Incorporation of Cu-Containing Bioactive Glass Nanoparticles in Gelatin-Coated Scaffolds Enhances Bioactivity and Osteogenic Activity

Micro-arc oxidation (MAO) and its potential for improving the performance of titanium implants in biomedical applications

Titanium (Ti) and its alloys have good biocompatibility, mechanical properties and corrosion resistance, making them attractive for biomedical applications. However, their biological inertness and lack of antimicrobial properties may compromise the success of implants. In this review, the potential of micro-arc oxidation (MAO) technology to create bioactive coatings on Ti implants is discussed. The review covers the following aspects: 1) different factors, such as electrolyte, voltage and current, affect the properties of MAO coatings; 2) MAO coatings affect biocompatibility, including cytocompatibility, hemocompatibility, angiogenic activity, corrosion resistance, osteogenic activity and osseointegration; 3) antibacterial properties can be achieved by adding copper (Cu), silver (Ag), zinc (Zn) and other elements to achieve antimicrobial properties; and 4) MAO can be combined with other physical and chemical techniques to enhance the performance of MAO coatings. It is concluded that MAO coatings offer new opportunities for improving the use of Ti and its alloys in biomedical applications, and some suggestions for future research are provided.

Surface Modification of 3D-Printed PCL/BG Composite Scaffolds via Mussel-Inspired Polydopamine and Effective Antibacterial Coatings for Biomedical Applications

A wide variety of composite scaffolds with unique geometry, porosity and pore size can be fabricated with versatile 3D printing techniques. In this work, we fabricated 3D-printed composite scaffolds of polycaprolactone (PCL) incorporating bioactive glass (BG) particles (13-93 and 13-93B3 compositions) by using fused deposition modeling (FDM). The scaffolds were modified with a "mussel-inspired surface coating" to regulate biological properties. The chemical and surface properties of scaffolds were analyzed by Fourier transform infrared spectroscopy (FTIR), contact angle and scanning electron microscopy (SEM). Polydopamine (PDA) surface-modified composite scaffolds exhibited attractive properties. Firstly, after the surface modification, the adhesion of a composite coating based on gelatin incorporated with strontium-doped mesoporous bioactive glass (Sr-MBGNs/gelatin) was significantly improved. In addition, cell attachment and differentiation were promoted, and the antibacterial properties of the scaffolds were increased. Moreover, the bioactivity of these scaffolds was also significantly influenced: a hydroxyapatite layer formed on the scaffold surface after 3 days of immersion in SBF. Our results suggest that the promoting effect of PDA coating on PCL-BG scaffolds leads to improved scaffolds for bone tissue engineering.

Using Copper-Doped Mesoporous Bioactive Glass Nanospheres to Impart Anti-Bacterial Properties to Dental Composites

Experimental dental resin composites containing copper-doped mesoporous bioactive glass nanospheres (Cu-MBGN) were developed to impart anti-bacterial properties. Increasing amounts of Cu-MBGN (0, 1, 5 and 10 wt%) were added to the BisGMA/TEGDMA resin matrix containing micro- and nano-fillers of inert glass, keeping the resin/filler ratio constant. Surface micromorphology and elemental analysis were performed to evaluate the homogeneous distribution of filler particles. The study investigated the effects of Cu-MBGN on the degree of conversion, polymerization shrinkage, porosity, ion release and anti-bacterial activity on S. mutans and A. naeslundii. Experimental materials containing Cu-MBGN showed a dose-dependent Cu release with an initial burst and a further increase after 28 days. The composite containing 10% Cu-MBGN had the best anti-bacterial effect on S. mutans, as evidenced by the lowest adherence of free-floating bacteria and biofilm formation. In contrast, the 45S5-containing materials had the highest S. mutans adherence. Ca release was highest in the bioactive control containing 15% 45S5, which correlated with the highest number of open porosities on the surface. Polymerization shrinkage was similar for all tested materials, ranging from 3.8 to 4.2%, while the degree of conversion was lower for Cu-MBGN materials. Cu-MBGN composites showed better anti-bacterial properties than composites with 45S5 BG.

