Mesoporous Bioglass Research Articles

Fabrication and characterization of nanocomposite scaffold containing zinc-doped mesoporous bioglass: Evaluation of the antioxidant properties, hemocompatibility and proliferation of apical papilla stem cells

Introduction: Nanocomposite scaffolds comprising mesoporous bioactive glass (MBG) were able to increase the viability, proliferation, and growth of stem cells in vitro, rendering them promising candidates for dental root tissue regeneration. Methods: The Sol-Gel process was utilized for the synthesis of MBG and zinc-doped MBG (Zn-MBG), the latter being integrated into alginate/chitosan scaffolds which in turn were cross-linked to strengthen mechanical properties, followed by freeze-drying. The scaffold's physicochemical characterizations were evaluated, followed by investigations of its antioxidant properties, swelling behavior, mechanical properties, and porosity. The capacity of these biomaterials to increase cell viability and growth of apical papilla stem cells (SCAPs) and hemocompatibility was assessed as a final step. Results: All fabricated scaffolds demonstrated proper porosity, biocompatibility, and hemocompatibility. Nanocomposite scaffolds with Zn-MBG presented a significant enhancement in cell viability for SCAPs compared to alginate/chitosan scaffolds. DPPH tests indicated that the Zn-MBG-alginate/chitosan scaffold showed the highest antioxidant properties. Conclusion: Zn-MBG-alginate/chitosan nanocomposite scaffolds demonstrated great physicochemical characteristics and biological and mechanical properties, marking them as suitable candidates for dental root tissue engineering.

Chitosan/oxidized-dextran dressings containing mesoporous bioglass nanoparticles for hemostatic applications

Chitosan/oxidized-dextran dressings containing mesoporous bioglass nanoparticles for hemostatic applications

The effect of mesoporous bioglass on hemostatic, antibacterial and biocompatible properties of composite sponge

AbstractHemostatic materials used in penetrating injuries or incompressible wounds must possess exceptional efficacy in preventing bleeding. In this study, mesoporous bioglass (MBG) was synthesized using a two‐step acid‐catalyzed self‐assembly method, and a novel hemostatic sponge (MBG/CH/GEL) was prepared by combining chitosan (CH), gelatin (GEL), and MBG using a freeze‐drying method. The characteristics and hemostatic effects of the MBG/CH/GEL composite hemostatic sponge were analyzed and evaluated. Research has shown that the high specific surface area of MBG (730 m2/g) provides more blood cell adhesion sites during hemostasis, resulting in a low hemolysis rate, favorable swelling rate, and porosity of the hemostatic sponge. Additionally, MBG can release Si4+ and Ca2+ ions during hemostasis, giving the composite hemostatic sponge excellent cell compatibility and promoting cell growth. Compared with commercially available gelatin hemostatic sponges, it cannot only quickly stop bleeding but also has a greater compressive strength (212.07 kPa) and adhesion strength (11.54 ± 0.16 kPa), making it suitable for use in hemostasis of incompressible wounds. Furthermore, the composite hemostatic sponge exhibited significant antibacterial effects against Staphylococcus aureus and Escherichia coli. These results indicate that the MBG/CH/GEL composite hemostatic sponge, which is a hemostatic material, has promising applications.

3D-Printed mesoporous bioglass/ polycaprolactone scaffolds induce macrophage polarization toward M2 phenotype and immunomodulates osteogenic differentiation of BMSCs

3D-Printed mesoporous bioglass/ polycaprolactone scaffolds induce macrophage polarization toward M2 phenotype and immunomodulates osteogenic differentiation of BMSCs

VR23 and Bisdemethoxycurcumin Enhanced Nanofiber Niche with Durable Bidirectional Functions for Promoting Wound Repair and Inhibiting Scar Formation.

