Evaluation of invitro degradation of commercially available breast implants

Polymer Testing 79 (2019) 106033

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Product Performance

Evaluation of invitro degradation of commercially available breast implants a

a

a

Izabelle de Mello Gindri , Lucas Kurth de Azambuja , Michele da Silva Barreto , ⁎ Gean Vitor Salmoriaa,b, , Carlos Rodrigo de Mello Roeslera

T

a

Laboratório de Engenharia Biomecânica, Hospital Universitário, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil Nimma, Núcleo de Inovação em Moldagem e Manufatura Aditiva, Departamento de Engenharia Mecânica, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil

b

ARTICLE INFO

ABSTRACT

Keywords: Breast implants PDMS Material characterization Degradation

Implantable silicone gel breast devices have been commonly used for augmentation mammaplasty and breast reconstruction. Nowadays, 13 manufacturers dominate the global breast implants market and about 1.5 million breast implants surgeries are performed every year. This study investigated the mechanical and physicochemical properties of breast implants from five manufactures. Surface morphology, chemical composition, thermal behavior, cross-linking degree and mechanical properties were monitored on samples as received and after submitted to degradation in acidic and basic conditions. All samples demonstrated changes in chemical structure after degradation experiments, and parameters such as cross-linking degree and chemical composition seems to play important role on material performance.

1. Introduction Breast implants are medical devices used to correct congenital defects, for breast reconstruction after mastectomy or for breast augmentation. The introduction of these devices, by Cronin in the 60s, started a new era in plastic surgery, which readily disseminated stimulating scientific and technological development. Currently, it is estimated that about 1.5 million breast implants surgeries are performed every year around the world [1]. Furthermore, by the year of 2024, the breast implants industry is projected to reach a market value of about $4.5 billion, in which manufacturers from several countries compete for new consumers [2]. This kind of procedure is on the top ranking of popularity in the world representing 15.8% (3.7 million procedures). Brazil is the second place in the rank, below the United States, proceeding an average of 2.5 million procedures/year [1]. Until 2024, according to Global Market Insights, the breast implant market will overpass the value of $4.5 billion, the study also indicate the difficult to detect a burst in the implant as a bounding for the development of the sector [2]. Silicone breast implants, consist of a shell filled with a fixed amount of silicone gel. Both the shell and the filler are usually manufactured with polydimethylsiloxane (PDMS), due to its excellent properties, such as biocompatibility, elastic behavior, thermal and chemical stabilities [3]. The main difference between the shell and gel is based on the cross-

linking degree, which is lower in the gel. Despite the improvements made over the years within device design and manufacturing technologies, the long-term safety of breast implants is still questioned. Regulatory agencies, such as Food and Drug Administration (FDA) in United States, Anvisa in Brazil, and European Commission in Europe, have implemented international standards for quality control of these devices. Currently, ISO 14607:2018(E) (Non-active surgical implants – Mammary implants – Particular requirements), specifies particular requirements for intended performance of mammary implants. However, most of the data generated during design verification and safety evaluations remains unpublished under the control of manufacturing companies. In 2010 the recall of Poly Implant Prothèse implants raised some concern about quality control of breast implants, including the investigation of their physicochemical and mechanical properties. Since then, a number of studies investigating retrieved implants have been published, including a protocol for retrieval analysis [4,6]. In spite of this interest, investigations on new implants characteristics is scarce, and do not offer a protocol, or a set of analysis that can provide complete information about the properties of these devices, as well as their potential performance. According to Holmich et. Al, the chances of rupture of a prosthesis increases as the prosthesis become older. In the first 3–5 years, the prosthesis has a chance of rupture between 0 and 2% increasing by 10% after 10 years [5]. However, the reasons of those

Corresponding author. Laboratório de Engenharia Biomecânica, Hospital Universitário, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil. E-mail addresses: [email protected] (G. Vitor Salmoria), [email protected] (C. Rodrigo de Mello Roesler). URL: http://www.lebm.ufsc.br (C. Rodrigo de Mello Roesler). ⁎

https://doi.org/10.1016/j.polymertesting.2019.106033 Received 2 April 2019; Accepted 6 August 2019 Available online 11 August 2019 0142-9418/ © 2019 Elsevier Ltd. All rights reserved.

