In vitro and in vivo study of commercial calcium phosphate cement HydroSet™

Octacalcium phosphate phase forming cements as an injectable bone substitute materials: Preparation and in vitro structural study

In the realm of regenerating damaged or degenerated bones through minimally invasive techniques, injectable materials have emerged as exceptionally promising. Among these, calcium phosphate bone cements (CPCs) have garnered significant interest due to their remarkable bioactivity, setting it apart from non-degradable alternatives such as polymethyl methacrylate cements. α-Tricalcium phosphate (α-TCP) is a widely used solid phase component in CPCs. It can transform into calcium-deficient hydroxyapatite (CDHAp) when it comes in contact with water. In this study, we aimed to create an injectable, self-setting bone cement using low-temperature synthesized α-TCP powder as a single precursor of the powder phase. We found that changes in the pH of the liquid phase (pH 6.0, pH 6.2, pH 7.0 and pH 7.4) significantly altered the cement's setting, handling, and mechanical properties. The formation of the octacalcium phosphate (OCP) phase was identified in our study, which positively affects the osteoblastic cell response. Hardened OCP-forming bone cements prepared using a liquid phase with pH 7.0 and 7.4 showed better osteogenic cell attachment and proliferation than those prepared with pH 6.0 and 6.2. Our study suggests that changes in the pH of the liquid phase can significantly affect the properties of α-TCP-based bone cement, and the presence of the OCP phase is crucial for optimal cement performance.

Ready-To-Use and Rapidly Biodegradable Magnesium Phosphate Bone Cement: In Vivo Evaluation in Sheep

In clinical practice, hydroxyapatite (HA) cements for bone defect treatment are frequently prepared by mixing a powder component and a liquid component shortly before implantation in the operation theater, which is time-consuming and error-prone. In addition, HA cements are only slightly resorbed, that is, cement residues can still be found in the bone years after implantation. Here, these challenges are addressed by a prefabricated magnesium phosphate cement paste based on glycerol, which is ready-to-use and can be directly applied during surgery. By using a trimodal particle size distribution (PSD), the paste is readily injectable and exhibits a compressive strength of 9-14 MPa after setting. Struvite (MgNH4 PO4 ·6H2 O), dittmarite (MgNH4 PO4 ·H2 O), farringtonite (Mg3 (PO4 )2 ), and newberyite (MgHPO4 ·3H2 O) are the mineral phases present in the set cement. The paste developed here features a promising degradation of 37% after four months in an ovine implantation model, with 25% of the implant area being newly formed bone. It is concluded that the novel prefabricated paste improves application during surgery, has a suitable degradation rate, and supports bone regeneration.

Is it possible to 3D bioprint load-bearing bone implants? A critical review

Rehabilitative capabilities of any tissue engineered scaffold rely primarily on the triad of (i) biomechanical properties such as mechanical properties and architecture, (ii) chemical behavior such as regulation of cytokine expression, and (iii) cellular response modulation (including their recruitment and differentiation). The closer the implant can mimic the native tissue, the better it can rehabilitate the damage therein. Among the available fabrication techniques, only 3D bioprinting (3DBP) can satisfactorily replicate the inherent heterogeneity of the host tissue. However, 3DBP scaffolds typically suffer from poor mechanical properties, thereby, driving the increased research interest in development of load-bearing 3DBP orthopedic scaffolds in recent years. Typically, these scaffolds involve multi-material 3D printing, comprising of at-least one bioink and a load-bearing ink; such that mechanical and biological requirements of the biomaterials are decoupled. Ensuring high cellular survivability and good mechanical properties are of key concerns in all these studies. 3DBP of such scaffolds is in early developmental stages, and research data from only a handful of preliminary animal studies are available, owing to limitations in print-capabilities and restrictive materials library. This article presents a topically focused review of the state-of-the-art, while highlighting aspects like available 3DBP techniques; biomaterials' printability; mechanical and degradation behavior; and their overall bone-tissue rehabilitative efficacy. This collection amalgamates and critically analyses the research aimed at 3DBP of load-bearing scaffolds for fulfilling demands of personalized-medicine. We highlight the recent-advances in 3DBP techniques employing thermoplastics and phosphate-cements for load-bearing applications. Finally, we provide an outlook for possible future perspectives of 3DBP for load-bearing orthopedic applications. Overall, the article creates ample foundation for future research, as it gathers the latest and ongoing research that scientists could utilize.

