In their natural environments microorganisms exist predominantly in aggregates and biofilms. The ability of bacteria to form aggregates is associated with the biosynthesis of polymers such as polysaccharides. In this study the physical mechanisms underlying bacterial aggregation by extracellular polysaccharides are investigated by utilising the bacterium Sinorhizobium meliloti. S. meliloti biosynthesises an extracellular polysaccharide called succinoglycan, which is well characterised in terms of its structure and biosynthesis. A range of previously constructed succinoglycan biosynthesis mutants were screened for altered aggregation. An S. meliloti exoS mutant (a gain of function mutation that results in a constitutively active two component regulator called ExoS) overproduces succinoglycan and has enhanced aggregation compared to the parent strain, Rm1021. The aggregates settle to the bottom of the culture vessel resulting in loss of turbidity of the cultures and phase separation. Microscopic observation showed that succinoglycan did not appear to be attached to the aggregates, which formed ordered structures of laterally aligned cells. By addition of purified succinoglycan it was found that the critical concentration of polymer required to induce aggregation and phase separation of the cultures decreased with increasing cell concentration. These observations suggest that aggregation of S. meliloti cultures in the presence of succinoglycan is driven by macromolecular crowding, otherwise known as depletion attraction. Depletion attraction can drive the ordered arrangement and aggregation of colloidal particles in the presence of polymers. Aggregation of the particles increases the volume available to the polymers, maximising their entropy and the entropy of the system. Addition of succinoglycan to stationary phase Escherichia coli cultures and polystyrene colloids also resulted in aggregation consistent with depletion attraction. Furthermore alternative polymers such as the bacterial extracellular polysaccharide xanthan produced by Xanthomonas campestris can result in aggregation of bacteria by depletion attraction. Depletion attraction may therefore be a ubiquitous force driving aggregation of crowded dispersions of bacteria and polymers. The second part of the thesis focuses on how depletion driven aggregation can lead to surface-associated biofilm formation. Imaging of the sediment formed by the exoS mutant showed that the structure formed at the base of the culture vessel leads to development of an ordered structure composed of interlinked aggregates. The role of succinoglycan in surface attachment is complex and varies with culture conditions. Depletion attraction may facilitate interaction with a surface but alternative factors may then play a role in anchoring the cells to the surface. Under certain conditions the cells may produce factors which allow binding of the cells to a surface independently of succinoglycan. This study has demonstrated for the first time that an extracellular polysaccharide produced by bacteria can result in aggregation via depletion attraction which may be an under explored mechanism by which aggregation of bacteria can occur.

While the genetic control of ureteric bud (UB) morphogenesis has been extensively studied, the cellular basis of this process remains unclear. The renal organoid system is a novel technique in which embryonic kidneys are dissociated into single cells and then reaggregated, where they reassociate to form organotypic structures. This system may be very beneficial for investigating the cellular basis of ureteric bud development. Here, we first used a fluorescent UB marker, Hoxb7:myrVenus, and time-lapse microscopy to characterize the cellular and tissue-level events during self-organization and UB morphogenesis of E12.5 or E14.5 renal organoids. Briefly, we found that UB structures self-assembled by aggregation of individual cells that sent out long cell processes. The cellular aggregates grew and elongated into epithelial tubes that displayed characteristic ampullae, bifurcated, and appropriately expressed UB tip markers analogous to their in vivo counterparts. We also found that cap mesenchymal cells are attracted to newly formed epithelial structures early in renal organoid development, and were later