Nanomedicine for safe healing of bone trauma: Opportunities and challenges

A graphene oxide-loaded processed pyritum composite hydrogel for accelerated bone regeneration via mediation of M2 macrophage polarization

A coordinated interaction between osteogenesis and the osteoimmune microenvironment plays a vital role in regulating bone healing. However, disturbances in the pro- and anti-inflammatory balance hinder the therapeutic advantages of biomaterials. In this study, a novel composite hydrogel was successfully fabricated using graphene oxide (GO)-loaded processed pyritum (PP) in combination with poly(ethylene glycol) diacrylate (PEGDA) and carboxymethyl chitosan (CMC). Subsequently, the immunomodulatory effects and bone regenerative potential of PP/GO@PEGDA/CMC were investigated. The results demonstrated that the PP/GO@PEGDA/CMC hydrogel possessed excellent mechanical properties, swelling capacity, and stability. Moreover, PP/GO@PEGDA/CMC prominently promoted M2 polarization and increased the levels of anti-inflammatory factors (interleukin (IL)-4, IL-10, and transforming growth factor-β). These beneficial effects facilitated the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells in vitro. Additionally, the in vivo results further verified that the implantation of PP/GO@PEGDA/CMC markedly reduced local inflammation while enhancing bone regeneration at 8 weeks post-implantation. Therefore, the results of this study provide potential therapeutic strategies for bone tissue repair and regeneration by modulating the immune microenvironment.

Tissue-Engineered Nanomaterials Play Diverse Roles in Bone Injury Repair

Nanomaterials with bone-mimicking characteristics and easily internalized by the cell could create suitable microenvironments in which to regulate the therapeutic effects of bone regeneration. This review provides an overview of the current state-of-the-art research in developing and using nanomaterials for better bone injury repair. First, an overview of the hierarchical architecture from the macroscale to the nanoscale of natural bone is presented, as these bone tissue microstructures and compositions are the basis for constructing bone substitutes. Next, urgent clinical issues associated with bone injury that require resolution and the potential of nanomaterials to overcome them are discussed. Finally, nanomaterials are classified as inorganic or organic based on their chemical properties. Their basic characteristics and the results of related bone engineering studies are described. This review describes theoretical and technical bases for the development of innovative methods for repairing damaged bone and should inspire therapeutic strategies with potential for clinical applications.

The function of immunomodulation and biomaterials for scaffold in the process of bone defect repair: A review

The process of bone regeneration involves the interaction of the skeletal, blood, and immune systems. Bone provides a solid barrier for the origin and development of immune cells in the bone marrow. At the same time, immune cells secrete related factors to feedback on the remodeling of the skeletal system. Pathological or traumatic injury of bone tissue involves changes in blood supply, cell behavior, and cytokine expression. Immune cells and their factors play an essential role in repairing foreign bodies in bone injury or implantation of biomaterials, the clearance of dead cells, and the regeneration of bone tissue. This article reviews the bone regeneration application of the bone tissue repair microenvironment in bone cells and immune cells in the bone marrow and the interaction of materials and immune cells.

Ultrashort Peptide-Based Hydrogel for the Healing of Critical Bone Defects in Rabbits

The use of hydrogels as scaffolds for three-dimensional (3D) cell growth is an active area of research in tissue engineering. Herein, we report the self-assembly of an ultrashort peptide, a tetrapeptide, Asp-Leu-IIe-IIe, the shortest peptide sequence from a highly fibrillogenic protein TDP-43, into the hydrogel. The hydrogel was mechanically strong and highly stable, with storage modulus values in MPa ranges. The hydrogel supported the proliferation and successful differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) in its matrix as assessed by cell viability, calcium deposition, alkaline phosphatase (ALP) activity, and the expression of osteogenic marker gene studies. To check whether the hydrogel supports 3D growth and regeneration in in vivo conditions, a rabbit critical bone defect model was used. Micro-computed tomography (CT) and X-ray analysis demonstrated the formation of mineralized neobone in the defect areas, with significantly higher bone mineralization and relative bone densities in animals treated with the peptide hydrogel compared to nontreated and matrigel treatment groups. The ultrashort peptide-based hydrogel developed in this work holds great potential for its further development as tissue regeneration and/or engineering scaffolds.

Application of Hydrogels as Sustained-Release Drug Carriers in Bone Defect Repair

Large bone defects resulting from trauma, infection and tumors are usually difficult for the body's repair mechanisms to heal spontaneously. Generally, various types of bones and orthopedic implants are adopted to enhance bone repair and regeneration in the clinic. Due to the limitations of traditional treatments, bone defect repair is still a compelling challenge for orthopedic surgeons. In recent years, bone tissue engineering has become a potential option for bone repair and regeneration. Amidst the various scaffolds for bone tissue engineering applications, hydrogels are considered a new type of non-toxic, non-irritating and biocompatible materials, which are widely used in the biomedicine field currently. Some studies have demonstrated that hydrogels can provide a three-dimensional network structure similar to a natural extracellular matrix for tissue regeneration and can be used to transport cells, biofactors, nutrients and drugs. Therefore, hydrogels may have the potential to be multifunctional sustained-release drug carriers in the treatment of bone defects. The recent applications of different types of hydrogels in bone defect repair were briefly reviewed in this paper.

