聚乳酸膜等离子接枝聚合聚乙烯基吡咯烷酮及表面性能研究_英文_李立华2

中国组织工程研究与临床康复 第 12 卷 第 14 期 2008–04–01 出版Journal of Clinical Rehabilitative Tissue Engineering Research April 1, 2008 Vol.12, No.14Basic MedicineSurface modification of poly-D, L-lactic acid film with plasma graft polymerization**☆Li Li-hua, Ding Shan, Tian Ye, Tian Jin-huan, Zhou Chang-renAbstractBACKGROUND: Polylactic acid (PLA) surface is hydrophobic and there are no natural recognition sites, so its application is limited. Many different strategies have been studied such as composition and chemical grafting, to produce hydrophilic groups. However, these traditional methods are always involved in complex process and many organic reagents, resulting in decrease of biocompatibility. OBJECTIVE: To conduct the surface modification of PLA and improve its hydrophilicity with low temperature plasma treatment. DESIGN: Controlled observation. SETTING: Department of Materials Science and Engineering in Jinan University. MATERIALS: The experiment was processed from October 2004 to October 2005 at Guangzhou Research Center of Artificial Organs and Materials Engineering (Ministry of Education). The mainly used materials were: Poly-D, L-lactic acid (Mr 2.9×104, Shandong Medical Instrument Institute), N-vinyl-pyrrolidone (NVP, Acros Company, purified before use). METHODS: The materials were treated in the plasma reactor under different conditions (power=150 W, t =3, 2, 1 minutes; power=30 W, t = 10, 8, 5, 3, 1 minutes) to choose the optimal condition, and then PLA were grafted with NVP by gas phase polymerization and liquid polymerization, respectively. MAIN OUTCOME MEASURES: The surface morphology of the films was observed with scanning electron microscopy and atomic force microscopy. The hydrophilicity of native and treated material surfaces was measured using a water contact angle meter. Surface composition was detected with Fourier transform infrared spectrometer. Mass changes measurement was applied to characterize the grafting efficiency. RESULTS: Scanning electron microscopy and atomic force microscopy showed that the plasma modified materials possessed coarse surface with pores and notches. Water contact angles decreased obviously from 78° to 50° after grafting. Fourier transform infrared spectrometer showed a new absorption peak at 1 637.19 cm 1, which corresponded to the carbonyl stretch vibration absorption of amide group in poly-N-vinyl-pyrrolidone. After the plasma treatment at low temperature, the mass change ratio of PLA film material was -0.6. CONCLUSION: The plasma treatment and polymerization can improve the hydrophilicity and cause coarse surface of PLA material, which will be helpful for the cell attachment.Department of Materials Science and Engineering, Jinan University, Guangzhou 510630, Guangdong Province, China Li Li-hua ☆ , Studying for doctorate, Lecturer, Department of Materials Science and Engineering, Jinan University, Guangzhou 510630, Guangdong Province, China floralee1977@ Correspondence to: Zhou Chang-ren, Professor, Doctor, Department of Materials Science and Engineering, Jinan University, Guangzhou 510630, Guangdong Province, China tcrz9@ Supported by: the National Natural Science Foundation of China, No. 30170272*; Major Program of Guangdong Science and Technology, No.A302020104* Received: 2007-12-18 Accepted: 2008-03-03 (07-50-12-7028/Y) Li LH, Ding S, Tian Y, Tian JH, Zhou CR.Surface modification of poly-D, L-lactic acid film with plasma graft polymerization. Zhongguo Zuzhi Gongcheng Yanjiu yu Linchuang Kangfu 2008;12(14): 2757-2760(China) [/zgl ckf/ejournal/upfiles/ 12-14/14k-2757 (ps).pdf]INTRODUCTIONPolymers are frequently used as biomaterials in areas of tissue engineering such as tissue replacement, tissue reinforcement and organ transplantation[1-5]. Polylactic acid (PLA) is one of the few synthetic biodegradable polymers, and is widely applied as sutures and orthopedic devices, for which high mechanical strength and toughness are required. However, it is hydrophobic and there are no natural recognition sites on the surface of PLA[6]. The surface hydrophobicity and low surface energy will affect cell adhesion on the PLA, which is critical because cell adhesion occurs before other events like cell spreading, cell migration and differentiation[7-8]. It has been reported that the cell adhesion to a substrate involves the following steps: adsorption of serum proteins on the substrate, contact of round cells to the substrate, attachment of the cells to the substrate and the spreading of the cells on the substrate[9]. Therefore, the surface properties of the materials are very important for the adhesion of proteins, and it