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I. de Mello Gindri, et al.

ruptures are not well understood and 74% of them are classified as “spontaneous”. A mechanism of interaction between the human body and breast implants has been proposed by Hamilton [7] in which both acidic and basic degradation reactions were considered. The results indicated that when exposed to extreme pH variation there is scission of polymeric chain into smaller molecules of PDMS, resulting in modification of many material's properties [7]. However, this study has been performed in only one brand of breast implant. The present paper investigates mechanical and physicochemical properties of five brands of breast implants which has high impact in Brazilian and international market. The samples were submitted to acidic and basic degradation environments to simulate the worst-case scenario these medical devices may face in the human body. Post degradation results were used to understand potential degradation mechanisms of PDMS-based materials. Results within each brand as well as between brands were evaluated and compared. A set of analysis was proposed for quality control of breast implants.

The samples were collected from the bottom of each implant and cut in small square of 2 mm × 2 mm. Those samples were covered by gold and dried for 24 h in a dissector. Subsequently, samples were evaluated using 30X magnification in a JEOL JSM-6390LV Scanning Electron Microscope. The same samples which were used for SEM were used for EDS coupled to the equipment. 2.4. Fourier transform infrared spectroscopy (FTIR) Attenuated total reflectance - Fourier transform infrared spectra (ATR-FT-IR) (spectral with 400–4000 cm−1, scans: n = 32, resolution = 4 cm) were recorded using a PerkinElmer spectrometer equipped with an ATR unit Pike GladiATR™ Vision. According to the chapter 6, subitem 6.2 of the ISO 14949:2011 [8] and ASTM 1252 [9], the infrared spectra of silicone samples should show six characteristics absorption peaks: 2962 ± 5 cm−1 (-Si(CH3)2); 2906 ± 5 cm−1 (-Si(CH3)); 1260 ± 5 cm−1 (-Si(CH3)2); 1094 ± 5 cm−1 (-Si(CH3)2–O–Si(CH3)2), 1022 ± 5 cm−1 (-Si-O-Si-) [10] and 765 ± 5 cm−1 (CH3). The samples were collected from the bottom of the prosthesis as described in section 2.1.

2.1. Materials and samples preparation Ten pristine implants, from five different manufacturers (two from each manufacturer) were selected and denominated as samples: A, B, C, D and E. Each breast implant was cut in two parts, bottom and top of the shell, and the gel was carefully removed. Subsequently, both portions of the shell were cleaned with isopropyl alcohol. Half of the samples from the superior and inferior portion were separated and analyzed with Fourier Transformation Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and swell tested. Half of the samples from the top were submitted to mechanical testing. The summary of. In a second moment the other half of the samples from brand A, B, C and D were exposed to adegradation environment to simulate, according to Hamilton [7], prostheses high degraded. Afterwards these samples were characterized as the others one. Samples E were not submitted to degradation due to the lack of material.

FTIR DSC Swell Mechanical

a b c d

2.5. Differential Scanning Calorimetry (DSC) DSC curves were recorded using a Perking Elmer 6000. Two samples extracted from the implant's shell of each brand were cut and weight in approximately 7 mg ± 1 mg. The samples were placed and sealed in aluminum pans. The analysis was conducted following the ISO 11357-1 [11] and ASTM D3418 [12] standards in an instrument supply by ultrapure nitrogen gas with 19,8 ml/min flow. The method consisted on five steps: (i) Isotherm at 30 °C for 3 min; (ii) Decrease the temperature from

Samples A

MEV

1

2.3. Scanning electron microscopy and energy dispersive spectroscopy

2. Experimental

Testing

Mbefore x100 Mafter

Mass loss % = 1

ARa Bab Acc ARa Bab Acc ARa Bab Acc ARa Bab Acc ARa Bab Acc

B

C

D

E

Supd

Infe

Supd

Infe

Supd

Infe

Supd

Infe

Supd

Infe

3 3

3 3 3 3 3 3 3 3 3 3 3 3 -

3 3 -

3 3 3 3 3 3 3 3 3 3 3 3 -

3 3

3 3 3 3 3 3 3 3 3 3 3 3 -

3 3 -

3 3 3 3 3 3 3 3 3 3 3 3 -

3 -

-

As received. Submitted to basic degradation. Submitted to acidic degradation. Superior portion of prosthesis.