found in cell clusters surrounding new branches. RET is a trans-membrane tyrosine kinase receptor (RTK), expressed in ureteric bud cells, whose expression is gradually restricted to the tips of the growing ureteric tree. We demonstrate that the renal organoid system can be used, as an alternative to the generation of in vivo chimeric embryos, to study Ret-dependent cell rearrangements previously shown to establish and maintain the UB tip progenitor domain. Chimeric renal organoids that juxtaposed wild-type cells with Sprouty1–/– mutant cells (higher Ret-signaling) or with Ret51/cre (lower Ret-signaling) mutant cells recapitulated the cell sorting pattern observed in similar in vivo chimeras. The cells with higher Ret-signaling preferentially sorted to, and were maintained in, the forming and growing tips of these mosaic ureteric bud structures, out-competing cells with lower Ret-signaling. We then used the mosaic organoid system to ask if fibroblast growth factor receptor 2 (Fgfr2), another RTK expressed in the ureteric bud and important for its development, also mediates individual cell rearrangements that generate and maintain the UB tips. UB cells null for Fgfr2 were largely unable to compete with wild-type cells for occupancy of the UB tips in chimeric renal organoids. Using the innovative MASTR (Mosaic Mutant Analysis with Spatial and Temporal Control of Recombination) technique in vivo, mosaic homozygous deletion of Fgfr2 in newly formed ureteric buds also revealed that mutant cells were slightly deficient in their ability to contribute to Fgfr2 heterozygous UB tips. This demonstrates a novel, cell-autonomous role of Fgfr2 in ureteric bud development. Matrix metalloproteinase 14 (MMP14) is a membrane-bound protein known to participate in a wide variety of cell functions including degradation of the extracellular matrix (ECM), cell signaling, and cell-autonomous cell migration. It is expressed in the UB and was discovered to act downstream of Ret-signaling. Although needed in the ureteric epithelium for ECM degradation and proper UB morphogenesis, its specific function in the UB has not been thoroughly investigated. In generating in vivo chimeras, we discovered that Mmp14 null cells could contribute to wild-type ureteric bud tips at E12.5 and E14.5, demonstrating that, despite its documented role in UB branching, Mmp14 does not have a cell-autonomous role in the cell rearrangements observed during UB morphogenesis.

A matriz extracelular do endométrio (ECM) é constituída por moléculas secretadas que compõem o microambiente celular e são ativadas ou suprimidas principalmente pelos hormônios esteróides ovarianos, estradiol (E2) e progesterona (P4) durante o ciclo estral. A identificação de genes envolvidos no remodelamento e receptividade pode levar à descoberta de importantes processos biológicos ligados ao sucesso gestacional. Os objetivos foram: 1. identificar a relação de diferentes tamanhos de folículos pré-ovulatórios (FPO) e corpo lúteo (CL) e de seus respectivos hormônios E2 e P4 com a expressão endometrial de genes associados com o remodelamento da ECM durante o período de pré-implantação; e 2. analisar a relação entre a expressão gênica de determinados componentes da ECM avaliada no dia 6 após inseminação artificial (IA) com sucesso gestacional. Para tal, dois experimentos foram realizados. No experimento 1, estudo 1 e estudo 2, 42 e 74 vacas Nelore (Bos indicus) adultas, respectivamente foram sincronizadas obtendo-se ao final dois grupos com distintos tamanhos FPO e CL consequentemente, distintas concentrações de E2 no proestro e P4 no diestro. Os grupos foram: Folículo Grande-CL Grande (FG-CLG; estudo 1, n=20; estudo 2, n=35) e Folículo Pequeno-CL Pequeno (FP-CLP; estudo 1, n=22; estudo 2, n=39). Amostras de tecido endometrial foram coletadas por biópsia no D0 (estro) e pós-mortem no D4 (estudo 1) e D7 (estudo 2). Concentrações de E2 e P4 foram mensuradas por radioimunoensaio (RIA) obtendo- se menores concentrações no grupo FP-CLP. No experimento 2, vacas adultas, Nelore (Bos indicus; n=33) foram sincronizadas utilizando um protocolo a base de prostaglandina F 2α (PGF2α) e observação de estro. As vacas foram inseminadas artificialmente (IA) e seis dias após, uma biópsia endometrial coletada. O diagnóstico de gestação foi realizado após 30 