Zn and Sr incorporated 64S bioglasses: Material characterization, in-vitro bioactivity and mesenchymal stem cell responses

Evaluation of the Structural, Biological, and Bone Induction Properties of Sol-Gel-Derived Lithium-Doped 68S Bioactive Glass-An in Vitro Study on Human Dental Pulp Stem Cells

OBJECTIVES

Calcium silicate-based bioactive glass shows enhanced ion release capabilities and promotes the formation of hydroxyapatite (HA). This study aimed to synthesize a sol-gel-derived 68S bioactive glass (BAG) incorporating lithium (Li) and evaluate its structural, biological, and osteoinductive properties using human dental pulp stem cells (hDPSCs).

MATERIALS AND METHODS

Two types of 68S BAG were synthesized using the sol-gel method: one containing 5 mol.% lithium nitrate (BGLi5) and a lithium-free control (BG). Structural characterization and HA formation were assessed using field emission scanning electron microscopy (FESEM) and Fourier-transform infrared spectroscopy (FTIR) before and after immersion in simulated body fluid (SBF) on Days 1, 3, and 7. The dissolution rates of the specimens were evaluated using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and pH analysis. Biological activities were investigated through cell viability (MTT assay), alkaline phosphatase (ALP) enzyme activity, and alizarin red staining to assess mineralization. Additionally, the antimicrobial efficacy of the materials was tested against Streptococcus mutans (SM).

RESULTS

FTIR and FESEM analyses confirmed the formation of HA crystals in BGLi5 specimens by Day 3 and in BG specimens by Day 7. The MTT assay demonstrated enhanced cell viability in both BG and BGLi5 compared to the control group. ALP activity, a marker of cell differentiation, was significantly elevated in the BGLi5-DM group by Day 14. Alizarin red staining on Day 21 revealed a marked increase in mineralization in both BG and BGLi5, with the BGLi5-DM group showing the highest mineralization levels. Furthermore, both BG and BGLi5 demonstrated significant antimicrobial activity against SM.

CONCLUSION

The sol-gel-derived 68S BAG containing 5 mol.% Li is a biocompatible material that enhances cell proliferation, differentiation, and mineralization. The combination of BGLi5 with differentiation-specific culture medium synergistically promotes osteogenic differentiation and mineralization, making it a promising candidate for dental and bone tissue engineering applications.

Impact of amino acid-regulated beta tricalcium phosphate hydroxyapatite on enamel: An updated perspective on hydroxyapatite crystal growth for adhesive bonding?

AIMS AND OBJECTIVES

To analyse development of hydroxyapatite (HAp) crystals doped with glutamic acid and phosphorine residue (Ser-OPO3) having self-remineralization, biocompatible and optimum bonding properties MATERIALS AND METHODS: β-tri calcium phosphate, ammonium phosphate dibasic HAp was dissolved with strontium Flouride Glu or Ser-OPO3 components and utilised in two 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL groups. HAp formulation was evaluated for particle-size analysis, crystal size and indices using FTIR. Demineralized enamel specimens were treated and characterized using transmission electron microscopy (TEM), Xray diffraction (XRD), solid state NMR, and mechanical properties. MC3T3 mouse fibroblastic cells were evaluated for alkaline-phosphate activity (ALP). Human gingival fibroblasts (PGF) were evaluated for morphology. After modifying Universal adhesives, tensile force was assessed at 24 hr and 3 months.

RESULT

Increasing concentrations of experimental solution exposure significantly affect mean diameter of HAp. The increasing FTIR intensity, were displayed; 0.2% TCPCa3(PO4)2 Str/FL > 0.1% TCPCa3(PO4)2 Str/FL> control. 0.2% TCPCa3(PO4)2 Str/FL revealed existence of distinct crystals, with planes orientated perpendicular to longer axis of tooth. XRD pattern indicated crystal growth with a rise in peak intensities in 0.2% TCPCa3(PO4)2 Str/FL group. The NMR spectra for Glu and Ser-OPO3 elucidated interactions between carbon atoms in amino acid and hydrogen atoms on HAp surfaces. Surface microhardness of 0.2% TCPCa3(PO4)2 Str/FL specimens showed significantly higher values on day 28 (p< 0.05). ALP density value of cells was significantly higher for 0.2% TCPCa3(PO4)2 Str/FL group on day 7 and 14. 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL enhanced migration of PGF cells in comparison to the control group (p<0.05). 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL groups showed significant differences in bond strength at different time points CONCLUSION: 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL were structurally integrated into the lattice demonstrating changes within the crystallite size and became conducive for adhesive bonding.

CLINICAL SIGNIFICANCE

The new amino acid-based hydroxyapatite formulation is chemically stable due to the substitution of OH- with F- and is crucial in the rehardening of caries and adhesive bonding.

