DESIGN AND FABRICATION OF HYDROXYAPATITE INCORPORATED POLYMER (NANOCOMPOSITE) MEMBRANES

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1 DESIGN AND FABRICATION OF HYDROXYAPATITE INCORPORATED POLYMER (NANOCOMPOSITE) MEMBRANES 1 QURAT ULAIN, 2 AHMAD NAWAZ KHAN 1,2 School of Chemical and Materials Engineering, NUST, Islamabad, Pakistan 1 qurat.ulainphd66@gmail.com Abstract This research has been conducted to develop and characterize bio mineral incorporated polymeric membranes. These type of membranes can be used for covering the bone scaffolds to enhance biomimetic properties as well as to improve mechanical properties, morphology and composition. The composition of this novel nanocomposite is a copolymer Cyclic Olefin Copolymer (TOPAS) and bone mineral hydroxyapatite nanoparticles. Pretreatment of nanoparticles with a coupling agent is carried out to increase the interaction of nanoparticles with polymer chains. The effect of various weight ratios of bio mineral hydroxyapatite has been studied to see their influence on morphology, mechanical properties and biocompatibility. These nanocomposites were characterized by using FTIR, SEM, EDX, Tensile testing, and biocompatibility tests. It was found that the fabricated nanocomposites are analogous to the natural bone from structural, compositional, and mechanical point of view. Keywords Key Words: TOPAS, Biocompatibility. I. INTRODUCTION In the areas of nanotechnology, polymer based nanocomposites have become a prominent area of current research and development. Biodegradable polymers from renewable resources have attracted much attention in recent years. Polymer nanocomposites have been extensively used in bone and cartilage repair tissue engineering. These nanocomposites have properties such as mechanical, morphology and biocompatibility in conjugation with natural bone and cartilage [1]. Hydroxyapatite is natural bone mineral and it comprise 40-50% of natural bone in the form of nanocrystals [2]. Hydroxyapatite in the form of nanocrystals gives high stiffness to bone while Collagen is natural matrix material of bone andgives overall strength to bone.natural bone is basically a nono composite of ceramic bio mineral incorporated collagen matrix[3]. The development of artificial scaffolds possessing all required properties of bone is necessary at this stage where Osteoporosis, Micro and macro fractures and many other bone problems are very common. Objectives of this researchis to develop and study nanocomposites containing biocompatible polymer matrix of Cyclic Olefenic Copolymer (TOPAS) reinforced with bioactive hydroxyapatite for bone repair. TOPAS is a copolymer, and a novel material to use in orthopedic application.whereas HA is bioactive, nontoxic and possesses similar structure to bones and forms a directbond with bones. These membranes can be further modified into bone cement which is used for anchoring artificial joints. The processing parameterswere optimized for the nanocomposite system and its properties were characterized using various experimental techniques like x-ray diffraction, FTIR, scanning electron microscope, EDX, Moreover, the biodegradability as well as the long-term performance of the nanocomposite will also be analyzed. II. MATERIALS AND METHODS 2.1. Materials Cyclic Olefenic Copolymer (TOPAS) was purchased from Sigma Aldrich and directly used as a matrix for the preparation of nanocomposite. Hydroxyapatite nanoparticles were synthesized by solution casting method in laboratory [4]. Sodium Dodecyl Sulphate used as a coupling agent was purchased from Sigma Aldrich. The amount of SDS and HA used is reported in Table 1. Solvents used in the experiment e.g. Ammonia, Cyclohexane were also purchased from Sigma Aldrich.Coupling agent was used for better dispersion of HA in TOPAS matrix. SDS as a coupling agent can increase the binding sites on. TOPAS for the attachment of HA nanoparticles and gives better dispersion. This improves the overall performance of nanocomposite 2.2. Methods Preparation of HA nanoparticles Calcium nitrate tetrahydrate Ca (NO 3 ).4H 2 O was used as a Calcium source and Diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 as a Phosphorus source for the synthesis of hydroxyapatite. PH was adjusted by using ammonia solution. For synthesis of HA, two solutions were prepared. First was prepared by dissolving 130 g of Ca (NO 3 ).4H 2 O in 800ml distilled water at 80 o C temperature with continuous stirring. Second was prepared by adding 38g of (NH 4 ) 2 HPO 4 in 550 ml distilled water under same conditions. The PH was adjusted at 12 by addition of few drops of ammonia. The PH above 10 is beneficial for pure HA. [5] After adjustment of PH, the two solutions were mixed by drop wise addition of Ca (NO 3 ).4H 2 O into 141

