Chitosan and silver sulfadiazine immobilization onto silicone membrane for wound dressing applications.
Autograft, allograft, or synthetic skin substitutes are of different ways for burn wound treatment. Due to the antigenicity or the limitation of donor sites, polymeric wound dressing could obviate these limitations. Therefore, to protect a skin defect from infections and dehydration in the intervening period between hospitalization and grafting, temporary closure of a wound with the use of biopolymeric material has become ordinary recently [1, 2]. Among the wound dressings, bilayer artificial skin or wound dressing composed of a dense top layer (skin layer) and a lower porous layer (sublayer) may be an excellent and promising one . The skin layer such as polydimethylsiloxane (PDMS) which possess physiological inertness, low toxicity, low modulus and good mechanical properties can prevent bacterial penetration and dehydration of the wound surface [3, 4] while the sublayer such as chitosan is designed to achieve high adsorption for fluid drainage of the wound and infiltration by fibroblasts for tissue regeneration. Chitosan is well known for accelerating the healing of wounds in humans while stimulated the migration of polymorphonuclear (PMN) and mononuclear cells due to possessing special functional groups. This suggests the acceleration of re-epithelialization and regeneration of normal skin that minimizes scar formation in wounded areas [5-7]. In artificial skin approach, covalently immobilization of sublayer like chitosan onto skin layer like PDMS is the efficient and reliable method reported earlier [8-10]. In order to immobilize, synthetic polymers of skin layer (such as PDMS) often required selective modification to introduce specific functional groups of spacer like AAc to the surface for the binding of biomolecules [11-13]. Graft polymerization is an attractive way in which a desired monomer can be grafted onto the skin layer before immobilization step. Among the common methods in graft co-polymerization, the two-step plasma (TSP) graft co-polymerization is a prominent and efficient technique developed by our group . In this TSP technique, a polymeric substrate treated with plasma immersed in monomer solution, and then undergoes a second step of plasma treatment that leads to co-polymerization of preadsorbed monomer. This technique possess benefits like lower graft polymerization time length, no controlling requirement on pH of monomer solution, higher grafting amount, and producing more homogeneous morphology and topology of the grafted surface compared to the other grafting method including one step plasma or laser technique.
Besides of promoting cellular function, fluid drainage and good mechanical properties required for potentially ideal wound dressing, risk of infection beneath the dressing is another issue associated with dressing [14, 15]. Infectious organisms preferentially invade wounds beneath dressing materials, leading to serious infections. This requires removal of the wound dressing and excision of cutaneous wounds. Thus, wound dressings or artificial skins containing antibiotic agents have been developed to decrease wound infection, and the laborious replacement of wound dressings that can avoid damage to the newly formed epithelium caused by replacement . In the present study, we developed a bilayer wound dressing that consists of an upper skin layer of PDMS and a porous sublayer of chitosan that have the ability to control the release of antibiotic agent. Silver sulfadiazine (AgSD), an effective and widely used antibiotic agent for burn injuries in humans , is used as an antibacterial drug for the treatment of infected wounds. Acrylic acid (AAc) employed as a spacer to covalently immobilized chitosan onto silicone. AAc was simultaneously grafted onto the surface of PDMS films using two-step oxygen plasma treatment (TSPT). Then the mixture of chitosan/AgSD was immobilized onto AAc grafted silicone. The in vitro biocompatibility, antibacterial activity and physical characterization of bilayer wound dressing are evaluated. To the best of our knowledge, there is no report in the literature to discuss about bilayer chitosan/AgSD immobilized onto AAc grafted silicone and the properties as a potential film for wound dressing applications.
Materials and methods
The silicone rubber, Silastic[R] MDX4-4210 medical grade elastomer was purchased from Dow Corning Corp (Midland, MI). The procedure of preparing silicone film was described elsewhere . The AAc was bought from Fluka (Buchs, Switzerland). AAc was redistilled under vacuum condition to make it free from the inhibitor . N-(3-dimethyl aminopropyl) M-ethyl carbodiimide hydrochloride (EDC) was purchased from Merck and used for activating COOH groups on the AAc grafted silicone. Chitosan ([M.sub.W] = 400KD and 85% deacetylated) was obtained from Sigma Aldrich, USA. Silver sulfadiazine was obtained by Iran Najoo lab. Other reagents were reagent grades and used without any further purification.