Synergistic Effect of Strontium Doping and Surfactant Addition in Mesoporous Bioactive Glass for Enhanced Osteogenic Bioactivity and Advanced Bone Regeneration

Mesoporous bioactive glass (MBG) is an advanced biomaterial widely recognized for its application in bone regenerative engineering. This study synthesized an MBG powder (80 mol% SiO2, 5 mol% P2O5, and 15 mol% CaO) using a facile sol-gel method with the non-ionic surfactant Pluronic® P123, which acted as a pore-forming agent. MBGs form bioactive surfaces that facilitate HA formation, and the presence of Pluronic® P123 increases the surface area and promotes HA nucleation. Various percentages of strontium (Sr) doping were examined to improve bioreactivity, biological response, and bone formation, with 3SMBG (3 mol% Sr) showing the highest specific surface area. In vitro biocompatibility tests revealed HA formation on all glass surfaces after immersion in simulated body fluid (SBF), indicated by sheet-like HA morphologies, the presence of PO43- and CO32- functional groups, and the amorphous structure along with SrCO3 crystalline phases corresponding to HA and Sr-HA structures. Sr doping resulted in delayed initial degradation and sustained release of Sr2+, achieving over 95% cell viability. Surfactant-induced mesoporous structure and Sr incorporation synergistically enhance osteocyte induction and formation in vitro. These findings suggest that Sr-doped MBG, particularly with P123-assisted Sr/Ca substitution, optimizes the material's properties for advanced bone regenerative applications.

Strontium doped 58S bioglass incorporated chitosan/gelatin porous scaffold for bone tissue engineering applications

Bioglass (Bg) is accepted as a revolutionary material, and doping with strontium (Sr) ions in the Bg network exhibits improved biofunctionality towards bone tissue regeneration and inhibits osteoclast formation. Keeping this in view, the present study focused on the development of chitosan (CS)/gelatin (GE) porous scaffolds incorporated with Sr-doped Bg nanoparticles (nSrBg) for bone tissue engineering applications. The SEM analysis of the fabricated scaffold exhibited that it possessed a homogenous microstructure with an interconnected porous network having pore sizes of 100-300 μm. A swelling of <6-fold and a degradation rate under 50 % were achieved. The compression test revealed that nSrBg improved the strength of the composite to 1.15 MPa. In vitro bioactivity assays suggested the presence of nSrBg enhanced the bone-like deposition of the apatite layer, which possessed cell-supportive properties, allowing the cells to attach and proliferate over the scaffold surface. MTT assay and live-dead staining revealed that the nSrBg enhanced the proliferation of the cells up to 0.48 OD. The ALP assay suggested that the nSrBg addition improved the osteogenic potential until 0.70 OD. Overall, the fabricated scaffold showed superior mechanical and biological properties that can be a promising platform for bone tissue regeneration.

Employing novel biocompatible composite scaffolds with bioglass 58S and poly L-lactic acid for effective bone defect treatment

BACKGROUND

Bioglass materials have gained significant attention in the field of tissue engineering due to their osteoinductive and biocompatible properties that promote bone cell differentiation. In this study, a novel composite scaffold was developed using a sol-gel technique to combine bioglass (BG) 58 S with a poly L-lactic acid (PLLA).

METHODS AND RESULTS

The physiochemical properties, morphology, and osteoinductive potential of the scaffolds were investigated by X-ray diffraction analysis, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The results showed that the SiO2-CaO-P2O5 system was successfully synthesized by the sol-gel method. The PLLA scaffolds containing BG was found to be osteoinductive and promoted mineralization, as demonstrated by calcium deposition assay, upregulation of alkaline phosphatase enzyme activity, and Alizarin red staining data.

CONCLUSIONS

These in vitro studies suggest that composite scaffolds incorporating hBMSCs are a promising substitute material to be implemented in bone tissue engineering. The PLLA/BG scaffolds promote osteogenesis and support the differentiation of bone cells, such as osteoblasts, due to their osteoinductive properties.

Effect of strontium fluoride on mechanical and remineralization properties of enamel: An in-vitro study on a modified orthodontic adhesive

OBJECTIVES

Evaluate the ability of strontium fluoride on bond strength and enamel integrity after incorporation within orthodontic adhesive system as a delivery vehicle.

METHODS

Experimental orthodontic adhesive system Transbond™ XT were modified with 1% Sr2+, 0.5% SrF2, 1% strontium, 0.5% Sr2+, 1% F-, 0.5% F-, and no additions were control. Mixing of formulation was monitored using Fourier transform infrared spectroscopy. Small-molecule drug-discovery suite was used to gain insights into Sr2+, F-, and SrF2 binding. Shear bond testing was performed after 6-months of ageing. Enamel blocks were cut, and STEM pictures were recorded. Specimens were indented to evaluate elastic modulus. Raman microscope was used to collect Raman spectra and inspected using a scanning electron microscope. Crystal structural analysis was performed using X-ray diffraction. Effect of material on cellular proliferation was determined. Confocal was performed to evaluate the effect of formulation on biofilms.

