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Physical characterization of acrylic bone cement cured with new accelerator systems
Clinical Materials
8 (1991) 131-136
Physical Characterization of Acrylic Bone Cement Cured with New Accelerator Systems M. C. Tanzi, I. Sket Department
of Bioingegneria, Politecnico di Milano, 20133 Milano, Italy
A. M. Gatti CstE. Monari Centro di Studio dei Biomateriali, Clinica Odontoiatrica,
UniversitB di Modena, 41100 Mbdena, Italy
Abstract: In the attempt to substitute dimethyl-p-toluidine (DMPT), a toxic tertiary aryl-amine accelerator, into the formulation of acrylic cements, less toxic accelerator systems are developed. These systems consist of benzoyl peroxide (BPO) and unsaturated tertiary-aryl-amines, such as acryloyl- (ANP) and methacryloyl-(MNP) N-phenylpiperazine, which can be chemically incorporated in the polymerizing resin or, at least, result in less leaching from cured materials. In this work compressive mechanical properties and ageing tests for colour stability of acrylic cement cured with BP0 and ANP or MNP have been considered. For compressive tests, cylindrical specimens were cured with BP0 and equivalent molecular amounts of DMPT, ANP and MNP. Compressive yield stress (a,), strain at yield (E,, %) and elastic modulus (E) gave very similar results for samples cured with DMPT and ANP, and slightly lower results for samples cured with MNP. In colour stability tests, the samples (disks of 15 cm diameter) were exposed to UV light at different irradiation times (up to 42 h). The evaluation of the colour change was performed with a digital analyser for images, and observed under scanning electron microscopy. From the obtained results, ANP appeared to be the best candidate as accelerator in the preparation of biomedical acrylic resins and composites.
INTRODUCTION
have been made up until now to develop new accelerators which can be chemically incorporated into the polymerizing materials, thus avoiding subsequent leaching. Taking into account this consideration, two new unsaturated tertiary aromatic amines (acryloyl-and methacryloyl-phenylpiperazine, ANP and MNP respectively) were synthesized :
Setting of self-curing acrylic resins for biomedical use (bone cements, dental base materials, neurosurgery) is at present achieved at room temperature by a redox system, consisting of an organic peroxide (usually benzoyl peroxide, BPO) as initiator, and a tertiary aromatic amine (usually dimethyl-p-toluidine, DIMPT) as accelerator. Tertiary aromatic amines are highly toxic, suspected carcinogen compoundls; after reacting with BP0 they become oxidized to secondary amines and amine oxides, and, in addition., some unchanged amines will be left over. All these products are capable of being leached out after the implantation, and can contaminate the body tissues.l Although less toxic amines have been recently studied for biomedical applications, no attempts
CH,=C
ANP: R=H;
MNP: R=CH,
131 Clinical Materials 10
0267-6605/91/$03.50
0
1991 Elsevier Science Publishers
Ltd, England ECM
8
M. c. Tanzi et al.
132
Their ability to homopolymerize and copolymerize with methylmethacrylate (MMA), their efficacy as accelerators in the curing reaction of polymethylmethacrylate (PMMA), and their leachability from cured PMMA have been studied with good results (ANP > MNP), and have been already described.2m4 In comparison with DMPT, ANP and MNP showed good efficacy as accelerators, even though PMMA setting times were slightly prolonged. ANP can easily homopolymerize and copolymerize with MMA. MNP does not homopolymerize; with MMA, it is able to form copolymers which contain only 3 % or less MNP.’ This work deals with further physical characterization of acrylic cement cured with BP ANP or MNP (DMPT for comparison), namely compressive mechanical properties and accelerated ageing tests. MATERIALS DMPT and MMA (commercial reagents) were vacuum distilled ; PMMA was the CMW-1 bone cement powder, which contains BP0 (272 % w/w) and a radiopaque agent (9.1% w/w barium sulphate). ANP and MNP were synthesized in the authors’ laboratory, as previously described.2q4
Ageing tests were Carrie samples to UV ght, ~~~l~wi~g the Ref. 5, to chec
filament mercury-arc transmission coefhcie 3000 A
amount of UV performed :
rays.