Chloroplast-inspired Scaffold for Infected Bone Defect Therapy: Towards Stable Photothermal Properties and Self-Defensive Functionality

Bone implant-associated infections induced by bacteria frequently result in repair failure and threaten the health of patients. Although black phosphorus (BP) material with superior photothermal conversion ability is booming in the treatment of bone disease, the development of BP-based bone scaffolds with excellent photothermal stability and antibacterial properties simultaneously remains a challenge. In nature, chloroplasts cannot only convert light into chemical energy, but also hold a protective and defensive envelope membrane. Inspired by this, a self-defensive bone scaffold with stable photothermal property is developed for infected bone defect therapy. Similar to thylakoid and stroma lamella in chloroplasts, BP is integrated with chitosan and polycaprolactone fiber networks. The mussel-inspired polydopamine multifunctional "envelope membrane" wrapped above not only strengthens the photothermal stability of BP-based scaffolds, but also realizes the in situ anchoring of silver nanoparticles. Bacteria-triggered infection of femur defects in vivo can be commendably inhibited at the early stage via these chloroplast-inspired implants, which then effectively promotes endogenous repair of the defect area under mild hyperthermia induced by near-infrared irradiation. This chloroplast-inspired strategy shows outstanding performance for infected bone defect therapy and provides a reference for the functionality of other biomedical materials.

Recent advances in 3D-printed polylactide and polycaprolactone-based biomaterials for tissue engineering applications

The three-dimensional printing (3DP) also known as the additive manufacturing (AM), a novel and futuristic technology that facilitates the printing of multiscale, biomimetic, intricate cytoarchitecture, function-structure hierarchy, multi-cellular tissues in the complicated micro-environment, patient-specific scaffolds, and medical devices. There is an increasing demand for developing 3D-printed products that can be utilized for organ transplantations due to the organ shortage. Nowadays, the 3DP has gained considerable interest in the tissue engineering (TE) field. Polylactide (PLA) and polycaprolactone (PCL) are exemplary biomaterials with excellent physicochemical properties and biocompatibility, which have drawn notable attraction in tissue regeneration. Herein, the recent advancements in the PLA and PCL biodegradable polymer-based composites as well as their reinforcement with hydrogels and bio-ceramics scaffolds manufactured through 3DP are systematically summarized and the applications of bone, cardiac, neural, vascularized and skin tissue regeneration are thoroughly elucidated. The interaction between implanted biodegradable polymers, in-vivo and in-vitro testing models for possible evaluation of degradation and biological properties are also illustrated. The final section of this review incorporates the current challenges and future opportunities in the 3DP of PCL- and PLA-based composites that will prove helpful for biomedical engineers to fulfill the demands of the clinical field.

Advances in Barrier Membranes for Guided Bone Regeneration Techniques

Guided bone regeneration (GBR) is a widely used technique for alveolar bone augmentation. Among all the principal elements, barrier membrane is recognized as the key to the success of GBR. Ideal barrier membrane should have satisfactory biological and mechanical properties. According to their composition, barrier membranes can be divided into polymer membranes and non-polymer membranes. Polymer barrier membranes have become a research hotspot not only because they can control the physical and chemical characteristics of the membranes by regulating the synthesis conditions but also because their prices are relatively low. Still now the bone augment effect of barrier membrane used in clinical practice is more dependent on the body’s own growth potential and the osteogenic effect is difficult to predict. Therefore, scholars have carried out many researches to explore new barrier membranes in order to improve the success rate of bone enhancement. The aim of this study is to collect and compare recent studies on optimizing barrier membranes. The characteristics and research progress of different types of barrier membranes were also discussed in detail.

Role of Implantable Drug Delivery Devices with Dual Platform Capabilities in the Prevention and Treatment of Bacterial Osteomyelitis

As medicine advances and physicians are able to provide patients with innovative solutions, including placement of temporary or permanent medical devices that drastically improve quality of life of the patient, there is the persistent, recurring problem of chronic bacterial infection, including osteomyelitis. Osteomyelitis can manifest as a result of traumatic or contaminated wounds or implant-associated infections. This bacterial infection can persist as a result of inadequate treatment regimens or the presence of biofilm on implanted medical devices. One strategy to mitigate these concerns is the use of implantable medical devices that simultaneously act as local drug delivery devices (DDDs). This classification of device has the potential to prevent or aid in clearing chronic bacterial infection by delivering effective doses of antibiotics to the area of interest and can be engineered to simultaneously aid in tissue regeneration. This review will provide a background on bacterial infection and current therapies as well as current and prospective implantable DDDs, with a particular emphasis on local DDDs to combat bacterial osteomyelitis.

