The Role of Nanomaterials in Diagnosis and Targeted Drug Delivery

Nanomaterials have evolved into the most useful resources in all spheres of life. Their small size imparts them with unique properties and they can also be designed and engineered according to the specific need. The use of nanoparticles (NPs) in medicine is particularly quite revolutionary as it has opened new therapeutic avenues to diagnose, treat and manage diseases in an efficient and timely manner. The review article presents the biomedical applications of nanomaterials including bioimaging, magnetic hypothermia and photoablation therapy, with a particular focus on disease diagnosis and targeted drug delivery. Nanobiosensors are highly specific and can be delivered into cells to investigate important biomarkers. They are also used for targeted drug delivery and deliver theranostic agents to specific sites of interest. Other than these factors, the review also explores the role of nano-based drug delivery systems for the management and treatment of nervous system disorders, tuberculosis and orthopaedics. The nano-capsulated drugs can be transported by blood to the targeted site for a sustained release over a prolonged period. Some other applications like their role in invasive surgery, photodynamic therapy and quantum dot imaging have also been explored. Despite that, the safety concerns related to nanomedicine are also pertinent to comprehend as well as the biodistribution of NPs in the body and the mechanistic insight.

An injectable tricalcium silicate/α-tricalcium phosphate/hydroxypropyl methylcellulose biocomposite with improved physicochemical properties and osteoinductive activity for endodontic application

Tricalcium silicate (TCS)-based bioactive cements have attracted great attention for various endodontic applications owing to their hydraulic property, sealing ability and biological properties. Nevertheless, poor handling property and anti-washout ability are the main challenges for traditional TCS-based cements and their osteoinductive capacity needs enhance for accelerated pulpal and periapical tissue repair/regeneration. Herein, we developed an injectable TCS/α-tricalcium phosphate (α-TCP)/hydroxypropyl methylcellulose (HPMC) biocomposite with improved physicochemical properties and osteoinductive ability via the incorporation of α-TCP/HPMC. HPMC endowed TCS/α-TCP cements excellent injectablity (above 93 %) and anti-washout property. The introduction of 10 wt% α-TCP shortened the setting time of cements and obtained high compressive strength while an excess quantity of α-TCP could compromise its setting property. TCS/α-TCP/HPMC cements had good apatite formation ability and dentin interface adhesion. Moreover, TCS/10α-TCP/HPMC could significantly enhance cell viability and osteogenic differentiation of osteoblasts by increasing alkaline phosphatase (ALP) activity, collagen secretion, and extracellular matrix (ECM) mineralization and up-regulating the osteogenesis-related proteins and gene expression. These results indicated that the injectable TCS/10α-TCP/HPMC biocomposite is a promising candidate for endodontic uses.

Polyaptamer-Driven Crystallization of Alendronate for Synergistic Osteoporosis Treatment through Osteoclastic Inhibition and Osteogenic Promotion

Osteoclastic inhibition using antiresorptive bisphosphonates and osteogenic promotion using antisclerostin agents represent two distinct osteoporosis treatments in clinical practice, each individual treatment suffers from unsatisfactory therapeutic efficacy due to its indirect intervention in osteoclasis and promotion of osteogenesis simultaneously. Although this issue is anticipated to be resolved by drug synergism, a tempting carrier-free dual-medication nanoassembly remains elusive. Herein, we prepare such a nanoassembly made of antiresorptive alendronate (ALN) crystal and antisclerostin polyaptamer (Apt) via a nucleic acid-driven crystallization method. This nanoparticle can protect Apt from rapid nuclease degradation, avoid the high cytotoxicity of free ALN, and effectively concentrate in the cancellous bone by virtue of the bone-binding ability of DNA and ALN. More importantly, the acid microenvironment of cancellous bone triggers the disassociation of nanoparticles for sustained drug release, from which ALN inhibits the osteoclast-mediated bone resorption while Apt promotes osteogenic differentiation. Our work represents a pioneering demonstration of nucleic acid-driven crystallization of a bisphosphonate into a tempting carrier-free dual-medication nanoassembly. This inaugural advancement augments the antiosteoporosis efficacy through direct inhibition of osteoclasis and promotion of osteogenesis simultaneously and establishes a paradigm for profound understanding of the underlying synergistic antiosteoporosis mechanism of antiresorptive and antisclerostin components. It is envisioned that this study provides a highly generalizable strategy applicable to the tailoring of a diverse array of DNA-inorganic nanocomposites for targeted regulation of intricate pathological niches.

Nano-Based Approaches in Surface Modifications of Dental Implants: A Literature Review

Rehabilitation of fully or partially edentulous patients with dental implants represents one of the most frequently used surgical procedures. The work of Branemark, who observed that a piece of titanium embedded in rabbit bone became firmly attached and difficult to remove, introduced the concept of osseointegration and revolutionized modern dentistry. Since then, an ever-growing need for improved implant materials towards enhanced material-tissue integration has emerged. There is a strong belief that nanoscale materials will produce a superior generation of implants with high efficiency, low cost, and high volume. The aim of this review is to explore the contribution of nanomaterials in implantology. A variety of nanomaterials have been proposed as potential candidates for implant surface customization. They can have inherent antibacterial properties, provide enhanced conditions for osseointegration, or act as reservoirs for biomolecules and drugs. Titania nanotubes alone or in combination with biological agents or drugs are used for enhanced tissue integration in dental implants. Regarding immunomodulation and in order to avoid implant rejection, titania nanotubes, graphene, and biopolymers have successfully been utilized, sometimes loaded with anti-inflammatory agents and extracellular vesicles. Peri-implantitis prevention can be achieved through the inherent antibacterial properties of metal nanoparticles and chitosan or hybrid coatings bearing antibiotic substances. For improved corrosion resistance various materials have been explored. However, even though these modifications have shown promising results, future research is necessary to assess their clinical behavior in humans and proceed to widespread commercialization.

