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Application of vibrational spectroscopy in the in vitro studies of carbon fiber-polylactic acid composite degradation.
Journal of Molecular Structure 482–483 (1999) 519–524
Application of vibrational spectroscopy in the in vitro studies of carbon fiber-polylactic acid composite degradation. Marta Blazewicz a,*, Maria Chomyszyn Gajewska b, Czeslawa Paluszkiewicz c a
Department of Advanced Ceramics, University of Mining and Metallurgy, 30 Mickiewicz Ave, 30-059 Cracow, Poland b Collegium Medicum, Jagiellonian University, 25 Smolensk str., 31-108 Cracow, Poland c Regional Laboratory, Jagiellonian University, 3 Ingardena str., 30-060 Cracow, Poland
Abstract Vibrational spectroscopy was used for assessment of new material for stomatology, for guided tissue regeneration (GTR) techniqe.Implants applied in the healing of periodontal defects using GTR technique have to meet stringent requirements concerning their chemical as well physical properties.At present the implants prepared from two layers membranes differing in porosity in their outer and inner layers are studied clinically. Composite plates prepared by us consist of three layers: polylactic acid film, carbon fibres coated with polylactic acid and carbon fabric.Vibrational spectroscopic studies of the material; polylactic acid- carbon fiber have made it possible to analyse chemical reactions occurring between the polymer and carbon surface. Analysis of the IR spectra of samples treated in Ringer solution allowed to describe the phenomena resulting from the composite degradation. It was shown that material biostability is related to the presence of carbon fibers. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Biomaterial; GTR technique; Composite material; Vibrational spectroscopy; Polylactic acid
1. Introduction Modern medicine requires high quality implant materials. At present, these requirements are fulfilled quite frequently by the materials of complex microstructure and chemical composition, designed based on the analysis of the tissue and reconstruction processes. Studies of implant materials directed at the preparation of biocompatible materials caused an increased interest in the investigation methods that allow to analyse the behaviour of the materials in natural and artificial body systems [1,2]. Vibrational infrared spectroscopy is a valuable tool
* Corresponding author. Fax: 1 48-12-6337161.
in the biomaterials engineering. It allows to study the processes occurring during the preparation of biomaterials as well as to analyse the interactions between an implant and biological system.Reconstruction of the losses in the bone tissue resulting from periodontitis requires the application of layered composites which are placed between gingival and the bone tissue [3,4]. The implant that was designed by us is a twocomponent composite of active carbon fabrics and polylactic acid. It was designed as a layered composite which is biodegraded in the living system thus eliminating the need for the second operation. Carbon fabrics which constitutes an inner part of the implant is a biocompatible material that stimulates the bone tissue growth [5]. The outer part of the composite, i.e. the one that has contact with gingival tissue is formed by polylactic acid, biocompatible, resorbable polymer
0022-2860/99/$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(98)00695-4
520
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
Fig. 1. FTIR spectra of composite: a, and both components used for its preparation, polylactic acid: b, carbon fabric: c.
that undergoes hydrolytic degradation in the biological system [6,7]. The middle part of the implant is made of polymer-fibre composite in which carbon fibres are coated with polylactic acid. This part plays a role of a binder for the inner and the
outer parts of the implant as well as it provides the appropriate mechanical strength and elasticity of the implant. Properties of the composites composed of fibres and polymer matrix depend mainly on the phenomena that take place at the fibres-polymer
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
521
Fig. 2. FTIR spectra of polylactic acid: a, after soaking in Ringer solution, 5 weeks:b, 10 weeks: c, 15 weeks: d.
matrix interface. Interactions between the two phases influence the mechanical properties and the transition phase which is formed in many cases may exhibit new chemical properties. Our studies carried out using FTIR spectroscopy concerned mainly the middle part of the implant prepared by us. The aim of these studies was to evaluate the influence of the carbon fibres surface on the polymer stability in the artificial biological system as well as on the course of hydrolytic degradation of polylactic acid coating on carbon fibres. It was expected that such studies would provide useful information for the application of the designed composite in stomatology and would also provide general information useful for the design of carbon-polymer implants for other fields of medicine.
