduous teeth (SHED) and alkaline phosphatase (ALP) activity. Pure-GYP was mixed with water (2.5 g: 1.9 mL); Gyp-CHT was prepared with gypsum, chitosan, and water (2.5 g: 0.285 g: 1.9 mL). Cell viability and ALP activity were assessed at different periods. Data were analyzed using SPSS (p<0.05). The setting times were 2.7 min and 2.8 min for pure-GYP and Gyp-CHT, respectively. Significantly higher compressive strength was observed with Gyp-CHT. SHED treatments with both materials were not cytotoxic. ALP was consistently higher in the treated groups compared with the control. Cellular attachments were evident with SEM. Excellent cellular viability with pure-GYP and Gyp-CHT, as well as increased ALP activities, suggested the possibility of tertiary dentin formation. Further studies are necessary to evaluate the biomaterials for its pulp protective potentialities.

Self-setting bioceramic microscopic protrusions for transdermal drug delivery

Self-setting bioceramic microneedles are fabricated using a simple manufacturing procedure under mild conditions and could be substitutes for current microneedles.

Bioerodible calcium sulfate/poly(β-amino ester) hydrogel composites

The capacity to quickly regenerate or augment bone lost as a result of resorption is crucial to ensure suitable application of prosthetics for restoring masticatory function. Calcium sulfate hemihydrate (CS)-based bone graft substitute composites containing poly(β-amino ester) (PBAE) biodegradable hydrogel particles were developed to act as a 'tenting' barrier to soft tissue infiltration, potentially providing adequate space to enable vertical bone regeneration. CS has long been recognized as an osteoconductive biomaterial with an excellent reputation as a biocompatible substance. Composite samples were fabricated with varying amounts (1 or 10 wt%) and sizes (53-150 or 150-250 μm) of gel particles embedded in CS. The swelling and degradation rates of PBAE gels alone were rapid, resulting in complete degradation in less than 24h, an important characteristic to aid in controlled release of drug. MicroCT images revealed a homogeneous distribution of gel particles within the CS matrix. All CS samples degraded via surface erosion, with the amount of gel particles (i.e., 10 wt% gel particles) having only a small, but significant, effect on the dissolution rate (4% vs. 5% per day). Compression testing determined that the amount, but not the size, of gel particles had a significant effect on the overall strength of the composites. As much as a 75% drop in strength was seen with a 10 wt% loading of particles. A pilot study using PBAE particles loaded with the multipotential drug curcumin demonstrated sustained release of drug from CS composites. By adjusting the amount and/or size of the biodegradable gel particles embedded in CS, mechanical strength and degradation rates of the composites, as well as the drug release kinetics, can be tuned to fabricate, multi-functional 'space-making' bone grafting substitutes.

Setting Time Comparison of Four Antimicrobial Laden Calcium Sulfate Plasters

Background

The surgeon may implant calcium sulfate pellets (aka gypsum) as a resorbable antimicrobial vehicle at the surgical site in severe cases of osteomyelitis. Gypsum setting times with or without antibiotic additives are found scattered throughout the literature, but often factors known to alter setting time are either not disclosed or not held constant between experiments. To our knowledge, no prior study compares the setting time of calcium sulfate plaster mixed with the four commonly used antibiotics under constant conditions as presented here.

Purpose

To compare the setting times of calcium sulfate hemihydrate mixtures containing vancomycin, cefazolin, tobramycin, or amphotericin B.

Materials and methods

Groups consisted of samples comprised of 6.3 gm calcium sulfate hemihydrate (CSH) mixed with approximately 1/4th a vial of lyophilized antimicrobial (vancomycin, cefazolin, tobramycin or amphotericin B) with CSH powder to normal saline ratio of 1.7 gm/ml and mixed for 30 seconds at controlled speed and humidity. Each sample initial setting time (Ti) and final setting time (Tf) were established by Gillmore needles method according to ASTM standard C266- 08 apparatus specifications.

Results

Kruskal-Wallis one-way analysis of variance by ranks revealed that antibiotic type affected the initial and final setting times of gypsum (p < 0.05). Post hoc analysis using Dunn's multiple comparisons indicated that there was no difference between control Ti (7.2 ± 1.1 min) and that of vancomycin or cefazolin group (9.8 ± 1.7 or 14.2 ± 1.3 min, respectively, p > 0.05), but the Ti of the tobramycin and amphotericin B groups (31.8 ± 5.7 and 140.4 ± 18.0 min) differed from the control Ti (p < 0.05). Likewise, there was no difference of control Tf (p > 0.05, 12.2 ± 1.1 min) when compared to vancomycin or cefazolin groups (22.2 ± 6.9 or 25.7 ± 4.1 min), but that the Tf of tobramycin and amphotericin B groups (76.3 ± 5.9 and 200.0 ± 21.1 min) each differed from the control group (p < 0.05).

