Abstract:There is broad interest in fabricating cell-membrane-mimicking, hybrid lipid bilayer (HLB) coatings on titanium oxide surfaces for medical implant and drug delivery applications. However, existing fabrication strategies are complex, and there is an outstanding need to develop a streamlined method that can be performed quickly at room temperature. Towards this goal, herein, we characterized the room-temperature deposition kinetics and adlayer properties of one- and two-tail phosphonic acid-functionalized molecu… Show more
“…We selected two-tail DOCP molecules to form SAMs on TiO 2 because they mimic the basic molecular properties of natural phospholipids and have also proven useful for robust HLB fabrication using vesicle fusion, whereas vesicles adsorbed but did not fully rupture on SAMs composed of one-tail phosphonic acid counterparts [31]. The difference in vesicle fusion efficiency to form the HLB on TiO 2 was previously attributed to differences in SAM packing order [51] between one-tail vs. two-tail SAMs.…”
Section: Docp Sam Formationmentioning
confidence: 99%
“…Recently, the use of two-tail inverse phosphocholine (CP) lipids [24][25][26][27] to form SAMs on flat TiO 2 surfaces based on phosphate chemistry (i.e., covalent P-O-Ti bond formation [28]) was also reported and enabled HLB formation across a well-defined set of ionic strength and pH conditions [19,29,30]. Compared to traditional silanization that requires organic solvent, high temperature, and/or a long incubation time (with special surface pretreatment in some cases), the CP lipid attachment scheme on TiO 2 is simpler because it can readily occur in aqueous solution and at room temperature with shorter incubation time and no special surface pretreatment (other than straightforward oxygen plasma treatment) [31]. Therefore, CP-based SAM formation is particularly promising from a fabrication perspective (e.g., to prepare HLBs on biomedically relevant TiO 2 ) and also advantageous from a biomimetic perspective since the attached CP lipids have two hydrocarbon chains (i.e., two tails) per molecule that resembles the structural arrangement of natural phospholipids.…”
Section: Introductionmentioning
confidence: 99%
“…In this context, HLBs have proven to be a particularly useful model to study cholesterol-related membrane properties since zwitterionic lipid vesicles containing up to ~40 mol% Chol can form the upper leaflet of HLBs on top of single-tail SAMs [20,38,39], whereas vesicles containing only up to ~20 mol% Chol can rupture to form SLBs on SiO 2 surfaces [40,41]. In the two-chain CP SAM context, we have previously demonstrated that upper leaflet formation for HLBs on TiO 2 can be achieved using zwitterionic lipid vesicles that contain a fraction of biotinylated lipids [31], but Chol incorporation into CP SAM-based HLBs has not been attempted. In addition to the vesicle fusion method, the solvent exchange method has excellent potential for Chol incorporation into the upper leaflet of CP SAM-based HLBs because the method can form SLBs on SiO 2 with lipid mixtures containing up to around 63 mol% Chol [40,41].…”
Hybrid lipid bilayers (HLBs) are rugged biomimetic cell membrane interfaces that can form on inorganic surfaces and be designed to contain biologically important components like cholesterol. In general, HLBs are formed by depositing phospholipids on top of a hydrophobic self-assembled monolayer (SAM) composed of one-tail amphiphiles, while recent findings have shown that two-tail amphiphiles such as inverse phosphocholine (CP) lipids can have advantageous properties to promote zwitterionic HLB formation. Herein, we explored the feasibility of fabricating cholesterol-enriched HLBs on CP SAM-functionalized TiO2 surfaces with the solvent exchange and vesicle fusion methods. All stages of the HLB fabrication process were tracked by quartz crystal microbalance-dissipation (QCM-D) measurements and revealed important differences in fabrication outcome depending on the chosen method. With the solvent exchange method, it was possible to fabricate HLBs with well-controlled cholesterol fractions up to ~65 mol% in the upper leaflet as confirmed by a methyl-β-cyclodextrin (MβCD) extraction assay. In marked contrast, the vesicle fusion method was only effective at forming HLBs from precursor vesicles containing up to ~35 mol% cholesterol, but this performance was still superior to past results on hydrophilic SiO2. We discuss the contributing factors to the different efficiencies of the two methods as well as the general utility of two-tail CP SAMs as favorable interfaces to incorporate cholesterol into HLBs. Accordingly, our findings support that the solvent exchange method is a versatile tool to fabricate cholesterol-enriched HLBs on CP SAM-functionalized TiO2 surfaces.