is commonly accepted that the adhesion of cells to solid substrate is influenced by several substrate surface properties, such as hydrophilicity, surface charge, roughness and topography. Plasma treatment is an effective and widely used method for modifying the surface of materials. It has been reported that the surface of cell culture devices,ISSN 1673-8225 CN 21-1539/R CODEN: ZLKHAHsuch as petri dishes, micro-carriers and membranes, can be modified by plasma treatment to improve cell adhesion[10-13]. An important feature of plasma treatment is that it affects only the surface of a material subjected to treatment and a very thin near-surface layer whose thickness varies from 100 Å to several micrometers. The bulk of the polymer remains intact under these conditions, retaining the mechanical, physicochemical, and electro-physical properties of the original material surfaces. As a rule, the improvement of adhesive properties by plasma treatment is caused by not only surface cleaning of contaminants but also the formation of hydrophilic groups differing in their chemical nature, which provide high adhesive properties of the modified surfaces[14]. N-vinyl-pyrrolidone (NVP) possesses active double bond, which can be initiated easily to produce its polymer poly-N-vinyl-pyrrolidone (PVP). PVP as a kind of water soluble polymer, has been applied widely in fields of medicine, cosmetics, vintage and drink, etc[15-16]. In this study, we tried to functionalize the surface of poly-D, L-lactic acid (PDLLA) film with plasma treatment and graft polymerization to improve its hydrophilicity.EXPERIMENTS AND CHARACTERIZATIONPlasma treatment and graft polymerization on PDLLA film surface A RF plasma graft polymerizer at low temperature2757李立华，等.聚乳酸膜等离子接枝聚合聚乙烯基吡咯烷酮及表面性能研究(VTC-FSN-200, Japan, 13.56 MHz) was used for the surface modification. PDLLA films were placed in the glass reactor with a diameter of 5 cm and a length of 20 cm, and then a vacuum pump was connected. When the pressure got to 3 Pa, argon gas was input to increase the pressure to 20 Pa. Afterwards the 13.56 MHz RF source supplied the input power to the plasma reactor. The materials were treated with following parameters respectively: Wf=150 W, t =3, 2, 1 minutes; Wf=30 W, t =10, 8, 5, 3, 1 minutes. Surface grafting polymerization was then carried out in two methods. ①Gas phase polymerization: NVP was input to the reactor under vacuum after plasma treatment. The gas state NVP reacted with films in reactor for certain minutes (1, 2 and 3 minutes);②Liquid polymerization: PDLLA films were taken out from the reactor after plasma treatment and then immersed into NVP water solution (at 0.1, 0.2, 0.3 and 0.4 mass fractions) under N2 atmosphere with shaking for 12 hours. The products were washed with distilled water to remove NVP monomer and homopolymer PVP and then dried at 60 ℃. Characterization and analysis of the modified PDLLA films The surface morphology of the films was observed with scanning electron microscopy (SEM, JSM-T300, Japan) and atomic force microscopy (AFM, CP-Research, USA). The water contact angle of native and treated material surfaces was measured using a Contact Angle Meter (CAM-PLUS, USA) at room temperature. Surface composition was measured with Fourier transform infrared spectrometer (FTIR, Bruke EQUINOX 55, Germany). Mass changes measurement was applied to characterize the grafting efficiency.notching with different size (up to 10 μm) were seen, which were formed during the film preparation and plasma treatment.0.95 μm/Div 0.40 μm/Div 0 10 μm/Div 10 μm/Div 0 20 40 μm a: Surface image from atomic force microscopy (50 μm×50 μm)b: Computer-produced imageFigure 2Atomic force microscopy observation of poly-D, L-lactic acid film surfaceSurface water contact angle measurement PDLLA films were hydrophobic with water contact angle (θ) of 78°. After plasma treatment, the value decreased to 10° (Table 1). Due to the plasma treatment, plenty of free radical such as -OH, -COOH and -C=O were produced on the PDLLA film surface, which improved the polarity of the films, therefore improved the hydrophilicity and decreased the water contact angle.Table 1Group 1 2 3 4 5 6 7 8Surface water contact angle of poly-D, L-lactic acid films under different conditionsPower (W) 150 150 150 30 30 30 30 30 t (min) 1 2 3 1 3 5 8 10 Surface contact angleθ(°) 40-45 20-25 30-35 10-20 0-10 0-10 10-20 0-10RESULTSSurface morphology observation Figure 1 shows the surface morphology of PDLLA films observed by SEM, which revealed that plasma had erosion effects on films.a: Treated by low-power plasma (30 W, 3 minutes)b: Induced graft polymerization of N-vinyl-pyrrolidone