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Force Interactions of Nonagglomerating Polylactide Particles Obtained through Covalent Surface Grafting with Hydrophilic Polymers
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, Fibre Technology.ORCID iD: 0000-0002-5444-7276
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.ORCID iD: 0000-0002-5850-8873
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
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2013 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 26, 8873-8881 p.Article in journal (Refereed) Published
Abstract [en]

 Nonagglomerating polylactide (PLA) particles with various interaction forces were designed by covalent photografting. PLA particles were surface grafted with hydrophilic poly(acrylic acid) (PAA) or poly(acrylamide) (PAAm), and force interactions were determined using colloidal probe atomic force microscopy. Long-range repulsive interactions were detected in the hydrophilic/hydrophilic systems and in the hydrophobic/hydrophilic PLA/PLA-g-PAAm system. In contrast, attractive interactions were observed in the hydrophobic PLA/PLA and in the hydrophobic/hydrophilic PLA/PLA-g-PAA systems. AFM was also used in the tapping mode to determine the surface roughness of both neat and surface-grafted PLA film substrates. The imaging was performed in the dry state as well as in salt solutions of different concentrations. Differences in surface roughness were identified as conformational changes induced by the altered Debye screening length. To understand the origin of the repulsive force, the AFM force profiles were compared to the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory and the Alexander de Gennes (AdG) model. The steric repulsion provided by the different grafted hydrophilic polymers is a useful tool to inhibit agglomeration of polymeric particles. This is a key aspect in many applications of polymer particles, for example in drug delivery.

Place, publisher, year, edition, pages
2013. Vol. 29, no 26, 8873-8881 p.
Keyword [en]
Atomic force microscopy, Drug delivery, Grafting (chemical), Hydrogels, Hydrophilicity, Polyesters, Surface roughness
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-122428DOI: 10.1021/la401076mISI: 000322059700013Scopus ID: 2-s2.0-84880322768OAI: oai:DiVA.org:kth-122428DiVA: diva2:622323
Funder
EU, European Research Council, 246776
Note

QC 20130909. Updated from manuscript to article in journal.

Available from: 2013-05-21 Created: 2013-05-21 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Steric Stabilization of Polylactide particles achieved by Covalent 'grafting-from' with Hydrophilic Polymers
Open this publication in new window or tab >>Steric Stabilization of Polylactide particles achieved by Covalent 'grafting-from' with Hydrophilic Polymers
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Despite numerous advantages of using particles in a wide range of applications, they have one drawback that is their tendency to agglomerate. One way to overcome this problem is to sterically  stabilize the particles by introducing polymeric  chains covalently attached to the surface. Surface modification by covalently attaching polymer chains to the particle surface can be achieved by e.g. a ‘grafting-from’ technique under UV irradiation.

In this thesis, polylactide (PLA) particles were surface modified, under UV irradiation, with the hydrophilic monomers: acrylamide (AAm), acrylic acid (AA), and maleic anhydride (MAH). The developed ‘grafting-from’ technique was shown to be nondestructive method for surface modification of PLA particles of two different geometries. The change in surface chemistry of the PLA particles was confirmed by FTIR and XPS, indicating the success of the surface grafting technique. Force interaction between two surface grafted PLA substrates was measured by colloidal probe AFM in different salt concentrations. In order to understand the repulsive force, the AFM force profiles were compared to the DLVO theory and AdG model. Long range repulsive interactions were mainly observed when hydrophilic polymers were covalently attached to the surface of PLA particles, leading to steric interaction. Attractive force dominated the interaction when neat PLA particle was approaching each other, resulting in particle aggregation, even though short range repulsion was observed at small separation distance, i.e. approximately 10 nm. Attractive interaction was also observed when neat PLA was approaching to PAA-grafted PLA substrate. This attractive interaction was much greater than force interaction between two neat PLA substrates.

 The surface grafted particles can be used in biomedical application where secondary interactions are important to overcome particle agglomeration such as particle-based drug delivery.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 41 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:27
Keyword
Steric stabilization, AFM, hydrophilicity, surface modification, poly(lactide), acrylamide, acrylic acid, maleic anhydride
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-122429 (URN)
Presentation
2013-06-10, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, European Research Council, 246776Swedish Research Council, 621-2010-3478
Note

QC 20130529

Available from: 2013-05-29 Created: 2013-05-21 Last updated: 2013-05-29Bibliographically approved
2. Modification of polymeric particles via surface grafting for 3D scaffold design
Open this publication in new window or tab >>Modification of polymeric particles via surface grafting for 3D scaffold design
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface modification techniques have played important roles in various aspects of modern technology. They have been employed to improve substrates by altering surface physicochemical properties. An ideal surface modifying technique would be a method that is applicable to any kind of materials prepared from a wide range of polymers and that can occur under mild reaction conditions. The work in this thesis has utilized four main concepts: I) the development of a ‘grafting-from’ technique by covalently growing polymer grafts from particle surfaces, II) the presence of steric and electrosteric forces due to long-range repulsive interactions between particles, III) a combined surface grafting and layer-by-layer approach to create polyelectrolyte multilayers (PEMs) on particle surfaces to fabricate strong and functional materials, and IV) the roles of hydrophilic polymer grafts and substrate geometry on surface degradation.

A non-destructive surface grafting technique was developed and applied to polylactide (PLA) particle surfaces. Their successful modification was verified by observed changes to the surface chemistry, morphology and topography of the particles. To quantify the aggregation behavior of grafted and non-grafted particles, force interaction measurements were performed using colloidal probe atomic force microscopy (AFM). Long-range repulsive interactions were observed when symmetric systems, i.e., hydrophilic polymer grafts on two interacting surfaces, and asymmetric system were applied. Electrosteric forces were observed when the symmetric substrates interacted at pH 7.4. When PEMs were alternately assembled on the surface of poly(L-lactide) (PLLA) particles, the grafted surfaces played a dominated role in altering the surface chemistry and morphology of the particles. Three-dimensional scaffolds of surface grafted particle coated with PEMs demonstrated high mechanical performance that agreed well with the mechanical performance of cancellous bone. Nanomaterials were used to functionalize the scaffolds and further influence their physicochemical properties. For example, when magnetic nanoparticles were used to functionalize the scaffolds, a high electrical conductivity was imparted, which is important for bone tissue regeneration. Furthermore, the stability of the surface grafted particles was evaluated in phosphate buffered saline (PBS) solution. The nature of the hydrophilic polymer grafts and the geometry of the PLLA substrates played central roles in altering the surface properties of films and particles. After 10 days of PBS immersion, larger alterations in the surface morphology were observed on the film compared with microparticles grafted with poly(acrylic acid) (PAA). In contrast to the PAA-grafted substrates, the morphology of poly(acrylamide) (PAAm)-grafted substrates was not affected by PBS immersion. Additionally, PAAm-grafted microparticulate substrates encountered surface degradation more rapidly than PAAm-grafted film substrates.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 61 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:48
Keyword
surface grafting, PLA, PLLA, hydrophilic polymers, particles, geometry, steric stabilization, atomic force microscopy (AFM), polyelectrolyte multilayers, 3D scaffold, bone tissue engineering, surface degradation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-174295 (URN)978-91-7595-686-2 (ISBN)
Public defence
2015-10-29, E3, Osquars backe 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20151002

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2015-10-02Bibliographically approved

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Pettersson, TorbjörnOdelius, Karin

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