An Overview of Hydrothermally Synthesized Titanate Nanotubes: The Factors Affecting Preparation and Their Promising Pharmaceutical Applications

Recently, titanate nanotubes (TNTs) have been receiving more attention and becoming an attractive candidate for use in several disciplines. With their promising results and outstanding performance, they bring added value to any field using them, such as green chemistry, engineering, and medicine. Their good biocompatibility, high resistance, and special physicochemical properties also provide a wide spectrum of advantages that could be of crucial importance for investment in different platforms, especially medical and pharmaceutical ones. Hydrothermal treatment is one of the most popular methods for TNT preparation because it is a simple, cost-effective, and environmentally friendly water-based procedure. It is also considered as a strong candidate for large-scale production intended for biomedical application because of its high yield and the special properties of the resulting nanotubes, especially their small diameters, which are more appropriate for drug delivery and long circulation. TNTs' properties highly differ according to the preparation conditions, which would later affect their subsequent application field. The aim of this review is to discuss the factors that could possibly affect their synthesis and determine the transformations that could happen according to the variation of factors. To fulfil this aim, relevant scientific databases (Web of Science, Scopus, PubMed, etc.) were searched using the keywords titanate nanotubes, hydrothermal treatment, synthesis, temperature, time, alkaline medium, post treatment, acid washing, calcination, pharmaceutical applications, drug delivery, etc. The articles discussing TNTs preparation by hydrothermal synthesis were selected, and papers discussing other preparation methods were excluded; then, the results were evaluated based on a careful reading of the selected articles. This investigation and comprehensive review of different parameters could be the answer to several problems concerning establishing a producible method of TNTs production, and it might also help to optimize their characteristics and then extend their application limits to further domains that are not yet totally revealed, especially the pharmaceutical industry and drug delivery.

Multifunctional electrospun nanofibrous scaffold enriched with alendronate and hydroxyapatite for balancing osteogenic and osteoclast activity to promote bone regeneration

Electrospun composite nanofiber scaffolds are well known for their bone and tissue regeneration applications. This research is focused on the development of PVP and PVA nanofiber composite scaffolds enriched with hydroxyapatite (HA) nanoparticles and alendronate (ALN) using the electrospinning technique. The developed nanofiber scaffolds were investigated for their physicochemical as well as bone regeneration potential. The results obtained from particle size, zeta potential, SEM and EDX analysis of HA nanoparticles confirmed their successful fabrication. Further, SEM analysis verified nanofiber's diameters within 200-250 nm, while EDX analysis confirmed the successful incorporation of HA and ALN into the scaffolds. XRD and TGA analysis revealed the amorphous and thermally stable nature of the nanofiber composite scaffolds. Contact angle, FTIR analysis, Swelling and biodegradability studies revealed the hydrophilicity, chemical compatibility, suitable water uptake capacity and increased in-vitro degradation making it appropriate for tissue regeneration. The addition of HA into nanofiber scaffolds enhanced the physiochemical properties. Additionally, hemolysis cell viability, cell adhesion and proliferation by SEM as well as confocal microscopy and live/dead assay results demonstrated the non-toxic and biocompatibility behavior of nanofiber scaffolds. Alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) assays demonstrated osteoblast promotion and osteoclast inhibition, respectively. These findings suggest that developed HA and ALN-loaded PVP/PVA-ALN-HA nanofiber composite scaffolds hold significant promise for bone regeneration applications.

Synthesis of Titanium Oxide Nanotubes Loaded with Hydroxyapatite

A simple method of synthesis of TiO2 nanotubes (TiNT) loaded with hydroxyapatite (HAP) is described. Such nanotubes find wide applications in various fields, including biomedicine, solar cells, and drug delivery, due to their bioactivity and potential for osseointegration. The Cp-Ti substrate was anodized at a constant voltage of 40 V, with the subsequent heat treatment at 450 °C. The resulting TiNT had a diameter of 100.3 ± 2.8 nm and a length of 3.5 ± 0.04 μm. The best result of the growth rate of HAP in Hanks' balanced salt solution (Hanks' BSS) was obtained in calcium glycerophosphate (CG = 0.1 g/L) when precipitates formed on the bottom and walls of the nanotubes. Structural properties, surface wettability, corrosion resistance, and growth rate of HAP as an indicator of the bioactivity of the coating have been studied. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), potentiodynamic polarization test (PPC), electrochemical impedance spectroscopy (EIS), and contact angle (CA) measurements were used to characterize HAP-loaded nanotubes (HAP-TiNT). The CA, also serving as an indirect indicator of bioactivity, was 30.4 ± 1.1° for the TiNT not containing HAP. The contact angle value for HAP-TiNT produced in 0.1 g/L CG was 18.2 ± 1.2°, and for HAP-TiNT exposed to Hanks' BSS for 7 days, the CA was 7.2 ± 0.5°. The corrosion studies and measurement of HAP growth rates after a 7-day exposure to Hanks' BSS confirmed the result that TiNT processed in 0.1 g/L of CG exhibited the most significant capacity for HAP formation compared to the other tested samples.

Bisphosphonate-incorporated coatings for orthopedic implants functionalization

Bisphosphonates (BPs), the stable analogs of pyrophosphate, are well-known inhibitors of osteoclastogenesis to prevent osteoporotic bone loss and improve implant osseointegration in patients suffering from osteoporosis. Compared to systemic administration, BPs-incorporated coatings enable the direct delivery of BPs to the local area, which will precisely enhance osseointegration and bone repair without the systemic side effects. However, an elaborate and comprehensive review of BP coatings of implants is lacking. Herein, the cellular level (e.g., osteoclasts, osteocytes, osteoblasts, osteoclast precursors, and bone mesenchymal stem cells) and molecular biological regulatory mechanism of BPs in regulating bone homeostasis are overviewed systematically. Moreover, the currently available methods (e.g., chemical reaction, porous carriers, and organic material films) of BP coatings construction are outlined and summarized in detail. As one of the key directions, the latest advances of BP-coated implants to enhance bone repair and osseointegration in basic experiments and clinical trials are presented and critically evaluated. Finally, the challenges and prospects of BP coatings are also purposed, and it will open a new chapter in clinical translation for BP-coated implants.

The Gradual Release of Alendronate for the Treatment of Critical Bone Defects in Osteoporotic and Control Rats

Purpose

Osteoporosis is a severe health problem with social and economic impacts on society. The standard treatment consists of the systemic administration of drugs such as bisphosphonates, with alendronate (ALN) being one of the most common. Nevertheless, complications of systemic administration occur with this drug. Therefore, it is necessary to develop new strategies, such as local administration.

Methods

In this study, emulsion/dispersion scaffolds based on W/O emulsion of PCL and PF68 with ALN, containing hydroxyapatite (HA) nanoparticles as the dispersion phase were prepared using electrospinning. Scaffolds with different release kinetics were tested in vitro on the co-cultures of osteoblasts and osteoclast-like cells, isolated from adult osteoporotic and control rats. Cell viability, proliferation, ALP, TRAP and CA II activity were examined. A scaffold with a gradual release of ALN was tested in vivo in the bone defects of osteoporotic and control rats.

Results

The release kinetics were dependent on the scaffold composition and the used system of the poloxamers. The ALN was released from the scaffolds for more than 22 days. The behavior of cells cultured in vitro on scaffolds with different release kinetics was comparable. The difference was evident between cell co-cultures isolated from osteoporotic and control animals. The PCL/HA scaffold show slow degradation in vivo and residual scaffold limited new bone formation inside the defects. Nevertheless, the released ALN supported bone formation in the areas surrounding the residual scaffold. Interestingly, a positive effect of systemic administration of ALN was not proved.

