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DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203118 Thomas Reske*, Thomas Eickner, Niels Grabow, Klaus-Peter Schmitz and Stefan Siewert Accelerated Degradation of polymeric surgical suture materials Abstract: The degradable polymer Polydioxanone (PDO) is 2 Materials and methods used for medical implants since 1981. Manufacturers state a degradation timeframe of <180 days or an absorption duration of 182-238 days [1, 2]. Aim of this study was to find 2.1 Samples in vitro-conditions to degrade PDO films within four weeks. Therefore the degradation of PDO was performed in PDO Resomer X 206 S and P(LLA-co-GA) Resomer LG 857 accelerated conditions in tempered alkaline glycine NaOH S were obtained by Sigma Aldrich. The polymer films were buffer. Molecular weight and mass loss were studied. PDO prepared as described by Petersen et al. . Briefly the results were compared with poly lactic-co-glycolic acid polymer was dissolved in a solvent (chloroform for P(LLA- P(LLA-co-GA). co-GA) and hexafluoroisopropanol for PDO) and poured into a glass petri dish. The solvent was allowed to evaporate until Keywords: biodegradable polydioxanone, poly lactic-co- an approx.100 µm thick film had formed. Polymer films were glycolic acid, accelerated degradation, alkaline. washed twice using methanol and water. Afterwards circular 6.0 mm punches were made. https://doi.org/10.1515/cdbme-2020-3118 2.2 Molecular weight analysis 1 Introduction The molecular weight data of polymer films were obtained at Degradable polymers like PDO, P(LLA-co-GA) or poly 30 ºC using a PSS SECcurity SEC system (Polymer Standard lactic acid (PLLA) and their combinations are used for Services GmbH, Mainz, Germany) including a RI detector medical implants since 40 years. Within the mentioned combined with a WGE Dr. Bures g 2010 viscosity detector polymers PDO shows a comparably fast degradation (WGE Dr. Bures GmbH, Dallgow, Germany). Separation 3 5 behavior. Therefore sutures, plates, meshes, screws, pins and was performed with three PSS SDV columns (10 , 10 and clips represent typical PDO applications. 10 Å respectively). Chloroform stabilized with ethanol was Degradation is induced by hydrolysis of the ester groups used as eluent at a flow rate of 1 ml/min. The samples were within the polymer. Lin et al. and Brito et al. showed PDO prepared with a concentration of 1.5 mg/ml in chloroform suture degradation in phosphate buffer (pH 7.4) at 37 °C [3, with hexylbenzene as internal standard and the injection 4]. There PDO showed a weight loss of 10% within 10 weeks volume was 0.1 ml. The molecular weights were calculated and 12 weeks, respectively [3, 4]. Molecular weight loss was by the universal calibration method using twelve polystyrene not reported there. calibration standards in a range between 376 and Here conditions for an accelerated degradation study 2,570,000 g/mol. were determined. 2.3 Degradation conditions ______ Test specimens were incubated in 4 ml alkaline glycine *Corresponding author: Thomas Reske: Institute for Implant buffer (pH 8.7). They were given on a rotating platform- Technology and Biomaterials e.V., Friedrich-Barnewitz-Str. 4, shaking device (Unimax 1010, Heidolph Instruments 18119 Rostock-Warnemünde, Germany, e-mail: GmbH&Co. KG, Schwabach, Germany) at 100 rpm and at a firstname.lastname@example.org temperature of 50 °C. Every seven days the medium was Thomas Eickner, Niels Grabow, Klaus-Peter Schmitz: Institute for Biomedical Engineering, Rostock University Medical Center, replaced by fresh buffer. Sample withdrawal occurred after 0, 18119 Rostock-Warnemünde, Germany 7, 14, 21 and 28 days. Klaus-Peter Schmitz, Stefan Siewert: Institute for Implant Technology and Biomaterials e.V., 18119 Rostock-Warnemünde, Germany Open Access. © 2020 Thomas Reske et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. Thomas Reske et al., Accelerated Degradation of polymeric surgical suture materials — 2 step the remaining polymer chains are removed by the 3 Results and discussion surrounding medium which leads to loss of polymer mass, molecular weight and physical properties [6, 7]. In consideration of the Q10 temperature coefficient a degradation temperature of 50 °C was chosen. Additionally Table 1: Mass loss and molecular weight loss values. the pH was increased to 8.7 compared to standard degradation conditions in phosphate buffer (pH 7.4) at 37 °C. As Figure 1 shows, the masses of the P(LLA-co-GA) PDO P(LLA-co-GA) samples do not decrease significantly after four weeks in Degradation Mass Molecular Mass Molecular medium. time weight weight [w] [%] [%] [%] [%] 1 100.0 100.0 100.0 100.0 100.0 100.0 100. 