impact of covalent and supramolecular crosslinks on the

Impact of covalent and supramolecular crosslinks on the mechanical

properties of fibrin-based hydrogels

Miriam Aischa Al Enezy-Ulbrich, Institue for Technical and Macromolecular Chemistry, Research Area Functional and

Interactive Polymers, RWTH Aachen University, Worringerweg 1, 52074 Aachen, Germany & DWI - Leibniz Institute

for Interactive Materials, RWTH Aachen University, Forckenbeckstraße 50, 52074 Aachen, Germany,

[email protected]

Miriam Aischa Al Enezy-Ulbrich1, 2, Shannon Anna Jung1, 2, Nicole Terefenko1, 2, Norina Labude-Weber3, 4, Hanna Mal-

yaran3, 4, Svenja Wein3, 4, Sabine Neuss3, 4, Andrij Pich1, 2

1 Institute for Technical and Macromolecular Chemistry, Research Area Functional and Interactive Polymers,

RWTH Aachen University, Worringerweg 1, 52074 Aachen

2 DWI - Leibniz Institute for Interactive Materials,

Forckenbeckstraße 50, 52074 Aachen

3 Helmholtz Institute for Biomedical Engineering, BioInterface Group, RWTH Aachen University, Pauwelsstrasse

20, 52074 Aachen, Germany

4 Institute of Pathology, RWTH Aachen University, Pauwelsstrasse 30, 52074 Aachen, Germany

Introduction

In modern implant development, researchers focus on the enhancement of both biocompatibility and reproducibility.

Commonly used cardiovascular implants have a few disadvantages as they either have a limited lifetime or a high risk of

thromboembolism, which also affects their properties and functionality. Many research activities face the optimization of

implant properties. The prevention of the formation of blood clots in mechanical implants (heart valves), bacterial biofilms

(dental implants) or the degradation of bioprotheses must be ensured. In addition, the organ implant may still be rejected

by the patient’s body. The aim of this work is the synthesis of a biohybrid heart valve consisting of a fibrin-based gel-

matrix with a textile reinforcement.

Methods

Fibrin-binding peptides are covalently bound to functional linear copolymers. The peptide-polymer constructs are ana-

lyzed by mass spectrometry measurements. They are then used for the synthesis of fibrin-based hydrogels. The mechan-

ical properties are characterized by rheological measurements and the hydrogel structure is analyzed by different micros-

copy methods. Their properties are compared to the characteristics of fibrin-based hydrogels reinforced with functional

linear polymers and to hydrogels reinforced with fibrin-binding peptides only.

Results

Experiments demonstrate that the use of copolymers has a high impact on the hydrogels’ properties and their long-term

stability. We prove that the fibrin-binding peptide alone can trigger the gelation of the hydrogel. Supramolecular interac-

tions are weaker than covalent crosslinks. Therefore the fibrin-binding peptide reinforced hydrogels are softer than fibrin-

based hydrogels crosslinked with functional linear copolymers.

Conclusion

Depending on the required mechanical properties, it may be useful to either use gels reinforced with fibrin-binding pep-

tides or to resort to gels modified with functional linear copolymers. Indeed, focussing at the structure of a native heart

valve, compartments with different mechanical characteristics are needed.

S23Abstracts – BMT 2021 – Hannover, 5 – 7 October • DOI 10.1515/bmt-2021-6005 Biomed. Eng.-Biomed. Tech. 2021; 66(s1): S23–S28 • © by Walter de Gruyter • Berlin • Boston

Special Session DFG PAK961 P2 – ArchiTissue – 3D-Architecture of

biohybrid cardiovascular implants by additive manufacturing

Klaus Kreuels*, Chair for Laser Technology LLT, RWTH Aachen University, Aachen, Germany,

[email protected]

Zhaoyang Zhong*, Chair of Medical Materials and Implants MMI, Technical University of Munich, Munich, Germany,

[email protected]

Nadine Nottrodt, Fraunhofer Institute for Laser Technology ILT, Aachen, Germany, [email protected]

Arnold Gillner, Chair for Laser Technology LLT, RWTH Aachen University and Fraunhofer Institute for Laser

Technology ILT, Aachen, Germany, [email protected]

Petra Mela, Chair of Medical Materials and Implants MMI, Technical University of Munich, Munich, Germany,

[email protected]

* Both authors contributed equally to this work.

Introduction

Biohybrid implants are composed of living cells and scaffolds for mechanical reinforcement of the tissue to be built up.