Chronic wounds pose a significant clinical challenge worldwide, which is characterized by impaired tissue regeneration and excessive scar formation due to over-repair. Most studies have focused on developing wound repair materials that either facilitate the healing process or control hyperplastic scars caused by over-repair, respectively. However, there are limited reports on wound materials that can both promote wound healing and prevent scar hyperplasia at the same time. In this study, VR23-loaded dendritic mesoporous bioglass nanoparticles (dMBG) are synthesized and electrospun in poly(ester-curcumin-urethane)urea (PECUU) random composite nanofibers (PCVM) through the synergistic effects of physical adsorption, hydrogen bond, and electrospinning. The physicochemical characterization reveals that PCVM presented matched mechanical properties, suitable porosity, and wettability, and enabled sustained and temporal release of VR23 and BDC with the degradation of PCVM. In vitro experiments demonstrated that PCVM can modulate the functions and polarization of macrophages under an inflammatory environment, and possess effective anti-scarring potential and reliable cytocompatibility. Animal studies further confirmed that PCVM can efficiently promote re-epithelialization and angiogenesis and reduce excessive inflammation, thereby remarkably accelerating wound healing while preventing potential scarring. These findings suggest that the prepared PCVM holds promise as a bidirectional regulatory dressing for effectively promoting scar-free healing of chronic wounds.

Ultra-thin electrospun nanocomposite scaffold of poly (3-hydroxybutyrate)-chitosan/magnetic mesoporous bioactive glasses for bone tissue engineering applications

Bioglass is widely used in skeletal tissue engineering due to its outstanding bioactive properties. In the present study, magnetic mesoporous bioglass (MMBG) synthesized through the sol-gel method was incorporated into poly(3-hydroxybutyrate)-chitosan (PHB-Cs) solution and the resulting electrospun nanocomposite scaffolds were investigated and compared with MMBG free scaffold. The addition of 10 wt% MMBG has an outstanding effect on producing ultra-thin electrospun nanocomposite fibers due to its magnetic content (diameter of ≃128 nm). This improvement led to better mechanical properties, including an increase in both tensile modulus (up to ≃229 MPa) and tensile strength (to ≃4.95 MPa). Although the inclusion of MMBG slightly decreased the surface roughness of the nanofibrous scaffold (RMS from ≃197 to 154 nm), it could improve the wettability (WCA from ≃54 to 44°). This achievement has the potential to bring an enhancement in biomineralization and biological response. These outputs, combined with the observed increase in human osteoblast MG-63 cell viability (≃53 % improvement) as measured by MTT assay, DAPI, and SEM indicate prefer cell behavior of this nanocomposite structure. Additionally, the qualitative improvement in Alizarin Red staining and the quantitative enhancement of ALP secretion, serve as further evidence of the PHB-Cs/MMBG ultrathin nanofibers potential in bone tissue engineering.

Chitosan based Janus cryogel with anisotropic wettability, antibacterial activity, and rapid shape memory for effective hemostasis

Excessive bleeding and bacterial infection leading to death is a major concern worldwide, particularly in cases of deep and narrow noncompressible hemorrhage. Herein, a novel Janus cryogel with anisotropic surface wettability, antibacterial activity, and rapid shape recovery was designed by constructing a hydrophilic porous cryogel using chitosan (CS), acacia gum (AG), and quaternized mesoporous bioglass (QMBG), with subsequent surface hydrophobic modification using octadecanol. The asymmetric hydrophobic surface modification of octadecanal endowed OCAQ with outstanding antiblood and antibacterial permeability, effectively preventing blood outflow and the invasion of bacteria to the wound. The hydrophilic parts with interconnected macroporous structure give the cryogel with ultra-high water uptake (5167 ± 182 %) and rapid water-trigged shape recover ability (≈2.1 s). The presence of active CS, AG, and QMBG in cryogel contributes to its exceptional blood clotting ability. Janus cryogel presents outstanding hemostatic performance (0.14 ± 0.03 g) in rat's liver injury model. Moreover, Janus cryogel exhibits excellent antibacterial properties due to the combination of its hydrophobic surface and antimicrobial quaternary amine groups. Meanwhile, the Janus cryogel has favorable hemocompatibility and biocompatibility. A Therefore, the Janus cryogel will become a candidate with great potential for clinical application of noncompressible wound as a multifunctional dressing.

Biodegradation and Cell Behavior of a Mg-Based Composite with Mesoporous Bioglass.

