Polymer/silica composites fabricated by sol-gel technique for medical applications.
Sol-gel method is a wet method used for the fabrication of glass and ceramic materials, wherein the solution (sol) evolves gradually towards the formation of a gel like network containing both a liquid and solid phase . Sol-gel techniques have become very popular recently due to their high chemical homogeneity, low processing temperatures, and the possibility of controlling the size and morphology of particles. The sol-gel-derived materials provide excellent matrices for a variety of organic and inorganic compounds. The advantages of sol-gel technology are used in the fields of biomedical sensors, laser materials and for sustained drug delivery applications. Hench et al.  showed that through the use of the sol-gel technique, it was possible to fabricate highly pure and homogeneous materials, with controlled pore structure. More information regarding the applications of sol--gel materials in medicine can be gathered from review of Avnir et al. .
A simple method to promote the fine dispersion of the inorganic component in polymers is to grow the inorganic phase by sol-gel process in the polymer solution [3, 4]. For the preparation of the inorganic phase, tetraethoxy silane can be added to the solution containing the organic polymer and hydrolysis and condensation induced by acid catalyst. Many researchers have investigated organic-inorganic polymer hybrids with poly methyl methacrylate (PMMA) as the organic matrix. Polymers such as poly methyl methacrylate, poly vinyl acetate, poly vinyl pyrrolidone, poly N,N-dimethyl acrylamide and poly(acrylic acid) are known to form hydrogen bonds with silanols on the silicate network . The carbonyl groups in organic polymer chains retard the phase separation during the vitrification of the hybrid film. However, the in situ polymerization of inorganic components in an organic polymer matrix may lead to phase separation if there is no specific interaction between organic and inorganic chains [3, 6].
Lobel and Hench  have shown that the biocompatibility and bioactivity of a sol-gel material is determined by the gel substrate concentration, surface texture, the size of the protein getting adsorbed on the material surface and the pH of the solution. The protein adsorption, including growth factor and morphogenetic proteins, occurs due to the formation of hydrogen and other long range electrostatic bonds between the negatively charged silica surface (dissociated silanols from the membrane) and protonated amine groups (from proteins).
Among the various synthetic polymers, PMMA is widely used in the medical field for prosthetic applications. It is known to be biocompatible with good mechanical and physical properties suitable for application in orthopedics and opthalmology [8, 9]. PMMA is often preferred because of its moderate properties, easy handling and processing, and low cost. There has been immense interest in the fabrication of PMMA/Si hybrid materials by sol-gel technique [4, 10-13]. Lee and Rhee  reported the positive influence of silica in the bioactivity of PMMA composite.
Polyether ether ketone (PEEK) has been used for load bearing orthopedic applications as it is biocompatible and has good mechanical properties . PEEK, being insoluble in most of the solvents, cannot be used for any other medical applications. Sulphonated PEEK (SPEEK) on the other hand is soluble in a variety of solvents and hence a variety of polymer blends of SPEEK can be obtained with potential for application in diverse fields such as drug delivery, tissue engineering, vascular grafts, soft tissue prosthesis, haemodialysis, etc. in various forms such as membranes, fibers and capsules. The conversion of PEEK to SPEEK using sulphuric acid is shown in fig. 1.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
The SPEEK thus formed can then be blended with PMMA and the proposed structure of SPEEK/PMMA blend is given in fig. 2.
Poly (vinyl alcohol) (PVA), is a non-toxic, water-soluble synthetic polymer having good physical and chemical properties along with film-forming ability. This polymer has important applications in areas such as controlled drug delivery systems and composite membranes for various prosthetic applications. Many research works based on PVA and its blends have been carried out for application in biomedical field .