Beside techniques such as electrospinning or textile weaving, additive manufacturing allows the production of complex

3D-structures. In this project, polymer scaffolds with different shapes, porosities and 3D-microarchitectures were addi-

tively manufactured by stereolithography (SLA) from different materials and cultivated with cells to mimic the biome-

chanically complex native heart valve. After cell seeding onto scaffolds, the dynamic conditioning is essential for in vitro

tissue-engineered heart valves (TEHVs) to promote synthesis and organization of the extracellular matrix and, ultimately,

valve’s functionality. To quantify the impact of the individual stimuli, i.e. cyclic stretching, pressure and shear stress, on

the maturation of TEHVs, a novel bioreactor was developed that enables to create a wide range of mechanical stimuli,

including physiological ones.

Methods

Polymeric scaffold structures were constructed by unit cells and designed based on either polyhedron or TPMS structures.

and then 3D printed via SLA. Acrylic photo resins were processed at wavelengths of λ=375 nm and λ=405 nm or thiol-

ene based photo resins at λ=266 nm. Thoroughly cleaned scaffolds were mechanically characterized. Computational fluid

dynamic (CFD) was performed to support the design of the bioreactor chamber to meet the requirement of creating lam-

inar flow in the region of interest of the tissue specimen.

Results

Polymeric scaffolds exhibit a minimum porosity of >65% for web thicknesses of 70µm and up to 90% porosity for higher

web thicknesses. Mechanical characterization indicates higher effective E-Moduli and lower elongation at break for pol-

yhedron-based scaffolds than for TPMS-based scaffolds. Bioreactor conditioning allows axial tensile strain of the scaffold

up to 25%, a shear stress up to 71 dynes/cm2 and aortic pressure (80-120 mmHg) can be reached.

Conclusion

Complex biocompatible polymeric scaffolds can be additively manufactured by SLA. The choice of material and scaffold

design facilitates the precise production of non-homogenous structures to mimic native tissue. The bioreactor developed

in this project allows the investigation of the interaction between 3D architecture and cells, and ultimately the develop-

ment of multi-layered biomimetic TEHV.


mailto:[email protected]





Special Session DFG PAK-961 P3: Computational Modelling of

Maturation Processes in Tissue-Engineered Implants

Mahmoud Sesa, RWTH Aachen, Institute of Applied Mechanics, Aachen, Germany, [email protected]

aachen.de

Lukas Lamm, RWTH Aachen, Institute of Applied Mechanics, Aachen, Germany, [email protected]

Hagen Holthusen, RWTH Aachen, Institute of Applied Mechanics, Aachen, Germany, [email protected]

Christian Böhm, RWTH Aachen, Institute of Applied Mechanics, Aachen, Germany, [email protected]

Stefan Jockenhövel, RWTH Aachen, Institute of Applied Medical Engineering, Aachen, Germany,

[email protected]

Stefanie Reese, RWTH Aachen, Institute of Applied Mechanics, Aachen, Germany, [email protected]

Introduction

The use of bio-engineered tissues opens new possibilities for the treatment of various cardiovascular diseases, such as

patient-specific aortic valve replacements. Due to the complexity of the maturation process during the implants

production process, computational models are important to investigate the influence of various parameters with respect

to the mechanical and hemodynamical properties of the final implant.

Methods

One of the key points of interests for modelling the maturation process is the maturation of the extracellular matrix.

During the maturation process, volumetric growth effects are encountered and therefore must be described adequately.

Whilst many publications covering isotropic volumetric growth exist, it has been shown that for loading scenarios

including complex boundary conditions, such approaches are not feasible. Therefore, we propose a newly derived

macroscopic modelling approach for stress-driven anisotropic volumetric growth. This approach is based on the

modelling of inelastic deformations within the finite strain regime. In addition to the volumetric growth of the

extracellular matrix, the heart valve maturation process can be influenced by many parameters such as fluid pressure

and stroke frequency. To optimize the maturation process, a detailed investigation of the design space is necessary. This

requires constructing a structural mechanics model for the heart valve that permits fast computations while achieving

accurate qualitative results. Therefore a novel finite element technology based on reduced integration is applied. The

reinforced structure of the heart valve is described by a continuum mechanics model.

Results

The newly developed volumetric growth model accurately models isotropic and anisotropic geometric changes.

Moreover, our finite element technology gives convergent results using a small number of elements.

Conclusion

The anisotropic volumetric growth model offers a flexible framework to model the maturation processes of tissue-

engineered implants. Together with our finite element technology, it offers the possibility to construct highly efficient

and accurate computational models.