Biodegradable magnesium (Mg) and its alloys show tremendous potential as orthopedic materials. Nevertheless, the fast degradation and insufficient osteogenic properties hinder their applications. In this study, mesoporous bioglass (MBG) with an ordered branch-like structure was synthesized via a modified sol-gel method and showed a high specific surface area of 656.45 m2/g. A Mg-based composite was prepared by introducing the MBG into a Mg matrix via powder metallurgy. Degradation tests showed that the introduction of MBG increased the adsorption sites for Ca and P ions, thus promoting the formation of a Ca-P protective layer on the Mg matrix. The Ca-P protective layer became thick and dense with an increase in the immersion time, improving the protection ability of the Mg matrix, as proven by electrochemical impedance spectroscopy measurements. Meanwhile, the Mg-based composite also exhibited excellent biocompatibility and osteogenic properties. This study demonstrated the advantages of MBG in the preparation of Mg-based bone implants and validated the feasibility of improving Mg matrix corrosion resistance and enhancing osteogenesis by introducing MBG.

Photocurable 3D-printed PMBG/TCP biphasic scaffold mimicking vasculature for bone regeneration.

Mesoporous bioglass (MBG) with excellent osteointegration, osteoinduction, and biodegradability is a promising material for bone regeneration. However, its clinical application is hindered by complex processing and a lack of personalization, low mechanical strength, and uncontrollable degradation rate. In this study, we developed a double-bond-functionalized photocurable mesoporous bioglass (PMBG) sol that enabled ultrafast photopolymerization within 5 s. By further integrating nanosized tricalcium phosphate (TCP) particles through three-dimensional (3D) printing technology, we fabricated personalized and highly porous PMBG/TCP biphasic scaffolds. The mechanical properties and degradation behavior of the scaffolds were regulated by varying the amount of TCP doping. In vitro and in vivo experiments verified that PMBG/TCP scaffolds slowly released SiO44- and Ca2+, forming a vascularized bone regeneration microenvironment within the fully interconnected pore channels of the scaffold. This microenvironment promoted angiogenesis and accelerated bone tissue regeneration. Overall, this work demonstrates the solution to the problem of complex processing and lack of personalization in bioglass scaffolds, and the developed PMBG/TCP biphasic scaffold is an ideal material for bone regeneration applications with broad clinical prospects.

Manufacture of Bilayered Composite Hydrogels with Strong, Elastic, and Tough Properties for Osteochondral Repair Applications.

Layered composite hydrogels have been considered attractive materials for use in osteochondral repair and regeneration. These hydrogel materials should be mechanically strong, elastic, and tough besides fulfilling some basic requirements such as biocompatibility and biodegradability. A novel type of bilayered composite hydrogel with multi-network structures and well-defined injectability was thus developed for osteochondral tissue engineering using chitosan (CH), hyaluronic acid (HA), silk fibroin (SF), CH nanoparticles (NPs), and amino-functionalized mesoporous bioglass (ABG) NPs. CH was combined with HA and CH NPs to build the chondral phase of the bilayered hydrogel, and CH, SF, and ABG NPs were used together to construct the subchondral phase of the bilayer hydrogel. Rheological measurements showed that the optimally achieved gels assigned to the chondral and subchondral layers had their elastic moduli of around 6.5 and 9.9 kPa, respectively, with elastic modulus/viscous modulus ratios higher than 36, indicating that they behaved like strong gels. Compressive measurements further demonstrated that the bilayered hydrogel with an optimally formulated composition had strong, elastic, and tough characteristics. Cell culture revealed that the bilayered hydrogel had the capacity to support the in-growth of chondrocytes in the chondral phase and osteoblasts in the subchondral phase. Results suggest that the bilayered composite hydrogel can act as an injective biomaterial for osteochondral repair applications.

In-situ deposition of apatite layer to protect Mg-based composite fabricated via laser additive manufacturing

Biodegradable magnesium (Mg) and its alloy show huge potential as temporary bone substitute due to the favorable biocompatibility and mechanical compatibility. However, one issue deserves attention is the too fast degradation. In this work, mesoporous bioglass (MBG) with high pore volume (0.59 cc/g) and huge specific surface area (110.78 m 2 /g) was synthesized using improved sol-gel method, and introduced into Mg-based composite via laser additive manufacturing. Immersion tests showed that the incorporated MBG served as powerful adsorption sites, which promoted the in-situ deposition of apatite by successively adsorbing Ca 2+ and HPO 4 2− . Such dense apatite film acted as an efficient protection layer and enhanced the corrosion resistance of Mg matrix, which was proved by the electrochemical impedance spectroscopy measurements. Thereby, Mg based composite showed a significantly decreased degradation rate of 0.31 mm/year. Furthermore, MBG also improved the mechanical properties as well as cell behavior. This work highlighted the advantages of MBG in the fabrication of Mg-based implant with enhanced overall performance for orthopedic application.

