Surface Functionalization of TiO2 Nanotubes with Bone Morphogenetic Protein 2 and Its Synergistic Effect on the Differentiation of Mesenchymal Stem Cells

Infection Microenvironment-Responsive Coating on Titanium Surfaces for On-Demand Release of Therapeutic Gas and Antibiotic

Aseptic loosening and bacterial infection pose significant challenges in the clinical application of titanium (Ti) orthopedic implants, which are primarily caused by insufficient osseointegration and bacterial contamination. To address these issues, a responsive coating on Ti surface is constructed, which achieves enhanced osseointegration and infection elimination by on-demand release of therapeutic gas hydrogen sulfide (H2S) and antibiotic. TiO2 nanotubes (TNT) are anodized on the Ti surface to enhance its bioactivity and serve as reservoirs for the antibiotic. An infection microenvironment-responsive macromolecular H2S donor layer is coated on top of TNT to inhibit premature leakage of antibiotic. This layer exhibits a sustained release of low-dosage H2S, which is capable of promoting the osteogenic differentiation and migration of cells. Moreover, the compactness of the macromolecular H2S donor layer could be broken by bacterial invasion, leading to rapid antibiotic release thus preventing infection. In vitro antibacterial experiments validates significant antibacterial activity of the coating against both Gram-negative (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). Crucially, this coating effectively suppresses implant-associated infection with 98.7% antibacterial efficiency in a rat femoral bone defect model, mitigates inflammation at the defect site and promotes osseointegration of the Ti orthopedic implant.

Surface-modified titanium and titanium-based alloys for improved osteogenesis: A critical review

As implantable materials, titanium, and its alloys have garnered enormous interest from researchers for dental and orthopedic procedures. Despite their success in wide clinical applications, titanium, and its alloys fail to stimulate osteogenesis, resulting in poor bonding strength with surrounding bone tissue. Optimizing the surface topology and altered compositions of titanium and titanium-based alloys substantially promotes peri-implant bone regeneration. This review summarizes the utilization and importance of various osteogenesis components loaded onto titanium and its alloys. Further, different surface-modification methods and the release efficacy of loaded substances are emphasized. Finally, we summarize the article with prospects. We believe that further investigation studies must focus on identifying novel loading components, exploring various innovative, optimized surface-modification methods, and developing a sustained-release system on implant surfaces to improve peri-implant bone formation.

Fit and forget: The future of dental implant therapy via nanotechnology

Unlike orthopedic implants, dental implants require the orchestration of both osseointegration at the bone-implant interface and soft-tissue integration at the transmucosal region in a complex oral micro-environment with ubiquitous pathogenic bacteria. This represents a very challenging environment for early acceptance and long-term survival of dental implants, especially in compromised patient conditions, including aged, smoking and diabetic patients. Enabling advanced local therapy from the surface of titanium-based dental implants via novel nano-engineering strategies is emerging. This includes anodized nano-engineered implants eluting growth factors, antibiotics, therapeutic nanoparticles and biopolymers to achieve maximum localized therapeutic action. An important criterion is balancing bioactivity enhancement and therapy (like bactericidal efficacy) without causing cytotoxicity. Critical research gaps still need to be addressed to enable the clinical translation of these therapeutic dental implants. This review informs the latest developments, challenges and future directions in this domain to enable the successful fabrication of clinically-translatable therapeutic dental implants that would allow for long-term success, even in compromised patient conditions.

Dual growth factor-modified microspheres nesting human-derived umbilical cord mesenchymal stem cells for bone regeneration

BACKGROUND

Modular tissue engineering (MTE) is a novel "bottom-up" approach that aims to mimic complex tissue microstructural features. The constructed micromodules are assembled into engineered biological tissues with repetitive functional microunits and form cellular networks. This is emerging as a promising strategy for reconstruction of biological tissue.

RESULTS

Herein, we constructed a micromodule for MTE and developed engineered osteon-like microunits by inoculating human-derived umbilical cord mesenchymal stem cells (HUMSCs) onto nHA/PLGA microspheres with surface modification of dual growth factors (BMP2/bFGF). By evaluating the results of proliferation and osteogenic differentiation ability of HUMSCs in vitro, the optimal ratio of the dual growth factor (BMP2/bFGF) combination was derived as 5:5. In vivo assessments showed the great importance of HUMSCs for osteogneic differentiation. Ultimately, direct promotion of early osteo-differentiation manifested as upregulation of Runx-2 gene expression. The vascularization capability was evaluated by tube formation assays, demonstrating the importance of HUMSCs in the microunits for angiogenesis.

CONCLUSIONS

The modification of growth factors and HUMSCs showed ideal biocompatibility and osteogenesis combined with nHA/PLGA scaffolds. The micromodules constructed in the current study provide an efficient stem cell therapy strategy for bone defect repair.

Advances in Multifunctional Bioactive Coatings for Metallic Bone Implants

To fix the bone in orthopedics, it is almost always necessary to use implants. Metals provide the needed physical and mechanical properties for load-bearing applications. Although widely used as biomedical materials for the replacement of hard tissue, metallic implants still confront challenges, among which the foremost is their low biocompatibility. Some of them also suffer from excessive wear, low corrosion resistance, infections and shielding stress. To address these issues, various coatings have been applied to enhance their in vitro and in vivo performance. When merged with the beneficial properties of various bio-ceramic or polymer coatings remarkable bioactive, osteogenic, antibacterial, or biodegradable composite implants can be created. In this review, bioactive and high-performance coatings for metallic bone implants are systematically reviewed and their biocompatibility is discussed. Updates in coating materials and formulations for metallic implants, as well as their production routes, have been provided. The ways of improving the bioactive coating performance by incorporating bioactive moieties such as growth factors, osteogenic factors, immunomodulatory factors, antibiotics, or other drugs that are locally released in a controlled manner have also been addressed.