2.2. Mass loss

30 °C to – 90 °C at 10 °C/min cooling rate; (iii) Isotherm at – 90 °C for 30 min; (iv) increase the temperature from 90 °C to 30 °C at 10 °C/min, and (iv) Isotherm at 30 °C for 3 min.

Samples were weight before (Mbefore) and after (Mafter) exposure to degradation solution. The mass loss was determined using Equation (1). 2

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2.6. Swelling test

3. Results

The crosslinking degree was determined according to the percentage of gel in the polymer structure. The percentage of gel was determined by the swelling of the PDMS samples, immersed in Toluene as proposed by Fernandes [13]. The process consists in: (i) Weigh the samples using a digital balance; (ii) Immerse the samples in toluene for 24 h; (iii) Remove the samples from toluene and weigh them on a digital balance; (iv) Dry the samples for 48 h at 100 °C; (v) Weigh the samples, using a digital balance; (vi) Dry for another 24 h to guarantee that there was not variation of the mass, assuring the samples are completely dried; (vii) Weigh the samples, using a digital balance; (viii) Determine the gel percentage using Equation (2) proposed by Elzubair [14].

This paper investigated the mechanical and physicochemical properties of commercially available breast implants before and after degradation. Changes in chemical composition and mechanical properties were monitored in order to evaluate the extension of material degradation when exposed to acidic and basic environment.

(

)

Gel (%) = Mo Ms x100

3.1. Morphological evaluation and SEM-EDS Macroscopic characteristics of samples investigated in this work are show in Fig. 1. Distinct features prior to degradation were observed, in which samples A, B, C and D presented a textured shell, while Sample E had a smooth shell. The surface finish properties of implants were further investigated using SEM, as demonstrated in Fig. 2. Distinct patterns were observed. Sample A and D presented smaller textured characteristics in comparison to Samples B and C, while the smooth feature of sample E was confirmed by SEM. All the samples presented similar chemical composition as investigated by EDS and shown in Figs. S1–S5 in supporting information. Carbon (C), Oxygen (O) and Silicon (Si), which composes the PDMS structure were identified. No sign of morphological modification and other elements were detected after degradation (data not shown).

2

where: Gel (%) is the crosslinking degree, Ms the inicial mass of the sample, Mo the final mass after dry. 2.7. Mechanical test The mechanical tests were conducted according to the ISO 14607:2018(E) [15] and ASTM D412 [16]. Three specimens of each implant were extracted according to ISO 37:2017–2[17], in tie shape and the thickness measured with a digital micrometer, totalizing 15 samples. For each test, were conducted in a universal test machine EMIC DL3000 with cell charge 50kfg EMIC-SV50, the specimen was attached in the extremity, between two claws, with a transducer, EMIC EE04, of displacement (clip cage) installed in the central portion. The tests were conducted by controlling the displacement with a speed control of 500 mm/min, with a pre-charge of 0,2 N, obtaining a curve Force (N) versus Displacement (mm). Dividing the force (N) by the transversal area (mm2) of each sample we obtained the curve Tension (MPa) versus displacement (mm). The results were normalized in 450% of deformation and compared between before and after degradation since the objective is to test the changes of the mechanical behavior for the medical device.