ProcessModelling – Process Control of the Maturation of Biohybrid

Heart Valves 1Maximilian Werner, Department of Biohybrid & Medical Textiles (BioTex), Institute of Applied Medical Engineering

(AME), Helmholtz Institute, RWTH Aachen University, Aachen, Germany; AMIBM-Aachen-Maastricht-Institute for

Biobased Materials, Maastricht University, Geleen, The Netherlands, [email protected]

2Vytautas Kucikas, Institute of Molecular Cardiovascular Research (IMCAR), RWTH Aachen University, Aachen, Ger-

many, [email protected]

3Kirsten Voß, Institute of Automatic Control (IRT), RWTH Aachen University, Aachen, Germany, [email protected]

chen.de

Dirk Abel, Institute of Automatic Control (IRT), RWTH Aachen University, Aachen, Germany, [email protected]

chen.de

Marc A.M.J. van Zandvoort, Department of Biophysics, Cardiovascular Research Institute Maastricht (CARIM), Maas-

tricht University, Maastricht, The Netherlands; Institute of Molecular Cardiovascular Research (IMCAR), RWTH Aachen

University, Aachen, Germany, [email protected]

Stefan Jockenhövel, Department of Biohybrid & Medical Textiles (BioTex), Institute of Applied Medical Engineering

(AME), Helmholtz Institute, RWTH Aachen University, Aachen, Germany; AMIBM-Aachen-Maastricht-Institute for

Biobased Materials, Maastricht University, Geleen, The Netherlands, [email protected]

Thomas Schmitz-Rode, Institute of Applied Medical Engineering (AME), Helmholtz Institute, RWTH Aachen Univer-

sity, Aachen, Germany, [email protected]

Introduction

Tissue engineered heart valves (TEHVs) are a promising therapy for the treatment of cardiovascular diseases. Their pre-

maturation in vitro requires a bioreactor for appropriate biochemical and mechanical conditioning, achieved by an in-

creasing pulsatile flowing medium, controlled by actuators and monitored by sensors. In order to observe the tissue mat-

uration on a microscopic scale, an endoscopic imaging system is needed, which would overcome the disadvantages of

currently used histological techniques. The object of this study was to develop a central operation unit that autonomously

controls the conditioning process of a TEHV. Furthermore, the development and integration of a two-photon endoscope

is aimed to allow the sterile observation of the tissue maturation.

Methods

The software-controlled conditioning process was elaborated using the example of an aortic heart valve. The experimental

setup includes a feedback-controlled software that is fed by sensors, including pressure transducers, a flow meter and a

gas- and pH-evaluation system. Pulsatile movement of the TEHV was provided by actuators which regulated the medium

flow and compliance. Integrating a two-photon endoscope allows on-line and non-destructive inspection of the tissue

under sterile conditions throughout the whole process.

Results

With the presented setup, TEHVs were successfully conditioned for three weeks. The majority of previously manual steps

were implementable in an autonomous-working process control that reduced the required conditioning time. Besides, the

current maturation state of the TEHV was traceable through the sensor and imaging data during the whole experiment.

Conclusion

In summary, the bioreactor could be automatically controlled by the combination of different sensors and actuators in a

centrally software-controlled system. The integration of a two-photon endoscopic system enabled the observation of the

tissue maturation throughout the whole conditioning process. The presented setup is a promising technique for the con-

trolled tissue maturation, which opens new prospects in the field of tissue engineering.


Fluorescent Fetuin-A-Based Calcification Testing Of Cardiovascular

Prostheses Materials

Jan Ritter, Dept. of Cardiovascular Engineering, Institute of Applied Medical Engineering, Helmholtz Institute, RWTH

Aachen University/University Hospital Aachen, Aachen, Germany, [email protected]

Andrea Büscher, Biointerface Lab, Helmholtz Institute, University Hospital Aachen, Aachen, Germany,

[email protected]

Aaron Morgan, Biointerface Lab, Helmholtz Institute, University Hospital Aachen, Aachen, Germany, amorgan@ukaa-

chen.de

Johanna C. Clauser, Dept. of Cardiovascular Engineering, Institute of Applied Medical Engineering, Helmholtz Institute,

RWTH Aachen University/University Hospital Aachen, Aachen, Germany, [email protected]

Willi Jahnen-Dechent, Biointerface Lab, Helmholtz Institute, University Hospital Aachen, Aachen, Germany, willi.jah-

[email protected]

Ulrich Steinseifer, Dept. of Cardiovascular Engineering, Institute of Applied Medical Engineering, Helmholtz Institute,

RWTH Aachen University/University Hospital Aachen, Aachen, Germany, [email protected]

Introduction

Calcification impedes the function of cardiovascular tissues including cardiovascular prostheses. Therefore, in-vitro test-

ing of materials used in cardiovascular applications is necessary to assess the calcification propensity. Currently, this is

already done using a large-scale testing device. Considering novel biological materials and cellularization of devices,

testing must be scale-adjusted and switched from simulated body fluids to cell compatible media to accomodate implants,

while maintaining sterile culture conditions. To this end, a chip-based testing device was developed that is suitable for

flow culture of cardiovascular cells on a scaffold under sterile conditions. To compare the performance of the chip-based

tester with the established large-scale tester, we studied the early stages of calcification of pericardium and polyurethane

patches using both devices. To detect early calcification, the patches were stained with fluorescent-labelled Fetuin-A, a

protein with high affinity for early-stage calcified lesions.