Among the natural polymers, Chitosan (Cs) is widely employed for biomedical applications. Apart from being biocompatible with a potential for complete biodegradability it is also porous. This porous nature is highly useful for drug delivery and tissue engineering applications. Some investigators have studied the properties of chitosan/poly vinyl alcohol (Cs/PVA) blend films and analysed their biocompatibility and bioactivity [15-19]. The proposed blend formation between Cs and PVA is shown in fig. 3
In this study, we have fabricated polymer composite membranes of SPEEK/PMMA/Si and Cs/PVA/Si composites by sol-gel method and evaluated their physical and biological properties. To the best of our knowledge, it is for the first time that SPEEK is being explored for applications in medicine.
Silica was chosen as the filler as it is highly biocompatible and is naturally available. Its incorporation was expected to not only increase the strength of the polymer composite but also positively influence the biological properties of the polymers. Silica based polymers such as silicones are being successfully used for various biomedical applications such as implants and artificial skin [20, 21]. The most important utility of silica is in the creation of apatite nucleation sites seen on immersion in SBF. The chelation of calcium ions by the negatively charged silanol groups precedes the formation of a cluster due to the subsequent adsorbtion of phosphates, hydroxyl, carbonates and calcium ions from SBF [7, 12, 22]. Experiments by S.H. Rhee et al.,  showed that PMMA/ Silica hybrids exhibited better responses to cell attachment, proliferation and differentiation than pure PMMA. The works of T. Yamaguchi  showed high proliferations of cells on silica nanofibers indicating that silica based materials are highly suited for many medical applications such as drug delivery, tissue engineering and as prosthetic material with good bioactivity and excellent biocompatibility.
[FIGURE 3 OMITTED]
Materials and Methods
The materials that were used for the study were procured commercially from different sources. PMMA (Mol. Wt 35,000 Da) was procured from Asian acrylates, Mumbai, PEEK (Mol. Wt. 1,00,000 Da) from Victrex while PVA (Mol. Wt. 1,10,000 Da) was obtained from B-Pura. Chitosan (Mol. Wt. 75 kDa) was received as a gift sample from India Sea Foods, Kochi. While the sulphonating agent [H.sub.2] S[O.sub.4], was purchased from Merck, the solvent Tetrahydro furan (THF) was purchased from Sisco Laboratories, India. Silica and Tetraethyl orthosilicate (TEOS, 99.5% pure) were purchased from Sigma Aldrich. Hydrochloric acid was purchased from Merck and acetic acid from Fischer Scientific.
The table 1 shows the system, their corresponding code and weight ratios of the polymers employed. In both the systems, the silica concentration was kept constant.
Preparation of composite membranes
SPEEK was prepared by sulphonating PEEK using sulphuric acid as the sulphonating agent as per the procedure described elsewhere [24, 25]. The polymers [SPEEK and PMMA; Cs and PVA] were dissolved separately in their respective common solvents of DMF and water (2% acetic acid in case of Cs) for first and second systems respectively. The polymer solutions were then mixed together so as to form the respective blends (SPEEK/PMMA and Cs/PVA). To each of the solutions, 0.025 g nano silica was added followed by stirring for 2 hours. The solutions were then ultrasonicated to obtain uniform dispersion of the filler.
To each of the polymer solutions, 0.25 ml of 35% HCl, 5 ml ethanol and 1ml of tetra ethoxy silane (TEOS) were added to improve the gelation process. The solutions were then stirred for 3 days to complete the gelation process. The gel obtained was now cast in petri dishes and aged for 3 days at room temperature. The membranes were then separated from the petridishes and studied.
Fourier Transform Infra-Red Spectroscopy (FTIR)
The samples were characterized for blend formation through Fourier Transform Infra Red spectra using Perkin Elmer Spectrum RXI IR spectrophotometer.
Scanning Electron Microscope (SEM)
The surface morphology of the composite membranes and the dispersion of silica filler were studied using HITACHI S-3400N Scanning Electron Microscope (SEM). The samples for the SEM analysis were prepared by drying them and then coating their surface with gold by sputtering.
