Studies on the gelation of gelatin solutions and on the use of resulting gels for medical scaffolds [Elektronische Ressource] / vorgelegt von Mojgan Zandi

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• Publié par: universitat_duisburg-essen
• Publié le: 01 janvier 2008
• Nombre de lectures: 64
• Langue: English
• Poids de l'ouvrage: 27 Mo

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Studies on the Gelation of Gelatin
Solutions and on the Use of Resulting
Gels for Medical Scaffolds
Dissertation
Zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
am Fachbereich Chemie
an der Universitaet Duisburg-Essen
Vorgelegt von
Mojgan Zandi
aus Kerman
Referent: Prof. Dr. Christian Mayer
Koreferent: Prof. Dr. Hamid Mirzadeh
Koreferent: Prof. Dr. Mathias Ulbricht
Tag der muendlichen Pruefung: 18 Feb. 2008Die vorliegende Arbeit wurde in der Zeit von Mai 2004 bis Oktober 2007 im
Fachgebiet der Physikalischen Chemie an der Universitaet Duisbiurg-Essen
unter Anleitung von Herr Prof. Dr. Christian Mayer and Herr Prof. Dr.
Hamid Mirzadeh angefertigt.Acknowledgment
First of all, I thank God for making me possible to fulfill my research.
I would like to express my sincere gratitude to my supervisor, Prof. Dr. Christian Mayer for his
encouragement, precious guidance and supporting me to participate in international conferences
during my research. His careful editing contributed enormously to complete my thesis.
I am deeply grateful to my supervisor Prof. Dr. Hamid Mirzadeh for his valuable guidance. I benefited
from his advices throughout my research.
I sincerely thank Prof. Dr. Mathias Ulbricht and Prof. Dr. Matthias Epple for dedicating their time to
evaluate my work.
I acknowledge Also Prof. Dr. Matthias Epple to provide me lab facilities during hydroxyapatite
preparation.
I acknowledge Mr. Henning Urch from research group of Prof. Dr. Epple for taking main part of SEM
photographs and preparation of spherical nano- hydroxyapatite which I needed.
I warmly thank Dr. Wassef Al Sekhaneh for worth information.
I acknowledge Mr. Mohsen Rahimi Asl in IPPI and Mr. Manfred Zähres in Duisburg-Essen
University for their assistance in rheology and NMR spectroscopy, respectively.
I would like to thank Dr. Sacha Broekman and Mr. Daniel Bressler in Duisburg-Essen University for
doing a part of freeze-drying tests.
I owe further thanks to Mr. W. Borchard for valuable ideas and fruitful discussions.
I would like also to thank all of my colleagues in Duisburg-Essen University for their help especially
Mr. Uwe Bachorski for his kind support in computer section, Ms. Kirsten Schwark in laboratory
section and Ms. Gudrun Bechmanna and Ms. Gudrun Ciolek the secretaries of the University and
also Mr. Sven Beuermann for his friendly help.
I really appreciate the help of my beloved friends and colleagues in Iran Polymer and Petrochemical
Institute and offer special thank to (Dr`s.) Parvin Shokrollahi, Mohammad Atai, Fahimeh Askari,
Fatemeh Shokrollahi, Farhid Farahmand-Ghavi, (Ms.`s) Farzane Ahmad-Khanbeygi, Mitra Hashemi-
Tabatabaie, Shadi Afghan, Samal Babanzadeh, Roya Mashayekhi and Shiva Irani.
I am thankful of my kind room-mates Ms. Katarina Tomić, Dr. Andreas Langer and Dr. Michael Vogt
for proving me a good and friendly atmosphere in my office during my study.
I acknowledge Ministry of Science, Research and Technology of Iran for supporting me to study in
Germany.
I would like to thank Prof. Dr. Shahram Shahbazpanahi my kind brother in-law for his help to
overcome obstacles during my research.
I thank Mr. Shervin Parvin for his encouragement and help.
Finally I would like to give my special thank to my brother in low Mr. Mohammad-Javade Abazari,
Marjan and Mojdeh Zandi, my sisters , Mohsen Zandi, my brother, Manijeh, my sister-in law and
Athareh pooladi and Ali-asghar Zandi my kind parents that endure the long distance during my study.Summary
This study focuses on the early stages of the gelation of an aqueous type A (Pig skin)
gelatin solution. The thermo-reversible mono and triple helix formation was observed
by rheology and proton NMR relaxation measurements.
