2012 International Conference on Biomedical Engineering (ICoBE),27-28 February 2012,Penang
Effect of Particulate Size on Mechanical Strength of Anadara Granosa Bioceramic Nur Farahiyah Mohammad1, Ghirubaagiri Kanesvaran1, Siti Marhainis Othman1 and Intan Shafinaz Mohammad2 1
School of Mechatronic, Ulu Pauh Campus, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia 1
[email protected],
[email protected],
[email protected] 2
Politeknik Merlimau, Karung Berkunci 1031, Pejabat Pos Merlimau, 77300 Merlimau, Melaka 4
[email protected]
Abstract— The Malaysian cockle (Anadara granosa) shells have a potential to be used as bone filler and bone graft for non-load bearing bone application. In this project, the effect of particulate size on mechanical strength of Anadara granosa’s bioceramic has been studied. The influences of particle size on mechanical strength are tested in order to determine the efficient particle size of Anadara granosa powders that suits the load bearing application of bone. Green bodies of Anadara granosa were prepared from Anadara granosa powders with different particles size (150, 300 and 600 µm) and sintered at 7000C. The morphological characteristic studied using scanning electron microscope (SEM) and the diametral tensile strength test was employed to characterize the effect of particulate size on the mechanical strength of Anadara granosa bioceramic. Result obtained shown that Anadara granosa bioceramic with intermediate particulate size and low porosity able to withstand high mechanical strength. Thus, it is suitable for cancellous bone substitute application. Keywords- Anadara granosa, particulate size, porosity, mechanical strength.
I.
INTRODUCTION
The strong and rigid structure of human bone allows it to act as a major supporting tissue of the body which capable for weight bearing. There are two types of bone, namely compact bone and spongy bone or cancellous bone [1]. Cortical bone or the compact bone has much higher strength compare to the spongy or cancellous bone. The mechanical strength of bone is due to the bone matrix which also acts as body’s mineral storage [2]. Extreme load, sudden impact or stress from unusual direction may crack the bone even though it has high mineral strength and leading to fracture. Bone fracture can be the result of high force impact or stress, or trivial injury as a result of certain medical conditions that weaken the bones, such as osteoporosis or bone cancer where this kind of fracture called pathological fracture. The surgical procedure to repair the bone fractures called bone grafting done by replacing the bone with material from patient’s own body, an artificial, synthetic, or natural substitute. The ability of bone to regenerate made the bone grafting possible. The biological mechanism such us
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osteoconduction, osteoinduction and osteogenesis favors bone grafting. Osteoconductivity is defined as the ability to support tissue in growth and bone formation. Whereas osteogenicity is defined as the formation of bone from cells within a bone graft [3]. The artificial bone that created from biomaterials for bone grafting purpose able overcomes the disadvantages of autograft and allograft. The important thing that should be considered in tissue engineering for developing bone substitute is that biodegradable ability of the material used to make scaffold for seeding cells for subsequent growth of bone tissue. The material chosen for scaffold at same time should posses appropriate porosity, mechanical strength and bioactivity such as osteoconductivity, osteoinductivity and osteogenesis [4]. Ceramics such as calcium phosphates for example hydroxyapatite (HaP) and tricalcium phosphate are the common material used as bone substitute. Hydroxyapatite is the main mineral component of bones and teeth with chemical formula CA10(PO4)6(OH)2. Hydroxyapatite favors to be used as bone substitute as it is biocompatible, osteoconductive, non-toxic, non-inflammatory and also bioactive where it able to form direct chemical bond with living tissue. Besides that, due to the bioresorbablity of hydroxyapatite, it will be replaced with regenerated bone tissue upon implantation as it is bioresorbable [3]. Hydroxyapatite used as a coating material on porous metal surfaces of orthopedic fixation prostheses because it will significantly affect the rate and vitality of bone ingrowth into the pores [5]. Coral obtained from deep seas is a source of hydroxyapatite but the coral facing extinctions and it is difficult to obtain as well. The mineral content of Anadara granosa was analyzed to verify its potential as alternative to coral exoskeleton as bone substitute. The Anadara granosa contain 98.68% of CaC which is similar to that of coral which contain 97-98% of CaC which actually vary with dept of the coral taken [6]. The cockle shells consist of comparable composition of calcium to that human’s wet cortical bone which consists of sub microscopic crystals of an apatite of calcium and phosphate resembling hydroxyapatite in its crystal structure [7]. The
