Evaluation of the sintering temperature on the mechanical behavior of β-tricalcium phosphate/calcium silicate scaffolds obtained by gelcasting method

https://doi.org/10.1016/j.jmbbm.2018.11.014Get rights and content

Highlights

  • β-TCP and β-TCP/CaSiO3 scaffolds were prepared by gelcasting method.

  • The scaffolds presented high porosity and pore sizes in the range of 160–500 µm.

  • The best scaffolds obtained were the β-TCP/CaSiO3 (β-TCP/W (95/5) 1300 C).

  • Morphology, compressive strength and HA deposition were the observed aspects.

Abstract

Scaffolds have been studied during the last decades as an alternative method to repair tissues. They are porous structures that act as a substrate for cellular growth, proliferation and differentiation. In this study, scaffolds of β-tricalcium phosphate with calcium silicate fibers were prepared by gel casting method in order to be characterized and validated as a better choice for bone tissue treatment. Gel-casting led to scaffolds with high porosity (84%) and pores sizes varying from 160 to 500 µm, which is an important factor for the neovascularization of the growing tissue. Biocompatible and bioactive calcium silicate fibers, which can be successfully produced by molten salt method, were added into the scaffolds as a manner to improve its mechanical resistance and bioactivity. The addition of 5 wt% of calcium silicate fibers associated with a higher sintering temperature (1300 °C) increased by 64.6% the compressive strength of the scaffold and it has also led to the formation of a dense and uniform apatite layer after biomineralization assessment.

Introduction

Scaffolds are temporary support structures that provide propitious conditions to cells proliferation, migration, and differentiation in 3D, allowing the formation of a specific tissue with appropriate functions. Some common properties for an ideal scaffold for tissue engineering are biocompatibility, porosity with interconnected pores and an adequate mechanical strength (Ikada, 2006, Katari et al., 2014, Fisher and Mauck, 2013, Yang et al., 2001). For an optimal performance, bone scaffolds should also be biodegradable, or bioresorbable, providing mechanical support while a new tissue is formed to replace it (Katari et al., 2014; Black et al., 2015; Amini et al., 2012; Bose et al., 2012).

There are many ceramics which have been used for bone tissue engineering as calcium phosphates, especially hydroxyapatite – HA (Ikada, 2006, Dash et al., 2015, Baradararan et al., 2012, Asif et al., 2014) and β-tricalcium phosphate – β-TCP (Ikada, 2006, Black et al., 2015, Baradararan et al., 2012), bioactive glasses (Fu et al., 2011, Chen et al., 2006), titania (Cunha et al., 2013) and alumina (Sarhadi et al., 2016, Song et al., 2013). Tricalcium phosphate (TCP) is a bioresorbable, bioactive and osteoconductive bioceramic and β-TCP, a TCP polymorph, stands out due to its solubility and degradation rate (Dorozhkin, 2010, Ratner et al., 2013).

Gel casting stands out among the many methods commonly employed to produce scaffolds (Ikada, 2006, Amini et al., 2012) such as three-dimensional printing (Zhang et al., 2015), replication technique (Black et al., 2015, Baradararan et al., 2012), and freeze casting (Rosset et al., 2014, Chen et al., 2015). A foaming agent is added into a ceramic suspension containing the ceramic powder, organic monomers and dispersant. After vigorous stirring a foam is formed and it became rigid after monomers polymerization. Scaffolds obtained are highly porous (40 – 90%) with spherical geometry, sizes between 50 and 800 µm and thick walls with homogeneous microstructure which improve mechanical properties, leading to a great performance for cellular growth and tissue engineering. Furthermore, this method is more feasible and cheaper when compared to others and does not require atmospheric control (Elliot, 1994, Janney et al., 1998, Young et al., 1991, Yang et al., 2011).

An ideal porosity of the scaffold is required to maximize the space for cellular adhesion, growth, revascularization, adequate nutrition and other factors that can influence cellular and tissue growth (Ikada, 2006, Katari et al., 2014, Fisher and Mauck, 2013, Yang et al., 2001). Unfortunately, porosity and mechanical resistance are indirectly related and as higher the porosity lower is the compressive strength and the reproducibility of the scaffold manufacturing (Ratner et al., 2013, Carter and Norton, 2007).