Bone Tissue Engineering in the Treatment of Bone Defects

Bones play an important role in maintaining exercise and protecting organs. Bone defect, as a common orthopedic disease in clinics, can cause tremendous damage with long treatment cycles. Therefore, the treatment of bone defect remains as one of the main challenges in clinical practice. Today, with increased incidence of bone disease in the aging population, demand for bone repair material is high. At present, the method of clinical treatment for bone defects including non-invasive therapy and invasive therapy. Surgical treatment is the most effective way to treat bone defects, such as using bone grafts, Masquelet technique, Ilizarov technique etc. In recent years, the rapid development of tissue engineering technology provides a new treatment strategy for bone repair. This review paper introduces the current situation and challenges of clinical treatment of bone defect repair in detail. The advantages and disadvantages of bone tissue engineering scaffolds are comprehensively discussed from the aspect of material, preparation technology, and function of bone tissue engineering scaffolds. This paper also summarizes the 3D printing technology based on computer technology, aiming at designing personalized artificial scaffolds that can accurately fit bone defects.

Accelerated bone regeneration through rational design of magnesium phosphate cements

Results of several studies during past years suggested that magnesium phosphate cements (MPCs) not only show excellent biocompatibility and osteoconductivity, but they also provide improved regeneration capacity due to higher solubility compared to calcium phosphates. These findings also highlighted that chemical similarity of bone substitutes to the natural bone tissue is not a determinant factor in the success of regenerative strategies. The aim of this study was to further improve the degradation speed of MPCs for a fast bone ingrowth within a few months. We confirmed our hypothesis, that decreasing the powder-liquid ratio (PLR) of cement results in an increased content of highly soluble phases such as struvite (MgNH₄PO₄⋅6H₂O) as well as K-struvite (MgKPO₄⋅6H₂O). Promising compositions with a low PLR of 1 g ml^-1 were implanted in partially-loaded tibia defects in sheep. Both cements were partially degraded and replaced by bone tissue after 4 months. The degradation speed of the K-struvite cement was significantly higher compared to the struvite cement, initially resulting in the formation of a cell-rich resorption zone at the surface of some implants, as determined by histology. Overall, both MPCs investigated in this study seem to be promising as an alternative to the clinically well-established, but slowly degrading calcium phosphate cements, depending on defect size and desired degradation rate. Whereas the K-struvite cement might require further modification towards a slower resorption and reduced inflammatory response in vivo, the struvite cement appears promising for the treatment of bone defects due to its continuous degradation with simultaneous new bone formation. STATEMENT OF SIGNIFICANCE: Cold setting bone cements are used for the treatment of bone defects that exceed a critical size and cannot heal on their own. They are applied pasty into the bone defect and harden afterwards so that the shape adapts to the individual defect. Magnesium phosphates such as magnesium ammonium phosphate hexahydrate (struvite) belong to a new class of these cold setting bone cements. They degrade much faster than the clinically established calcium phosphates. In this study, a magnesium phosphate that has hardly been investigated so far was implanted into partially-loaded defects in sheeps: Potassium magnesium phosphate hexahydrate. This showed even faster resorption compared to the struvite cement: after 4 months, 63% of the cement was already degraded.

Biological and mechanical performance and degradation characteristics of calcium phosphate cements in large animals and humans

Calcium phosphate cements (CPCs) have been used to treat bone defects and support bone regeneration because of their good biocompatibility and osteointegrative behavior. Since their introduction in the 1980s, remarkable clinical success has been achieved with these biomaterials, because they offer the unique feature of being moldable and even injectable into implant sites, where they harden through a low-temperature setting reaction. However, despite decades of research efforts, two major limitations concerning their biological and mechanical performance hamper a broader clinical use. Firstly, achieving a degradation rate that is well adjusted to the dynamics of bone formation remains a challenging issue. While apatite-forming CPCs frequently remain for years at the implant site without major signs of degradation, brushite-forming CPCs are considered to degrade to a greater extent. However, the latter tend to convert into lower soluble phases under physiological conditions, which makes their degradation behavior rather unpredictable. Secondly, CPCs exhibit insufficient mechanical properties for load bearing applications because of their inherent brittleness. This review places an emphasis on these limitations and provides an overview of studies that have investigated the biological and biomechanical performance as well as the degradation characteristics of different CPCs after implantation into trabecular bone. We reviewed studies performed in large animals, because they mimic human bone physiology more closely in terms of bone metabolism and mechanical loading conditions compared with small laboratory animals. We compared the results of these studies with clinical trials that have dealt with the degradation behavior of CPCs after vertebroplasty and kyphoplasty.

