A novel strategy to enhance interfacial adhesion in fiber-reinforced calcium phosphate cement

The Osteogenic Properties of Calcium Phosphate Cement Doped with Synthetic Materials: A Structured Narrative Review of Preclinical Evidence

Bone grafting is commonly used as a treatment to repair bone defects. However, its use is challenged by the presence of medical conditions that weaken the bone, like osteoporosis. Calcium phosphate cement (CPC) is used to restore bone defects, and it is commonly available as a bioabsorbable cement paste. However, its use in clinical settings is limited by inadequate mechanical strength, inferior anti-washout characteristics, and poor osteogenic activity. There have been attempts to overcome these shortcomings by adding various natural or synthetic materials as enhancers to CPC. This review summarises the current evidence on the physical, mechanical, and biological properties of CPC after doping with synthetic materials. The incorporation of CPC with polymers, biomimetic materials, chemical elements/compounds, and combination with two or more synthetic materials showed improvement in biocompatibility, bioactivity, anti-washout properties, and mechanical strength. However, the mechanical property of CPC doped with trimethyl chitosan or strontium was decreased. In conclusion, doping of synthetic materials enhances the osteogenic features of pure CPC. The positive findings from in vitro and in vivo studies await further validation on the efficacy of these reinforced CPC composites in clinical settings.

Mechanical Properties of Calcium Aluminate Cement Reinforced with Plasma-Treated Basalt Fibers for In Situ Combustion

Brittleness and poor tensile/flexural properties restrict the application of calcium aluminate cement (CAC) in oil and gas wells. Reinforcing CAC with fibers is an effective method for improving its strength and toughness and overcoming the shortcomings of its mechanical properties. In this article, as an auxiliary cementing material, slag does not affect the thickening time of CAC. After adding slag, the cement slurry meets the thickening time during cementing construction, and basalt fiber is selected as the toughening material. The enhancement effect of basalt fiber on the mechanical properties of CAC slag composites is studied, including the evaluation of the macroscopic mechanical properties and microstructure at a high temperature (500 °C). The optimum composition of basalt and fiber-reinforced CAC was determined. Basalt fibers were added to CAC at different contents of 0, 0.1, 0.2, 0.3, 0.4, and 0.5% based on the weight of the cement. All the results showed that the introduction of basalt fibers could significantly enhance the strength of the cement at high temperatures. Compared with the control samples, an additional increase in the compressive and tensile strengths of the samples of 35.1 and 85.2%, respectively, was achieved at high temperature with approximately 0.4% fiber content. Plasma treatment further improved the reinforcing effect of the basalt fibers, where the high-temperature compressive and tensile strengths of the samples increased from 28.88 and 1.52 to 35.23 and 1.87 MPa, respectively, an increase of 21.98 and 20.6%, respectively, compared with the untreated basalt fibers. When the cement paste is cured by simulated curing for 28 d, the high-temperature compressive strength and tensile strength with plasma modification increased from 28.26 and 1.5 to 29.1 and 2.15 MPa, respectively, an increase of 3.0 and 43.3%, respectively. The structure of the formed hydrates was studied using scanning electron microscopy. Furthermore, toughening of the basalt fiber-reinforced CAC-based composites resulted mainly from crack bridging and fiber pull-out.

Calcium Phosphate Cement Promotes Odontoblastic Differentiation of Dental Pulp Cells In Vitro and In Vivo

In the case of pulp injury, odontoblastic differentiation of dental pulp cells (DPCs) at the site of the exposed pulp is necessary for a successful direct pulp capping treatment. Calcium phosphate cement (CPC), a kind of hydroxyapatite-like bone cement, exhibits therapeutic potential in osteogenesis by regulating cell cycle progression and promoting osteoblastic differentiation. Based on the similar biological process of osteo/odontoblastic differentiation, the present study evaluated the effects of CPC on odontoblastic differentiation of DPCs in vitro and in vivo, respectively. The morphology of CPC was observed by scanning electron microscopy. Colony-forming units were used to assess the antibacterial activity. The effects of CPC on cell proliferation and odontoblastic differentiation of human dental pulp cells (hDPCs) were also measured. Histological staining was performed to observe the reparative dentin formation in rat molars. In vitro, results of antibacterial studies showed that CPC significantly inhibited the growth of Streptococcus mutans. The appropriate concentration of CPC extract showed low cytotoxicity on hDPCs. Furthermore, CPC extract also promoted odontoblastic differentiation and mineralization compared with the control group, as shown by a dynamic increase in the expression of odontogenic marker genes and the increased number of mineralized nodules at 21 days. The pulpotomy models with CPC facilitated the formation of dentin bridge with the highly expressed dentin matrix protein 1 (DMP1) in odontoblast-like cells. In conclusion, the favorable biocompatibility, antibacterial property and bio-inductivity of CPC suggest that CPC can be used as a promising direct pulp capping material.

