Biomaterials research has undergone a variety of evolutionary developments in recent years. In this perspective, bulk materials properties and biomechanics took relevance in view of the stringent mechanical and tribological demands of the bio-implants. However, such issues cannot be the sole determinants of clinical outcome. Interest in bulk properties has inevitably shifted to the important consideration of the surface with the interfacial phenomena, conditioning their performance. These events are extremely important for biosensor devices. The application focus of biosensors has also broadened with time and whilst clinical diagnostics probably remains the single biggest area, roles are also being found in environmental (including food) monitoring, personal security (including warfare), drug discovery, and basic biological research. The development of suitable materials for biosensor applications requires a thorough understanding of the structure and chemistry of the solid-liquid interface when such a material has to work in the actual context. The research domain is complex due to the diversity of materials and applications of interest and the variety of biological species the biosensor device has to interface. In order to begin to follow the interactions that may occur when a material is placed in a particular environment, it is of fundamental importance to have information on the composition and structure of the top few atomic layers. In general, the statement that surface properties of a material differ from that of the bulk can be also applied to biomaterials. Thus, since the interaction between the material and the biological species occur at their interface, that is at molecular level in a narrow interface zone (< 1 nm), the surface properties of the material can greatly influence the biomaterial tissue/cell/protein interaction. Surface modification techniques have become a key method for designing materials to produce specific biological and chemical interactions. Modification of surface properties by altering the surface functionalities or by thin film deposition allow us to create and optimize surfaces with desired chemical and physical properties suitable for subsequent biological evaluation and indeed, for such applications as the promotion of specific cell/protein responses to a surface. Nowadays, the wet chemical conventional methods, used for surface functionalization, involve in some cases the use of toxic liquid reagents thus environment detrimental; for this reason they are progressively being replaced by other techniques, in particular by plasma surface modification processes. Low-temperature plasmas are produced by electrical discharge sustained by gases at low-pressure condition. They consist of a mixture of highly reactive species, i.e., ions, radicals, electrons, photons and excited molecules. The nature of plasmas, the modalities of transferring electric or electromagnetic field intensities to the reaction systems, the geometry of reactor (shape and volumes of the reaction vessel, geometrical location of electrodes and substrates, etc.) and the selected experimental conditions (pressure, power, flow rates of gases, temperature of the substrates, etc.) crucially influence the gas-phase and surface-related plasma chemistry. Recently, surface treatments and modification based on vapor phase plasma-assisted techniques have been widely applied to several biomedical fields. These processes are able to provide specific mono-type chemical functionalities, exposed at materials surfaces. Respect to traditional liquid phase procedures, advantages such as the high process control and the use of small quantities of reagents, are crucial for the enhancement of efficiency of the interactions that materials must perform according to the application. In particular, procedures for in situ plasma polymerization, starting from vapor released by liquid monomers, are presently used to synthesize innovative polymeric thin films applicable as substrates for cell culture, as adhesion promoter in prosthetic implants and for molecular recognition in sensors and biosensors. This method achieves the chemical and morphological modification of surfaces leaving the bulk properties practically intact, thus enabling its applicability to a great variety of materials independently from their chemical properties. By plasma treatment completely different chemistry, hydrophilicity or surface roughness can be obtained in final resulting materials. Advantages of plasma polymerization include the possibility to obtain conformal thin films, pinhole free, deposited on most substrates, by means of a relatively simple one-step coating. Additionally, a wide range of compounds can be chosen as a monomer for plasma polymerization, even saturated hydrocarbons, providing a great diversity of possible surface modifications. Among these compounds, Acrylic Acid is an important monomer, finding applications as a coating in a great number of biological experiments, for example, as a novel cell-delivery vehicle. Using acrylic acid as a monomer for plasma polymerization, layers, containing carboxylic acid groups (-COOH), can be produced to make surfaces reactive towards different biomolecules containing amino groups (NH2). In this kind of applications the density of the carboxylic functionalities exposed at the surface of the plasma polymer is a crucial point. The modulation of the applied power, typically through variation of the pulse frequency and duty cycle, enables greater control over the processing plasma properties, for instance, the retention of the degree of monomer functional groups in the resulting polymer structure.. It worth of note that, by selectively acting the monomer fragmentation, through the plasma discharge pulsing, it is possible to promote the chain propagation of the polymer without affecting the chemical structure of the functional groups and so obtaining a high density of reactive surface species. These advantages have resulted in the rapid development of plasma technology, during the past decades, for applications ranging from adhesion to composite materials, protective coatings, printing, membranes, biomedical applications and so on. 1) Concerning the first part of the experimental work of this thesis, a twofold aim can be singled out: • by means of the study and the optimization of plasma polymerization processes, the achievement of thin films exposing the desired properties of stability, biocompatibility and bioreactivity • the experimental validation of such films performance in biosensor devices For these purposes, thin functional films deposited by plasma-polymerization process, were applied to different devices, in particular a plasma poly-acrylic acid thin film was used for the surface functionalization of a Microarray platform for biodiagnostic detection analysis. Then, a patterned functional polymer obtained by the combination of a non-bio-adhesive layer of plasma poly-styrene and the functional coating of the plasma poly acrylic acid, was used for the functionalization of a photonic mono-dimensional crystal able to couple Bloch Surface Waves on its surface to Fluorescence emission specifically localized to poly-acrylic acid guides for photonic biosensing . 2) A last chapter of this thesis is dedicated to the study and optimization of maleic anhydride functionalization according to different technical approaches, compared in terms of technical feasibility and achievable surface properties, in order to obtain a stable surface functionalization with a sufficient anhydride density for subsequent protein binding

Surface Chemical Functionalization based on Plasma Techniques / Ricciardi, Serena. - (2012). [10.6092/polito/porto/2497126]