by plasma (30 W, 3 minutes, 0.2 mass fraction of N-vinyl-pyrrolidone solution)Figure 1 Scanning electron microscopy images of polylactic acid film surfaceFigure 1a is the surface of plasma treated PDLLA film with low power (30 W, 3 minutes), and Figure 1b shows the surface morphology of the films which were grafted with PVP. The obvious pores and notches on both surfaces were visible. The toughness of the surface will be helpful for the cell attachment[17]. Figure 2a is the AFM images of micro area on the surface. Figure 2b is produced by computer. Many micro pores, juts and2758With high power 150 W, time affected the contact angle slightly, which ranged from 20° to 45°. θvalue changed greatly for each sample because of the coarse surface of the materials. To avoid the damage of high power to materials, low power 30 W was studied as well. It was very interesting that contact angle decreased much more. For some samples, the contact angle decreased even to 0 ° . Similarly, time affected the results not so much. According to the contact angle, 30 W was preferred to 150 W for reaction. With higher power, more corrosion was caused, and on the other hand, many polar groups were removed as well, and then caused the decrease of the polarity and increase of the water contact angle. The water contact angel of the treated films increased with time and recovered to about 70° two weeks later. Therefore plasma polymerization was applied, which were expected to improve the hydrophilicity. Plasma polymerization will make up for these defects and modify the surface of materials eternally. According to above results, the PDLLA films were first treated with plasma (Wf=30 W, t =3 minutes), and then with the newly produced active freeP.O. Box 1200, Shenyang 110004 kf23385083@李立华，等.聚乳酸膜等离子接枝聚合聚乙烯基吡咯烷酮及表面性能研究M%radials on the surface to initiate polymerization of NVP. The polymerization was carried out in gas phase method and liquid method respectively. The effects of grafting polymerization by gas method on surface contact angle were studied first. The results showed that θ value decreased from 78 ° to about 50 ° after polymerization. But time affected not so much on the surface hydrophilicity, and after polymerization of 1, 2 and 3 minutes, the contact angles were 50-55, 48-52 and 47-53, respectively. Comparing to gas method, liquid method had less effects on surface water contact angle of PDLLA film (Table 2). Modified with 0.2 mass fraction of NVP solution, contact angle decreased to 53°-55°, which was close to the value of gas method. Either lower or higher concentration of NVP solution could not decrease the value more. However, liquid method is easier to be operated. Therefore, polymerization with 0.2 mass fraction of NVP would be the best method for plasma surface modification of PDLLA films.Table 2 Effect of grafting polymerization by liquid method on surface water contact angle (Wf=30 W, t =3 min)Group Mass fraction of N-vinyl-pyrrolidone solution Water contact angleθ(°) 1 0.1 55-57 2 0.2 53-55 3 0.3 58-60 4M% was used to characterize indirectly the grafting efficiency of the polymerization. In this study, only liquid polymerization was studied because of its more merits than gas method. Figure 4 demonstrates that after plasma treatment, the mass of PDLLA films decreased with the M% of -0.6, because plasma damaged the materials surface (Figure 1), even though there were newly produced groups. The mass increased obviously after the films were reacted with NVP solution. NVP solution at 0.2 mass fraction had highest M%, which was in accordance with the results of Table 2. The higher concentration (0.3 and 0.4 mass fraction) of NVP solution dissolved the materials in some degrees, and then caused the mass decrease of the films.2.0 1.5 1.0 0.5 0 -0.5 -1.0 0 10 20 30 40NVP (%)Figure 40.4 60-66Effects of N-vinyl-pyrrolidone (NVP) concentration on grafting efficiencyDISCUSSIONFTIR spectroscopy FTIR spectra of the plasma treated PDLLA films and PVP grafted PDLLA films are shown in Figure 3. The absorption of -C-H of PLA was at 2 992.73 cm 1. 