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Minimise thermo-mechanical batch variations when processing medical grade lactide based copolymers in additive manufacturing
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology.ORCID iD: 0000-0002-6877-7858
IMT Lille Douai, Ecole nationale supérieure Mines-Télécom Lille Douai, Materials & Processes Center, Cité scientifique, Villeneuve d'Ascq Cedex, France.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology.ORCID iD: 0000-0001-7135-9158
IMT Lille Douai, Ecole nationale supérieure Mines-Télécom Lille Douai, Materials & Processes Center, Cité scientifique, Villeneuve d'Ascq Cedex, France.
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2020 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 181, article id 109372Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing is suitable for producing complex geometries; however, variation in thermo-mechanical properties are observed during one batch cycle when degradable aliphatic polyesters of medical grade are used in melt extrusion-based methods. This is one important reason for why additive manufacturing has not yet been fully utilised to produce degradable medical implants. Herein, the internal variation has been minimised during one batch cycle by assessing the effect of different processing parameters when using commercially available medical grade copolymers. To minimise the molar mass, thermal and mechanical variation within one batch cycle, the rheological fingerprint of the commercially available medical grade poly(L-lactide-co-ε-caprolactone) and poly(L-lactide-co-trimethylene carbonate) has been correlated to the process parameters of the ARBURG Plastic Freeforming. An increase in the temperature up to 220°C and the associated increase in pressure are beneficial for the viscoelastic and thermally stable poly(L-lactide-co-ε-caprolactone). In contrast, a temperature below 220°C should be used for the poly(L-lactide-co-trimethylene carbonate) to reduce the variation in strain at break during one batch cycle. The residence time is decreased through the increase of the discharge parameter. An increase in temperature is however required to reduce the viscosity of the polymer and allow the pressure to stay within the machine limitations at higher discharge parameters. The results are highly relevant to the development of additive manufacturing for the production of degradable medical devices with identical properties. In fact, Food and Drug Administration guidelines for additive manufacturing of medical implants specify the need to control changes in material properties during the process.

Place, publisher, year, edition, pages
Elsevier BV , 2020. Vol. 181, article id 109372
Keywords [en]
Additive manufacturing, e-caprolactone, Freeforming, L-lactide, medical device, polyester, polymer degradation, trimethylene carbonate, Aliphatic compounds, Food additives, Functional polymers, Melt spinning, Aliphatic polyester, Discharge parameters, Food and Drug Administration, Increase in pressure, Mechanical variations, Processing parameters, Thermomechanical properties, 3D printers
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-287950DOI: 10.1016/j.polymdegradstab.2020.109372ISI: 000600681700052Scopus ID: 2-s2.0-85091516900OAI: oai:DiVA.org:kth-287950DiVA, id: diva2:1512012
Note

QC 20210203

Available from: 2020-12-21 Created: 2020-12-21 Last updated: 2022-06-25Bibliographically approved
In thesis
1. Degradable copolymers in additive manufacturing: controlled fabrication of pliable scaffolds
Open this publication in new window or tab >>Degradable copolymers in additive manufacturing: controlled fabrication of pliable scaffolds
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [sv]

Inom vävnadsregenerering är produktionen av väldefinieradematriser med en porös arkitektur av nedbrytbara polymerer av stortintresse, dessa kan nu skapas genom additiva tillverkningsprocesser. Vidadditiv tillverkning krävs ett smalt munstycke för att skapa detaljrikastrukturer och detta ställer krav på att de reologiska egenskapernaanpassat. Lägre viskositet av smältan gör de lättare att använda, men enhög molmassa krävs för tillverka matriser där de mekaniska egenskapernakan bibehållas under tiden som krävs för vävnadsregenerering. Ytterligareen utmaning uppstår när nedbrytbara polymerer används i smältbaseradadditiva tillverkningsprocesser är att termisk nedbrytning ofta reducerarmolmassan redan under produktionsfasen. För att kunna användanedbrytbara polymerer av medicinsk kvalitet i smältbaserad additivtillverkning och samtidigt minimera den termiska nedbrytningen har, idenna avhandling, reologiska fingeravtryck av nedbrytbara syntetiskapolymerer med medicinsk kvalitet använts för att bestämmaprocessparametrar. Termisk nedbrytning beroende av processparamaterar har analyserats och minimeras i två smältbaserade additivatillverkningsprocesser.En additiv tillverkningsprocess var designad där nedbrytbarapolymerer av hög molmassa kunde användas utan termisk nedbrytning närprocessparametrar hade valts utifrån polymerens egenskaper. Kunskapenom användningen av dessa polymerer inom additiv tillverkning kundeappliceras på en sampolymer som utvecklats inom forskningsgruppen förmjukvävnad, poly(ε-kaprolakton-co-p-dioxanon) för att skapa böjbaramatriser. Genom att använda reologisk analys och polymerkarakteriseringerhölls processparametrar som möjliggjorde additiv tillverkning utantermisk nedbrytning. I tillägg till val av polymer och processparametrar såkan mekaniska egenskaper också styras av den strukturella designen.Poly(ε-kaprolakton) användes som modellmaterial för att reducerastyvheten med hjälp av designen, resultatet visade att det var möjligt medmer än en faktor 10 och mjuka böjbara matriser skapades.

Abstract [en]

In tissue engineering, the production of well-defined scaffolds with a porous architecture from degradable polymers is of great interest. Detailed designs have become feasible through the development of additive manufacturing. A small nozzle size is needed to obtain detailed scaffold structures, and careful control of the rheological properties is therefore required during production. A lower viscosity of the melt allows for easier printability, but a high molar mass is required to produce scaffolds that can retain mechanical properties over the time needed for tissue regeneration. An additional challenge of using degradable polymers with high molar mass in any melt-based processing is that thermal degradation can reduce the molar mass during the production stage. To utilise medical grade degradable polymers whilst limiting the thermal degradation a rheological analysis of the most commonly used commercial medical-grade degradable synthetic polymers was performed. Their rheological behaviours aided in setting process parameters for two different melt-based additive manufacturing routes. The variation in thermal degradation in the two routes was assessed, and the parameters were adjusted to minimise it.

A nondegradative additive manufacturing method was designed, and knowledge regarding printability was developed based on rheological analysis and polymer characterisation methods. This knowledge was applied to the copolymer poly(e-caprolactone-co-p-dioxanone) developed within the group to fabricate pliable scaffolds for tissue engineering with an increased rate of hydrolysis in comparison to poly(e-caprolactone). In addition to the selection of the polymer and process parameters, the mechanical properties were also controlled through the structural design. Poly(e-caprolactone) was used as a model material to show how the mechanical properties of scaffolds could be controlled based on the design solely. The results showed that the stiffness could be reduced by more than a factor of 10 through tuning of the design, resulting in soft pliable scaffold structures.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2021. p. 86
Series
TRITA-CBH-FOU ; 2021:7
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-290799 (URN)978-91-7873-778-9 (ISBN)
Public defence
2021-03-26, https://kth-se.zoom.us/j/68298579714, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Fibre and Polymer Science
Funder
Swedish Foundation for Strategic Research , RMA15-0010
Note

QC 2021-02-23

Available from: 2021-02-23 Created: 2021-02-23 Last updated: 2022-06-25Bibliographically approved

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Ahlinder, AstridFuoco, TizianaFinne Wistrand, Anna

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