- Email: [email protected]
Release of doxycycline through cellulose acetate symmetric and asymmetric membranes produced from recycled agroindustrial residue: Sugarcane bagasse
Industrial Crops and Products 33 (2011) 566–571
Contents lists available at ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Release of doxycycline through cellulose acetate symmetric and asymmetric membranes produced from recycled agroindustrial residue: Sugarcane bagasse Guimes Rodrigues Filho a,∗ , Sabrina Dias Ribeiro a , Carla da Silva Meireles a , Leandro Gustavo da Silva a , Reinaldo Ruggiero a , Moacir Fernandes Ferreira Junior a , Daniel Alves Cerqueira b , Rosana Maria Nascimento de Assunc¸ão c , Mara Zeni d , Patricia Polleto d a
Chemistry Institute of the Federal University of Uberlandia, Av. João Naves de Ávila 2121, CEP 38400-902, Cx. Postal 593, Uberlândia, Minas Gerais, Brazil Institute of Environmental Sciences and Sustainable Development, Federal University of Bahia (ICADS/UFBA), Barreira, BA, Brazil c College of Integrated Sciences, Federal University of Uberlândia, Ituiutaba, Minas Gerais, Brazil d Department of Physical and Chemistry, Federal University of Caxias do Sul (UCS), Caxias do Sul, RS, Brazil b
a r t i c l e
i n f o
Article history: Received 16 September 2010 Received in revised form 25 October 2010 Accepted 30 October 2010 Available online 11 January 2011 Keywords: Controlled-release Doxycycline Cellulose triacetate Sugarcane bagasse Symmetric and asymmetric membranes
a b s t r a c t Cellulose acetate is one of the components employed in drug controlled-release systems in the form of membranes. The aim of this study was to examine the controlled-release of doxycycline employing cellulose acetate symmetric and asymmetric membranes as matrices. The cellulose triacetate was produced from sugarcane bagasse through a homogeneous acetylation reaction, using acetic acid as the solvent, acetic anhydride as the acetylating agent and sulfuric acid as the catalyst. The viscosity average molecular weight of the cellulose acetate produced was 39,000 g mol−1 . The symmetric membranes were produced using a system solvent of dichloromethane/ethanol (9:1, v/v) and the asymmetric membranes were produced from the same solvent system and 10% of water. For the formulation of both, 5% of doxycycline was used. The membranes were characterized by thermal analysis (DSC and TGA) and scanning electron microscopy SEM. The release of doxycycline through cellulose triacetate matrices was examined using spectrophotometric analysis in the ultraviolet–visible region, at 275 nm. The results revealed that asymmetric membranes release 80% of the drug in 100 min, while symmetric membranes release 14% of the drug during the same time interval. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Drug controlled-release technology represents one of science’s frontiers, which involves varied multidisciplinary aspects and presents a profound impact in almost all areas of specialization in medicine, such as cardiology, ophthalmology, endocrinology, oncology and dentistry. Controlled-release systems offer innumerable advantages when compared to other conventional drug administration systems, such as greater therapeutic efficacy, with progressive and controlled release of drug by means of matrix degradation and significant decrease in toxicity; and greater drug retention in the bloodstream. Physical phenomena as the dissolution and diffusion through polymeric matrices, as well as the chemical degradation of the matrices are very important for the system (Meier et al., 2004; Thombre et al., 1989). Drug delivery systems using membrane controlled diffusion are: membranes for transdermal delivery, coating films formed around a core contain-
∗ Corresponding author. Tel.: +55 34 3239 4174x201; fax: +55 34 3239 4208. E-mail addresses: guimes.rodriguesfi[email protected], [email protected] (G. Rodrigues Filho). 0926-6690/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2010.10.037
ing drug material, a polymeric matrix containing dispersed drug (Toledo et al., 2007). Cellulose acetate is one of the components employed in drug controlled-release systems in the form of membranes (Bhargava et al., 2007; Thombre et al., 1989). These can be classified symmetric or asymmetric, depending on the existence or not of a homogeneous structure throughout the membrane thickness (Borges et al., 2006). Symmetric membranes may be either porous, with evenly sized pores throughout its thickness, or dense, without pores. Membranes regarded as asymmetric may either have a porosity gradient along the structure or may be formed by a thin layer (skin) that can be dense or have small pores, responsible for the selectivity of the membrane, and that is supported by a porous layer that provides mechanical resistance (Borges et al., 2006). Symmetric membranes produced from cellulose acetate, obtained from sugarcane bagasse, have been previously reported in the literature as an alternative matrix for doxycycline controlledreleased. The main advantages of this system are the high doxycycline absorption and the absence of cytotoxic effects of the polymer matrix (Ribeiro et al., 2009; Rodrigues Filho et al., 2007, 2009). Besides high drug absorption by the polymeric matrix,
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
factors such as morphology and porosity play an important role in controlling the rate of drug permeation through a membrane. Previous studies by Ma and McHugh (2007) have demonstrated that drug molecules can be encapsulated into an asymmetric membrane, and that the morphology of the resulting membrane plays an important role in the release kinetics. Ma and McHugh (2007) produced drug encapsulated cellulose acetate membranes and showed that membrane morphologies, mass transfer paths, and drug–polymer interactions had a dramatic effect on the drug release kinetics. In this work, cellulose acetate was produced from sugarcane bagasse. Films containing the drug were produced from solution containing cellulose acetate, doxycycline, dichloromethane and water (asymmetric membranes) or without water (symmetric membranes), in order to obtain different morphologies. Cellulose acetate was characterized by the determination of its degree of substitution and molecular weight. Membranes were characterized according to their morphologies (scanning electronmicroscopy – SEM), by thermal analysis (differential scanning calorimetry – DSC/themogravimetric analysis – TGA) and doxycycline release.