Smart Bacteria-Responsive Drug Delivery Systems in Medical Implants

With the rapid development of implantable biomaterials, the rising risk of bacterial infections has drawn widespread concern. Due to the high recurrence rate of bacterial infections and the issue of antibiotic resistance, the common treatments of peri-implant infections cannot meet the demand. In this context, stimuli-responsive biomaterials have attracted attention because of their great potential to spontaneously modulate the drug releasing rate. Numerous smart bacteria-responsive drug delivery systems (DDSs) have, therefore, been designed to temporally and spatially release antibacterial agents from the implants in an autonomous manner at the infected sites. In this review, we summarized recent advances in bacteria-responsive DDSs used for combating bacterial infections, mainly according to the different trigger modes, including physical stimuli-responsive, virulence-factor-responsive, host-immune-response responsive and their combinations. It is believed that the smart bacteria-responsive DDSs will become the next generation of mainstream antibacterial therapies.

Smart biomaterials and their potential applications in tissue engineering

Smart biomaterials have been rapidly advancing ever since the concept of tissue engineering was proposed. Interacting with human cells, smart biomaterials can play a key role in novel tissue morphogenesis. Various aspects of biomaterials utilized in or being sought for the goal of encouraging bone regeneration, skin graft engineering, and nerve conduits are discussed in this review. Beginning with bone, this study summarizes all the available bioceramics and materials along with their properties used singly or in conjunction with each other to create scaffolds for bone tissue engineering. A quick overview of the skin-based nanocomposite biomaterials possessing antibacterial properties for wound healing is outlined along with skin regeneration therapies using infrared radiation, electrospinning, and piezoelectricity, which aid in wound healing. Furthermore, a brief overview of bioengineered artificial skin grafts made of various natural and synthetic polymers has been presented. Finally, by examining the interactions between natural and synthetic-based biomaterials and the biological environment, their strengths and drawbacks for constructing peripheral nerve conduits are highlighted. The description of the preclinical outcome of nerve regeneration in injury healed with various natural-based conduits receives special attention. The organic and synthetic worlds collide at the interface of nanomaterials and biological systems, producing a new scientific field including nanomaterial design for tissue engineering.

ROS-responsive hydrogel coating modified titanium promotes vascularization and osteointegration of bone defects by orchestrating immunomodulation

Ideal titanium implants are required to participate in bone repair actively to improve in situ osteointegration. However, the traditional surface functionalization methods of titanium implants are difficult to both achieve the active regulation and long-term stability of bioactive components. Here, a novel functionalized titanium which loaded with thymosin β4 (Tβ4) and covered by a hydrogel coating was designed and evaluated. A strong adhesion between the coating and the titanium substrate was realized by the synergistic action of borate ester bonds and surface topological structure. The hydrogel coating also achieved an in vivo adhesion between implant and tissue through hydrogen bonds and borate bonds. In addition, based on the ROS response property of borate bonds, the implant can release Tβ4 in response to the immune reaction of bone healing by regulating the polarization of macrophages, thereby reducing the fibrosis formation around the implant interface and promoting vascularization and osteointegration of bone defects.

Application of biomolecules modification strategies on PEEK and its composites for osteogenesis and antibacterial properties

As orthopedic and dental implants, polyetheretherketone (PEEK) is expected to be a common substitute material of titanium (Ti) and its alloys due to its good biocompatibility, chemical stability, and elastic modulus close to that of bone tissue. It could avoid metal allergy and bone resorption caused by the stress shielding effect of Ti implants, widely studied in the medical field. However, the lack of biological activity is not conducive to the clinical application of PEEK implants. Therefore, the surface modification of PEEK has increasingly become one of the research hotspots. Researchers have explored various biomolecules modification methods to effectively enhance the osteogenic and antibacterial activities of PEEK and its composites. Therefore, this review mainly summarizes the recent research of PEEK modified by biomolecules and discusses the further research directions to promote the clinical transformation of PEEK implants.

TiO2 Nanotubes Functionalized with Icariin for an Attenuated In Vitro Immune Response and Improved In Vivo Osseointegration

Due to their superior mechanical and chemical properties, titanium (Ti) and its alloys have been widely used as orthopedic implantable devices. However, their bioinertness represents a limitation, which can be overcome by employing various surface modifications, such as TiO₂ nanotube (TNT) fabrication via electrochemical anodization. Anodic TNTs present tunable dimensions and unique structures, turning them into feasible drug delivery platforms. In the present work, TNTs were loaded with icariin (Ica) through an adhesive intermediate layer of polydopamine (DP), and their in vitro and in vivo biological performance was evaluated. The successful fabrication of the modified surfaces was verified by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements (CA), while the in vitro release of Ica was evaluated via UV-VIS spectrophotometry. In terms of in vitro behaviour, comparative studies on RAW 264.7 macrophages demonstrated that the TNT substrates, especially TNT-DP-Ica, elicited a lower inflammatory response compared to the Ti support. Moreover, the in vivo implantation studies evinced generation of a reduced fibrotic capsule around this implant and increased thickness of the newly formed bone tissue at 1 month and 3 months post-implantation, respectively. Overall, our results indicate that the controlled release of Ica from TNT surfaces could result in an improved osseointegration process.