2. Experimental 2.1. Materials Carbon fabrics-polylactic acid composites in the form of 3 mm × 25 mm × 30 mm plates as well as the 0.5 mm × 25 mm × 30 mm plates of polylactic acid were studied. For the preparation of these materials carbon fabrics prepared by carbonization of poly(acrylonitrile) and polylactic acid produced by Fluka (Mw 126 000) were used. 2.2. Material degradation Samples of composite materials as well as plates of polylactic acid were incubated in the Ringer solution of pH 7.4 at the temperature of 408C for 15 weeks.
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M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
Fig. 3. FTIR spectra of polylactic acid: a, and polylactic acid–carbon fibres composite: b, after 5 weeks soaking in Ringer solution.
Samples for the studies were taken after different time periods, dried at the temperature not exceeding 508C for 1 h and subjected to IR measurements. 2.3. FTIR studies Starting composite materials as well as the samples after incubation were studied by IR spectroscopy. All the samples were ground in the same conditions, mixed with KBr and pressed into pellets. IR studies were performed in transmission geometry in the middle infrared range on a FTS Digilab 60, BioRad spectrometer. Spectra of the starting samples as well as after their treatment in the Ringer solution are shown in Figs. 1–4. 3. Results and discussion In Fig. 1 three spectra of the composite (a) and both components used for its preparation, i.e. polylactic acid (b) and carbon fabrics (c) are collected. The spectrum of carbon fabrics does not show any visible absorption bands, This spectrum consists of an increasing envelope as a result of electronic absorption characteristic of carbon containing low amount of
oxygen. In the spectrum of polylactic acid the bands originating from CZO and CZOZC stretching vibrations in the range 1050–1250 cm 21 and the bands owing to stretching CyO vibrations at 1760 cm 21 can be seen. The spectrum in the range of 2800– 3000 cm 21 shows the presence of hydrocarbon groups, i.e. CH and CH3 characteristic of polylactic acid. The bands at 1207 cm 21, 1456 cm 21 as well as the complex shape of the band caused by CyO vibrations may be explained by the presence of carboxylic groups. High absorption in in the range of stretching vibrations may result from the method applied for the preparation of the samples for IR studies. The composite spectrum differs from the one of polylactic acid. The intensity of the bands caused by carboxylic groups is much lower in the composite spectrum. Differences concern also the range of the spectrum in which the bands originating from CH3 vibrations (deformational: 1383, 1456 cm 21 and stretching: 2879, 2996 cm 21) appear. Intensities of these bands are also much lower. From the analysis of the spectra of the composite and polyactic acid it can be concluded that the polymer interacts with the carbon fibres surface.
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
523
Fig. 4. FTIR spectra of polylactic acid: a, and polylactic acid–carbon fibres composite: b, after 10 weeks soaking in Ringer solution.
This surface is strongly non-uniform: free radicals, p electrons and active sites or acidic and basic type are present on it. The reaction taking place between the polymer and the fibres surface involves mainly CH and carboxylic polymer end groups. The spectra presented in Fig. 2 show different steps of polylactic acid degradation in the artificial biological fluid. It can be seen that the first step involves the disappearance of ester CZO groups and the spectrum shows the presence of both acid and alcohol in the system. In the final degradation step in the spectrum the bands proving acidic groups hydrolysis leading to the formation of carboxylic anions (COO 2) whose absorption bands are located at 1413 and 1578 cm 21. Figs. 3 and 4 illustrate the spectra corresponding to different steps of polymer and composite degradation. From these spectra it can be concluded that degradation of the polymer in the composite is slightly faster than that of polylactic acid. In both cases in the spectra of composite samples one can observe much lower intensities of the bands corresponding to the presence of an acid. Lower intensities show also the bands in the range of CZO vibrations (1050–1200 cm 21). In the composite spectrum (Fig. 3) a complex band in the range of 1550–1640 cm 21
appears. This can be explained by chemisorption of oxygen on carbon fibres surface.