The Use of Fibers in Bone Tissue Engineering

Bone tissue engineering aims to restore and maintain the function of bone by means of biomaterial-based scaffolds. This review specifically focuses on the use of fibers in biomaterials used for bone tissue engineering as suitable environment for bone tissue repair and regeneration. We present a bioinspired rationale behind the use of fibers in bone tissue engineering and provide an overview of the most common fiber fabrication methods, including solution, melt, and microfluidic spinning. Subsequently, we provide a brief overview of the composition of fibers that are used in bone tissue engineering, including fibers composed of (i) natural polymers (e.g., cellulose, collagen, gelatin, alginate, chitosan, and silk, (ii) synthetic polymers (e.g., polylactic acid [PLA], polycaprolactone, polyglycolic acid [PGA], polyethylene glycol, and polymer blends of PLA and PGA), (iii) ceramic fibers (e.g., aluminium oxide, titanium oxide, and zinc oxide), (iv) metallic fibers (e.g., titanium and its alloys, copper and magnesium), and (v) composite fibers. In addition, we review the most relevant fiber modification strategies that are used to enhance the (bio)functionality of these fibers. Finally, we provide an overview of the applicability of fibers in biomaterials for bone tissue engineering, with a specific focus on mechanical, pharmaceutical, and biological properties of fiber-functionalized biomaterials for bone tissue engineering. Impact statement Natural bone is a complex composite material composed of an extracellular matrix of mineralized fibers containing living cells and bioactive molecules. Consequently, the use of fibers in biomaterial-based scaffolds offers a wide variety of opportunities to replicate the functional performance of bone. This review provides an overview of the use of fibers in biomaterials for bone tissue engineering, thereby contributing to the design of novel fiber-functionalized bone-substituting biomaterials of improved functionality regarding their mechanical, pharmaceutical, and biological properties.

Experimental Characterization and Mathematical Modeling of the Adsorption of Proteins and Cells on Biomimetic Hydroxyapatite

Biomaterial development is a long process consisting of multiple stages of design and evaluation within the context of both in vitro and in vivo testing. To streamline this process, mathematical and computational modeling displays potential as a tool for rapid biomaterial characterization, enabling the prediction of optimal physicochemical parameters. In this work, a Langmuir isotherm-based model was used to describe protein and cell adhesion on a biomimetic hydroxyapatite surface, both independently and in a one-way coupled system. The results indicated that increased protein surface coverage leads to improved cell adhesion and spread, with maximal protein coverage occurring within 48 h. In addition, the Langmuir model displayed a good fit with the experimental data. Overall, computational modeling is an exciting avenue that may lead to savings in terms of time and cost during the biomaterial development process.

Toward stronger robocast calcium phosphate scaffolds for bone tissue engineering: A mini-review and meta-analysis

Among different treatments of critical-sized bone defects, bone tissue engineering (BTE) is a fast-developing strategy centering around the fabrication of scaffolds that can stimulate tissue regeneration and provide mechanical support at the same time. This area has seen an extensive application of bioceramics, such as calcium phosphate, for their bioactivity and resemblance to the composition of natural bones. Moreover, recent advances in additive manufacturing (AM) have unleashed enormous potential in the fabrication of BTE scaffolds with tailored porous structures as well as desired biological and mechanical properties. Robocasting is an AM technique that has been widely applied to fabricate calcium phosphate scaffolds, but most of these scaffolds do not meet the mechanical requirements for load-bearing BTE scaffolds. In light of this challenge, various approaches have been utilized to mechanically strengthen the scaffolds. In this review, the current state of knowledge and existing research on robocasting of calcium phosphate scaffolds are presented. Applying the Gibson-Ashby model, this review provides a meta-analysis from the published literature of the compressive strength of robocast calcium phosphate scaffolds. Furthermore, this review evaluates different approaches to the mechanical strengthening of robocast calcium phosphate scaffolds. The aim of this review is to provide insightful data and analysis for future research on mechanical strengthening of robocast calcium phosphate scaffolds and ultimately for their clinical applications.