Analytical Techniques for the Characterization of Bioactive Coatings for Orthopaedic Implants

The development of bioactive coatings for orthopedic implants has been of great interest in recent years in order to achieve both early- and long-term osseointegration. Numerous bioactive materials have been investigated for this purpose, along with loading coatings with therapeutic agents (active compounds) that are released into the surrounding media in a controlled manner after surgery. This review initially focuses on the importance and usefulness of characterization techniques for bioactive coatings, allowing the detailed evaluation of coating properties and further improvements. Various advanced analytical techniques that have been used to characterize the structure, interactions, and morphology of the designed bioactive coatings are comprehensively described by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 3D tomography, quartz crystal microbalance (QCM), coating adhesion, and contact angle (CA) measurements. Secondly, the design of controlled-release systems, the determination of drug release kinetics, and recent advances in drug release from bioactive coatings are addressed as the evaluation thereof is crucial for improving the synthesis parameters in designing optimal bioactive coatings.

Calcium Peroxide Nanoparticles-Embedded Coatings on Anti-Inflammatory TiO2 Nanotubes for Bacteria Elimination and Inflammatory Environment Amelioration

Implant-associated bacterial infections significantly impair the integration between titanium and soft tissues. Traditional antibacterial modifications of titanium implants are able to eliminate bacteria, but the resulting pro-inflammatory reactions are usually ignored, which still poses potential risks to human bodies. Here, a dual drug-loading system on titanium has been developed via the adhesion of a catechol motif-modified methacrylated gelatin hydrogel onto TiO₂ nanotubes. Then synthesized CaO₂ nanoparticles (NPs) are embedded into the hydrogel, and interleukin-4 (IL-4) is loaded into the nanotubes to achieve both antibacterial and anti-inflammatory properties. The dual drug-loading system can eliminate Staphylococcus aureus (S. aureus) rapidly, attributed to the H₂ O₂ release from CaO₂ NPs. The potential cytotoxicity of CaO₂ NPs is also remarkably reduced after being embedded into the hydrogel. More importantly, with the gradual release of IL-4, the dual drug-loading system is capable of modulating pro-inflammatory reactions by inducing M2 phenotype polarization of macrophages. In a subcutaneous infection model, the S. aureus contamination is effectively resolved after 2 days, and the resulting pro-inflammatory reactions are also inhibited after 7 days. Finally, the damaged tissue is significantly recovered. Taken together, the dual drug-loading system exhibits great therapeutic potential in effectively killing pathogens and inhibiting the resulting pro-inflammatory reactions.

Anodic TiO2 Nanotubes: Tailoring Osteoinduction via Drug Delivery

TiO₂ nanostructures and more specifically nanotubes have gained significant attention in biomedical applications, due to their controlled nanoscale topography in the sub-100 nm range, high surface area, chemical resistance, and biocompatibility. Here we review the crucial aspects related to morphology and properties of TiO₂ nanotubes obtained by electrochemical anodization of titanium for the biomedical field. Following the discussion of TiO₂ nanotopographical characterization, the advantages of anodic TiO₂ nanotubes will be introduced, such as their high surface area controlled by the morphological parameters (diameter and length), which provides better adsorption/linkage of bioactive molecules. We further discuss the key interactions with bone-related cells including osteoblast and stem cells in in vitro cell culture conditions, thus evaluating the cell response on various nanotubular structures. In addition, the synergistic effects of electrical stimulation on cells for enhancing bone formation combining with the nanoscale environmental cues from nanotopography will be further discussed. The present review also overviews the current state of drug delivery applications using TiO₂ nanotubes for increased osseointegration and discusses the advantages, drawbacks, and prospects of drug delivery applications via these anodic TiO₂ nanotubes.

Microstructured titanium functionalized by naringin inserted multilayers for promoting osteogenesis and inhibiting osteoclastogenesis

Osteoporosis is the most common cause of fractures in middle-aged and elderly people. Fracture repair can be difficult due to the decreased bone volume in osteoporosis patients and implants are often required. In this study, a slow-release system for microstructured titanium (Micro-Ti) was designed to promote osteogenesis and inhibit osteoclastogenesis. Firstly, Micro-Ti was prepared on titanium surfaces by dual acid etching. Micro-Ti was covered with naringin (NA), chitosan (CHI) and gelatin (GEL) multilayers through layer by layer technique, which is denoted as LBL (NA) coated-Ti. Osteoblasts (ME3T3-E1) and macrophages (RAW 264.7) were cultured on untreated and treated titanium surfaces in vitro. Osteoblasts grown on LBL (NA) coated-Ti showed higher alkaline phosphatase (ALP) and mineralization, consistent with qRT-PCR analysis of osteoblast genes including runt-related transcription factor 2 (Runx2), ALP, collagen I (Col I), osteocalcin (OCN), osteopontin (OPN), and osteoprotegerin (OPG). In contrast, acid tartarate-resistant phosphatase activity and the expression of osteoclastic differentiation related genes comprising of cathepsin K (CTSK), nuclear factor of activated T cells (NFAT), tartrate resistant acid phosphatase (TRAP) and V-ATPase (VATP) in osteoclasts were significantly reduced on LBL (NA) coated-Ti surfaces compared with other groups. These results indicate that microstructured titanium functionalized by naringin inserted multilayers enhanced the differentiation of osteoblasts and inhibited osteoclast formation. The proposed approach in this research provides a novel way to modify titanium-based implants for fracture repair in osteoporosis patients.