4. Conclusion To summarize, it can be concluded that between carbon fibres surface and functional groups of the polymer chemical reaction occurs which most probably influences the polymer stability in biological systems. From the analysis of the spectra it follows that the course of the reaction is similar in both cases, however its kinetics are different. Differences in the rate of both samples degradation in biological fluids caused by the carbon surface may be because of its catalytic influence on the degradation of the ester groups of the polymer. Based on the results of the studies it can be assumed that carbon fibres do not influence chemical biocompatibility of polyester-based composites but they may alter their biofunctionality influencing their degradation period and microstructure within close-to-surface layers. Degradation period of the implants degraded in the living systems should be relevant to the tissue
524
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
reconstruction time. It seems that in the development of degradable composite implants made of resorbable polyesters and carbon fibres the main factor influencing their degradation rate may be chemical composition of carbon surface. The appropriate treatment of this surface may make it possible to tailor the degradation of biomaterials in biological systems. References [1] B.D. Ratner, J. Biomed. Mater. Res. 27 (1993) 837.
[2] J.D. Andreade, Clin. Mater. 11 (1992) 19. [3] D. Lundgren, T. Mathisen, J. Gottlow, The Journal of the SDA 86 (1994) 13. [4] A.K. Schlegel, H. Mohler, F. Busch, A. Mehl, Biomaterials 18 (1997) 535. [5] T. Cieslik, B. Pogorzelska-Stronczak, Z. Szczurek, R. Koszowski, D. Sabat, Engineering of Biomaterials 2 (1998) 16. [6] P. Mainil-Varlet, R. Curtis, S. Gogolewski, J. Biomed. Mater. Res. 36 (1997) 360. [7] I. Grizzi, H. Garreau, S. Li, M. Vert, Biomaterials 16 (1995) 305.
Application of vibrational spectroscopy in the in vitro studies of carbon fiber-polylactic acid composite degradation. Marta Blazewicz a,*, Maria Chomyszyn Gajewska b, Czeslawa Paluszkiewicz c a
Department of Advanced Ceramics, University of Mining and Metallurgy, 30 Mickiewicz Ave, 30-059 Cracow, Poland b Collegium Medicum, Jagiellonian University, 25 Smolensk str., 31-108 Cracow, Poland c Regional Laboratory, Jagiellonian University, 3 Ingardena str., 30-060 Cracow, Poland
Abstract Vibrational spectroscopy was used for assessment of new material for stomatology, for guided tissue regeneration (GTR) techniqe.Implants applied in the healing of periodontal defects using GTR technique have to meet stringent requirements concerning their chemical as well physical properties.At present the implants prepared from two layers membranes differing in porosity in their outer and inner layers are studied clinically. Composite plates prepared by us consist of three layers: polylactic acid film, carbon fibres coated with polylactic acid and carbon fabric.Vibrational spectroscopic studies of the material; polylactic acid- carbon fiber have made it possible to analyse chemical reactions occurring between the polymer and carbon surface. Analysis of the IR spectra of samples treated in Ringer solution allowed to describe the phenomena resulting from the composite degradation. It was shown that material biostability is related to the presence of carbon fibers. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Biomaterial; GTR technique; Composite material; Vibrational spectroscopy; Polylactic acid
1. Introduction Modern medicine requires high quality implant materials. At present, these requirements are fulfilled quite frequently by the materials of complex microstructure and chemical composition, designed based on the analysis of the tissue and reconstruction processes. Studies of implant materials directed at the preparation of biocompatible materials caused an increased interest in the investigation methods that allow to analyse the behaviour of the materials in natural and artificial body systems [1,2]. Vibrational infrared spectroscopy is a valuable tool
* Corresponding author. Fax: 1 48-12-6337161.
