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Elastomeric hydrolyzable porous scaffolds: Copolymers of aliphatic polyesters and a polyether-ester
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-5850-8873
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2005 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 5, 2718-2725 p.Article in journal (Refereed) Published
Abstract [en]

Porous scaffolds of 1,5-dioxepan-2-one (DXO), L-lactide (LLA), and epsilon-caprolactone (CL) were prepared by a solvent casting, salt particulate leaching technique in which the composites were detached from their mold using a novel methanol swelling procedure. By incorporating DXO segments into polymers containing LLA or CL, an increase in hydrophilicity is achieved, and incorporating soft amorphous domains in the crystalline sections enables tailoring of the mechanical properties. The porosities of the scaffolds ranged from 89.2% to 94.6%, and the pores were shown to be interconnected. The materials were synthesized by bulk copolymerization of 1,5-dioxepan-2-one (DXO), L-lactide (LLA), and epsilon-caprolactone (CL) using stannous 2-ethylhexanoate as catalyst. The copolymers formed varied in structure; poly(DXO-co-CL) is random in its arrangement, whereas poly(DXO-co-LLA) and poly(LLA-co-CL) are more blocky in their structures.

Place, publisher, year, edition, pages
2005. Vol. 6, no 5, 2718-2725 p.
Keyword [en]
biodegradable polymeric scaffolds, epsilon-caprolactone, l-lactide, mechanical-properties, phase-separation, 1, 5-dioxepan-2-one, degradation, poly(epsilon-caprolactone), poly(l-lactide), polylactones
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-14414DOI: 10.1021/bm050190bISI: 000231899200042Scopus ID: 2-s2.0-25844458172OAI: oai:DiVA.org:kth-14414DiVA: diva2:332435
Note
QC 20100805Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Design of Functional Degradable Aliphatic Polyesters and Porous Tissue Engineering Scaffolds
Open this publication in new window or tab >>Design of Functional Degradable Aliphatic Polyesters and Porous Tissue Engineering Scaffolds
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The regeneration of damaged tissues or organs using porous scaffolds which act as temporary guides for the patient’s own cells, i.e. tissue engineering, is a means to overcome the shortcomings of current standard medical treatments. The large number of tissue engineering applications and the high demands on materials make it necessary to design materials and scaffolds with innovative characteristics tailored to suit specific applications. The purpose of the work presented in this thesis was to design aliphatic polyester (co)polymers and porous scaffolds in order to tailor material and scaffold properties and to control the property changes induced by radiation sterilization.

Porous scaffolds were created, with an emphasis on tailoring the scaffolds thermal and mechanical properties. Stannous octoate was used in ring-opening polymerizations of L,L-lactide (LLA), ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO) to attain three copolymer types with a wide assortment of monomer compositions. A solvent casting and salt leaching scaffold fabrication technique was developed, and highly porous scaffolds possessing a range of predetermined properties were obtained.

Highly porous tubular scaffolds of different designs for use in nerve regeneration were developed using copolymers of LLA, CL, DXO or trimethylene carbonate (TMC) and a versatile immersion coating and porogen leaching technique.

Reactions induced by electron beam and gamma irradiation were used to finalize the scaffold properties. By changing the nature of the radiation, the radiation dose, the type of monomers, the monomer composition and the chain microstructure, it was possible to alter the susceptibility and the degradation mechanisms of the polymers. Predicted end-properties were obtainable and the sterilization procedure was incorporated as a final step in the scaffold fabrication.

The free radical ring-opening polymerization of the cyclic ketene acetal 2-methylene-1,3-dioxe-5-pene was developed, a reaction mechanism was proposed and the reaction products were characterized as a first step towards the creation of an innovative multifunctional aliphatic polyester. The reaction mechanism was shown to be temperature-dependent and propagation was inhibited by the formation of an allylic radical in the ring-opening step. The primary reaction product at higher temperatures was the cyclic ester 3-vinyl-1,4-butyrolactone. At lower temperatures, the main product was oligomers of ring-opened and ring-retained repeating units.

Abstract [sv]

Regenerering av skadade vävnader eller organ genom användning av porösa bionedbrytbara implantat som temporära byggnadsställningar för patientens egna celler är ett sätt att lösa de tillkortakommanden som finns i dagens medicinska behandlingsmetoder. De många möjliga applikationerna för vävnadsersättning och de höga krav som ställs på materialen skapar ett behov av nya material med innovativa egenskaper. I denna avhandling används design av alifatiska polyetrar och porösa strukturer för att skräddarsy deras egenskaper och för att kontrollera de förändringar i egenskaper som sker när materialet strålningssteriliseras.