567
glacial acetic acid was added to 2.0 g of purified sugarcane bagasse. The mixture was stirred for 30 min at room temperature. Subsequently, a solution containing 0.16 mL of H2 SO4 concentrated in 18.0 mL of glacial acetic acid was added, and the mixture was stirred for 25 min at room temperature. The mixture was filtered and the bagasse was put in a flask 64.0 mL of acetic anhydride was combined to the filtrate, stirred and returned to the initial flask with the bagasse. The solution was agitated for another 30 min and left at rest. After 14 h, the solution was filtered through a funnel equipped with a porous plate, with the Kitasato flask containing a certain amount of distilled water for the precipitate to form. The mixture was vacuum filtered, washed with distilled water, and the material was neutralized with a 10% sodium bicarbonate solution. The material was oven dried for 2 h at 70 ◦ C. 2.4. Degree of substitution (DS) The degree of substitution was determined by a saponification reaction as described in Rodrigues Filho et al. (2000). 2.5. Viscosity average molecular weight
2. Experimental 2.1. Purification of sugarcane bagasse The purification is based in the oxidation of lignin. In this case, the sugarcane bagasse reaction with nitric acid in alcoholic solution oxidizes lignin, leading to its fragmentation and dissolution in the reaction medium (Sobolev, 1960). Sugarcane bagasse purification was conducted through a modification in the methodology described in Rodrigues Filho et al. (2000), explained as follows: 10.0 g of washed and ground bagasse was placed in a round bottomed flask and refluxed with three successive portions of a 20/80 (v/v) mixture of nitric acid and ethanol. The reactional solution was replaced every hour, and the bagasse was washed before returning to reflux. After reflux, the mixture was washed with distilled water until the solution left from the wash was clear, followed by the addition of 40.0 mL of a 1.0 mol L−1 sodium hydroxide solution. After 24 h, the bagasse was washed and neutralized with a 10% acetic acid solution and oven dried at 105 ◦ C for 3 h. Once dry, the bagasse was triturated in a blender. 2.2. Klason lignin
The molecular weight was calculated by viscometry using the single point methodology as presented in Cerqueira et al. (2007). The solvent used for viscosity measurements was the system dichloromethane/ethanol (8/2, v/v), and the viscosity average molecular weight was determined through the Mark–Houwink–Sakurada equation (Eq. (1)): [] = kMva
(1)
where k and a are constants related to the type of polymer, solvent and temperature, [] is the intrinsic viscosity and Mv is the viscosity average molecular weight. For the solvent system used, k equals 13.9 × 10−3 mL g−1 and the value of the constant a is 0.834 (Knaus and Bauer-Heim, 2003). 2.6. Production of membranes with the incorporation of doxycycline The symmetric and asymmetric membranes were produced by using a modification of the procedure described in Toledo et al. (2007): cellulose triacetate (CTA) solutions, containing 5% (w/w) of doxycycline (DOX) and a mixture of dichloromethane/methanol (9:1, v/v) were employed to produce symmetric membranes. As for asymmetric membranes, 10% of water was added to be used as a pore-forming agent. The solution was cast on a glass plate using a casting knife with a 200 m gap. The evaporation time was approximately 10 min, enough for the membranes to detach from the glass plate.
1.00 g of washed, dried and ground sugarcane bagasse was weighed and put in a round bottomed flask, in which 30.0 mL of sulfuric acid (72%) was slowly added under agitation. The sample was kept for two hours in water bath at room temperature (25 ◦ C) under agitation. Then, 560.0 mL of distilled water was added to the contents of the round bottomed flask. The system was set to a temperature of 100 ◦ C under reflux, in order to avoid water loss as a result of evaporation, and consequently, alterations in concentration in the acid solution. Four hours later, the system was put to rest for sedimentation of the insoluble material. This material was then filtered through a funnel equipped with a porous plate, previously tared and washed with 500.0 mL of hot distilled water. Lastly, the system was oven dried at 105 ◦ C for 12 h, and weighed to quantify the insoluble residue and determine the Klason lignin (Vieira et al., 2007).
DSC experiments were performed on a Q-20, TA equipment. The heating rate was 10 ◦ C min−1 under a nitrogen flow of 50 cm3 min−1 . TGA experiments were performed in a DTG 60-H, Shimadzu. Ten milligrams of the samples were heated from room temperature to 600 ◦ C at a rate of 10 ◦ C min−1 under nitrogen atmosphere.
2.3. Homogeneous acetylation
2.8. SEM
The material used for acetylation consists in a purified bagasse with 87.59% cellulose and 12.00% hemicellulose. The acetylation reaction was performed in accordance to the methodology described in Cerqueira et al. (2007, 2009), as follows: 50.0 mL of
The samples were initially coated in gold, followed by the examination of the surface and cross-section morphology of the membranes on a scanning electron microscope, Shimadzu SSX-550 model, operating at 10 kV.
2.7. DSC and TGA experiments
568
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
Fig. 1. SEM of the cross-section asymmetric membrane (A), symmetric membrane (C) and surface asymmetric membrane (B), symmetric membrane (D) (1000×).
2.9. Release of doxycycline As for the release of the drug, a thermostatic bath MA 184 Marconi was used to ensure that the temperature of the experiment was kept at 36.5 ◦ C. A buffer solution with pH 7.4 was prepared. The dry membranes, with a superficial area of 2 cm2 , were initially weighed. The release of the drug in the solution was spectrophotometrically observed every hour by employing a spectrophotometer in the UV–visible region (UV-250 1 PC Shimadzu) at wavelength of 275 nm. The experiments were carried out in duplicate. 3. Results and discussion
effects: increase of coalescence rate, leading to the separation of phases for the formation of the matrix, and increase of non-solvent concentration in the polymeric structure, leading to the formation of pores. These characteristics classify this membrane as asymmetric. On cross-section C and surface D, a completely dense structure is observed, which characterizes the membrane as symmetric. In this case, the solution components on the formulation of the membranes are the solvent (dichloromethane), the polymer, and the drug. Once the solvent evaporates freely when a non-solvent is absent, static pores are not formed on the matrix, and dense layers are formed instead.
3.1. Material characterization The cellulose obtained from sugarcane bagasse presents a lignin content of 0.41%. After the acetylation reaction, the material was characterized as a cellulose triacetate with a degree of substitution of 2.80 ± 0.09 and a viscosity average molecular weights of 39,000 g mol−1 . 3.2. Microscopy of the membranes Fig. 1 shows the morphology found on the structures of the membranes, cross-section (A and C) and surface (B and D). On cross-section A, a porous structure with a non-uniform pore size arrangement and with regions of greater polymer density can be observed. The existence of pores can also be noted on the membrane surface (B). Such morphological observations can be directly associated to the processing of the membrane, as during its coalescence for the formation of the matrix from the solution (CTA/dichloromethane/water), the solvent (dichloromethane) and the non-solvent (water) evaporate at different rates. The solvent evaporates more rapidly than the non-solvent resulting in two main
3.3. Thermal analysis of symmetric and asymmetric membranes One fundamental aspect on the employment of thermal analysis when evaluating matrices for drug controlled-release is the fact that this method permits the investigation of thermal stability of both matrix and drug, as well as the nature of dispersion of the drug in the matrix. The thermal stability of the membranes was evaluated by thermogravimetric curves of weight loss, shown in Fig. 2. Generally, three main thermal events are observed for all membranes: desorption of water adsorbed in the structure of the cellulosic derivative (between 30 and 110 ◦ C), polymer deacetylation and depolymerization between 315 and 375 ◦ C, and pyrolitic decomposition of the cellulosic skeleton between 380 and 530 ◦ C (Shaikh et al., 2009). In membranes with doxycycline, slight shifts in the weight loss curves are observed when compared to membranes without the drug. The phenomenon is more significant in asymmetric membranes, in which a shift towards high temperatures is observed, indicating an increase in thermal stability in asymmetric membranes with DOX.