Swelling property of the polymer composite membranes were studied by immersing the pre weighed dry membranes in the deionized water in a glass beaker for 24 hours. The wet membranes were then retrieved and the excess water was blotted gently using a tissue paper. The wet samples were then again weighed and the water absorption percentage was calculated using the formula
% water absorption = [(wt of wet membrane - wt of dry membrane)/wt of dry membrane] x 100
Bioactivity of the membranes was studied by immersing the membranes in Simulated Body Fluid (SBF) for 15 days and analyzing their surface for the formation of mineral (hydroxycarbonate apatite) layer using SEM (Quanta 200 FEG scanning electron microscope). Elemental analysis was also performed using Energy Dispersive X-ray spectrometry (EDX), to determine the quantity as well as the composition of the minerals formed on the composites. SBF also known as Kokubo's Solution was prepared according to the specification given by Kokubo et al . The chemicals required to prepare SBF were dissolved in deionized water in the specified quantity while the pH was maintained at 7.25.
Biocompatibility of the composites is a major criterion for the selection of the composites for various medical applications. Biocompatibility
is evaluated by several in vitro methods, the most significant of them being cytotoxicity. In vitro cytotoxicity was evaluated by MTT method as described by Mossman in 1983. He first reported the use of a tetrazolium salt to determine the cell viability and proliferation . Today, this method has become a standard and accepted experiment to determine the in vitro cytotoxicity of biomaterials. The cytotoxicity test for the samples was performed using Human breast carcinoma cells (HBL 100 cell line) grown on Dulbecco's Modified Eagle's Medium. SPEEK, being considered for the first time for biomedical applications, and due to the scarcity in the literature with regards to its cytotoxicity unlike that of PMMA, Cs and PVA, it was included in the cytotoxicity study. The study was carried out in triplicate and the average value taken.
Results and Discussions
Fourier Transform Infrared Spectroscopy
Fourier Transform-Infra red spectra of SPEEK/PMMA/ Si and Cs/PVA/Si composite membranes are shown in fig. 4a and b respectively. In the spectrum of PMMA (Fig 4a), the weak peak at 1274 [cm.sup.-1] was assigned to O - C[H.sub.3] stretching. The peak at wave number 1462 [cm.sup.-1] was assigned to the C[H.sub.2] stretching vibrations while the peak at wave number 1738 [cm.sup.-1] was attributed to the stretching of the C = O bond . The peak seen at 1388 [cm.sup.-1] and the double peak at 2408 [cm.sup.-1] represented O = C - O vibrations while the broad peak at 2599 [cm.sup.-1] was due H - C = O stretching vibrations. The alkane CH stretching was interpreted from the peaks at 2964 and 3001 [cm.sup.-1]. The occurrence of sharp peak at 3559 [cm.sup.-1] pointed to the OH stretch which was probably due to hydrogen bonding.
[FIGURE 4 OMITTED]
In the spectrum corresponding to SPEEK, the peak at 1594 [cm.sup.-1] was assigned to the Ar-O-Ar stretch while the peak at 1698 [cm.sup.-1] was assigned to Ar-C(=O)-Ar stretching vibrations. The C - O stretch was visualised by the appearance of a peak at 1318 [cm.sup.-1]. The peaks at 1229 and 1028 [cm.sup.-1] corresponded to the asymmetric and symmetric stretching vibrations of O=S=O bond . The peak at 2614 [cm.sup.-1] was assigned to S - H bond vibrations from the sulphonic group.
In the spectra corresponding to SP1, SP2 and SP3, the peaks occurring in the regions of 1430 and 1609 [cm.sup.-1] were assigned to C[H.sub.2] and the Ar-C(=O)-Ar stretching vibrations respectively. The observance of a shift from their original positions (1462 [cm.sup.-1] in the PMMA spectrum and 1698 [cm.sup.-1] in the SPEEK spectrum) suggested of an interaction between the carbonyl group of SPEEK and the methyl group of PMMA. Additionally, the C = O stretching was found to be shifted to 1742 [cm.sup.-1] in the composites from their original position of 1738 [cm.sup.-1] observed in the spectrum of PMMA. The peaks at 2361 and 2934 [cm.sup.-1] were considered to be a shift of the peaks occurring at 2599 and 2964 [cm.sup.-1] respectively in PMMA. The observation of the shift in the above discussed peaks along with the absence of a peak in the region of 2600 [cm.sup.-1] was explained as occurring due to the formation of hydrogen bond between the sulphonic group of SPEEK and the carbonyl group of PMMA along with another hydrogen bond between the methyl group of PMMA and the carbonyl group of SPEEK. The FTIR study suggested a good blend formation between PMMA and SPEEK facilitated hydrogen bonding.
