Biomechanical Assessment of Native and Tissue Engineered Articular Cartilage

120 Pages·2006·2.89 MB·English

ETH Library
Biomechanical assessment of
native and tissue engineered
articular cartilage
Doctoral Thesis
Author(s):
Knecht, Sven
Publication date:
2006
Permanent link:
https://doi.org/10.3929/ethz-a-005271897
Rights / license:
In Copyright - Non-Commercial Use Permitted
This page was generated automatically upon download from the ETH Zurich Research Collection.
For more information, please consult the Terms of use.
Diss. ETH No. 16804
Biomechanical Assessment of Native and
Tissue Engineered Articular Cartilage

A dissertation submitted to the
ETH ZURICH
for the degree of
Doctor of Sciences

presented by
SVEN KNECHT
Dipl. Ing., University Stuttgart
born 13.07.1975
Citizen of Germany

Accepted on the recommendation of
Accepted on the recommendation of

Prof. Dr. Edgar Stüssi, examiner
Prof. Dr. Edoardo Mazza, co-examiner
Prof. Dr. Klaas Prüssmann, co-examiner

2006

Für meine Eltern

Table of Content
Summary......................................................................................................................................vii
Zusammenfassung........................................................................................................................ix
Abbreviations and Notations.......................................................................................................xi
Chapter 1 Introduction.................................................................................................................1
Chapter 2 Articular Cartilage......................................................................................................5
2.1 Composition and Structure of Articular Cartilage................................................................7
2.2 Plasticity of Articular Cartilage............................................................................................9
2.3 Osteoarthritis......................................................................................................................10
2.4 Tissue Engineering.............................................................................................................16
2.5 Assessment of Articular Cartilage......................................................................................18
2.6 Mechanical Quality of Articular Cartilage.........................................................................21
2.6.1 Theoretical Models......................................................................................................21
2.6.2 Mechanical Measurement Techniques........................................................................23
2.7 Finite Element Modelling and Inverse Techniques............................................................26
2.7.1 Finite Element Modelling in Biomechanics................................................................26
2.7.2 Inverse Technique.......................................................................................................27
Chapter 3 Aims of the Present Study........................................................................................29
Chapter 4 Assessment of Native Cartilage................................................................................33
4.1 Materials and Methods.......................................................................................................35
4.1.1 Patellofemoral in vitro Compression...........................................................................35
4.1.2 Biochemical Assessment.............................................................................................37
4.1.3 Conventional Mechanical Assessment........................................................................38
4.1.4 Quantitative Magnetic Resonance Imaging.................................................................41
4.1.5 Inverse FE Approach...................................................................................................45
4.1.6 Statistical Analysis......................................................................................................51
4.2 Results................................................................................................................................53
4.2.1 Biochemical Assessment.............................................................................................53
4.2.2 Conventional Mechanical Assessment........................................................................53
4.2.3 Quantitative Magnetic Resonance Imaging.................................................................55
4.2.4 Inverse FE Approach...................................................................................................58
4.3 Discussion...........................................................................................................................67
4.3.1 Patellofemoral in vitro Compression...........................................................................67
4.3.2 Biochemical and Conventional Mechanical Assessment............................................68
4.3.3 Quantitative Magnetic Resonance Imaging.................................................................69
4.3.4 Inverse FE Approach...................................................................................................71
4.3.5 Mechanical Assessment using the Inverse FE Approach............................................72
4.3.6 Problems and Limitations............................................................................................74
Chapter 5 Assessment of Tissue Engineered Cartilage...........................................................75
5.1 Mechanical Characterization of Tissue Engineered Articular Cartilage from Mesenchymal
Stem Cells.................................................................................................................................77
5.1.1 Introduction.................................................................................................................77
v
5.1.2 Mechanical Testing and Analysis................................................................................78
5.1.3 Results.........................................................................................................................78
5.1.4 Discussion...................................................................................................................79
5.2 Mechanical Testing of Fixation Techniques for Scaffold-based Tissue Engineering Grafts
..................................................................................................................................................79
5.2.1 Introduction.................................................................................................................79
5.2.2 Material and Methods..................................................................................................81
5.2.3 Results.........................................................................................................................83
5.2.4 Discussion...................................................................................................................86
Chapter 6 Conclusion and Outlook...........................................................................................89
References....................................................................................................................................93
Acknowledgment.......................................................................................................................103
Curriculum Vitae......................................................................................................................107