Two
ageing
cycles
were
(I) whole disks were irradiated for 6, 32, 18, 24 and 42 h; (2) the time of irradiation was ecreased (0~5, 1, ) to check the begi darking) p~e~~rne~o~ in the first cycle. Nine samples for each were thus used. The colour change q~ant~fficati~~ was digital analyser of images (V In this case the analyser wa being able to ‘read ’ simultan~~~~~y luminosity of several points.
hen the surface 9 or yellowish, the
Samples Cylindrical specimens (according to IS0 5833/l, 1987) for compressive tests, and 1.5-cm diameter disks for ageing tests were prepared by mixing at room temperature the appropriate amount of PMMA (CMW-1 powder) with MMA (previously additioned with increasing equimolecular amounts of DMP, ANP or MNP, in turn), in a 2: 1 ratio, according to standard preparations of the acrylic bone cement. The same amount of BP0 was used in each preparation, i.e. that originally present in the CMW- 1 powder. The specimens for the compressive test were post-cured for 48 h at 50 “C, while those for ageing tests were kept in the dark at room temperature until the beginning of the tests. METHODS Compressive tests were performed by testing the specimens along the longitudinal axis, according to IS0 5833, with an Instrom testing machine at a cross head speed of 20 mm/min.
BESIJ Compressive mechanica Compressive
strength
(cr,), % strain
at yie
Ageing tests irradiation
metry
cycle, i.e. fro
was lost. The consistent
e round plane geowhite layer whit
Acrylic 140
120
bone cement cured with new accelerators Table 1. Luminous reflectance and MNP-cured samples
F_.
of UV irradiated
DMPT,
ANP
D.f'T
Irradiation time Accelerator DMPT MNP ANP
1.2
1.7
23
19
28
37
activators
4.7
3
2
(weight
4
5
%)
Fig. 1. Compressive yield stress of DMPT, ANP and MNPcured samp!les. Values are the mean f SD of at least five specimens.
a 3 6 > W 4 7
n
Y
133
1.2
1.7
23
19
28
37
activators
47
2
(weight
3
4
5
%I
Fig. 2. Strain at yield of DMPT, ANP and MNP-cured samples. Valiues are the mean *SD of at least five specimens.
0 214k8 215f3 21454
30 min
4h
186+7 203&S 201f7
176+ 13 1851-4 187&5
appeared on the surface of the samples cured with DMPT was almost absent in the case of samples cured with ANP and MNP. In addition, DMPTcured samples were much more damaged at 42 h than the corresponding MNP- anld ANP-cured samples (see Fig. 4). Sections of 42-h-aged DMPT samples were observed under SEM:, in order to identify the white layer. SEM photographs of some sections of DMPTcured samples, before and after the ageing test (42 h), are shown in Fig. 5. After the test, the round holes created by the entrapment of air bubbles during the preparation of the samples were enlarged, and took an irregular shape. This difference can be also seen at higher magnification (Fig. 5(a2) and (b2)). The arrows in Fig. 5 indicate the zones where the EDS analysis was carried out. The EDS spectra showed the peaks of barium and sulphur, related to the presence of BaSO, ; this radiopaque material was present also in the inner part of the sample, but its concentration was lower. Figure 6 shows the overlay of these spectra. The ageing test at shorter time intervals showed that the darkening phenomenon occurred within the first hour of irradiation in the case of DMPT, and later on for MNP (2 h) and ANP (4 h). DMPT showed a darkening, while AMP and MNP a yellowing phenomenon. The quantification of the colour change, made on 9000 readings, is reported in Table 1. For DMPT the relative reflectance [(LR- LR,)/LR,] decreased by 13 % after 30 min, and 18 % after 1 h. Instead for MNP and ANP the changes are 5 % and 6 % after 38 min, and 14 % and 13 % after 4 h, respectively.
CONCLUSIONS 0
1.2
1.7
23
1.9
activators
28
37
47
(weight
2
3
4
5
%I
Fig. 3. Elastic modulus of DMPT, ANP and MNP-cured samples. Values are the mean &SD of at least five specimens.