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
A symmetric membranes
3
100
A
CTA/dox CTA
2
60
Temperature [ºC]
40
Heat flow [W/g]
1
Weight Loss %
80
Weight Loss %
569
endo 20
0 -1 -2 -3 -4 -5
0 0
100
200
300
400
500
50
600
100
Temperature [°C] 2,0
B Asymmetric membranes
100
150
200
250
300
Temperature[ºC]
B
CTA/dox CTA
1,5 1,0
60
Heat flow [W/g]
Weight Loss %
Weight Loss %
80
40
Temperature [ºC]
endo
0,5 0,0 -0,5 -1,0 -1,5
20
-2,0 -2,5
0 0
100
200
300
400
500
600
Temperature [°C]
50
100
150
200
250
300
Temperature[ºC]
Fig. 2. Weight loss curve of symmetric CTA and CTA/DOX (A), and asymmetric CTA and CTA/DOX (B) membranes.
Fig. 3. DSC thermogram, 1st scan, of symmetric CTA and CTA/DOX (A) and asymmetric CTA and CTA/DOX (B) membranes.
Fig. 3 presents DSC thermograms for cellulose triacetate symmetric and asymmetric membranes with and without the incorporation of doxycycline. The thermograms presented are typical of cellulose triacetate, in which an endotherm between 75 and 85 ◦ C may be observed, along with desorption of water associated with the polymer structure (Shaikh et al., 2009). An exothermic peak at approximately 192 ◦ C relative to the crystallization of the polymer during the scan (He et al., 2009; Kamide and Saito, 1985), and an endotherm at approximately 300 ◦ C due to CTA fusion (He et al., 2009; Kamide and Saito, 1985; Mark, 1998). Thermal degradation of cellulose acetate also starts near the temperature of 300 ◦ C. However, in TGA curves at a temperature of 300 ◦ C only about 4–5% of cellulose acetate weight is lost. That indicates the beginning of the thermal degradation process, but also indicates that the resulting peak is predominantly the result of fusion of crystals of the TAC, the final process being accompanied by thermal degradation of the polymer. Although the thermograms of all membranes present the same characteristics qualitatively, the difference between the values obtained concerning the enthalpy of fusion and the glass transition temperature, Tg , is clear, particularly in asymmetric membranes with DOX when compared to asymmetric membranes without the drug. Fig. 4 shows the second scan DSC thermogram for the determination of glass transition temperature in the membranes analyzed. According to Kamide and Saito (1985) cellulose acetate Tg is observed in the range from 170 ◦ C to 190 ◦ C. Regarding the sym-
metric membranes in Fig. 4(A), it is possible to observe a reduction in the value of Tg in the CTA/DOX membrane of approximately 2 ◦ C (176.45 ◦ C CTA and 174.25 ◦ C CTA/DOX). This variation is even more significant in asymmetric membranes (Fig. 4(B)), for which the reduction in Tg noted is approximately 7 ◦ C (174.18 ◦ C CTA and 167.00 ◦ C CTA/DOX). The decline in Tg shows that the presence of drug molecules favors an increase in mobility of segments of the macromolecule. The alterations in the values of glass transition temperature, Tg , with the addition of the drug indicate its interaction with the polymeric matrix. The fact that this phenomenon is more accentuated in asymmetric membranes is related to the existence of pores in the structure, which leads to the production of regions with lower polymeric density, and therefore allows, with the presence of the drug, segments of the chains to have greater mobility. Another aspect related to the processing and the presence of the drug is the change in the values of enthalpy of fusion. Asymmetric membranes without the drug had a more amorphous matrix than the symmetric membranes, as the enthalpy of fusion for the first is 9.70 J g−1 and 26.44 J g−1 for the later. When the drug is incorporated in the membranes some changes occur, such as alterations in the degree of order of the matrix. In symmetric membranes, changes are less significant when compared to the asymmetric membranes and they indicate the existence of interactions that result in a slight disorder in the system, once the enthalpy of fusion drops from 26.44 J g−1 to 22.40 J g−1 . In this case, the increase in
570
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
20
A 18
A
0,0 -0,2 -0,4 CTA/dox -0,6 CTA -0,8
doxycycline content released %
Heat Flow [W/g]
0,2
16 14 12 10 8 6 4 2
80
100
120
140
160
180
200
220
240
0
Temperature[ºC]
0
100
200
300
400
500
Time[min.] B 100
B
-0,5
-1,0
CTA
CTA/dox -1,5 50
100
150
200
250
Temperature[ºC] Fig. 4. DSC thermogram, 2nd scan, of symmetric CTA and CTA/DOX (A) and asymmetric CTA and CTA/DOX (B) membranes.
mobility is restricted to very small segments, generating just a slight disorder. In asymmetric membranes, however, the enthalpy of fusion of the matrix with the drug raises to 21.07 J g−1 , much greater than the value found for this membrane without the drug, 9.70 J g−1 . The increase in crystallinity of the matrix with the incorporated drug is the result of its interaction with polymeric chains. This fact corroborates the observations regarding the changes in Tg for this system, in which the drug acts as a modification agent of chain mobility, favoring an increase in crystallinity in the asymmetric membrane. Such increase in crystallinity in the asymmetric membrane with DOX leads to a greater thermal stability for this system, Fig. 3, when compared to the system without doxycycline. 3.4. Release of doxycycline Doxycycline is a water-soluble drug with high polarity due to the presence of amine, carbonyl and hydroxyl functional groups in its structure. Although interactions between the hydroxyl and acetyl groups from the cellulose triacetate with the drug exist, in experiments of drug controlled-release using buffered aqueous solutions, it is expected for the doxycycline to have greater affinity with the solution being released by the polymeric matrix. That is due to the release occurring as the solution comes into contact with the polymeric system, resulting in the relaxation of polymeric chains with volume expansion. In Fig. 5, kinetic curves of doxycycline release from symmetric and asymmetric membranes are presented.
doxycycline content released (%)
Heat flowr[W/g]
0,0 80
60
40
20
0 0
100
200
300
400
500
Time [min.] Fig. 5. Curve of doxycycline release from symmetric (A) and asymmetric (B) membranes.