in the biomaterials engineering. It allows to study the processes occurring during the preparation of biomaterials as well as to analyse the interactions between an implant and biological system.Reconstruction of the losses in the bone tissue resulting from periodontitis requires the application of layered composites which are placed between gingival and the bone tissue [3,4]. The implant that was designed by us is a twocomponent composite of active carbon fabrics and polylactic acid. It was designed as a layered composite which is biodegraded in the living system thus eliminating the need for the second operation. Carbon fabrics which constitutes an inner part of the implant is a biocompatible material that stimulates the bone tissue growth [5]. The outer part of the composite, i.e. the one that has contact with gingival tissue is formed by polylactic acid, biocompatible, resorbable polymer
0022-2860/99/$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(98)00695-4
520
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
Fig. 1. FTIR spectra of composite: a, and both components used for its preparation, polylactic acid: b, carbon fabric: c.
that undergoes hydrolytic degradation in the biological system [6,7]. The middle part of the implant is made of polymer-fibre composite in which carbon fibres are coated with polylactic acid. This part plays a role of a binder for the inner and the
outer parts of the implant as well as it provides the appropriate mechanical strength and elasticity of the implant. Properties of the composites composed of fibres and polymer matrix depend mainly on the phenomena that take place at the fibres-polymer
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
521
Fig. 2. FTIR spectra of polylactic acid: a, after soaking in Ringer solution, 5 weeks:b, 10 weeks: c, 15 weeks: d.
matrix interface. Interactions between the two phases influence the mechanical properties and the transition phase which is formed in many cases may exhibit new chemical properties. Our studies carried out using FTIR spectroscopy concerned mainly the middle part of the implant prepared by us. The aim of these studies was to evaluate the influence of the carbon fibres surface on the polymer stability in the artificial biological system as well as on the course of hydrolytic degradation of polylactic acid coating on carbon fibres. It was expected that such studies would provide useful information for the application of the designed composite in stomatology and would also provide general information useful for the design of carbon-polymer implants for other fields of medicine.
2. Experimental 2.1. Materials Carbon fabrics-polylactic acid composites in the form of 3 mm × 25 mm × 30 mm plates as well as the 0.5 mm × 25 mm × 30 mm plates of polylactic acid were studied. For the preparation of these materials carbon fabrics prepared by carbonization of poly(acrylonitrile) and polylactic acid produced by Fluka (Mw 126 000) were used. 2.2. Material degradation Samples of composite materials as well as plates of polylactic acid were incubated in the Ringer solution of pH 7.4 at the temperature of 408C for 15 weeks.
522
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
Fig. 3. FTIR spectra of polylactic acid: a, and polylactic acid–carbon fibres composite: b, after 5 weeks soaking in Ringer solution.
Samples for the studies were taken after different time periods, dried at the temperature not exceeding 508C for 1 h and subjected to IR measurements. 2.3. FTIR studies Starting composite materials as well as the samples after incubation were studied by IR spectroscopy. All the samples were ground in the same conditions, mixed with KBr and pressed into pellets. IR studies were performed in transmission geometry in the middle infrared range on a FTS Digilab 60, BioRad spectrometer. Spectra of the starting samples as well as after their treatment in the Ringer solution are shown in Figs. 1–4. 3. Results and discussion In Fig. 1 three spectra of the composite (a) and both components used for its preparation, i.e. polylactic acid (b) and carbon fabrics (c) are collected. The spectrum of carbon fabrics does not show any visible absorption bands, This spectrum consists of an increasing envelope as a result of electronic absorption characteristic of carbon containing low amount of
oxygen. In the spectrum of polylactic acid the bands originating from CZO and CZOZC stretching vibrations in the range 1050–1250 cm 21 and the bands owing to stretching CyO vibrations at 1760 cm 21 can be seen. The spectrum in the range of 2800– 3000 cm 21 shows the presence of hydrocarbon groups, i.e. CH and CH3 characteristic of polylactic acid. The bands at 1207 cm 21, 1456 cm 21 as well as the complex shape of the band caused by CyO vibrations may be explained by the presence of carboxylic groups. High absorption in in the range of stretching vibrations may result from the method applied for the preparation of the samples for IR studies. The composite spectrum differs from the one of polylactic acid. The intensity of the bands caused by carboxylic groups is much lower in the composite spectrum. Differences concern also the range of the spectrum in which the bands originating from CH3 vibrations (deformational: 1383, 1456 cm 21 and stretching: 2879, 2996 cm 21) appear. Intensities of these bands are also much lower. From the analysis of the spectra of the composite and polyactic acid it can be concluded that the polymer interacts with the carbon fibres surface.