The compressive mechanical properties of ANPcured PMMA were very similar to those of DMPcured PMMA; the ageing behaviour of the former materials being better than that of the latter ones. IO-2
34
C. Timzi et al.
Fig. 4. Photographs
of unaged
(0 h), and UV-aged
(42 h) for DMPT
(D), ANP (A) and MNP (M)-cured
samples
Acrylic
bone cement cured with new accelerators
Fig. 5. SEIU photographs of unaged (al, 20 x ; bl, 320 x ) and 42-h-aged (a2, 20 x ; b2, 320 x ) DMPT-cured samples. indicate the zones (1, white layer; 2, inner portion) in which EDS spectra were carried out.
The arrow:
M. G. Tanzi et al.
136 ; K,
2.0
revious experiences chemically into fore slightly released from cured In conclusion, from the results appears to be the best candidate aroma of t~adit~olla~ tertiary preparation of iomedical acrylic resins and corn--” posites.
3.0
4.0
5.0
6.0
Fig. 6. EDS spectra of the zones indicated in Fig. 5: (1) white surface layer; (2) inner part of the sample. The magnification is shown in the rectangle below.
The use of MNP seems to produce materials with accelerated ageing and less satisfactory mechanical properties, when compared with ANP. In addition,
De Wijn, J. R. & van Mullen, acrylic implants. In Bkmmpa~ib vol. II, ed. D. F. Williams. CRC Press, Boca 1981, pp. 99~-126. 2. Danusso, F., Tank, M. C, Levi, M. & Martini, A.; Polymers and copolymers of Pa-acryloyl-N’-ghenylpiperazine. Pobjmzer, 31 (1990) li577-80. 15th Annual SFB 3. Tanzi, M. @. & Levi, M., Proceedings Meeting, Lake Buena Vista 4/Y&?&5/2,1989, p. 47. 4. Tanzi, M. CL, Levi, M. 4% 1 F., Amides from W~he~y~~~pe~a~~~e as low activatoxs m radical polymerization. Polymer, 31 (1990) 1735-8. Gatti, A. M., UV-radiation aging test on compos materials for dental restoration. J. Biomed. .%faler. Rcs., (198’7) 603-12.
8 (1991) 131-136
Physical Characterization of Acrylic Bone Cement Cured with New Accelerator Systems M. C. Tanzi, I. Sket Department
of Bioingegneria, Politecnico di Milano, 20133 Milano, Italy
A. M. Gatti CstE. Monari Centro di Studio dei Biomateriali, Clinica Odontoiatrica,
UniversitB di Modena, 41100 Mbdena, Italy
Abstract: In the attempt to substitute dimethyl-p-toluidine (DMPT), a toxic tertiary aryl-amine accelerator, into the formulation of acrylic cements, less toxic accelerator systems are developed. These systems consist of benzoyl peroxide (BPO) and unsaturated tertiary-aryl-amines, such as acryloyl- (ANP) and methacryloyl-(MNP) N-phenylpiperazine, which can be chemically incorporated in the polymerizing resin or, at least, result in less leaching from cured materials. In this work compressive mechanical properties and ageing tests for colour stability of acrylic cement cured with BP0 and ANP or MNP have been considered. For compressive tests, cylindrical specimens were cured with BP0 and equivalent molecular amounts of DMPT, ANP and MNP. Compressive yield stress (a,), strain at yield (E,, %) and elastic modulus (E) gave very similar results for samples cured with DMPT and ANP, and slightly lower results for samples cured with MNP. In colour stability tests, the samples (disks of 15 cm diameter) were exposed to UV light at different irradiation times (up to 42 h). The evaluation of the colour change was performed with a digital analyser for images, and observed under scanning electron microscopy. From the obtained results, ANP appeared to be the best candidate as accelerator in the preparation of biomedical acrylic resins and composites.