In order to improve the mechanical properties some recent researchers have been discussing the use of additives in scaffolds composition such as fibers (Panzavolta et al., 2012, Abdullah et al., 2012) and whiskers (Fang et al., 2013). Fibers and whiskers can be characterized by their aspect ratio (L/D, where L is the length of the fiber and D is its diameter) and as higher the value the better is the interaction between fiber and matrix (Dorozhkin, 2016, Motisuke et al., 2014).

As studied in previous works, molten salt synthesis is a method that may be used to produce fibers and whiskers since it is a low cost process with high control of properties (Motisuke et al., 2014, Hayashi et al., 2000). Calcium silicate (wollastonite – CaSiO3) is highly suitable to produce fibers for bone tissue scaffolds reinforcement due to its outstanding biocompatibility, bioactivity and biodegradability (Motisuke et al., 2014, Fei et al., 2012, De Aza et al., 1994). Moreover, its positive effect on bone formation processes has been recognized and debated in the literature (Zhou et al., 2017).

To increase the accessibility of the technology and improve quality of life, the research on methods and materials that are feasible and efficient for bone tissue therapy is necessary. Therefore, the aim of this work was to produce by gel-casting β-TCP scaffolds with calcium silicate fibers with appropriated porosity, interconnectivity and mechanical strength for application in tissue engineering, as scaffolds.

Section snippets

Synthesis and characterization of β-TCP and CaSiO3 fibers

β-TCP powder was obtained by solid state reaction of calcium carbonate (CaCO3 – Synth, Brazil) and calcium phosphate (CaHPO4 – Synth, Brazil) in the molar ratio of 1:2 (CaCO3:CaHPO4). The powder was calcined at 1050 °C for 6 h and afterwards it was dry milled in a horizontal ball-mill (MA500, Marconi, Piracicaba, SP, Brazil) for 48 h.

The of calcium silicate (CaSiO3) fiber used in this work were prepared as published elsewhere (Motisuke et al., 2014) by molten salt method using an alkaline flux

Results

Fig. 1 shows the XRD pattern of the β-TCP powder and CaSiO3 fibers. From the analysis of Fig. 1-a it was possible to identify only and exclusively XRD lines of β-TCP (JCPDS 09–0169; 2θ = 22.20°, 27.76°, 31.02°, 34.37°). The XRD diffraction of the CaSiO3 fibers is shown in Fig. 1-b. The analysis reveals that the fibers have a considerable degree of crystalline phase purity (JCPDS 043–1460), except by the peak (2θ = 31.03°) characteristic of substance Ca6(SiO4)(Si3O10) (JCPDS 029–0370), whose

Conclusions

The presence of CaSiO3 fibers, associated with a higher sintering temperature, resulted in an increase of the mechanical properties of the β-TCP scaffolds. The best mechanical performance (1.16 ± 0.16 MPa) was achieved by the composition containing 5 wt% fibers sintered at 1300 °C, representing an increase of 64.65% of the maximum load under compression stress. Besides of the β →α polymorphic transformation which have happened at this temperature and should led to some structural defects, there

Acknowledgements

The authors would like to thank the São Paulo Research Foundation – FAPESP - (Grant IDs: 2010/00863-0, 2011/09240-9 and 2012/07897-3) and the National Council for Scientific and Technological Development (CNPq/PIBITI, Grant: 456461/2014-0) for the financial support. We also thank the LNNano/CNPEM by the X ray microtomograph facility.

References (51)

  • J. Duncan et al.

    Furthering the understanding of silicate-substitution in a-tricalcium phosphate: an X-ray diffraction, X-ray fluorescence and solid-state nuclear magnetic resonance study

    Acta Biomater.

    (2014)
  • R. Enderle et al.

    Influence of magnesium doping on the phase transformation temperature of β-TCP ceramics examined by Rietveld refinement

    Biomaterials

    (2005)
  • Z. Fang et al.

    In-situ grown hydroxyapatite whiskers reinforced porous HA bioceramic

    Ceram. Int.

    (2013)
  • Q. Fu et al.

    Bioactive glass scaffolds for bone tissue engineering: state of the art and future perspectives

    Mat. Sci. Eng. C Mater Biol Appl.