Strontium-doped mesoporous bioglass nanoparticles for enhanced wound healing with rapid vascularization.

Tissue engineered skin and its substitutes have a promising future in wound healing. However, enabling fast formation of blood vessels during the wound healing process is still a huge challenge to the currently available wound substitutes. In this work, active mesoporous bioglass nanoparticles with a high specific surface area and doped with strontium (Sr) were fabricated for rapid microvascularization and wound healing. The as-prepared bioglass nanoparticles with Sr ions significantly promoted the proliferation of fibroblasts and microvascularization of human umbilical vein endothelial cells in vitro. Silk fibroin sponges encapsulating the nanoparticles accelerated wound healing by promoting the formation of blood vessels and epithelium in vivo. This work provides a strategy for the design and development of active biomaterials for enhancing wound healing by rapid vascularization and epithelial reconstruction.

Preparation and characterization of mesoporous Lanthanum-doped bioactive glass nanoparticles

In this study, novel compositions of mesoporous Bioglass (BG) and Lanthanum-doped BG (La-BG) were prepared using the sol-gel method. Microstructure analysis of the produced composites was performed using XRD, FESEM, FTIR, TGA, and BET techniques. The XRD patterns of BG and La-BG show a good match with the combeite phase. The silicate and phosphate groups in the BG and La-BG lattice were detected in FTIR spectra. The BG particles were spherical, with a surface area of 11.54 m2 /g, a pore volume of 0.02491cc/g, and a pore size of 31.35Å. With the addition of La, the BG structure revealed (i) increased crystallinity of diffraction peaks, (ii) the particles changed from a spherical to a petal-like shape with an expansion in surface area and pore volume, and (iii) increased thermal stability of the BG structure. In conclusion, BG's physiochemical characteristics were greatly enhanced by adding La.

Flame retardancy and smoke suppression of multi-metal doped mesoporous bio-glass based hybrid microsphere on epoxy resin

Bioactive glass (BG) has been a focus of research for biomedical applications due to its unique biological properties. Owning to its special composition (SiO2–CaO–P2O5) and structure, BG becomes a potential flame retardant. In this paper, a novel type of BGs was synthesized and employed as a flame retardant for epoxy resin (EP). To further improve its flame retardancy properties, firstly, the chemical compositions of BGs were modified by doping Cu, Zn, Sr ions into the SiO2 network by a sol-gel method combined with a template method and hydrothermal method; secondly, the microstructure of BGs was designed as a microsphere with a hollow mesoporous structure. Moreover, the obtained BGs were further functionalized with a polyphosphazene derivative (PZS) to integrate the excellent flame retardancy and mechanical properties. The results showed that Cu/Zn/Sr ions entered the SiO2 network, while PZS was successfully deposited on the surface of mesoporous BGs. An improved comprehensive performance including flame retardancy, smoke suppression and mechanical strength enhancement was achieved by the presence of multiple flame-retardant atoms (Cu, Zn, Sr, Si, P, S, N, Cl) in the mesoporous BG microspheres. This study successfully applied BGs with high biocompatibility as flame retardant, broadening the types and categories of flame retardants.

Multi-Crosslinked Strong and Elastic Bioglass/Chitosan-Cysteine Hydrogels with Controlled Quercetin Delivery for Bone Tissue Engineering.

Chitosan-cysteine (CH-CY) conjugate with an optimal content of thiol groups was synthesized and combined with amino-functionalized mesoporous bioglass (ABG) nanoparticles (NPs) with radially-porous architecture to build multi-crosslinked ABG/CH-CY composite hydrogels. Besides the network formed by self-crosslinking of thiol groups in CY-derived side chains, difunctionalized PEG (DF-P) crosslinkers with varying lengths of PEG segments were used to crosslink amino groups on CH-CY or ABG NPs to form other networks in the composite gels. Quercetin (Que) was loaded into ABG NPs before these NPs were incorporated into the hydrogel, intending to achieve sustainable and controllable Que release from so-built ABG/CH-CY gels. The lengths of PEG segments in DF-P were found to impose remarkable impacts on the strength or elasticity of multi-crosslinked ABG/CH-CY hydrogels. Some ABG/CH-CY hydrogels had their elastic modulus of around 8.2 kPa or higher along with yielding strains higher than 70%, specifying their mechanically strong and elastic characteristics. In addition, these gels showed the ability to release Que and Si or Ca ions in controllable ways for various durations. The optimally achieved ABG/CH-CY hydrogels were injectable and also able to support the growth of seeded MC3T3-E1 cells as well as the specific matrix deposition. The obtained results suggest that these ABG/CH-CY gels have promising potential for bone repair and regeneration.