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hydroxyapatite has poor mechanical properties thus; this project is conducted to analyze the effect of particulate size on mechanical strength of Anadara granosa bioceramic. The particulate size plays important role in determining the pore sizes thus an improved mechanical strength of hydroxyapatite can be obtained. According to Sumit Pramanik et.al [8], mechanical strength of HAp mainly depends on grain size, grain size distribution, porosity and other microstructural defects. Bioactivity of the synthetic HAp has found to be strongly affected by structural crystallinity [9]. The strength of a material is defined as the maximum stress that the material can sustain under uniaxial tensile loading. Strength strongly depends on the stress transfer between the particle and the matrix. For well-bounded particles, the applied stress can be effectively transferred to the particles from the matrix [10]. The grain size, grain size distribution, porosity, and other micro structural defects influence the mechanical strength of a material. II.
METHODOLOGY
A. Collecting and Processing Raw Material Anadara granosa, locally known as cockle shells collected from Kuala Perlis seacoast. Shells with average size about 36 mm x 23 mm x 22 mm and average weight of 80 mg are selected from the collected sample. The shells then cleaned with distilled water. The toothbrush was used to remove dirt on the shells surface and once again rinsed through the distilled water. The shells used for this project were ensured free from any sediment to reduce any external factor that may interfere the final result. The cleaned shells then air-dried for one day and oven dried at 500C for two days to prevent agglomerate during grinding process. B. Sample Preparation Dried Anadara granosa were crushed into small pieces using the crusher. The planetary grinding Pulverisette 6 used to grind the crushed raw material into powder. The original powder made from grinding the anadara granosa was screened to produce powder with different particulate size. Three fraction of different particulate sized sample which was 600 µm, 300 µm and 150 µm obtained using Tyler certified U.S series sieves. It is cannot be concluded that each powder samples only contain particles with the mentioned size. This is because while sieving for a specific sized particle, the particle with that specific size and particle with size below than that was obtained. Thus, powder sample of 600 µm contain particle of 600 µm and lower. The sample of 300 µm contain particle that sized 300 µm, smaller than 300 µm but larger than 150 µm. The sample of 150 µm contain particle size of 150µm and smaller than 150µm. Hand press machine with maximum force of 20 ton used to press the Andara granosa powder into pallet. A mold made of hardens steel used to mold six gram of powder into shape when the 2.46 ton force which is equivalent to 120 MPa applied. A pellet with approximately 15 mm diameter and 12 mm length was produced. The pellets are now called green bodies dried in oven at 700C for two
hours to remove the residual moisture left then left to cool at room temperature. Cooling down is important after the oven drying process to make sure the green bodies are stable at molecule level. The green bodies were sintered in a carbolite furnace at 7000C for three hours with a heating rate of 50C /min with subsequent furnace cooling to room temperature. Sintering is the critical stage because at certain times, the sample might break and damage due to humidity and sample preparation step must be repeated if the samples rupture. C. Characterization The morphological structure of sample that varies in particulate size was studied with analytical scanning electron microscope (SEM) model Jeol JSM-6460LA to identify the effect of particulate size on pore size and amount of pore produced after sintering. The length and diameter of samples before and after sintering process measured with Vanier caliper and the weight of the samples before and after sintering measured with balance weight to analyze the elimination of water in high temperature and calculate the linear shrinkage rate. The measurement of bulk density and porosity of the bioceramic carried out using Archimedes’s principle based on standard test method for water absorption, bulk density, apparent porosity, and apparent specific gravity of fired whiteware products (ASTM C 373-88). Mechanical properties of the samples measured by diametral tensile strength using Shimadzu autograph AG-X 250kN universal tensile machine. The samples for the diametral tensile strength or known as Brazilian test were prepared according to ASTM C496/C 496M-04e1 because it is more suitable for brittle material like bioceramic. III.
