Table of Contents  
Year : 2014  |  Volume : 5  |  Issue : 1  |  Page : 25-32  

Formulation and optimization of mucoadhesive microemulsion containing mirtazapine for intranasal delivery

Department of Pharmacy, Faculty of Technology and Engineering, The M.S. University of Baroda, Kalabhavan, Vadodara, Gujarat, India

Date of Web Publication25-Mar-2014

Correspondence Address:
Hetal P Thakkar
Department of Pharmacy, Faculty of Technology and Engineering, The M.S. University of Baroda, Kalabhavan, Vadodara - 390 001, Gujarat
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2229-5186.129333

Rights and Permissions

Background: Mirtazapine, an antidepressant drug, has absolute bioavailability of only 50% due to high first pass metabolism. Aim: The purpose of this study was to develop and optimize mucoadhesive microemulsion containing mirtazapine for intranasal delivery. Materials and Methods: Based on solubility study, Capmul Medium chain Monoglyceride, Tween 80 and polyethylene glycol (PEG) 400 were selected as oil, surfactant and co surfactant respectively. Microemulsions were prepared using water titration method. 3:1% w/w ratio (Tween 80: PEG 400) was selected for formulation development. The prepared microemulsions were optimized for globule size, zeta potential, % transmittance and polydispersity index. The optimized batch was further characterized for % drug content, conductivity and transmission electron microscopy. Results and Conclusion: All the parameters showed the suitability of microemulsion of mirtazapine for intranasal delivery. Chitosan (0.5% w/w) was used as a polymer for the preparation of mucoadhesive microemulsion to enhance the retention time in the nasal mucosa. Results of nasal toxicity study using excised sheep nasal mucosa showed comparatively no damage to epithelium and so formulation was considered safe for nasal administration. mirtazapine mucoadhesive microemulsion showed the highest percentage of diffusion (57.11 ± 0.710%) after 210 min during in-vitro drug diffusion study through sheep nasal mucosa, followed by mirtazapine microemulsion (46.08 ± 0.674%) and finally by mirtazapine solution (17.63 ± 0.612%).

Keywords: Intranasal, microemulsion, mirtazapine, optimization

How to cite this article:
Thakkar HP, Patel AA, Chauhan NP. Formulation and optimization of mucoadhesive microemulsion containing mirtazapine for intranasal delivery. Chron Young Sci 2014;5:25-32

How to cite this URL:
Thakkar HP, Patel AA, Chauhan NP. Formulation and optimization of mucoadhesive microemulsion containing mirtazapine for intranasal delivery. Chron Young Sci [serial online] 2014 [cited 2020 Jan 29];5:25-32. Available from:

   Introduction Top

Anxiety and depression are the growing problems in many nations of the world. Generalized anxiety disorder is characterized by excessive, exaggerated anxiety and worry about everyday life events with no obvious reasons while depression is a state of low mood and aversion to activity that can affect a person's thoughts, behavior, feelings and physical well-being. All over the world there are 40 crore patients living with depression indicating its global prevalence. [1]

The treatment of central nervous system (CNS) disorders is challenging because of a variety of formidable obstacles for effective and persistent delivery of drugs. Even though the drugs used for the treatment of CNS disorders are potent, their clinical failure is often not due to lack of drug efficacy but mainly due to shortcomings in the drug delivery approach. However, potent the drug may be, but if it cannot cross the blood brain barrier and reach the CNS in order to elicit its pharmacological action, it is ineffective. [2],[3] Hence, scientists are exploring the novel approaches so that delivery of the drugs can be enhanced and/or restricted to the brain and CNS.

Intranasal drug delivery is one of the focused delivery options for brain targeting as brain and nose compartments are connected to each other through olfactory/trigeminal route via peripheral circulation. [4] Intranasal administration delivers drug directly to the brain circumventing the blood brain barrier and reduces drug distribution to the non-targeted sites. [5],[6] This may result in reduction in dose, systemic dilution and first pass metabolism of the drug. [7] Nasal delivery route is convenient, patient friendly and also prevents the risk of the gastrointestinal tract irritation. [8] Direct nose to brain transport results in rapid and/or higher uptake in the brain, which proves to be an alternative option of self-medication in the management of emergencies. [4]