RESULTS

FTIR of modified adhesives depicted peak changes within range due to various functional groups existing within samples. TEM represented structurally optimized hexagonal unit-cell of hydroxyapatite. Mean shear bond strength is recorded highest for Transbond XT with 1% SrF2. Dead bacterial percentage appeared higher in 0.5% SrF2 and 1% F- specimens. Crystal lengths showed an increase in 0.5% and 1% SrF2 specimens. Phase contrast within TEM images showed a union of 0.5% SrF2 crystal with enamel crystal with higher elastic modulus and highly mineralized crystalline hydroxyapatite. Intensity of ν1 PO43- and ν1 CO32- along with carbonate - / ν1PO43- ratio displayed good association with strontium fluoride. The formulation showed acceptable cell biocompatibility (p < 0.353). All specimens displayed characteristic diffraction maxima of different apatite angles within XRD.

SIGNIFICANCE

Experimental results suggested good biocompatibility, adequate mechanical strength, and far-ranging crystallization ability. This would provide a new strategy to overcome the two major challenges of fixed orthodontics, biofilm growth, and demineralization of enamel.

Influence of Strontium on the Biological Behavior of Bioactive Glasses for Bone Regeneration

Bioactive glasses (BGs) can potentially be applied in biomedicine, mainly for bone repair and replacement, given their unique ability to connect to natural bone tissue and stimulate bone regeneration. Since their discovery, several glass compositions have been developed to improve the properties and clinical abilities of traditional bioactive glass. Different inorganic ions, such as strontium (Sr2+), have been incorporated in BG due to their ability to perform therapeutic functions. Sr2+ has been gaining prominence due to its ability to stimulate osteogenesis, providing an appropriate environment to improve bone regeneration, in addition to its antibacterial potential. However, as there are still points in the literature that are not well consolidated, such as the influence of ionic concentrations and the BG production technique, this review aims to collect information on the state of the art of the biological behavior of BGs containing Sr2+. It also aims to gather data on different types of BGs doped with different concentrations of Sr2+, and to highlight the manufacturing techniques used in order to analyze the influence of the incorporation of this ion for bone regeneration purposes.

Synthesis, Characterization, and Bioactivity of Mesoporous Bioactive Glass Codoped with Zinc and Silver

Due to the overconsumption of antimicrobials, antibiotic-resistant bacteria have become a critical health issue worldwide, especially methicillin-resistant S. aureus (MRSA) and vancomycin-resistant E. faecalis (VRE). Recently, many efforts have been made to load metals into bioactive glasses to enhance the multifunctionality of materials, such as antibacterial and osteoinductive functions. Zinc has been documented to stimulate the gene expression of various regulatory factors in bone cells. Meanwhile, previous studies have reported that silver and zinc could be a promising antibacterial combination with synergistic antimicrobial effects. Here, we sought to develop a biomaterial coreleasing zinc and silver, designated 80S-ZnAg, and to evaluate its antibacterial activity and biocompatibility. The textural analyses demonstrated different coreleasing patterns of zinc and silver for the materials. The chemical characterization revealed that the zinc in 80S-ZnAg could be the network modifier when its molar ratio was high, releasing more zinc; zinc could also be the network former when its molar ratio was low, showing an extremely low rate of release. However, the ICP results for 80S-Zn3Ag2 demonstrated up to 7.5 ppm of zinc and 67.6 ppm of silver. Among all the 80S-ZnAg materials, 80S-Zn3Ag2 demonstrated more marked antibacterial activity against MRSA and VRE than the others, with inhibition zones of 11.5 and 13.4 mm, respectively. The cytotoxicity assay exhibited nearly 90% cell viability at 20 mg/mL of 80-Zn3Ag2. Further clinical study is needed to develop an innovative biomaterial to address the issue of antibiotic resistance.

Advanced applications of strontium-containing biomaterials in bone tissue engineering

Strontium (Sr) and strontium ranelate (SR) are commonly used therapeutic drugs for patients suffering from osteoporosis. Researches have showed that Sr can significantly improve the biological activity and physicochemical properties of materials in vitro and in vivo. Therefore, a large number of strontium containing biomaterials have been developed for repairing bone defects and promoting osseointegration. In this review, we provide a comprehensive overview of Sr-containing biomaterials along with the current state of their clinical use. For this purpose, the different types of biomaterials including calcium phosphate, bioactive glass, and polymers are discussed and provided future outlook on the fabrication of the next-generation multifunctional and smart biomaterials.