2 (NH 4 ) 2 HPO 4 solution. The whole solution was allowed to mix for 2 hours maintaining 80 o C temperature. After complete mixing, the solution was left for 24 hours for the precipitation of HA. It is then filtered by repeated washing with distilled water. After filtration, the powder was dried at 80 o C for 24 hours followed by the calcinations of powder at 550 o C for 3 hours. Lastly, it was grounded by using piston and mortar to obtain fine powder Preparation of nanocomposite Nanocomposites membranes were prepared by simple solution casting method. Polymer, nanoparticles and coupling agent were placed in 20ml glass bottles. Two separate solutions of TOPAS in addition with HA, SDS as a coupling agent in 10ml Cyclohexane as a solvent were prepared. These solutions are then mixed and stirred for 12 hours. After complete dispersion of HA into TOPAS, it was poured into 90mm diameter Petri dishes and allowed to heat at 60 o C for 2 hours in vacuum oven. Samples were then dried overnight in air and uniform membranes with 0.3 mm thickness were obtained Preparation of SBF Solution For preparation of SBF solution, pre-determined amounts of reagent grade NaCl, KCl, K 2 HPO 4.3H 2 O, NaHCO 3, MgCl 2.6H 2 O, CaCl2, Na 2 SO 4, (CH 2 OH) 3 CNH 2, were weighted with analytical balance and added to 500m l deionized water (DI). Ionic concentrations in SBF were Na mm, K mm, Mg mm, Ca mm, Cl mm, HCO , HPO mm, SO mm. This concentration is nearly equal to human blood plasma at 37 o C. Solution was buffered by adding 40 ml of 1M HCL and Tri(hydroxymethyl) amino methane. [6] 3.2. SEM The investigation of morphology and microstructure of nanocomposite films was carried out using JEOL JSM-6490A Scanning Electron Microscopy equipped with EDX. All samples were sputtered with conductive layer of gold XRD The Crystallite size and crystal phase of pure HA and nanocomposites was characterized by using Xray Diffraction Spectrometer X Rat Diffractometer. After eliminating background data, the analysis was carried out using X pert High Score Plus Software and graphs were drawn for comparison purpose Mechanical Testing Tensile testing was performed using SHIMADZU Universal Testing Machine (UTM) according to the standard ASTM D at room temperature. The load cell used for testing was 50kN and strain rate was 2mm/min. 3 samples were tested for each composite specimen. IV. RESULTS AND DISCUSSION 4.1. Characterizationof Hydroxyapatite The SEM image in figure 1. Shows that nanoparticles of HA are successfully made and the shape of HA nanoparticles is spherical Bio mineralization testing TOPAS/HA nanocomposite films with 0, and 10% were immersed in 10 ml SBF solution in tissue culture petri dishes. Samples were cut 1x1 mm dimensions. 3 samples of both concentrations were used to immerse in SBF for bioactivity testing. Fresh SBF was changed after 3 days for up to 3 weeks. Every sample was allowed to wash with distilled water and dry for 24 hours before characterization. SEM, EDX and Mapping were performed on each sample after drying and coating with gold conductive layer. III. CHARACTERIZATION TECHNIQUES 3.1. FTIR FTIR was performed on samples for chemical analysis purpose using FTIR spectrometer (). Range for FTIR spectrometer was cm -1. KBr powder was mixed with samples at room temperature and background data for KBr was subtracted from each sample. Figure 1. SEM Micrographs of Spherical shape Nano Hydroxyapatite (Average Particle Size: nm, Shape: Spherical) Figure 2. shows that HA nanoparticles are crystalline in nature, the specific peaks for HA nanoparticles is visible in graph (211). Figure 3. is FTIR image of HA nanoparticles showing its successful formation by indicating peaks of functional groups present in Hydroxyapatite. Whereas by EDX image in table 1, the percentage of elements in synthesized HA nanoparticles is obvious. By looking into these results of characterization of synthesized HA nanoparticles, it is obvious that nanoparticles with spherical shape were successfully made. After successful synthesis of nanoparticles, nanocomposites were made with composition following thetable