Conventionally drugs were administered through intranasal route in the form of solutions, suspensions, gels, emulsions, powders etc. Such conventional dosage forms are having some disadvantages such as lack of dose precision, high particle size, high viscosity, lack of drug stability, solubility problem due to lipophilicity of drug etc. Some novel formulations such as microspheres, nanoparticles are also explored as drug delivery system for intranasal delivery. [9] However, their toxicity/irritancy on the nasal mucosa cells due to the presence of a variety of polymers/excipients is a major concern. Microemulsion is one such novel formulation which is optically isotropic and thermodynamically stable system composed of oil, water, surfactant (and/or co surfactant). [10] Microemulsions offer several advantages like high solubilization of lipophilic drugs, stability, ease of preparation and stabilization of hydrolytically susceptible compounds. Microemulsions provide a large surface area for better absorption of drugs due to smaller globule size. Various drugs such as Sumatriptan, [11] Zolmitriptan, [12] Cabergoline, [13] Clonazepam, [14] Nimodipine, [15] Tacrine, [16] and Diazepam [17] have been successfully delivered through nasal route in the form of microemulsion and it resulted in improved drug absorption. In order to formulate a nasal formulation with desirable performance, it is advisable to focus on maximizing the residence time in the nasal mucosa and thus ensuring efficient absorption of drug. [18] Use of mucoadhesive polymers in the nasal formulations is expected to increase the residence time and thereby enhance the absorption of the drug.

Mirtazapine is an antidepressant drug used for the treatment of moderate to severe depression. It is the only tetracyclic antidepressant that has been approved by the Food and drug administration to treat depression and anxiety. Mirtazapine is a potent antagonist at postsynaptic 5-HT2 and 5-HT3 (serotonergic) and central noradrenergic receptors and acts by increasing central noradrenergic and serotonergic (5-HT1) neurotransmission. Absolute bioavailability of mirtazapine is only 50% due to high first-pass metabolism. Common side-effects of mirtazapine include dizziness, blurred vision, sedation, dry mouth, constipation, nightmares, joint pain, muscle pain, back pain, etc. [19]

In the light of the above facts, an alternative drug delivery system is needed, which can selectively target the candidate drug to the brain. Due to preferential transport of the drug to the brain, intranasal delivery approach may be expected to reduce the wide distribution of the drug to the non-targeted sites such as systemic/peripheral circulation. The delivery system must be meticulously designed to provide rapid transport of the drug across nasal mucosa and longer residence time in the nasal cavity. The aim of this investigation was to deliver mirtazapine in the form of mucoadhesive microemulsion through nasal route for the effective treatment of CNS disorders like anxiety and depression. The research work was carried out with objectives in mind to provide rapid drug delivery to the brain, to reduce side-effects, maximize therapeutic index and to reduce the dose and dosing frequency.

   Materials and Methods Top


Mirtazapine was gifted by Sun Pharma Advanced Research Centre, Vadodara, India. Capmul MCM was gifted by Abitec Corporation Limited, Janesville, USA. Tween 80 and polyethylene glycol (PEG) 400 were purchased from the standard deviation (SD) fine chemicals. Mumbai, India. Chitosan was gifted by Indian Sea Foods Limited, Cochin, India. Other chemicals were of analytical grade and purchased from SD Fine chemicals, Mumbai, India.


Solubility determination

Solubility of mirtazapine was determined in various oils, surfactants and cosurfactants. Drug was added in excess to different oils, surfactants and co surfactants and shaken using mechanical shaker (Model: RIS 24BL, Make: Remi Equipments, Mumbai, India) for 72 h. The samples were then centrifuged at 8000 revolutions per minute (RPM) (Model: R4C, Make: Remi Equipments, Mumbai, India) for 10 min and the drug content in the supernatant was analyzed using ultraviolet (UV) spectrophotometric method (UV 1700, Shimadzu, Japan) at λmax of 292 nm after suitable dilution with methanol. [20]

Construction of the phase diagram

The phase diagrams with different ratios of surfactant: Co surfactant (1:1, 2:1, 3:1, 4:1% w/w) with selected oil were constructed to explore the microemulsion region. The area of the monophasic region was used as a tool for the selection of suitable surfactant and co surfactant mixture. Aliquots of each surfactant and co surfactant mixture (Smix) were mixed with oil at ambient temperature. For each phase diagram, the ratio of oil to the Smix was varied as 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9 (%w/w). Water was added drop wise to each oil-Smix mixture under constant stirring. After equilibrium, the samples were visually checked and determined as being clear microemulsions. Phase diagrams were constructed using Chemix software (Chemix school, version 3.6).