The FTIR spectra of the samples of the 2nd system are shown in fig. 4b. In the spectrum of chitosan, the characteristic peaks for polysaccharide are seen at 898 and 1154 [cm.sup.-1]. The amide I and amide III peaks were represented by the peaks 1652 and 1379 [cm.sup.-1] respectively . The peak at 2872 [cm.sup.-1] was assigned to the H - C = O vibrations indicating the presence of acetyl groups. The peaks corresponding to O - H and N - H appear to have overlapped and produce a broad peak at the region of 3443 [cm.sup.-1]. The peak at 1262 [cm.sup.-1] was assigned to C - N stretching . The spectrum of PVA shows a broad peak at the region of 3437 [cm.sup.-1] which was associated with the stretching of O - H from the intermolecular and intramolecular hydrogen bonds. The peaks at 2920 [cm.sup.-1] and 2352 [cm.sup.-1] were assigned to the alkyl C - H stretching and the peak at 1645 [cm.sup.-1] was assigned to C = O stretching vibrations.
The FTIR spectra of the composites of the 2nd system were different from that of chitosan due to the amination of primary amino groups . In the composite samples, the peak corresponding to C = O was observed to have shifted to the right occurring at the region of 1590 [cm.sup.-1] It was also observed that, the peak corresponding to amide 1 (from chitosan), and that corresponding to C = O (from PVA) were shifted and appeared at 1700 and 1590 [cm.sup.-1] respectively. The peaks corresponding to N - H and O - H stretching vibrations (from chitosan and PVA respectively) were found to be sharper and shifted to the right (between 3460 and 3352 [cm.sup.-1]) in the spectra of the composites. The observed shift in the peaks indicated a blend between Cs and PVA via hydrogen bonds between the OH groups of PVA and the N- H groups of chitosan [19, 30]. El-Hefian et al.  observed that, the intensity of the CH group in the FTIR of Cs/PVA blends increased proportionally with increase in the concentration of PVA. In the present study, the C - H vibrations in the composites were found to have shifted to the left (1710 [cm.sup.-1]) and their relative intensity was found to be maximum in the case of CP2 and minimum in the case of CP3. Though the above observation was in concurrence with the findings of El--Hefian et al., it was difficult to conclusively infer since, the present study involved only three different weight ratios of PVA.
[FIGURE 5 OMITTED]
Water absorption studies
The results of the water absorption studies for the two systems is shown in fig. 5 (a and b). From fig. 5 a, it was observed that the membrane sample of SP3, having a higher percentage of SPEEK, exhibited higher percentage of water absorption while SP1 showed the least water absorption. From this it was inferred that increasing the concentration of SPEEK increased the hydrophilicity of the composite membranes. This was not surprising considering that SPEEK is more hydrophilic than PMMA. With increase in the degree of sulphonation  the hydrophilicity of SPEEK increases and it is possible to even make it water soluble. This property is useful and can be exploited for drug loading and release applications. Additionally the presence of pores (obtained as a result of the sol-gel technique), would draw one's interest in exploring this polymer for tissue engineering applications.
Fig. 5b shows the swelling percentage of composite membranes belonging to the second system (CP). From the fig., it can be seen that all the composite samples were more or less hydrophilic to the same extent. However, a slight increase in water uptake was observed on increasing the PVA concentration indicating that the swelling behavior of the composites was influenced by the concentration of PVA. This implied that the interaction between Cs and PVA increased the hydrophilicity of the composites. Another factor favouring higher swelling of the composites was the formation of hydrogel network due to the physical entangling of the PVA chains with chitosan chains .