A novel hierarchical biofunctionalized 3D-printed porous Ti6Al4V scaffold with enhanced osteoporotic osseointegration through osteoimmunomodulation

Background

Femoral stem of titanium alloy has been widely used for hip arthroplasty with considerable efficacy; however, the application of this implant in patients with osteoporosis is limited due to excessive bone resorption. Macrophages participate in the regulation of inflammatory response and have been a topic of increasing research interest in implant field. However, few study has explored the link between macrophage polarization and osteogenic–osteoclastic differentiation. The present study aims to develop a novel hierarchical biofunctionalized 3D-printed porous Ti6Al4V scaffold with enhanced osteoporotic osseointegration through immunotherapy.

Method

To improve the osteointegration under osteoporosis, we developed a hierarchical biofunctionalized 3D-printed porous Ti6Al4V scaffold (PT). Biomimetic extracellular matrix (ECM) was constructed inside the interconnected pores of PT in micro-scale. And in nano-scale, a drug cargo icariin@Mg-MOF-74 (ICA@MOF) was wrapped in ECM-like structure that can control release of icariin and Mg²⁺.

Results

In this novel hierarchical biofunctionalized 3D-printed porous Ti6Al4V scaffold, the macroporous structure provides mechanical support, the microporous structure facilitates cell adhesion and enhances biocompatibility, and the nanostructure plays a biological effect. We also demonstrate the formation of abundant new bone at peripheral and internal sites after intramedullary implantation of the biofunctionalized PT into the distal femur in osteoporotic rats. We further find that the controlled-release of icariin and Mg²⁺ from the biofunctionalized PT can significantly improve the polarization of M0 macrophages to M2-type by inhibiting notch1 signaling pathway and induce the secretion of anti-inflammatory cytokines; thus, it significantly ameliorates bone metabolism, which contributes to improving the osseointegration between the PT and osteoporotic bone.

Conclusion

The therapeutic potential of hierarchical PT implants containing controlled release system are effective in geriatric orthopaedic osseointegration.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01277-0.

Nanotechnology for Targeted Detection and Removal of Bacteria: Opportunities and Challenges

The emergence of nanotechnology has created unprecedented hopes for addressing several unmet industrial and clinical issues, including the growing threat so-termed "antibiotic resistance" in medicine. Over the last decade, nanotechnologies have demonstrated promising applications in the identification, discrimination, and removal of a wide range of pathogens. Here, recent insights into the field of bacterial nanotechnology are examined that can substantially improve the fundamental understanding of nanoparticle and bacteria interactions. A wide range of developed nanotechnology-based approaches for bacterial detection and removal together with biofilm eradication are summarized. The challenging effects of nanotechnologies on beneficial bacteria in the human body and environment and the mechanisms of bacterial resistance to nanotherapeutics are also reviewed.

Polyphenols-loaded electrospun nanofibers in bone tissue engineering and regeneration

Bone is a complex structure with unique cellular and molecular process in its formation. Bone tissue regeneration is a well-organized and routine process at the cellular and molecular level in humans through the activation of biochemical pathways and protein expression. Though many forms of biomaterials have been applied for bone tissue regeneration, electrospun nanofibrous scaffolds have attracted more attention among researchers with their physicochemical properties such as tensile strength, porosity, and biocompatibility. When drugs, antibiotics, or functional nanoparticles are taken as additives to the nanofiber, its efficacy towards the application gets increased. Polyphenol is a versatile green/phytochemical small molecule playing a vital role in several biomedical applications, including bone tissue regeneration. When polyphenols are incorporated as additives to the nanofibrous scaffold, their combined properties enhance cell attachment, proliferation, and differentiation in bone tissue defect. The present review describes bone biology encompassing the composition and function of bone tissue cells and exemplifies the series of biological processes associated with bone tissue regeneration. We have highlighted the molecular mechanism of bioactive polyphenols involved in bone tissue regeneration and specified the advantage of electrospun nanofiber as a wound healing scaffold. As the polyphenols contribute to wound healing with their antioxidant and antimicrobial properties, we have compiled a list of polyphenols studied, thus far, for bone tissue regeneration along with their in vitro and in vivo experimental biological results and salient observations. Finally, we have elaborated on the importance of polyphenol-loaded electrospun nanofiber in bone tissue regeneration and discussed the possible challenges and future directions in this field.