Preparation of microemulsion

Based on the phase diagram, the optimum Smix ratio was selected and the drug loaded microemulsions were prepared by dissolving the drug (26 mg) in the oil-Smix mixture, then titrated with water on the magnetic stirrer (Remi instrument, Mumbai, India) at 150 RPM for 10 min.

Optimization of parameters

Different batches of microemulsions were prepared by water titration method. The prepared batches were evaluated for zeta potential, globule size, polydispersity index (PDI) and % Transmittance. Optimized batch was selected on the basis of lower zeta potential, globule size and PDI and higher % transmittance. [21]

Preparation of mucoadhesive microemulsion

The mucoadhesive microemulsions were prepared by first preparing a microemulsion of the drug using minimum volume of external phase and then adding required volume of chitosan solution (1% w/w chitosan in acetate buffer pH 5) such that the final concentration of chitosan was 0.5% w/w in the formulation.

Characterization of microemulsion

Globule size determination

The globule size of mirtazapine microemulsion (MME) and mucoadhesive microemulsion was determined using photon correlation spectroscopy (Model: Nano zs, Malvern instruments, UK) at 633 nm. The globule size of microemulsion was determined after diluting it 10 times with distilled water.

Zeta potential determination

Malvern Zetasizer Nano zs was used to measure the zeta potential of the globules based on the electrophoresis and electrical conductivity of the formed microemulsion. The electrophoretic mobility (μm/s) of the particles was converted to the zeta potential by in-built software based on Helmholtz-Smoluchowski equation. Measurements were performed using small volume disposable zeta cell. Zeta potential was studied and recorded for MME and mirtazapine mucoadhesive microemulsion (MMME).

% Transmittance

The % transmittance of the microemulsion was checked against distilled water using UV-Visible spectrophotometer at λmax of 633 nm.

% Drug content

A definite volume of formulation, i.e., MME or MMME was taken in a 10 ml volumetric flask and diluted with methanol. The resultant solution was sonicated for 3 min at ambient temperature and the absorbance of the resultant solution was measured at λmax of 292 nm against placebo formulation treated in the similar manner as blank.

Transmission electron microscopy (TEM)

To perform TEM observations, a drop of diluted (1 in 10 dilution) microemulsion was directly deposited on the copper grid and observed after drying. The images were taken with Tecnai 200 charge coupled device camera operating at 200 kV and capable of point to point resolution.

Nasal toxicity study

Freshly excised sheep nasal mucosa was collected from a local slaughter house and was kept in phosphate buffer saline pH 6.4 for 15 min. Sheep nasal mucosa pieces having uniform thickness of 0.2 mm were taken. Mucosa treated with phosphate buffer pH 6.4 was taken as a negative control and the mucosa treated with isopropyl alcohol was taken as a positive control. Other two mucosae were treated with microemulsion and mucoadhesive microemulsion for 1 h separately. After 1 h, the both the mucosae were rinsed with phosphate buffer pH 6.4 and all of them were carried to the pathological laboratory in 10% formalin for the preparation of pathological slides. The sectioned tissue was then stained with hematoxylin and eosin. The prepared pathological slides were studied under an optical microscope at ×10 resolution for any sign of toxicity and the images were taken.

In-vitro drug release study

The in-vitro drug diffusion study was performed using Franz diffusion cell of diameter 10 mm mounted with excised sheep nasal mucosa [22],[23] of thickness (height) 0.2 mm. A total volume of 0.8 ml mirtazapine solution (MS) (MS in acetate buffer pH 5); MME and MMME were placed in the donor compartment along with 1.2 ml diffusion media. Receptor compartment contained 20 ml of acetate buffer pH 5 stirred with Teflon coated magnetic stirrer (120 RPM). A total volume of 1 ml sample was withdrawn from the receptor compartment at predetermined time intervals and analyzed using UV spectrophotometric method. [20] Each sample removed was replaced with an equal volume of acetate buffer pH 5. Each study was carried out for a period of 3.5 h and in triplicate. The mean cumulative values for percentage drug diffused and diffusion coefficients for mirtazapine were calculated for the formulations [Table 1].
Table 1: In-vitro diffusion study of mirtazapine formulations