Conclusion

The prepared scaffolds enabled tunable control release of ALN. The effect of ALN was proved in vitro and in in vivo study supported peri-implant bone formation.

How Efficient are Alendronate-Nano/Biomaterial Combinations for Anti-Osteoporosis Therapy? An Evidence-Based Review of the Literature

Osteoporosis is defined as a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. Because of the systemic nature of osteoporosis, the associated escalation in fracture risk affects virtually all skeletal sites. The problem is serious since it is estimated that more than 23 million men and women are at high risk of osteoporotic-like breakages in the European Union. Alendronate (ALN) is the most commonly prescribed oral nitrogen-containing bisphosphonate (BP) for the prevention and the therapy of osteoporosis. This is also one of the most intensely studied drugs in this field. However, ALN is characterized by restricted oral absorption and bioavailability and simultaneously its administration has serious side-effects (jaw osteonecrosis, irritation of the gastrointestinal system, nausea, musculoskeletal pain, and cardiovascular risks). Therefore, delivery systems enabling controlled release and local action of this drug are of great interest, being widely researched and presented in the literature. In this review, we discuss the current trends in the design of various types of alendronate carriers. Our paper is focused on the most recent developments in the field of nano/biomaterials-based systems for ALN delivery, including nano/microformulations, synthetic/natural polymeric and inorganic materials, hydrogel-based materials, scaffolds, coated-like structures, as well as organic-inorganic hybrids. Topics related to the treatment of complex bone diseases including osteoporosis have been covered in several more general reviews; however, the systems for this particular drug have not yet been discussed in detail.

Enhanced healing process of tooth sockets using strontium-doped TiO2

Prevention of residual ridge resorption is important for tooth socket healing in clinical treatment. As a well known biomaterial, titanium dioxide (TiO₂) has been reported to show desirable bone regeneration capability. On the other hand, strontium plays a role in maintaining normal function in organisms and balancing bone remodeling. Hence, we synthesized strontium-doped titanium dioxide mesoporous nanospheres functionalized with amino-group using diphenyl diisocyanate. After incorporation with segmented polyurethane, the obtained injectable SPU/Sr-TiO₂/MDI nanocomposite adhesive showed satisfactory antibacterial activity and cell nontoxicity. This nanocomposite was used for tooth socket healing, and greatly promoted the formation of new bone tissue in the tooth extraction socket.

Histomorphometry of Ossification in Functionalised Ceramics with Tripeptide Arg-Gly-Asp (RGD): An In Vivo Study

The present study investigated the osseointegration promoted by functionalised ceramics with peptide Arg-Gly-Asp (RGD) in a rabbit model in vivo. Histomorphometry of the RGD functionalised ceramic implants was conducted by a trained pathologist to quantify the amount of mature and immature ossification at the bone interface, and then compared to titanium alloy implants. The region of interest was the area surrounding the implant. The percentage of ROI covered by osteoid implant contact and mature bone implant contact were assessed. The presence of bone resorption, necrosis, and/or inflammation in the areas around the implant were quantitatively investigated. All 36 rabbits survived the experimental period of 6 and 12 weeks. All implants remained in situ. No necrosis, bone resorption, or inflammation were identified. At 12 weeks follow-up, the overall mean bone implant contact (p = 0.003) and immature osteoid contact (p = 0.03) were improved compared to the mean values evidenced at 6 weeks. At 6 weeks follow-up, the overall osteoid implant contact was greater in the RGD enhanced group compared to the titanium implant (p = 0.01). The other endpoints of interest were similar between the two implants at all follow-up points (p ≥ 0.05). Functionalised ceramics with peptide RGD promoted ossification in vivo. The overall osteoid and bone implant contact improved significantly from 6 to 12 weeks. Finally, RGD enhanced ceramic promoted faster osteoid implant contact in vivo than titanium implants. Overall, the amount of ossification at 12 weeks is comparable with the titanium implants. No necrosis, bone resorption, or inflammation were observed in any sample.

Construction of Local Drug Delivery System on Titanium-Based Implants to Improve Osseointegration

Titanium and its alloys are the most widely applied orthopedic and dental implant materials due to their high biocompatibility, superior corrosion resistance, and outstanding mechanical properties. However, the lack of superior osseointegration remains the main obstacle to successful implantation. Previous traditional surface modification methods of titanium-based implants cannot fully meet the clinical needs of osseointegration. The construction of local drug delivery systems (e.g., antimicrobial drug delivery systems, anti-bone resorption drug delivery systems, etc.) on titanium-based implants has been proved to be an effective strategy to improve osseointegration. Meanwhile, these drug delivery systems can also be combined with traditional surface modification methods, such as anodic oxidation, acid etching, surface coating technology, etc., to achieve desirable and enhanced osseointegration. In this paper, we review the research progress of different local drug delivery systems using titanium-based implants and provide a theoretical basis for further research on drug delivery systems to promote bone–implant integration in the future.

Simultaneous acceleration of osteogenesis and angiogenesis by surface oxygen vacancies of rutile nanorods

Advanced implants with simultaneous accelerated osteogenic and angiogenic capacities are of great importance for osteointegration. Much attention has been paid to simultaneously enhancing the osteogenesis and angiogenesis by surface decoration of bioactive molecules or ions on biomaterial surface, but the inherent physical cue of material surface down to the atomic-scale features have always been ignored. In this study, we demonstrate that regulation of surface oxygen vacancies defects of rutile nanorods are able to simultaneous accelerate the osteogenesis and angiogenesis. The concentration of surface oxygen vacancies defects of rutile nanorods can be manipulated by simple redox processing. The osteogenic differentiation of mesenchymal stem cells (MSCs), angiogenic differentiation and vessel-like tube structures of human umbilical vein endothelial cells (HUVECs) on oxygen vacancies rich surface are significantly up-regulated. This work therefore emphasizes the critical role of the inherent material atomic-scale features and provides a novel strategy to accelerate the osteogenesis and angiogenesis of Ti-based implant.

Inorganic Nanoparticles in Bone Healing Applications

Modern biomedicine aims to develop integrated solutions that use medical, biotechnological, materials science, and engineering concepts to create functional alternatives for the specific, selective, and accurate management of medical conditions. In the particular case of tissue engineering, designing a model that simulates all tissue qualities and fulfills all tissue requirements is a continuous challenge in the field of bone regeneration. The therapeutic protocols used for bone healing applications are limited by the hierarchical nature and extensive vascularization of osseous tissue, especially in large bone lesions. In this regard, nanotechnology paves the way for a new era in bone treatment, repair and regeneration, by enabling the fabrication of complex nanostructures that are similar to those found in the natural bone and which exhibit multifunctional bioactivity. This review aims to lay out the tremendous outcomes of using inorganic nanoparticles in bone healing applications, including bone repair and regeneration, and modern therapeutic strategies for bone-related pathologies.