Laser ablation combined with Nanoimprint Lithography technology as new surface engineering approach to produce novel polymer-based heteronucleants for recalcitrant protein crystallization

Macromolecule crystallography is currently the most powerful technique for determining the three dimensional structure of proteins at atomic resolution. However, despite its enormous level of technical development achieved, it is still limited by the great difficulty of obtaining crystals that, after exposure to X-rays, allow a high-resolution diffraction pattern from which the structure of the target protein can be elucidated. Even today, the crystallization process is a trial-and-error procedure that requires enormous experimental effort and high economic costs. In this research work, Laser Ablation technology in combination with NanoImprint Lithography was applied on Polycarbonate surfaces to produce novel heteronucleating agents containing multiscale surface topographies (in the micro- and submicro-scale) that promote the growth of protein crystals. Two human proteins, known to be recalcitrant to crystallization when using standard protocols, were used in the assays: (i) a construct of the CNNM4 magnesium transporter lacking amino acid residues 545–730 (HsCNNM4545-730) and (ii) cystathionine beta-synthase enzyme lacking residues 516–525 (HsCBSΔ516-525). The surface engineering solution was validated by comparing the number of novel crystallization conditions induced by those surfaces compared against the control and the use of the Naomi’s Nucleant, a commercially available heteronucleant made of mesoporous bioglass. The aspect ratio of the topography emerges as the topographical parameter that most contributes to protein growth on patterned surfaces. Additionally, the presence of a random distribution of micropores as well as a hierarchical (merging micro- and nano - scale features) surface topography also resulted in a more efficient crystallization process, showing an increment of between 38 and 68% in the number of new crystallization conditions, depending on the surface topography and protein selected. A conclusion is made that Laser Ablation with ultrashort pulses and the combination with Nanoimprint Lithography can be efficiently applied on polymeric substrates to produce a novel concept of heteronucleants that would bridge the gap to the development of universal nucleation agents.

The effect of pore size on cell behavior in mesoporous bioglass scaffolds for bone regeneration

The material properties of bone tissue repair scaffolds dictate the interaction between the material and tissues or cells in vivo. The interface between them at the nanoscale can regulate cell adhesion, migration, and differentiation behaviors, thereby reshaping osteogenic properties of the material in vivo. In this study, a series of 3 nm, 8 nm and 20 nm mesoporous bioactive glass scaffolds (MSX-3, MSX-8 and MSX-20) were prepared by employing sol-gel technique and active self-assembly, with mesoporous bioglass serving as matrix. We then further examined effects of different mesopore pore sizes on the material biology of scaffolds and effects of osteogenic properties both in vitro and in vivo. The prepared multi-level micro-nano-structured bone repair scaffolds all had ∼300 μm macropores and possessed good biocompatibility and in vitro mineralizing activity. In vitro mineralization experiments proved that a large amount of calcium and phosphate salts were deposited on the surfaces of MSX-3 and MSX-8 scaffolds, while MSX-20 had conspicuous adsorption/deposition effects on organic compounds such as proteins in solution. MSX-20 multi-level micro-nano-structured bone repair scaffold could significantly promote the cell adhesion of BMSCs, and the cell spreading area was significantly larger than that of MSX-3 and MSX-8 scaffolds. MSX-20 multi-level micro-nano structured bone repair scaffold had a good sustained release effect on BMP-2, which could promote the osteogenic differentiation effect of BMP-2 on BMSCs. In vivo animal experiments also showed that MSX-20 loaded with BMP-2 could significantly promote in vivo osteogenesis. These findings suggest that when the mesopore pore size is 20 nm, the scaffold can be more conductive to bone regeneration due to the enhanced adhesion of stem cells and more sustained release of BMP-2.

