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Synthetic Pathways to Aliphatic Polyesters and Scaffold Design
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As the field of tissue engineering progresses, a continuous development of scaffold fabrication techniques and suitable degradable materials is required to obtain scaffolds with tunable characteristics. This thesis has focused on the development of pathways to synthesize degradable aliphatic polyesters and on the design of highly porous scaffolds from this class of materials.

Porous scaffolds aimed for tissue engineering applications were successfully created from poly(L-lactide-co-trimethylene carbonate) copolymers, with an emphasis on obtaining highly porous scaffolds, possessing well interconnected pores throughout the scaffold structure. To obtain the porous structures, sugar templates were used in a combined phase separation and porogen leaching scaffold fabrication technique. The technique developed for these materials was simple and versatile and scaffolds of up to 55 mol% TMC were effectively produced.

Poly(p-dioxanone) (PPDX) is a degradable polyether-ester with a comparatively short degradation time, making it useful for many biomedical applications. A synthetic route to PPDX polymers was developed using the cyclic tin (IV) alkoxide initiator 1-di-n-butyl-1-stanna-2,5-dioxacyclopentane. Our work demonstrated that the polymerization route with this initiator is indeed a promising alternative to the more commonly used stannous octoate. Under the appropriate reaction conditions, PPDX polymers with inherent viscosities over 1 dL/g and promising mechanical properties were synthesized.

The design of functional materials is an important step towards fulfilling the material demands within tissue engineering. The free radical ring-opening polymerization of the cyclic ketene acetal monomer 2-methylene-1,3-dioxe-5-pene was developed. As a first step towards the creation of a new multifunctional polyester, the reaction mechanism and the reaction products at different reaction temperatures were mapped. At higher reaction temperatures, the main reaction product was the cyclic ester 3-vinyl-1,4-butyrolactone. At lower reaction temperatures, low molecular weight oligomeric products of both ring-opened and ring-retained repeating units were formed.

Combining scaffold design with sugar templates and the synthesis of functional polyesters led to the creation of highly porous functional scaffolds. Both functional scaffolds and functional films were obtained from poly(ɛ-caprolactone) and poly(L-lactide), synthesized using multifunctional poly(but-2-ene-1,4-diyl malonate) and stannous octoate as initiating system. The mechanical characteristics of the cross-linkable scaffolds and films were evaluated by cyclic compression test under physiological conditions and by cyclic tensile tests.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:36
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-33875ISBN: 978-91-7415-997-4 (print)OAI: oai:DiVA.org:kth-33875DiVA: diva2:418249
Public defence
2011-06-10, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110527Available from: 2011-05-27 Created: 2011-05-20 Last updated: 2011-05-27Bibliographically approved
List of papers
1. Degradable Porous Scaffolds from Various L-Lactide and Trimethylene Carbonate Copolymers Obtained by a Simple and Effective Method
Open this publication in new window or tab >>Degradable Porous Scaffolds from Various L-Lactide and Trimethylene Carbonate Copolymers Obtained by a Simple and Effective Method
2009 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 1, 149-154 p.Article in journal (Refereed) Published
Abstract [en]

A simple and effective method of fabricating scaffolds with open pore structures was successfully used on several copolymers. The method, which is straightforward and fast, was developed to overcome problems such as low pore interconnectivity and to achieve thick three-dimensional scaffolds. Copolymers are of particular interest because it is possible to tune their mechanical and degradable properties, and in this work, copolymers of L-lactide (LLA) and trimethylene carbonate (TMC) were synthesized through ring-opening polymerization. The copolymers formed had molecular weights ranging from close to 60000 g/mol to over 300000 g/mol and they were composed of 12-55 molar percentages of TMC and 88-45 molar percentages of LLA. The synthesized copolymers were evaluated as scaffold materials using a combined phase separation and particulate leaching technique, in which sugar templates were used as the leachable porosifiers. Differences in molecular weights, molar compositions, and degrees of crystallinity were all factors that influenced the properties of the prepared scaffolds. The copolymers with high LLA contents and high degrees of crystallinity were best suited for the scaffold fabrication technique used and gave degradable scaffolds with interconnected pores.