The fig. 6 depicts the SEM images of the composite samples. The images show uniform distribution of the silica particles in a porous matrix surface. Interestingly, there are some micro cracks which are evident in the image corresponding to SP2. These cracks were due to capillary pressure occurring during the drying process . The appearance of these cracks though may be detrimental to the mechanical properties of the composites, it could be exploited for drug delivery and tissue engineering applications or to bring about osseointegration. The presence of these pores and cracks on the surface will help in the ingrowth of the hydroxyapatite crystals thus enabling good mechanical and chemical bonding of the composite with the bone. It can however be noted that the crack formation occurs only in the sample containing the least volume of SPEEK. Thus it can be inferred that increase in the SPEEK concentration leads to good interaction between PMMA and SPEEK and consequently reducing the capillary pressure resulting in either nil or negligible amount of crack formation.
[FIGURE 6 OMITTED]
The SEM images corresponding to Cs/PVA composites showed that in all the composites, a smooth surface was obtained which indicated that Cs and PVA form good blends irrespective of their weight percentages in the composite. The silica can be seen to be uniformly distributed throughout the polymer matrix. There was no evidence of any micro cracks on the surface of the Cs/ PVA composites although the pores appeared to be larger in size and more numerous than those occurring in SPEEK/PMMA composites. The chitosan blend membranes, fabricated by solvent evaporation technique by Balau et. al.  and Mansur et. al.  displayed surface morphologies which were similar to that of the CP system in the present study. On the other hand, membranes fabricated by freeze drying technique [33-35] resulted in a highly interconnected porous structure. While such highly porous freeze dried chitosan based hydrogels were ideal for tissue engineering applications, the less porous and bioactive membranes obtained in the present study are intended for filling of bone defects with a potential for osseointegration and subsequent mineralization in a process mimicking the natural mineralization of bone.
Bioactivity of the membranes was determined by immersing the samples in the SBF solution and observing the growth of the mineral crystals under the SEM as shown in fig. 7. The minerals formed on the surface of the composites could possibly be composed of crystals of either calcium phosphate or sodium chloride. Studies by various investigators have indicated that, the calcium phosphate crystals formed in SBF are actually hydroxycarbonate apatite [36, 37]
In samples of system 1, the SP3 exhibited higher growth of hydroxyapatite as is evident from the SEM pictures (fig. 7). This corresponds to higher concentration of SPEEK resulting in higher bioactivity. It is believed that the mechanism of bioactivity of silica containing polymers is due to the negative charge on the silanol groups. Another hypothesis is that the nucleation of [Ca.sub.3] P[O.sub.4] is induced on the material surface when the material surface is negatively charged . The negative charge attracts the [Ca.sup.2+] and subsequently HP[O.sub.4.sup.2-] and OH anions which are present in the SBF solution. Highest bioactivity observed in samples containing higher concentration of SPEEK is explained as occurring due to the negative charge possessed by the S[O.sub.3.sup.-] ions. The additional negative charge due to the S[O.sub.3.sup.-] ions enhances the bioactivity of the samples when compared with the samples containing lower concentrations of SPEEK.