Advancing of titanium medical implants by surface engineering: recent progress and challenges

Introduction:Titanium (Ti) and their alloys are used as main implant materials in orthopedics and dentistry for decades having superior mechanical properties, chemical stability and biocompatibility. Their rejections due lack of biointegration and bacterial infection are concerning with considerable healthcare costs and impacts on patients. To address these limitations, conventional Ti implants need improvements where the use of surface nanoengineering approaches and the development of a new generation of implants are recognized as promising strategies.Areas covered:This review presents an overview of recent progress on the application of surface engineering methods to advance Ti implants enable to address their key limitations. Several promising surface engineering strategies are presented and critically discussed to generate advanced surface properties and nano-topographies (tubular, porous, pillars) able not only to improve their biointegration, antibacterial performances, but also to provide multiple functions such as drug delivery, therapy, sensing, communication and health monitoring underpinning the development of new generation and smart medical implants.Expert opinion:Recent advances in cell biology, materials science, nanotechnology and additive manufacturing has progressively influencing improvements of conventional Ti implants toward the development of the next generation of implants with improved performances and multifunctionality. Current research and development are in early stage, but progressing with promising results and examples of moving into in-vivo studies an translation into real applications.

Titanium dioxide nanotubes as drug carriers for infection control and osteogenesis of bone implants

Titanium implants have been widely used as one of the most effective treatments of bone defects. However, the lack of osteogenesis and bacteria-resistant activities result in high infection and loosening rates of titanium implants. Anodic oxidation could easily construct titanium dioxide nanotubes (TNTs) array on the surface of titanium, and the rough surface of TNTs is beneficial to the growth of osteoblast-related cells on the surface. And TNTs could be excellent drug carriers because of their single-entry tubular hollow structure. In this review, we aim at detailing the application of TNTs as drug carriers in the field of bone implants. Starting from the topography of TNTs, we illustrated the biological activity of the TNTs surface, the drugs for loading in TNTs, and the controlled and responsive release strategies of drug-loaded TNTs, respectively. At the end of this review, the shortcomings of TNTs as the drug carrier in the field of bone implants are discussed, and the development direction of this research field is also prospected.

Bone morphogenetic protein-2 delivery from polyelectrolyte multilayers enhances osteogenic activity on nanostructured titania

Incomplete osseointegration is primary cause of failure for orthopedic implants. New biomaterials that present stable signals promoting osteogenesis could reduce failure rates of orthopedic implants. In this study bone morphogenetic protein-2 (BMP-2) was delivered from titania nanotubes (Nt) modified with chitosan/heparin polyelectrolyte multilayers (PEMs). The surfaces were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. BMP-2 release from the surfaces was measured in vitro for up to 28 days. After an initial burst release of BMP-2 during the first 2 days, most of the BMP-2 remained on the surface. To determine the osteogenic properties of these surfaces, they were seeded with rat bone marrow cells; alkaline phosphatase (ALP) activity, total protein, calcium deposition, and osteocalcin were measured up to 4 weeks in vitro. When compared to Nt surfaces, the surfaces with BMP-2 induce greater osteocalcin and calcium deposition. PEMs provide sustained presentation of BMP-2, from a biomimetic surface. This enhances the osteogenic properties of the surface without requiring supraphysiologic growth factor dose. This growth factor delivery strategy could be used to improve bone healing outcomes and reduce complications for recipients of orthopedic implants.

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.

Modulation of bone formation and resorption using a novel zoledronic acid loaded gelatin nanoparticles integrated porous titanium scaffold: an in vitro and in vivo study

Osteoporotic bone defects are a major challenge in clinics for bone regeneration. With the condition of osteoporosis, excessive bone absorption and impaired osteogenesis result in unexpectedly long healing procedures for defects. In order to simultaneously enhance bone formation and reduce bone resorption, a polydopamine-coated porous titanium scaffold was designed, to be integrated with anti-catabolic drug zoledronic acid nanoparticles (ZOL loaded gelatin NPs), which was able to achieve a local sustained release of ZOL as expected. The in vitro study demonstrated that extracts of the composite scaffolds would stimulate osteoblast differentiation; they also inhibited osteoclastogenesis at a ZOL loading concentration of 50 μmol l^-1. In the subsequent in vivo study, the composite scaffolds were implanted into ovariectomy-induced osteoporotic rabbits suffering from femoral condyles defects. The results indicated that the composite scaffolds without ZOL loaded gelatin NPs only induced callus formation, mainly at the interface margin between the implant and bone, whereas the composite scaffolds with ZOL loaded gelatin NPs were capable of further enhancing osteogenesis and bone growth into the scaffolds. Moreover, the research proved that the promoting effect was optimal at a ZOL loading concentration of 50 μmol l^-1. In summary, the present research indicated that a new type of porous titanium scaffold integrated with ZOL loaded gelatin NPs inherited a superior biocompatibility and bone regeneration capability. It would be an optimal alternative for the reconstruction of osteoporosis-related defects compared to a traditional porous titanium implant; in other words, the new type of scaffold offers a new effective and practical procedure option for patients suffering from osteoporotic bone defects.

IL-4 functionalized titanium dioxide nanotubes modulate the inflammatory response of macrophages

Inflammatory response is an essential part of optimal tissue-implant integration and the regeneration process. Due to their highly plastic properties, macrophages display phenotypic changes during inflammatory signaling. Investigating these changes on implant surfaces is essential for evaluating implant stability and longevity. In order to control macrophage polarization, IL-4 was conjugated to titanium dioxide nanotubes (TNTs) through polydopamine, and successful fabrication was checked by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle, respectively. In vitro experiments including immunofluorescence staining, cell proliferation, the expression of genes associated with pro-inflammatory M1 phenotype (tumor necrosis factor-alpha (TNF-α), Interleukin-18 (IL-18)) and cytokines related to the anti-inflammatory M2 phenotype (IL-4 and IL-10), and the production of nitric oxide (NO) and cytokines TNF-α, IL-10 were detected. Macrophage response showed that IL-4 functionalized TNTs favored macrophage polarization towards an anti-inflammatory M2-phenotype. This study provides a new strategy for use in medical devices and the development of advanced nano-biomaterials in immunotherapy applications.