The data regarding the release of doxycycline as a function of time, shown in Fig. 5, indicates the influence of the structure of the membrane in drug release. One may observe clearly that with the asymmetric membrane, a great quantity of drug incorporated to the matrix is released, reaching approximately 80% of doxycycline released in about 100 min of assay. This differs from what is observed with the symmetric membrane, through which only a small quantity of drug is released (∼14%). One of the aspects that explain the difference in the percentage of drug released for each one of the membranes is the existence of pores on the asymmetric membrane (Fig. 1(A) and (B)). The pores on the membrane surface control the transfer and facilitate the movement of the drug through the membrane. When the porous substructure is reached, it does not offer resistance to the flux of doxycycline. The diffusion of an active agent consists of a process of mass transfer of individual molecules which preferably occur through the amorphous regions of the polymer, where the chains are more disorderly set and the free volume is greater. The presence of pores augments the low polymer density regions, resulting in an increase in mobility of polymeric chains. Such enhancement in mobility favors drug transport and its consequent release. This fact was confirmed by the decrease in glass transition temperature, Tg , in asymmetric CTA/DOX membranes, observed in the DSC thermogram (Fig. 4(A) and (B)).
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
4. Conclusions Cellulose triacetate membranes produced from sugarcane bagasse can be employed for doxycycline controlled-release applications. The main factors influencing the total percentage of drug released are the drug–matrix interaction and the morphology of the membranes (symmetric and asymmetric). The drug interacts with the matrix and parts of it are retained as a result of these superficial interactions. This constitutes a prevailing factor for symmetric membranes, in which the absence of static pores is responsible for the low mobility of polymeric chains, significantly reducing the total amount of drug released. In asymmetric membranes, the presence of pores and regions of low polymer density allows an increase in mobility of polymeric chains and drug molecules, therefore increasing its release into the medium and reaching levels of approximately 80% of the drug incorporated to the membrane during its production. In symmetric membranes, the maximum quantity of drug released in the same time interval is 14%. Acknowledgements The authors acknowledge CNPq for project Casadinho UFU/UFG/UFMS (620181/2006-0), CAPES for the access to “Portal Periódicos”, and FAPEMIG for CEX-APQ-02356/08 project. Ribeiro thanks PIBIC/CNPq A-042/2009 for the scholarships. Meireles thanks CAPES for her PhD scholarship. References Bhargava, H.N., Garg, A., Gupta, M., 2007. Effect of formulation parameters on the release characteristics of propranolol from asymmetric membrane coated tablets. Eur. J. Pharm. Biopharm. 67, 725–731. Borges, C.P., Habert, A.C., Nobrega, R., 2006. Processos de separac¸ão por membranas, E-papers, Rio de Janeiro. Cerqueira, D.A., Rodrigues Filho, G., Meireles, C.S., 2007. Optimization of sugarcane bagasse cellulose acetylation. Carbohydr. Polym. 69, 579–582. Cerqueira, D.A., Valente, A.J.M., Rodrigues Filho, G., Burrows, H.D., 2009. Synthesis and properties of polyaniline–cellulose acetate blends: the use of sugarcane
571
bagasse waste and the effect of the substitution degree. Carbohydr. Polym. 78, 402–408. He, J., Zhang, M., Cui, S., Wang, S., 2009. High-quality cellulose triacetate prepared from bamboo dissolving pulp. J. Appl. Polym. Sci. 113, 456–465. Kamide, K., Saito, M., 1985. Thermal analysis of cellulose acetate solids with total degrees of substitution of 0.49, 1.75, 2.46 and 2.92. Polym. J. 17, 919–928. Knaus, S., Bauer-Heim, B., 2003. Synthesis and properties of anionic cellulose ethers: influence of functional groups and molecular weight on flowability of concrete. Carbohydr. Polym. 53, 383–394. Ma, D., McHugh, A.J., 2007. The interplay of phase inversion and membrane formation in the drug release characteristics of a membrane-based delivery system. J. Membr. Sci. 298, 156–168. Mark, J.E., 1998. Polymer Handbook Data, Online Version. Oxford University Press, Oxford. Meier, M.M., Kanis, L.A., Soldi, V., 2004. Characterization and drug-permeation profiles of microporous and dense cellulose acetate membranes: influence of plasticizer and poreforming agent. Int. J. Pharm. 278, 99–110. Ribeiro, S.D., Mundim, E.A., Silva, L.G., Ruggiero, R., Cerqueira, D.A., Meireles, C.S., Rodrigues Filho, G., 2009. Doxycycline release through membranes of cellulose triacetate obtained from chemical recycling of sugarcane bagasse. In: Proceedings of the 10th Congresso Brasileiro de Polímeros , Foz do Iguac¸u, Brazil. Rodrigues Filho, G., Cruz, S.F., Pasquini, D., Cerqueira, D.A., Prado, V.D., Assunc¸ão, R.M.N., 2000. Water flux through cellulose triacetate films produced from heterogeneous acetylation of sugar cane bagasse. J. Membr. Sci. 177, 225–231. Rodrigues Filho, G., Toledo, L.C., Cerqueira, D.A., Assunc¸ão, R.M.N., Meireles, C.S., Lugão, A.B., Rogero, S.O., Otaguro, H., 2007. Water flux, DSC, and cytotoxicity characterization of membranes of cellulose acetate produced from sugar cane bagasse, using PEG 600. Polym. Bull. 59, 73–81. Rodrigues Filho, G., Toledo, L.C., Silva, L.G., Assunc¸ão, R.M.N., Meireles, C.S., Cerqueira, D.A., Ruggiero, R., 2009. Membranes of cellulose triacetate produced from sugarcane bagasse cellulose as alternative matrices for doxycycline incorporation. J. Appl. Polym. Sci. 113, 3544–3549. Shaikh, H.M., Pandare, K.V., Nair, G., Varma, A.J., 2009. Utilization of sugarcane bagasse cellulose for producing cellulose acetates: novel use of residual hemicellulose as plasticizer. Carbohydr. Polym. 76, 23–29. Sobolev, I., 1960. Lignin model compounds. Nitric acid oxidation of 4Methylguaiacol. J. Org. Chem. 26, 5080–5085. Thombre, A.G., Zentner, G.M., Himmelstein, K.J., 1989. Mechanism of water transport in controlled porosity osmotic devices. J. Membr. Sci. 40, 279–310. Toledo, L.C., Silva, L.G., Rodrigues Filho, G., Ruggiero, R., Cerqueira, D.A., Assunc¸ão, R.M.N., Meireles, C.A., 2007. Incorporation of doxycycline in membranes of cellulose acetate (from sugar cane bagasse) produced with PEG 600 as additive. In: Proceedings of the 4th International Conference on Science and Technology of Composites Materials , Rio de Janeiro, Brazil. Vieira, R.G.P., Rodrigues Filho, G., Assunc¸ão, R.M.N., Meireles, C.S., Vieira, J.G., Oliveira, G.S., 2007. Synthesis and characterization of methylcellulose from sugar cane bagasse cellulose. Carbohydr. Polym. 67, 182–189.