A novel self-healing triple physical cross-linked hydrogel for antibacterial dressing

The poor mechanical properties of wound dressings have always been a challenge in their application as wound protective barriers. In particular, when the hydrogel dressing absorbs the tissue fluid, the mechanical properties of the hydrogel will decrease greatly due to the swelling effect. In this study, an original antibacterial hydrogel dressing was prepared by a one-step process with acrylic acid, 1-vinyl-3-butylimidazolium, COOH-modified gum arabic, and aluminium chloride. The mechanical properties of this hydrogel were improved after water absorption due to hydrophobic interactions, so the hydrogel dressing could maintain good mechanical properties after absorption of the tissue fluid. Furthermore, 1-vinyl-3-butylimidazolium as an ionic liquid was introduced into the polymer backbone of hydrogels via covalent bonds and could promote the self-healing of hydrogels by facilitating the migration of aluminum ions with charge. The obtained hydrogels showed good self-healing properties, with a strain self-healing rate of 98.2% and a stress self-healing rate of 92.3%. In addition, this hydrogel exhibited excellent antibacterial activity against E. coli, S. aureus, and C. albicans. The results of the study on rat wound closure indicated that this hydrogel effectively accelerated the healing of a full-thickness skin defect. Therefore, this novel hydrogel has a broad application prospect in the field of wound dressing.

Large fuzzy biodegradable polyester microspheres with dopamine deposition enhance cell adhesion and bone regeneration in vivo

The biodegradable polymer microparticles with different surface morphology and chemical compositions may influence significantly the behaviors of cells, and thereby further the performance of tissue regeneration in vivo. In this study, multi-stage hierarchical textures of poly(D,L-lactic-co-glycolide) (PLGA)/PLGA-b-PEG (poly(ethylene glycol)) microspheres with a diameter as large as 50-100 μm are fabricated based on interfacial instability of an emulsion. The obtained fuzzy structures on the microspheres are sensitive to annealing, which are changed gradually to a smooth one after treatment at 37 °C for 6 d or 80 °C for 1 h. The surface microstructures that are chemically dominated by PEG can be stabilized against annealing by dopamine deposition. By the combination use of annealing and dopamine deposition, a series of microspheres with robust surface topologies are facilely prepared. The fuzzy microstructures and dopamine deposition show a synergetic role to enhance cell-material interaction, leading to a larger number of adherent bone marrow-derived mesenchymal stem cells (BMSCs), A549 and MC 3T3 cells. The fuzzy microspheres with dopamine deposition can significantly promote bone regeneration 12 w post surgery in vivo, as revealed by micro-CT, histological, western blotting and RT-PCR analyses.

Luminescent net-like inorganic scaffolds with europium-doped hydroxyapatite for enhanced bone reconstruction

Bone reconstruction is an urgent problem during clinical treatment. In the past few decades, the construction of composite scaffolds has been a hot spot in the research field of bone tissue engineering (BTE). However, the disadvantages of composite materials raise our awareness to explore the potential application of hydroxyapatite (HAp) in bone substitutes due to the closest properties of HAp to natural bone tissue. In our study, we synthesized Eu³⁺-doped HAp (HAp:Eu³⁺) ultralong nanowires, which can be transformed to hydrophilic net-like scaffolds via a thiol-ene click reaction. The property of luminescence of HAp from Eu³⁺ is beneficial for identifying the relative position of materials and bone marrow mesenchymal stem cells (BMSCs). HAp:Eu³⁺ scaffolds with excellent cell biocompatibility could promote the expression of early bone formation markers (ALP and ARS) and enhance the expression of genes and proteins associated with osteogenesis (Runx 2, OCN, and OPN). In the end, the results of the in vivo osteogenesis experiment showed that pure HAp scaffolds presented different effects of bone tissue reconstruction compared with the composite scaffolds with HAp nanorods and polymer materials. The superior osteogenic effect could be observed in net-like pure HAp scaffold groups. Furthermore, the absorption of HAp:Eu³⁺ scaffolds could be monitored due to the luminescence property of Eu³⁺. This strategy based on ultralong HAp nanowires proved to be a new method for the construction of simple reticular scaffolds for potential osteogenic applications.

Bile acid-based dual-functional prodrug nanoparticles for bone regeneration through hydrogen peroxide scavenging and osteogenic differentiation of mesenchymal stem cells

A high level of reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) upregulates pro-inflammatory cytokines and inhibits the osteogenic differentiation of mesenchymal stem cells (MSCs), which are key factors in bone regeneration. Ursodeoxycholic acid (UDCA), a hydrophilic bile acid, has antioxidant and anti-inflammatory activities and also plays beneficial roles in bone regeneration by stimulating the osteogenic differentiation of MSCs while suppressing their adipogenic differentiation. Despite its remarkable capacity for bone regeneration, multiple injections of UDCA induce adverse side effects such as mechanical stress and contamination in bone defects. To fully exploit the beneficial roles of UDCA, a concept polymeric prodrug was developed based on the hypothesis that removal of overproduced H₂O₂ will potentiate the osteogenic functions of UDCA. In this work, we report bone regenerative nanoparticles (NPs) formulated from a polymeric prodrug of UDCA (PUDCA) with UDCA incorporated in its backbone through H₂O₂-responsive peroxalate linkages. The PUDCA NPs displayed potent antioxidant and anti-inflammatory activities in MSCs and induced osteogenic rather than adipogenic differentiation of the MSCs. In rat models of bone defect, the PUDCA NPs exhibited significantly better bone regeneration capacity and anti-inflammatory effects than equivalent amounts of UDCA. We anticipate that PUDCA NPs have tremendous translational potential as bone regenerative agents.