Porösa strukturer tillverkades med fokus på design av deras materialegenskaper. Genom sampolymerisation av L,L-laktid (LLA), ε-kaprolakton (CL) och 1,5-dioxepan-2-on (DXO) med utvalda sammansättningar och monomerkombinationer kunde dessa skräddarsys. Porösa strukturer med hög porositet och ett stort register av förutbestämbara mekaniska och termiska egenskaper framställdes via en utvecklad saltlakningsteknik.

Porösa tuber för nervregenerering, med olika design, utvecklades genom användning av sampolymerer av LLA, CL, DXO eller trimetylenkarbonat (TMC) och en mångsidig stöpnings- och saltlakningsteknik.

Genom att utnyttja de reaktioner som uppstod i de polymera materialen vid sterilisering, med elektron- eller gammastrålning, erhölls förutbestämbara slutgiltiga egenskaper för de porösa strukturerna. Detta uppnåddes genom att skapa material som påverkas på ett specifikt sätt vid bestrålning. Genom att förändra strålningstyp, strålningsdos, monomerer och sammansättningar ändrades känsligheten mot strålning och de reaktionsmekanismer som inducerats. Steriliseringsprocessen blir härmed inkorporerad som ett sista steg i framställningen av de porösa strukturerna.

En fri radikal ringöppningspolymerisation utvecklades för monomeren 2-metylen-1,3-dioxe-5-pen. Reaktionsprodukterna bestämdes och en reaktionsmekanism föreslogs, som ett första steg i framställningen av en innovativ multifunktionell polyester. Reaktionsmekanismen är temperaturberoende och propagering är hämmad på grund av stabiliteten av den allylradikal som bildas vid ringöppning. Vid högre reaktionstemperaturer bildades den cykliska estern 3-vinyl-1,4-butyrolakton som huvudprodukt. Vid lägre temperaturer var den huvudsakliga produkten oligomerer bestående av både ringöppnade och ringslutna repeterande enheter.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 58 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:20
Keyword
Ring-opening polymerization, Stannous octoate, 2, 2’-azoisobutyronitrile, 1, 5-dioxepane-2-one, ε-caprolactone, L-lactide, Trimethylene carbonate, 2-methylene-1, 3-dioxe-5-pene, Copolymer, Porous scaffold, Porous tubular scaffold, Electron beam, Gamma irradiation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-10368 (URN)978-91-7415-309-5 (ISBN)
Public defence
2009-05-29, E1, KTH, Lindstedtsvägen 3, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100805Available from: 2009-05-14 Created: 2009-05-08 Last updated: 2010-08-05Bibliographically approved
2. Macromolecular design and architecture of aliphatic polyesters
Open this publication in new window or tab >>Macromolecular design and architecture of aliphatic polyesters
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Public health care has reached a level where tissue or organ reconstruction by means of biodegradable short-term implants via e.g. tissue engineering will be practicable in the near future. The vital issue now is to be able to reproducibly fabricate and design new materials with the appropriate properties and three-dimensional shape, and to facilitate their sterilization. In this thesis, macromolecular design and polymer architecture techniques are used to synthesize well-defined polymers with narrow molecular weight distributions (MWD), and to control the reactions upon sterilization, and the degradation rate and profile.

A model system for the ring-opening polymerization of L-lactide (LLA) initiated by a spirocyclic tin initiator was developed to synthesize star-shaped polymers. It was shown that an increase in temperature and a decrease in the dielectrical constant of the solvents increased the reaction rate. The versatility of the spirocyclic tin initiator system was subsequently established, by homopolymerization of ε-caprolactone (CL) and 1,5-dioxepan-2-one (DXO) and this system was compared with a conventional system using stannous octoate (Sn(Oct)2) and pentaerythritol ethoxylate. Two different strategies were assessed for the two initiator systems for the synthesis of copolymers that are random or blocky in their nature. Random copolymers with distinct sequence lengths were synthesized using both initiator systems, together with block poly(DXO-co-LLA) and poly(CL-co-LLA) with narrow MWD.

Three different types of copolymers of LLA, CL and DXO were synthesized using Sn(Oct)2 and ethylene glycol. A solvent casting and particulate leaching technique was developed and applied to construct porous scaffolds of the copolymers. The porous scaffolds were subsequently sterilized using electron beam or γ-irradiation and it was shown that the reactions induced by radiation can be used to tailor the end-properties of the materials.

