61 / 2018-07-29 21:09:55

Surface Hydroxyl Groups Regulate the Osteogenic Differentiation of Mesenchymal Stem Cells on Titanium and Tantalum Metals

Titanium,tantalum,msc,uv,bridging-OH,terminal-OH

全体主题 > ii. Biomaterials and formulation of novel “bioinks” for tissue-specific applications

Introduction
Titanium (Ti) and tantalum (Ta) have become promising metals for orthopedic and dental implant applications due to their superior mechanical properties, high corrosion resistance, and excellent biocompatibility.1–4 Titanium and its alloys in the past few decades have been widely used for dental implants and prosthesis components. However, Ti prosthesis frequently causes bone atrophy and reabsorption due to its high elastic modules (100 GPa).5 Therefore, porous Ti is used preferentially for its similar mechanical properties to cancellous bone, thus providing great potential for bone reconstruction.6 Used clinically since 1997, Ta has been gaining more attention as a new metallic biomaterial. Through the formation of a bone-like apatite layer in simulated body fluid, Ta has shown to promote surface osteointegration and bone ingrowth. However, Ta has obvious shortcomings in terms of its high elastic modulus (186 GPa) and extremely high melting temperature (3017℃), making it difficult to process Ta structures and apply it in bulk metallic forms in clinic.
Although the surface topography has not been changed, ultraviolet (UV) treatment of titanium implants immediately prior to clinic use, named photofunctionalization, has been demonstrated to improve the osteointegration. The UV treatment always increases the hydrophilicity and removes hydrocarbons on the titanium surface, which might be attributed to the distinct situation of the surface hydroxyl groups. Furthermore, the hydroxyl group has been reported to be an intrinsic factor which has strong electrostatic interactions with the amino group in proteins, regulating the initial protein adsorption and subsequent cellular behaviors. Therefore, it is reasonable to speculate that the surface hydroxyl groups on Ti and Ta metals play a critical role in their inherent osteogenic capacity.
We have recently demonstrated that surface hydroxyl groups could regulate the protein adsorption behaviors on TiO2 films. However, these previous efforts have only focused on the differences of protein adsorption. The observations still show a lack of the effects of surface hydroxyl groups on stem cell fate. Moreover, the significant scope of the effects of surface hydroxyl groups on the osteogenic capacity of Ti and Ta surfaces still needs to be explored. In this work, we directly compare the osteogenic response of marrow mesenchymal stem cells (MSCs) to Ti and Ta metal surfaces with alterable surface hydroxyl groups by using UV treatment. The amount and comparative quantity of the distinct type of surface hydroxyl group of Ti and Ta metals were controlled by UV light treatment. The osteogenic activity of Ti and Ta was evaluated by a series of in vitro experiments. And a possible mechanism underlying the different cellular responses of Ti and Ta was also proposed based on the considerations of cell–material interactions.
Materials and methods
SEM observation was carried out to reveal the cell attachment, growth and spreading on Ti and Ta substrates before and after UV treatment. The CCK-8 assay was used to quantitatively determine the proliferation of viable MSCs on Ta and Ti substrates before and after UV treatment. To understand how the surface hydroxyl group feature directed cellular focal adhesion (FA) formation and morphology, we further stained cells for the focal adhesion protein vinculin and the actin cytoskeleton after 1 days of culture on Ti and Ta substrates before and after UV treatment. To probe the effects of surface hydroxyl groups of Ti and Ta substrates on stem cells fate on a molecular level, the polymerase chain reaction (PCR) method was employed for analyzing gene expression level associated with the osteogenic differentiation related gene markers (Col-1, OCN and RunX-2) of MSCs for 7 days and 14 days of culture. We used circular dichroism (CD) spectra to study the relative amount and secondary structure of bovine serum albumin (BSA) protein adsorbed on Ti and Ta substrates.
Results
Although no difference was found on both surface topographies, cellular adhesion, proliferation and the expression of osteogenic-related markers were upregulated with the increasing amount of surface hydroxyl groups (-OH) after ultraviolet (UV) light treatment. Moreover, Ti showed better effects in promoting osteogenic differentiation of MSCs than Ta before UV light treatment, but demonstrated the opposite after UV light treatment.