Click here to view

   Results and Discussion Top

Solubility study

Microemulsions are essentially clear systems and hence solubility of drug in all the components is necessary. The volume capacity of the nasal cavity is 7.5 mL per each nostril in humans. However, 150 μL per nostril is the maximum possible volume for convenient nasal administration. [23],[24],[25] Hence, it is necessary that the effective dose of the drug should be delivered within minimum volume of formulation. Hence, solubility study of mirtazapine was carried out in number of solvents which are generally regarded as safe (GRAS listed) for nasal administration. Based on solubility data, Capmul MCM was selected as oil phase, Tween 80 as surfactant and PEG 400 as cosurfactant as these components showed better solubility for mirtazapine. Results are tabulated in [Table 2].
Table 2: Solubility data of mirtazapine in different solvents

Click here to view

Psuedo ternary phase diagram

In microemulsion system surfactant and co surfactant get preferentially adsorbed at the interface, reducing the interfacial energy as well as providing a mechanical barrier to coalescence. The selection of oil and surfactant and the mixing ratio of oil to S/CoS, play an important role in the formation of the microemulsion. This can be ascertained by pseudo ternary phase diagram as it differentiates the microemulsion region from that of macroemulsion region. By preparing phase diagram, microemulsion region can be obtained. Phase diagrams with different weight ratios of surfactant: Co surfactant (1:1, 2:1, 3:1, 4:1%w/w) were prepared and depending upon the microemulsion region the surfactant to co surfactant ratio was selected as 3:1 for further formulation development. The phase diagram is shown in [Figure 1].
Figure 1:

Click here to view

Preparation and optimization of microemulsion

Numbers of batches were prepared for the optimization of the microemulsion. The % oil and % Smix were varied and different batches were prepared. The prepared microemulsion batches were analyzed for zeta potential, globule size, PDI and % transmittance. The formulation, which had lesser globule size, PDI and zeta potential and higher % transmittance from among all the batches, was selected as an optimum batch. The reason for selecting lower globule size was that it increases the permeation through the nasal mucosa as well as lower globule size can provide enhanced interfacial area for drug release and absorption. [4],[21] Lesser the PDI, more uniform the formulation is considered. [21] Lesser the zeta potential toward negative side (near to-30 mV), the more physical stability of the formulation one can expect. [21],[26],[27] In the same way, formulation with higher % transmittance was selected as it is indicative of isotropic and clear formulation. The result of the all the prepared batches is recorded in [Table 3]. From the Table, it shows that Microemulsion batch-7 was considered as optimized batch. It is having composition of 7% Capmul MCM, 45% Smix and 48% water. Mucoadhesive microemulsion was prepared with the same composition having 0.5% chitosan as mucoadhesive polymer. The detailed composition of optimized batch of MME and mucoadhesive microemulsion is shown in [Table 4].
Table 3: Results of globule size, PDI, zeta potential and % transmittance

Click here to view
Table 4: Optimized batch of microemulsion and mucoadhesive microemulsion

Click here to view

Characterization of microemulsion

The drug loaded microemulsion and mucoadhesive microemulsion were prepared and characterized for their pH, globule size, zeta potential, conductivity, % transmittance, % drug content and the results are recorded in [Table 5]. As per the result of qualitative and conductivity tests, prepared microemulsion were found to be o/w type. Globule size of prepared microemulsion was found to be in nano range (below 50 nm). Nano globule size can help in enhanced permeation through nasal mucosa as well as result in enhanced interfacial area for drug release and absorption. The PDI is the measure of uniformity of the formulation. Less than 1 and near to 0.1 PDI is desirable for the formulation. Both microemulsion and mucoadhesive microemulsion showed PDI less than 1 and hence can be considered as uniform formulation. The zeta potential was found to be on the negative side for MME therefore the physical stability of the formulation on storage can be expected. For mucoadhesive microemulsion zeta potential was towards positive side because of presence of mucoadhesive polymer chitosan. The formulations are not expected to pose any problem due to electrostatic interaction between the microemulsion and nasal mucosa on intranasal administration. The % drug content was more than 99% for both microemulsion and mucoadhesive microemulsion, which indicates very high drug entrapment efficiency of the system. More than 99% transmittance indicated that the microemulsion is optically clear and isotropic system. TEM image of the MME is shown in [Figure 2]. The globule size was found to be 13.91 nm, which was in correlation with the globule size obtained by zetasizer.
Figure 2: Transmission electron microscopy image of mirtazapine microemulsion