“…We selected two-tail DOCP molecules to form SAMs on TiO 2 because they mimic the basic molecular properties of natural phospholipids and have also proven useful for robust HLB fabrication using vesicle fusion, whereas vesicles adsorbed but did not fully rupture on SAMs composed of one-tail phosphonic acid counterparts [31]. The difference in vesicle fusion efficiency to form the HLB on TiO 2 was previously attributed to differences in SAM packing order [51] between one-tail vs. two-tail SAMs.…”
Section: Docp Sam Formationmentioning
confidence: 99%
“…Recently, the use of two-tail inverse phosphocholine (CP) lipids [24][25][26][27] to form SAMs on flat TiO 2 surfaces based on phosphate chemistry (i.e., covalent P-O-Ti bond formation [28]) was also reported and enabled HLB formation across a well-defined set of ionic strength and pH conditions [19,29,30]. Compared to traditional silanization that requires organic solvent, high temperature, and/or a long incubation time (with special surface pretreatment in some cases), the CP lipid attachment scheme on TiO 2 is simpler because it can readily occur in aqueous solution and at room temperature with shorter incubation time and no special surface pretreatment (other than straightforward oxygen plasma treatment) [31]. Therefore, CP-based SAM formation is particularly promising from a fabrication perspective (e.g., to prepare HLBs on biomedically relevant TiO 2 ) and also advantageous from a biomimetic perspective since the attached CP lipids have two hydrocarbon chains (i.e., two tails) per molecule that resembles the structural arrangement of natural phospholipids.…”
Section: Introductionmentioning
confidence: 99%
“…In this context, HLBs have proven to be a particularly useful model to study cholesterol-related membrane properties since zwitterionic lipid vesicles containing up to ~40 mol% Chol can form the upper leaflet of HLBs on top of single-tail SAMs [20,38,39], whereas vesicles containing only up to ~20 mol% Chol can rupture to form SLBs on SiO 2 surfaces [40,41]. In the two-chain CP SAM context, we have previously demonstrated that upper leaflet formation for HLBs on TiO 2 can be achieved using zwitterionic lipid vesicles that contain a fraction of biotinylated lipids [31], but Chol incorporation into CP SAM-based HLBs has not been attempted. In addition to the vesicle fusion method, the solvent exchange method has excellent potential for Chol incorporation into the upper leaflet of CP SAM-based HLBs because the method can form SLBs on SiO 2 with lipid mixtures containing up to around 63 mol% Chol [40,41].…”
Hybrid lipid bilayers (HLBs) are rugged biomimetic cell membrane interfaces that can form on inorganic surfaces and be designed to contain biologically important components like cholesterol. In general, HLBs are formed by depositing phospholipids on top of a hydrophobic self-assembled monolayer (SAM) composed of one-tail amphiphiles, while recent findings have shown that two-tail amphiphiles such as inverse phosphocholine (CP) lipids can have advantageous properties to promote zwitterionic HLB formation. Herein, we explored the feasibility of fabricating cholesterol-enriched HLBs on CP SAM-functionalized TiO2 surfaces with the solvent exchange and vesicle fusion methods. All stages of the HLB fabrication process were tracked by quartz crystal microbalance-dissipation (QCM-D) measurements and revealed important differences in fabrication outcome depending on the chosen method. With the solvent exchange method, it was possible to fabricate HLBs with well-controlled cholesterol fractions up to ~65 mol% in the upper leaflet as confirmed by a methyl-β-cyclodextrin (MβCD) extraction assay. In marked contrast, the vesicle fusion method was only effective at forming HLBs from precursor vesicles containing up to ~35 mol% cholesterol, but this performance was still superior to past results on hydrophilic SiO2. We discuss the contributing factors to the different efficiencies of the two methods as well as the general utility of two-tail CP SAMs as favorable interfaces to incorporate cholesterol into HLBs. Accordingly, our findings support that the solvent exchange method is a versatile tool to fabricate cholesterol-enriched HLBs on CP SAM-functionalized TiO2 surfaces.