3.2. Mass loss Results of mass loss for shells exposed to degradation solution during 90 days are shown in Table 1. Mass loss was observed for all samples indicating interaction between solution and material. However, this process has been more accentuated in shells exposed to acidic solution. 3.3. FTIR The chemical composition of all samples was monitored before and after degradation tests using the FTIR. The spectra of samples as aeceived are shown in Fig. 3. All samples demonstrated PDMS characteristic [18] peaks at 2955 cm−1 (CH in CH3), 2921 cm−1 (CH3), 1456 cm−1 (CH3 with asymmetrical deformation), 1412 cm−1 (CH2), 1257 cm−1 (CH3 with asymmetrical deformation), 1078 cm−1 (Si–O–Si), 1006 cm−1 (-Si(CH3)2–O–Si(CH3)2) and 765 cm−1 (Si(CH3)2) [18]. In addition, peaks at 842 cm−1 and 698 cm−1 were reported only for samples A and B which are related with vinylic groups and the crosslink network [19]. The FTIR spectra before and after degradation in acidic and basic solutions are shown in Fig. 4 for sample A and in Figs. S6–S9 for samples B, C, D and E in supporting information. Distinct features were notice for all samples in peaks at 1078 cm−1 and 765 cm−1 as well as the appearance of a broad peak at 3500 cm−1 associated with the material hydrolysis (OH functional groups). For samples A and B, the peak at 842 cm−1 was not observed after degradation. Since the peaks ranging from 1078 cm−1 to 1006 cm−1 (Peak I) are related to the polymer backbone and the peak at 1257 cm−1 (Peak II)

2.8. Degradation Half of the samples A, B, C and D were separated and exposed to degradation environment for 90 days at 37.5 °C. Mechanical samples A and C were exposed to one solution composed by hydrochloric acid in a pH of 1.25 measured by a Peg Tecnopon with an Ag/AgCl cell. While mechanical samples B and D were exposed to a solution composed by sodium hydroxide in a pH 13, also measured by the same peg as done for acidic solution. Physic-chemical samples A, B, C and D were exposed in both solutions. The notation of samples exposed to basic degradation will be followed by “ba” while the notation of samples exposed to acidic degradation will be followed by “ac”.

Fig. 1. Samples A, B, C, D and E, respectively. 3

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Fig. 2. SEM of samples A, B, C on the top and D and E below.

3.4. DSC

Table 1 Mass loss after 90 days degradation. Sample

Mass loss (g)

Mass loss (%)

Aac Bba Cac Dba

0.005 0.001 0.005 0.001

0.75 0.32 0.87 0.12

± ± ± ±

0.002 0.000 0.001 0.000

± ± ± ±

DSC curves are reported in Fig. 5 and thermal parameters, such as melting temperature and enthalpy, are shown in Table 3. The melting temperature was verified around - 40 °C (Tf1) in all samples, which is in accordance with previous results obtained for PDMS [18]. An extra endothermic peak was detected around −56 °C for samples A and B during the analysis, which was denominated as Tf2. Crystallinity results are summarized in Table 4 and after degradation only sample C presented decrease in the crystallinity values, in which higher reduction was observed on samples exposed to the acidic medium. The effect of degradation on Samples B and C are represented in Fig. 6, while results of samples A, D and E are shown in Fig. S10, S11and S12 in supporting information.

0.24 0.04 0.22 0.04

refers to CH3, the ratio of those peaks was calculated to investigate changes in polymer composition resulting from degradation. The values are shown in Table 2. All samples presented reduction in the Ratio I/II after degradation, indicating changing in the chemical structure of materials under investigation.

Fig. 3. FTIR spectra of samples A-E as aeceived studies. 4

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Fig. 4. FTIR spectra from sample A as received, Aac and Aba.

Cross-linking increased as follow A < B < D < E < C. There were no changes in the cross-linking results after degradation experiments.

Table 2 Peak area and the ratio of peaks of 1078 cm−1, 1006 cm−1. Sample

Area Peak I (1006 - 1078 cm−1)

Area Peak II (1257 cm−1)

Ratio I/II

A Aa Aba B Bac Bba C Cac Cba D Dac Dba

70.7 105.0 106.4 75.4 98.5 94.1 66.4 79.5 87.2 67.0 103.6 104.0

4.4 9.5 9.0 4.4 7.4 8.2 4.6 6.7 6.1 3.8 9.7 9.8

16.2 11.1 11.8 17.1 13.4 11.5 14.4 11.9 14.4 17.8 10.7 10.6

3.6. Mechanical test The mechanical tests were executed according to the ISO 14607:2018(E) [15] and the results are described in Table 6. Mechanical strength measured at 450% of deformation for samples A-E as received ranged from 3.69 to 9.71 MPa, demonstrating heterogenic mechanical properties among the samples. Since sample E was not subjected to degradation, mechanical tests were conducted only on pristine samples of this brand. After degradation samples A and B demonstrated decreased strength after exposure to acidic and basic environments, respectively, while samples C and D did not show any effect. Sample B demonstrated the poorest properties after degradation, rupturing before the end of the experiment.