A programmed surface on polyetheretherketone for sequentially dictating osteoimmunomodulation and bone regeneration to achieve ameliorative osseointegration under osteoporotic conditions

Polyetheretherketone (PEEK) is a desirable alternative to conventional biomedical metals for orthopedic implants due to the excellent mechanical properties. However, the inherent bioinertness of PEEK contributes to inferior osseointegration of PEEK implants, especially under pathological conditions of osteoporosis. Herein, a programmed surface is designed and fabricated on PEEK to dictate osteoimmunomodulation and bone regeneration sequentially. A degradable hybrid coating consisting of poly(lactide-co-glycolide) and alendronate (ALN) loaded nano-hydroxyapatite is deposited on PEEK and then interleukin-4 (IL-4) is grafted onto the outer surface of the hybrid coating with the aid of N₂ plasma immersion ion implantation and subsequent immersion in IL-4 solution. Dominant release of IL-4 together with ALN and Ca²⁺ during the first few days synergistically mitigates the early acute inflammatory reactions and creates an osteoimmunomodulatory microenvironment that facilitates bone regeneration. Afterwards, slow and sustained delivery of ALN and Ca²⁺ in the following weeks boosts osteogenesis and suppresses osteoclastogenesis simultaneously, consequently ameliorating bone-implant osseointegration even under osteoporotic conditions. By taking into account the different phases in bone repair, this strategy of constructing advanced bone implants with sequential functions provides customizable and clinically viable therapy to osteoporotic patients.

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A programmed surface is designed and fabricated on PEEK to dictate osteoimmunomodulation and bone regeneration sequentially.

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A degradable coating consisting ALN loaded nano-HA is deposited on PEEK, with IL-4 being grafted onto the outmost surface.

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Dominant release of IL-4 together with ALN and Ca²⁺ synergistically mitigates the early acute inflammatory reactions.

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Slow and sustained delivery of ALN and Ca²⁺ boosts osteogenesis and suppresses osteoclastogenesis simultaneously.

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Sequential regulation of peri-implant biological responses is achieved to match the dynamic process of bone regeneration.

Applications of Calcium-Based Nanomaterials in Osteoporosis Treatment

With rapidly aging populations worldwide, osteoporosis has become a serious global public health problem. Caused by disordered systemic bone remodeling, osteoporosis manifests as progressive loss of bone mass and microarchitectural deterioration of bone tissue, increasing the risk of fractures and eventually leading to osteoporotic fragility fractures. As fracture risk increases, antiosteoporosis treatments transition from nonpharmacological management to pharmacological intervention, and finally to the treatment of fragility fractures. Calcium-based nanomaterials (CBNMs) have unique advantages in osteoporosis treatment because of several characteristics including similarity to natural bone, excellent biocompatibility, easy preparation and functionalization, low pH-responsive disaggregation, and inherent pro-osteogenic properties. By combining additional ingredients, CBNMs can play multiple roles to construct antiosteoporotic biomaterials with different forms. This review covers recent advances in CBNMs for osteoporosis treatment. For ease of understanding, CBNMs for antiosteoporosis treatment can be classified as locally applied CBNMs, such as implant coatings and filling materials for osteoporotic bone regeneration, and systemically administered CBNMs for antiosteoporosis treatment. Locally applied CBNMs for osteoporotic bone regeneration develop faster than the systemically administered CBNMs, an important consideration given the serious outcomes of fragility fractures. Nevertheless, many innovations in construction strategies and preparation methods have been applied to build systemically administered CBNMs. Furthermore, with increasing interest in delaying osteoporosis progression and avoiding fragility fracture occurrence, research into systemic administration of CBNMs for antiosteoporosis treatment will have more development prospects. Deep understanding of the CBNM preparation process and optimizing CBNM properties will allow for increased application of CBNMs in osteoporosis treatments in the future.

Controlled release of dopamine coatings on titanium bidirectionally regulate osteoclastic and osteogenic response behaviors

Bone diseases, for example, osteoporosis, cause excessive differentiation of osteoclasts and decreased bone formation, resulting in imbalance of bone remodeling and poor osseointegration, which can be considered a relative contraindication for titanium implants. Dopamine (DA) might provide a solution to this problem by inhibiting osteoclasts and promoting osteoblasts at different concentrations. However, current commercial implants cannot load bone-active molecules, such as DA. Therefore, this study aimed to develop a surface modification method for implants to achieve a controlled release of DA and enhance the resistance of titanium implants to bone resorption and bone regeneration. DA-loaded alginate-arginine-glycine-aspartic acid (RGD) (AlgR) coatings on a vaterite-modified titanium surface were successfully assembled, which continuously and steadily released DA. In vitro studies have shown that materials showing good biocompatibility can not only inhibit receptor activator of nuclear factor-kappa B (NFκB) ligand (RANKL)-induced osteoclastogenesis but also enhance the adhesion and osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs). The optimal DA-loaded concentration of this bidirectional regulation is 100 μM. Interestingly, DA more effectively attenuated osteoclastogenesis when released in a sustained manner from titanium coatings than it did via traditional, free administration, and the alginate-RGD coating and DA clearly exhibited great synergy. This study provides a design of titanium implant surface modification to improve bone remodeling around implants.

Dental Implant Nano-Engineering: Advances, Limitations and Future Directions

Titanium (Ti) and its alloys offer favorable biocompatibility, mechanical properties and corrosion resistance, which makes them an ideal material choice for dental implants. However, the long-term success of Ti-based dental implants may be challenged due to implant-related infections and inadequate osseointegration. With the development of nanotechnology, nanoscale modifications and the application of nanomaterials have become key areas of focus for research on dental implants. Surface modifications and the use of various coatings, as well as the development of the controlled release of antibiotics or proteins, have improved the osseointegration and soft-tissue integration of dental implants, as well as their antibacterial and immunomodulatory functions. This review introduces recent nano-engineering technologies and materials used in topographical modifications and surface coatings of Ti-based dental implants. These advances are discussed and detailed, including an evaluation of the evidence of their biocompatibility, toxicity, antimicrobial activities and in-vivo performances. The comparison between these attempts at nano-engineering reveals that there are still research gaps that must be addressed towards their clinical translation. For instance, customized three-dimensional printing technology and stimuli-responsive, multi-functional and time-programmable implant surfaces holds great promise to advance this field. Furthermore, long-term in vivo studies under physiological conditions are required to ensure the clinical application of nanomaterial-modified dental implants.