Surface Chemical Functionalization based on Plasma Techniques

RICCIARDI, SERENA
2012

Abstract

Biomaterials research has undergone a variety of evolutionary developments in recent years. In this perspective, bulk materials properties and biomechanics took relevance in view of the stringent mechanical and tribological demands of the bio-implants. However, such issues cannot be the sole determinants of clinical outcome. Interest in bulk properties has inevitably shifted to the important consideration of the surface with the interfacial phenomena, conditioning their performance. These events are extremely important for biosensor devices. The application focus of biosensors has also broadened with time and whilst clinical diagnostics probably remains the single biggest area, roles are also being found in environmental (including food) monitoring, personal security (including warfare), drug discovery, and basic biological research. The development of suitable materials for biosensor applications requires a thorough understanding of the structure and chemistry of the solid-liquid interface when such a material has to work in the actual context. The research domain is complex due to the diversity of materials and applications of interest and the variety of biological species the biosensor device has to interface. In order to begin to follow the interactions that may occur when a material is placed in a particular environment, it is of fundamental importance to have information on the composition and structure of the top few atomic layers. In general, the statement that surface properties of a material differ from that of the bulk can be also applied to biomaterials. Thus, since the interaction between the material and the biological species occur at their interface, that is at molecular level in a narrow interface zone (< 1 nm), the surface properties of the material can greatly influence the biomaterial tissue/cell/protein interaction. Surface modification techniques have become a key method for designing materials to produce specific biological and chemical interactions. Modification of surface properties by altering the surface functionalities or by thin film deposition allow us to create and optimize surfaces with desired chemical and physical properties suitable for subsequent biological evaluation and indeed, for such applications as the promotion of specific cell/protein responses to a surface. Nowadays, the wet chemical conventional methods, used for surface functionalization, involve in some cases the use of toxic liquid reagents thus environment detrimental; for this reason they are progressively being replaced by other techniques, in particular by plasma surface modification processes. Low-temperature plasmas are produced by electrical discharge sustained by gases at low-pressure condition. They consist of a mixture of highly reactive species, i.e., ions, radicals, electrons, photons and excited molecules. The nature of plasmas, the modalities of transferring electric or electromagnetic field intensities to the reaction systems, the geometry of reactor (shape and volumes of the reaction vessel, geometrical location of electrodes and substrates, etc.) and the selected experimental conditions (pressure, power, flow rates of gases, temperature of the substrates, etc.) crucially influence the gas-phase and surface-related plasma chemistry. Recently, surface treatments and modification based on vapor phase plasma-assisted techniques have been widely applied to several biomedical fields. These processes are able to provide specific mono-type chemical functionalities, exposed at materials surfaces. Respect to traditional liquid phase procedures, advantages such as the high process control and the use of small quantities of reagents, are crucial for the enhancement of efficiency of the interactions that materials must perform according to the application. In particular, procedures for in situ plasma polymerization, starting from vapor released by liquid monomers, are presently used to synthesize innovative polymeric thin films applicable as substrates for cell culture, as adhesion promoter in prosthetic implants and for molecular recognition in sensors and biosensors. This method achieves the chemical and morphological modification of surfaces leaving the bulk properties practically intact, thus enabling its applicability to a great variety of materials independently from their chemical properties. By plasma treatment completely different chemistry, hydrophilicity or surface roughness can be obtained in final resulting materials. Advantages of plasma polymerization include the possibility to obtain conformal thin films, pinhole free, deposited on most substrates, by means of a relatively simple one-step coating. Additionally, a wide range of compounds can be chosen as a monomer for plasma polymerization, even saturated hydrocarbons, providing a great diversity of possible surface modifications. Among these compounds, Acrylic Acid is an important monomer, finding applications as a coating in a great number of biological experiments, for example, as a novel cell-delivery vehicle. Using acrylic acid as a monomer for plasma polymerization, layers, containing carboxylic acid groups (-COOH), can be produced to make surfaces reactive towards different biomolecules containing amino groups (NH2). In this kind of applications the density of the carboxylic functionalities exposed at the surface of the plasma polymer is a crucial point. The modulation of the applied power, typically through variation of the pulse frequency and duty cycle, enables greater control over the processing plasma properties, for instance, the retention of the degree of monomer functional groups in the resulting polymer structure.. It worth of note that, by selectively acting the monomer fragmentation, through the plasma discharge pulsing, it is possible to promote the chain propagation of the polymer without affecting the chemical structure of the functional groups and so obtaining a high density of reactive surface species. These advantages have resulted in the rapid development of plasma technology, during the past decades, for applications ranging from adhesion to composite materials, protective coatings, printing, membranes, biomedical applications and so on. 1) Concerning the first part of the experimental work of this thesis, a twofold aim can be singled out: • by means of the study and the optimization of plasma polymerization processes, the achievement of thin films exposing the desired properties of stability, biocompatibility and bioreactivity • the experimental validation of such films performance in biosensor devices For these purposes, thin functional films deposited by plasma-polymerization process, were applied to different devices, in particular a plasma poly-acrylic acid thin film was used for the surface functionalization of a Microarray platform for biodiagnostic detection analysis. Then, a patterned functional polymer obtained by the combination of a non-bio-adhesive layer of plasma poly-styrene and the functional coating of the plasma poly acrylic acid, was used for the functionalization of a photonic mono-dimensional crystal able to couple Bloch Surface Waves on its surface to Fluorescence emission specifically localized to poly-acrylic acid guides for photonic biosensing . 2) A last chapter of this thesis is dedicated to the study and optimization of maleic anhydride functionalization according to different technical approaches, compared in terms of technical feasibility and achievable surface properties, in order to obtain a stable surface functionalization with a sufficient anhydride density for subsequent protein binding
2012
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