Contents lists available at ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Release of doxycycline through cellulose acetate symmetric and asymmetric membranes produced from recycled agroindustrial residue: Sugarcane bagasse Guimes Rodrigues Filho a,∗ , Sabrina Dias Ribeiro a , Carla da Silva Meireles a , Leandro Gustavo da Silva a , Reinaldo Ruggiero a , Moacir Fernandes Ferreira Junior a , Daniel Alves Cerqueira b , Rosana Maria Nascimento de Assunc¸ão c , Mara Zeni d , Patricia Polleto d a
Chemistry Institute of the Federal University of Uberlandia, Av. João Naves de Ávila 2121, CEP 38400-902, Cx. Postal 593, Uberlândia, Minas Gerais, Brazil Institute of Environmental Sciences and Sustainable Development, Federal University of Bahia (ICADS/UFBA), Barreira, BA, Brazil c College of Integrated Sciences, Federal University of Uberlândia, Ituiutaba, Minas Gerais, Brazil d Department of Physical and Chemistry, Federal University of Caxias do Sul (UCS), Caxias do Sul, RS, Brazil b
a r t i c l e
i n f o
Article history: Received 16 September 2010 Received in revised form 25 October 2010 Accepted 30 October 2010 Available online 11 January 2011 Keywords: Controlled-release Doxycycline Cellulose triacetate Sugarcane bagasse Symmetric and asymmetric membranes
a b s t r a c t Cellulose acetate is one of the components employed in drug controlled-release systems in the form of membranes. The aim of this study was to examine the controlled-release of doxycycline employing cellulose acetate symmetric and asymmetric membranes as matrices. The cellulose triacetate was produced from sugarcane bagasse through a homogeneous acetylation reaction, using acetic acid as the solvent, acetic anhydride as the acetylating agent and sulfuric acid as the catalyst. The viscosity average molecular weight of the cellulose acetate produced was 39,000 g mol−1 . The symmetric membranes were produced using a system solvent of dichloromethane/ethanol (9:1, v/v) and the asymmetric membranes were produced from the same solvent system and 10% of water. For the formulation of both, 5% of doxycycline was used. The membranes were characterized by thermal analysis (DSC and TGA) and scanning electron microscopy SEM. The release of doxycycline through cellulose triacetate matrices was examined using spectrophotometric analysis in the ultraviolet–visible region, at 275 nm. The results revealed that asymmetric membranes release 80% of the drug in 100 min, while symmetric membranes release 14% of the drug during the same time interval. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Drug controlled-release technology represents one of science’s frontiers, which involves varied multidisciplinary aspects and presents a profound impact in almost all areas of specialization in medicine, such as cardiology, ophthalmology, endocrinology, oncology and dentistry. Controlled-release systems offer innumerable advantages when compared to other conventional drug administration systems, such as greater therapeutic efficacy, with progressive and controlled release of drug by means of matrix degradation and significant decrease in toxicity; and greater drug retention in the bloodstream. Physical phenomena as the dissolution and diffusion through polymeric matrices, as well as the chemical degradation of the matrices are very important for the system (Meier et al., 2004; Thombre et al., 1989). Drug delivery systems using membrane controlled diffusion are: membranes for transdermal delivery, coating films formed around a core contain-
∗ Corresponding author. Tel.: +55 34 3239 4174x201; fax: +55 34 3239 4208. E-mail addresses: guimes.rodriguesfi[email protected], [email protected] (G. Rodrigues Filho). 0926-6690/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2010.10.037
ing drug material, a polymeric matrix containing dispersed drug (Toledo et al., 2007). Cellulose acetate is one of the components employed in drug controlled-release systems in the form of membranes (Bhargava et al., 2007; Thombre et al., 1989). These can be classified symmetric or asymmetric, depending on the existence or not of a homogeneous structure throughout the membrane thickness (Borges et al., 2006). Symmetric membranes may be either porous, with evenly sized pores throughout its thickness, or dense, without pores. Membranes regarded as asymmetric may either have a porosity gradient along the structure or may be formed by a thin layer (skin) that can be dense or have small pores, responsible for the selectivity of the membrane, and that is supported by a porous layer that provides mechanical resistance (Borges et al., 2006). Symmetric membranes produced from cellulose acetate, obtained from sugarcane bagasse, have been previously reported in the literature as an alternative matrix for doxycycline controlledreleased. The main advantages of this system are the high doxycycline absorption and the absence of cytotoxic effects of the polymer matrix (Ribeiro et al., 2009; Rodrigues Filho et al., 2007, 2009). Besides high drug absorption by the polymeric matrix,
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
factors such as morphology and porosity play an important role in controlling the rate of drug permeation through a membrane. Previous studies by Ma and McHugh (2007) have demonstrated that drug molecules can be encapsulated into an asymmetric membrane, and that the morphology of the resulting membrane plays an important role in the release kinetics. Ma and McHugh (2007) produced drug encapsulated cellulose acetate membranes and showed that membrane morphologies, mass transfer paths, and drug–polymer interactions had a dramatic effect on the drug release kinetics. In this work, cellulose acetate was produced from sugarcane bagasse. Films containing the drug were produced from solution containing cellulose acetate, doxycycline, dichloromethane and water (asymmetric membranes) or without water (symmetric membranes), in order to obtain different morphologies. Cellulose acetate was characterized by the determination of its degree of substitution and molecular weight. Membranes were characterized according to their morphologies (scanning electronmicroscopy – SEM), by thermal analysis (differential scanning calorimetry – DSC/themogravimetric analysis – TGA) and doxycycline release.