Plasma treatment step
TSPT were carried out onto silicone samples according to our previous works [3, 17, 18]. Briefly, Nano-RF-PC (Diener Electronic GmbH, Germany) apparatus was utilized for both plasma pretreatment and copolymerization of silicone films. The films were placed on the bottom of the reaction chamber, which was evacuated to 6 x [10.sup.-1] mbar, and pretreated with 60 W of oxygen plasma up to 35 second. Then, the plasma pretreated films were immersed in aqueous monomer solutions with the given ratios of AAc for up to 30 min at room temperature, and dried at the same temperature. The dried plasma pretreated silicone films with a preadsorbed layer of reactive monomer of AAc on their surfaces were placed into the reaction chamber for plasma graft copolymerization for up to 3 min. The time of treatment was chosen based on our previous results to obtain maximum graft density (GD) as summarized in Table 1 . Then, by using Soxhlet extraction in distilled water for 72 h the residual monomers and homopolymers were removed.
[FIGURE 1 OMITTED]
Determination of GD
The carboxyl group density on the PAAc-g-PDMS surface was measured by a colorimetric method using toluidine blue O staining . Grafted samples were immersed in an aqueous solution of toluidine blue (5 x [10.sup.-4] M) for 6 h at 30[degrees]C. Then samples were rinsed with an aqueous solution of NaOH (5 x [10.sup.3] M) in order to remove uncomplexed dye. Astandard series was done with seven different concentrations between 4 x [10.sup.-6] and 5 x [10.sup.-5] M, which allows us to determine the concentration of decomplexed toluidine blue using the molar extinction coefficient. Decomplexation of toluidine blue occurs by immersing samples in an aqueous solution of acetic acid (50 vol.%) for 24 h. Concentration of decomplexed toluidine blue is measured via UV-VIS spectrophotometry (Shimudza, 1650PC, Japan) at 633 nm. A different formulation of silicone plasma treated film was shown in Table 1.
Immobilization of CS/AgSD
PAAc-g-PDMS films were placed in 10 mg.[mL.sup.-1] of an aqueous solution of (EDC) at room temperature for 2 h to activate carboxyl groups in the grafted PAAc chains. The activated PAAc-g-PDMS films were immersed into CS and AgSD in 0.5% (v/v) lactic acid solution (Table 2) at 4[degrees]C for 24 h to allow the activated carboxyl groups in the grafted PAAc chains and amino groups in the CS to form covalent bonds. During immobilization step, the pH of CS solution was 3.0. The AgSD concentration in CS solution was 1% (w/w) (in relation to CS mass). Silver sulfadiazine concentration was chosen based on previous study that showed a solubility threshold of AgSD in CS solution . All the PDMS-g-PAAc-CS/AgSD samples were rinsed with distilled water many times and then the samples were stored in desiccators at 4 [degrees]C before use.
Inductively couple plasma methods (ICP)
To evaluate the presence of AgSD in wound dressing, silver concentrations were measured in a immobilization solution containing only CS and AgSD (Table 2) before and after soaking PDMS-g-AAc (Max sample refer to Table 1) into the solution by inductively coupled plasma (ICP-OES, VISTA-PROVARIAN) method. This ICP apparatus has 0.06 ppm silver assay accuracy. The difference in silver concentration of the immobilization solution before and after of immobilizing step was considered as AgSD loading in wound dressing film.
Contact angle and surface tension measurements
The static contact angles of the untreated film, PAAc-g-PDMS films and also immobilized with CS/AgSD were measured by the sessile drop method using Kruss G10 goniometer (Kruss GmbH, Germany) contact angle measurement equipment. A 5 iL double distilled water droplet was used for each point and the contact angle was recorded after 1 min . The average values of three measurements on different points of each sample were recorded. Moreover, double distilled water and diiodomethane attributed to polar and disperse parts of the sample were used to calculate surface tensions using Owens-Wendt equation .