Introduction
Titanium (Ti) and tantalum (Ta) have become promising metals for orthopedic and dental implant applications due to their superior mechanical properties, high corrosion resistance, and excellent biocompatibility.1–4 Titanium and its alloys in the past few decades have been widely used for dental implants and prosthesis components. However, Ti prosthesis frequently causes bone atrophy and reabsorption due to its high elastic modules (100 GPa).5 Therefore, porous Ti is used preferentially for its similar mechanical properties to cancellous bone, thus providing great potential for bone reconstruction.6 Used clinically since 1997, Ta has been gaining more attention as a new metallic biomaterial. Through the formation of a bone-like apatite layer in simulated body fluid, Ta has shown to promote surface osteointegration and bone ingrowth. However, Ta has obvious shortcomings in terms of its high elastic modulus (186 GPa) and extremely high melting temperature (3017℃), making it difficult to process Ta structures and apply it in bulk metallic forms in clinic.
Although the surface topography has not been changed, ultraviolet (UV) treatment of titanium implants immediately prior to clinic use, named photofunctionalization, has been demonstrated to improve the osteointegration. The UV treatment always increases the hydrophilicity and removes hydrocarbons on the titanium surface, which might be attributed to the distinct situation of the surface hydroxyl groups. Furthermore, the hydroxyl group has been reported to be an intrinsic factor which has strong electrostatic interactions with the amino group in proteins, regulating the initial protein adsorption and subsequent cellular behaviors. Therefore, it is reasonable to speculate that the surface hydroxyl groups on Ti and Ta metals play a critical role in their inherent osteogenic capacity.
We have recently demonstrated that surface hydroxyl groups could regulate the protein adsorption behaviors on TiO2 films. However, these previous efforts have only focused on the differences of protein adsorption. The observations still show a lack of the effects of surface hydroxyl groups on stem cell fate. Moreover, the significant scope of the effects of surface hydroxyl groups on the osteogenic capacity of Ti and Ta surfaces still needs to be explored. In this work, we directly compare the osteogenic response of marrow mesenchymal stem cells (MSCs) to Ti and Ta metal surfaces with alterable surface hydroxyl groups by using UV treatment. The amount and comparative quantity of the distinct type of surface hydroxyl group of Ti and Ta metals were controlled by UV light treatment. The osteogenic activity of Ti and Ta was evaluated by a series of in vitro experiments. And a possible mechanism underlying the different cellular responses of Ti and Ta was also proposed based on the considerations of cell–material interactions.
Materials and methods
SEM observation was carried out to reveal the cell attachment, growth and spreading on Ti and Ta substrates before and after UV treatment. The CCK-8 assay was used to quantitatively determine the proliferation of viable MSCs on Ta and Ti substrates before and after UV treatment. To understand how the surface hydroxyl group feature directed cellular focal adhesion (FA) formation and morphology, we further stained cells for the focal adhesion protein vinculin and the actin cytoskeleton after 1 days of culture on Ti and Ta substrates before and after UV treatment. To probe the effects of surface hydroxyl groups of Ti and Ta substrates on stem cells fate on a molecular level, the polymerase chain reaction (PCR) method was employed for analyzing gene expression level associated with the osteogenic differentiation related gene markers (Col-1, OCN and RunX-2) of MSCs for 7 days and 14 days of culture. We used circular dichroism (CD) spectra to study the relative amount and secondary structure of bovine serum albumin (BSA) protein adsorbed on Ti and Ta substrates.
Results
Although no difference was found on both surface topographies, cellular adhesion, proliferation and the expression of osteogenic-related markers were upregulated with the increasing amount of surface hydroxyl groups (-OH) after ultraviolet (UV) light treatment. Moreover, Ti showed better effects in promoting osteogenic differentiation of MSCs than Ta before UV light treatment, but demonstrated the opposite after UV light treatment.