The sustained release of dexamethasone from TiO2 nanotubes reinforced by chitosan to enhance osteoblast function and anti-inflammation activity

Controlling macrophage response to biomaterials is critical for the reduction of inflammation after implantation. Here we designed a sustained release system from TiO₂ nanotubes (TNTs) to improve osteogenesis on titanium implants with anti-inflammatory properties. TNTs (around 70 nm diameter) were first fabricated on titanium surfaces by anodization, directly filled with the anti-inflammatory drug, dexamethasone (DEX) and then covered by chitosan (CHI) multilayer films. Primary osteoblast and macrophage (RAW 264.7) cells were cultured on untreated and treated titanium surfaces in vitro. Osteoblasts grown on CHI-coated Dex-filled TNTs surfaces displayed higher alkaline phosphatase (ALP) and mineralization, which was consistent with qRT-PCR analysis of osteoblastic genes including collagen type I (Col I), osteocalcin (OCN), osteopontin (OPN) and runt related transcription factor 2 (Runx2). In contrast, protein levels of nitric oxide (NO) and proinflammatory cytokines (TNF-α and IL-1β) from macrophages on Dex-filled TNTs, CHI-coated TNTs and CHI-coated Dex-filled TNTs were significantly lower, especially on CHI-coated Dex-filled TNTs surfaces compared to levels on titanium and TNTs. These results indicate that CHI-coated Dex-filled TNTs enhanced osteoblast differentiation and decreased the inflammatory response of macrophages. The approach presented here provides new insight into the modification of TNTs for the development of titanium-based implants.

Immobilization of Growth Factors for Cell Therapy Manufacturing

Cell therapy products exhibit great therapeutic potential but come with a deterring price tag partly caused by their costly manufacturing processes. The development of strategies that lead to cost-effective cell production is key to expand the reach of cell therapies. Growth factors are critical culture media components required for the maintenance and differentiation of cells in culture and are widely employed in cell therapy manufacturing. However, they are expensive, and their common use in soluble form is often associated with decreased stability and bioactivity. Immobilization has emerged as a possible strategy to optimize growth factor use in cell culture. To date, several immobilization techniques have been reported for attaching growth factors onto a variety of biomaterials, but these have been focused on tissue engineering. This review briefly summarizes the current landscape of cell therapy manufacturing, before describing the types of chemistry that can be used to immobilize growth factors for cell culture. Emphasis is placed to identify strategies that could reduce growth factor usage and enhance bioactivity. Finally, we describe a case study for stem cell factor.

Drug Delivery Systems Based on Titania Nanotubes and Active Agents for Enhanced Osseointegration of Bone Implants

TiO2 nanotubes (TNTs) are attractive nanostructures for localized drug delivery. Owing to their excellent biocompatibility and physicochemical properties, numerous functionalizations of TNTs have been attempted for their use as therapeutic agent delivery platforms. In this review, we discuss the current advances in the applications of TNT-based delivery systems with an emphasis on the various functionalizations of TNTs for enhancing osteogenesis at the bone-implant interface and for preventing implant-related infection. Innovation of therapies for enhancing osteogenesis still represents a critical challenge in regeneration of bone defects. The overall concept focuses on the use of osteoconductive materials in combination with the use of osteoinductive or osteopromotive factors. In this context, we highlight the strategies for improving the functionality of TNTs, using five classes of bioactive agents: growth factors (GFs), statins, plant derived molecules, inorganic therapeutic ions/nanoparticles (NPs) and antimicrobial compounds.

Icariin/Aspirin Composite Coating on TiO2 Nanotubes Surface Induce Immunomodulatory Effect of Macrophage and Improve Osteoblast Activity

Surface coating modification of titanium-based alloys is an efficient way to accelerate early osseointegration in dental implant fields. Icariin (ICA) is a traditional Chinese medicine that has bone activating functions, while aspirin (ASP) is a classical non-steroidal anti-inflammatory drug with good antipyretic and analgesic capabilities. Moreover, poly(lactic–co–glycolic acid) (PLGA) has attracted great attention due to its excellent biocompatibility and biodegradability. We superimposed an ASP/PLGA coating onto ICA loaded TiO2 nanotubes structure so as to establish an icariin/aspirin composite coating on TiO2 nanotubes surface. Scanning electron microscopy, X-ray photoelectron spectroscopy, a contact angle test and a drug release test confirmed the successful preparation of the NT–ICA–ASP/PLGA substrate, with a sustained release pattern of both ICA and ASP. Compared to those cultured on the Ti surface, macrophage cells on the NT-ICA-ASP/PLGA substrate displayed decreased M1 proinflammatory and enhanced M2 proregenerative genes and proteins expression, which implied activated immunomodulatory effect. Moreover, when cultured with conditioned medium from macrophages, osteoblast cells on the NT-ICA-ASP/PLGA substrate revealed improved cell proliferation, adhesion and osteogenic genes and proteins expression, compared with those on the Ti surface. The abovementioned results suggest that the established NT-ICA-ASP/PLGA substrate is a promising candidate for functionalized coating material in Ti implant surface modification.

