Eltohamy M; Hamzawy E; Kundu B; Azooz M

Special Article - Biomaterials and Regenerative Medicine

Austin J Biotechnol Bioeng. 2017; 4(3): 1083

Akermanite Reinforced Wollastonteas Bioactive Ceramic Biomaterial

Eltohamy M^1-3*, Hamzawy E², Kundu B¹ and Azooz M²

¹Institute of Tissue Regeneration Engineering (ITREN), Dankook University, Republic of Korea

²Department of Glass Research, National Research Centre, Egypt

³Department of Nanobiomedical Science, Dankook University, Republic of Korea

*Corresponding author: Eltohamy M, Department of Glass Research, National Research Centre, Dokki, Cairo 12622, Egypt

Received: June 22, 2017; Accepted: October 30, 2017; Published: November 06, 2017

Abstract

Despite substantial amount of research on ceramic biomaterials, the re-cycling of cement kiln dust is still a problem. Additionally, the quest of development of low cost, adequate amount of bioactive bone ceramic biomaterials in ease hastens the research focus to recycle the cement kiln dust for biomedical applications. Cement kiln dust is modified by addition of talc quarry and quartz fine sand to obtain the well-defined SiO₂-MgO-CaO system. The glass ceramic is generated by melting all components and casting; followed by heat-treatment (1000 ºC) to prompt crystallization in presence of TiO₂ or CaF₂ served as nucleating agents to accelerate the crystallization. Akermanitewollastonite phases are created, which results hydroxyl-carbonate-apatite layer formation in stimulated body fluid. The akermanite-wollastoniteceramic exhibits microhardness of 440-680 Kg/mm² with sustain degradability. The presence of Mg in akermanite is well known for bone regeneration performance; suggesting the promising candidature of the synthesized ceramic as bone implant in future.

Keywords: Cement kiln dust; Glass-ceramic; Akermanite; Wollastonite

Abbreviations

CKD: Cement Kiln Dust; [Ca₂Mg (Si₂O₇)]: Akermanite; [CaSiO₃]: Wollastonite; CaF₂: Calcium Fluoride; TiO₂: Titanium Oxide

Introduction

The disposal of Cement Kiln Dust (CKD) during Portland cement production is considered as significant financial loss to cement industries as well as environmental threatening that is ever increasing; approximately 30 million tons worldwide per year [1]. In reality, this jeopardize the production of Portland cement and non-recycling of by-products like CKD results resource depletion of many beneficial key ions. Enormous body of literatures represent the recycling of CKD as soil modifiers [2,3], in road construction [4,5] and solidification of hazardous wastes [6,7].

A class of Ca, Si and Mg containing bioceramic, gaining immense technological attention as promising bone scaffold, which stimulates apatite mineralization, osteoinduction [8] and osteo-differentiation of diverse cell types including human aortic endothelial cells [8], periodontal ligament cells [9] and bone marrow stem cells [10]. Alkermanite is of desirable ceramic in biomedical bone implant [8]; however, high contents of alkalis and chlorides in CKD [11] restricts the processing of akermanite from it. In addition, no single study exists that embraces the sustainable development of akermanitelike translational medicinal product by recycling CKD. Therefore, we hereby propose a facile, low-environmental impact, sustainable cost-effective method to obtain stable akermanite. Though, because of its brittleness, akermanite scaffolds alone are commonly referred as ‘poorly mechanically stable” in literature [12]. Therefore, to encompass the favorable osteogenic properties of akermanite, we utilize the reinforcement strategy that stabilizes akermanite [Ca₂Mg (Si₂O₇)] within wollastonite [CaSiO₃] phase.

Wollastonite possesses well osteoconductivity and bioresorbability [13], exhibits high bioactivity and fast rate of degradation compared with clinically used bone fillers [14]. The release of Ca²⁺ and SiO₃ from wollastonite forms apatite layer on its surface imparting the bioactivity [15]. The incorporation of akermanite within wollastonite prompts us to investigate the chemical durability of the resultant synthesized material. Furthermore, we establish the relationship between the structure and its thermal - mechanical and bioactivity for biomedical applications.