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used in order to confirm PAAc and CS grafting onto silicone plasma treated film in comparison with untreated film. A KRS5 prism (Bruker Optik GmbH, Germany) FTIR spectrometer was applied with incident contact angle 45[degrees] and progressive scanning range from 4000 [cm.sup.-1] to 600 [cm.sup.-1].
[FIGURE 5 OMITTED]
Scanning electron microscopy
Scanning electron microscopy (SEM) was performed on gold-coated samples using a Polaron sputter coater. A Cambridge S360 SEM operating typically at an accelerating voltage of 10 kV in secondary electron mode to ensure a suitable image resolution was employed for morphology measurements of untreated film, plasma treated film, PAAc-g-PDMS film and also immobilized samples.
In vitro assay
The immobilized silicone films with different PAAc graft densities were immersed into sterilized saline for 12 h just before cell culture. The mouse fibroblast cells (L929) were gently gifted from National Cell Bank, Pasteur Institute of Iran. The cells were maintained in RPMI-1640 growth medium (Sigma Chemical Company, St. Louis, USA), supplemented with 10% heatin-activated fetal bovine serums (Gibco, BRL), 100 IU [mL.sup.-1] streptomycin. A routine subculture was employed to prepare the cell line . The cells were incubated in a humidified atmosphere of 5% CO2 at 37[degrees]C. After one week incubation, the monolayer was harvested by trypsinization. The samples were placed into each well using a multi-well plate with 5 mL of cell suspension with 4 x [10.sup.5] cell.[mL.sup.-1] concentration and seeded in each well, keeping one well as a control without any sample, and then maintained them in the incubator for 48 h. The samples were removed from the well, washed with phosphate buffer saline solution twice, placed on a glass slide and fixed with ethanol and then stained with 5 % Giemsa (Sigma-Aldrich). All the samples were air-dried and then cover slips were mounted on them. The samples were examined by an inverted light microscope (E200, Nikon, Japan).
The quantitative antimicrobial activities of the unloaded and AgSD loaded films were determined using a viable cell count method. The results were presented as surviving bacteria and population reduction in logarithmic scale on the test pathogenic bacterium. All film samples (CS and Max-g-CS/AgSD) were cut into square pieces (1.5 x 1.5 [cm.sup.2]) and placed in individual sterile flasks containing the test bacteria, Escherichia coli; E. coli (ATCC 8739) at a concentration of 5.2 x [10.sup.6] CFU.[mL.sup.-1] in the Nutrient Broth solution (Merck, Germany). The inoculated broth was adjusted photometrically at 600 nm to a cell density equivalent to approximately 0.5 McFarland standards (1.5 x [10.sup.8] CFU/mL). The suspensions were then diluted in Nutrient Broth solution to reach the final concentration of about [10.sup.6] CFU.[mL.sup.-1]. The tubes were kept in an incubated shaker at 37[degrees]C and 100 rpm. During the incubation, the cell viability count of the medium was measured every hour for 6 h. At the intervals, 1 mL of the solution was diluted with 9 mL of sterilized distilled water, and decimal serial dilution was performed and repeated. Then 100 pL of the solution was taken out and quickly spread on the surface of the plate containing nutrient agar (Merck, Germany). After inoculation, the plates were kept at 37[degrees]C, and the colonies were counted after 24 h. The number of colonies on each plate was counted and reported as CFU.mL-1. An inoculum of cell suspension in a flask with no film sample was used as a control. The population reduction of the test organism were calculated using equation (1) :
Log population reduction = Log cell count of control - Log survivor count on sample (1)
[FIGURE 6 OMITTED]
Analysis of Variance (ANOVA) and linear regression were the main statistical tools used for data analysis. The unpaired student's t-tests were used for all statistical analyses. Results are expressed as mean[+ or -]standard deviation (SD).