Calcium phosphate bone cement with enhanced physicochemical properties via in situ formation of an interpenetrating network

Calcium phosphate cement (CPC), which exhibits excellent biocompatibility and bioactivity, is a well-established material for the repair of bone defects. However, its disadvantages such as poor washout resistance and low mechanical strength limit its clinical applications. In this study, CPC with enhanced washout resistance and mechanical properties has been developed by the in situ crosslinking of glycidyl methacrylate modified γ-polyglutamic acid (m-PGA) within the cement matrix, forming an interpenetrating network. Compared with unmodified CPC, the final setting time of the composite cements was shortened and its washout resistance was significantly improved. In addition, the composite cements showed enhanced mechanical strength and degradation properties. An in vitro study demonstrated that the composite cements exhibited good biocompatibility. The in vivo results showed that the composite cements promoted bone formation. These results suggest that the biocompatible, injectable α-tricalcium phosphate (α-TCP)/m-PGA cements may have the potential to be used as bone filling materials for future clinical applications.

Reinforcement and Fatigue of a Bioinspired Mineral-Organic Bioresorbable Bone Adhesive

Bioresorbable bone adhesives may provide remarkable clinical solutions in areas ranging from fixation and osseointegration of permanent implants to the direct healing and fusion of bones without permanent fixation hardware. Mechanical properties of bone adhesives are critical for their successful application in vivo. Reinforcement of a tetracalcium phosphate-phosphoserine bone adhesive is investigated using three degradable reinforcement strategies: poly(lactic-co-glycolic) (PLGA) fibers, PLGA sutures, and chitosan lactate. All three approaches lead to higher compressive strengths of the material and better fatigue performance. Reinforcement with PLGA fibers and chitosan lactate results in a 100% probability of survival of samples at 20 MPa maximum compressive stress level, which is almost ten times higher compared to compressive loads observed in the intervertebral discs of the spine in vivo. High adhesive shear strength of 5.1 MPa is achieved for fiber-reinforced bone adhesive by tuning the surface architecture of titanium samples. Finally, biological and biomechanical performance of the fiber-reinforced adhesive is evaluated in a rabbit distal femur osteotomy model, showing the potential of the bone adhesive for clinical use.

The Addition of Poly(Vinyl Alcohol) Fibers to Apatitic Calcium Phosphate Cement Can Improve Its Toughness

Calcium phosphate cements, and in particular hydroxyapatite cements, have been widely investigated for use as bone void fillers due to their chemical similarity to bone and related osteoconductivity. However, they are brittle, which limits their use to non-load-bearing applications. The aim of the current study was to improve the toughness of hydroxyapatite cements through fiber reinforcement. The effect of the addition of hydrophilic, poly(vinyl-alcohol) (PVA) fibers to hydroxyapatite cement was evaluated in terms of mechanical properties, including compressive strength, diametral tensile strength and toughness (work of fracture), as well as setting time, phase composition and cement morphology. The fiber reinforcement enhanced the fracture resistance of the hydroxyapatite cement, but also simultaneously reduced the compressive strength and setting time of the cements. However, cement with 5 wt % of fibers (of the powder component) could be considered a good compromise, with a compressive strength of 46.5 ± 4.6 MPa (compared to 62.3 ± 12.8 MPa of that without fibers), i.e., still much greater than that of human trabecular bone (0.1–14 MPa). A significantly higher diametral tensile strength (9.2 ± 0.4 MPa) was found for this cement compared to that without fibers (7.4 ± 1.5 MPa). The work of fracture increased four times to 9.1 ± 1.5 kJ/m² in comparison to the pristine apatite. In summary, the hydroxyapatite cements could be reinforced by suitable amounts of PVA fibers, which resulted in enhancing the material’s structural integrity and ductility, and increased the material’s resistance to cracking.