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.

Targeting Drug Delivery in the Elderly: Are Nanoparticles an Option for Treating Osteoporosis?

Nanoparticles bearing specific targeting groups can, in principle, accumulate exclusively at lesion sites bearing target molecules, and release therapeutic agents there. However, practical application of targeted nanoparticles in the living organism presents challenges. In particular, intravasally applied nanoparticles encounter physical and physiological barriers located in blood vessel walls, blocking passage from the blood into tissue compartments. Whereas small molecules can pass out of the blood, nanoparticles are too large and need to utilize physiological carriers enabling passage across endothelial walls. The issues associated with crossing blood-tissue barriers have limited the usefulness of nanoparticles in clinical applications. However, nanoparticles do not encounter blood-tissue barriers if their targets are directly accessible from the blood. This review focuses on osteoporosis, a disabling and common disease for which therapeutic strategies are limited. The target sites for therapeutic agents in osteoporosis are located in bone resorption pits, and these are in immediate contact with the blood. There are specific targetable biomarkers within bone resorption pits. These present nanomedicine with the opportunity to treat a major disease by use of simple nanoparticles loaded with any of several available effective therapeutics that, at present, cannot be used due to their associated side effects.

Research to Clinics: Clinical Translation Considerations for Anodized Nano-Engineered Titanium Implants

Titania nanotubes (TNTs) fabricated on titanium orthopedic and dental implants have shown significant potential in "proof of concept" in vitro, ex vivo, and short-term in vivo studies. However, most studies do not focus on a clear direction for future research towards clinical translation, and there exists a knowledge gap in identifying key research challenges that must be addressed to progress to the clinical setting. This review focuses on such challenges with respect to anodized titanium implants modified with TNTs, including optimized fabrication on clinically utilized microrough surfaces, clinically relevant bioactivity assessments, and controlled/tailored local release of therapeutics. Further, long-term in vivo investigations in compromised animal models under loading conditions are needed. We also discuss and detail challenges and progress related to the mechanical stability of TNT-based implants, corrosion resistance/electrochemical stability, optimized cleaning/sterilization, packaging/aging, and nanotoxicity concerns. This extensive, clinical translation focused review of TNTs modified Ti implants aims to foster improved understanding of key research gaps and advances, informing future research in this domain.

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.

Nanotube-decorated hierarchical tantalum scaffold promoted early osseointegration

This study aimed to fabricate a hierarchical tantalum scaffold mimicking natural bone structure to enhance osseointegration. Porous tantalum scaffolds (p-Ta) with microgradients were fabricated by selective laser melting according to a computer-aided design model. Electrochemical anodization produced nanotubes on the p-Ta surface (p-Ta-nt). SEM verified the construction of a unique nanostructure on p-Ta-nt. Contact angle and protein adsorption measurements demonstrated that p-Ta-nt have enhanced hydrophilicity and protein absorption. MC3T3-E1 preosteoblasts showed increased filamentous pseudopods and comparable cell proliferation when cultured on p-Ta-nt. Osteogenic marker gene (Osterix, Runx2, COL-I) transcription was significantly upregulated in MC3T3-E1 cells cultured on p-Ta-nt after 7 days. After implantation into the femurs of New Zealand white rabbits for 2 weeks, histological examination found improved early osseointegration in the p-Ta-nt group. This study showed that a hierarchical tantalum structure could enhance early osteogenic effects in vitro and in vivo.

Additively Manufactured Continuous Cell-Size Gradient Porous Scaffolds: Pore Characteristics, Mechanical Properties and Biological Responses In Vitro

Porous scaffolds with graded open porosity combining a morphology similar to that of bone with mechanical and biological properties are becoming an attractive candidate for bone grafts. In this work, scaffolds with a continuous cell-size gradient were studied from the aspects of pore properties, mechanical properties and bio-functional properties. Using a mathematical method named triply periodic minimal surfaces (TPMS), uniform and graded scaffolds with Gyroid and Diamond units were manufactured by selective laser melting (SLM) with Ti-6Al-4V, followed by micro-computer tomography (CT) reconstruction, mechanical testing and in vitro evaluation. It was found that gradient scaffolds were preferably replicated by SLM with continuous graded changes in surface area and pore size, but their pore size should be designed to be ≥ 450 μm to ensure good interconnectivity. Both the Gyroid and Diamond structures have superior strength compared to cancellous bones, and their elastic modulus is comparable to the bones. In comparison, Gyroid exhibits better performances than Diamond in terms of the elastic modulus, ultimate strength and ductility. In vitro cell culture experiments show that the gradients provide an ideal growth environment for osteoblast growth in which cells survive well and distribute uniformly due to biocompatibility of the Ti-6Al-4V material, interconnectivity and suitable pore size.

Adjuvant Drug-Assisted Bone Healing: Advances and Challenges in Drug Delivery Approaches

Bone defects of critical size after compound fractures, infections, or tumor resections are a challenge in treatment. Particularly, this applies to bone defects in patients with impaired bone healing due to frequently occurring metabolic diseases (above all diabetes mellitus and osteoporosis), chronic inflammation, and cancer. Adjuvant therapeutic agents such as recombinant growth factors, lipid mediators, antibiotics, antiphlogistics, and proangiogenics as well as other promising anti-resorptive and anabolic molecules contribute to improving bone healing in these disorders, especially when they are released in a targeted and controlled manner during crucial bone healing phases. In this regard, the development of smart biocompatible and biostable polymers such as implant coatings, scaffolds, or particle-based materials for drug release is crucial. Innovative chemical, physico- and biochemical approaches for controlled tailor-made degradation or the stimulus-responsive release of substances from these materials, and more, are advantageous. In this review, we discuss current developments, progress, but also pitfalls and setbacks of such approaches in supporting or controlling bone healing. The focus is on the critical evaluation of recent preclinical studies investigating different carrier systems, dual- or co-delivery systems as well as triggered- or targeted delivery systems for release of a panoply of drugs.

