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Synthesis of Biomedical Polymers and Scaffold Design
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This work has focused on the development of new improved synthesis methods of biodegradable aliphatic polymers and on the preparation of porous scaffolds for tissue engineering applications. The aim of the first part of the work was the synthesis of poly(p-dioxanone) (PPDX) homopolymers with high molecular weights using the cyclic tin alkoxide initiator 1-di-n-butyl-1-stanna-2,5-dioxacyclopentane. PPDX is a polymer with both mechanical properties and a degradation rate suitable for many biomedical applications. The polymerizations were carried out in bulk and the results were compared with polymerizations using tin (II) 2-ethylhexanoate (stannous octoate, Sn(Oct)2), a co-initiator which has previously been found effective in the polymerization of p-dioxanone (PDX). The hypothesis of this work was that the cyclic tin alkoxide initiator would bring several benefits to the synthesis of PPDX. It has been shown to catalyze low amounts of transesterfication reactions and materials with very low amounts of tin residues have been synthesized using an efficient purification technique. Our work demonstrated that the cyclic tin alkoxide initiator is indeed a promising alternative in the synthesis of PPDX with high inherent viscosities. Under the appropriate reaction conditions, PPDX polymers with inherent viscosities over, or around, 1 dL/g were synthesized. One of the most interesting materials made had an inherent viscosity of 1.16 dL/g, a strain-at-break of 515 %, a stress-at-break of 43 MPa, and was synthesized using the cyclic tin alkoxide initiator.

As a second part of this work, copolymers of L-lactide (LLA) and trimethylene carbonate (TMC) were synthesized using either Sn(Oct)2 with ethylene glycol or the cyclic tin alkoxide initiator 1-di-n-butyl-1-stanna-2,5-dioxacyclopentane. The copolymers, which had molecular weights ranging from close to 60 000 g/mol to over 300 000 g/mol, were composed of 12 to 55 molar percentages of TMC and 88 to 45 molar percentages of LLA. The copolymers were evaluated as porous scaffold materials intended for tissue engineering, using a combined phase separation and particulate leaching technique, in which sugar templates were used as the leachable porogens. The aim of this part of the work was to develop a simple and effective method for preparing scaffolds with high porosities and well interconnected pores and to overcome problems with formation of a solid surface side and limitations in scaffold thickness. The preparation method was successfully used on several copolymers. Differences in molecular weights, molar compositions and degrees of crystallinity were all factors which influenced the properties of the prepared scaffolds. Copolymers with TMC contents of up to 55 % were successfully used in the preparation of scaffolds. The results indicated however that materials with lower TMC contents and higher degrees of crystallinity in many cases were better suited for the combined phase separation and particulate leaching technique used.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , 42 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:74
Keyword [en]
ring-opening polymerization, tin alkoxide initiator, stannous octoate, poly(p-dioxanone), copolymer, L-lactide, trimethylene carbonate, degradable porous scaffold
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-9674ISBN: 978-91-7415-185-5 (print)OAI: oai:DiVA.org:kth-9674DiVA: diva2:126939
Presentation
2008-12-11, K1, Teknikringen 56, 100 44, Stockholm, KTH, 09:15 (English)
Supervisors
Note
QC 20101125Available from: 2008-11-28 Created: 2008-11-26 Last updated: 2010-11-25Bibliographically approved
List of papers
1. 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
2. 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

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