Cryogel-PCL combination scaffolds for bone tissue repairJ Mater Sci: Mater Med

About

Authors
Jonas Van Rie, Heidi Declercq, Jasper Van Hoorick, Manuel Dierick, Luc Van Hoorebeke, Ria Cornelissen, Hugo Thienpont, Peter Dubruel, Sandra Van Vlierberghe
Year
2015
DOI
10.1007/s10856-015-5465-8
Subject
Biophysics / Chemical Engineering (all) / Bioengineering

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Text

TISSUE ENGINEERING CONSTRUCTS AND CELL SUBSTRATES

Cryogel-PCL combination scaffolds for bone tissue repair

Jonas Van Rie • Heidi Declercq • Jasper Van Hoorick • Manuel Dierick •

Luc Van Hoorebeke • Ria Cornelissen • Hugo Thienpont • Peter Dubruel •

Sandra Van Vlierberghe

Received: 7 October 2014 / Accepted: 16 January 2015  Springer Science+Business Media New York 2015

Abstract The present work describes the development and the evaluation of cryogel-poly-e-caprolactone combinatory scaffolds for bone tissue engineering. Gelatin was selected as cell-interactive biopolymer to enable the adhesion and the proliferation of mouse calvaria pre-osteoblasts while poly-ecaprolactone was applied for its mechanical strength required for the envisaged application. In order to realize suitable osteoblast carriers, methacrylamide-functionalized gelatin was introduced into 3D printed poly-e-caprolactone scaffolds created using the Bioplotter technology, followed by performing a cryogenic treatment which was concomitant with the redox-initiated, covalent crosslinking of the gelatin derivative (i.e. cryogelation). In a first part, the efficiency of the cryogelation process was determined using gel fraction experiments and by correlating the results with conventional hydrogel formation at room temperature. Next, the optimal cryogelation parameters were fed into the combinatory approach and the scaffolds developed were characterized for their structural and mechanical properties using scanning electron microscopy, micro-computed tomography and compression tests respectively. In a final part, in vitro biocompatibility assays indicated a good colonization of the pre-osteoblasts and the attachment of viable cells onto the cryogenic network. However, the results also show that the cellular infiltration throughout the entire scaffold is suboptimal, which implies that the scaffold design should be optimized by reducing the cryogel density. 1 Introduction

The regeneration and replacement of tissue defects including bone can be performed using a tissue engineering approach [1]. In general, this strategy is the result of a perfect match between cells and scaffolds [2, 3]. In order to create a suitable environment for cells enabling extracellular matrix (ECM) development, nutrients and cytokines, (mechanical) stimulation and an optimal oxygen concentration are required. To this end, a scaffold can be developed which fulfils several requirements including biocompatibility, biodegradability, porosity enabling diffusion of nutrients, pore interconnectivity enabling cellular ingrowth and sufficient mechanical capacity [3–8].

In the present work, the selected method to develop tissue engineered scaffolds is a combination of cryogelation with rapid prototyping (RP) [9]. Depending on the polymer phase (solid vs. liquid), different classes of direct and indirect RP techniques are available [3]. Possible extrusion methods for liquid polymers are, among other, fused deposited modelling (FDM), three-dimensional fiber deposition techniques (3DFDP), precision extruding deposition (PED), etc. Another possibility is to dispend the polymer solution through a nozzle or a syringe [3D

J. Van Rie  J. Van Hoorick  P. Dubruel 

S. Van Vlierberghe (&)

Polymer Chemistry & Biomaterials Group, Ghent University,

Krijgslaan 281, Building S4-Bis, 9000 Ghent, Belgium e-mail: Sandra.VanVlierberghe@UGent.be; svvlierb@b-phot.org

H. Declercq  R. Cornelissen

Department of Basic Medical Sciences, Ghent University,

De Pintelaan 185 6B3, 9000 Ghent, Belgium

M. Dierick  L. Van Hoorebeke

Department of Physics and Astronomy, Ghent University,

Proeftuinstraat 86, 9000 Ghent, Belgium

H. Thienpont  S. Van Vlierberghe

Brussels Photonics Team, Department of Applied Physics and

Photonics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels,

Belgium 123

J Mater Sci: Mater Med (2015) 26:123

DOI 10.1007/s10856-015-5465-8 bioplotting, low-temperature deposition manufacturing (LDM), pressure-assisted microsyringe (PAM), etc.]. In the present work, poly-e-caprolactone (PCL) is processed into a porous scaffold using the BioplotterTM technique. The application of PCL as a starting material to develop implants can be considered advantageous for several reasons.

First, there exist several production methods, while the supply can be considered nearly limitless. Looking at biomedical applications, its biodegradability and the slow degradation rate are important characteristics of this polyester [8]. The latter can be accelerated by using more hydrophilic, acidic end groups, incorporation of a more reactive hydrolytic group in the backbone or PCL possessing a lower molecular weight. Hutmacher et al. studied the biocompatibility of PCL using different approaches [10, 11, 12]. Both long-term as well as short-term biocompatibility of PCL scaffolds was tested using animal models. Interestingly, no negative effects were observed up to a period of 2 years.

Other important features include its hydrophobicity and the semi-crystalline nature of PCL [7]. Moreover, PCL can be processed into scaffolds possessing the desired pore and fibre size. Finally, the mechanical properties and scaffold geometry can be controlled.

One important disadvantage, however, is its lack of intrinsic biomimetic and bioactive properties, although strategies have already been elaborated to overcome this issue [13]. To this end, biopolymer-based cryogels will be introduced in the porous PCL scaffolds by the cryogenic treatment of PCL scaffolds containing a gelatin precursor solution, resulting in novel PCL-cryogel combination scaffolds. Gelatin is a natural protein possessing differentiation and proliferation potential upon cell adhesion [3, 13–17]. It has already been applied previously as a cell carrier to support the adhesion and growth of a range of cell types including endothelial cells, osteoblasts, glial cells, adiposetissue derived stem cells and fibroblasts [16, 18–20].

Cryogels are the result of phase inhomogeneous systems, including a non-frozen liquid micro-phase (NFLMP, i.e. region with comparable solubility of molecules as in liquids, embedded in a frozen solution) which originate from moderate freezing of solvent–polymer systems. In the presence of gel-forming agents, the polymer framework of the corresponding gelatin cryogel is formed in the nonfrozen micro-regions of the frozen material. To date, several research groups have already been active in cryogel development [4, 10–12, 21]. However, to the best of our knowledge, this is the first report on the development of combinatory scaffolds by merging 3D printed PCL scaffolds with biopolymer-based cryogels.