PhD thesis - theoretical considerations

The second month of PhD studies at the Institute of Metallurgy and Materials Science passed so quickly… Christmas time will come and be gone in the blink of an eye...However, during that time I had been working on my PhD thesis a little bit and made literature review concerning surface zeta-potential topic.
Interactions between medical implants and their surrounding tissues are affected by the physicochemical surface properties of the implants. The electric charge of a material surface is considered to be one of the most important physical factors involved in the biological evolution of the tissue around an implant. This charge depends on several features, such as the chemical composition of the material, the inflammatory situation, the composition of the surrounding body fluid and the environmental pH value. The electric surface properties could be indicated by a biomaterial’s zeta-potential.
The zeta-potential is measured by electrophoresis or alternatively by streaming potential methods. The result of zeta-potential measurement is the potential of a material in an ionic solution at the boundary between the so-called Stern layer and the diffuse layer.
It is based on the charge displacement in the electric double layer caused by an external force shifting the liquid phase tangentially against the solid. Charge carriers temporarily bound in the double layer will be removed by the external flow with pressure, and the potential can be measured between two electrodes. Larger positive values of the zeta-potential at a fixed pH indicate positive charge of the surface which could attract anions or negatively charged proteins, while lower values reflect a negative charge of a material surface that tends to attract positively charged particles.
The aim of my nearest study will be to investigate the relationship between surface zeta-potential (surface charge property), protein adsorption and cell proliferation on PEM (polyelectrolyte multilayers) films, deposited on polyurethane base materials via “Layer by Layer” method.

1. Cai K., Frant M., Bossert J., Hildebrand G., Liefeith K., Jandt K. (2006) Surface functionalized titanium thin films: Zeta-potential, protein adsorption and cell proliferation, Colloids and Surfaces B: Biointerfaces 50:1-8.
2. Caster D., Ratner B. (2002) Biomedical surface science: foundations to frontiers, Surf. Sci. 500:28-60.
3. Lavenus S., Pilet P., Guichex J., Weiss P., Louarn G., Layolle P. (2011) Behaviour of mesenchymal stem cells, fibroblasts and osteoblasts on smooth surfaces, Acta Biomater. 7:1525-1534.

PhD thesis – experimental investigation

So far a series of trials designed to investigate the electrokinetic potential of the surface was done. The base material were coverslips. In accordance with the methodology at the outset coverslips were treated with NaOH solution at a concentration of 2M, 5M and 10M respectively. This treatment was carried out in order to produce a negative surface charge allowing binding of the first positively charged polyelectrolyte layer. Some treated samples were left to the quantitative and qualitative comparison of the effects of various NaOH concentration on base material activation. The proper series of nine samples was covered by twelve polyelectrolyte bilayers consist of poly-L-lysine and hyaluronan.

Seminars participation

-“Physical properties of liquid crystal mixtures of chiral and achiral compounds applied in LCDs” given by MSc. Eng. J. Czerwiec
-“Simulation of microstructure and texture development using Digital Material Representation and ‘Crystal Plasticity’ model” given by Dr Eng. W. Wajda
-“Unconventional methods of producing TiB2-TiN composites” given by MSc. Eng. P. Wyzga

This month I have been trying to develope some foundations - implementation of mathematical tools and very basic algorithms, for instance, for conversion from Miller indices into Cartesian coordinates and vice versa, these are basics which will be used very often in the future and therefore must be prepared correctly and carefully.

While Brenda Lee was beginning to rock around the Christmas tree and the year 2011 was nearing its inevitable end I carried on with my research work and I actually succeeded in obtaining some scientific data. Once the alloys, which are under my investigation, ranging in composition with respect to Sn /Al ratio were cast and adequately heat treated an optical, XRD and SEM analysis were performed in order to examine their microstructure, morphology and composition. EDS analysis confirmed that the composition of the samples corresponded to the intended composition. Also initial studies of both SEM and XRD results revealed the presence of structures typical for Heusler L21 and martenistic phases in the considered materials.
The research goes on…

At 02.12.2011 I conducted a lecture about my master thesis and a short introduction into my research during PhD studies. Title of the first part of the presentation was: “Bioactive glass/poly(L-lactide-co-glycolide) composite scaffolds for bone tissue engineering”, the second part of the presentation covered topic: “Biodegradable magnesium alloys for medical applications”.

In connection with the development of all fields of medicine, especially in connection with the emergence of regenerative medicine, arose the need to produce a new generation of biomaterials. New materials must fulfill higher demands, all materials have to be biocompatible and more often - bioactive. Currently, if patient’s tissue is damaged, there are two options: transplantation or implantation. Organ transplantation is the moving of an organ from one body to another, or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. Implantation takes place, when medical device made of biomaterials is placed into the patient. Both approaches have their advantages and disadvantages.

Due to the development of biomaterials engineering, it has become possible to obtain a bioactive material. Thanks to this, now we have a new, third option - the application of a biomaterial, which replaces the missed tissue function and stimulates the regeneration of damaged tissue around prostheses. Such bone inductive materials are often made of calcium phosphates, e.g. hydroxyapatite or bioglass, because these materials directly connect to the bone. Equally interesting materials are aliphatic polyesters – resorbable polymers; inside the human body they undergo hydrolysis and products of their decomposition are removed together with metabolic products.

Every material, which is considered to be a biomaterial, must satisfy certain physical, mechanical and chemical behavior requirements and also be characterized as biocompatible. For example, the material must be strong enough to bear physiological load, resist undesired degradation or corrosion, be not carcinogenic, not immunogenic, antileukotactic, and so on. Many factors, such as implant size, shape, material composition, surface wettability, roughness and charge influence implant biocompatibility.

The purpose of this study was to manufacture composite materials based on resorbable polymer (PLGA) with addition of sol-gel derived bioglasses from the system CaO-SiO2-P2O5 and in vitro evaluation of these scaffolds. As a result, polymer-bioglass composites containing 10 vol. % and 20 vol. % of two types of bioglasses were prepared. Their bioactive properties were assessed by measuring of the ability to create hydroxyapatite layers on the surface when in contact with simulated body fluid (SBF). Porosity, water absorption and kinetics of degradation of the scaffolds were estimated. In addition, bioactivity of the scaffolds was evaluated in cell culture with MG-63 cell line.

During my PhD studies I want to focus on the evaluation of biodegradable magnesium alloys for bone implants. These alloys, in comparison with PLGA/bioglass scaffolds, have strength and Young’s modulus close to the natural bone. However, the corrosion ratio and hydrogen gas production during the degradation process need to be investigated.

My research in November:

During the second month of my PhD studies at the Institute of Metallurgy and Material Polish Academy of Sciences I paid attention on preparation of a lecture about “Bioactive glass/poly(L-lactide-co-glycolide) composite scaffolds for bone tissue engineering”. In the second part of the presentation I gave the introduction into biodegradable magnesium alloys. In November I also have made and literature studies connected with biodegradation of magnesium alloys. Together with my supervisor, we have choosen the probable candidate for our research: Mg-Zn-Ca (3-5 wt% Zn, 0.5-1.5 wt% Ca).

Between 14th and 18th of November I participated in “PhD School on nanoanalysis using finely focused ion and electron beams” in Gabriel Lippmann Center in Luxemburg.