The SEM images of CP1, CP2 and CP3 showed evidence of mineralization which were reminiscent of [Ca.sub.3] P[O.sub.4] On comparing the three images, maximum mineral density was seen in the samples of CP1 and CP2. In the composites of CP1 and CP2, the concentration of PVA was higher than that of CP3 and hence there would be better blend formation between the polymers. Studies by L. Kong et al  have shown that chitosan by itself possessed a certain degree of bioactivity. Li et al.,  demonstrated the biomimetic mineralization of chitosan using urea, dicalcium phosphate, and calcium chloride. In their study, the aqueous solution used was weakly alkaline due to the production of anions namely HC[O.sub.3.sup.-] or C[O.sub.2.sup.-] and the cation N[H.sub.4.sup.+] from urea facilitated the mineralization of chitosan scaffolds. In the present study, with increase in the PVA concentration, there was a higher probability of hydroxylation of the silanol groups due to the associated increase in the hydrophilicity. Jun et al.,  in their evaluation of titanium samples coated with silica hydrogel/chitosan hybrid, observed that the Si ions released from the matrix formed silanol groups and reacted with the nucleation sites of calcium phosphate minerals. The apatite nuclei, once formed grew spontaneously by reaction with [Ca.sup.2+] and P[O.sub.4.sup.2-] ions in the SBF solution. In the present study, since the composites contained silica particles, a similar explanation would justify the observation of higher bioactivity in the samples having higher PVA concentration due to an increase in the quantity of silanol groups.
[FIGURE 7 OMITTED]
Confirmation of bioactivity using Energy Dispersive X-ray spectroscopy
The elemental composition of the minerals formed on the composite was analyzed at different areas using Energy Dispersive X-ray spectroscopy (EDX). It was found that the major mineral components present were Ca, P, Na and Cl. The weight percentages of these minerals are listed in table 2. Although Si was also detected, it was not included in the table as it was considered to be a part of the composite. From the table it is evident that, in all the composites, excepting that of CP2 and CP3, there was significant formation of NaCl along with the formation of [Ca.sub.3]P[O.sub.4] minerals. In the case of system 1 composites, SP3, having the maximum wt% of SPEEK, exhibited the highest amount of [Ca.sub.3]P[O.sub.4] formation and the least amount of NaCl. This observation leads to the interpretation that while all the composites of system 1 exhibited bioactivity, SP3 showed more favourable mineralization process with regards to bone bonding applications.
On the other hand, in system 2, it was also observed that, while the amount of [Ca.sub.3]P[O.sub.4] formed in CP2 was the highest, CP3 showed very low levels of mineralization. Surprisingly, the Na and Cl elements were not detected in CP2 which suggested that concentration of chitosan influenced the mineralization process. Considering that chitosan, when used alone is weakly bioactive [41,42] and PVA by itself is not bioactive, the observation of good bioactivity in the case of CP2 suggested that, in the presence of good bioactive fillers such as silica and low levels of PVA (which would form O[H.sup.-] in aqueous solution), the nucleation of [Ca.sub.3]P[O.sub.4] was favoured over NaCl. From the above discussion, it can be inferred that amongst the composites studied in system 2, CP2 exhibited the most favourable bioactivity profile which could be of significance in the designing and development of bioactive scaffolds for orthopedic applications.
Evaluation of cytotoxicity by MTT method
The cytotoxicity studies performed showed interesting results. The percentage viability of the epithelial cells was calculated after noting the OD values of the control and the samples according to the method described in the materials and methods section. The results are displayed in fig. 8 in which a graph was plotted by taking the cell count of the control group as 100 percentage.
From the graph it is seen that in SP system, the cell growth was more than that observed in the control group (i.e., > 100%). This was significant as it implied that SPEEK was also biocompatible and that the blending of the two polymers (SPEEK and PMMA), in any weight ratio, did not affect the biocompatibility of the composites. It was also noted that the all the samples of the SP system exhibited almost equal levels of cytocompatibility. The cytocompatibility of SPEEK was further confirmed by evaluating the SPEEK sample alone. It was seen that SPEEK samples showed slightly greater values than the control groups. This result implied that PEEK, which is a popular orthopedic prosthetic polymer, did not exhibit cytotoxicity after sulphonation. In our previous study , we had reported that SPEEK samples showed very low adsorption of bovine serum albumin which could be related to the higher hydrophilicity subsequent to sulphonation. In the case of system II samples (CP), the biocompatibility seemed to be influenced by the concentration of PVA. Though in all the samples excellent cell viability values were obtained (between 72 and 90%), the higher concentration of chitosan could possibly lead to marginal lowering of the cell viabilities. This may be explained by considering the interaction between chitosan and PVA and also the pH of the medium. In samples containing higher concentrations of PVA, better interactions and blending between Cs and PVA occurred resulting in a decrease in the negative charge of the scaffold. Additionally, when the medium became slightly acidic, protonation of amine groups occurred which probably influenced the cytotoxicity results. Similar results were reported by H. S. Mansur et al  who additionally observed good adhesion and spreading morphology of the fibroblasts on the surface of chitosan/ PVA scaffolds. From the above discussion, it could be concluded that the sol-gel derived SPEEK/PMMA/Si and Cs/PVA/Si composites were well suited for application as biomaterials.