dias por meio de ultrasonografia (US) e então as vacas foram divididas em grupo Prenhe e Não- Prenhe (P e NP) para análise retrospectiva. Abundância de transcritos foi avaliada por sequenciamento (RNAseq) assim como qPCR em amostras de ambos experimentos. Realizaram-se também exames histológicos em amostras do D4 e D7 (estudo 2) para avaliação de colágeno total assim como espessura de fibras colágenas. Resultados determinaram uma maior abundância de transcritos relacionados ao remodelamento de MEC, em destaque TGFβ, MMPs, TIMPs e colágenos em vacas pertencentes aos grupos NP e FP-CLP. O mesmo foi observado para abundância de colágeno. No entanto, não observou-se diferença na relação entre fibras grossas e finas entre os tratamentos. Análises de correlação e regressão indicaram que folículos pré-ovulatórios de maior tamanho geram CL maiores e assim maiores concentrações de P4, a qual está negativamente associada à abundância de colágenos. Assim, de acordo com resultados aqui descritos, assume-se que a alteração da homeostase da MEC devido ao incremento na abundância de colágeno pode ser prejudicial à gestação em bovinos. / The endometrial extracellular matrix (ECM) é build up of secretory molecules that make up the cellular microenvironment and suffer activation or suppression mainly by the ovarian steroid hormones, estradiol (E2) and progesterone (P4) during the estrous cycle. The identification of genes involved in endometrial remodeling and receptivity may reveal important biological processes linked to gestational success. The objectives were: 1. identify the relationship among preovulatory follicle (POF) size and corpus luteum (CL) and its respective hormones, E2 and P4 on the endometrial expression of genes related to extracellular matrix remodeling during the pre-implantation period; and 2. analyze the relationship between endometrial ECM gene expression evaluated on day 6 post artificial insemination (AI) with pregnancy outcome. For such, two experiments were carried on. On experiment 1, study 1 and study 2, 42 and 74, respectively, adult Nelore (Bos indicus) cows were synchronized aiming to manipulate the peri-ovulatory endocrine environment, obtaining at the end of the protocol, two groups with distinct pre-ovulatory follicle (POF) and corpus luteum (CL) sizes, leading to groups with distinct E2 and P4 concentrations. The groups were: Large Follicle/CL (LF/CL; study 1, n=20, study 2, n=35) and Small Follicle/Cl (SF/CL; study 1, n=22; study 2, n=39). Endometrial samples were collected by biopsy on D0 (Estrus) and post-mortem on D4 and on study 2 post-mortem on D7. P4 and E2 concentrations were measured by RIA with a significative difference between the groups, being lower hormonal concentrations in the SF- SCL group and higher concentrations in the LF-LCL group . In experiment 2, adult Nelore (Bos indicus) cows (n=33) were synchronized using a prostaglandin 2α (PGF2α) and heat detection based protocol. The cows were AI and six days after an endometrial biopsy was collected. Pregnancy diagnosis was performed on day 30 by ultrasound (US) examination and cows were divided into pregnant and non-pregnant (P vs. NP) groups for a retrospective analysis. Histology was performed on D4 and D7 samples for total collagen abundance as well as fiber thickness. Correlation and regression analysis indicate that larger preovulatory follicles as well as higher P4 concentrations have a negative effect on collagen content. RNA- Seq analysis and confirmation by qPRC was performed on selected samples from experiment 1, study 2 and experiment 2. Comparison of mRNA levels of ECM components samples revealed higher levels of transcripts envolved in ECM remodeling, highlighting TGFβ MMPs, TIMPs and collagens in NP cows when compared with P cows as well as in the SF- SCL compared to the LF-LCL group. The same was observed for collagen abundance. However, there was no difference between thin and thick collagen fibers between treatments. Correlation and regression analysis indicate that larger POF lead to larger CL and hence, higher P4 concentrations, which has a negative effects on collagen abundance. Therefore, according to the results presented here, we can imply that an alteration in ECM homeostasis due to increased collagen abundance may be harmful to pregnancy in cows.