Materials and Methods

Materials

Cement kiln dust (Domestic company, Egypt), was cleaned in dilute HCl and distilled water (to remove soluble impurities) for several time, dried at 120ºC prior to use. Talc (Hamata, Eastern Desert, Egypt) and Quartz sand (Abu Zenima, Sinai, Egypt) were used as neutral raw materials for glass ceramic preparation. Calcium fluoride (CaF₂) and titanium oxide (TiO₂) were purchased from Sigma Aldrich (USA) and were used as nucleating agents to promote crystallization of both akermanite and wollastonite phases.

Preparation of Akermanite-Wollastonite ceramic biomaterials

The chemical composition of cement kiln dust, talc and quartz sand used in the present investigation is summarized in Table 1 (all compositions in this study are given in Wt%, unless otherwise stated). Since the amount of nucleating agent in the raw materials were quite low, additional appropriate amounts of CaF₂ and TiO₂ were added into the batch and mentioned in Table 2. The raw powders were weighed and grinded using conventional ball mills for 24 h to obtain homogenous powders. The ceramic powder batches were then melted in electrical furnace using sealed Pt-crucibles at 1400ºC (melting temperature) for about 4 h to ensure complete homogenization.

Table 1: Chemical analysis of the starting raw materials (wt. %).




  
    Oxide%
    Raw Material
  
  
    CKD
    Talc
    Quartz
  
  
    CaO
    65.60
    0.42
    0.10
  
  
    SiO₂
    16.64
    65.17
    99.59
  
  
    K₂O
    5.42
    0.12
    0.00
  
  
    Al₂O₃
    4.68
    1.68
    0.28
  
  
    Na₂O
    3.95
    0.34
    0.00
  
  
    Fe₂O₃
    2.73
    0.42
    0.03
  
  
    MgO
    0.77
    31.85
    0.00
  
  
    TiO₂
    0.20
    0.00
    0.00



Table 1: Chemical analysis of the starting raw materials (wt. %).

Table 2: Glass batches and nucleating agents in (wt. %).




  
    Glass No.
    Batch composition %
  
  
    Raw Materials
    Nucleating Agents
  
  
    CKD
    Talc
    Quartz
    TiO₂
    Cr₂O₃
    CaF₂
  
  
    GB
    62.48
    15.03
    22.49
    0
    0
    0
  
  
    GTiO₂
    6
    0
    0
  
  
    GCaF₂
    0
    0
    6



Table 2: Glass batches and nucleating agents in (wt. %).

Following that, the melt was cast into pre-heated steel molds and annealed at 500ºC for 4 h to remove thermal residual stresses prior to the nucleation and crystallization step.

Characterization

Differential thermal analysis (DTA, Shimadzu DTG60, Japan) scans of as-cast glass with or without nucleating agents were carried out in order to determine the characteristic glass transition temperatures (T_g) and peak crystallization temperatures (T_p). About 100 mg of powdered sample of grain size 30μm were used in a platinum crucible. Equal amount of Al₂0₃ was used as inert reference in a temperature range between 25 to 1300ºC at a heating rate of 10ºC min^-1 under N₂ gas flow. Data for each run were collected directly from DTA. On the basis of dilatometer and DTA analysis of exothermic and endothermic temperature, nucleation experiments were conducted at 725ºC and holding time of 10h. Following nucleation, the temperature was raised to 1000ºC for 4h for crystal growth followed by air cooling gradually at furnace atmosphere.

Identification of precipitated crystals during the process of crystallization were investigated by X-ray diffraction carried out with a diffractometer (Brukur D8, Germany)adapting Ni-filtered CuKa radiation at 40 kV and 30 mA settings in the range from 20 to 80º at a scanning speed of 0.03º min^-1. The phases were identified by comparing the peak positions and intensities with those listed in the JCPDS (Joint Committee on Powder Diffraction Standards).