567
glacial acetic acid was added to 2.0 g of purified sugarcane bagasse. The mixture was stirred for 30 min at room temperature. Subsequently, a solution containing 0.16 mL of H2 SO4 concentrated in 18.0 mL of glacial acetic acid was added, and the mixture was stirred for 25 min at room temperature. The mixture was filtered and the bagasse was put in a flask 64.0 mL of acetic anhydride was combined to the filtrate, stirred and returned to the initial flask with the bagasse. The solution was agitated for another 30 min and left at rest. After 14 h, the solution was filtered through a funnel equipped with a porous plate, with the Kitasato flask containing a certain amount of distilled water for the precipitate to form. The mixture was vacuum filtered, washed with distilled water, and the material was neutralized with a 10% sodium bicarbonate solution. The material was oven dried for 2 h at 70 ◦ C. 2.4. Degree of substitution (DS) The degree of substitution was determined by a saponification reaction as described in Rodrigues Filho et al. (2000). 2.5. Viscosity average molecular weight
2. Experimental 2.1. Purification of sugarcane bagasse The purification is based in the oxidation of lignin. In this case, the sugarcane bagasse reaction with nitric acid in alcoholic solution oxidizes lignin, leading to its fragmentation and dissolution in the reaction medium (Sobolev, 1960). Sugarcane bagasse purification was conducted through a modification in the methodology described in Rodrigues Filho et al. (2000), explained as follows: 10.0 g of washed and ground bagasse was placed in a round bottomed flask and refluxed with three successive portions of a 20/80 (v/v) mixture of nitric acid and ethanol. The reactional solution was replaced every hour, and the bagasse was washed before returning to reflux. After reflux, the mixture was washed with distilled water until the solution left from the wash was clear, followed by the addition of 40.0 mL of a 1.0 mol L−1 sodium hydroxide solution. After 24 h, the bagasse was washed and neutralized with a 10% acetic acid solution and oven dried at 105 ◦ C for 3 h. Once dry, the bagasse was triturated in a blender. 2.2. Klason lignin
The molecular weight was calculated by viscometry using the single point methodology as presented in Cerqueira et al. (2007). The solvent used for viscosity measurements was the system dichloromethane/ethanol (8/2, v/v), and the viscosity average molecular weight was determined through the Mark–Houwink–Sakurada equation (Eq. (1)): [] = kMva
(1)
where k and a are constants related to the type of polymer, solvent and temperature, [] is the intrinsic viscosity and Mv is the viscosity average molecular weight. For the solvent system used, k equals 13.9 × 10−3 mL g−1 and the value of the constant a is 0.834 (Knaus and Bauer-Heim, 2003). 2.6. Production of membranes with the incorporation of doxycycline The symmetric and asymmetric membranes were produced by using a modification of the procedure described in Toledo et al. (2007): cellulose triacetate (CTA) solutions, containing 5% (w/w) of doxycycline (DOX) and a mixture of dichloromethane/methanol (9:1, v/v) were employed to produce symmetric membranes. As for asymmetric membranes, 10% of water was added to be used as a pore-forming agent. The solution was cast on a glass plate using a casting knife with a 200 m gap. The evaporation time was approximately 10 min, enough for the membranes to detach from the glass plate.
1.00 g of washed, dried and ground sugarcane bagasse was weighed and put in a round bottomed flask, in which 30.0 mL of sulfuric acid (72%) was slowly added under agitation. The sample was kept for two hours in water bath at room temperature (25 ◦ C) under agitation. Then, 560.0 mL of distilled water was added to the contents of the round bottomed flask. The system was set to a temperature of 100 ◦ C under reflux, in order to avoid water loss as a result of evaporation, and consequently, alterations in concentration in the acid solution. Four hours later, the system was put to rest for sedimentation of the insoluble material. This material was then filtered through a funnel equipped with a porous plate, previously tared and washed with 500.0 mL of hot distilled water. Lastly, the system was oven dried at 105 ◦ C for 12 h, and weighed to quantify the insoluble residue and determine the Klason lignin (Vieira et al., 2007).
DSC experiments were performed on a Q-20, TA equipment. The heating rate was 10 ◦ C min−1 under a nitrogen flow of 50 cm3 min−1 . TGA experiments were performed in a DTG 60-H, Shimadzu. Ten milligrams of the samples were heated from room temperature to 600 ◦ C at a rate of 10 ◦ C min−1 under nitrogen atmosphere.
2.3. Homogeneous acetylation
2.8. SEM
The material used for acetylation consists in a purified bagasse with 87.59% cellulose and 12.00% hemicellulose. The acetylation reaction was performed in accordance to the methodology described in Cerqueira et al. (2007, 2009), as follows: 50.0 mL of
The samples were initially coated in gold, followed by the examination of the surface and cross-section morphology of the membranes on a scanning electron microscope, Shimadzu SSX-550 model, operating at 10 kV.
2.7. DSC and TGA experiments
568
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
Fig. 1. SEM of the cross-section asymmetric membrane (A), symmetric membrane (C) and surface asymmetric membrane (B), symmetric membrane (D) (1000×).
2.9. Release of doxycycline As for the release of the drug, a thermostatic bath MA 184 Marconi was used to ensure that the temperature of the experiment was kept at 36.5 ◦ C. A buffer solution with pH 7.4 was prepared. The dry membranes, with a superficial area of 2 cm2 , were initially weighed. The release of the drug in the solution was spectrophotometrically observed every hour by employing a spectrophotometer in the UV–visible region (UV-250 1 PC Shimadzu) at wavelength of 275 nm. The experiments were carried out in duplicate. 3. Results and discussion
effects: increase of coalescence rate, leading to the separation of phases for the formation of the matrix, and increase of non-solvent concentration in the polymeric structure, leading to the formation of pores. These characteristics classify this membrane as asymmetric. On cross-section C and surface D, a completely dense structure is observed, which characterizes the membrane as symmetric. In this case, the solution components on the formulation of the membranes are the solvent (dichloromethane), the polymer, and the drug. Once the solvent evaporates freely when a non-solvent is absent, static pores are not formed on the matrix, and dense layers are formed instead.
3.1. Material characterization The cellulose obtained from sugarcane bagasse presents a lignin content of 0.41%. After the acetylation reaction, the material was characterized as a cellulose triacetate with a degree of substitution of 2.80 ± 0.09 and a viscosity average molecular weights of 39,000 g mol−1 . 3.2. Microscopy of the membranes Fig. 1 shows the morphology found on the structures of the membranes, cross-section (A and C) and surface (B and D). On cross-section A, a porous structure with a non-uniform pore size arrangement and with regions of greater polymer density can be observed. The existence of pores can also be noted on the membrane surface (B). Such morphological observations can be directly associated to the processing of the membrane, as during its coalescence for the formation of the matrix from the solution (CTA/dichloromethane/water), the solvent (dichloromethane) and the non-solvent (water) evaporate at different rates. The solvent evaporates more rapidly than the non-solvent resulting in two main
3.3. Thermal analysis of symmetric and asymmetric membranes One fundamental aspect on the employment of thermal analysis when evaluating matrices for drug controlled-release is the fact that this method permits the investigation of thermal stability of both matrix and drug, as well as the nature of dispersion of the drug in the matrix. The thermal stability of the membranes was evaluated by thermogravimetric curves of weight loss, shown in Fig. 2. Generally, three main thermal events are observed for all membranes: desorption of water adsorbed in the structure of the cellulosic derivative (between 30 and 110 ◦ C), polymer deacetylation and depolymerization between 315 and 375 ◦ C, and pyrolitic decomposition of the cellulosic skeleton between 380 and 530 ◦ C (Shaikh et al., 2009). In membranes with doxycycline, slight shifts in the weight loss curves are observed when compared to membranes without the drug. The phenomenon is more significant in asymmetric membranes, in which a shift towards high temperatures is observed, indicating an increase in thermal stability in asymmetric membranes with DOX.