A regulação da expressão gênica é essencial para os fungos se adaptarem às adversidades ambientais, como alterações no pH extracelular, escassez de nutrientes, força iônica e oscilações de temperatura. A resposta adaptativa ao pH ambiente é bem caracterizada em fungos modelo como Aspergillus nidulans, e envolve a via de transdução de sinal constituída pelos produtos dos genes pal e pacC. No dermatófito Trichophyton rubrum, o gene pacC foi inativado, e a linhagem mutante apresentou uma diminuição na atividade das queratinases, indicando que, de alguma forma, este gene está envolvido na regulação da atividade queratinolítica deste dermatófito, e consequentemente na sua virulência e patogenicidade. Além disto, a glicosilação protéica é uma importante forma de regulação pós traducional, estruturando e estabilizando glicoproteínas que podem ser da via secretória, da parede ou da membrana celular. O processo de glicosilação protéica sofre influência do pH extracelular e da fonte nutricional. Foi ainda relatado que este tipo de regulação pós traducional também sofre influência dos genes palB e pacC, indicando que estes genes tenham um papel na glicosilação de enzimas secretadas. O objetivo deste trabalho foi analisar a influência do pH e da fonte nutricional na expressão de genes que codificam enzimas de N- e O-manosilação, e sua possível modulação pela proteína PacC no dermatófito T. rubrum. Para tanto, foi analisado, por PCR em tempo real, o perfil transcricional destes genes nas linhagens H6 (controle) e pacC-1, utilizando-se como fonte de carbono glicose, glicose e glicina ou queratina em vários tempos de cultivo, em pH 5,0 ou 8,0. A análise da expressão gênica revelou que quando a linhagem controle é cultivada em queratina em pH 5,0 ocorre um aumento da expressão da O-manosiltransferase, comparado com o cultivo em glicina com glicose e glicose. Porém, nestas mesmas condições o gene da N-manosiltransferase da linhagem mutante apresenta maiores níveis de expressão que os da linhagem controle. Em pH 8,0 pode-se notar grande semelhança entre os perfis de expressão apresentados por estes dois genes. Os resultados obtidos indicam que o gene pacC tem um papel importante no sensoriamento de nutrientes em meio ácido, modulando a expressão destas transferases, nas condições avaliadas. Estas enzimas podem ativar proteínas que atuam na hidrólise da queratina, ou mesmo formar glicoproteínas de parede celular que são essenciais na adesão do fungo à célula do hospedeiro, sugerindo um papel das manosiltransferases no processo infeccioso. / Gene expression regulation is essential for fungi to adapt to environmental adversities, such as changes in the extracellular pH, nutrient starvation, ionic strength, and temperature. The adaptive response to ambient pH is well characterized in model fungi such as Aspergillus nidulans, and involves the signal transduction pathway consisting of the products of the pal and pacC genes. In the dermatophyte Trichophyton rubrum, the pacC gene was inactivated and the mutant strain showed a decreased activity of keratinases, indicating that, somehow, this gene is involved in the regulation of the keratonolytic activity of this dermatophyte, and consequently in its virulence and pathogenicity. Moreover, protein glycosylation is an important form of post-translational regulation, playing a role in protein folding and stability of glycoproteins of the secretory pathway, cell wall or membrane. The process of protein glycosylation is influenced by extracellular pH and nutritional source. It has also been reported that this type of post-translational regulation is also influenced by the palB and pacC genes, indicating that these genes have a role in glycosylation of secreted enzymes. The objective of this study was to analyze the influence of the pH and nutritional source in the expression of the genes coding for the N-and O-manosylation enzymes, and their possible modulation by PacC in the dermatophyte T. rubrum. To this end, the transcriptional profile of these genes was analyzed, by Real Time PCR, in the H6 (control) and pacC-1 strains, using glucose, glucose with glycine, or keratin as the carbon source, in several culture times, at pH 5.0 or 8.0. Gene expression analysis showed that when the control strain is grown in keratin at pH 5.0 there is an increased expression of the O-manosyltransferase encoding gene, compared to the cultivation in glucose and glucose with glycine. However, at the same conditions the gene coding for the N-manosyltransferase presented higher levels of expression in the mutant strain in relation to the control strain. At pH 8.0 there is a great similarity between the expression profile of these two genes. The obtained results indicate that pacC gene plays an important role in nutrient sensing at acidic pH by modulating the expression of these transferases in the conditions evaluated. These enzymes can activate proteins that play roles in the hydrolysis of keratin, or even forming cell wall glycoproteins that are essential for the adhesion of the fungus to the host cell, suggesting a role of the manosyltransferases in the infectious process.