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100. 100.0 1 95.2 38.8 99.5 86.6 95.0 37.9 99.6 98.0 75.2 36.1 99.6 91.6 88.5 37.6 99.6 92.1 2 87.7 26.7 99.7 75.7 Figure 1: Accelerated polymer degradation of PDO and P(LLA- 68.8 26.1 99.7 75.9 co-GA); mass loss; Mean values, n = 3. PDO values shown with linear regression. Regression executed with Microsoft Excel. 86.4 19.4 99.7 75.2 80.9 24.0 99.7 75.6 However, PDO shows a linear decrease of the polymer mass 3 73.6 16.1 99.7 64.8 resulting in a value of 68% of the initial mass (see table 1). A weight loss of 10% was found after 1 week. 77.1 14.8 99.7 70.2 69.4 13.6 100. 61.5 73.4 14.8 99.9 65.5 4 57.8 12.8 100.9 48.2 72.7 12.9 99.8 44.2 72.2 12.7 99.5 45.8 67.6 12.8 100.0 46.1 Regarding the molecular weight loss (Figure 2), PDO shows the major changes in the first week resulting in a value of 38% (see table 1) caused by the hydrolysis of amorphous PDO regions, enhanced by temperature and elevated pH. Figure 2: Accelerated polymer degradation of PDO and P(LLA- P(LLA-co-GA) shows a different degradation behavior. Here co-GA); molecular weight loss; Mean values, n = 3. P(LLA-co-GA) values shown with linear regression. PDO values shown with a linear molecular weight loss during the whole study was exponential regression. Regression executed with Microsoft Excel. observed. Comparison of the P(LLA-co-GA) values with data recorded under standard conditions (37 °C, phosphate Polymer degradation usually passes several steps. In the buffer, pH 7.4) shows a three times accelerated degradation beginning of the degradation, water diffuses into the bulk. (Figure 3) at the half value of the initial molecular weight. There hydrolysis starts predominantly in the amorphous This acceleration cannot be transferred straightly to phase. This reduces the molecular weight but not the mass. PDO, but an approximation is supposed. Short crystalline polymer chains are hydrolized and in a last Thomas Reske et al., Accelerated Degradation of polymeric surgical suture materials — 3 Author Statement Research funding: Partial financial support by the European Regional Development Fund (ERDF) and by the Federal Ministry of Education and Research (BMBF) within RESPONSE “Partnership for Innovation in Implant Technology” is gratefully acknowledged. The author thanks Rieke Latzitis and Caroline Dudda for technical support. Conflict of interest: Authors state no conflict of interest. References  https://healthcare.evonik.com/product/health- care/en/products/biomaterials/RESOMER/ (accessed 09 March 2020) Figure 3: Molecular weight loss of P(LLA-co-GA); degradation in  Ethicon. Z997G, www.ethicon.com/na/epc/code/z997g standard and accelerated conditions; Mean values, n = 3. Values (accessed 09 March 2020). shown with linear regression (executed with Microsoft Excel).  Lin HL, Chu CC, Grubb D. Hydrolytic degradation and morphologic study of poly-p-dioxanone. J Biomed Mater Res 1993;27:153–166.  Brito Y, Sabino MA, Ronca G, Müller AJ. Changes in 4 Conclusion Crystalline Morphology, Thermal, and Mechanical Properties with Hydrolytic Degradation of Immiscible Biodegradable PPDX/PCL Blends. J Appl Polymer Science 2008;3848- Conditions to degrade PDO in vitro within four weeks were developed. Therefore degradation was performed at 50 °C in  Petersen S, Hussner J, Reske T, Grabow N, Senz V, Begunk alkaline NaOH glycine buffer (pH 8.7). Mass loss followed a R, Arbeiter D, Krömer HK, Schmitz KP, Meyer zu Schwabe- linear progress. Last withdrawal of the PDO samples was dissen HE, Sternberg K. In vitro study of dual drug-eluting stents with locally focused sirolimus and atorvastatin release. conducted with a remaining mass of 68% of the initial mass. J Mater Sci: Mater Med 2013;24:2589–2600. Samples showed fragmentation at that time. Medium change  Martins JA, Lach AA, Morris HL, Carr AJ, Mouthuy PA. was no longer feasible without sample loss. Molecular weight Polydioxanone implants: A systematic review on safety and degradation followed a non-linear, exponential-like progress performance in patients. J Biomat Appl:2020;34(7):902-916.  Sabino MA, Gonzalez S, Marquez L, Feijoo JL. Study of the with a molecular weight loss of 76% after two weeks and hydrolytic degradation of polydioxanone PPDX. Polym 87% after four weeks. In the same degradation medium Degrad Stab 2000;69:209–216. P(LLA-co-GA) showed a three times accelerated degradation compared to standard conditions (37 °C, pH 7.4).
Current Directions in Biomedical Engineering – de Gruyter
Published: Sep 1, 2020
Keywords: biodegradable polydioxanone; poly lactic-coglycolic acid; accelerated degradation; alkaline
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