vi
Summary
Articular cartilage covers the bony ends of the long bone in diarthrodial joints. Its function is to
protect the subjacent bone from high stress. Furthermore, cartilage enables in combination with
the synovial fluid an almost frictionless movement of the joint over the whole lifespan of a
person. However, this functional behavior is disturbed by degenerative joint diseases such as
osteoarthritis. Today osteoarthritis produces enormous economic, social and psychological
consequences. Hence, the overall goal for the future is to improve the diagnosis and treatment of
musculoskeletal diseases, such as osteoarthritis before they become irreversible.
In the framework of this thesis, we investigated biomechanically two strategies, which aim
preventing irreversible osteoarthritic changes. In the first part (Chapter 4), we developed and
validated a novel compression device to assess the patellofemoral articular cartilage based on its
mechanical properties to improve diagnosis. In the second part (Chapter 5), we investigated
novel tissue engineering grafts and their fixation stability within the healthy cartilage used for the
treatment of full-thickness cartilage defects.

In the first part of the thesis, we present a Magnetic Resonance (MR) compatible loading device
based on the lever principle to apply a static load of 400 N on excised equine patellofemoral
joints. We tested two patellas with healthy cartilage, one with superficial defects and the one,
which was treated biochemically with trypsin to simulate an early stage of osteoarthritis. During
mechanical compression for 2 h, cartilage deformation was acquired in the transversal plane with
a 1.5 T Magnetic Resonance Scanner using a validated 3D sequence. Quantitative analysis of the
images allowed generating individual Finite Element (FE) models of the compression test.
Coupling of the Finite Element methods with the experimental deformation data allowed
calculating the mechanical properties of the cartilage.
In the second part of the thesis, we performed confined compression test on tissue engineered
cartilage-like graft to assess their mechanical properties. Additionally, we tested mechanically
the fixation stability of four commonly used biomaterials for autologous chondrocyte
implantation attached by four different fixation techniques (unfixed, fibrin glue, chondral suture,
and transosseous suture). Therefore, three-dimensional scaffolds, two-dimensional collagen
membranes, and a gel-like matrix material were fixed within rectangular full-thickness cartilage
defects and loaded in tension until failure.

Mechanical loading of the equine patellofemoral joint with 400 N resulted in volumetric changes
of about 190 mm3 for the healthy patellar cartilage and about 480 mm3 for the degenerated
cartilage. In contrast to cartilage samples with intact surfaces, the deformation of samples with
superficial defects relaxed completely 5 min after removal of the load. The Young’s modulus,
calculated from the compression test using a linear elastic material model, was 5.54 MPa and
5.63 MPa for the healthy samples, 4.64 MPa for the superficially disrupted and 2.18 MPa for the
degenerated patellar cartilage. Corresponding Poisson’s ratio were 0.10, 0.13, 0.08, and 0.05,
respectively. Young’s moduli calculated from indentation test were about 1.55 MPa for healthy
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cartilage and 0.40 MPa for degenerated cartilage. By trypsin degeneration the Young’s modulus
from indentation test decreased by 74% and from the inverse FE calculation by about 59%.
The aggregate modulus of the tissue-engineered cartilage using silk scaffolds was 0.04 MPa after
21 days of culture. Analysis of the load-to-failure tension test of the fixed samples showed a
maximal load of 2.18 ± 0.47 N for the fibrin glue fixation, 26.29 ± 1.55 N for the chondral
sutured, and 38.18 ± 9.53 N for the transosseous fixed scaffolds.

In this thesis, we have shown the applicability of the MR-controlled patellofemoral compression
to detect minor mechanical changes in situ. Difference between the Young’s moduli calculated
from indentation and inverse FE test arise from the tension-compression nonlinearity of the
(collagen) fibril reinforced cartilage. The accuracy of this approach allows to distinguish between
patellar cartilage with differences in the Young’s moduli between 20 and 30% and consequently
to distinguish between healthy and moderately degenerated articular cartilage in the early stage
of the osteoarthritis process. Furthermore, considering solely the morphological properties,
statements about the intactness of the superficial zone and about a rough estimate of the modulus
of the material might be possible. The adaptation of this method for the in vivo application will
provide a novel approach to determine functional changes of articular cartilage for the first time
non-invasively and quantitatively.
The aggregate modulus of the tissue-engineered graft was approximately ten-fold lower than
native cartilage. Nevertheless, these samples are suited for the application in vivo. The findings
from fixation test serve as basis for selecting the most suitable fixation technique for scaffold-
based tissue engineering grafts according to the expected in vivo loads.