Homo- and copolymers of CL and DXO with different macromolecular designs (triblock and multiblock) and different polymer architectures (linear and cross-linked) were synthesized and degraded in a phosphate buffer solution for up to 364 days. By altering the network composition, the release pattern of acidic degradation products was controlled, where an increase in DXO content led to an increase in the release of both monomeric hydroxy-acids. Varying the distribution of the more hydrolysis-susceptible DXO-sequences in the linear copolymers also enabled the amount of monomeric hydroxy acids released to be controlled, where the triblock copolymer showed the highest release.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 62 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:11
Keyword
Ring-opening polymerization, L-lactide, 1, 5-dioxepane-2-one, ε-caprolactone, Polymerization kinetics, Star-shaped architecture, Spirocyclic tin initiator
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-4657 (URN)978-91-7178-883-2 (ISBN)
Public defence
2008-03-20, F3, KTH, Lindstedtsvägen 26, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20100901Available from: 2008-03-03 Created: 2008-03-03 Last updated: 2010-09-01Bibliographically approved
3. Design of polyester and porous scaffolds
Open this publication in new window or tab >>Design of polyester and porous scaffolds
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The use of synthetic materials for tissue and organ reconstruction, i. e. tissue engineering, has become a promising alternative to current surgical therapies and may overcome the shortcomings of the methods in use today. The challenge is in the design and reproducible fabrication of biocompatible and bioresorbable polymers, with suitable surface chemistry, desirable mechanical properties, and the wanted degradation profile. These material properties can be achieved in various manners, including the synthesis of homo- and copolymers along with linear and star-shaped architectures. In many applications the materials’ three-dimensional structure is almost as important as its composition and porous scaffolds with high porosity and interconnected pores that facilitate the in-growth of cells and transportation of nutrients and metabolic waste is desired.

In this work linear and star-shaped polymers have been synthesized by ring-opening polymerization using a stannous-based catalyst and a spirocyclic tin initiator. A series of linear copolymers with various combinations of 1,5-dioxepane-2-one (DXO), Llactide (LLA) and ε-caprolactone (CL) have been polymerized using stannous octoate as catalyst. It is shown that the composition of the polymers can be chosen in such a manner that the materials’ mechanical and thermal properties can be predetermined. A solvent-casting and particulate leaching scaffold preparation technique has been developed and used to create three-dimensional structures with interconnected pores. The achieved physical properties of these materials’ should facilitate their use in both soft and hard tissue regeneration.

Well defined star-shaped polyesters have been synthesized using a spirocyclic tin initiator where L-lactide was chosen as a model system for the investigation of the polymerization kinetics. Neither the temperature nor the solvent affects the molecular weight or the molecular weight distribution of the star-shaped polymers, which all show a molecular weight distribution below 1.19 and a molecular weight determined by the initial monomer-to-initiator concentration.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 47 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2005:36
Keyword
ring-opening polymerization, porous scaffold, L-lactide, 5-dioxepane-2-one, ε-caprolactone, spirocyclic initiator, star-shaped polyester
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-493 (URN)91-7178-182-X (ISBN)
Presentation
2005-11-25, Salongen, KTHB, Osquara backe 31, Stockholm, 11:00
Opponent
Supervisors
Note
QC 20101217Available from: 2005-11-17 Created: 2005-11-17 Last updated: 2010-12-17Bibliographically approved
4. Porous degradable polyester scaffolds
Open this publication in new window or tab >>Porous degradable polyester scaffolds
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Tissue engineering is a growing research field in which degradable porous scaffolds are used to regenerate tissue from the patients own cells. The problems due to donor shortage or the lack of full property restoration from prosthetic implants can thereby be overcome. It is important that the polymers used in tissue engineering, as in any medical application, have well controlled properties. Equally important is the ability to tailor these properties to suite a specific application. The development of fabrication processes that enables tailoring, without any uncontrolled changes in characteristics, is thereby imperative.

In this thesis, the creation of porous scaffolds focusing on tailoring and customizing the scaffold properties is described. Tailoring was achieved by selecting the proper monomers and their compositions when copolymerizing different cyclic aliphatic ester monomers and an ether-ester monomer. Porous structures applicable for both soft and hard tissue regeneration were obtained comprising a range of predetermined mechanical and thermal properties. In detail, stannous octoate was used as the catalyst in ring-opening polymerization of L,L-lactide (LLA), ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO) to attain the wide assortment of copolymers with different monomers and monomer compositions. Highly porous scaffolds having well interconnected pores were obtained through the development of a versatile solvent casting and porogen leaching technique.

The reactions induced by high energy radiation in the form of electron beam and gamma-ray were used to finalize the scaffold properties. This was achieved by creating polymers possessing predetermined reaction mechanisms when irradiated. Changes in the nature of the radiation, the radiation dose, the type of monomers, the composition and thus the microstructure of the chain gave ways to alter the susceptibility and the reaction mechanism of the polymers. Thus, predicted end-products are obtainable and the sterilization procedure is consequently incorporated as a final step in the scaffold fabrication.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 48 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:15
Keyword
aliphatic polyester, copolymer, porous scaffold, ring-opening polymerization, electron beam, gamma irradiation, Polymerteknologi
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-3960 (URN)91-7178-366-0 (ISBN)
Presentation
2006-06-01, Sal E2, Huvudbyggnaden, KTH, Lindstedtsvägen 3, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20101123Available from: 2006-05-11 Created: 2006-05-11 Last updated: 2010-11-23Bibliographically approved

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