[FIGURE 8 OMITTED]
Sol-gel technique was successfully utilized to fabricate novel polymer composites of SPEEK/PMMA/Si and Cs/ PVA/Si as evidenced by FTIR and SEM analysis. The fabrication technique employed resulted in the formation of a porous composite along with surface microcracks which can be exploited for biomedical applications. The appearance of the microcracks can also be controlled by varying the polymer composition. The SPEEK/PMMA/ Si composites showed good biocompatibility and bioactivity. The Cs/PVA/Si composites showed excellent bioactivity with evidence of mineralization visible under SEM and EDX analysis. The interaction of PVA with chitosan was considered to be important in influencing the biocompatibility of the composite. The cytotoxicity results of SPEEK and SPEEK/PMMA/Si composites showed that SPEEK can be used either alone or by blending with other polymers to yield valuable biomaterials that are useful for applications involving drug delivery. This study conclusively proves that sol-gel is a versatile technique for the fabrication of polymer blend composites having immense applications in the field of biomaterials, especially for applications involving filling of bone defects where osseointegration of the prosthetic material is desired. These polymer composites could further be explored for controlled drug delivery and tissue engineering applications.
The authors are pleased to acknowledge the contribution of Dr. Kaveri of King's Institute for Preventive Medicine, Chennai, India who helped in the cytotoxicity studies. The authors also acknowledge the generous funding by ICMR vide their Letter No. 5/20/5(Bio)/09-NCD-1 and fellowship by AICTE vide their ref. no.--1-10/RID/NDF-PG(5)/2009-10.
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Kalambettu Aravind Bhat, Narayanaswamy Venkatesan Prabhu, Dharmalingam Sangeetha *
Department of Chemistry, Anna University, Chennai--600 025, India
* Corresponding author: Dr. D. Sangeethaemail@example.com
Received 10 February 2012; Accepted 20 February 2012; Available online 1 July 2012
Table 1: Weight ratios of the polymers in their blends. The codes SP and CP denote the SPEEK/PMMA and Cs/PVA blends respectively System Group code Weight ratio of polymers 1 SP1 1:1 SP2 1:2 SP3 2:1 2 CP1 1:1 CP2 1:2 CP3 2:1 Table 2: Elemental composition of the minerals formed on the surface of the composites as determined using EDX analysis Composite Wt% of Ca Wt% of P Wt% of Na Wt% of Cl SP1 0.15-1.05 0.02-0.16 0.5-4.46 0.93-7.0 SP2 0.39-0.80 0.13-0.31 0.06-2.26 0.96-4.06 SP3 0.34-1.28 0.07-0.33 0.98-1.97 0.88-1.96 CP1 0.10-0.74 0.03-0.60 0.57-2.67 1.19-6.08 CP2 2.72-7.26 1.41-4.12 -- -- CP3 0.09-0.23 0.12-0.34 0.02-0.24 0.04-0.31
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|Title Annotation:||Original Article|
|Author:||Bhat, Kalambettu Aravind; Venkatesan Prabhu, Narayanaswamy; Sangeetha, Dharmalingam|
|Publication:||Trends in Biomaterials and Artificial Organs|
|Date:||Jul 1, 2012|
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