1 451.85 cm 1 and 1 367.32 -1 cm were the absorption of -CH3 bending vibrations. Strong peak of 1 751.25 cm 1 was from -C=O of ester. Comparing with both spectra (Figure 3a) and (Figure 3b), there was a new weak peak at 1 637.19 cm 1 on NVP grafted PDLLA films, which was from -C=O of amide group. The result revealed that PVP was grafted on the surface of PDLLA film. Mass change of PDLLA films The mass change of the PDLLA was calculated with the following equation: M%= (M-M0)/M0×100% M0 is the original mass of films, and M is the mass of films after grafting polymerization. There are plenty of electrons, ions and neutral ions in plasma, which will transfer the energy to the atoms or molecules of the materials surface when they contact with the materials and then generate different physical and chemical changes. Some particles can also be implanted to the material surface to cause collision, scattering, re-arrangement or crystallize, etc. and change the original surface properties. Therefore, after plasma treatment, PLA surface presented many micro pores and juts. In addition, due to the plasma treatment, plenty of free radicals such as -OH, -COOH and -C=O were produced on the PDLLA film surface, which improved the polarity of the films, therefore improved the hydrophilicity and decreased the water contact angle. According to the contact angle, 30 W was preferred to 150 W for reaction. With higher power, more corrosion was caused, and on the other hand, many polar groups were removed as well, and then caused the decrease of the polarity and increase of the water contact angle. The water contact angel of the treated films increased with time and recovered to about 70° two weeks later. There are many reasons for such phenomena, i.e. polar groups reacted with each other, or active groups in surrounding etc. Yasuda thought that the main reason is that the new produced polar groups turned to below the surface of the materials[18]. Plasma polymerization will make up for these defects and modify the surface of materials eternally[19-20]. According to above results, the PDLLA films were first treated with plasma (Wf=30 W, t =3 minutes), and then with the newly produced active free radial on the surface to initiate polymerization of NVP. The polymerization was carried out in gas method and liquid method, respectively.2759ab4 000 3 500 3 000 2 500 2 000 1 500 1 000 500 a: plasma treatment; b: induced graft polymerization of NVPFigure 3Infrared spectrometer spectra of poly-D, L-lactic acid films before and after grafting N-vinyl-pyrrolidone (NVP)ISSN 1673-8225 CN 21-1539/RCODEN: ZLKHAH李立华，等.聚乳酸膜等离子接枝聚合聚乙烯基吡咯烷酮及表面性能研究NVP was able to dissolve PLA to some degrees, which removed the newly produced active polar groups. Meantime polymerization and interaction between the active groups will get to a balance during certain period and terminate the reactions. Although gas grafting method could improve the hydrophilicity obviously, it has many disadvantages. It wastes much solvent during the process, and it is not quantitative when the reactors are concerned. Similarly, as liquid method, high concentration of NVP could dissolve more PLA surface. NVP polymerization at 0.2 mass fraction would be the best method for plasma surface modification of PDLLA films.1516 17 18 19 20CONCLUSIONPlasma modification of PDLLA films was studied in this experiment. Water contact angle measurement showed that the hydrophilicity of the films was improved much after surface plasma treatment even at lower power (30 W) and in less time (3 minutes), but it recovered to original level two weeks later. Plasma graft polymerization of NVP could modify the material eternally, which was carried out in gas method and liquid method. Although both methods decrease the contact angle greatly, liquid method with NVP solution at 0.2 mass fraction is preferable considering the operation and accuracy of reaction. Furthermore, plasma treatment and polymerization may cause coarse surface, which will be helpful for the cell attach. Its more physiochemical properties and biocompatibility will be studied in the future.Chen H, Wang CG, Zhang WX, et al. Effect of acrylonitrile-N-vinylpyrrolidone copolymerization systems on monomer reactivity ratios. Gaofenzi Cailiao Kexue yu Gongcheng 2003;19(3):72-74 Chuang WY, Young TH, Yao CH, et al. Properties of the poly(vinyl alcohol)/chitosan blend and its effect on the culture of fibroblast in vitro. Biomaterials 1999;20(16):1479-1487 Ding S, Li LH, Zhou CR. Novel tissue engineering scaffolds. Shengwu Yixue Gongchengxue Zazhi 2002;19(1):122-126 Zhu HS, Gu JW, Wang LY, et al. Use of plasma-treated silk fibroin as culture matrix for human endothelial cells. Zhongguo Shengwu Yixue Gongcheng Xuebao 2002;21(6):525-535 Luo HL, Sheng J, Wan YZ. Plasma polymerization of styrene with carbon dioxide under glow discharge conditions. Appl Surface Sci 2007;253(12):5203-5207 Kumar DS, Fujioka M, Asano K, et al. Surface modification of poly(ethylene terephthalate) by plasma polymerization of poly(ethylene glycol). J Mater Sci Mater Med 2007;18(9):1831-1835聚乳酸膜等离子接枝聚合聚乙烯基 吡咯烷酮及表面性能研究**☆李立华，丁 珊， 田 冶，田金环，周长忍 暨南大学科学与工程系，广东省广州市 510630 李立华☆，女，1977 年生，山东省德州市人，汉族，暨南大学在读 博士，讲师，主要从事组织工程及相关生物材料的研究。