A review on borate bioactive glasses (BBG): effect of doping elements, degradation, and applications

Because of their excellent biologically active qualities, bioactive glasses (BGs) have been extensively used in the biomedical domain, leading to better tissue-implant interactions and promoting bone regeneration and wound healing. Aside from having attractive characteristics, BGs are appealing as a porous scaffold material. On the other hand, such porous scaffolds should enable tissue proliferation and integration with the natural bone and neighboring soft tissues and degrade at a rate that allows for new bone development while preventing bacterial colonization. Therefore, researchers have recently become interested in a different BG composition based on borate (B₂O₃) rather than silicate (SiO₂). Furthermore, apatite synthesis in the borate-based bioactive glass (BBG) is faster than in the silicate-based bioactive glass, which slowly transforms to hydroxyapatite. This low chemical durability of BBG indicates a fast degradation process, which has become a concern for their utilization in biological and biomedical applications. To address these shortcomings, glass network modifiers, active ions, and other materials can be combined with BBG to improve the bioactivity, mechanical, and regenerative properties, including its degradation potential. To this end, this review article will highlight the details of BBGs, including their structure, properties, and medical applications, such as bone regeneration, wound care, and dental/bone implant coatings. Furthermore, the mechanism of BBG surface reaction kinetics and the role of doping ions in controlling the low chemical durability of BBG and its effects on osteogenesis and angiogenesis will be outlined.

Fabrication, Structural and Biological Characterization of Zinc-Containing Bioactive Glasses and Their Use in Membranes for Guided Bone Regeneration

Polymeric membranes are widely used in guided bone regeneration (GBR), particularly in dentistry. In addition, bioactive glasses can be added to the polymers in order to develop a matrix that is osteoconductive and osteoinductive, increasing cell adhesion and proliferation. The bioactive glasses allow the insertion into its network of therapeutic ions in order to add specific biological properties. The addition of zinc into bioactive glasses can promote antibacterial activity and induce the differentiation and proliferation of the bone cells. In this study, bioactive glasses containing zinc (0.25, 0.5, 1 and 2 mol%) were developed and structurally and biologically characterized. The biological results show that the Zn-containing bioactive glasses do not present significant antibacterial activity, but the addition of zinc at the highest concentration does not compromise the bioactivity and promotes the viability of Saos-2 cells. The cell culture assays in the membranes (PCL, PCL:BG and PCL:BGZn2) showed that zinc addition promotes cell viability and an increase in alkaline phosphatase (ALP) production.

Electrospun polylactic acid scaffolds with strontium- and cobalt-doped bioglass for potential use in bone tissue engineering applications

The development of nanoscale biomaterials associated with polymers has been growing over the years, due to their important structural characteristics for applications in biological systems. The present study aimed to produce and test polymeric scaffolds composed of polylactic acid (PLA) fibers associated with a 58S bioglass doped with therapeutic ions for use in tissue engineering. Three 58S Bioglass was obtained by the sol-gel route, pure and doped with 5% strontium and cobalt ions. Solutions of 7% PLA was used as control and added the three different bioglass, 4% of 58S bioglass (PLA-BG), 4% bioglass-doped strontium (PLA-BGSr) and 4% bioglass-doped cobalt (PLA-BGCo). Scaffolds were produced through electrospinning process, and was characterized chemical and morphologically. The in vitro tests were performed using mesenchymal cells cultures from femurs of nine rats, grown in osteogenic supplemented total culture medium. After osteoblastic differentiation induction cell viability, alkaline phosphatase activity, total protein content quantification, and visualization of mineralization nodule tests were performed. Analysis of normal distribution used the Shapiro-Wilk test (nanofibers diameter and biological assay). Data were compared using the Kruskal-Wallis nonparametric test (p = 0.05). The bioglasses produced proved to be free of nitrate, chlorinated and nano-sized, with effective incorporation of therapeutic ions in their structure. All materials showed cell viability (>70%), total protein production, and alkaline phosphatase activity. It was possible to develop polylactic acid scaffolds associated with 58S bioglass doped with therapeutic ions without cytotoxicity. Scaffolds characteristics appear to sustain its application in bone tissue engineering.

A novel amelogenesis-inspired hydrogel composite for the remineralization of enamel non-cavitated lesions

Enamel non-cavitated lesions (NCLs) are subsurface enamel porosity from carious demineralization. The developed enamel cannot repair itself once NCLs occurs. The regeneration of mineral crystals in a biomimetic environment is an effective way to repair enamel subsurface defects. Previously, an amelogenin-derived peptide named QP5 was proven to repair demineralized enamel. In this work, inspired by amelogenesis, a novel biomimetic hydrogel composite containing the QP5 peptide and bioactive glass (BG) was designed, in which QP5 could promote enamel remineralization by guiding the calcium and phosphorus ions provided by BG. Also, BG could adjust the mineralization micro-environment to alkalinity, simulating the pH regulation of ameloblasts during enamel maturity. The BQ hydrogel composite showed biosafety and possessed capacity for enamel binding, ion release and pH buffering. Enamel NCLs treated with the BQ hydrogel composite showed a higher reduction in lesion depth and mineral loss both in vitro and in vivo. Moreover, compared to the hydrogels containing only BG or QP5, groups treated with the BQ hydrogel composite attained more surface microhardness recovery and color recovery, exhibiting resistance to erosion and abrasion of the remineralization layer. We envision that the BQ hydrogel composite can provide a biomimetic micro-environment to favor enamel remineralization, thus reducing the lesion depth and increasing the mineral content as a promising biomimetic material for enamel NCLs.