Click here to view
Table 5: Characterization of microemulsion

Click here to view

Nasal toxicity study

The prepared mirtazapine formulations were subjected to nasal toxicity study to evaluate the safety of the ingredients used in the formulation. The optical microscopy images of nasal mucosa treated with mirtazapine formulations are shown in [Figure 3]. The nasal mucosa treated with isopropyl alcohol (mucociliary toxic agent) showed complete destruction of epithelial layer while nasal mucosa treated with microemulsion and mucoadhesive microemulsion were found to be intact without any damage to the epithelial layer. Thus prepared formulations were found to be safe on nasal mucosa. However, further toxicity studies have to be conducted prior to clinical application of the prepared formulations.
Figure 3:

Click here to view

In-vitro drug diffusion study

The prepared formulations of mirtazapine were subjected to in-vitro drug diffusion studies through excised sheep nasal mucosa for 210 min. The % cumulative drug diffused across nasal mucosa from the formulations were calculated and recorded in [Table 1]. The MMME showed higher % drug release [Figure 4] as compared to MME, which was reflected in higher diffusion coefficient value than MME. This may be explained by bio-adhesion and absorption enhancement property of chitosan across the mucosal membrane by opening tight epithelial junctions of the mucosal membranes like nasal membrane and although, MS showed lowest % of drug diffused as compared to MME and MMME because of lesser nasal retention time of MS.
Figure 4: % drug diffused versus time

Click here to view

   Results and Conclusion Top

Microemulsion of mirtazapine was prepared and optimized by using in-vitro parameters like particle size, PDI, zeta potential, pH, conductivity, % drug content. Optimal microemulsion contains Capmul MCM as oil phase, Tween 80 as a surfactant and PEG 400 as co surfactant. The % weight ratio of surfactant to co surfactant was selected as 3:1. The developed optimal microemulsion containing mirtazapine had globule size 12.3 nm, PDI 0.214, zeta potential − 16.9 mV, % transmittance 99.93%. Mucoadhesive microemulsion was also developed using 0.5% chitosan. Nasal toxicity study was carried out in an excised sheep nasal mucosa to evaluate the effect of microemulsion components on nasal mucosa and the results showed that prepared formulations were safer for nasal administration. Our study illustrated the potential use of microemulsion system to administer mirtazapine by nasal route.

   Acknowledgment Top

We are thankful to Sun Pharma Advanced Research Center, Vadodara, India for providing mirtazapine as a gift sample and Abitec Corporation, USA for providing Capmul MCM for the project work.