Artificial Extracellular Matrices Containing Bioactive Glass Nanoparticles Promote Osteogenic Differentiation in Human Mesenchymal Stem Cells

The present study analyzes the capacity of collagen (coll)/sulfated glycosaminoglycan (sGAG)-based surface coatings containing bioactive glass nanoparticles (BGN) in promoting the osteogenic differentiation of human mesenchymal stroma cells (hMSC). Physicochemical characteristics of these coatings and their effects on proliferation and osteogenic differentiation of hMSC were investigated. BGN were stably incorporated into the artificial extracellular matrices (aECM). Oscillatory rheology showed predominantly elastic, gel-like properties of the coatings. The complex viscosity increased depending on the GAG component and was further elevated by adding BGN. BGN-containing aECM showed a release of silicon ions as well as an uptake of calcium ions. hMSC were able to proliferate on coll and coll/sGAG coatings, while cellular growth was delayed on aECM containing BGN. However, a stimulating effect of BGN on ALP activity and calcium deposition was shown. Furthermore, a synergistic effect of sGAG and BGN was found for some donors. Our findings demonstrated the promising potential of aECM and BGN combinations in promoting bone regeneration. Still, future work is required to further optimize the BGN/aECM combination for increasing its combined osteogenic effect.

Integration of Mesoporous Bioactive Glass Nanoparticles and Curcumin into PHBV Microspheres as Biocompatible Composite for Drug Delivery Applications

Bioactive glasses (BGs) are being increasingly considered for biomedical applications. One convenient approach to utilize BGs in tissue engineering and drug delivery involves their combination with organic biomaterials in order to form composites with enhanced biocompatibility and biodegradability. In this work, mesoporous bioactive glass nanoparticles (MBGN) have been merged with polyhydroxyalkanoate microspheres with the purpose to develop drug carriers. The composite carriers (microspheres) were loaded with curcumin as a model drug. The toxicity and delivery rate of composite microspheres were tested in vitro, reaching a curcumin loading efficiency of over 90% and an improving of biocompatibility of different concentrations of MBGN due to its administrations through the composite. The composite microspheres were tested in terms of controlled release, biocompatibility and bioactivity. Our results demonstrate that the composite microspheres can be potentially used in biomedicine due to their dual effects: bioactivity (due to the presence of MBGN) and curcumin release capability.

Incorporation of Copper-Doped Mesoporous Bioactive Glass Nanospheres in Experimental Dental Composites: Chemical and Mechanical Characterization

Experimental dental resin composites incorporating copper-doped mesoporous bioactive glass nanospheres (Cu-MBGN) were designed to impart antibacterial and remineralizing properties. The study evaluated the influence of Cu-MBGN on the mechanical properties and photopolymerization of resin composites. Cu-MBGN were synthesized using a microemulsion-assisted sol-gel method. Increasing amounts of Cu-MBGN (0, 1, 5, and 10 wt %) were added to the organic polymer matrix with inert glass micro- and nanofillers while maintaining a constant resin/filler ratio. Six tests were performed: X-ray diffraction, scanning electron microscopy, flexural strength (FS), flexural modulus (FM), Vickers microhardness (MH), and degree of conversion (DC). FS and MH of Cu-MBGN composites with silica fillers showed no deterioration with aging, with statistically similar results at 1 and 28 days. FM was not influenced by the addition of Cu-MBGN but was reduced for all tested materials after 28 days. The specimens with 1 and 5% Cu-MBGN had the highest FS, FM, MH, and DC values at 28 days, while controls with 45S5 bioactive glass had the lowest FM, FS, and MH. DC was high for all materials (83.7-93.0%). Cu-MBGN composites with silica have a potential for clinical implementation due to high DC and good mechanical properties with adequate resistance to aging.