Dual-Wavelength Photosensitive Nano-in-Micro Scaffold Regulates Innate and Adaptive Immune Responses for Osteogenesis

The immune response of a biomaterial determines its osteoinductive effect. Although the mechanisms by which some immune cells promote regeneration have been revealed, the biomaterial-induced immune response is a dynamic process involving multiple cells. Currently, it is challenging to accurately regulate the innate and adaptive immune responses to promote osteoinduction in biomaterials. Herein, we investigated the roles of macrophages and dendritic cells (DCs) during the osteoinduction of biphasic calcium phosphate (BCP) scaffolds. We found that osteoinductive BCP directed M2 macrophage polarization and inhibited DC maturation, resulting in low T cell response and efficient osteogenesis. Accordingly, a dual-targeting nano-in-micro scaffold (BCP loaded with gold nanocage, BCP-GNC) was designed to regulate the immune responses of macrophages and DCs. Through a dual-wavelength photosensitive switch, BCP-GNC releases interleukin-4 in the early stage of osteoinduction to target M2 macrophages and then releases dexamethasone in the later stage to target immature DCs, creating a desirable inflammatory environment for osteogenesis. This study demonstrates that biomaterials developed to have specific regulatory capacities for immune cells can be used to control the early inflammatory responses of implanted materials and induce osteogenesis.

Silver Nanoparticles Coated Poly(L-Lactide) Electrospun Membrane for Implant Associated Infections Prevention

Bacterial infection has been a critic problem for implant infections. Poly(L-lactide) (PLLA) membrane has great potential for Guided bone regeneration (GBR), however, PLLA lack antibacterial property and thus may face bacterial infections. In this work, a mussel inspired method was used to treat PLLA membrane with dopamine and formed polydopamine (PDA) coated PLLA (PLLA@PDA), and then silver Nanoparticles (AgNPs) was immobilized on the surface of PLLA via the reduction effect of PDA. The XPS results showed that the silver element contents may be tuned from 1.6% to 15.4%. The AgNPs coated PLLA (PLLA@Ag) showed good antibacterial property (98.3% bactericidal efficiency may be obtained) and good biocompatibility, implying that the PLLA@Ag membrane have potential application as antibacterial GBR membrane, which may enhance the application of PLLA.

Green nanotechnology-based drug delivery systems for osteogenic disorders

Introduction: Current treatments for osteogenic disorders are often successful, however they are not free of drawbacks, such as toxicity or side effects. Nanotechnology offers a platform for drug delivery in the treatment of bone disorders, which can overcome such limitations. Nevertheless, traditional synthesis of nanomaterials presents environmental and health concerns due to its production of toxic by-products, the need for extreme and harsh raw materials, and their lack of biocompatibility over time.Areas covered: This review article contains an overview of the current status of treating osteogenic disorders employing green nanotechnological approaches, showing some of the latest advances in the application of green nanomaterials, as drug delivery carriers, for the effective treatment of osteogenic disorders.Expert opinion: Green nanotechnology, as a potential solution, is understood as the use of living organisms, biomolecules and environmentally friendly processes for the production of nanomaterials. Nanomaterials derived from bacterial cultures or biomolecules isolated from living organisms, such as carbohydrates, proteins, and nucleic acids, have been proven to be effective composites. These nanomaterials introduce enhancements in the treatment and prevention of osteogenic disorders, compared to physiochemically-synthesized nanostructures, specifically in terms of their improved cell attachment and proliferation, as well as their ability to prevent bacterial adhesion.