INTRODUCTION
have been made up until now to develop new accelerators which can be chemically incorporated into the polymerizing materials, thus avoiding subsequent leaching. Taking into account this consideration, two new unsaturated tertiary aromatic amines (acryloyl-and methacryloyl-phenylpiperazine, ANP and MNP respectively) were synthesized :
Setting of self-curing acrylic resins for biomedical use (bone cements, dental base materials, neurosurgery) is at present achieved at room temperature by a redox system, consisting of an organic peroxide (usually benzoyl peroxide, BPO) as initiator, and a tertiary aromatic amine (usually dimethyl-p-toluidine, DIMPT) as accelerator. Tertiary aromatic amines are highly toxic, suspected carcinogen compoundls; after reacting with BP0 they become oxidized to secondary amines and amine oxides, and, in addition., some unchanged amines will be left over. All these products are capable of being leached out after the implantation, and can contaminate the body tissues.l Although less toxic amines have been recently studied for biomedical applications, no attempts
CH,=C
ANP: R=H;
MNP: R=CH,
131 Clinical Materials 10
0267-6605/91/$03.50
0
1991 Elsevier Science Publishers
Ltd, England ECM
8
M. c. Tanzi et al.
132
Their ability to homopolymerize and copolymerize with methylmethacrylate (MMA), their efficacy as accelerators in the curing reaction of polymethylmethacrylate (PMMA), and their leachability from cured PMMA have been studied with good results (ANP > MNP), and have been already described.2m4 In comparison with DMPT, ANP and MNP showed good efficacy as accelerators, even though PMMA setting times were slightly prolonged. ANP can easily homopolymerize and copolymerize with MMA. MNP does not homopolymerize; with MMA, it is able to form copolymers which contain only 3 % or less MNP.’ This work deals with further physical characterization of acrylic cement cured with BP ANP or MNP (DMPT for comparison), namely compressive mechanical properties and accelerated ageing tests. MATERIALS DMPT and MMA (commercial reagents) were vacuum distilled ; PMMA was the CMW-1 bone cement powder, which contains BP0 (272 % w/w) and a radiopaque agent (9.1% w/w barium sulphate). ANP and MNP were synthesized in the authors’ laboratory, as previously described.2q4
Ageing tests were Carrie samples to UV ght, ~~~l~wi~g the Ref. 5, to chec
filament mercury-arc transmission coefhcie 3000 A
amount of UV performed :
rays.
Two
ageing
cycles
were
(I) whole disks were irradiated for 6, 32, 18, 24 and 42 h; (2) the time of irradiation was ecreased (0~5, 1, ) to check the begi darking) p~e~~rne~o~ in the first cycle. Nine samples for each were thus used. The colour change q~ant~fficati~~ was digital analyser of images (V In this case the analyser wa being able to ‘read ’ simultan~~~~~y luminosity of several points.
hen the surface 9 or yellowish, the
Samples Cylindrical specimens (according to IS0 5833/l, 1987) for compressive tests, and 1.5-cm diameter disks for ageing tests were prepared by mixing at room temperature the appropriate amount of PMMA (CMW-1 powder) with MMA (previously additioned with increasing equimolecular amounts of DMP, ANP or MNP, in turn), in a 2: 1 ratio, according to standard preparations of the acrylic bone cement. The same amount of BP0 was used in each preparation, i.e. that originally present in the CMW- 1 powder. The specimens for the compressive test were post-cured for 48 h at 50 “C, while those for ageing tests were kept in the dark at room temperature until the beginning of the tests. METHODS Compressive tests were performed by testing the specimens along the longitudinal axis, according to IS0 5833, with an Instrom testing machine at a cross head speed of 20 mm/min.
BESIJ Compressive mechanica Compressive
strength
(cr,), % strain
at yie
Ageing tests irradiation
metry
cycle, i.e. fro
was lost. The consistent
e round plane geowhite layer whit
Acrylic 140
120
bone cement cured with new accelerators Table 1. Luminous reflectance and MNP-cured samples
F_.
of UV irradiated
DMPT,
ANP
D.f'T
Irradiation time Accelerator DMPT MNP ANP
1.2
1.7
23
19
28
37
activators
4.7
3
2
(weight
4
5
%)
Fig. 1. Compressive yield stress of DMPT, ANP and MNPcured samp!les. Values are the mean f SD of at least five specimens.
a 3 6 > W 4 7
n
Y
133
1.2
1.7
23
19
28
37
activators
47
2
(weight
3
4
5
%I
Fig. 2. Strain at yield of DMPT, ANP and MNP-cured samples. Valiues are the mean *SD of at least five specimens.