Keyword
ring-opening polymerization, 1, 5-dioxepan-2-one, architectures, polyesters, initiator, solvents, ester
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-18096 (URN)10.1021/bm801052m (DOI)000262399600020 ()2-s2.0-58549092276 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Bulk polymerization of p-dioxanone using a cyclic tin alkoxide as initiator
Open this publication in new window or tab >>Bulk polymerization of p-dioxanone using a cyclic tin alkoxide as initiator
2007 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 45, no 23, 5552-5558 p.Article in journal (Refereed) Published
Abstract [en]

Poly(p-dioxanone) with an inherent viscosity of over 1 dL/g has been synthesized using the cyclic tin alkoxide 1-di-n-butyl-1-stanna-2,5-dioxacyclopentane as initiator. Poly(p-dioxanone) was synthesized in bulk and the results have been compared with polymerizations using tin (II) 2-ethylhexanoate (Sn(Oct)(2)) as catalyst. Sn(Oct)(2) has often been reported to be an effective catalyst for the synthesis of poly(p-dioxanone), but here it is compared with an initiator which is less prone to catalyze transesterification reactions. The results demonstrate that the cyclic tin initiator is a promising alternative for the synthesis of poly(p-dioxanone) with a high inherent viscosity. Poly(p-dioxanone) is a polymer with mechanical properties and a degradation rate suitable for tissue engineering applications. Both the cyclic tin initiator and Sn(Oct)(2) gave, under some reaction conditions, inherent viscosities around 1 dL/g. The best polymer synthesized using the cyclic tin initiator had a strain-at-break of 515% and a stress-at-break of 43 MPa. The inherent viscosity of this polymer was 1.16 dL/g, while Sn(Oct)(2) resulted in a polymer with an inherent viscosity less than 0.4 dL/g under the same reaction conditions.

Keyword
initiators, mechanical properties, poly(p-dioxanone), ring-opening, polymerization, synthesis, ring-opening polymerization, poly(p-dioxanone), poly(1, 4-dioxan-2-one), 1, 4-dioxan-2-one, behavior
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-17163 (URN)10.1002/pola.22301 (DOI)000251631100018 ()2-s2.0-36549057790 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Mapping the Characteristics of the Radical Ring-Opening Polymerization of a Cyclic Ketene Acetal Towards the Creation of a Functionalized Polyester
Open this publication in new window or tab >>Mapping the Characteristics of the Radical Ring-Opening Polymerization of a Cyclic Ketene Acetal Towards the Creation of a Functionalized Polyester
2009 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 47, no 18, 4587-4601 p.Article in journal (Refereed) Published
Abstract [en]

Radical ring-opening polymerization of cyclic ketene acetals is a means to achieve novel types of aliphatic polyesters. 2-methylene-1,3-dioxe-5-pene is a seven-membered cyclic ketene acetal containing an unsaturation in the 5-position in the ring structure. The double bond functionality enables further reactions subsequent to polymerization. The monomer 2-methylene-1,3-dioxe-5-pene was synthesized and polymerized in bulk by free radical polymerization at different temperatures, to determine the structure of the products and propose a reaction mechanism. The reaction mechanism is dependent on the reaction temperature. At higher temperatures, ring-opening takes place to a great extent followed by a new cyclization process to form the stable five-membered cyclic ester 3-vinyl-1,4-butyrolactone as the main reaction product. Thereby, propagation is suppressed and only small amounts of other oligomeric products are formed. At lower temperatures, the cyclic ester formation is reduced and oligomeric products containing both ring-opened and ring-retained repeating units are produced at higher yield.

Keyword
cyclic ketene acetal, polyester, radical polymerization, reaction mechanism, ring-opening polymerization
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-14418 (URN)10.1002/pola.23511 (DOI)000269632500011 ()2-s2.0-69549083370 (Scopus ID)
Note
QC 20100805Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
4. Functional and highly porous scaffolds for biomedical applications
Open this publication in new window or tab >>Functional and highly porous scaffolds for biomedical applications
Show others...
2011 (English)In: Macromolecular Bioscience, ISSN 1616-5187, E-ISSN 1616-5195, Vol. 11, no 10, 1432-1442 p.Article in journal (Refereed) Published
Abstract [en]

Highly porous functional scaffolds were obtained from linear and cross-linked multifunctional poly(ε-caprolactone) and poly(L-lactide). The polymers were synthesized by ring-opening polymerization of ε-caprolactone and L-lactide using poly(but-2-ene-1,4-diyl malonate) (PBM) as macroinitiator and stannous 2-ethylhexanoate. The presence of a double bond in each repeating unit of PBM enabled cross-linking of both scaffolds and films. Soft and flexible scaffolds were created from cross-linked PBM. The mechanical properties of scaffolds and films were evaluated under cyclic conditions, with a focus on the compositions and molecular weights. It was obvious that PBM in the polymers and its cross-linking ability resulted in tunable material characteristics, including an increased ability to recover after repeated loading.

Keyword
functionalization of polymers, porous scaffolds, ring-opening polymerization, tissue engineering
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-34173 (URN)10.1002/mabi.201100166 (DOI)000296138500016 ()2-s2.0-80053929414 (Scopus ID)
Funder
Swedish Research Council, 2008-5538
Available from: 2011-05-27 Created: 2011-05-27 Last updated: 2017-12-11Bibliographically approved

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