Construction of multilayered molecular reservoirs on a titanium alloy implant for combinational drug delivery to promote osseointegration in osteoporotic conditions

In this study, β-cyclodextrin (β-CD) molecules are used as molecular reservoirs and grafted onto chitosan molecules for calcitriol (VD3) loading, which is a hormonally active metabolite of vitamin D. The resultant molecular complex is co-assembled with an antiosteoporosis drug calcitonin (CT) to form bio-functional multilayer structure on Ti6Al7Nb substrate via layer-by-layer self-assembly, which is capable of releasing VD3 and calcitonin in a sustained manner to modulate osteoblasts, osteoclasts, and macrophages at the bone-implant interface. In vitro results show that the released VD3 and CT individually upregulated the expression of calcium-binding protein (including Calbindin D9k and Calbindin D28k) and BMP2 in osteoblasts in peri-implant regions to stimulate their Ca deposition and differentiation. RAW264.7 cells (a murine macrophage) on the biofunctional implant displayed improved M2 phenotypical differentiation and expression of BMP2 and VEGF genes, but M1 phenotypical differentiation potential and MCF and TRAP gene expression levels are evidently lower. Results from in vivo micro-CT and histological analysis also demonstrate that VD3/CT co-loaded implant can dramatically enhance the bone remodeling under osteoporotic conditions with significantly enhanced interfacial shear strength and improved osseointegration as compared to other groups. The insights in this study offer new avenues for the rational functionalization of titanium implants to effectively repair osteoporotic fractures. STATEMENT OF SIGNIFICANCE: A promising strategy to enhance the recovery rate of osteoporotic fractures is to immobilize antiosteoporotic drugs onto the surface of titanium-based implants. In this study, we grafted beta-cyclodextrin (β-CD) onto chitosan (Chi) molecules to load VD3, which was co-assembled with calcitonin (CT) onto Ti6Al7Nb implants by the layer-by-layer assembly technique. The obtained functional titanium alloy implant (Ti6Al7Nb/LBL/Chi-CD@VD3/ CT) could stably release VD3 and calcitonin agents in a sustained manner. RAW264.7 cells grown on Ti6Al7Nb/LBL/Chi-CD@VD3/CT showed superior M2 phenotypical differentiation efficiency, but lower MCF/TRAP gene expression levels. In vitro and in vivo results showed that the released VD3 and CT individually upregulated the expression of calcium binding proteins and BMP2 in osteoblasts, promoting new bone formation in the peri-implant region.

Effects of a Coating of Nano Silicon Nitride on Porous Polyetheretherketone on Behaviors of MC3T3-E1 Cells in Vitro and Vascularization and Osteogenesis in Vivo

To improve the bioperformances of porous polyetheretherketone (PPK) for bone repair, silicon nitride-coated PPK (CSNPPK) was prepared by a method of suspension coating and melt binding. The results revealed that, as compared with PPK, the surface roughness, compressive strength, and water absorption of CSNPPK increased, while the pore size and porosity of CSNPPK exhibited no obvious changes. In addition, the cellular responses (including attachment, proliferation, and differentiation as well as osteogenically related gene expressions) of the MC3T3-E1 cells to CSNPPK were remarkably promoted compared with PPK and dense polyetheretherketone in vitro. Moreover, in the model of rabbit femoral condyle defects, the results of micro computed tomography and histological and mechanical evaluation revealed that the ingrowth of new vessels and bone tissues into CSNPPK was significantly greater than that into PPK in vivo. Furthermore, the load-displacement and push-out loads for CSNPPK with bone tissues were higher than for PPK, indicating good osseointegration. In short, CSNPPK not only promoted vascularization but also enhanced osteogenesis as well as osseointegration in vivo. Therefore, it can be suggested that CSNPPK with good biocompatibility, osteogenic activity, and vascularization might be a promising candidate as an implant for bone substitute and repair.

Promoted Osteoconduction of Polyurethane-Urea Based 3D Nanohybrid Scaffold through Nanohydroxyapatite Adorned Hierarchical Titanium Phosphate

The lack of optimal physiological properties, bacterial colonization, and auto-osteoinduction, are the foremost issues of orthopedic implantations. In terms of bone healing, many researchers have reported the release of additional growth factors of the implanted biomaterials to accelerate the bone regeneration process. However, the additional growth factor may cause side effects such as contagion, nerve pain, and the formation of ectopic bone. Thus, the design of an osteoconductive scaffold having excellent biocompatibility, appropriate physicomechanical properties, and promoted auto osteoinductivity with antibacterial activity is greatly desired. In this study, 2D rodlike nanohydroxyapatite (nHA) adorned titanium phosphate (TP) with a flowerlike morphology was synthesized by a hydrothermal precipitation reaction. The nanohybrid material (nHA-TP) was incorporated into the synthesized polycaprolactone diol and spermine based thermoplastic polyurethane-urea (PUU) via in situ technique followed by salt leaching to fabricate the macroporous 3D polymer nanohybrid scaffold (PUU/nHA-TP). Structure explication of PUU was performed by NMR spectroscopy. The synthesized nanohybrid scaffold with 1% nHA-TP showed 67% increase of tensile strength and 18% improved modulus compared to the pristine PUU via formation of H-bonding or dative bonds between the metal and the amide linkage of the polyurethane or polyurea. In vitro study showing improved cell viability and proliferation of the seeded cell revealed the superior osteoconductivity of the nanohybrid scaffold. Most importantly, the in vivo experiments revealed a significant amount of bone regeneration in the nanohybrid scaffold implanted tibial site compared to the pristine scaffold without any toxic effect. Introduction of the minute amount of titanium phosphate within the adorned nHA promotes the osteoconductivity significantly by the capability of forming coordinate bonds of the titanium ion. Depending on the mechanical, physicochemical, in vitro characteristics, and in vivo osteoconductivity, the PUU/nHA-TP nanohybrid scaffold has great potential as an alternative biomaterial in bone tissue regeneration application.

Functionalization of titanium substrate with multifunctional peptide OGP-NAC for the regulation of osteoimmunology

The immune response to an orthopedic implant is closely related to the nearby bone metabolism balance. To modify titanium (Ti) substrates and accordingly regulate the balance between osteoclast activation and osteoblast differentiation, a multifunctional peptide OGP-NAC was synthesized via conjugating an osteogenic growth peptide (OGP) with N-acetylcysteine (NAC). Then, the synthesized peptide was employed to functionalize Ti substrates and the response of both osteoblasts and osteoclasts was investigated in vitro. The results showed that OGP-NAC was successfully prepared and immobilized onto Ti substrate surfaces. Thereafter, studies on introducing RAW 264.7 cells (one kind of monocyte macrophage responsible for immune responses) to osteoclasts demonstrated that the peptide modified Ti surface could inhibit RAW 264.7 cells from secreting important inflammatory cytokines (TNF-α and IL-1β), and suppress the activation of MAPK, NF-κB and NFAT c1, which are important transcription factors for osteoclastogenesis. Meanwhile, the modified surface promoted osteoblast spreading, proliferation and differentiation. The study offers a feasible strategy to mediate the balance between osteoclast activation and osteoblast differentiation, having great potential for improving osseointegration of an orthopedic implant.