Nonwoven fabric supported, chitosan membrane anchored with curcumin/TiO2 complex: Scaffolds for MRSA infected wound skin reconstruction

Use of biomaterial scaffolds as drug carriers for infected wounds treatment is of wide scope. A series of curcumin/TiO₂ complex loaded chitosan scaffolds are fabricated for the same. Synthesized wound dressing material is screened for their morphology, water absorption capacity; in vitro drug release patterns, in vitro antibacterial studies against gram +ve and a gram -ve bacteria, cell viability for 3T3-L1 cell lines as well as in vivo MRSA infected wound healing capability. Formation of curcumin/TiO₂ complex was confirmed by X-ray diffraction studies, the anchoring pattern of them on the chitosan scaffold was analyzed by FESEM and EDS mapping. All membranes showed a better performance towards in vitro antibacterial and in vivo wound healing properties than the control ones in 14 days. The bacterial count on wound for a regular time period was measured and the scaffold with higher amount of curcumin in its complex is found to give the better performance, along with skin regeneration due to synergistic effect of curcumin and TiO₂.

Construction of Complex Structures Containing Micro-Pits and Nano-Pits on the Surface of Titanium for Cytocompatibility Improvement

The surface topography of medical implants plays an important role in the regulation of cellular responses. Microstructure and nanostructure surfaces have been proved to enhance cell spreading and proliferation with respect to smooth surfaces. In this study, we fabricated a new structure including micro-pits and nano-pits on the surface of titanium via sandblasting, acid etching and chemical oxidation to investigate the influence of composite structures on cell behavior. Meanwhile, the surface properties and corrosion resistance of treated samples were also tested. The micro/nanostructured titanium surface comprising of micro-pits and nano-pits presented enhanced roughness and hydrophilicity. In addition, the corrosion resistance of the titanium substrate with micro-pits and nano-pits was significantly improved compared to that of polished titanium. More importantly, the micro/nanostructured titanium surface proved a good interfacial environment to promote osteoblast functions such as cell adhesion and spreading. Taken together, these results showed that the construction of micro/nanostructure on the titanium surface is an effective modification strategy to improve osteoblast cell responses.

Polydopamine coating promotes early osteogenesis in 3D printing porous Ti6Al4V scaffolds

BACKGROUND

Titanium implants are widely used in orthopedic and dental for more than 30 years. Its stable physicochemical properties and mechanical strength are indeed appropriate for implantation. However, the Bioinertia oxidized layer and higher elastic modulus often lead to the early implantation failure.

METHODS

In this study, we proposed a simple design of porous structure to minimize the disparity between scaffold and natural bone tissue, and introduced a one-step reaction to form a polydopamine (PDA) layer on the surface of titanium for the purpose of improving osteogenesis as well. The porous scaffolds with pore size of 400 µm and porosity of 44.66% were made by additive manufacturing. The cell behavior was tested by seeding MC3T3-E1 cells on Ti6Al4V films for 15 days. The biomechanical properties were then analyzed by finite element (FE) method and the in vivo osteogenesis effect was accordingly evaluated by implanting the scaffolds for 5 weeks in rabbits.

RESULTS

According to the achieved results, it was revealed that the immersion for 40 min with dopamine could significantly improve the cell adhesion. The proposed method for design of porous structure can avoid the stress shielding effect and bone growth inside the PDA coating scaffolds, which were observed at the early stage of bone healing process.

CONCLUSIONS

It can be concluded that the proposed PDA coating method is effective in promoting early osteogenesis, as well as being easy to operate, and can be helpful in the future clinical application of titanium implants.

Adsorption of DNA by using polydopamine modified magnetic nanoparticles based on solid-phase extraction

A polydopamine magnetic composite (PDA@Fe₃O₄) was prepared for the extraction of human genomic DNA and characterized by transmission electron microscopy, X-ray diffraction, FT-IR spectrometer, zeta potential and vibrating sample magnetometry. PDA@Fe₃O₄ based on magnetic solid phase extraction (MSPE) method have highly efficient capture of genomic deoxyribonucleic acid (DNA)and gene fragments ranging from about 100 bp to 200 bp. Compared with commercial beads (Shenggong, China) and spin column nucleic acid extraction kit (Tiangen, China), the PDA coated magnetic nanoparticles display superior genomic DNA extraction capacity (116 mg/g) and yield (90.2%). The isolation protocol used the solutions (composed of PEG and NaCl) with a specific pH for the binding and release of DNA. The procedure can be attributed to the charge switch of amino and hydroxyl groups on surface of the magnetic particle. The extracted DNA with high quality (A260/A280 = 1.82 ± 0.04) can be directly used as template for polymerase chain reaction (PCR) followed by agarose gel electrophoresis. The results showed the new composite to be an ideal adsorbent for separation of DNA which had the advantage of its low cost, high extraction capacity and yield.

Surface Immobilization of TiO2 Nanotubes with Bone Morphogenetic Protein-2 Synergistically Enhances Initial Preosteoblast Adhesion and Osseointegration