Results and Discussion
Determination of graft density (GD)
The AAc grafting onto silicone films was carried out to develop a surface which is carrying a high density of carboxyl groups. The overall process of AAc grafting through TSPT involved the pretreatment of silicone film with oxygen plasma and subsequent exposure to AAc solution. Produced polar groups (hydro peroxide radicals) on the surface of chemically inert silicone due to plasma pretreatment helped it out to physically react with hydrophilic monomer (i.e. AAc) via hydrogen bonding, and the produced peroxide groups may act as initiators in copolymerization step. We chose a different pretreatment time and the polymerization time of plasma to produce optimum conditions in order to get the maximum amount of GD by introducing maximum peroxides on the surface. Peroxides are known to be the species responsible for initiating the graft copolymerization when silicone reacts with AAc . In the next step, the dried plasma pretreated silicone films with a preadsorbed layer of AAc monomer on their surfaces were placed into the plasma reaction chamber for plasma graft copolymerization. During propagation step of the plasma copolymerization, the preadsorbed AAc react with radicals, which create as a result of plasma treatment, and graft onto the surface of the film until the copolymerization reaction terminates. In fact, before the second step of plasma treatment co-polymerization would not occur as also reported earlier . The amount of grafted copolymer was sensibly affected by pretreatment time length and the polymerization time length. The relationship between the amount of grafted copolymer per square centimeter and plasma pretreatment duration and polymerization time is plotted in Fig. 1. As shown in Fig. 1 with increasing plasma treatment time the amount of GD increased from 28.105 [+ or -] 10.147 [micro]g.[cm.sup.-2] for the Min sample to 32.299 [+ or -] 9.163 [micro]g.[cm.sup.-2] for the Med sample, and 86.969 [+ or -] 10.634 fig.am1 about the Max sample. Based on results of our previous study, there is an optimum t in treatment time. Further increment above optimum point affects unfavorably the amount of GD. This can be explained by the fact that further increase in time causes plasma etching rather than co-polymerization .
Surface wettability and surface tension
The contact angle test is used to obtain hydrophilic or hydrophobic surface properties. The changes in hydrophilicity of untreated silicone and surface modified silicone films were summarized in Table 3 as water contact angle and surface tension. The contact angle of silicone surface decreased due to grafting of PAAc and also immobilizing of CS/AgSD onto surface of plasma treated silicone. These phenomena could be associated with introducing hydrophilic groups such as carboxyl and amine functional groups onto surface of the silicone film. The presence of these functional groups may possibly improve the hydrophilicity of biomaterials surface and suggest additional interactions with water molecules that influence the wettability of the films. As presented in Table 3, the more increase in plasma treatment time, the more decrease in contact angle, demonstrating that these materials have good hydrophilicity thereby they are suitable for cell supporting . Previous studies revealed that the fibrobroblast cells show maximum adhesion to the surface of materials with contact angle in the range of 60[degrees]and 80[degrees] . Thus, the as-prepared membranes have suitable surface hydrophilicity for effective contribution in cellular activity. Changes in the surface tensions of the samples are also presented in Table 3. More GD of AAc caused the more amount of CS immobilization which was reported earlier . According to the results, grafting of hydrophilic monomer (AAc) and hydrophilic group (CS/AgSD) onto the surface of silicone films increased the surface tension from 22.67[+ or -]0.32 to 40.35 [+ or -] 1.28 (n= 3, p < 0.005). On the other hand, [[??].sub.p] (polar part of surface tension) also significantly increased for untreated silicone and PDMS-g-AAc-g-CS/AgSD with maximum amount of GD, respectively, indicating an increment in the polar groups existing on the surface.