3.5. Cross-linking degree (swell)

4. Discussion

Following the methodology proposed by Fernandes [13] the crosslinking density was obtained and the results are presented in Table 5.

Samples A, B, C and D presented a textured membrane which is

Fig. 5. (a) DSC curves of samples A-E and (b) magnification of samples A and B curves to demonstrate the additional melting transition (Tf2). 5

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Table 3 DSC results for samples before and after degradation. Brand

As Received Tf1 (°C)

Condition Tf2 (°C)

ΔH (J/g)

a

a

A

−43.2

-

0.1

-

B

−44.2

−56.2

0.1

0.8

C

−40.2

-a

17.4

-a

D

−40.2

-a

12.2

-a

Aac Aba Bac Bba Cac Cba Dac Dba

After Degradation Tf1 (°C)

Tf2 (°C)

ΔH (J/g)

−45.2 −43.2 −42.2 −44.2 −40.2 −40.2 −40.2 −40.2

−56.2 -a −57.2 −56.2 -a -a -a -a

0.1 0.1 0.1 0.1 15.5 16.4 11.5 12.2

0.1 -a 0.2 0.1 -a -a -a -a

-aNot detected. Table 4 Crystallinity of samples as received and after degradation.

a

Sample

As received Crystallinity (%)

A

Normal 0.27

Cold -a

B

0.21

2.15

C

62.83

-a

D

51.44

-a

E

38.83

-a

Sample Aac Aba Bac Bba Cac Cba Dac Dba –

After Degradation (%) Normal 0.32 0.22 0.26 0.21 48.52 51.31 51.08 52.00 -b

Table 5 Crosslinking percent data from samples non degraded and After degradation in acidic or basic solution.

Crystallinity

As received Sample A B C D E

Cold 3.42 – 4.33 1.94 -a -a -a -a -b

a

Cross-linking (%) 91.4 ± 0.7 91.3 ± 0.3 82.6 ± 0.6 90.5 ± 0.5 87.6 ± 0.8

After degradation Sample Aac Bba Cac Dba -a

Cross-linking (%) 91.8 ± 2.6 91 ± 0.7 81 ± 1.4 91.3 ± 0.2 -a

Sample not exposed to degradation.

Table 6 Strenght resistance for 450% deformation for samples non degraded and degraded in acidic or basic envirnment.

Not detected. -bSample not exposed to degradation.

achieved after an additional step in the manufacturing process consisting of using foams or salts to generated a rougher pattern on the material surface. Two distinct process are suggested for the prosthesis under investigation. Due to the square shape texture shape, samples A, B and C were suggested to be pushed into granular salt before being allowed to cure in the laminar flow oven. The resulting shape is related to the macroscopic feature of salt crystals, which are usually cubic. According to Barr and Bayant [20], once the surface is cured, the salt is removed by washing the implant surface with water. As the salt is eliminated, the implant surface remains pitted with randomly-arranged cubed indentations. On the other hand, Sample D texture is suggested to be created with a negative contact imprint from a polyurethane foam between the coating and curing stages [20]. Although the surface finish results in different morphological features, the chemical composition of

As received Sample Mechanical Strength for 450% deformation (MPa) A 8.07 ± 2.15 B 3.69 ± 1.09 C 5.92 ± 1.17 D 9.71 ± 1.41 E 6.03 ± 0.24 a b

After degradation Sample Mechanical Strength for 450% deformation (MPa) 4.46 ± 0.04 AAc a BBa – CAc 4.86 ± 0.34 8.14 ± 0.01 DBa E -b

Brand B ruptured before reach 450% of deformation. Sample was not exposed to degradation.

silicone membranes is not expected to be modified during this procedure as confirmed by the FTIR data [20]. According to the ABNT NBR 14949:2011 there is a limit quantity of metals and chlorine concentration in breast implants, which may be residual from synthesis and