Although titanium (Ti) alloys have been widely used as implant materials, the bioinertness of pristine Ti impairs their bioactivity and early osseointegration. In the present work, we prepared TiO₂ nanotubes (TNT) layer on the titanium (Ti) surface by anodic oxidation. The anodized surface was functionalized with human bone morphogenetic protein-2 coating to form the hBMP-2/TNT surface. The release behavior of hBMP-2 on the hBMP-2/TNT surface displayed a controlled and sustained pattern, compared to that on the hBMP-2/Ti surface, which showed a rapid release. In vitro cellular activity tests demonstrated that both TNT and hBMP-2/Ti surfaces, particularly the hBMP-2/TNT surface, enhanced adhesion, proliferation, and differentiation of osteoblast cells. Increased cell adhesion, improved cytoskeleton organization, and immunofluorescence staining of vinculin were observed on the modified surfaces. The TNT, hBMP-2/Ti, and hBMP-2/TNT surfaces, especially the hBMP-2/TNT surface, further displayed an upregulated gene expression of adhesion and osteogenic markers vinculin, collagen type 1, osteopontin, and osteocalcin, compared to the pristine Ti surface. In vivo experiments using a rat model demonstrated that the TNT and hBMP-2/Ti surfaces, in particular the hBMP-2/TNT surface, improved osseointegration and showed a superior bone bonding ability compared to Ti. Our study revealed a synergistic role played by TiO₂ nanotubes nanotopography and hBMP-2 in promoting initial osteoblast adhesion, proliferation, differentiation, and osseointegration, thus suggesting a promising method for better modifying the implant surface.

Engineered titanium implants for localized drug delivery: recent advances and perspectives of Titania nanotubes arrays

INTRODUCTION

Therapeutics delivery to bones to treat skeletal diseases or prevent postsurgical infections is challenging due to complex and solid bone structure that limits blood supply and diffusion of therapeutics administered by systemic routes to reach effective concentration. Titanium (Ti) and their alloys are employed as mainstream implant materials in orthopedics and dentistry; having superior mechanical/biocompatibility properties which could provide an alternative solution to address this problem.

AREAS COVERED

This review presents an overview of recent development of Ti drug-releasing implants, with emphasis on nanoengineered Titania nanotubes (TNTs) structures, for solving key problems to improve implants osseointegration, overcome inflammation and infection together with providing localized drug delivery (LDD) for bone diseases including cancer. Critical analysis of the advantages/disadvantages of developed concepts is discussed, their drug loading/releasing performances and specific applications.

EXPERT OPINION

LDD to bones can address many disorders and postsurgical conditions such as inflammation, implants rejection and infection. To this end, TNTs-Ti implants represent a potential promise for the development of new generation of multifunctional implants with drug release functions. Even this concept is extensively explored recently, there is a strong need for more preclinical studies using animal models to confirm the long-term safety and stability of TNTs-Ti implants for real-life medical applications.

Simple and facile preparation of recombinant human bone morphogenetic protein-2 immobilized titanium implant via initiated chemical vapor deposition technique to promote osteogenesis for bone tissue engineering application

Over the past few decades, titanium (Ti) implants have been widely used to repair fractured bones. To promote osteogenesis, immobilization of osteoinductive agents, such as recombinant human bone morphogenic protein-2 (rhBMP2), onto the Ti surface is required. In this study, we prepared rhBMP2 immobilized on glycidyl methacrylate (GMA) deposited Ti surface through initiated chemical vapor deposition (iCVD) technique. After preparation, the bio-functionalized Ti surface was characterized by physicochemical analysis. For in vitro analysis, the developed Ti was evaluated by cell proliferation, alkaline phosphatase activity, calcium deposition, and real-time polymerase chain reaction to verify their osteogenic activity against human adipose-derived stem cells (hASCs). The GMA deposited Ti surface was found to effectively immobilize a large dose of rhBMP2 as compared to untreated Ti. Additionally, rhBMP2 immobilized on Ti showed significantly enhanced osteogenic differentiation and increased calcium deposition with nontoxic cell viability. These results clearly confirm that our strategy may provide a simple, solvent-free strategy to prepare an osteoinductive Ti surface for bone tissue engineering applications.

Exosome-integrated titanium oxide nanotubes for targeted bone regeneration

Exosomes are extracellular nanovesicles that play an important role in cellular communication. The modulatory effects of bone morphogenetic protein 2 (BMP2) on macrophages have encouraged the functionalization of scaffolds through the integration of the exosomes from the BMP2-stimulated macrophages to avoid ectopic bone formation and reduce adverse effects. To determine the functionality of exosomal nanocarriers from macrophages after BMP2 stimulation, we isolated the exosomes from Dulbecco's modified Eagle's medium (DMEM)- or BMP2-stimulated macrophages and evaluated their effects on osteogenesis. Morphological characterization of the exosomes derived from DMEM- or BMP2-treated macrophages revealed no significant differences, and the bone marrow-derived mesenchymal stromal cells showed similar cellular uptake patterns for both exosomes. In vitro study using BMP2/macrophage-derived exosomes indicated their beneficial effects on osteogenic differentiation. To improve the bio-functionality for titanium implants, BMP2/macrophage-derived exosomes were used to modify titanium nanotube implants to favor osteogenesis. The incorporation of BMP2/macrophage-derived exosomes dramatically increased the expression of early osteoblastic differentiation markers, alkaline phosphatase (ALP) and BMP2, indicative of the pro-osteogenic role of the titanium nanotubes incorporated with BMP2/macrophage-derived exosomes. The titanium nanotubes functionalized with BMP2/macrophage-derived exosomes activated autophagy during osteogenic differentiation. In conclusion, the exosome-integrated titanium nanotube may serve as an emerging functional material for bone regeneration. STATEMENT OF SIGNIFICANCE: The clinical application of bone morphogenetic protein 2 (BMP2) is often limited by its side effects. Exosomes are naturally secreted nanosized vesicles derived from cells and play an important role in intercellular communication. The contributions of this study include (1) the demonstration of the potential regulatory role of BMP2/macrophage-derived exosomes on the osteogenic differentiation of mesenchymal stromal cells (MSCs); (2) fabrication of titanium nanotubes incorporated with exosomes; (3) new insights into the application of titanium nanotube-based materials for the safe use of BMP2.