The in vitro bioactivity of akermanite-wollastonite ceramic materials was studied by its apatite forming ability after immersing the ceramic discs (10mm x 5 mm) in SBF at 37ºC with a surface areato- volume ratio of 0.1 cm^-1 in static water bath [16]. After specific period, the disks were gently removed from SBF solutions, rinsed with deionized water and acetone; followed by drying. The surface morphology was characterized by scanning electron microscopy (SEM, JEOL JSM-T20, Hitachi Japan). The infrared spectra of the discs were obtained using a Varian 640-IR Fourier Transform Infrared (FT-IR) spectrometer (Varian, Australia) with a resolution of 4 cm^-1 in the range of 4000-400 cm^-1.

Chemical durability study was carried out using 1.5 grams of the grains (0.25 mm < diameter < 0.50 mm) accurately weighed within sintered glass crucible of the Jena 1G4 type (average pore diameter is 5-10μm) and placed in a closed polyethylene container contain 200 ml SBF for 2 weeks at 37 ºC under continuous stirring. The percentage of weight loss was taken as measure of relative magnitude of rate of leaching and the released amount of cation was determined.

The microhardness properties of as-cast glass-ceramics crystallized at different temperatures were determined by Vickers and Knoop values using Shimadzu Microhardness Tests of M type under load of 100 g. The empirical relation formulated by Ponton and Rawlings, which utilizes fracture lines emanating from Vickers diamond indentation was used to determine the fracture toughness values [17].

Results and Discussion

Chemical composition of bioceramic materials are crucial for their therapeutic applications. The positive effects of released ions such as calcium, silicon on the formation of apatite layer is well known [18]. Magnesium is the fourth abundant intra-cellular element of human body [19] stimulating neo-bone formation; its depletion results bone resorption and osteoporosis [20]. Wollastonite bioceramic rationally tuned into a and β phase by using Mg content in small amount with varying hardness [13]. Wollastonite exhibits rapid rate of degradation compared to clinically used Ca-phosphate bone implants [14]; therefore, research interest focuses on optimizing wollastonite derivatives with suitable mechanical property. The synergistic effects of Ca and Mg ions facilitate osteogenesis in osteoporotic condition [21]. The released Mg of akermanite weakens the alkaline microenvironment in vivo, which stimulates osteoblastic anabolic effects; results in bone regeneration. Approximately 60% of Mg is stored in bone in human body [22]. Therefore, adulteration of akermanite within wollastonite is hypothesized to be beneficial of its application as biomedical materials for bone tissue engineering.

The chemical compositions of three investigated components including Base Glass (BG), created akermanite and wollastonite are represented in the ternary subsystem (Figure 1). According to the theories of phase equilibria, the assemblage of the thermodynamic stable phases should be the same for the investigated glass-ceramics (i.e., akermanite and wollastonite) [23, 24].

Figure 1: Triangle of CaO-MgO-SiO₂ system; akermanite-wollastonite and starting Base Glass (BG) composition location is clarified.

    
    
    Figure 1:  Triangle of CaO-MgO-SiO₂ system; akermanite-wollastonite and
starting Base Glass (BG) composition location is clarified.

The well-ordered regular lattice crystal is necessity for withstanding the deformation under load for tissues such as bone. DTA data evidences the crystallization characteristics of glass from less ordered structure (Figure 2a). The glass softening temperature (T_s) was nearly similar to 735-755ºC confirming the viscosity was indifferent by the nucleation doped into the base glass composition. The addition of TiO₂ to GTiO₂ modified the local glass structures, pushed T_s to 762ºC; while incorporation of CaF₂ in GCaF₂ decreased it at 735ºC. In comparing the exothermic peaks with the BG at 930ºC, CaF₂ decreased it to 877ºC in GCaF₂; while TiO₂ increased it to 935ºC in GTiO₂. Because of, the DTA data highlighted intensive crystallization process around 877-935ºC interval, so crystallization temperature is selected at 1000ºC.

The crystalline phases of the heat-treated glasses at 1000ºC temperature range are showed in (Figure 2b). The resultant CaOMgO- SiO₂ glass system exhibited the crystallization phases of wollastonite and akermanite; developed in all glass samples. However the intensity of both phases in the XRD patterns were in the order sample containing-CaF₂GTiO₂ BG.