   References Top

1.Available from: [Last accessed on 2011 Jan 02].  Back to cited text no. 1
2.Löscher W, Potschka H. Role of drug efflux transporters in the brain for drug disposition and treatment of brain diseases. Prog Neurobiol 2005;76:22-76.  Back to cited text no. 2
3.Misra A, Ganesh S, Shahiwala A, Shah SP. Drug delivery to the central nervous system: A review. J Pharm Pharm Sci 2003;6:252-73.  Back to cited text no. 3
4.Vyas TK, Shahiwala A, Marathe S, Misra A. Intranasal drug delivery for brain targeting. Curr Drug Deliv 2005;2:165-75.  Back to cited text no. 4
5.Illum L. Transport of drugs from the nasal cavity to the central nervous system. Eur J Pharm Sci 2000;11:1-18.  Back to cited text no. 5
6.Ugwoke MI, Verbeke N, Kinget R. The biopharmaceutical aspects of nasal mucoadhesive drug delivery. J Pharm Pharmacol 2001;53:3-21.  Back to cited text no. 6
7.Pires A, Fortuna A, Alves G, Falcão A. Intranasal drug delivery: How, why and what for? J Pharm Pharm Sci 2009;12:288-311.  Back to cited text no. 7
8.Wermeling DP, Miller JL, Rudy AC. Systematic intranasal drug delivery: Concepts and applications. Drug Deliv Technol 2002;2.  Back to cited text no. 8
9.Joshi HM, Bhumkar DR, Joshi K, Pokharkar V, Sastry M. Gold nanoparticles as carriers for efficient transmucosal insulin delivery. Langmuir 2006;22:300-5.  Back to cited text no. 9
10.Mehta SK, Kaur G, Bhasin KK. Incorporation of antitubercular drug isoniazid in pharmaceutically accepted microemulsion: Effect on microstructure and physical parameters. Pharm Res 2008;25:227-36.  Back to cited text no. 10
11.Vyas TK, Babbar AK, Sharma RK, Singh S, Misra A. Preliminary brain-targeting studies on intranasal mucoadhesive microemulsions of sumatriptan. AAPS PharmSciTech 2006;7:E8.  Back to cited text no. 11
12.Vyas TK, Babbar AK, Sharma RK, Misra A. Intranasal mucoadhesive microemulsions of zolmitriptan: Preliminary studies on brain-targeting. J Drug Target 2005;13:317-24.  Back to cited text no. 12
13.Sharma G, Mishra AK, Mishra P, Misra A. Intranasal cabergoline: Pharmacokinetic and pharmacodynamic studies. AAPS PharmSciTech 2009;10:1321-30.  Back to cited text no. 13
14.Vyas TK, Babbar AK, Sharma RK, Singh S, Misra A. Intranasal mucoadhesive microemulsions of clonazepam: Preliminary studies on brain targeting. J Pharm Sci 2006;95:570-80.  Back to cited text no. 14
15.Zhang Q, Jiang X, Jiang W, Lu W, Su L, Shi Z. Preparation of nimodipine-loaded microemulsion for intranasal delivery and evaluation on the targeting efficiency to the brain. Int J Pharm 2004;275:85-96.  Back to cited text no. 15
16.Jogani VV, Shah PJ, Mishra P, Mishra AK, Misra AR. Intranasal mucoadhesive microemulsion of tacrine to improve brain targeting. Alzheimer Dis Assoc Disord 2008;22:116-24.  Back to cited text no. 16
17.Li L, Nandi I, Kim KH. Development of an ethyl laurate-based microemulsion for rapid-onset intranasal delivery of diazepam. Int J Pharm 2002;237:77-85.  Back to cited text no. 17
18.Illum L. Nasal drug delivery - Possibilities, problems and solutions. J Control Release 2003;87:187-98.  Back to cited text no. 18
19.Available from: [Last accessed on 2011 Mar 02].  Back to cited text no. 19
20.Karaºen N, Altinöz S. Determination of mirtazapine in tablets by UV spectrophotometric and derivative spectrophotometric methods. J Pharm Biomed Anal 2000;24:11-7.  Back to cited text no. 20
21.Patel ZB, Patel KS, Shah AS, Surti NI. Preparation and optimization of microemulsion of rosuvastatin calcium. J Pharm Bioallied Sci 2012;4:S118-9.  Back to cited text no. 21
22.Willimann H, Walde P, Luisi PL, Gazzaniga A, Stroppolo F. Lecithin organogel as matrix for transdermal transport of drugs. J Pharm Sci 1992;81:871-4.  Back to cited text no. 22
23.Du G, Gao Y, Nie S, Pan W. The permeation of nalmefene hydrochloride across different regions of ovine nasal mucosa. Chem Pharm Bull (Tokyo) 2006;54:1722-4.  Back to cited text no. 23
24.Pires A, Fortuna A, Alves G, Falcão A. Intranasal drug delivery: How, why and what for? J Pharm Pharm Sci 2009;12:288-311.  Back to cited text no. 24
25.Costantino HR, Illum L, Brandt G, Johnson PH, Quay SC. Intranasal delivery: Physicochemical and therapeutic aspects. Int J Pharm 2007; 337:1-24.  Back to cited text no. 25
26.Available from: [Last accessed on 2011 Jan 05].  Back to cited text no. 26
27.Kaur P, Kim K. Pharmacokinetics and brain uptake of diazepam after intravenous and intranasal administration in rats and rabbits. Int J Pharm 2008;364:27-35.  Back to cited text no. 27


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

  In this article
    Materials and Me...
    Results and Disc...
    Results and Conc...
    Article Figures
    Article Tables

 Article Access Statistics
    PDF Downloaded474    
    Comments [Add]    

Recommend this journal