RESULT AND DISSCUSSION
A. Linear and Shrinkage Analysis The percentage of reduction in the size of bioceramic sample after sintering is known as the linear shrinkage rate. During sintering, bioceramic sample are fired at high temperature below the melting point to adhere its particle to each other where porosity of the bioceramic eliminated gradually causing the particle become closer to each other resulting net shrinkage in size of the sample. The linear shrinkage rate of bioceramic samples increases with increasing particulate size from 150 µm to 600 µm. Larger pore and space present in green bodies of sample with larger particulate size like 600 µm thus, pore size of the sample shrink and the particle are brought closer together during sintering process eliminating more space between the particles which results larger decrement in size of bioceramic sample with larger particulate size. It can be concluded that, the larger the particulate size the higher the linear shrinkage rate will be after sintering the green bodies. Figure 1 shows the percentage of linear shrinkage on diameter, length, and weight of sample with different particulate size.
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µm having 8.93 g/cm3. Sample with 600 µm particulate size has highest porosity lead large void where solidification is lesser resulting low density. In contrast, sample with particulate size 300 µm has the lowest porosity which allows more densification.
Figure 1. The bar graph shows the percentage of linear shrinkage between sample of different particulate size.
B. Morphological Analysis The pore size and amount differ with the variation in particulate size. The bioceramic with 150 µm particle size showed to contain higher quantity of smaller pores. In contrast, the bioceramic sample with 600 µm particle size showed to contain small quantity of larger pores. The intermediate amount and size of pores showed by the sample with particle size 300 µm. The length of pores produced by each sample that varies in particulate size measured to differentiate and relate the size and amount of pore produced with particulate size of the sample using Motic Images Plus 2.0ML software. It shows that sample with 150 µm particulate size has smallest pore followed by sample with 300 µm and then sample with 600 µm. In summary, the pore size increases with increase in particle size. Figure 2 shows the structure of pore produced in a samples with different particulate size observed via scanning elctron microscope (SEM). C. Porosity and Density Analysis Table 1 shows the apparent porosity and bulk density of Anadara granosa bioceramic with 150 µm, 300 µm, and 600µm particulate sizes. The result shows that sample with 600µm particulate size has the highest porosity that is 14.67%, followed by the sample with 150 µm with medium porosity that is 12.75 % and finally 300 µm with lowest porosity that is 11.48 %. The bioceramic sample with smallest particulate size will produce a pellet that has high amount of small pores. Similarly, the sample with biggest particulate size will produce a pellet that has fewer amounts of large pores. As particulate size increases the size of pore increases where else amount of pores decreases [11]. Bioceramic sample with 600µm particulate size consist of larger pore resulting higher porosity and in contrast, 150 µm particulate size samples consist of smaller pore resulting slightly lower porosity than 600µm particulate size. The sample with intermediate particle 300µm has lowest porosity compared to larger particle and smaller particle sample. Sintering of bioceramic sample made of pure Anadara granosa promote the densification. When the porosity of sample decreases the density of the sample will increase [12]. The sample with 300 µm shows the highest density that is 9.52 g/cm3 as it has the lowest porosity compare to other samples. Followed by sample with particulate size 150 µm with 9.07 g/cm3 then sample with particulate size 600
(a)
(b)
(c) Figure 2. Anadara granosa bioceramic with a different particulate size (a) 150 µm (b) 300 µm and 600 µm.
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TABLE I.