Microbial biofilms are significant in a variety of settings including the human microbiome, infectious disease, industrial processes, and environmental remediation. Due to the ubiquitous nature of biofilms, there is a great interest in understanding cellular activities within the biofilm matrix. Biofilm cells are able to better withstand environmental stress, experience increased horizontal gene transfer, and live longer. The purpose of this research is to grow Pseudomonas sp. strain ADP as a biofilm and examine the chemical and physical characteristics the microbe undertakes in a sticky extracellular matrix. ADP is the organism of choice because of its ability to metabolize atrazine. Cells are grown in a drip biofilm reactor and flow cells under varying time lapse to gain insight to biofilm formation. Some cells are grown with atrazine as the sole nitrogen source, while others are grown in a nutrient-rich medium to compare cells response under nutrient-limited conditions with atrazine particles in the matrix. As a positive control, Escherichia coli are grown in a similar manner. Raman spectroscopy was the main analytical technique used to evaluate the chemical and molecular characteristics of this system. Scanning electron microscopy is used to examine cellular distribution, and several assays are performed for molecular composition analysis. Raman analysis in the fingerprint region revealed distinct differences between free cells and cells in biofilm. Soluble extracellular polymeric substances (EPS) were found to be more prevalent than tightly bound EPS and lightly bound EPS in the biofilm matrix. Comparison of relative peak intensity ratios suggests that it is possible to track atrazine degradation by means of intermediates using Raman spectroscopy. SEM micrographs revealed EPS role as an immobilizing agent when in contact with compounds, such as atrazine. Further research is needed to determine if atrazine can bind to EPS fractions outside the presence of cells and whether its affinity to EPS is mostly attributed to physical conditions, due to the architecture of biofilm, or chemical, based on functional groups presents. The results obtained from this research will contribute to the development of a less invasive microscale approach to address the acquisition and induction of biotransformation activity occurring in xenobiotic degrading systems. The extracellular interactions observed can be used to further characterize biofilm-mediated bioremediation. Results have contributed to the Raman spectra library for microorganisms and organic compounds. .