Role of Zinc-Doped Bioactive Glass Encapsulated with Microspherical Gelatin in Localized Supplementation for Tissue Regeneration: A Contemporary Review

Gelatin, a natural polymer, provides excellent tissue compatibility for use in tissue rehabilitation. Bioactive glasses (BAG) offer superior capacity in stimulating a bioactive response but show high variability in uptake and solubility. To tackle these drawbacks, a combination of gelatin with BAG is proposed to form composites, which then offer a synergistic response. The cross-linked gelatin structure's mechanical properties are enhanced by the incorporation of the inorganic BAG, and the rate of BAG ionic supplementation responsible for bioactivity and regenerative potential is better controlled by a protective gelatin layer. Several studies have demonstrated the cellular benefits of these composites in different forms of functional modification such as doping with zinc or incorporation of zinc such as ions directly into the BAG matrix. This review presents a comprehensive perspective on the individual characteristics of BAG and gelatin, including the synthesis and mechanism of action. Further, adaptation of the composite into various applications for bone tissue engineering is discussed and future challenges are highlighted.

Cellulose acetate-gelatin-coated boron-bioactive glass biocomposite scaffolds for bone tissue engineering

In this study, we aimed to prepare and characterize porous scaffolds composed of pure and boron oxide (B₂O₃)-doped bioactive glass (BG) that were infiltrated by cellulose acetate-gelatin (CA-GE) polymer solution for bone tissue engineering applications. Composite scaffolds were cross-linked with glutaraldehyde after polymer coating to protect the structural integrity of the polymeric-coated scaffolds. The impact of B₂O₃ incorporation into BG-polymer porous scaffolds on the cross-sectional morphology, porosity, mechanical properties, degradation and bioactivity of the scaffolds was investigated. Human dental pulp stem cells (hDPSCs) were enzymatically isolated and used for cell culture studies. According to scanning electron microscope analysis, the porous structure of the scaffolds was preserved after polymer coating. After polymer infiltration, the porosity of the scaffolds decreased from 64.2% to 59.35% for pure BG scaffolds and from 67.3% to 58.9% for B₂O₃-doped scaffolds. Meanwhile, their compressive strengths increased from 0.13 to 0.57 MPa and from 0.20 to 0.82 MPa, respectively. After polymer infiltration, 7% B₂O₃-incorporated BG scaffolds had higher weight loss and Ca-P layer deposition than pure BG scaffolds, after 14 d of incubation in simulated body fluid at 37 °C. Higher attachment and proliferation of hDPSCs were observed on 7% B₂O₃-BG-CA/GE scaffolds. In addition, the alkaline phosphatase activity of the cells was about 1.25-fold higher in this group than that observed on BG-CA/GE scaffolds after 14 d of incubation in osteogenic medium, while their intracellular calcium amounts were 1.7-fold higher than observed on BG-CA/GE after 7 d of incubation in osteogenic medium. Our results suggested that porous cellulose acetate-gelatin-coated boron-BG scaffolds hold promise for bone tissue engineering applications.

Bioactive Glasses: A Promising Therapeutic Ion Release Strategy for Enhancing Wound Healing

The morbidity, mortality, and burden of burn victims and patients with severe diabetic wounds are still high, which leads to an extensively growing demand for novel treatments with high clinical efficacy. Biomaterial-based wound treatment approaches have progressed over time from simple cotton wool dressings to advanced skin substitutes containing cells and growth factors; however, no wound care approach is yet completely satisfying. Bioactive glasses are materials with potential in many areas that exhibit unique features in biomedical applications. Today, bioactive glasses are not only amorphous solid structures that can be used as a substitute in hard tissue but also are promising materials for soft tissue regeneration and wound healing applications. Biologically active elements such as Ag, B, Ca, Ce, Co, Cu, Ga, Mg, Se, Sr, and Zn can be incorporated in glass networks; hence, the superiority of these multifunctional materials over current materials results from their ability to release multiple therapeutic ions in the wound environment, which target different stages of the wound healing process. Bioactive glasses and their dissolution products have high potency for inducing angiogenesis and exerting several biological impacts on cell functions, which are involved in wound healing and some other features that are valuable in wound healing applications, namely hemostatic and antibacterial properties. In this review, we focus on skin structure, the dynamic process of wound healing in injured skin, and existing wound care approaches. The basic concepts of bioactive glasses are reviewed to better understand the relationship between glass structure and its properties. We illustrate the active role of bioactive glasses in wound repair and regeneration. Finally, research studies that have used bioactive glasses in wound healing applications are summarized and the future trends in this field are elaborated.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Systematically Designed Periodic Electrophoretic Deposition for Decorating 3D Carbon-Based Scaffolds with Bioactive Nanoparticles