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
A symmetric membranes
3
100
A
CTA/dox CTA
2
60
Temperature [ºC]
40
Heat flow [W/g]
1
Weight Loss %
80
Weight Loss %
569
endo 20
0 -1 -2 -3 -4 -5
0 0
100
200
300
400
500
50
600
100
Temperature [°C] 2,0
B Asymmetric membranes
100
150
200
250
300
Temperature[ºC]
B
CTA/dox CTA
1,5 1,0
60
Heat flow [W/g]
Weight Loss %
Weight Loss %
80
40
Temperature [ºC]
endo
0,5 0,0 -0,5 -1,0 -1,5
20
-2,0 -2,5
0 0
100
200
300
400
500
600
Temperature [°C]
50
100
150
200
250
300
Temperature[ºC]
Fig. 2. Weight loss curve of symmetric CTA and CTA/DOX (A), and asymmetric CTA and CTA/DOX (B) membranes.
Fig. 3. DSC thermogram, 1st scan, of symmetric CTA and CTA/DOX (A) and asymmetric CTA and CTA/DOX (B) membranes.
Fig. 3 presents DSC thermograms for cellulose triacetate symmetric and asymmetric membranes with and without the incorporation of doxycycline. The thermograms presented are typical of cellulose triacetate, in which an endotherm between 75 and 85 ◦ C may be observed, along with desorption of water associated with the polymer structure (Shaikh et al., 2009). An exothermic peak at approximately 192 ◦ C relative to the crystallization of the polymer during the scan (He et al., 2009; Kamide and Saito, 1985), and an endotherm at approximately 300 ◦ C due to CTA fusion (He et al., 2009; Kamide and Saito, 1985; Mark, 1998). Thermal degradation of cellulose acetate also starts near the temperature of 300 ◦ C. However, in TGA curves at a temperature of 300 ◦ C only about 4–5% of cellulose acetate weight is lost. That indicates the beginning of the thermal degradation process, but also indicates that the resulting peak is predominantly the result of fusion of crystals of the TAC, the final process being accompanied by thermal degradation of the polymer. Although the thermograms of all membranes present the same characteristics qualitatively, the difference between the values obtained concerning the enthalpy of fusion and the glass transition temperature, Tg , is clear, particularly in asymmetric membranes with DOX when compared to asymmetric membranes without the drug. Fig. 4 shows the second scan DSC thermogram for the determination of glass transition temperature in the membranes analyzed. According to Kamide and Saito (1985) cellulose acetate Tg is observed in the range from 170 ◦ C to 190 ◦ C. Regarding the sym-
metric membranes in Fig. 4(A), it is possible to observe a reduction in the value of Tg in the CTA/DOX membrane of approximately 2 ◦ C (176.45 ◦ C CTA and 174.25 ◦ C CTA/DOX). This variation is even more significant in asymmetric membranes (Fig. 4(B)), for which the reduction in Tg noted is approximately 7 ◦ C (174.18 ◦ C CTA and 167.00 ◦ C CTA/DOX). The decline in Tg shows that the presence of drug molecules favors an increase in mobility of segments of the macromolecule. The alterations in the values of glass transition temperature, Tg , with the addition of the drug indicate its interaction with the polymeric matrix. The fact that this phenomenon is more accentuated in asymmetric membranes is related to the existence of pores in the structure, which leads to the production of regions with lower polymeric density, and therefore allows, with the presence of the drug, segments of the chains to have greater mobility. Another aspect related to the processing and the presence of the drug is the change in the values of enthalpy of fusion. Asymmetric membranes without the drug had a more amorphous matrix than the symmetric membranes, as the enthalpy of fusion for the first is 9.70 J g−1 and 26.44 J g−1 for the later. When the drug is incorporated in the membranes some changes occur, such as alterations in the degree of order of the matrix. In symmetric membranes, changes are less significant when compared to the asymmetric membranes and they indicate the existence of interactions that result in a slight disorder in the system, once the enthalpy of fusion drops from 26.44 J g−1 to 22.40 J g−1 . In this case, the increase in
570
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
20
A 18
A
0,0 -0,2 -0,4 CTA/dox -0,6 CTA -0,8
doxycycline content released %
Heat Flow [W/g]
0,2
16 14 12 10 8 6 4 2
80
100
120
140
160
180
200
220
240
0
Temperature[ºC]
0
100
200
300
400
500
Time[min.] B 100
B
-0,5
-1,0
CTA
CTA/dox -1,5 50
100
150
200
250
Temperature[ºC] Fig. 4. DSC thermogram, 2nd scan, of symmetric CTA and CTA/DOX (A) and asymmetric CTA and CTA/DOX (B) membranes.
mobility is restricted to very small segments, generating just a slight disorder. In asymmetric membranes, however, the enthalpy of fusion of the matrix with the drug raises to 21.07 J g−1 , much greater than the value found for this membrane without the drug, 9.70 J g−1 . The increase in crystallinity of the matrix with the incorporated drug is the result of its interaction with polymeric chains. This fact corroborates the observations regarding the changes in Tg for this system, in which the drug acts as a modification agent of chain mobility, favoring an increase in crystallinity in the asymmetric membrane. Such increase in crystallinity in the asymmetric membrane with DOX leads to a greater thermal stability for this system, Fig. 3, when compared to the system without doxycycline. 3.4. Release of doxycycline Doxycycline is a water-soluble drug with high polarity due to the presence of amine, carbonyl and hydroxyl functional groups in its structure. Although interactions between the hydroxyl and acetyl groups from the cellulose triacetate with the drug exist, in experiments of drug controlled-release using buffered aqueous solutions, it is expected for the doxycycline to have greater affinity with the solution being released by the polymeric matrix. That is due to the release occurring as the solution comes into contact with the polymeric system, resulting in the relaxation of polymeric chains with volume expansion. In Fig. 5, kinetic curves of doxycycline release from symmetric and asymmetric membranes are presented.
doxycycline content released (%)
Heat flowr[W/g]
0,0 80
60
40
20
0 0
100
200
300
400
500
Time [min.] Fig. 5. Curve of doxycycline release from symmetric (A) and asymmetric (B) membranes.