Reinforcement of calcium phosphate cement using alkaline-treated silk fibroin

BACKGROUND

Bone cement plays an important role in the treatment of osteoporotic vertebral compression fractures. Calcium phosphate cement (CPC) is a potential alternative to poly(methyl methacrylate), currently the gold standard of bone cements. However, the poor mechanical properties of CPCs limit their clinical applications. The objective of this study was to develop reinforced CPCs for minimally invasive orthopedic surgeries by compositing silk fibroin (SF) with α-tricalcium phosphate.

METHODS

SF solution was treated with calcium hydroxide and characterized by Zeta potential analyzer and Fourier transform infrared spectroscopy. The alkaline-treated SF (tSF) was com-posited with α-tricalcium phosphate to obtain tSF/CPC composite, which was characterized using mechanical tests, scanning electron microscopy, handling property and biocompatibility tests, and sheep vertebral augmentation tests.

RESULTS

Upon treatment with calcium hydroxide, larger SF particles and more abundant negative charge appeared in tSF solution. The tSF/CPCs exhibited a compact structure, which consisted of numerous SF -CPC clusters and needle-like hydroxyapatite (HAp) crystals. In addition, high transition rate of HAp in tSF/CPCs was achieved. As a result, the mechanical property of tSF/ CPC composite cements was enhanced remarkably, with the compressive strength reaching as high as 56.3±1.1 MPa. Moreover, the tSF/CPC cements showed good injectability, anti-washout property, and decent biocompatibility. The tSF/CPCs could be used to augment defected sheep vertebrae to restore their mechanical strength.

CONCLUSION

tSF/CPC may be a promising composite bone cement for minimally invasive orthopedic surgeries.

Bioceramics and bone healing

Calcium phosphates have long been used as synthetic bone grafts. Recent studies have shown that the modulation of composition and textural properties, such as nano-, micro- and macro-porosity, is a powerful strategy to control and synchronize material resorption and bone formation.Biomimetic calcium phosphates, which closely mimic the composition and structure of bone mineral, can be produced using low-temperature processing routes, and offer the possibility to modulate the material properties to a larger extent than conventional high temperature sintering processes.Advanced technologies open up new possibilities in the design of bioceramics for bone regeneration; 3D-printing technologies, in combination with the development of hybrid materials with enhanced mechanical properties, supported by finite element modelling tools, are expected to enable the design and fabrication of mechanically competent patient-specific bone grafts.The association of ions, drugs and cells allows leveraging of the osteogenic potential of bioceramic scaffolds in compromised clinical situations, where the intrinsic bone regeneration potential is impaired. Cite this article: EFORT Open Rev 2018;3 DOI: 10.1302/2058-5241.3.170056.

Bone biomaterials and interactions with stem cells

Bone biomaterials play a vital role in bone repair by providing the necessary substrate for cell adhesion, proliferation, and differentiation and by modulating cell activity and function. In past decades, extensive efforts have been devoted to developing bone biomaterials with a focus on the following issues: (1) developing ideal biomaterials with a combination of suitable biological and mechanical properties; (2) constructing a cell microenvironment with pores ranging in size from nanoscale to submicro- and microscale; and (3) inducing the oriented differentiation of stem cells for artificial-to-biological transformation. Here we present a comprehensive review of the state of the art of bone biomaterials and their interactions with stem cells. Typical bone biomaterials that have been developed, including bioactive ceramics, biodegradable polymers, and biodegradable metals, are reviewed, with an emphasis on their characteristics and applications. The necessary porous structure of bone biomaterials for the cell microenvironment is discussed, along with the corresponding fabrication methods. Additionally, the promising seed stem cells for bone repair are summarized, and their interaction mechanisms with bone biomaterials are discussed in detail. Special attention has been paid to the signaling pathways involved in the focal adhesion and osteogenic differentiation of stem cells on bone biomaterials. Finally, achievements regarding bone biomaterials are summarized, and future research directions are proposed.