The coating of porous scaffolds with nanoparticles is crucial in many applications, for example to generate scaffolds for catalysis or to make scaffolds bioactive. A standard and well-established method for coating surfaces with charged nanoparticles is electrophoresis, but when used on porous scaffolds, this method often leads to a blockage of the pores so that only the outermost layers of the scaffolds are coated. In this study, the electrophoretic coating process is monitored in situ and the kinetics of nanoparticle deposition are investigated. This concept can be extended to design a periodic electrophoretic deposition (PEPD) strategy, thus avoiding the typical blockage of surface pores. In the present work we demonstrate successful and homogeneous electrophoretic deposition of hydroxyapatite nanoparticles (HAn, diameter ≤200 nm) on a fibrous graphitic 3D structure (ultralightweight aerographite) using the PEPD strategy. The microfilaments of the resulting scaffold are covered with HAn both internally and on the surface. Furthermore, protein adsorption assays and cell proliferation assays were carried out and revealed that the HAn-decorated aerographite scaffolds are biocompatible. The HAn decoration of the scaffolds also significantly increases the alkaline phosphatase activity of osteoblast cells, showing that the scaffolds are able to promote their osteoblastic activity.

Toward Highly Dispersed Mesoporous Bioactive Glass Nanoparticles With High Cu Concentration Using Cu/Ascorbic Acid Complex as Precursor

Copper (Cu) ions have a variety of advantageous biological functionalities, such as proangiogenic and bactericidal activities. Given the intrinsic biodegradability and biocompatibility, silicate-based mesoporous bioactive glass nanoparticles (MBGNs) are considered as promising platforms for the delivery of Cu ions. However, effective incorporation of Cu into MBGNs still faces challenges, e.g., particle aggregation, the formation of insoluble crystalline Cu-based nanoparticles, and a low loading amount of Cu. We report a novel method to synthesize chemically homogenous and highly dispersed Cu-containing MBGNs (Cu-MBGNs) with tunable Cu concentration by using ascorbic acid/Cu complexes as the precursor of Cu in a microemulsion-assisted sol-gel approach. Cu-MBGNs exhibited a sphere-like shape with a particle size between 100 and 300 nm while their pore size varied from 2 to 10 nm. The inclusion of Cu, regardless of the incorporated concentration, did not significantly affect the morphology of particles. ICP-AES results indicated that the concentration of Cu in the particles could be conveniently tuned from 0 to ~6 mol% by controlling the amount of ascorbic acid/Cu complexes added, while the formation of crystalline Cu-based nanoparticles was avoided. The amorphous feature of Cu-MBGNs was proved by XRD, while the predominant oxidation state of Cu was evidenced to be Cu2+ by XPS. The incorporation of Cu did not inhibit the apatite-forming ability (bioactivity) of the particles in contact with simulated body fluid. Cu-MBGNs exhibited the capability of releasing Cu, Si, and Ca ions over time in the physiological fluid. The concentration of released Cu ions could be controlled by selecting specific Cu-MBGNs of different Cu contents. The dissolution products of most Cu-MBGNs at the dosage of 1, 0.1, and 0.01 mg/mL did not exhibit cytotoxicity, while only 7Cu-MBGN was cytotoxic at the dosage of 1 mg/mL. This study provided a feasible strategy to synthesize highly dispersed amorphous Cu-MBGNs with high Cu concentrations for biomedical applications. The particles exhibit great potential as building blocks for developing composite 3D scaffolds, coatings, and drug carriers, particularly when a large amount of particles incorporated may compromise the properties of (polymer) matrix materials while a relatively high concentration of released Cu ions is still required.