Angiogenesis, Osseointegration, and Antibacterial Applications of Polyelectrolyte Multilayer Coatings Incorporated With Silver/Strontium Containing Mesoporous Bioactive Glass on 316L Stainless Steel

The main causes for failure in implant surgery are prolonged exposure of implants or wound and tissue ischemia. Bacterial infection caused by the surrounding medical environment and equipment is also a major risk factor. The medical risk would be greatly reduced if we could develop an implant coating to guide tissue growth and promote antibacterial activity. Mesoporous bioactive glasses are mainly silicates with good osteoinductivity and have been used in medical dentistry and orthopedics for several decades. Strontium ions and silver ions could plausibly be incorporated into bioactive glass to achieve the required function. Strontium ions are trace elements in human bone that have been proposed to promote osseointegration and angiogenesis. Silver ions can cause bacterial apoptosis through surface charge imbalance after bonding to the cell membrane. In this study, functional polyelectrolyte multilayer (PEM) coatings were adhered to 316L stainless steel (SS) by spin coating. The multilayer film was composed of biocompatible and biodegradable collagen as a positively charged layer, γ-polyglutamic acid (γ-PGA) as a negatively charged layer. Chitosan was incorporated to the 11th positively charged layer as a stabilizing barrier. Spray pyrolysis prepared mesoporous bioactive glass incorporated with silver and strontium (AgSrMBG) was added to each negatively charged layer. The PEM/AgSrMBG coating was well hydrophilic with a contact angle of 37.09°, hardness of 0.29 ± 0.09 GPa, Young’s modulus of 5.35 ± 1.55 GPa, and roughness of 374.78 ± 22.27 nm, as observed through nano-indention and white light interferometry. The coating’s antibacterial activity was sustained for 1 month through the inhibition zone test, and was biocompatible with rat bone marrow mesenchymal stem cells (rBMSCs) and human umbilical vein endothelial cells (HUVECs), as observed in the MTT assay. There was more hydroxyapatite precipitation on the PEM/AgSrMBG surface after being soaked in simulated body fluid (SBF), as observed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In both in vitro and in vivo tests, the PEM/AgSrMBG coating promoted angiogenesis, osseointegration, and antibacterial activity due to the sustained release of silver and strontium ions.

In Vitro Dissolution of Na-Ca-P-Oxynitrides

Sodium-calcium-phosphate based oxynitride glasses and glass-ceramics doped with Mg, Si, and Nb were studied in vitro in simulated body fluid (SBF) under static conditions. The release of ions and pH changes up to 7 days of immersion were investigated. The nitrogen incorporation into phosphate glass matrix was found to notably influence in vitro dissolution only of homogenous glasses. Increasing the nitrogen content in the samples decreased the mean mass loss, while the niobate incorporation increased it. The correlation between the nitrogen content and increase in pH of SBF was also observed. The presence of phosphates crystallites was found to support the dissolution process at the beginning step (up to 3 days).

Multi-functional silica-based mesoporous materials for simultaneous delivery of biologically active ions and therapeutic biomolecules

Mesoporous silica-based materials, especially mesoporous bioactive glasses (MBGs), are being highly considered for biomedical applications, including drug delivery and tissue engineering, not only because of their bioactivity and biocompatibility but also due to their tunable composition and potential use as drug delivery carriers owing to their controllable nanoporous structure. Numerous researches have reported that MBGs can be doped with various therapeutic ions (strontium, copper, magnesium, zinc, lithium, silver, etc.) and loaded with specific biomolecules (e.g., therapeutic drugs, antibiotics, growth factors) achieving controllable loading and release kinetics. Therefore, co-delivery of ions and biomolecules using a single MBG carrier is highly interesting as this approach provides synergistic effects toward improved therapeutic outcomes in comparison to the strategy of sole drug or ion delivery. In this review, we discuss the state-of-the-art in the field of mesoporous silica-based materials used for co-delivery of ions and therapeutic drugs with osteogenesis/cementogenesis, angiogenesis, antibacterial and anticancer properties. The analysis of the literature reveals that specially designed mesoporous nanocarriers can release multiple ions and drugs at therapeutically safe and relevant levels, achieving the desired biological effects (in vivo, in vitro) for specific biomedical applications. It is expected that this review on the ion/drug co-delivery concept using MBG carriers will shed light on the advantages of such co-delivery systems for clinical use. Areas for future research directions are identified and discussed. STATEMENT OF SIGNIFICANCE: Many studies in literature focus on the potential of single drug or ion delivery by mesoporous silica-based materials, exploiting the bioactivity, biocompatibility, tunable composition and controllable nanoporosity of these materials. Recenlty, studies have adopted the "dual-delivery" concept, by designing multi-functional mesoporous silica-based systems which are capable to deliver both biologically active ions and biomolecules (growth factors, drugs) simultaneously in order to achieve synergy of their complementary therapeutic activities. This review summarizes the state of the art in the field, with focus on osteogenesis/cementogenesis, angiogenesis, antibacterial and anticancer properties, and discusses the challenges and prospects for further progress in this area, expecting to generate broader interest in the technology for applications in disease treatment and regenerative medicine.