[FIGURE 7 OMITTED]
The presence of the grafted AAc and CS was confirmed by comparing the ATR-FTIR spectra of unmodified and modified silicone film (Fig. 2). A peak at 1715 [cm.sup.-1] was observed in the spectrum of the Max-g-Cs/AgSD sample (Table 2) that was due to the grafted carboxyl groups (C=O) onto the silicone surface in comparison with unmodified silicone (Fig. 2 (a, b)). The two characteristic absorption bands of CS appearing at consisted of two bands (medium intensity) at 1645 [cm.sup.-1] and 1542 [cm.sup.-1]; corresponds to the grafted amine groups of CS (amide I and amide II) onto the surface of Max-g-CS/AgSD (Fig. 2 (a, b)) . However, the intensity of amide band at 1645 [cm.sup.-1] was lowered that could not be detected in FTIR spectra likely due to adsorption of [Ag.sup.+]. In the adsorption process amino groups become protonated resulted in changing the intensity of amide band. The presence of CH2OH groups of polysaccharide of chitosan is attributed to the peak at 1450 [cm.sup.-1] which is also another site of Ag+ sorption [25, 26] while the intensity is very low due to sorption.
Surface morphology of control and modified silicone was evaluated using SEM micrographs of surface of the films as illustrated in Fig. 3. SEM micrographs of sample indicated that oxygen plasma pretreatment made the surface of silicone became cleaner and smoother due to the plasma etching effect since small molecules and occasional fragments which were attached onto the surface were removed. Furthermore, some cracks, which are shown in Fig. 3 (a, b) could be attributed to the silica-like layer . However, by grafting PAAc onto silicone plasma treated film, the surface of silicone became rougher in comparison with control and oxygen plasma treated silicone (Fig. 3 (c)).
Immobilization of CS/AgSD solution onto the surface of PDMS-g-AAc changes the surface morphology of silicone which is grafted by PAAc (Fig. 3 (c, d)). The cross-section of the grafted layer was observed in SEM micrographs (Fig. 4). According to Fig. 4 the thickness of the grafted layers was directly depend on grafted amount. This statement suggests that an increase in the grafted amount lead to increase the thickness of the grafted layer. As shown in Fig. 4, cross section of the grafted film is about 5 pm thickness, which is comparable with what already published .
The presence of AgSD drug which is known as an antibacterial agent in the wound dressing was confirmed via ICP methods. Silver sulfadiazine was dissolved in CS and lactic acid solution. AgSD bonded with CS and produced chelate structure with CS [25, 26]. Chitosan contains N[H.sub.2] functional groups which makes it capable of binding with silver. The Max-g-CS/AgSD membrane has 2.5 ppm AgSD content at film with 1 cm x 2 cm.
Cell culture and microscopy images
Affinity of cells for adhesion to the surface is an excellent indication for studying of cytocompatibility of biomaterials. The effects of the three different PAAc densities grafted onto silicone surface and immobilized with CS and AgSD were quantitatively and qualitatively evaluated on cell adhesion, and are shown in Fig. 5 (a-f). The mean number of cells cultured on different surfaces was quantified by Image Pro Plus software (version 220.127.116.110). As shown in Fig. 5 with increasing GD of PAAc to increasing treatment time onto the surface of silicone immobilization of CS and silver sulfadiazine, the more hydrophilic group such as carboxyl and amine group were introduced onto the surface of wound dressing, and the more cells were attached as consequently. It is known that hydrophilicity property strongly correlates with protein adsorption, and also cell adhesion. It was suggested that hydrophilic substrates influence adsorption of serum proteins in the quality, amount, and conformation that favors adhesion and subsequent growth . Those factors cause more cell adhesion on hydrophilic surfaces. In our work, according to Table 3, the Max-g-CS/AgSD with the lowest amount of water contact angle (e = 63 [+ or -] 6.12[degrees]) resulted in the most number of adhering cells which was depicted in Fig. 5 (d). This formulation showed the best behaviour; however, there is a less significant difference in cell number between control and Min-g-CS/AgSD and Med-g-CS/AgSD samples (p <0.05) (Fig. 5 (a, b, c)) in comparison with the Max-g-CS/AgSD (p <0.005). On the other hand, after 48 h of fibroblast culture, dense cellular monolayer covered the Max-g-CS/AgSD samples which are similar to the tissue culture polystyrene plate; although, the morphology of cells in contact with the Max-g-CS/AgSD sample is more conical than those in tissue culture polystyrene plate (Fig. 5 (d, e)). The Max-g-CS/AgSD showed greater tendency for entering into a rapid proliferative growth phase, build up critical cell-cell interactions and grow to confluence on the membranes.