Use of Nanoparticles in Tissue Engineering and Regenerative Medicine

Advances in nanoparticle (NP) production and demand for control over nanoscale systems have had significant impact on tissue engineering and regenerative medicine (TERM). NPs with low toxicity, contrasting agent properties, tailorable characteristics, targeted/stimuli-response delivery potential, and precise control over behavior (via external stimuli such as magnetic fields) have made it possible their use for improving engineered tissues and overcoming obstacles in TERM. Functional tissue and organ replacements require a high degree of spatial and temporal control over the biological events and also their real-time monitoring. Presentation and local delivery of bioactive (growth factors, chemokines, inhibitors, cytokines, genes etc.) and contrast agents in a controlled manner are important implements to exert control over and monitor the engineered tissues. This need resulted in utilization of NP based systems in tissue engineering scaffolds for delivery of multiple growth factors, for providing contrast for imaging and also for controlling properties of the scaffolds. Depending on the application, materials, as polymers, metals, ceramics and their different composites can be utilized for production of NPs. In this review, we will cover the use of NP systems in TERM and also provide an outlook for future potential use of such systems.

Electrophoretic Deposition of Bioadaptive Drug Delivery Coatings on Magnesium Alloy for Bone Repair

Biodegradable polymer coatings on magnesium alloys are attractive, as they can provide corrosion resistance as well as additional functions for biomedical applications, e.g., drug delivery. A gelatin nanospheres/chitosan (GNs/CTS) composite coating on WE43 substrate was fabricated by electrophoretic deposition with simvastatin (SIM) loaded into the GNs. Apart from a sustained drug release over 28 days, an anticorrosion behavior of the coated WE43 substrates was confirmed by electrochemical tests. Both the degradation and corrosion rates of the coated substrate were significantly minimized in contrast to bare WE43. The cytocompatibility of the coated samples was analyzed  both quantitatively and qualitatively. Additionally, the osteogenic differentiation of MC3T3-E1 cells on SIM-containing coatings was assessed by measuring the expression of osteogenic genes and related proteins, alkaline phosphatase (ALP) activity, and extracellular matrix mineralization, showing that the SIM-loaded composite coating could upregulate the expression of osteogenic genes and related proteins, promote ALP activity, and enhance extracellular matrix mineralization. In summary, the SIM-loaded GNs/CTS composite coatings were able to enhance the corrosion resistance of the WE43 substrate and promote osteogenic activity, thus demonstrating a promising coating system for modifying the surface of magnesium alloys targeted for orthopedic applications.

Bioactive Carbon-Based Hybrid 3D Scaffolds for Osteoblast Growth

Bone, nerve, and heart tissue engineering place high demands on the conductivity of three-dimensional (3D) scaffolds. Fibrous carbon-based scaffolds are excellent material candidates to fulfill these requirements. Here, we show that highly porous (up to 94%) hybrid 3D framework structures with hierarchical architecture, consisting of microfiber composites of self-entangled carbon nanotubes (CNTs) and bioactive nanoparticles are highly suitable for growing cells. The hybrid 3D structures are fabricated by infiltrating a combination of CNTs and bioactive materials into a porous (∼94%) zinc oxide (ZnO) sacrificial template, followed by the removal of the ZnO backbone via a H2 thermal reduction process. Simultaneously, the bioactive nanoparticles are sintered. In this way, conductive and mechanically stable 3D composites of free-standing CNT-based microfibers and bioactive nanoparticles are formed. The adopted strategy demonstrates great potential for implementing low-dimensional bioactive materials, such as hydroxyapatite (HA) and bioactive glass nanoparticles (BGN), into 3D carbon-based microfibrous networks. It is demonstrated that the incorporation of HA nanoparticles and BGN promotes the biomineralization ability and the protein adsorption capacity of the scaffolds significantly, as well as fibroblast and osteoblast adhesion. These results demonstrate that the developed carbon-based bioactive scaffolds are promising materials for bone tissue engineering and related applications.