The regulating effect of trace elements Si, Zn and Sr on mineralization of gelatin-hydroxyapatite electrospun fiber

Biomineralization approaches have been increasingly adopted to synthesizing advanced materials with superior properties. Nevertheless, the potential influence of inorganic trace elements on the mineralization process of collagen has been rarely reported, despite of the significant progress achieved on exploiting the critical roles of organic polymers in regulating the collagen mineralization. To this aim, the potential roles of Si, Zn and Sr in regulating the mineralization of gelatin-hydroxyapatite (HA) composite fibers have been examined in this study. The results indicated that the incorporation of trace elements not only promoted the biomineralization of gelatin, but also led to drastic change in the mineralization behavior. In particular, the gelatin-SiHA sample showed uniform mineralization predominantly inside the fibers, with nucleation and growth directions along the c-axis of the gelatin fibers. On the contrary, the gelatin-HA sample showed nucleation outside the fibers and spherical mineral crystals on top of fibers, typical structure for heterogeneous nucleation. As the mineralization process proceeded, the gelatin-ZnHA and gelatin-SrHA samples evolved into having similar structure as the gelatin-SiHA sample, despite of showing totally different mineralization behaviors at early time. Overall, the incorporation of trace elements seemed to lower the nucleation barriers, led to a more homogeneous mineralization mode within the fiber region and formation of mineralized structures closer to those in natural bone. Moreover, mineralized samples with trace elements demonstrated improved adhesion and cytoskeleton organization of osteoblastic cells. Such finding would provide important insight for understanding the mineralization process and the optimal design of advanced biological materials.

The effects of strontium-doped bioactive glass and fluoride on hydroxyapatite crystallization

OBJECTIVES

This study investigated the effects of a new strontium-doped bioactive glass and fluoride on hydroxyapatite crystallization.

METHODS

We designed an in vitro experiment with calcium phosphate (CaCl₂·2H₂O + K₂HPO₄ in buffer solution) with different concentrations of strontium-doped bioactive glass (1 mg/mL or 5 mg/mL), and different concentrations of fluoride (0 ppm, 1 ppm or 5 ppm). Tris-buffered saline served as negative control. After incubation at 37 ℃ for 48 h, the shape and organization of crystals were examined by transmission electron microscopy (TEM) and electron diffraction. Structure of the crystals was assessed by powder X-ray diffraction (P-XRD) and unit cell parameters were calculated. Characterization of the crystals were performed by Raman spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR).

RESULTS

TEM and selected-area electron diffraction revealed that the precipitates in all experimental groups were crystalline apatite. There was an interaction between strontium and fluoride with different concentrations on crystal thickness (p = 0.008). P-XRD indicated the formation of strontium-substituted-fluorohydroxyapatite and strontium-substituted-hydroxyapatite in the groups with both bioactive glass and fluoride. Expansion or contraction of crystal unit cell was influenced by the concentrations of strontium and fluoride. Raman spectra showed strong phosphate band at 960 cm^-1 in all experimental groups and displayed no obvious shift. FTIR results confirmed the formation of apatite.

CONCLUSIONS

The results of this study suggest that strontium-doped bioactive glass and fluoride have synergistic effects on hydroxyapatite crystallization.

CLINICAL SIGNIFICANCE

Strontium-doped bioactive glass and fluoride have synergistic effects on hydroxyapatite crystallization by producing strontium-substituted-hydroxyapatite and strontium-substituted-fluorohydroxyapatite with enhanced bioactivity and reduced solubility which could be beneficial for caries management.