POROSITY AND BULK DENSITY OF ANADARA GRANOSA BIOCERAMIC FROM DIFFERENT PARTICULATE SIZE Particulate Size Of Bioceramic
Parameters
150 µm
300 µm
600 µm
Porosity (%)
12.75
11.48
14.67
Density (g/cm3)
9.07
9.52
8.93
16 14 12 10 8 Porosity (%) 6
Density (g/cm³)
4 2 0 0
100
200
300
400
500
600
700
Particle size (µm)
Figure 3. Relationship between porosity and density of bioceramic
Figure 3 shows the relationship between porosity and density of the bioceramic sample made of Anadara granosa vary in particulate size. When the porosity of the sample reduces the density of the sample will increases. Reduction in porosity of a sample promotes densification thus lead to increase in bulk density. D. Diametral Tensile Strength Diametral compressive force applied along the cylindrical bioceramic sample at a strain rate one mm/min until failure occurs. The diametral tensile strength for bioceramic sample with three different particulate sizes is shown in Table 2. Bioceramic with particulate size of 300 µm resulted in highest diametral tensile strength followed by 150 µm and 600 µm. The average diametral tensile strength of sample with particulate size 300 µm is 9.91 MPa whereas, 150 µm and 600 µm are 8.86 MPa and 5.68 MPa respectively. TABLE II. Mechanical Properties Splitting tensile strength, σT (MPa)
and amount reduce the cross sectional areas over which a load can be applied thus lower the stress that these biceramic can support [13]. The bioceramic sample made of pure Anadara granosa with particulate size of 600 µm has the lowest mechanical strength. This is because it is more porous compare to other two samples. Larger particulate sized sample will have larger pore size and small amount of pore. Large pores will act as a stress grainer making the sample to withstand only small amount of applied load reducing the mechanical strength. Similarly, smaller particulate sized sample will have small pores thus has better mechanical strength. This is proven by the sample with particulate size 150 µm and 300 µm which are small in size compared to 600 µm has much higher mechanical strength. But, this trend is not followed by samples with particulate size 300 µm and 150 µm. This is because sample with 150 µm has large amount of small pores whereas, sample with 300 µm has moderate amount of medium sized pores as it the medium size particle compared to 600 µm and 150µm. Bioceramic sample with 600 µm and 150 µm are porous sampel with larger pore and bigger number of pore respectively thus, both have low mechanical strength than sample made of 300 µm which has intermediate pore size and amount. F. Sanchez et.al [11] describes that, intermediate particle size will have maximum value of mechanical strength due to the effect of particle morphology and number of bonds in another word the contact zone. Where, the small particle size causes less interlocking between particles and large particle size has a fewer average number of mechanical bonds between particles producing weaker samples [11]. The bioceramic that had been produced from various particulate sizes can be used as bone substitute material due to the ability to withstand compressive stress which comparable to that of human bone where mechanical strength of human bone vary according to location and function of the bone. Human cancellous bone from proximal to tibia has mechanical strength of 3.5 ± 1.9 MPa, femoral to heads has 1-15 MPa, and 3-23 MPa for cortical from plateau [14]. These values are within the range of mechanical strength obtained by bioceramic made from various particle size of pure Anadara granosa powder.
DIAMETRAL TENSILE STRENGTH OF BIOCERAMIC SAMPLE WITH DIFFERENT PARTICULATE SIZE Particulate Size Of Bioceramic 150 µm
300 µm
600 µm
8.86
9.91
5.68
The mechanical strength of bioceramic is affected by pores in two ways. Foremost, presence of pores in a bioceramic sample produces stress concentration. The bioceramic material possess no plastic deformation attributes to absorb any energy transferred to material thus, once the stress reaches critical level due to applied force, crack is formed and propagated until fracture occurs. Secondly, pores that are its size shape
Figure 4: The relationship between porosity, density and mechanical strength of Anarada granosa bioceramic.
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REFERENCES Figure 4 shows the relationship between porosity, density and mechanical strength of Anadara granosa bioceramic. When the porosity of the sample reduce the density and mechanical strength on bioceramic increases. The porosity of the sample can be reduced by manipulating the particle size. The sample with average particulate size will produce low porous , high density and strong bioceramic to withstand load bearing application. IV.