Introduction
Titanium (Ti) and tantalum (Ta) have become promising metals for orthopedic and dental implant applications due to their superior mechanical properties, high corrosion resistance, and excellent biocompatibility.1–4 Titanium and its alloys in the past few decades have been widely used for dental implants and prosthesis components. However, Ti prosthesis frequently causes bone atrophy and reabsorption due to its high elastic modules (100 GPa).5 Therefore, porous Ti is used preferentially for its similar mechanical properties to cancellous bone, thus providing great potential for bone reconstruction.6 Used clinically since 1997, Ta has been gaining more attention as a new metallic biomaterial. Through the formation of a bone-like apatite layer in simulated body fluid, Ta has shown to promote surface osteointegration and bone ingrowth. However, Ta has obvious shortcomings in terms of its high elastic modulus (186 GPa) and extremely high melting temperature (3017℃), making it difficult to process Ta structures and apply it in bulk metallic forms in clinic.
Although the surface topography has not been changed, ultraviolet (UV) treatment of titanium implants immediately prior to clinic use, named photofunctionalization, has been demonstrated to improve the osteointegration. The UV treatment always increases the hydrophilicity and removes hydrocarbons on the titanium surface, which might be attributed to the distinct situation of the surface hydroxyl groups. Furthermore, the hydroxyl group has been reported to be an intrinsic factor which has strong electrostatic interactions with the amino group in proteins, regulating the initial protein adsorption and subsequent cellular behaviors. Therefore, it is reasonable to speculate that the surface hydroxyl groups on Ti and Ta metals play a critical role in their inherent osteogenic capacity.
We have recently demonstrated that surface hydroxyl groups could regulate the protein adsorption behaviors on TiO2 films. However, these previous efforts have only focused on the differences of protein adsorption. The observations still show a lack of the effects of surface hydroxyl groups on stem cell fate. Moreover, the significant scope of the effects of surface hydroxyl groups on the osteogenic capacity of Ti and Ta surfaces still needs to be explored. In this work, we directly compare the osteogenic response of marrow mesenchymal stem cells (MSCs) to Ti and Ta metal surfaces with alterable surface hydroxyl groups by using UV treatment. The amount and comparative quantity of the distinct type of surface hydroxyl group of Ti and Ta metals were controlled by UV light treatment. The osteogenic activity of Ti and Ta was evaluated by a series of in vitro experiments. And a possible mechanism underlying the different cellular responses of Ti and Ta was also proposed based on the considerations of cell–material interactions.
Materials and methods
SEM observation was carried out to reveal the cell attachment, growth and spreading on Ti and Ta substrates before and after UV treatment. The CCK-8 assay was used to quantitatively determine the proliferation of viable MSCs on Ta and Ti substrates before and after UV treatment. To understand how the surface hydroxyl group feature directed cellular focal adhesion (FA) formation and morphology, we further stained cells for the focal adhesion protein vinculin and the actin cytoskeleton after 1 days of culture on Ti and Ta substrates before and after UV treatment. To probe the effects of surface hydroxyl groups of Ti and Ta substrates on stem cells fate on a molecular level, the polymerase chain reaction (PCR) method was employed for analyzing gene expression level associated with the osteogenic differentiation related gene markers (Col-1, OCN and RunX-2) of MSCs for 7 days and 14 days of culture. We used circular dichroism (CD) spectra to study the relative amount and secondary structure of bovine serum albumin (BSA) protein adsorbed on Ti and Ta substrates.
Results
Although no difference was found on both surface topographies, cellular adhesion, proliferation and the expression of osteogenic-related markers were upregulated with the increasing amount of surface hydroxyl groups (-OH) after ultraviolet (UV) light treatment. Moreover, Ti showed better effects in promoting osteogenic differentiation of MSCs than Ta before UV light treatment, but demonstrated the opposite after UV light treatment.
Conclusion
The surface hydroxyl groups on Ti and Ta metals regulate the osteogenic differentiation of mesenchymal stem cells. Increasing the amount of surface hydroxyl groups on both Ti and Ta substrates by UV treatment could promoted the protein adsorption as well as the subsequent cellular adhesion, proliferation and osteogenic differentiation. Furthermore, Ti showed better effects in promoting osteogenic differentiation of MSCs than Ta before UV light treatment, but demonstrated the opposite after UV light treatment. These results might be attributed to the comparative quantity of distinct terminal-OH, which regulated the conformation of initial protein adsorption and subsequent cellular behaviors. This work therefore provides new insights into the fundamental understanding of cell-material interactions, and will have a profound impact on further designing materials to improve cellular response and function.