Fig. 6. Effects of degradation on DSC curves of Sample B (a) and Sample C (b). 6

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crosslinking reactions of the PDMS. During the chemical characterization, neither metals nor chlorine was verified. Discrete mass loss was verified in all samples, in which the acidic medium resulted in higher values in comparison to basic medium. All samples presented PDMS chemical characteristic in FTIR spectra, however, distinct peaks at 842 cm−1 and 698 cm−1 were observed for samples A and B, which correspond to vinylic groups. Vinylic functional groups are usually used as end groups in the siloxane monomers to create three-dimensional structure of cross-linked PDMS [3,13]. The presence of these peaks in the spectrum may be related to residual monomers in the polymer structure. According to Hamilton [7], the degradation of PDMS may happen in acidic and basic conditions via hydrolysis. During this reaction the polymeric chains are broken into smaller linear molecules with hydroxyl end groups or into cyclic and more stable structures. After degradation, there was a reduction in the ratio between peaks associated with polymer backbone (1006 - 1078 cm−1) and terminal methyl groups (1257 cm−1), indicating changing in the chemical compositions. This change associated with a broad peak ranging from 2800 to 3500 cm−1 may indicate hydrolysis of investigated materials and formation of HPDMS [7]. PDMS degradation may occur via specific or general catalysis in acidic and basic media. Considering the conditions used in the present work we suggest that degradation was mediated via specific catalysis, once strong acidic and basic solutions were used along de experiments. In DSC analyses, all samples presented melting points according to values reported in the literature. Some samples have also presented an extra peak around −56 °C, which may to an additional crystalline arrangement resulting from cold crystallization[21-23]. This crystallization process is inefficient and generates metastable crystals [22]. The presence of cold crystallization in sample B as received may indicate higher concentration of low molecular weight species, which are known to melt at lower temperature in comparison to molecules with higher molecular weight. After degradation, the crystallinity of sample C was observed to reduce, while the crosslinking degree did not change. This result may indicate that areas which were not crosslinked were more susceptible to the degradation. Results shown in Tables 3 and 4 demonstrated that the crosslinking has a direct influence in the mechanical strength. Sample C had the lowest crosslinking of all samples and presents the second lowest strength, after sample B. Brands A and D which had a higher crosslinking, also presented higher mechanical strength. However, according to the ISO 14607:2018(E), all the samples reached the approve criteria. Sample B has the lowest strength, even though having a high crosslinking degree. This result suggests that not only the crosslinking degree affects the mechanical performance of material. The composition of non-cross-linked portion of material may also influence its behaviour in which the presence of lower material weight compounds is suggested to decrease the mechanical strength. After degradation the samples had a decrease in the mechanical strength, which can be related to the changes in physicochemical properties. Since crystallinity of the material has reduced for samples C and the changes were more significant for those samples, it seems that non-crosslinked structure are more susceptible to chemical degradation of the polymer. Moreover, since sample A had a higher crosslink than sample C and D, and also were not so affected by the degradation, it may be suggested that higher crosslinking degree is related to samples more resistant to chemical degradation.