Zn-incorporation with graphene oxide on Ti substrates surface to improve osteogenic activity and inhibit bacterial adhesion

The poor osseointegration and postoperative bacterial infection are prominently responsible for the failure of titanium (Ti)-based implant in clinic. To address above issues, methacryloyl modified graphene oxide (GOMA) as zinc ions (Zn²⁺ ) reservoir and release platform was fabricated on the Ti substrates with cathode electrophoresis deposition (EPD). Afterward, phenylboronic acid (PBA) functionalization methacryloyl-gelatin (GelMA-PBA) was reacting with GOMA through in situ free-radical polymerization to prepare GO-Zn/GelMA-PBA coating. The obtained coating was confirmed by scanning electron microscopy, X-ray photoelectron spectroscopy, and Zn ions release property, respectively. in vitro cellular experiments including cell activity, alkaline phosphatase, collagen secretion, extracellular matrix (ECM) mineralization, osteogenic genes and proteins, revealed that GO-Zn/GelMA-PBA coating was beneficial for enhancing the adhesion, proliferation, and differentiation of osteoblasts. The positive results were related to the existence of gelatin, formation of boronic ester between PBA groups, and carbohydrates of osteoblasts surface. Meanwhile, antibacterial assay against Staphylococcus aureus and Pseudomonas aeruginosa confirmed that GO-Zn/GelMA-PBA coating on Ti substrates had superior antibacterial capacity, availably inhibited the bacterial adhesion, and prevented formation of biofilm. Hence, the study provides a promising strategy for designing pro-osteogenesis and antibacterial coating on Ti substrates for orthopedic applications.

Substitutions of strontium in bioactive calcium silicate bone cements stimulate osteogenic differentiation in human mesenchymal stem cells

Calcium silicate cements have been considered as alternative bone substitutes owing to its extraordinary bioactivity and osteogenicity. Unfortunately, the major disadvantage of the cements was the slow degradation rate which may limit the efficiency of bone regeneration. In this study, we proposed a facile method to synthesize degradable calcium silicate cements by incorporating strontium into the cements through solid-state sintering. The effects of Sr incorporation on physicochemical and biological properties of the cements were evaluated. Although, our findings revealed that the incorporation of strontium retarded the hardening reaction of the cements, the setting time of different cements (11-19 min) were in the acceptable range for clinical use. The presence of Sr in the CS cements would hampered the precipitation of calcium phosphate products on the surface after immersion in SBF, however, a layer of precipitated calcium phosphate products can be formed on the surface of the Sr-CS cement within 1 day immersion in SBF. More importantly, the degradation rate of the cements increased with increasing content of strontium, consequentially raised the levels of released strontium and silicon ions. The elevated dissolving products may contribute to the enhancement of the cytocompatibility, alkaline phosphatase activity, osteocalcin secretion, and mineralization of human Wharton's jelly mesenchymal stem cells. Together, it is concluded that the strontium-incorporated calcium silicate cement might be a promising bone substitute that could accelerate the regeneration of irregularly shaped bone defects.

Functionalization of Ceramic Coatings for Enhancing Integration in Osteoporotic Bone: A Systematic Review

Background: The success of reconstructive orthopaedic surgery strongly depends on the mechanical and biological integration between the prosthesis and the host bone tissue. Progressive population ageing with increased frequency of altered bone metabolism conditions requires new strategies for ensuring an early implant fixation and long-term stability. Ceramic materials and ceramic-based coatings, owing to the release of calcium phosphate and to the precipitation of a biological apatite at the bone-implant interface, are able to promote a strong bonding between the host bone and the implant. Methods: The aim of the present systematic review is the analysis of the existing literature on the functionalization strategies for improving the implant osteointegration in osteoporotic bone and their relative translation into the clinical practice. The review process, conducted on two electronic databases, identified 47 eligible preclinical studies and 5 clinical trials. Results: Preclinical data analysis showed that functionalization with both organic and inorganic molecules usually improves osseointegration in the osteoporotic condition, assessed mainly in rodent models. Clinical studies, mainly retrospective, have tested no functionalization strategies. Registered trademarks materials have been investigated and there is lack of information about the micro- or nano- topography of ceramics. Conclusions: Ceramic materials/coatings functionalization obtained promising results in improving implant osseointegration even in osteoporotic conditions but preclinical evidence has not been fully translated to clinical applications.

Fabrication of magnesium/zinc-metal organic framework on titanium implants to inhibit bacterial infection and promote bone regeneration

The residual bacteria in the second revision surgery caused by infection would further lead to the failure of the implantation. Pathogenic bacteria adhesion to an implant surface not only interfere the functions of bone-formation related cells, but also activate the host immune system, thus resulting in inflammation and osteogenesis inhibition. Thus, to fabricate multifunctional (antibacterial, anti-inflammation and pro-osteogenesis) titanium implants is essential to address this issue. In this work, hybrid magnesium/zinc-metal organic framework (Mg/Zn-MOF74) coating was constructed on alkali-heat treated titanium (AT) surface. The hybrid Mg/Zn-MOF74 coating displayed good stability and its stability was related to the content of Zn²⁺. The MOF74-modified samples were sensitive to bacterial acid microenvironment and displayed strong antibacterial ability against both Escherichia coli and Staphylococcus aureus due to the degradation of MOF74 coating, leading to alkaline microenvironment (about pH 8.0) and degradation products (2,5-dihydroxyterephthalic acid and Zn²⁺). The coating also showed good early anti-inflammatory property to native Ti substrates. In vivo results further verified that AT-Mg/Zn3 implants had high antibacterial and anti-inflammatory properties at early stage of implantation, and greatly improved new bone formation around implants both at non-infected and infected femur sites.

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.

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.

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed.

Chemical Self-Assembly of Multifunctional Hydroxyapatite with a Coral-like Nanostructure for Osteoporotic Bone Reconstruction

Bone defects/fractures are common in older people suffering from osteoporosis. Traditional hydroxyapatite (HA) materials for osteoporotic bone repair face many challenges, including limited bone formation and aseptic loosening of orthopedic implants. In this study, a new multifunctional HA is synthesized by spontaneous assembly of alendronate (AL) and Fe₃O₄ onto HA nanocrystals for osteoporotic bone regeneration. The chemical coordination of AL and Fe₃O₄ with HA does not induce lattice deformation, resulting in a functionalized HA (Func-HA) with proper magnetic property and controlled release manner. The Func-HA nanocrystals have been encapsulated in polymer substrates to further investigate their osteogenic capability. In vitro and in vivo evaluations reveal that both AL and Fe₃O₄, especially the combination of two functional groups on HA, can inhibit osteoclastic activity and promote osteoblast proliferation and differentiation, as well as enhance implant osseointegration and accelerate bone remodeling under osteoporotic condition. The as-developed Func-HA with coordinating antiresorptive ability, magnetic property, and osteoconductivity might be a desirable biomaterial for osteoporotic bone defect/fracture treatment.