The data regarding the release of doxycycline as a function of time, shown in Fig. 5, indicates the influence of the structure of the membrane in drug release. One may observe clearly that with the asymmetric membrane, a great quantity of drug incorporated to the matrix is released, reaching approximately 80% of doxycycline released in about 100 min of assay. This differs from what is observed with the symmetric membrane, through which only a small quantity of drug is released (∼14%). One of the aspects that explain the difference in the percentage of drug released for each one of the membranes is the existence of pores on the asymmetric membrane (Fig. 1(A) and (B)). The pores on the membrane surface control the transfer and facilitate the movement of the drug through the membrane. When the porous substructure is reached, it does not offer resistance to the flux of doxycycline. The diffusion of an active agent consists of a process of mass transfer of individual molecules which preferably occur through the amorphous regions of the polymer, where the chains are more disorderly set and the free volume is greater. The presence of pores augments the low polymer density regions, resulting in an increase in mobility of polymeric chains. Such enhancement in mobility favors drug transport and its consequent release. This fact was confirmed by the decrease in glass transition temperature, Tg , in asymmetric CTA/DOX membranes, observed in the DSC thermogram (Fig. 4(A) and (B)).
G. Rodrigues Filho et al. / Industrial Crops and Products 33 (2011) 566–571
4. Conclusions Cellulose triacetate membranes produced from sugarcane bagasse can be employed for doxycycline controlled-release applications. The main factors influencing the total percentage of drug released are the drug–matrix interaction and the morphology of the membranes (symmetric and asymmetric). The drug interacts with the matrix and parts of it are retained as a result of these superficial interactions. This constitutes a prevailing factor for symmetric membranes, in which the absence of static pores is responsible for the low mobility of polymeric chains, significantly reducing the total amount of drug released. In asymmetric membranes, the presence of pores and regions of low polymer density allows an increase in mobility of polymeric chains and drug molecules, therefore increasing its release into the medium and reaching levels of approximately 80% of the drug incorporated to the membrane during its production. In symmetric membranes, the maximum quantity of drug released in the same time interval is 14%. Acknowledgements The authors acknowledge CNPq for project Casadinho UFU/UFG/UFMS (620181/2006-0), CAPES for the access to “Portal Periódicos”, and FAPEMIG for CEX-APQ-02356/08 project. Ribeiro thanks PIBIC/CNPq A-042/2009 for the scholarships. Meireles thanks CAPES for her PhD scholarship. References Bhargava, H.N., Garg, A., Gupta, M., 2007. Effect of formulation parameters on the release characteristics of propranolol from asymmetric membrane coated tablets. Eur. J. Pharm. Biopharm. 67, 725–731. Borges, C.P., Habert, A.C., Nobrega, R., 2006. Processos de separac¸ão por membranas, E-papers, Rio de Janeiro. Cerqueira, D.A., Rodrigues Filho, G., Meireles, C.S., 2007. Optimization of sugarcane bagasse cellulose acetylation. Carbohydr. Polym. 69, 579–582. Cerqueira, D.A., Valente, A.J.M., Rodrigues Filho, G., Burrows, H.D., 2009. Synthesis and properties of polyaniline–cellulose acetate blends: the use of sugarcane
571
bagasse waste and the effect of the substitution degree. Carbohydr. Polym. 78, 402–408. He, J., Zhang, M., Cui, S., Wang, S., 2009. High-quality cellulose triacetate prepared from bamboo dissolving pulp. J. Appl. Polym. Sci. 113, 456–465. Kamide, K., Saito, M., 1985. Thermal analysis of cellulose acetate solids with total degrees of substitution of 0.49, 1.75, 2.46 and 2.92. Polym. J. 17, 919–928. Knaus, S., Bauer-Heim, B., 2003. Synthesis and properties of anionic cellulose ethers: influence of functional groups and molecular weight on flowability of concrete. Carbohydr. Polym. 53, 383–394. Ma, D., McHugh, A.J., 2007. The interplay of phase inversion and membrane formation in the drug release characteristics of a membrane-based delivery system. J. Membr. Sci. 298, 156–168. Mark, J.E., 1998. Polymer Handbook Data, Online Version. Oxford University Press, Oxford. Meier, M.M., Kanis, L.A., Soldi, V., 2004. Characterization and drug-permeation profiles of microporous and dense cellulose acetate membranes: influence of plasticizer and poreforming agent. Int. J. Pharm. 278, 99–110. Ribeiro, S.D., Mundim, E.A., Silva, L.G., Ruggiero, R., Cerqueira, D.A., Meireles, C.S., Rodrigues Filho, G., 2009. Doxycycline release through membranes of cellulose triacetate obtained from chemical recycling of sugarcane bagasse. In: Proceedings of the 10th Congresso Brasileiro de Polímeros , Foz do Iguac¸u, Brazil. Rodrigues Filho, G., Cruz, S.F., Pasquini, D., Cerqueira, D.A., Prado, V.D., Assunc¸ão, R.M.N., 2000. Water flux through cellulose triacetate films produced from heterogeneous acetylation of sugar cane bagasse. J. Membr. Sci. 177, 225–231. Rodrigues Filho, G., Toledo, L.C., Cerqueira, D.A., Assunc¸ão, R.M.N., Meireles, C.S., Lugão, A.B., Rogero, S.O., Otaguro, H., 2007. Water flux, DSC, and cytotoxicity characterization of membranes of cellulose acetate produced from sugar cane bagasse, using PEG 600. Polym. Bull. 59, 73–81. Rodrigues Filho, G., Toledo, L.C., Silva, L.G., Assunc¸ão, R.M.N., Meireles, C.S., Cerqueira, D.A., Ruggiero, R., 2009. Membranes of cellulose triacetate produced from sugarcane bagasse cellulose as alternative matrices for doxycycline incorporation. J. Appl. Polym. Sci. 113, 3544–3549. Shaikh, H.M., Pandare, K.V., Nair, G., Varma, A.J., 2009. Utilization of sugarcane bagasse cellulose for producing cellulose acetates: novel use of residual hemicellulose as plasticizer. Carbohydr. Polym. 76, 23–29. Sobolev, I., 1960. Lignin model compounds. Nitric acid oxidation of 4Methylguaiacol. J. Org. Chem. 26, 5080–5085. Thombre, A.G., Zentner, G.M., Himmelstein, K.J., 1989. Mechanism of water transport in controlled porosity osmotic devices. J. Membr. Sci. 40, 279–310. Toledo, L.C., Silva, L.G., Rodrigues Filho, G., Ruggiero, R., Cerqueira, D.A., Assunc¸ão, R.M.N., Meireles, C.A., 2007. Incorporation of doxycycline in membranes of cellulose acetate (from sugar cane bagasse) produced with PEG 600 as additive. In: Proceedings of the 4th International Conference on Science and Technology of Composites Materials , Rio de Janeiro, Brazil. Vieira, R.G.P., Rodrigues Filho, G., Assunc¸ão, R.M.N., Meireles, C.S., Vieira, J.G., Oliveira, G.S., 2007. Synthesis and characterization of methylcellulose from sugar cane bagasse cellulose. Carbohydr. Polym. 67, 182–189.