3 Figure 2. XRD Patterns of Spherical Shape Nano Hydroxyapatite (Average Crystallite Size: 28nm) Figure 5. EDS image showing mineral composition on 10 % TOPAS/HA membrane. Figure 3. FTIR peaks of Spherical shape Nano Hydroxyapatite Table 1. Surface Composition of Spherical Shape Nano Hydroxyapatite Table 1. Weight of dry ingredients used to produce TOPAS/HA nanocomposites Bio mineralization on TOPAS/HA membranes Figure 4. SEM Micrographs showing mineral deposition on neat TOPAS (abc) and 10% TOPAS/HA (def) membranes after 7 days (a,d) 14 days (b,e) 21 days (c,f). (g), (h) and (i) show higher magnification images of mineral deposit clusters. Scale Bars are 20 µm. Figure 6.EDS Mapping shows mineral composition on 10% TOPAS/HA membrane Figure 4 Shows SEM images of pure TOPAS and 10% TOPAS/HA dispersed in SBF for 7, 14 and 21 days. It is obvious from the images that the deposition of minerals on membranes surface is increasing gradually with increasing time. The surface of membrane immersed for 14 days have more and larger apatite particles as compared to the 7 days immersed membrane and even more can be observed on 21 daysimmersed membrane. The higher magnification SEM images (g,h) in Figure 5 show that these apatite particles have spheroids like structure and they are in the form of clusters. The agglomerates observed in our experiments resemble with the bone like structure and salts deposition on PLLA polymer after incubation in SBF for 2 weeks. [7] The morphology of apatite particles also resembles with the apatite deposits formation on Nano-Diamond PLLA composites dispersed in SBF for 1,2 and 3 weeks. [8] Figure 5. shows the EDS image of apatite particles composition. This shows that particles are mainly composed of Carbon (C), Oxygen (O), Magnesium (Mg), Calcium (Ca), Chlorine (Cl), and Phosphorus (P). For longer periods of dispersion of membranes into SBF solution, Calcium phosphate will crystallize on bioactive scaffolds and grow with time to form carbonated apatite which is the main component of bone. It can be suggested by keeping this deposition of apatite particles on membranes that formation of apatite with time on membranes is due to the bioactive nature of neat TOPAS and TOPAS/HA and due to this activity, they will allow themselves to 143

4 grow with human bone when use as a tissue scaffolds [9, 10]. EDS Mapping also confirms the apatite mineral composition on membranes Figure FTIR analysis crystallinity and mechanical properties of nanocomposites XRD Figure 9. XRD patterns of Pure TOPAS, HA and nanocomposites Transmittance (%) Figure 7. FTIR graph of nanocomposite Wavelength (cm-1) 10% Pure Figure 8. FTIR graph of Pure TOPAS and nanocomposite (10% TOPAS/HA) In order to evaluate the Chemical interactions between TOPAS, HA and coupling agent (SDS) FTIR was implemented. The intensity of hydroxyl peak OH -1 present in nanocomposite decreased 3571cm -1 after incorporation of Hydroxyapatite and coupling agent as compared to the pure TOPAS which is 3744cm -1. This shift in frequency is due to the consumption of hydroxyl groups by the formation of hydrogen bonding between Na + of coupling agent SDS and OH -1 of hydroxyapatite. The Frequency from 900 to 1200 are attributed to the phosphate groups and 1300 to 1460 are for carbonate groups in nanocomposite. The peaks at 3571 are hydroxyl groups OH -1 of Hydroxyapatite. Phosphate groups peaks are shifting towards write side in case of nanocomposites. This Shift in the peaks is due to the molecular interactions between HA and polymer. It can be suggested that the OH -1 of HA makes bonding with the Coupling agent and this coupling agent binds polymer using its phosphate group and carboxylic group. By adding SDS the interaction of HA and TOPAS would enhance due to increase in binding sites for functional groups. This will lead to more interactions of HA and TOPAS resulting in increase in crystallinity of nanocomposites by the addition of