Chitosan-Based Bioactive Glass Gauze: Microstructural Properties, In Vitro Bioactivity, and Biological Tests

Passive commercial gauzes were turned into interactive wound dressings by impregnating them with a chitosan suspension. To further improve healing, and cell adhesion and proliferation, chitosan/bioactive glass wound dressings were produced with the addition of (i) 45S5, (ii) a Sr- and Mg-containing bioactive glass, and (iii) a Zn-containing bioactive glass to the chitosan suspension. SEM and FTIR analyses evidenced positive results in terms of incorporation of bioactive glass particles. Bioactivity was investigated by soaking chitosan-based bioactive glass wound dressings in simulated body fluid (SBF). Cell viability, proliferation, and morphology were investigated using NIH 3T3 (mouse embryonic fibroblast) cells by neutral red (NR) uptake and MTT assays. Furthermore, the wound-healing rate was evaluated by means of the scratch test, using NIH 3T3. The results showed that bioactive glass particles enhance cell adhesion and proliferation, and wound healing compared to pure chitosan. Therefore, chitosan-based bioactive glass wound dressings combine the properties of the organic matrix with the specific biological characteristics of bioactive glasses to achieve chitosan composites suitable for healing devices.

Fabrication of a Cu/Zn co-incorporated calcium phosphate scaffold-derived GDF-5 sustained release system with enhanced angiogenesis and osteogenesis properties

Synthetic scaffolds with multifunctional properties, including angiogenesis and osteogenesis capacities, play an essential role in accelerating bone regeneration. In this study, various concentrations of Cu/Zn ions were incorporated into biphasic calcium phosphate (BCP) scaffolds, and then growth differentiation factor-5 (GDF-5)-loaded poly(lactide-co-glycolide) (PLGA) microspheres were attached onto the ion-doped scaffold. The results demonstrated that with increasing concentration of dopants, the scaffold surface gradually changed from smooth grain crystalline to rough microparticles, and further to a nanoflake film. Additionally, the mass ratio of β-tricalcium phosphate/hydroxyapatite increased with the dopant concentration. Furthermore, GDF-5-loaded PLGA microspheres attached onto the BCP scaffold surface exhibited a sustained release. In vitro co-culture of bone mesenchymal stem cells and vascular endothelial cells showed that the addition of Cu/Zn ions and GDF-5 in the BCP scaffold not only accelerated cell proliferation, but also promoted cell differentiation by enhancing the alkaline phosphatase activity and bone-related gene expression. Moreover, the vascular endothelial growth factor secretion level increased with the dopant concentration, and attained a maximum when GDF-5 was added into the ions-doped scaffold. These findings indicated that BCP scaffold co-doped with Cu/Zn ions exhibited a combined effect of both metal ions, including angiogenic and osteogenic capacities. Moreover, GDF-5 addition further enhanced both the angiogenic and osteogenic capacities of the BCP scaffold. The Cu/Zn co-incorporated BCP scaffold-derived GDF-5 sustained release system produced multifunctional scaffolds with improved angiogenesis and osteogenesis properties.

A comparative study on the in vitro formation of hydroxyapatite, cytotoxicity and antibacterial activity of 58S bioactive glass substituted by Li and Sr

Lithium and strontium up to 10 mol% have been substituted for calcium in 58S bioactive glasses in order to enhance specific biological properties such as proliferation, alkaline phosphatase (ALP) activity of cells as well as antibacterial activity. In-vitro formation of hydroxyapatite was studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopy (SEM). Substitution of either Li or Sr for Ca in the composition had a retarding effect on the bioactivity while Li decreased and Sr increased the rate of ion release in the simulated body fluid solution. The dissolution rate showed to be inversely proportional to oxygen density of the bioactive glasses. The proposed mechanisms for the lowered bioactivity are a lower supersaturation degree for nucleation of apatite in Li substituted bioactive glasses and blocking of the active growth sites of calcium phosphate by Sr²⁺ in Sr substituted bioactive glasses. The proliferation rate and alkaline phosphate activity of osteoblast cell line MC3T3-E1 treated with Li and Sr bioactive glasses were studied. 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and alkaline phosphate assay showed that all synthesized bioactive glasses with exception of 58S with 10 mol% SrO, exhibited statistically significant increase in both cell proliferation and alkaline phosphatase activity. Finally, 58S bioactive glass with 5 mol% Li₂O substitution for CaO was considered as a potential biomaterial in bone repair/regeneration therapies with enhanced biocompatibility, and alkaline phosphate activity, with a negligible loss in the bioactivity compared to the 58S bioglass. At the same time this composition had the highest antibacterial activity against methicillin-resistant Staphylococcus aureus bacteria among all synthesized Li and Sr substituted bioactive glasses.