Since the catabolism of amino acids in cheese results in the formation of most volatile flavor compounds, a proper intracellular pool of amino acids must be established in order to produce a desirable flavor production in cheese. Generation of this pool of amino acids requires complex interactions among casein and its derivatives, proteolytic enzymes, and transport systems in the associated bacteria, including lactococci. In this project, we hypothesized that casein hydrolysis by the extracellular proteinases of Brevibacterium linens BL2 modulates the expression profile of proteolytic related genes in Lactococcus lactis spp. lactis IL1403. In order to monitor the global gene regulation patterns in L. lactis ssp. lactis IL1403, a high-throughput gene expression tool was needed to study the gene expression profiles on a genomic scale. In this project, we developed a novel oligonucleotide-based filter DNA array protocol for this purpose. The success of this oligonucleotide-based DNA array was dependent on technical innovations including polyI tailing, indirect high density biotin labeling, careful probe design, and integrated computational data analysis. The utility and validity of this protocol were demonstrated by profiling the expression of 375 metabolically related genes in L. lactis ssp. lactis IL1403 during heat, acid, and osmotic stresses. Subsequently the DNA macroarray was used to profile the gene expression changes of L. lactis spp. lactis IL1403 growing in a peptide-limited medium, in a casitone-based peptide-rich medium, and in a casein hydrolyte by B. linens BL2 proteolytic enzymes. L. lactis ssp. lactis IL1403 experienced nitrogen starvation even with an abundance of peptide resources because of lack of expression of peptide transporter genes. Conversely, a peptide pool generated by B. linens BL2 proteolytic activities was sufficient to sustain the growth of L. lactis ssp. lactis IL1403. The repression of the peptide transporter and other peptidase genes of L. lactis ssp. lactis IL1403 was relieved in this medium. Interestingly, the Opt system, a di-tripeptide transporter, was used as a primary peptide transporter, instead of the Opp system whose genes were not actively transcripted in IL1403. We also conducted additional experiments to further describe the protease in B. linens BL2 responsible for the peptide pool generation. This enzyme was secreted as a non-active zymogen and matured into the active protease. Both proteolysis and maturation processes were regulated. Collectively, this work demonstrated that a unique protease of B. linens BL2 generated a pool of pep tides transportable by L. lactis IL1403 and induced changes in gene expression in L. lactis IL1403. Consequently, this body of work demonstrated the hypothesis to be true.

Os implantes utilizados para regeneração tecidual ainda falham na tentativa de mimetizar as propriedades da matriz extracelular (ECM), o que compromete a viabilidade e aplicabilidade do material. Além disso, permanece o desafio de desenvolver um método de aplicação minimamente invasivo para evitar danos teciduais adicionais (Badylak et al., 2015; Crapo et al., 2011; Xing et al., 2014). Assim, o objetivo do projeto é desenvolver um hidrogel injetável composto de ECM de pericárdio, tendão e osso bovino enzimaticamente digerida e reticulada com glutaraldeído, ésteres ativados de NHS e derivados de polietilenoglicol (PEG). O protocolo de digestão foi modificado de Willians (Williams et al., 2015), utilizando tripsina, pepsina e colagenase. A quantificação de GAGs e peptídeos mostrou que, independentemente do substrato e enzima utilizados, o processo em etapas gerou uma maior concentração de estruturas em relação ao processo contínuo. Adicionalmente, a análise de dicroísmo circular mostrou que o processo em etapas preservou mais estruturas secundárias. O perfil proteico das ECMs foi analisado como descrito em Flores (Flores et al., 2016), e foi verificado que ele é altamente diverso e tecido - específico. A ECM do pericárdio possui 94 tipos diferentes de proteínas, seguidas pela ECM do tendão (48) e pela ECM óssea (35), sendo o colágeno α1 (1) e o colágeno α2 (1) presentes em todas elas. Além disso, os produtos digeridos ECMp aumentaram a proliferação e diferenciação de células-tronco mesenquimais da medula óssea a osteoblastos maduros. A cinética do processo de gelificação, bem como as propriedades mecânicas do gel são dependentes do tipo de agente reticulante, assim como da concentração da gelatina. Este novo material é altamente personalizável e adaptável à aplicação biológica desejada. / The implants used for tissue regeneration still fail to mimic properties of extracellular matrix. It compromises the material viability and applicability. Furthermore, the challenge to manufacture a minimally invasive delivery system for it to avoid extra tissue damage still remains (Badylak et al., 2015; Crapo et al., 2011; Xing et al., 2014). Thus, the project goal is to develop an injectable hydrogel composed of pericardium, tendon and bovine bone ECM enzymatically digested and crosslinked with glutaraldehye, activated esters of NHS and polyethylene glycol (PEG) derivatives. The digestion protocol was modified from Willians (Williams et al., 2015), using trypsin, pepsin and collagenase as lytic enzymes. GAGs and peptides quantification showed that regardless of the substrate and enzyme, the stepwise process yields a higher amount of GAGs and peptides in comparison with the continuous process. In addition, circular dicroism analysis showed that the stepwise process preserves more secondary structures of proteins. ECMs protein profile was analyzed as in Flores (Flores et al., 2016) and verified that it is the highly diverse and tissue-specific. Pericardium ECM has 94 different types of proteins, followed by tendon ECM (48) and bones ECM (35), being collagen α1(1) and collagen α2(1) present in all of them. Furthermore, the ECMp digested products enhanced bone marrow mesenchymal stem cells proliferation and differentiation in mature osteoblast. The kinetics of the gelification process, as well as mechanical properties of the gel is dependent of the type of crosslinker and concentration of gelatin. This new material is highly customizable and adaptable to the biological application.

