Effect of thermal treatment on the physico-chemical properties of bioactive hydroxyapatite derived from caprine bone bio-waste
Graphical abstract
Introduction
Owing to the growing demand and wide range of utility, the recent research on material science has shifted its paradigm from conventional engineering materials to biomaterials. Among different varieties of biomaterials, Calcium phosphate (CaP) based biomaterials have gained wide attention of the researchers. Hydroxyapatite (Ca10(PO4)6(OH)2, HA) is one of the most popular CaP based ceramic biomaterial used in various biomedical applications. It is thermodynamically the most stable crystalline form of CaP at room temperature with a very similar chemical composition to that of the mineral portion of bones and teeth [1]. Due to its extraordinary biocompatibility, bioactivity, high osteoconductivity, non-cytotoxicity, non-inflammatory and non-immunogenic properties, it has been utilized as a drug carrier in drug delivery systems [2]. Additionally, for dental, periodontal, oral/maxillofacial and skeletal bone repair or replacement, HA-based tissue-engineered scaffolds have been widely researched and applied in biomedical industries [3].
The process of obtaining HA largely influences the size, morphology, crystallinity and density of HA particles, which critically determines its effectivity in terms of physico-chemical and mechanical properties [4]. Hence, there is a great deal of ongoing research for application-oriented and tunable synthesis of HA. The synthesis routes followed for producing HA can be broadly classified into two major categories; inorganic synthesis and synthesis from naturally derived sources. Inorganic synthesis process includes techniques like wet chemical precipitation [5], sol-gel [6], hydrothermal process [7], microwave irradiation [8] and so on. Synthetic or stoichiometric HA have non-inflammatory and non-immunological properties on host bodies [9] and its microstructure contains fine grain particles [6]. However, the synthetic routes adopted for producing HA involves the use of harsh chemicals [10] and are complicated, time-consuming and expensive. These processes yield HA which lacks elements like carbon, magnesium, sodium, aluminium, etc. That forms a major part of the inorganic components of natural bone [11] which aids in bone metabolism process [12]. The mechanical properties of synthetic HA are also reported to be poor in wet environments which limit its usage to low load-bearing biomedical applications only [13]. Naturally derived HA, on the contrary, has better metabolic activity and a more dynamic response to the environment [14,15]. It incorporates all the inherent inorganic minerals of natural bone and other trace elements [16]. Also, the naturally found bone apatite tends to be carbonated apatite with B-type substitution [17]. Extracting HA from naturally derived sources provide a brilliant alternative to obtain such apatite structures. The trace elements have been found to be a great boost in avoiding bacterial, fungal as well as inflammatory response of the bone grafts and scaffolds that often complicates the applicability of these systems in vivo [18]. Moreover, the isolation process is simple, economical and environment friendly which yields HA with good biocompatibility, bioactivity and better osteoconductive properties compared to synthetic HA [19].
HA is isolated from a natural source by defatting and deproteinization process followed by high-temperature calcination of animal bone bio-wastes [11], fish scales [20,21], eggshells [22], etc. Animal bones are good reserves of biological HA. Boutinguiza et al. [14] derived biological HA from bones of sword and tuna fish with non-cytotoxic properties. Bovine bones have been explored by Ooi et al. [23] for isolation of bio-ceramic HA and its properties are investigated over a sintering temperature range of 400–1200 °C. Bovine bones annealed between 800 and 1000 °C have been found to have properties similar to that of natural bone. Rajesh et al. [24] isolated natural HA from chicken bone bio-waste by thermal calcination at a temperature range of 200–1000 °C. The optimum calcination temperature has been found to be 600 °C at which carbonated HA of B-type is formed with hexagonal structure. Wei et al. [25] prepared fluorinated HA by incorporating fluoride into HA derived from pig (porcine) bone bio-waste and observed significant improvement in the morphological characteristics of the fluorinated HA. Ramesh et al. [26] isolated HA from caprine bone and compared its properties with that of bovine and galline bone. However, the in vitro bioactivity and degradation of caprine bone-derived HA has not been explored yet to the best of authors’ knowledge. Besides, the calcination temperature adopted for the synthesis of HA plays an important role in the properties of HA. Zhou et al. and Herliyanshah et al. [27,28] reported the paramount effect of sintering temperature on the strength, toughness and other chemical and structural properties of HA. But in the case of caprine bone-derived HA, the effect of calcination temperature on the various physico-chemical properties of caprine bone derived HA has not been addressed properly. This inspired the authors for a systematic evaluation of the effect of calcination temperature on various parameters of HA that can dictate its applicability for different biomedical applications.
The present work aimed to study the in vitro bioactivity and degradability of HA derived from caprine bone bio-waste for the first time and the effect of calcination temperature on its properties. Bioactive HA is derived by thermal calcination of chemically treated caprine bone. The treated bones are calcined at different temperatures varying from 700 to 1300 °C and characterized to study the impact of heat treatment process on its physico-chemical properties.
Section snippets
Pre-treatment of caprine bones
Caprine bones are collected from the femur region of an adult goat (2–3 years old) from a local slaughterhouse. The bone samples are first cleaned by washing with distilled water to remove impurities and macroscopic adhering substances like meat, tissues and ligaments. The cleaned bones are then crushed into smaller particles and defatted by autoclaving in 4% NaCl (analytical reagent grade, Merck-India) solution at 90 °C for 2 h which also removes the adhering bone marrow. The crushed pieces of
(%) yield
The % yield obtained by calcination of caprine bone at 700-1300 °C is tabulated and presented in Table 2. It can be observed from Table 2 that calcination of caprine bone at 700 °C yields 58.8% of bio-ceramic HA powder. However, with an increase in calcination temperature from 700 to 1300 °C, the % of yield gradually decreases from 59.8% to 54.3%. This may be due to the complete removal of water, fats and proteins present in the bone samples at high calcination temperature. Nevertheless, the %
Conclusions
The present study shows the feasibility of extracting HA from caprine bone bio-waste by a thermal calcination process. The in vitro bioactivity and degradability of the derived HA is studied for the first time by SBF treatment. The calcined bone powders are characterized and the following conclusions have been drawn from the obtained results:
- 1.
Calcination of caprine bones at 700 °C yields a total amount of 59.8% of ceramic residue, which decreases to 54.7% with an increase in the calcination
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declarations of interest
None.
Acknowledgement
The authors acknowledge the Indovation Lab, Central Instrumentation Facility (CIF) and TEQIP-III of NIT Silchar for providing technical and financial support for carrying out the research work. The authors thank the Central Instrumentation Facility (CIF), IIT Guwahati and DST-FIST funded XRD facility in Physics Department, IIT Guwahati for material characterization. The authors also acknowledge MHRD, Government of India, for providing financial support to carry out the research work.
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