One-step deposition of antibacterial Ag@Pdop hybrid films on an NiTi alloy

In this study, by one-step immersion, silver aggregates enwrapped in a polydopamine (Pdop) film (Ag@Pdop hybrid film) were deposited onto a nickel–titanium (NiTi) surface. The Ag aggregates in the Ag@Pdop hybrid films were formed through burst formation, following the Ostwald ripening and oriented attachment of Ag nanoparticles (NPs). As the coating time was increased, thickening of the Pdop film covered on the Ag aggregates could affect the antibacterial ability and biocompatibility of the Ag@Pdop hybrid films. When comprehensively comparing the experimental results, the film prepared for 12 h (Ag@12Pdop) exhibited excellent antibacterial activity against Staphylococcus aureus (S. aureus) and ideal cytocompatibility with human bone mesenchymal stem cells (hBMSCs). In addition, Ag@12Pdop exhibited better anticorrosion performance than polished NiTi in Hank's solution. Meanwhile, Ag@12Pdop showed sustainable Ag release and effectively inhibited the leaching of nickel (Ni) from the NiTi substrate. In this study, a simple method to fabricate Ag-containing films has been presented. The Ag@Pdop hybrid film may be able to significantly prevent infections induced by implantations.

Ag@12Pdop modified NiTi was fabricated by one-step immersion method; it exhibited strong antibacterial activity, enhanced anticorrosion performance, and ideal cytocompatibility.

The controlled naringin release from TiO2 nanotubes to regulate osteoblast differentiation

To design titanium (Ti)-based biomaterials with controlled drug-releasing bioactive property, TiO2 nanotubes with a diameter of approximately 110 nm was fabricated by electrochemical anodization. TiO2 nanotubes were then loaded with naringin by direct dropping and coated with chitosan layers. The surface morphologies, chemical compositions and wettability of different substrates were characterized by field emission scanning electron microscopy, atomic force microscope, X-ray photoelectron spectroscopy and contact angle measurement, respectively. The in vitro release behavior of naringin was evaluated by UV-visible-spectrophotometer. The biological properties of osteoblasts on different substrates were investigated in vitro. Our results indicate that the chitosan-coated naringin-loaded TiO2 nanotubes enhanced osteoblast spreading, proliferation, alkaline phosphatase activity and late-stage osteoblast mineralization. This study provides a platform to help enhance osteointegration between the bone and implant surface in clinical applications.

Effects of aspirin-loaded graphene oxide coating of a titanium surface on proliferation and osteogenic differentiation of MC3T3-E1 cells

Graphene oxide (GO) has attracted considerable attention for biomedical applications such as drug delivery because of its two-dimensional structure, which provides a large surface area on both sides of the nanosheet. Here, a new method for titanium (Ti) surface modification involving a GO coating and aspirin (A) loading (A/Ti-GO) was developed, and the bioactive effects on mouse osteoblastic MC3T3-E1 cells were preliminarily studied. The X-ray photoelectron spectrometry indicated new C-O-N, C-Si-O-C, and C-N=C bond formation upon GO coating. Remarkably, the torsion test results showed stable bonding between the GO coating and Ti under a torsional shear force found in clinical settings, in that, there was no tearing or falling off of GO coating from the sample surface. More importantly, through π-π stacking interactions, the release of aspirin loaded on the surface of Ti-GO could sustain for 3 days. Furthermore, the A/Ti-GO surface displayed a significantly higher proliferation rate and differentiation of MC3T3-E1 cells into osteoblasts, which was confirmed by a water-soluble tetrazolium salt-8 (WST-8) assay and alkaline phosphatase activity test. Consequently, Ti surface modification involving GO coating and aspirin loading might be a useful contribution to improve the success rate of Ti implants in patients, especially in bone conditions.

Mesoporous Titanium Dioxide: Synthesis and Applications in Photocatalysis, Energy and Biology

Mesoporous materials are materials with high surface area and intrinsic porosity, and therefore have attracted great research interest due to these unique structures. Mesoporous titanium dioxide (TiO₂) is one of the most widely studied mesoporous materials given its special characters and enormous applications. In this article, we highlight the significant work on mesoporous TiO₂ including syntheses and applications, particularly in the field of photocatalysis, energy and biology. Different synthesis methods of mesoporous TiO₂-including sol⁻gel, hydrothermal, solvothermal method, and other template methods-are covered and compared. The applications in photocatalysis, new energy batteries and in biological fields are demonstrated. New research directions and significant challenges of mesoporous TiO₂ are also discussed.

The response of bone cells to titanium surfaces modified by simvastatin-loaded multilayered films

The aim of this study was to enhance cytocompatibility of titanium substrates by loading a multilayer film of chitosan (Chi), gelatin (Gel) and simvastatin (SV). This was fabricated using a spin-assisted layer-by-layer (LBL) technique. The surface properties of the different substrates were characterized by field emission scanning electron microscopy (FE-SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurement, respectively. Simvastatin release in vitro was measured by ultraviolet-visible spectrophotometer. A well morphology with filopodia extensions was observed in mesenchymal stem cells (MSCs) grown on simvastatin loaded multilayered films-modified titanium substrates. After 7, 14 and 21 days of culture, the simvastatin loaded multilayered films increased cell proliferation, improved osteoblastic differentiation of alkaline phosphatase (ALP) and mineralization. Additionally, osteoclast diffentiation marker tartrate-resistant acid phosphatase (TRAP) was decreased in simvastatin loaded multilayered films. This study provides a new insight for the fabrication of titanium-based implants to enhance osseointegration especially for osteoporosis patients in orthopedic application.