Methods

The experiment compared early calcification in a chip-based flow cell with an established large-scale tester also developed

in house. The samples consisted of pericardium and polyurethane patches (36 mm diameter) in the large tester, and peri-

cardium and polyurethane patches (10 mm diameter) in the flow chip. The patches were secured into the chip-based

testing system filled with calcification-inducing medium. Each chip was connected to a peristaltic pumping system for

perfusion then incubated at 37C for two weeks. The large-scale tester requires 400 ml of medium, while the chip-based

tester requires 35 ml. The calcification medium was exchanged after the first week. After two weeks, the patches were

stained using fluorescence-labelled Fetuin-A and viewed with an epifluorescence microscope to assess the degree of

calcification.

Results

Fluorescence microscopy revealed small calcified lesions in pericardium patches from both the large-scale tester and the

chip-based testing device. Over the two week incubation period, calcification of the pericardium increased in both the

chip-based and large-scale testers. Serving as a negative control, polyurethanes patches showed no signs of calcification

in either testing device.

Conclusion

The comparability of the novel chip-based testing method to the large-scale testing device was validated. The results of

the novel chip-based testing device consistently reproduced material-specific calcification propensity previously estab-

lished using the large-scale calcifcation tester while allowing for significantly smaller samples and fluid volumes to be

used. We will further modify the chip design to accomodate both a wider range of biohybrid implant materials as well as

cellularized materials for calcification propensity testing.










Characterization and molecular imaging of a biohybrid tissue

engineered vascular graft

1Saurav Ranjan Mohapatra, Dept. of Biohybrid & Medical Textile, RWTH Aachen University Clinic, Aachen, Gemany,

[email protected] 2Elena Rama, Dept. of Experimental Molecular Imaging, RWTH Aachen University Clinic, Aachen, Germany,

[email protected] 3 Christoph Melcher, Institute of Textile Technology, RWTH Aachen University Clinic, Aachen, Germany,

[email protected]

Christian Apel, Dept. of Biohybrid & Medical Textile, RWTH Aachen University Clinic, Aachen, Germany,

[email protected]

Fabian Kiessling , Dept. of Experimental Molecular Imaging, RWTH Aachen University Clinic, Aachen, Germany,

[email protected]

Stefan jockenhövel, Dept. of Biohybrid & Medical Textile, RWTH Aachen University Clinic, Aachen, Germany,

[email protected]

Introduction

Vascular diseases represent approximately 28% of the causes of death worldwide. Though conventional tissue-engineered

graft is a significant approach but the long duration to make them is a limitation. We present a molding method and a

bioreactor that can give distinct conditions such as flow, pressure, and temperature to make the tissue-engineered vascular

grafts (TEVG) implantable within four days.For in situ monitoring, we established reliable non-invasive imaging methods

to monitor the degradation of the synthetic structural elements, ECM production and signs of inflammation of biohybrid

TEVG by integrating contrast agents.

Methods

A polyvinylidene fluoride (PVDF) tubular textile mesh was used as a scaffold and the construct was coated with biode-

gradable Uspio-labeled PLGA fibers. The TEVGs were prepared by a molding process which consists of the scaffold,

fibrin gel, and arterial SMCs. An endothelialization process and bioreactor conditioning mimicking physiological blood

flow and pressure values followed after molding. The ECM production was studied in TEVGs after 14 days of maturation

using elastin- and collagen type I-targeted MR molecular gadolinium-based probes and immunohistology. The αvβ3 in-

tegrin expression as a marker of inflamed endothelium was assessed by molecular targeted US using RGD-poly(butyl

cyanoacrylate) microbubbles and compared to RAD-control MBs.

Results

The bioreactor conditioning provided a suitable environment to the TEVG in which the cells could proliferate and produce

extracellular matrices. The histological study proved the development of smooth muscle actin, collagen I, Collagen IV,

and also the endothelial linings at the lumen. The presence of collagen was further identified by the MRI by using the

contrast agent and the expression of integrin by the ECs were identified by introducing RGD microbubbles to the TEVG.

Conclusion

We introduce a biohybrid TEVG with a coated scaffold for longitudinal monitoring by non-invaisve molecular imaging

methods. After 4 days of bioreactor cultivation, this graft provides sufficient stability for implantation and the possibil-

ity of longutidinal monitoring in situ.





impact of covalent and supramolecular crosslinks on the

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