Biomimetic anti-inflammatory nano-capsule serves as a cytokine blocker and M2 polarization inducer for bone tissue repair

Controlling of pro-inflammation induced by pro-inflammatory cytokines and anti-inflammatory response induced by M2 macrophages is important for osteogenesis in the process of bone tissue repair. Thus, we fabricated biomimetic anti-inflammatory nano-capsule (BANC) that can block cytokines and promote M2 macrophage polarization, presenting a positive role for bone tissue repair. The BANC is a biomimic nanosystem, coated with lipopolysaccharide-treated macrophage cell membranes with cytokine receptors enveloping gold nanocage (AuNC) as "cytokine blocker", and loaded with resolvin D1 inside into AuNC as "M2 polarization inducer" whose controlled-release could be triggered under near-infrared laser irradiation in sequence, and these chronological events were consistent with the healing process of bone tissue repair. Moreover, in vivo application of femoral bone defects revealed that the BANC composite boron-containing mesoporous bioactive glass scaffolds improved the final effects of bone tissue repair through preventing inflammatory response, promoting M2 polarization in sequence in accord with the in vitro investigation. Hence, cytokine neutralization and M2 macrophage polarization enables the BANC to enhance the bone tissue repair as a biomimetic anti-inflammation effector. Therefore, this study provides potential therapeutic strategies for trauma-mediated or inflammation-related bone defects based on a biomimetic nanomaterial with weakened pro-inflammatory and enhanced anti-inflammatory effects. STATEMENT OF SIGNIFICANCE: Cell membrane-mimic nanomaterials have been popular for blocking natural cell responses for some infection diseases, yet their role in biological process of bone repair is unknown. Here, we fabricated Biomimetic Anti-inflammatory Nano-Capsule (BANC), coated with cell membrane with cytokines receptors on the surface which could neutralize the pro-inflammatory cytokine receptor to block activated pro-inflammation, loaded with Resolvin D1 inside which could be controllably released by NIR irradiation to promote M2 macrophage polarization for the following bone formation during the process of bone repair. Administration of BANC as cytokines blocker and M2 polarization inducer to enhance the bone regeneration, thus presenting a promising potential for the treatment of bone repair and regeneration.

Bone tissue regeneration: biology, strategies and interface studies

Nowadays, bone diseases and defects as a result of trauma, cancers, infections and degenerative and inflammatory conditions are increasing. Consequently, bone repair and replacement have been developed with improvement of orthopedic technologies and biomaterials of superior properties. This review paper is intended to sum up and discuss the most relevant studies performed in the field of bone biology and bone regeneration approaches. Therefore, the bone tissue regeneration was investigated by synthetic substitutes, scaffolds incorporating active molecules, nanomedicine, cell-based products, biomimetic fibrous and nonfibrous substitutes, biomaterial-based three-dimensional (3D) cell-printing substitutes, bioactive porous polymer/inorganic composites, magnetic field and nano-scaffolds with stem cells and bone-biomaterials interface studies.

Nanomaterials for bone tissue regeneration: updates and future perspectives

Joint replacement and bone reconstructive surgeries are on the rise globally. Current strategies for implants and bone regeneration are associated with poor integration and healing resulting in repeated surgeries. A multidisciplinary approach involving basic biological sciences, tissue engineering, regenerative medicine and clinical research is required to overcome this problem. Considering the nanostructured nature of bone, expertise and resources available through recent advancements in nanobiotechnology enable researchers to design and fabricate devices and drug delivery systems at the nanoscale to be more compatible with the bone tissue environment. The focus of this review is to present the recent progress made in the rationale and design of nanomaterials for tissue engineering and drug delivery relevant to bone regeneration.

Multifunctional Magnetic Nanoplatform Eliminates Cancer Stem Cells via Inhibiting the Secretion of Extracellular Heat Shock Protein 90

Cancer stem cells (CSCs) are responsible for malignant tumor initiation, recurrences, and metastasis. Therefore, targeting CSCs is a promising strategy for the development of cancer therapies. A big challenge for CSC-based cancer therapy is the overexpression of therapeutic stress protein, heat shock protein 90 (Hsp90), which protects CSCs from further therapeutic-induced damage, leading to the failure of treatment. Thus, efficient strategies to target CSCs are urgently needed for cancer therapy. To this end, a multifunctional nanoparticle (MNP) for CSC-based combined thermotherapy and chemotherapy is reported. This strategy dramatically suppresses tumor growth in breast CSC xenograft-bearing mice. Furthermore, a new mechanism is present that the MNP exerts its striking effects on CSCs by inhibiting the secretion of extracellular Hsp90 (eHsp90), resulting in the interruption of several key signaling pathways. These findings open new perspectives on the use of an MNP for effective CSC-based cancer treatment by inhibiting the function of eHsp90.