Abstract not available

<p>Staphylococcus aureus is an important human and animal pathogen that causes a wide range of infections. These infections can be very serious and sometimes hard to get rid of, because of the many virulence factors the bacteria produce during infections.</p><p>This project was a research of the extracellular fibrinogen-binding protein, Efb, which is a 15.9 kDa protein that has been shown to be an important virulence factor during S. aureus infections.</p><p>The purpose with the project was to find out if the protein has more than one binding site to fibrinogen and if people produce antibodies against Efb.</p><p>This was performed with methods such as affinity chromatography, ELISA, coagulation test and western blot. It was shown that Efb has two binding sites to fibrinogen. One is placed on the C-terminal part of Efb and the other on the N-terminal. It was also shown that the production of antibodies against Efb rises significantly in people during an ongoing infection.</p>

During the past several decades polymer materials become widely used as components of medical devices and implants such as hemodialysers, bioartificial organs as well as vascular and recombinant surgery. Most of the devices cannot avoid the blood contact in their use. When the polymer materials come in contact with blood they can cause different undesired host responses like thrombosis, inflammatory reactions and infections. Thus the materials must be hemocompatible in order to minimize these undesired body responses. The earliest and one of the main problems in the use of blood-contacting biomaterials is the surface induced thrombosis. The sequence of the thrombus formation on the artificial surfaces has been well established. The first event, which occurs, after exposure of biomaterials to blood, is the adsorption of blood proteins. Surface physicochemical properties of the materials as wettability greatly influence the amount and conformational changes of adsorbed proteins. In turn the type, amount and conformational state of the adsorbed protein layer determines whether platelets will adhere and become activated or not on the artificial surface and thus to complete the thrombus formation. The adsorption of fibrinogen (FNG), which is present in plasma, has been shown to be closely related to surface induced thrombosis by participating in all processes of the thrombus formation such as fibrin formation, platelet adhesion and aggregation. Therefore study the FNG adsorption to artificial surfaces could contribute to better understanding of the mechanisms of platelet adhesion and activation and thus to controlling the surface induced thrombosis. <br /> <br /> Endothelization of the polymer surfaces is one of the strategies for improving the materials hemocompatibility, which is believed to be the most ideal solution for making truly blood-compatible materials. Since at physiological conditions proteins such as FNG and fibronectin (FN) are the usual extracellular matrix (ECM) for endothelial cells (EC) adhesion, precoating of the materials with these proteins has been shown to improve EC adhesion and growth in vitro. ECM proteins play an essential role not only like a structural support for cell adhesion and spreading, but also they are important factor in transmitting signals for different cell functions. The ability of cells to remodel plasma proteins such as FNG and FN in matrix-like structures together with the classical cell parameters such as actin cytoskeleton and focal adhesion formation could be used as an criteria for proper cell functioning. The establishment and the maintaining of delicate balance between cell-cell and cell-substrate contacts is another important factor for better EC colonization of the implants. The functionality of newly established endothelium in order to produce antithromotic substances should be always considered when EC seeding is used for improving the hemocompatibility of the polymer materials. <br /> <br /> Controlling the polymer surface properties such as surface wettability represents a versatile approach to manipulate the above cellular responses and therefore can be used in biomaterial and tissue engineering applications for producing better hemocompatible materials.