HA. Further tests were performed to check the XRD patterns of nanocomposite membranes having different concentration of HA nanoparticles are plotted in figure 9. It is obvious from the figure that HA alone has high and visible crystalline peak which is characteristic of HA while pure TOPAS is semi crystalline. The hump in the start of peak indicates the amorphous behavior of polymer. Nanocomposites with varying concentration of HA nanoparticles shows HA characteristic peak as well as hump indicating the mixed nature of nanocomposite SEM Morphology of pure TOPAS membrane and nanocomposites are shown in figure 10. With increasing concentration of nanoparticles of HA, the images shows that the tendency of formation of agglomerates is increasing. The dispersionof nanoparticles in TOPAS is very important to make good membranes which are useful for biomimitic applications. It is obvious from SEM images taken at high resolution that upto 10% HA nanoparticle concentration, the formation of agglomerates is fine but beyond that concentration e.g. 20% and 30% have more agglomerates which has furthure imparts more stiffness to the membranes and are not useful for the application point of view. Figure 10. SEM images of nanocomposite membranes with different HA concentrations. 144

5 4.7. Mechanical Testing The samples were tested to evaluate the tensile strength and elastic modulus and to plot stress- strain curves of HA/TOPAS samples. We can relate these results on the basis of SEM results. With increasing HA nanoparticles concentration, the tensile strength as well as elastic modulus increased. This increase is up to 10% and after this concentration, these values are decreasing. The reason for increase and then decrease is good dispersion of nanoparticles at lower concentration and they increase the stiffness as well as tensile strength. After 10 %, most of the nanoparticles starts making agglomerates and do not participate in increasing the strength of nanocomposite. We can conclude from these results that 5 % and 10 % nanoparticles concentration in TOPAS are good and useful for the application. Elastic Modulus (N/mm2) Figure 11. Tensile Strength vs Conc. Elastic Modulus vs HA conc wt% HA Figure 12. Elastic Modulus vs concentration CONCLUSION Hydroxyapatite (HA) nanoparticles were synthesis successfully. The nanocomposites of TOPAS/HA have good bio mineralization capability which confirms that these membranes allow better growth of minerals on it and are biomimetic as wells. TOPAS and HA both are biocompatible materials and their combination provides better mechanical properties upto 5% and 10%. Also, these have better surface morphology. The addition of SDS as a surfactant has a good role in formation of nanocomposites membrane because it is imparting high dispersion rates. REFERENCES [1] X. Gao,J.Song,P.Ji,X. Zhang,X. Li,X. Xu,M. Wang, S. Zhang,Yi Deng,Feng Deng,and S. Wei, Polydopamine- Templated Hydroxyapatite ReinforcedPolycaprolactone Composite Nanofibers with EnhancedCytocompatibility and Osteogenesis for Bone Tissue Engineering,ACS Appl. Mater. Interfaces, 8, (2016). [2] F. Peng, M. T. Shaw,J. R. Olson, and M. Wei,Hydroxyapatite Needle-Shaped Particles/Poly(Llactic acid)electrospun Scaffolds with Perfect Particlealong-NanofiberOrientation and Significantly Enhanced Mechanical Properties, Phys. Chem. C, 115, , (2011). [3] S. Deepthia, J. Venkatesanb, Se-Kwon Kimb, Joel D. Bumgardnerc, R. Jayakumara,b, An overview of chitin or chitosan/nano ceramic composite scaffoldsfor bone tissue engineering, International Journal of Biological Macromolecules, (2016). [4] M. Khalida, M.Mujahida, S.Aminb, R.S.Rawatc, A.Nusaird, G.R.Deen. Ceramics International. 39 (2013) [5] Agrawal CM, Ray RB. Biodegradable polymeric scaffolds for musculoskeletal tissue engineering. J Biomed Mater Res. 55 (2001) [6] Cüneyt Tas A. Biomaterials. 21(2000) [7] Zhang R, Ma PX. Porous poly(l-lactic acid)/apatite composites created by biomimetic process. J Biomed Mater Res. (1999)45: [8] Q. Zhang, V. N. Mochalin, I. Neitzel, Kavan Hazeli, Junjie Niu, A. Kontsos,J. G. Zhou, P. I. Lelkes, Y. Gogotsi, Biomaterials 33. (2012) [9] C. Tas A. Biomaterials. (2000) 21, [10] Zhang R, Ma PX. Porous J Biomed Mater Res. 45 (1999), Figure 13. Stress-Strain curves of HA/TOPAS 145