University of Minho

School of Engineering

3B’s Research Group

Uma Escola a Reinventar o Futuro – Semana da Escola de Engenharia – 24 a 27 de Outubro de 2011

DANIELA F. COUTINHO*

Supervisors: Nuno M. Neves, Manuela E. Gomes

* d.coutinho@dep.uminho.pt

PROCESSING A POLYELECTROLYTE COMPLEX HYDROGEL AT THE MICRO-SCALE

ACKNOWLEDGEMENTS

DFC acknowledges FCT and the MIT-Portugal Program for personal grant SFRH/BD/37156/2007.

CONCLUSIONS

We successfully fabricated a stable photocrosslinkable PEC hydrogel

using cationic CHT and photocrosslinkable anionic MeGG. This

biomaterial system is potentially useful for a variety of biomedical

applications simply by adjusting the microfabrication tools used.

INTRODUCTION

Natural tissues are structured at the micro-scale. Thus, a lot of effort

has been devoted to develop biomaterial systems enabling replicating

those natural structures in vitro. Microfabrication techniques have been

applied in the development of these biomaterials structures with tailored

architectural details. Hydrogels have been selected for the development

of engineered tissues, mainly due to their similarity with the extracellular

matrix (ECM) of tissues. Several mechanisms for the development of

hydrogels have been reported, namely the use of two oppositely

charged polyelectrolytes that complex when mixed together, forming a

physical hydrogel. This hydrogel is held together by molecular

entanglements that are reversible and can be disrupted by changes in

physical conditions (ionic strength, pH or temperature). Another key

feature of hydrogels is their ability to be micro-processed, allowing to

obtain biomaterials that replicate the micro-architecture of tissues.

MAIN GOAL

To develop a stable polyelectrolyte-complex hydrogel amenable to

microfabrication.

MATERIALS AND METHODS

Photolithography Microfluidics

Figure 5. Schematics of the microfabrication techniques used and Live/dead images of encapsulated rat cardiac fibroblasts

Chitosan - 1% (w/v) in acetic acid solution

Methacrylated Gellan Gum - 1% (w/v) in dionized water

Figure 4. TEM of the cross-section of the PEC hydrogel and confocal microscopy of the distribution of FITC-labeled CHT within a cross-section of the hydrogel.

Figure 3. FTIR and XPS analysis of the PEC hydrogel and the plain materials.

FTIR XPS

Figure 2. SEM of a cross-section of the PEC hydrogel (MeGG-CHT) and of the plain materials.

Figure 1. Schematics of the PEC hydrogel formation and representation of the electrostatic interactions between the polymers.

1st - Hydrogel formed through electrostatic interactions2nd - Hydrogel stabilized by UV

RESULTS AND DISCUSSION

Scanning electron microscopy (SEM) (Figure 2) showed a porous

structure with the presence of fibrous structures over the pores of the

PEC hydrogel that might be a result of the interaction between the

polymer chains of MeGG and CHT.

MeGG-CHT PEC hydrogel

The chemical structure of the PEC hydrogel (Figure 3) revealed the

presence of the absorption peaks characteristic of both raw polymers.

Analysis of the bulk of the hydrogel revealed that upon hydrogel

formation, the mixing of both polymers proceeded slowly. X-ray

photoelectron spectroscopy (XPS) (Figure 3) showed the presence of

protonated amines in the section of MeGG-CHT hydrogel, indicating the

migration of CHT to the interior of the apparent MeGG hydrogel.

MeGG-CHT MeGG-CHT sectionCHT

Transmission electron microscopy

(TEM) and confocal microscopy of

FITC-labeled CHT (Figure 4)

visually confirmed the presence of

CHT in the interior of the hydrogel.

The photocrosslinkable feature of MeGG enabled the formation of a

number of micro-scaled units. Encapsulated rat cardiac fibroblasts

showed to remain viable after the being exposed to the processing

methodologies used. Micro-building blocks with different shapes and

sizes were fabricated simply by changing a photomask (Figure 5).

These micro-units could potentially be used for replicating the micro-

environment features of tissues. On the other hand, the microfluidic

channel used to direct the formation of the PEC hydrogel resulted on

the engineering of a fibrous hydrogel that replicates at a micro-scale the

architecture of fiber bundles found in a variety of tissues (Figure 5).

Development of a MeGG-CHT PEC hydrogel (Figure 1). Morphological

and chemical characterization of PEC hydrogel. Rat cardiac fibroblasts

were isolated and encapasulated in MeGG before microfabrication. TEM Confocal