Conclusion

This experiment is aimed to help surgeons plan when they should begin preparing their calcium sulfate antibiotic beads during surgery. As a general guideline, allow 15 minutes to set when adding a 1 gm vial of vancomycin or cefazolin, 30 minutes for adding a 1.2 gm vial tobramycin, and 2.5 hours for adding a 50 mg vial of amphotericin B.

Kroger J, Beaufond P, Inceoglu S, Maskiewicz V, Cheng W, Brier-Jones JE. Setting Time Comparison of Four Antimicrobial Laden Calcium Sulfate Plasters. The Duke Orthop J 2013;3(1):36-40.

Physicochemical properties and cellular responses of strontium-doped gypsum biomaterials

This paper describes some physical, structural, and biological properties of gypsum bioceramics doped with various amounts of strontium ions (0.19-2.23 wt%) and compares these properties with those of a pure gypsum as control. Strontium-doped gypsum (gypsum:Sr) was obtained by mixing calcium sulfate hemihydrate powder and solutions of strontium nitrate followed by washing the specimens with distilled water to remove residual salts. Gypsum was the only phase found in the composition of both pure and gypsum:Sr, meanwhile a shift into lower diffraction angles was observed in the X-ray diffraction patterns of doped specimens. Microstructure of all gypsum specimens consisted of many rod-like small crystals entangled to each other with more elongation and higher thickness in the case of gypsum:Sr. The Sr-doped sample exhibited higher compressive strength and lower solubility than pure gypsum. A continuous release of strontium ions was observed from the gypsum:Sr during soaking it in simulated body fluid for 14 days. Compared to pure gypsum, the osteoblasts cultured on strontium-doped samples showed better proliferation rate and higher alkaline phosphatase activity, depending on Sr concentration. These observations can predict better in vivo behavior of strontium-doped gypsum compared to pure one.

In vitro release kinetics and physical, chemical and mechanical characterization of a POVIAC®/CaCO3/HAP-200 composite

Coralline calcium-hydroxyapatite and calcium carbonate from Porites Porites coral were added to a polymeric matrix based on polyvinyl acetate (POVIAC(®)), to obtain a novel bone substitute composite as well as a system for the controlled drug (cephalexin) release. Composite samples with different compositions were characterized by physical-chemical and mechanical methods. Furthermore, the in vitro release profile of cephalexin and the kinetic behavior of its release from these composites were analyzed by appropriate mathematical models. It was shown that there is no chemical interaction between the inorganic filler and the polymer matrix, each conserving the original properties of the raw materials. The compressive mechanical strength and Young modulus of the composite with 17.5% of POVIAC(®), has better mechanical properties than those of cancellous bone. The variation of POVIAC(®) content can affect the cephalexin release kinetic in the composite. The cephalexin release mechanism from the composites can be considered as the result of the joint contribution of a prevailing Fickian diffusion and of polymer chain relaxation. It was also demonstrated that cephalexin is occluded inside the composites and not on their surface.

Evaluation of colloidal silica suspension as efficient additive for improving physicochemical and in vitro biological properties of calcium sulfate-based nanocomposite bone cement

In the present study new calcium sulfate-based nanocomposite bone cement with improved physicochemical and biological properties was developed. The powder component of the cement consists of 60 wt% α-calcium sulfate hemihydrate and 40 wt% biomimetically synthesized apatite, while the liquid component consists of an aqueous colloidal silica suspension (20 wt%). In this study, the above mentioned powder phase was mixed with distilled water to prepare a calcium sulfate/nanoapatite composite without any additive. Structural properties, setting time, compressive strength, in vitro bioactivity and cellular properties of the cements were investigated by appropriate techniques. From X-ray diffractometer analysis, except gypsum and apatite, no further phases were found in both silica-containing and silica-free cements. The results showed that both setting time and compressive strength of the calcium sulfate/nanoapatite cement improved by using colloidal silica suspension as cement liquid. Meanwhile, the condensed phase produced from the polymerization process of colloidal silica filled the micropores of the microstructure and covered rodlike gypsum crystals and thus controlled cement disintegration in simulated body fluid. Additionally, formation of apatite layer was favored on the surfaces of the new cement while no apatite precipitation was observed for the cement prepared by distilled water. In this study, it was also revealed that the number of viable osteosarcoma cells cultured with extracts of both cements were comparable, while silica-containing cement increased alkaline phosphatase activity of the cells. These results suggest that the developed cement may be a suitable bone filling material after well passing of the corresponding in vivo tests.