CONCLUSION
The effect of particulate size on porosity, density and mechanical strength of Anadara granosa bioceramic studied in this project. Porosity represents the void space in the sintered sample. Bioceramic made of pure Anadara granosa with particulate size 600 µm found to have highest porosity followed by sample with 150 µm and finally sample with 300 µm having the lowest porosity. When the particle size is big, the size of pore formed between the particles is large leading to high porosity, low density and low mechanical strength such as in bioceramic made from 600 µm particle. On the other hand, when the particle size is small the size of pore formed between the particle are small but the number of small pores are higher leading to porosity that slightly lower than porosity of the larger particulate size sample such as in sample with 150 µm. Bioceramic sample with particulate size of 300 µm is the intermediate size. It posses moderate amount of medium sized pore that lead to reduced porosity compare to other sample. To conclude, the intermediate particulate sized (300 µm) sample are the most suitable to be used to produce Anadara granosa bioceramic compared with larger (600 µm) and smaller (150 µm ) particulate sized due to its low porosity, high density and high mechanical strength. ACKNOWLEDGMENT Acknowledge Universiti Malaysia Perlis (Unimap) for given opportunity and guidance.
[1]
S. S. Tate, Essentials of Anatomy & Physiology, 6th ed. China: Mc Graw Hill, 2007. [2] Zhang, X. (2007). Preparation and Characterization of Calcium Phosphate Ceramics and Composites as Bone Substitutes. Materials Science and Engineering. San Diego, University of California. [3] A. Hanifi and M. H. Fathi, "Bioresorbability Evaluation of Hydroxyapatite Nanopowders in a Stimulated Body Fluid Medium," Iranian Journal of Pharmaceutical Sciences, vol. 2, pp. 141-148, 2008. [4] M. Wang, "Composite Scaffolds for Bone Tissue Engineering," American Journal of Biochemistry and Biotechnology, vol. 2, pp. 80-84, 2005. [5] L. L. Hench, "Bioceramics: From Concept to Clinic," Journal of the American Ceramic Society vol. 74, pp. 1487-1510, 1991. [6] N. Z. a. Z. K. Zuki Abu Bakar Zakaria, "Journal of Animal and Veterinary Advances " Mineral Composition of the Cockle (Anadara granosa) Shells, Hard Clamp (Meretrix meretrix) shells, and coral (Porites spp.): A Comparative studies, vol. 7, pp. 445-447, 2004. [7] M. A. Z. Nur Farahiyah Mohammad, Saidatul Ardeenawatie Awang, Zulkarnay Zakaria, Azian Azamimi Abdullah, "Synthesis and Characterization of Bioceramic from Malaysian Cockle Shell," IEEE Symposium on Industrial Electronics and Applications, pp. 395-398, 2010. [8] A. K. A. Sumit Pramanik, K.N.Rai, "Delopment of High Strength Hydroxyapatite for Hard Tissue Replacement," Trends Biomaterial and Artificial Organ, vol. 19, pp. 46-51, 2005. [9] M. Y. Kazuto Honma, "Fabrication of calcite (CaCo3) ceramics with high density," Journal of materials science letters, vol. 17, pp. 745-746, 1998. [10] Ignjatovic, N., Uskokovic, D.,” Synthesis and application of hydroxyapatite/polylactide composite biomaterial ”, Applied Surface Science, 238: p. 314–319,2004. [11] F. Sánchez, et al., "Relationship between particle size and manufacturing processing and sintered characteristic of iron powder," Revista Latinoamericana de Metalurgia y Materiales, vol. 23, pp. 35-40, 2004. [12] S. H. Na, et al., "Relation Between Density and Porosity in Sintered UO2 Pellets," Journal of Korean Nuclear Society, vol. 34, pp. 433-435, 2002. [13] Engineering Materials Technology [Online] Avilable:http://me.mit.edu/2.01/Taxonomy/Characteristics/Ceramics/Ma inCeramics.html#SiliconNitrides [14] J.C.L. Huec, "Effect of porosity on mechanical strength of hyroxyapatite," Biomaterial, vol. 16, pp. 113-117, 1995.
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