Graphene Oxide Finely Tunes the Bioactivity and Drug Delivery of Mesoporous ZnO Scaffolds

Mesoporous zinc oxide (ZnO) scaffolds coated with drop-cast graphene oxide (GO) flakes are proposed to be a novel bilayer system featuring bioactivity, biocompatibility, and promising loading/release properties for controlled drug-delivery systems. The high-surface-area ZnO scaffolds show clear apatite deposition, but their particular surface chemistry and topography prevent the formation of a continuous coating, resulting in micrometric crystalline apatite aggregates after 28 days in simulated body fluid (SBF). When gentamicin sulfate (GS) is considered as a model molecule, pure ZnO scaffolds also show functional GS loading efficiency, with fast in vitro release kinetics driven by a simple diffusion mechanism. Strikingly, the bioactivity and GS delivery properties of mesoporous ZnO are efficiently triggered by drop-casting GO flakes atop the mesoporous scaffold surface. The resulting ZnO@GO bilayer scaffolds show the formation of a uniform apatite coating after 28 days in SBF and demonstrate a biocompatible behavior, supporting the culture of SaOS-2 osteoblast-like cells. Moreover, the GO coating also leads to a barrier-layer effect, preventing fast GS release, particularly in the short time range. This barrier effect, coupled with the existence of nanopores within the GO structure, sieves drug molecules from the mesoporous ZnO matrix and allows for a delayed release of the GS molecule. We, thus, demonstrated a new-generation ZnO@GO bilayer system as effective multifunctional and biocompatible scaffold for bone tissue engineering.

Bioinspired Mineral-Organic Bioresorbable Bone Adhesive

Bioresorbable bone adhesives have potential to revolutionize the clinical treatment of the human skeletal system, ranging from the fixation and osteointegration of permanent implants to the direct healing and fusion of bones without permanent fixation hardware. Despite an unmet need, there are currently no bone adhesives in clinical use that provide a strong enough bond to wet bone while possessing good osteointegration and bioresorbability. Inspired by the sandcastle worm that creates a protective tubular shell around its body using a proteinaceous adhesive, a novel bone adhesive is introduced, based on tetracalcium phosphate and phosphoserine, that cures in minutes in an aqueous environment and provides high bone-to-bone adhesive strength. The new material is measured to be 10 times more adhesive than bioresorbable calcium phosphate cement and 7.5 times more adhesive than non-resorbable poly(methyl methacrylate) bone cement, both of which are standard of care in the clinic today. The bone adhesive also demonstrates chemical adhesion to titanium approximately twice that of its adhesion to bone, unlocking the potential for adherence to metallic implants during surrounding bony incorporation. Finally, the bone adhesive is shown to demonstrate osteointegration and bioresorbability over a 52-week period in a critically sized distal femur defect in rabbits.

Characterization of doxycycline-loaded calcium phosphate cement: implications for treatment of aneurysmal bone cysts

Percutaneous doxycycline for treatment for aneurysmal bone cysts (ABCs) has been shown to decrease recurrence rates, however, this requires multiple procedures, includes the risks soft tissue necrosis, and does not provide structural support. We propose utilizing curettage with doxycycline-loaded calcium phosphate cement. This study aimed to evaluate the elution profile of doxycycline from calcium phosphate cement. Calcium phosphate cement underwent an in vitro elution protocol evaluating doxycycline concentrations of 0, 5, 10, and 15 mg/mL. Eluted concentrations were quantified utilizing high performance liquid chromatography at predetermined time points over 96 h. Compressive strength was evaluated both pre- and post-elution and micro-computed tomography was utilized to assess changes in cement porosity. Cement with 15 mg/mL of doxycycline maintained a higher average concentration (mean, 95% confidence intervals) (14.5 µg/mL [9.2-19.9 µg/mL]) compared to both 5 mg/mL (5.8 µg/mL [3.1-8.6 µg/mL]; P < 0.001) and 10 mg/mL (8.4 ± µg/mL [6.0-10.9 µg/mL]; P < 0.001). Ultimate stress significantly decreased between pre- and post-elution samples for 10 mg/mL (P= 0.001) and 15 mg/mL (P = 0.004) groups. This study demonstrated a dose-dependent response in ultimate strength and compressive modulus with addition of doxycycline to calcium phosphate cement.