At high temperatures (T > 330 K), gelatin molecules form flexible random coils of
small hydrodynamic radius, the elastic modulus of the solution is relatively low. On
decreasing the temperature, mono helix formation begins, connected with an increase
of the storage modulus and the hydrodynamic radius. The absence of a significant
concentration dependence of this early variation of the modulus indicates the
intramolecular nature of this structural change. The simultaneous decrease of the spin-
1spin relaxation times of the H signals of certain amino acids confirms its effect on the
molecular mobility. As this affects especially the signals of arginine and lysine, we
conclude that these basic amino acids play a significant role in forming the
intramolecular interactions. Triple helix formation occurs at a point at which the
viscosity begins to increase rapidly near the gel point (T < 320 K). This process is
clearly dominated by intermolecular interactions, as the slope as well as the starting
point of the rapid increase significantly depends on the concentration.
In this work the coil structure of gelatin in the early stage of gelatin gelation under
variation of temperature (283-330 K), pH (3, 6.5, 11) and concentration (1, 3, 5 %
w/w) were also evaluated by NMR spectroscopy. In addition, changes in the
rheological characteristics such as storage modulus and complex viscosity of the
gelatin solutions were measured and the effect of acidity, temperature and
concentration are evaluated. The experimental results are analyzed to obtain the polar
contribution to the relaxation behavior and the mobility of aminoacids in different
temperature and different acidity. It was indicated by spin-spin relaxation time that
mobility of amino acids in acidic and basic solution are much more than in neutral
solution and some amino acids have different behavior in acidic and basic media.
Besides, gelation temperature shifted to lower temperature in both acidic and basic
solutions. Rheological behavior also confirms that inter-molecular and intra-
molecular interaction will be decreased in acidic and basic media and the gelation time decreased. Therefore, by controlling the temperature, concentration and also pH,
folding of the amino acids could be controlled.
Gelation process of gelatin after mineralization with nano-particulate hydroxyapatite
was monitored and investigation of relaxation behavior of aminoacids in gelatin
chains and changes in the coil structure of 3 and 5 % gelatin solution under variation
of temperature (298-330 K). The NMR state diagrams, i.e. plots of ln (T ) vs. the 2
reciprocal temperature (1/T), were produced for 3 % and 5 % gelatin solutions
mineralized with hydroxyapatite. We found that the different concentrations (3 and 5
%) have no drastic effect on the T relaxation time but different amino acids have 2
different patterns, so a different mobility during heat scan can be postulated. It may
relate to this fact that they are well designed to have an interaction with phosphate and
calcium anion.
In our study, we introduced new n-HAp (spherical, mixed shape and rod-like) /gelatin
scaffolds coated with n-HAp using Chemical Bath Deposition technique. In this
research n-HAp was prepared by wet chemical process and according to the present
state of knowledge; the samples prepared at 25˚ show spherical (via continuous
method) and mixed shape (via non-continuous method) particles and aggregate
readily. The n-HAp particles fabricated at 40, 70˚ and 24 h aging time are needle
and rod-like with widths ranging 30-60 nm and lengths from 100-300 nm,
respectively. They distribute in gelatin much better than spherical and mixed shape
particles, due to their higher surface area and higher reactivity. Therefore, the good
mechanical properties of the nano-rod HAp/gelatin scaffold may result from their
uniform distribution in the gelatin matrix, from their surface activity and their
interface chemical bonding which makes it possible for n-HAp to link with gelatin.
Spin-spin relaxation time measurements confirm that n-HAp may link with gelatin by
2+interactions with Ca and phosphate ions.
The compressive modulus of the n-HAp/gelatin scaffolds coated with n-HAp was
8.459 and 4.584 MPa for 5 and 3 % gelatin concentration respectively which is
comparable to the compressive modulus of a human cancellous bone. Both
compressive strength and moduli seem to increase by coating of the scaffolds. N-HAp particles coat the scaffold wall and easily enter the microscopic fractures resulting
from inter particle contact and increase the mechanical strength.
According to the cell culture experiments, the incorporation of rod-like n-HAp and
coating of scaffolds with n-HAp particles enable the prepared scaffolds to possess
good biocompatibility, high bioactivity and sufficient mechanical strength in
comparison with pure one. Coated scaffolds seem to have a better cell attachment and
proliferation. This research suggests that the newly developed rod-like HAp/gelatin
coated with n-HAp fulfill most of the requirements for the use as a suitable bone
replacement and may be superior for bone tissue engineering.Table of Contents: Part 1 .
Table of Contents: Part 1
Chapter 1 Introduction.............................................................................................. 1
1.1. Gelatin. ................................................ 1
1.2. Calcium Hydroxyapatite....................................................................................... 2