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
523
Fig. 4. FTIR spectra of polylactic acid: a, and polylactic acid–carbon fibres composite: b, after 10 weeks soaking in Ringer solution.
This surface is strongly non-uniform: free radicals, p electrons and active sites or acidic and basic type are present on it. The reaction taking place between the polymer and the fibres surface involves mainly CH and carboxylic polymer end groups. The spectra presented in Fig. 2 show different steps of polylactic acid degradation in the artificial biological fluid. It can be seen that the first step involves the disappearance of ester CZO groups and the spectrum shows the presence of both acid and alcohol in the system. In the final degradation step in the spectrum the bands proving acidic groups hydrolysis leading to the formation of carboxylic anions (COO 2) whose absorption bands are located at 1413 and 1578 cm 21. Figs. 3 and 4 illustrate the spectra corresponding to different steps of polymer and composite degradation. From these spectra it can be concluded that degradation of the polymer in the composite is slightly faster than that of polylactic acid. In both cases in the spectra of composite samples one can observe much lower intensities of the bands corresponding to the presence of an acid. Lower intensities show also the bands in the range of CZO vibrations (1050–1200 cm 21). In the composite spectrum (Fig. 3) a complex band in the range of 1550–1640 cm 21
appears. This can be explained by chemisorption of oxygen on carbon fibres surface.
4. Conclusion To summarize, it can be concluded that between carbon fibres surface and functional groups of the polymer chemical reaction occurs which most probably influences the polymer stability in biological systems. From the analysis of the spectra it follows that the course of the reaction is similar in both cases, however its kinetics are different. Differences in the rate of both samples degradation in biological fluids caused by the carbon surface may be because of its catalytic influence on the degradation of the ester groups of the polymer. Based on the results of the studies it can be assumed that carbon fibres do not influence chemical biocompatibility of polyester-based composites but they may alter their biofunctionality influencing their degradation period and microstructure within close-to-surface layers. Degradation period of the implants degraded in the living systems should be relevant to the tissue
524
M. Blazewicz et al. / Journal of Molecular Structure 482–483 (1999) 519–524
reconstruction time. It seems that in the development of degradable composite implants made of resorbable polyesters and carbon fibres the main factor influencing their degradation rate may be chemical composition of carbon surface. The appropriate treatment of this surface may make it possible to tailor the degradation of biomaterials in biological systems. References [1] B.D. Ratner, J. Biomed. Mater. Res. 27 (1993) 837.
[2] J.D. Andreade, Clin. Mater. 11 (1992) 19. [3] D. Lundgren, T. Mathisen, J. Gottlow, The Journal of the SDA 86 (1994) 13. [4] A.K. Schlegel, H. Mohler, F. Busch, A. Mehl, Biomaterials 18 (1997) 535. [5] T. Cieslik, B. Pogorzelska-Stronczak, Z. Szczurek, R. Koszowski, D. Sabat, Engineering of Biomaterials 2 (1998) 16. [6] P. Mainil-Varlet, R. Curtis, S. Gogolewski, J. Biomed. Mater. Res. 36 (1997) 360. [7] I. Grizzi, H. Garreau, S. Li, M. Vert, Biomaterials 16 (1995) 305.