An injectable cationic hydrogel electrostatically interacted with BMP2 to enhance in vivo osteogenic differentiation of human turbinate mesenchymal stem cells

We have designed and characterized an injectable, electrostatically bonded, in situ-forming hydrogel system consisting of a cationic polyelectrolyte [(methoxy)polyethylene glycol-b-(poly(ε-caprolactone)-ran-poly(L-lactic acid)] (MP) copolymer derivatized with an amine group (MP-NH₂) and anionic BMP2. To the best of our knowledge, there have been hardly any studies that have investigated electrostatically bonded, in situ-forming hydrogel systems consisting of MP-NH₂ and BMP2, with respect to how they promote in vivo osteogenic differentiation of human turbinate mesenchymal stem cells (hTMSCs). Injectable formulations almost immediately formed an electrostatically loaded hydrogel depot containing BMP2, upon injection into mice. The hydrogel features and stability of BMP2 inside the hydrogel were significantly affected by the electrostatic attraction between BMP2 and MP-NH₂. Additionally, the time BMP2 spent inside the hydrogel depot was prolonged in vivo, as evidenced by in vivo near-infrared fluorescence imaging. Biocompatibility was demonstrated by the fact that hTMSCs survived in vivo, even after 8 weeks and even though relatively few macrophages were in the hydrogel depot. The osteogenic capacity of the electrostatically loaded hydrogel implants containing BMP2 was higher than that of a hydrogel that was simply loaded with BMP2, as evidenced by Alizarin Red S, von Kossa, and hematoxylin and eosin staining as well as osteonectin, osteopontin, osteocalcin, and type 1α collagen mRNA expression. The results confirmed that our injectable, in situ-forming hydrogel system, electrostatically loaded with BMP2, can enhance in vivo osteogenic differentiation of hTMSCs.

Multilayered composite coatings of titanium dioxide nanotubes decorated with zinc oxide and hydroxyapatite nanoparticles: controlled release of Zn and antimicrobial properties against Staphylococcus aureus

Purpose: This study aimed to decorate the surface of TiO₂ nanotubes (TiO₂ NTs) grown on medical grade Ti-6Al-4V alloy with an antimicrobial layer of nano zinc oxide particles (nZnO) and then determine if the antimicrobial properties were maintained with a final layer of nano-hydroxyapatite (HA) on the composite.

Methods: The additions of nZnO were attempted at three different annealing temperatures: 350, 450 and 550 °C. Of these temperatures, 350°C provided the most uniform and nanoporous coating and was selected for antimicrobial testing.

Results: The LIVE/DEAD assay showed that ZnCl₂ and nZnO alone were >90% biocidal to the attached bacteria, and nZnO as a coating on the nanotubes resulted in around 70% biocidal activity. The lactate production assay agreed with the LIVE/DEAD assay. The concentrations of lactate produced by the attached bacteria on the surface of nZnO-coated TiO₂ NTs and ZnO/HA-coated TiO₂ NTs were 0.13±0.03 mM and 0.37±0.1 mM, respectively, which was significantly lower than that produced by the bacteria on TiO₂ NTs alone, 1.09±0.30 mM (Kruskal–Wallis, P<0.05, n=6). These biochemical measurements were correlated with electron micrographs of cell morphology and cell coverage on the coatings.

Conclusion: nZnO on TiO₂ NTs was a stable and antimicrobial coating, and most of the biocidal properties remained in the presence of nano-HA on the coating.

Treatment of tumor-like lesions in the femoral neck using free nonvascularized fibular autografts in pediatric patients before epiphyseal closure

Objectives

Surgical resection of benign bone tumors and tumor-like lesions at the femoral neck presents a difficult reconstructive challenge. However, the safety and efficacy of free nonvascularized fibular autografts (FNFAs) in the treatment of femoral neck tumor-like lesions before epiphyseal closure in young patients remain unknown.

Methods

Sixteen pediatric patients who had not yet undergone epiphyseal closure were treated with FNFAs after resection of tumor-like lesions in the femoral neck from August 2012 to September 2016. All patients underwent supplementary skeletal traction through the supracondylar femur for 4 to 6 weeks after resection. Demographic data were recorded and clinical and radiological outcomes were evaluated during the follow-up.

Results

All patients could walk with partial weight bearing 4 weeks postoperative, and full weight bearing was permitted after a mean of 8 weeks. Graft union was attained in all 16 patients at a mean of 2 months. The donor site of the fibular cortical strut showed good regeneration in all patients. The Harris hip score significantly improved from 65% to 95%.

Conclusions

Application of an FNFA is a feasible method in the treatment of tumor-like lesions in the femoral neck before epiphyseal closure in pediatric patients.

Level of Evidence

Level IV.

Off-the-Shelf Biomimetic Graphene Oxide-Collagen Hybrid Scaffolds Wrapped with Osteoinductive Extracellular Matrix for the Repair of Cranial Defects in Rats

