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Functional and highly porous scaffolds for biomedical applications
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.ORCID iD: 0000-0002-1922-128X
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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.

Place, publisher, year, edition, pages
2011. Vol. 11, no 10, 1432-1442 p.
Keyword [en]
functionalization of polymers, porous scaffolds, ring-opening polymerization, tissue engineering
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-34173DOI: 10.1002/mabi.201100166ISI: 000296138500016Scopus ID: 2-s2.0-80053929414OAI: oai:DiVA.org:kth-34173DiVA: diva2:419656
Funder
Swedish Research Council, 2008-5538
Available from: 2011-05-27 Created: 2011-05-27 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Synthetic Pathways to Aliphatic Polyesters and Scaffold Design
Open this publication in new window or tab >>Synthetic Pathways to Aliphatic Polyesters and Scaffold Design
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:nbn:se:kth:diva-33875 (URN)978-91-7415-997-4 (ISBN)
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
2. Macromolecular synthesis of functional degradable aliphatic polyesters and porous scaffold design
Open this publication in new window or tab >>Macromolecular synthesis of functional degradable aliphatic polyesters and porous scaffold design
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There is an increasing demand for new materials in biomedical applications with material properties that are highly specific for each application area. The search for new materials requires the creation of materials with suitable mechanical properties, functionalities, three-dimensional structures and a controlled degradation profile. The focus of the work described in this thesis has been on the synthesis of functional degradable aliphatic polyesters, on the design of porous scaffolds and on their synthesis with bio-safe catalyst/initiator systems.  

An unsaturated aliphatic polyester has been synthesized by condensation polymerization to produce poly(but-2-ene-1,4-diyl malonate) (PBM), which was applicable as a cross-linked network and as a macro-co-initiator for the ring-opening polymerization (ROP) of cyclic ester monomers. The method of preparation of PBM was simple and straightforward and there was no need to purify the monomers or add a catalyst. PBM was successfully cross-linked with UV-radiation to form a transparent, colorless, flexible and strong film. When PBM was used as a macro-co-initiator, a triblock copolymer was formed with PBM middle blocks and poly(L-lactide) (PLLA) or poly(ε-caprolactone) side blocks. The ductility of the triblock copolymer of PLLA was greatly enhanced and the strength was maintained compared to the polymer obtained when PLLA was polymerized with ethylene glycol as co-initiator. The triblock copolymers were easily cross-linked to give materials with greater strength and higher modulus as a result. When these polymers were subjected to hydrolysis, a rapid initial hydrolysis of the amorphous PBM middle block changed the microstructure from triblock to diblock, with a significant reduction in ductility and number average molecular weight. Highly porous scaffolds were created from these functional materials and the mechanical properties were evaluated by a cyclic compression test under mimicked physiological conditions.

Copolymers of L-lactide (LLA) and ε-caprolactone (CL), trimethylene carbonate (TMC) or 1,5-dioxepane-2-one (DXO) have been synthesized with a low stannous-2-ethyl hexanoate  (Sn(Oct)2) ratio and used to fabricate porous tubular scaffolds. The tubes were designed to have a range of mechanical properties suitable for nerve regeneration, with different porosities and different numbers of layers in the tube wall. The adaptability of an immersion-coating and porogen-leaching technique was demonstrated by creating tubes with different dimensions.

Although a low amount of residual tin (monomer-to-initiator ratio of 10000:1) is accepted in biomedical applications, an efficient bio-safe catalyst/initiator system would be favored. The catalytic activities of bio-safe Bi (III) acetate and creatinine towards the ROP of LLA have been compared with those of Sn(Oct)2-based systems and with those of a system catalyzed by enzymes. All these systems were shown to be suitable catalysts for the synthesis of high and moderate molecular weight PLLAs.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 75 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:45
Keyword
functional polyesters, condensation polymerization, L-lactide, ε-caprolactone, triblock copolymer, mechanical properties, porous scaffolds, tissue engineering, ring-opening polymerization, Bi(III) acetate, creatinine, stannous 2-ethylhexanoate, enzyme, degradation products
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-38583 (URN)978-91-7501-060-1 (ISBN)
Public defence
2011-09-22, F3, Lindstedtsvägen 26, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20110901Available from: 2011-08-30 Created: 2011-08-29 Last updated: 2011-09-01Bibliographically approved

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