Intracellular co-delivery of Sr ion and phenamil drug through mesoporous bioglass nanocarriers synergizes BMP signaling and tissue mineralization

Inducing differentiation and maturation of resident multipotent stem cells (MSCs) is an important strategy to regenerate hard tissues in mal-calcification conditions. Here we explore a co-delivery approach of therapeutic molecules comprised of ion and drug through a mesoporous bioglass nanoparticle (MBN) for this purpose. Recently, MBN has offered unique potential as a nanocarrier for hard tissues, in terms of high mesoporosity, bone bioactivity (and possibly degradability), tunable delivery of biomolecules, and ionic modification. Herein Sr ion is structurally doped to MBN while drug Phenamil is externally loaded as a small molecule activator of BMP signaling, for the stimulation of osteo/odontogenesis and mineralization of human MSCs derived from dental pulp. The Sr-doped MBN (85Si:10Ca:5Sr) sol-gel processed presents a high mesoporosity with a pore size of ∼6nm. In particular, Sr ion is released slowly at a daily rate of ∼3ppm per mg nanoparticles for up to 7days, a level therapeutically effective for cellular stimulation. The Sr-MBN is internalized to most MSCs via an ATP dependent macropinocytosis within hours, increasing the intracellular levels of Sr, Ca and Si ions. Phenamil is loaded maximally ∼30% into Sr-MBN and then released slowly for up to 7days. The co-delivered molecules (Sr ion and Phenamil drug) have profound effects on the differentiation and maturation of cells, i.e., significantly enhancing expression of osteo/odontogenic genes, alkaline phosphatase activity, and mineralization of cells. Of note, the stimulation is a result of a synergism of Sr and Phenamil, through a Trb3-dependent BMP signaling pathway. This biological synergism is further evidenced in vivo in a mal-calcification condition involving an extracted tooth implantation in dorsal subcutaneous tissues of rats. Six weeks post operation evidences the osseous-dentinal hard tissue formation, which is significantly stimulated by the Sr/Phenamil delivery, based on histomorphometric and micro-computed tomographic analyses. The bioactive nanoparticles releasing both Sr ion and Phenamil drug are considered to be a promising therapeutic nanocarrier platform for hard tissue regeneration. Furthermore, this novel ion/drug co-delivery concept through nanoparticles can be extensively used for other tissues that require different therapeutic treatment.

STATEMENT OF SIGNIFICANCE

This study reports a novel design concept in inorganic nanoparticle delivery system for hard tissues - the co-delivery of therapeutic molecules comprised of ion (Sr) and drug (Phenamil) through a unique nanoparticle of mesoporous bioactive glass (MBN). The physico-chemical and biological properties of MBN enabled an effective loading of both therapeutic molecules and a subsequently sustained/controlled release. The co-delivered Sr and Phenamil demonstrated significant stimulation of adult stem cell differentiation in vitro and osseous/dentinal regeneration in vivo, through BMP signaling pathways. We consider the current combination of Sr ion with Phenamil is suited for the osteo/odontogenesis of stem cells for hard tissue regeneration, and further, this ion/drug co-delivery concept can extend the applications to other areas that require specific cellular and tissue functions.

Gene delivery nanocarriers of bioactive glass with unique potential to load BMP2 plasmid DNA and to internalize into mesenchymal stem cells for osteogenesis and bone regeneration

The recent development of bioactive glasses with nanoscale morphologies has spurred their specific applications in bone regeneration, for example as drug and gene delivery carriers. Bone engineering with stem cells genetically modified with this unique class of nanocarriers thus holds great promise in this avenue. Here we report the potential of the bioactive glass nanoparticle (BGN) system for the gene delivery of mesenchymal stem cells (MSCs) targeting bone. The composition of 15% Ca-added silica, proven to be bone-bioactive, was formulated into surface aminated mesoporous nanospheres with enlarged pore sizes, to effectively load and deliver bone morphogenetic protein-2 (BMP2) plasmid DNA. The enlarged mesopores were highly effective in loading BMP2-pDNA with an efficiency as high as 3.5 wt% (pDNA w.r.t. BGN), a level more than twice than for small-sized mesopores. The BGN nanocarriers released the genetic molecules in a highly sustained manner (for as long as 2 weeks). The BMP2-pDNA/BGN complexes were effectively internalized to rat MSCs with a cell uptake level of ∼73%, and the majority of cells were transfected to express the BMP2 protein. Subsequent osteogenesis of the transfected MSCs was demonstrated by the expression of bone-related genes, including bone sialoprotein, osteopontin, and osteocalcin. The MSCs transfected with BMP2-pDNA/BGN were locally delivered inside a collagen gel to the target calvarium defects. The results showed significantly improved bone regeneration, as evidenced by the micro-computed tomographic, histomorphometric and immunohistochemical analyses. This study supports the excellent capacity of the BGN system as a pDNA-delivery nanocarrier in MSCs, and the engineered system, BMP2-pDNA/BGN with MSCs, may be considered a new promising candidate to advance the therapeutic potential of stem cells through genetic modification, targeting bone defects and diseases.