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Degradable copolymers in additive manufacturing: controlled fabrication of pliable scaffolds
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology. KTH Royal Institute of Technology.ORCID iD: 0000-0002-6877-7858
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: urn:nbn:se:kth:diva-290799ISBN: 978-91-7873-778-9 (print)OAI: oai:DiVA.org:kth-290799DiVA, id: diva2:1530592
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
List of papers
1. Medical grade polylactide, copolyesters and polydioxanone: Rheological properties and melt stability
Open this publication in new window or tab >>Medical grade polylactide, copolyesters and polydioxanone: Rheological properties and melt stability
2018 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 72, p. 214-222Article in journal (Refereed) Published
Abstract [en]

Rheological measurements have shown that lactide-based copolymers with L-lactide content between 50 and 100 mol% with varying comonomers, as well as polydioxanone (PDX), can be used in additive manufacturing analogously to poly(L-lactide) (PLLA) if their melt behaviour are balanced. The results indicate that copolymers can be melt processed if the temperature is adjusted according to the melting point, and parameters such as the speed are tuned to conteract the elastic response. Small amplitude oscillatory shear (SAOS) rheology, thermal and chemical characterisation allowed us to map the combined effect of temperature and frequency on the behaviour of six degradable polymers and their melt stability. Values of complex viscosity and Tan delta obtained through nine time sweeps by varying temperature and frequency showed that the molecular structure and the number of methylene units influenced the results, copolymers of L-lactide with D-Lactide (PDLLA) or glycolide (PLGA) had an increased elastic response, while copolymers with trimethylene carbonate (PLATMC) or epsilon-caprolactone (PCLA) had a more viscous behaviour than PLLA, with respect to their relative melting points. PDLLA and PLGA require an increased temperature or lower speed when processed, while PLATMC and PCLA can be used at a lower temperature and/or higher speed than PLLA. PDX showed an increased viscosity compared to PLLA but a similar melt behaviour. Negligible chain degradation were observed, apart from PLGA.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Degradable polymers, Melt rheology, Polyesters, Melt stability and polylactide
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-241208 (URN)10.1016/j.polymertesting.2018.10.007 (DOI)000454464600025 ()2-s2.0-85055196906 (Scopus ID)
Note

QC 20190118

Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2022-06-26Bibliographically approved
2. Minimise thermo-mechanical batch variations when processing medical grade lactide based copolymers in additive manufacturing
Open this publication in new window or tab >>Minimise thermo-mechanical batch variations when processing medical grade lactide based copolymers in additive manufacturing
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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
Keywords
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:nbn:se:kth:diva-287950 (URN)10.1016/j.polymdegradstab.2020.109372 (DOI)000600681700052 ()2-s2.0-85091516900 (Scopus ID)
Note

QC 20210203

Available from: 2020-12-21 Created: 2020-12-21 Last updated: 2022-06-25Bibliographically approved
3. Nondegradative additive manufacturing of medical grade copolyesters of high molecular weight and with varied elastic response
Open this publication in new window or tab >>Nondegradative additive manufacturing of medical grade copolyesters of high molecular weight and with varied elastic response
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2020 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 137, no 15, article id 48550Article in journal (Refereed) Published
Abstract [en]

Although additive manufacturing through melt extrusion has become increasingly popular as a route to design scaffolds with complex geometries the technique if often limited by the reduction in molecular weight and the viscoelastic response when degradable aliphatic polyesters of high molecular weight are used. Here we use a melt extruder and fused filament fabrication printer to produce a reliable nondegradative route for scaffold fabrication of medical grade copolymers of L-lactide, poly(epsilon-caprolactone-co-L-lactide), and poly(L-lactide-co-trimethylene carbonate). We show that degradation is avoided using filament extrusion and fused filament fabrication if the process parameters are deliberately chosen based upon the rheological behavior, mechanical properties, and polymer composition. Structural, mechanical, and thermal properties were assessed throughout the process to obtain comprehension of the relationship between the rheological properties and the behavior of the medical grade copolymers in the extruder and printer. Scaffolds with a controlled architecture were achieved using high-molecular-weight polyesters exhibiting a large range in the elastic response causing negligible degradation of the polymers.