    (2011)
  • S. Hayashi et al.

    Preparation of CaSiO3 whiskers from alkali halide fluxes

    J. Eur. Ceram. Soc.

    (2000)
  • R.S. Katari et al.

    Tissue engineering

    Adv. Surg.

    (2014)
  • T. Kokubo

    Apatite formation on surfaces of ceramics, metals and polymers in body environment

    Acta Biomater.

    (1998)
  • I.B. Leonor et al.

    Growth of a bonelike apatite on chitosan microparticles after a calcium silicate treatment

    Acta Biomater.

    (2008)
  • J.H. Lopes et al.

    Hierarchical structures of β-TCP/45S5 bioglass hybrid scaffolds prepared by gelcasting

    J. Mech. Behav. Biomed. Mater.

    (2016)
  • N. Matsumoto et al.

    Thermal stability of β-tricalcium phosphate doped with monovalent metal ions

    Mater. Res. Bull.

    (2009)
  • J.W. Reid et al.

    Phase transformation and evolution in the silicon substituted tricalcium phosphate/apatite system

    Biomaterials

    (2005)
  • J.W. Reid et al.

    Synthesis and characterization of single-phase silicon-substituted α-tricalcium phosphate

    Biomaterials

    (2006)
  • P. Rosset et al.

    Cell therapy for bone repair

    Orthop. Traumatol. Surg. Res.

    (2014)
  • J. Yang et al.

    Recent developments in gelcasting of ceramics

    J. Eur. Ceram. Soc.

    (2011)
  • Y. Zhang et al.

    Constructing a 3D-printable, bioceramic sheathed articular spacer assembly for infected hip arthroplasty

    J. Med. Hypotheses Ideas

    (2015)
  • Cited by (20)

    • A comparative study of physicomechanical and in vitro bioactivity properties of β-wollastonite/cordierite scaffolds obtained via gel casting method

      2022, Ceramics International
      Citation Excerpt :

      The resulting scaffolds are highly porous (40%–90%), have spherical, or rounded geometry with homogeneous microstructures, and thick walls that improve mechanical properties. Among the many methods for fabricating scaffolds, gel casting stands out [8–10], including freeze casting [11,12], replication technique [13,14], and three-dimensional (3D) printing [15]. Compared to the other methods, gel casting is more attainable and low cost, and it does not necessitate atmospheric control [8].

    • Crystalline hydroxyapatite/graphene oxide complex by low-temperature sol-gel synthesis and its characterization

      2021, Ceramics International
      Citation Excerpt :

      In hard tissue engineering, the realization of native bone-like components and mechanical properties are crucial study fields. Although artificial bone manufacturing was realized by simulating native bone components or bone structure through development in biomaterial study, metals or ceramic materials that can withstand high load are still being utilized as primary materials in hard tissue engineering [1–3]. Hydroxyapatite (HA) is a major inorganic component that constitutes bone, and it has been extensively studied as a material for regenerative therapy of hard tissue because of its excellent biocompatibility and osteoconduction (i.e., the ability to form new bones) [4–6].

    • Fabrication and properties of 3D printed zirconia scaffold coated with calcium silicate/hydroxyapatite

      2021, Ceramics International
      Citation Excerpt :

      When the heating temperature reached the burning point it began to burn, which is consistent with TG curve mass reduction at 245 °C and the exothermic interval in the DSC (differential scanning calorimetry) curve [32]. According to the research results of relevant paper [7,33],1300 °C was selected as the sintering temperate, green bodies were heated to 1300 °C at 2 °C/min and held for 2 h to obtain the sintered scaffold. Fig. 2(d) is the heating curve of the coating material.

    • Processing of biomaterials for bone tissue engineering: State of the art

      2021, Materials Today: Proceedings
      Citation Excerpt :

      High brittleness, low tancity and low stability these properties limit the use of TCP in BTE applications. ( α + β) -TCP with the inclusion of graphene is studied for bone cement and scaffold material [32], β–TCP mixed with calcium silicate fibres for increasing mechanical strength and bioactivity [33]. These studies on CaP bioceramics present the increase in the mechanical properties and stability associated with tremendous biocompatibility, osteoconductivity and biodegradability.

    View all citing articles on Scopus
    View full text