For finding better insight regarding the state of adhered cells, the morphology of fixed cells was investigated with SEM. Fig. 6 shows the typical SEM micrographs of the adhered cells on the PAAc-g-PDMS immobilized with CS and AgSD compared with the unmodified silicone. Anchorage-dependent cells such as fibroblast need to adhere in order to proliferate .
As depicted in Fig. 6 (a), the carboxylic acid functional groups of PDMS-g-PAAC had a negative effect on the adhesion, spreading of fibroblast cells, while the amino groups of chitosan immobilized on the surfaces, showed better adhesion, spreading (Fig. 6 (b,c,d)). Fortunately, the fibbroblast cells were grown properly in all chitosan immobilized samples. They were flat and elongated with spindle-shaped morphology on the surface of the immobilized membranes confirming their excellent ability to support cell growth and proliferation. While, the cells in Med-g-CS/AgSD show more cytoplasm extension comparing with Min-g-CS/AgSD whereas the round cells can be seen onto the surface of untreated silicone. The Max-g-CS/AgSD sample presented the best results among treated membranes (Fig. 6 (d)). Surface properties, especially surface energy have great effect on the type of protein adsorption and also their orientation. Protein adsorption is a determining step for the first phase of cell attachment and further control of cell morphology, as well as their proliferation capacity. In addition, it has been proved that since polar and disperse components of surface energy is a key factor for interfacial interaction, an optimal distribution of polar and disperse components of surface energy should be reached . As can be seen from the surface energy results (Table 3), the Max-g-CS/AgSD samples have more amounts of cell attachment, more elongated fibroblast cells and large pseudopodia-like structure, and also it can be assumed increasing silver ion concentration has no adverse effect on cell response in all modified samples.
Using wound dressing membranes with promising antibacterial activity boosts their performance of protection of wounded area from bacteria likley provide faster healing. By close inspection of antibacterial dressing materials available in the market, silver is popular as a powerful broad spectrum antimicrobial agent to control infection of the eyes, burns, acute and chronic wounds. For instance, silver containing wound dressings were found to kill gram-negative bacteria gram-positive bacteria . To monitor the effectiveness of the cumulative antibiotic agent release from the films as wound dressings, antimicrobial activity of CS films and CS loaded with AgSD were quantitatively evaluated. The surviving bacteria and population reduction of the films are depicted in Fig. 7 (a,b). As mentioned in the standard method, at least a 1 Log reduction of bacterial load is required to claim antibacterial property . All films inhibited the growth of this test strain and reduced the number of E. coli by approximately at least 3 Log CFU.[mL.sup.-1] comparing to the positive control at each interval. The AgSD-loaded CS film with maximum GD (Max sample) exhibited higher antibacterial activity than that of CS film against E. coli. The CS-AgSD could kill most of the bacteria within 6 h, whereas; the CS film was bacteriostatic on the bacteria concentration of about 5.2*106 CFU.[mL.sup.-1]. By comparison of CS-AgSD films to the control without films, a decrement of >7 log cycles after 6 h of cultivation was observed. In the presence of the AgSD-loaded CS films, high bacterial inoculations of 5.2*106 CFU.mL-1 were decreased by 99.99% after 1 h and this decrement will continue to 6 h. It is reported that a slow AgSD releasing rate from the designed wound dressing allows for better trapping of silver in the wound than can be achieved with a traditional cream. It also reduces the potentially cytotoxicity caused by silver . Penetration of Ag through cell wall of bacteria, possibly causes DNA loses its replication ability and denaturation of cellular proteins that is one mechanism for antibacterial effect of Ag .