N-halamine-based multilayers on titanium substrates for antibacterial application

Bacterial infection is one of the most severe postoperative complications leading to clinical orthopedic implants failure. To improve the antibacterial property of titanium (Ti) substrates, a bioactive coating composed of chitosan-1-(hydroxymethyl)- 5,5-dimethylhydantoin (Chi-HDH-Cl) and gelatin (Gel) was fabricated via layer-by-layer (LBL) assembly technique. The results of Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (¹HNMR) and X-ray photoelectron spectroscopy (XPS) showed that Chi-HHD-Cl conjugate was successfully synthesized. Scanning electron microscopy (SEM), atomic force microscope (AFM) and water contact angle measurements were employed to monitor the morphology, roughness changes and surface wettability of Ti substrates, which proved the multilayers coating formation. Antibacterial assay against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) revealed that the Gel/Chi-HDH-Cl modified Ti substrates most efficiently inhibited the adhesion and growth of bacteria. Meanwhile, in vitro cellular tests confirmed that Gel/Chi-HDH-Cl multilayers had no obvious cytotoxicity to osteoblasts. The study thus provides a promising method to fabricate antibacterial Ti-based substrates for potential orthopedic application.

Fabrication of hyaluronidase-responsive biocompatible multilayers on BMP2 loaded titanium nanotube for the bacterial infection prevention

Infection associated with orthopedic implants is the chief cause of implant failure. An important consideration to prevent the infection at implants is to inhibit the biofilm formation for the initial 6 h. Therefore, we fabricated hyaluronidase-sensitive multilayers of chitosan (Chi)/sodium hyaluronate-lauric acid (SL) onto the surface of bone morphogenetic protein 2 (BMP2) loaded titanium nanotube (TNT) via spin-assisted layer-by-layer technique. The results of both Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR) confirmed the successful synthesis of SL. The multilayer structure on BMP2 loaded TNT was characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and water contact angle, respectively. The release profiles confirmed that hyaluronidase could trigger the release of lauric acid (LA) from the SL multilayer and accelerate the release of BMP2 in the system. The hyaluronidase-sensitive-multilayer-coated BMP2-loaded TNT (TNT/BMP2/(Chi/SL/Chi/Gel)₄) not only demonstrated good antibacterial capability, but also showed good biocompatibility in in vitro usage, which was supported by the efficient growth inhibition of both Staphylococcus aureus and Escherichia coli, as well as higher cell viability, alkaline phosphatase activity, mineralization capability, and higher gene expression of osteoblasts on TNT/BMP2/(Chi/SL/Chi/Gel)₄. This study developed an alternative approach to fabricate effective antibacterial implants for orthopedic implantation.

Progress in TiO2 nanotube coatings for biomedical applications: a review

Titanium dioxide nanotubes (TNTs) have drawn wide attention and been extensively applied in the field of biomedicine, due to their large specific surface area, good corrosion resistance, excellent biocompatibility, and enhanced bioactivity. This review describes the preparation of TNTs and the surface modification that entrust the nanotubes with better antibacterial property and enhanced osteoblast adhesion, proliferation, and differentiation. Considering the contact between TNTs' surface and surrounding tissues after implantation, the interactions between TNTs (with properties including their diameter, length, wettability, and crystalline phase) and proteins, platelets, bacteria, and cells are illustrated. The state of the art in the applications of TNTs in dentistry, orthopedic implants, and cardiovascular stents are introduced. In particular, the application of TNTs in biosensing has attracted much attention due to its ability for the rapid diagnosis of diseases. Finally, the difficulties and challenges in the practical application of TNTs are also discussed.

An in vitro Experimental Insight into the Osteoblast Responses to Vitamin D3 and Its Metabolites

BACKGROUND

25-hydroxyvitamin D3 (25[OH]VD3) has recently been found to be an active hormone. Its biological actions are also demonstrated in various cell types. However, the precise influences of vitamin D3 (VD3) and its metabolites (25[OH]VD3, 1α,25-dihydroxyvitamin D3 [1α,25-(OH)2VD3]) on the osteoblast differentiation remain largely unknown. In this work, we investigated the effects of VD3 and its metabolites in different concentrations on the early and later osteoblast differentiation and biomineralization.

METHODS

We first used quantitative real-time polymerase chain reaction (RT-qPCR) to evaluate the responsiveness of osteoblasts to VD3, 25(OH)VD3 or 1α,25-(OH)2VD3. We also evaluated the proliferation, differentiation and biomineralization of osteoblast at different time points via cell counting kit-8 assay and the analysis of osteogenic markers.

RESULTS

The experimental results confirmed that osteoblasts could be responsive to 25(OH)VD3 and 1α,25-(OH)2VD3 but could not directly metabolize VD3 and 25(OH)VD3. Only 200 nmol/L VD3 significantly promoted osteoblast proliferation, while 25(OH)VD3 and 1α,25-(OH)2VD3 did not show obvious actions. Moreover, the early osteogenic markers were increased by 25(OH)VD3 and 1α,25-(OH)2VD3 in a dose-dependent manner. More importantly, only 25(OH)VD3 had accelerated the gene and protein expressions of osteocalcin and the biomineralization level of osteoblasts.

CONCLUSIONS

Our findings provide reliable evidence that 25(OH)VD3 at 100-200 nmol/L can induce the early and later osteoblast differentiation and biomineralization for clinical bone tissue engineering.

Calcium Phosphates as Delivery Systems for Bisphosphonates

Bisphosphonates (BPs) are the most utilized drugs for the treatment of osteoporosis, and are usefully employed also for other pathologies characterized by abnormally high bone resorption, including bone metastases. Due to the great affinity of these drugs for calcium ions, calcium phosphates are ideal delivery systems for local administration of BPs to bone, which is aimed to avoid/limit the undesirable side effects of their prolonged systemic use. Direct synthesis in aqueous medium and chemisorptions from solution are the two main routes proposed to synthesize BP functionalized calcium phosphates. The present review overviews the information acquired through the studies on the interaction between bisphosphonate molecules and calcium phosphates. Moreover, particular attention is addressed to some important recent achievements on the applications of BP functionalized calcium phosphates as biomaterials for bone substitution/repair.

Investigation of osteogenic responses of Fe-incorporated micro/nano-hierarchical structures on titanium surfaces

Fe incorporated micro/nano topographical titanium substrates are fabricated to synergistically regulate osteogenic responses in vitro and osseointegration in vivo.