mechanical resistance. Exception was verified in sample B, which may be explained by the composition of non-crosslinked region. Exposure to acidic and basic media during 90 days resulted in physicochemical and mechanical changes in samples evaluated, demonstrating that both conditions caused degradation of materials. Cross-linking degree was the only property that was not affect after degradation, indicating that these regions are more resistant against degradation. However distinct behaviour of samples with different cross-link degree indicates that these regions also play important role in the material performance. Acknowledgements The authors would like to thank Programa de Apoio a Núcleos de Excelência (PRONEX)/Fundação de Amparo à Pesquisa e Inovação de Santa Catarina (FAPESC), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (I.M.G and L.K.A), CNPQ (G.V·S and C.R.M.R) and Financiadora de Estudos e Projetos (FINEP) for financial support. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.polymertesting.2019.106033. References [1] ISAPS, Demand For Cosmetic Surgery Procedures Around The World Continues To Skyrocket – Usa, Brazil, Japan, Italy And Mexico Ranked In The Top Five Countries, ISAPS, 2017. [2] G.M. Insights, Breast Implants Market Worth $4.5 Billion by 2024: Global Market Insights, Inc (2017) Available at: https://globenewswire.com/news-release/2017/ 08/16/1086500/0/en/Breast-Implants-Market-worth-4-5-Billion-by-2024-GlobalMarket-Insights-Inc.html Accessed: 4th November 2017. [3] A.C.C. Esteves, et al., Influence of cross-linker concentration on the cross-linking of PDMS and the network structures formed, Polymer 50 (2009) 3955–3966. [4] H.J. Brandon, V.L. Young, M.E. Watson, C.J. Wolf, K.L. Jerina, Protocol for retrieval and analysis of breast implants, J. Long Term Eff. Med. Implant. 13 (2003) 49–61. [5] L. Hölmich, et al., Incidence of silicone breast implant rupture, Am. Med. Assoc. 138 (2015). [6] W.Y. Baek, D.H. Lew, D.W. Lee, A retrospective analysis of ruptured breast implants, Arch. Plast. Surg. 41 (6) (2014) 734–739. [7] R. Hamilton, Hydrolysis of Silicone Polymers in Aqueous Systems, Lakehead University, 2008. [8] ISO, ISO 14949:2001 - Implants for Surgery – Two-Part Addition-Cure Silicone Elastomers, (2001). [9] ASTM, ASTM E1252, Available at: https://compass.astm.org/EDIT/html_annot.cgi? E1252+98(2013)e1, (1998) Accessed: 6th February 2018. [10] G. Beretta, et al., Analytical investigations on elastomeric shells of new Poly Implant Prothese (PIP) breast and from sixteen cases of surgical explantation, J. Pharm. Biomed. Anal. 98 (2014) 144–152. [11] ISO, ISO 11357-1:2016 - Plastics – Differential Scanning Calorimetry (DSC) – Part 1: General Principles, (2016). [12] ASTM, ASTM D3418, Available at: https://compass.astm.org/EDIT/html_annot. cgi?D3418+15, (2015) Accessed: 6th February 2018. [13] B.M.P. Fernandes, Influência do processo de reticulação no comportamento de um compósito de poli(dimetilsiloxano), Instituto Militar de Engenharia, 2009. [14] A. Elzubair, J.C.M. Suarez, C.M.C. Bonelli, E.B. Mano, Gel fraction measurements in gamma-irradiated ultra high molecular weight polyethylene, Polym. Test. 22 (2003) 647–649. [15] ISO 14607 Non-active surgical implants - mammary implants - particular requirements, Int. Stand (2007). [16] ASTM, ASTM D412, Available at: https://compass.astm.org/EDIT/html_annot.cgi? D412+16, (2016) Accessed: 6th February 2018. [17] ISO, ISO 37 - Rubber, Vulcanized or Thermoplastic - Determination of Tensile Stress-Strain Properties, (2017). [18] P. Class, Polymer Data October (1999) 1264, https://doi.org/10.1021/ja907879q. [19] A.C.C. Esteves, et al., Influence of cross-linker concentration on the cross-linking of PDMS and the network structures formed, Polymer 50 (2009) 3955–3966. [20] S. Barr, A. Bayat, Breast implant surface development: perspectives on development and manufacture, Aesthet. Surg. J. 31 (2010) 56–67. [21] Dollase, T., Spiess, HW., G. M. Cristalização do PDMS: efeito das reticências físicas e químicas - IOPscience. [22] M. Belbachir, Green Synthesis of Copolymer (PDMS-Co-PEO) Catalyzed by an Ecocatalyst Maghnite-H +, (2017). [23] J. Shawe, R. Riesen, J. Widmann, M. Schubnell, Interpreting DSC curves Part 1: dynamic measurements, Mettler Toledo (2000) 1–28.

5. Conclusion This study investigated the mechanical and physicochemical properties of breast implants from five different manufacturers. Material morphology, composition, crystallinity, cross-linked degree and mechanical strength were evaluated in samples as received and after degradation in acidic and basic solutions. Results demonstrated that crosslinking density has important influence in mechanical strength of PDMS, in which samples with higher cross-linking presented better 7