Rapid promoting thrombus formation and fibrin cross-linked Bi-doped mesoporous bioglass for hemostatic agent

Despite decades of development of biomaterials, hemorrhage remains a primary cause of death in surgeries and accidents. Effective hemostatic agents that induce hemostasis and rapid coagulation are needed by surgeons and in daily life. Here, we report on the application of hemostatic agents by studying mesoporous bioglass (MBG) doped with bismuth oxide via a two-step acid-catalyzed self-assembly (TSACSA) process. The results show that all the samples have an ordered mesoporous structure and a large surface area, especially MBG doped with 2 mol% Bi2O3 has the highest specific surface area (704.06 m2/g). MBG doped with different proportions of Bi accelerated the intrinsic coagulation pathway and was not found to exhibit severe erythrocyte cytotoxicity. It is worth noting that MBG added with 1 and 2 mol% Bi2O3 had higher thrombus formation, fibrin polymerization rates, and platelet adhesion; however, higher content of Bi2O3 (3 mol%) may affect the consequence of coagulation. These results of our investigation suggest that MBG doped with a low range of Bi is a potential hemostatic biomaterial for clinical applications.

A careob-like nanofibers with a sustained drug release profile for promoting skin wound repair and inhibiting hypertrophic scar

Excessive or disordered wound repair results in abnormal hyperplasia of scars, which intensifies the complexity and difficulty of treatment. The reported wound repair dressings, which only possess single function, can promote wound healing diminutively or treat hypertrophic scars solely. Wound healing and scar formation are the two affiliated successive stages of the wound repair process. Therefore, it is crux for the promotion of wound healing and the inhibition of scar hyperplasia synergistically. In this study, we have synthesized a 5-fluorouracil (5-Fu)-loaded dendritic mesoporous bioglass nanoparticles (dMBG) coaxial electrospun in polyethylene oxide (PEO)-poly(ether-ester-urethane)urea (PEEUU) careob-like core-shell composite nanofibers (((F@B)/P)@PU) through synergistic effect of hydrogen bonding networking and physical adsorption, and coaxial electrospinning . The 5-Fu-loaded dBMG (5-Fu@dMBG) with an optimized 5-Fu loading efficiency of 23% were shown to be successfully contained in PEO matrix, and the formed ((F@B)/P)@PU exhibited a uniform and smooth morphology, appropriate surface wettability , high protein adsorption rate, as well as matched degradation rate and mechanical properties with autologous skin tissue. Importantly, the loaded 5-Fu within ((F@B)/P)@PU exhibiteda sustained-release profile and anti-adhesion/anti-proliferation active to inhibit the growth of Hela cells , which is a model cell with the property of rapid proliferation. In addition, the wound model of rat back and H&E staining, Masson trichrome staining, CD31, CD68 and collagen I immunofluorescence staining were performed for evaluating therapeutic efficiency of ((F@B)/P)@PU. All the results revealed the better wound treatment effect of 5-Fu-loaded multistructure nanofibers for the repair of scar skin tissue defects, indicating great potential for wounds healing clinically.

Vancomycin loaded-mesoporous bioglass/hydroxyapatite/chitosan coatings by electrophoretic deposition

In the current research, vancomycin loaded-mesoporous bioglass/hydroxyapatite whiskers/chitosan composite coatings with drug delivery capability were fabricated on titanium substrate via electrophoretic deposition. Hydroxyapatite with whisker morphology demonstrated improvement in microhardness of the coatings. Among different initial vancomycin concentrations of 1, 5, 15, 25 and 50 mg/ml to load mesoporous bioglass particles, maximum loading efficiency and drug content (95%) were achieved at 25 mg/ml. Based on the quality of the coatings, bioglass loaded with initial concentrations of 1, 5 and 15 mg/ml drug were chosen as optimal samples for further investigations. Synergistic effect of bioglass and hydroxyapatite caused the composition with 20% and 50%Wt MBG to have faster bioactivity response. Regarding the drug delivery capability of the composite coatings, sample containing 50%Wt bioglass encapsulated with 15 mg/ml drug exhibited rapid and maximal drug release due to the facile diffusion of the solved bioglass particles. The achieved results showed the acceptable antibacterial potency of vancomycin-loaded coating to prevent infection. Moreover, existence of antibiotic did not have any toxic effect over the osteoblast cells cultured on the coatings.