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Zusammenfassung
Der Gelenkknorpel bedeckt die artikulierenden Knochenflächen in den Gelenken. Seine Aufgabe
ist es zum einen, den Knochens vor hohen Spannungen zu schützen und zum anderen, zusammen
mit der Synovialflüssigkeit, eine annähernd reibungslose Bewegung des Gelenks während des
gesamten Lebens einer Person zu ermöglichen. Diese Funktion wird jedoch durch degenerative
Gelenkserkrankungen, wie der Arthrose, gestört. Heutzutage verursacht die Gelenksarthrose
enorme wirtschaftliche, soziale und psychologische Belastungen. Deshalb ist ein wichtiges Ziel,
die Diagnose und die Behandlungsformen von solchen muskuloskeletalen Erkrankungen zu
verbessern, bevor es zu irreversibelen Veränderungen kommt.
Im Rahmen dieser Arbeit wurden zwei Strategien zur Verhinderung irrversibeler arthrotischer
Veränderungen im Gelenkksknorpel biomechanisch Untersucht. Zur Verbesserung der Diagnose
entwickelten und validierten wir im ersten Teil (Kapitel 4) einen neuartigen
Kompressionsapparat zur Beurteilung des patellofemoralen Gelenkknorpels anhand seiner
mechanischen Eigenschaften. Im zweiten Teil (Kapitel 5) untersuchten wir neuartigen
Implantate, die zur Behandlung von tiefen Knorpeldefekten beim „Tissue Engineering“
verwendet werden und deren Fixation in dem gesunden Knorpel.

Im ersten Teil der Arbeit präsentieren wir ein Gerät, mit welchem im
Magnetresonanztomographen (MRT) eine statische Last von 400 N nach dem Hebelprinzip auf
frei präparierte patellofemorale Gelenke aufgebracht werden kann. Wir untersuchten zwei
Kniescheiben mit gesundem Knorpel, eine mit oberflächigen Defekten und eine, die biochemisch
mit Trypsin degeneriert wurde, um ein frühes Stadium der Arthrose zu simulieren. Während des
zweistündigen mechanischen Tests wurde die Deformation des Knorpels in der transversalen
Ebene mit einem 1.5 T Kernspinnresonanztomographen und einer validierten dreidimensionalen
Sequenz aufgezeichnet. Die quantitative Auswertung der Bilder erlaubte es, individuelle Finit
Element (FE) Modelle der Kompressionsversuche zu erstellen. Die Kopplung der Finit Element
Methode mit den experimentellen Deformationsdaten ermöglichte die Berechnung der
mechanischen Eigenschaften des Knorpels.
Im zweiten Teil der Arbeit führten wir mechanische Tests an künstlich gezüchteten,
knorpelähnlichen Implantaten durch, um deren mechanischen Eigenschaften zu bestimmen.
Zusätzlich testeten wir mechanische Fixierung von vier, häufig bei der autologen
Chondrozytenimplatation verwendeten Biomaterialien, die mit vier unterschiedlichen
Fixationstechniken befestigt wurden (unfixiert, mit Fibrin-Kleber, mit Knorpelnaht und mit
transossärer Naht). Hierbei wurden dreidimensionale Materialien, eine zweidimensionale
Kollagen-Membran und ein gelartiges Matrixmaterial in rechteckigen Knorpledefekten fixiert
und unter Zug belastet bis zum Versagen.

Mechanische Belastungen des patellofemoralen Gelenks führten zu Volumenänderungen von
rund 190 mm3 für gesunden Knorpel und von rund 480 mm3 für degenerierten Knorpel. Im
Gegensatz zum Knorpel mit intakter Oberfläche relaxierte die Verformung der Probe mit den
ix