Plasma functionalized surfaces of PDMS with different surface COOH density used successfully for covalent immobilization of CS and AgSD to obtain a specific cell response and antibacterial activity by enhancing the hydrophilicity of surfaces. The positive effect of the increasing plasma treatment time was confirmed by a successful fibroblast response with respect to film with a maximum grafting density of AAc that showed high cell adhesion properties and also the most cytoplasmic extension. The presence of AgSD significantly improved the antibacterial activity of the wound dressing compared to CS film. The findings of this study are expected to be promising antibacterial wound dressing for burn treatment.
The authors gratefully acknowledge the Iran national science foundation for financial support and also wish to thank to Dr. Morteza Daliri from National Institute of Genetic Engineering and Biotechnology for his helps in cell culture tests.
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Elham Babaie (a,b) *, Hamid Mirzadeh (b), Hamid Keshvari (b), Atefeh Solouk (b), Azadehsadat Hashemi Doulabi (b)
(a) Department of Bioengineering, University of Toledo, P.O. Box: 43606/3390, Toledo, Ohio (b) Department of Biomedical Engineering, Amirkabir University of Technology (Tehran Polytechnic), P.O. Box: 15875/4413, Tehran, Iran
* Coresponding author: Dr. Elham Babaie; E-mail: Elham.firstname.lastname@example.org
Received 12 January 2016; Accepted 7 June 2016; Published online 10 June 2016
Table 1: AAc grafted PDMS via TSPT with variable process time with fixed power of 60 (W) and AAc concentration 30% (v/v) Sample # Plasma Plasma pretreatment polymerization time (s) time (s) Untreated Silicone Blank (control) PDMS-p-AAc Min 10 60 PDMS-g-AAc Med 20 120 PDMS-g-AAc Max 35 180 Table 2: Silicone grafted with AAc and immobilized with CS and AgSD mixture Sample # Chitosan and Lactic acid concentration Min-g-CS/AgSD 0.25% w/v, 0.5% v/v Med-g-CS/AgSD 0.25% w/v, 0 5% v/v Max-g-CS/AgSD 0.25% w/v. 0.5% v/v Table 3: Surface tension and water contact angle of untreated silicone, PDMS-g-AAc and Min-g-AAc-g-CS/AgSD, Med-g-AAc-g-CS/AgSD, Max-g-AAc-g-CS/AgSD Sample Polar part Disperse part [[gamma].sub.D] (mN/m) [[gamma].sub.D] (mN/m) Untreated Silicone 0.02 [+ or -] 0.00 22.65 [+ or -] 0.32 Min-g-CS/AgSD 7.2 [+ or -] 0.27 29.29 [+ or -] 0.38 Med-g-CS/AgSD 10.63 [+ or -] 0.68 29.97 [+ or -] 0.35 PDMS-g-AAc (Max) 8.86 [+ or -] 0.79 33.68 [+ or -] 0.42 Max-g-CS/AgSD 19.05 [+ or -] 0.83 21 30 [+ or -] 0.45 Sample Total surface tension Water contact [[gamma].sub.[tau]] angle (degree) (mN/m) Untreated Silicone 22.67 [+ or -] 0.32 111.10 [+ or -] 2.01 * Min-g-CS/AgSD 36.50 [+ or -] 0.65 77.20 [+ or -] 15.50 * Med-g-CS/AgSD 40.06 [+ or -] 1.03 72.80 [+ or -] 13.70 * PDMS-g-AAc (Max) 42.54 [+ or -] 1.21 70.08 [+ or -] 7.07 * Max-g-CS/AgSD 40.35 [+ or -] 1.28 63.40 [+ or -] 6.12 * n = 3, mean [+ or -] SD, *p < 0.005 compared to untreated silicone
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|Title Annotation:||Original Article|
|Author:||Babaie, Elham; Mirzadeh, Hamid; Keshvari, Hamid; Solouk, Atefeh; Doulabi, Azadehsadat Hashemi|
|Publication:||Trends in Biomaterials and Artificial Organs|
|Date:||Jan 1, 2016|
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