0 214k8 215f3 21454
30 min
4h
186+7 203&S 201f7
176+ 13 1851-4 187&5
appeared on the surface of the samples cured with DMPT was almost absent in the case of samples cured with ANP and MNP. In addition, DMPTcured samples were much more damaged at 42 h than the corresponding MNP- anld ANP-cured samples (see Fig. 4). Sections of 42-h-aged DMPT samples were observed under SEM:, in order to identify the white layer. SEM photographs of some sections of DMPTcured samples, before and after the ageing test (42 h), are shown in Fig. 5. After the test, the round holes created by the entrapment of air bubbles during the preparation of the samples were enlarged, and took an irregular shape. This difference can be also seen at higher magnification (Fig. 5(a2) and (b2)). The arrows in Fig. 5 indicate the zones where the EDS analysis was carried out. The EDS spectra showed the peaks of barium and sulphur, related to the presence of BaSO, ; this radiopaque material was present also in the inner part of the sample, but its concentration was lower. Figure 6 shows the overlay of these spectra. The ageing test at shorter time intervals showed that the darkening phenomenon occurred within the first hour of irradiation in the case of DMPT, and later on for MNP (2 h) and ANP (4 h). DMPT showed a darkening, while AMP and MNP a yellowing phenomenon. The quantification of the colour change, made on 9000 readings, is reported in Table 1. For DMPT the relative reflectance [(LR- LR,)/LR,] decreased by 13 % after 30 min, and 18 % after 1 h. Instead for MNP and ANP the changes are 5 % and 6 % after 38 min, and 14 % and 13 % after 4 h, respectively.
CONCLUSIONS 0
1.2
1.7
23
1.9
activators
28
37
47
(weight
2
3
4
5
%I
Fig. 3. Elastic modulus of DMPT, ANP and MNP-cured samples. Values are the mean &SD of at least five specimens.
The compressive mechanical properties of ANPcured PMMA were very similar to those of DMPcured PMMA; the ageing behaviour of the former materials being better than that of the latter ones. IO-2
34
C. Timzi et al.
Fig. 4. Photographs
of unaged
(0 h), and UV-aged
(42 h) for DMPT
(D), ANP (A) and MNP (M)-cured
samples
Acrylic
bone cement cured with new accelerators
Fig. 5. SEIU photographs of unaged (al, 20 x ; bl, 320 x ) and 42-h-aged (a2, 20 x ; b2, 320 x ) DMPT-cured samples. indicate the zones (1, white layer; 2, inner portion) in which EDS spectra were carried out.
The arrow:
M. G. Tanzi et al.
136 ; K,
2.0
revious experiences chemically into fore slightly released from cured In conclusion, from the results appears to be the best candidate aroma of t~adit~olla~ tertiary preparation of iomedical acrylic resins and corn--” posites.
3.0
4.0
5.0
6.0
Fig. 6. EDS spectra of the zones indicated in Fig. 5: (1) white surface layer; (2) inner part of the sample. The magnification is shown in the rectangle below.
The use of MNP seems to produce materials with accelerated ageing and less satisfactory mechanical properties, when compared with ANP. In addition,
De Wijn, J. R. & van Mullen, acrylic implants. In Bkmmpa~ib vol. II, ed. D. F. Williams. CRC Press, Boca 1981, pp. 99~-126. 2. Danusso, F., Tank, M. C, Levi, M. & Martini, A.; Polymers and copolymers of Pa-acryloyl-N’-ghenylpiperazine. Pobjmzer, 31 (1990) li577-80. 15th Annual SFB 3. Tanzi, M. @. & Levi, M., Proceedings Meeting, Lake Buena Vista 4/Y&?&5/2,1989, p. 47. 4. Tanzi, M. CL, Levi, M. 4% 1 F., Amides from W~he~y~~~pe~a~~~e as low activatoxs m radical polymerization. Polymer, 31 (1990) 1735-8. Gatti, A. M., UV-radiation aging test on compos materials for dental restoration. J. Biomed. .%faler. Rcs., (198’7) 603-12.