Place, publisher, year, edition, pages
WILEY, 2020
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-267140 (URN)10.1002/app.48550 (DOI)000508022900024 ()2-s2.0-85073154893 (Scopus ID)
Note

QC 20200217

Available from: 2020-02-17 Created: 2020-02-17 Last updated: 2022-06-26Bibliographically approved
4. Poly(epsilon-caprolactone-co-p-dioxanone): a Degradable and Printable Copolymer for Pliable 3D Scaffolds Fabrication toward Adipose Tissue Regeneration
Open this publication in new window or tab >>Poly(epsilon-caprolactone-co-p-dioxanone): a Degradable and Printable Copolymer for Pliable 3D Scaffolds Fabrication toward Adipose Tissue Regeneration
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2020 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 21, no 1, p. 188-198Article in journal (Refereed) Published
Abstract [en]

The advancement of 3D printing technologies in the fabrication of degradable scaffolds for tissue engineering includes, from the standpoint of the polymer chemists, an urgent need to develop new materials that can be used as ink and are suitable for medical applications. Here, we demonstrate that a copolymer of epsilon-caprolactone (CL) with low amounts of p-dioxanone (DX) (15 mol %) is a degradable and printable material that suits the requirements of melt extrusion 3D printing technologies, including negligible degradation during thermal processing. It is therefore a potential candidate for soft tissue regeneration. The semicrystalline CL/DX copolymer is processed at a lower temperature than a commercial polycaprolactone (PCL), shaped as a filament for melt extrusion 3D printing and as porous and pliable scaffolds with a gradient design. Scaffolds have Young's modulus in the range of 60-80 MPa, values suitable for provision of structural support for damaged soft tissue such as breast tissue. SEM and confocal microscope indicate that the CL/DX copolymer scaffolds support adipose stem cell attachment, spreading, and proliferation.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2020
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-267517 (URN)10.1021/acs.biomac.9b01126 (DOI)000507429500017 ()31549825 (PubMedID)2-s2.0-85073161599 (Scopus ID)
Note

QC 20200409

Available from: 2020-04-09 Created: 2020-04-09 Last updated: 2022-06-26Bibliographically approved
5. Computational and experimental characterization of 3D-printed PCL structures toward the design of soft biological tissue scaffolds
Open this publication in new window or tab >>Computational and experimental characterization of 3D-printed PCL structures toward the design of soft biological tissue scaffolds
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2020 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 188, article id 108488Article in journal (Refereed) Published
Abstract [en]

Degradable porous polymeric structures are attractive candidates for biological tissue scaffolds, and adequate mechanical, transport, chemical and biological properties determine their functionality. Aside from the properties of polymer-based materials, the scaffold's meso-structure controls its elasticity at the organ length-scale. This study investigated the effect of the meso-structure on scaffolds' mechanical and transport properties using finite element analysis (FEA) and computational fluid dynamics (CFD). A number of poly (ε-caprolactone) (PCL) - based scaffolds were 3D printed, analyzed by microcomputed tomography (micro-CT) and mechanically tested. We found that the gradient (G) and gradient and staggered (GS) meso-structure designs led to a higher scaffold permeability, a more homogeneous flow inside the scaffold, and a lower wall shear stress (WSS) in comparison with the basic (B) meso-structure design. The GS design resulted in scaffold stiffness as low as 1.07/0.97 MPa under compression/tension, figures that are comparative with several soft tissues. Image processing of micro-CT data demonstrated that the imposed meso-structures could have been adequately realized through 3D printing, and experimental testing validated FEA analysis. Our results suggest that the properties of 3D-printed PCL-based scaffolds can be tuned via meso-structures toward soft tissue engineering applications. The biological function of designed scaffolds should be further explored in-situ studies.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
3D printing, Computational fluid dynamics, Finite element analysis, Meso-structure, Scaffold, Soft tissue engineering
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-267795 (URN)10.1016/j.matdes.2020.108488 (DOI)000514567900012 ()2-s2.0-85077922391 (Scopus ID)
Note

QC 20200220

Available from: 2020-02-20 Created: 2020-02-20 Last updated: 2022-06-26Bibliographically approved

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