Page 61 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

3.2 Introduction
Electrospun polymer meshes have received significant attention in the last few years and strongly contributed to the development of advanced biomaterials for tissue engineering,1,2 wound dressing3 and drug delivery.4 Potential use in commodities has become a research target for clothes,5 in hygiene applications6 or for use in membranes7 and filtration.8 Most applications for electrospun polymer meshes are based on the reproducible and controlled fiber geometry of such materials. Only a limited process control has been achieved up to present for the mesh porosity and limits accessible material properties, particularly for biomedical applications.
The influence of process parameters on the fiber diameter and the inter-fiber spacing has therefore been investigated in detail and today allows adjusting the porosity or net density in flat structures, i.e. in two dimensions.9–16 More specifically, the 2D inter-fiber distance can be modified, amongst others, by adapting solution properties including the viscosity or solvent volatility or the voltage used during electrospinning. Sanders et al. showed that the inter-fiber void space strongly depends on the surface area and the dielectric strength of the collection target while using a melt electrospinning setup.17 Kidoaki et al. reported a limited control on the porosity of three dimensional structures by using a series of increasingly volatile solvents.18
The present work investigates a simple method
to substantially increase the degree of porosity in the
third dimension by using ice crystals as removable
void templates. Since the control of sca old
pores in three dimensions is of crucial interest in
tissue engineering applications, we investigated 3 the e ect of ice crystal co-deposition using two representative biodegradable and biocompatible
polymers, a poly(lactic acid-co-glycolic acid) and a poly(ester-urethane) (Resomer ®,19–22 Degrapol®,23–29 respectively).
3.3 Materials and methods
3.3.1 Materials
The poly(lactic acid-co-glycolic acid) (Resomer ®, PLGA, Typ RG 85:15, Mw = 280’000) was obtained from Boehringer Ingelheim, Germany. The polyester- urethane (DegraPol®,30 PEU, molecular weight Mw = 70’000) was produced according to the procedure described by Lendlein et al.31,32 For electrospinning, an 8 wt% solution of PLGA or a 28 wt% solution of the PEU in chloroform (J.T. Baker, puriss) was prepared by dissolving the polymer under stirring overnight.
3.3.2 Experimental setup
The low-temperature electrospinning setup consisted of a liquid pump for polymer solution feeding, an electrospinning head and a collection
ULTRA-POROUS 3D POLYMER MESHES BY LOW-TEMPERATURE ELECTROSPINNING
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