“…The highly specific and stable nature of avidin–biotin binding across various environments (e.g., diverse temperature and pH ranges) enables the specific capture and recognition of biomolecules that can be useful for applications such as biosensing, immunoassays, and targeted drug delivery. Moreover, the avidin–biotin interaction has been utilized in nanoscale drug delivery, diagnostic, and biosensor systems due to its favorable merits such as ease of functionalization, efficiency, and stability [ 7 , 8 , 9 , 10 , 11 ]. The main feature of these nanotechnology-focused applications lies in the modification of interacting surfaces with biotin- and/or avidin-conjugated biomolecules, either directly or through multi-step binding sequences and the specifics of the surface modification can be tuned according to the application needs.…”
The exceptional strength and stability of noncovalent avidin-biotin binding is widely utilized as an effective bioconjugation strategy in various biosensing applications, and neutravidin and streptavidin proteins are two commonly used avidin analogues. It is often regarded that the biotin-binding abilities of neutravidin and streptavidin are similar, and hence their use is interchangeable; however, a deeper examination of how these two proteins attach to sensor surfaces is needed to develop reliable surface functionalization options. Herein, we conducted quartz crystal microbalance-dissipation (QCM-D) biosensing experiments to investigate neutravidin and streptavidin binding to biotinylated supported lipid bilayers (SLBs) in different pH conditions. While streptavidin binding to biotinylated lipid receptors was stable and robust across the tested pH conditions, neutravidin binding strongly depended on the solution pH and was greater with increasingly acidic pH conditions. These findings led us to propose a two-step mechanistic model, whereby streptavidin and neutravidin binding to biotinylated sensing interfaces first involves nonspecific protein adsorption that is mainly influenced by electrostatic interactions, followed by structural rearrangement of adsorbed proteins to specifically bind to biotin functional groups. Practically, our findings demonstrate that streptavidin is preferable to neutravidin for constructing SLB-based sensing platforms and can improve sensing performance for detecting antibody–antigen interactions.
“…The biological basis for secondary stability is the establishment of a direct connection between MSIs and living bone, also known as osteointegration, during the bone remodeling process [ 6 , 11 , 12 , 13 ]. As a high-quality osteointegration is a critical factor to determine the loading occasion and to ensure the long-term success of MSIs [ 14 ], many efforts have been made to accelerate and enhance the osteointegration of MSIs with an aim to enable an early loading and reduce the failure rate [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ].…”
Miniscrew implants (MSIs) have been widely used as temporary anchorage devices in orthodontic clinics. However, one of their major limitations is the relatively high failure rate. We hypothesize that a biomimetic calcium phosphate (BioCaP) coating layer on mini-pin implants might be able to accelerate the osseointegration, and can be a carrier for biological agents. A novel mini-pin implant to mimic the MSIs was used. BioCaP (amorphous or crystalline) coatings with or without the presence of bovine serum albumin (BSA) were applied on such implants and inserted in the metaphyseal tibia in rats. The percentage of bone to implant contact (BIC) in histomorphometric analysis was used to evaluate the osteoconductivity of such implants from six different groups (n=6 rats per group): (1) no coating no BSA group, (2) no coating BSA adsorption group, (3) amorphous BioCaP coating group, (4) amorphous BioCaP coating-incorporated BSA group, (5) crystalline BioCaP coating group, and (6) crystalline BioCaP coating-incorporated BSA group. Samples were retrieved 3 days, 1 week, 2 weeks, and 4 weeks post-surgery. The results showed that the crystalline BioCaP coating served as a drug carrier with a sustained release profile. Furthermore, the significant increase in BIC occurred at week 1 in the crystalline coating group, but at week 2 or week 4 in other groups. These findings indicate that the crystalline BioCaP coating can be a promising surface modification to facilitate early osseointegration and increase the success rate of miniscrew implants in orthodontic clinics.
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