Hydrogels such as type I collagen (COL) have been widely studied in bone tissue repair, whereas their weak mechanical strength has limited their clinical application. By adding graphene oxide (GO) nanosheets, researchers have successfully improved the mechanical properties and biocompatibility of the hydrogels. However, for large bone defects, the osteoinductive and cell adhesion ability of the GO hybrid hydrogels need to be improved. Mesenchymal stem cell (MSC) secreted extracellular matrix (ECM), which is an intricate network, could provide a biomimetic microenvironment and functional molecules that enhance the cell proliferation and survival rate. To synergize the advantages of MSC-ECM with GO-COL hybrid implants, we developed a novel ECM scaffold construction method. First, an osteoinductive extracellular matrix (OiECM) was created by culturing osteodifferentiated bone marrow mesenchymal stem cells (BMSCs) for 21 days. Then, the GO-COL scaffold was fully wrapped with the OiECM to construct the OiECM-GO-COL composite for implantation. The morphology, physical properties, biocompatibility, and osteogenic performance of the OiECM-GO-COL implants were assessed in vitro and in vivo (5 mm rat cranial defect model). Both gene expression and cell level assessments suggested that the BMSCs cultured on OiECM-GO-COL implants had a higher proliferation rate and osteogenic ability compared to the COL or GO-COL groups. In vivo results showed that the OiECM-GO-COL implants achieved better repair effects in a rat critical cranial defect model, whereas bone formation in other groups was limited. This study provides a promising strategy, which greatly improves the osteogenic ability and biocompatibility of the GO hydrogels without the procedure of seeding and culturing MSCs on scaffolds in vitro, demonstrating its potential as an off-the-shelf method for bone tissue engineering.

Promoted Angiogenesis and Osteogenesis by Dexamethasone-loaded Calcium Phosphate Nanoparticles/Collagen Composite Scaffolds with Microgroove Networks

Reconstruction of large bone defects remains a clinical challenge because current approaches involving surgery and bone grafting often do not yield satisfactory outcomes. For artificial bone substitutes, angiogenesis plays a pivotal role to achieve the final success of newly regenerated bone. In this study, dexamethasone-loaded biphasic calcium phosphate nanoparticles/collagen composite scaffolds with several types of concave microgrooves were prepared for simultaneous promotion of angiogenesis and osteogenesis. Microgrooves in the scaffolds were supposed to guide the assembly of human umbilical vascular endothelial cells (HUVECs) into well aligned tubular structures, thus promoting rapid angiogenesis. The scaffolds were used for co-culture of HUVECs and human bone marrow-derived mesenchymal stem cells. Subcutaneous implantation in mice showed that more blood vessels and newly formed bone were observed in the microgrooved composite scaffolds than in the control scaffold. Scaffold bearing parallel microgrooves with a concave width of 290 µm and a convex ridge width of 352 µm showed the highest promotion effect on angiogenesis and osteogenesis among the parallelly microgrooved composite scaffolds. The scaffolds bearing a grid network had further superior promotion effect to the scaffolds bearing parallel microgrooves. The results indicated that microgrooves in the composite scaffolds facilitated angiogenesis and stimulated new bone formation. The microgrooved composite scaffolds should be useful for repairing of large bone defects.

Preparation and characterization of porous hydroxyapatite/β-cyclodextrin-based polyurethane composite scaffolds for bone tissue engineering

In this study, novel porous scaffolds containing hydroxyapatite and β-cyclodextrin-based polyurethane were first successfully fabricated by polymerizing β-cyclodextrin with hexamethylene diisocyanate and hydroxyapatite in situ for bone tissue engineering. The physicochemical and mechanical properties as well as cytocompatibility of porous scaffolds were investigated. The results showed that polyurethane reinforced with hydroxyapatite composites had cancellous bone-like porous structure. The mechanical strength of the scaffolds increased with increasing the hydroxyapatite content in scaffolds. Synthesized scaffolds (PU1, PUHA1, PU2, and PUHA2) presented compressive strength values of 0.87 ± 0.24 MPa, 1.81 ± 0.10 MPa, 6.16 ± 0.89 MPa, and 12.95 ± 2.05 MPa, respectively. The pore size and porosity of these scaffolds were suitable for bone regeneration. Cytocompatibility of composite scaffolds was proven via favorable interactions with MC3T3-E1 cells. The addition of hydroxyapatite into CD-based polyurethane scaffolds improved cell attachment, well-spread morphology, and higher proliferation. The hydroxyapatite-polyurethane scaffolds have the potential to be applied in bone repair and regeneration.

Mechanical and biological performance of axially loaded novel bio-nanocomposite sandwich plate-type implant coated by biological polymer thin film

Post-surgical infection is one of the essential problems in bone scaffolds that is usually treated with antibiotics. This issue may be related to the poor blood supply for bone tissue due to high concentrations of drug. In the current study, the effect of zinc oxide (ZnO) nanoparticles on the antibacterial behavior of the nanocrystalline hydroxyapatite (n-HA) scaffolds coated by gelatin-ibuprofen (GN-IBO) is evaluated. To this end, the bio-nanocomposite scaffolds are fabricated via the space holder technique and then characterized with the aid of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The compressive strength, fracture toughness, porosity, elastic modulus as the mechanical properties, and the apatite formation, biodegradation, drug release and wettability beside the roughness as the biological properties are predicted. The obtained experimental results indicate that the bio-nanocomposite scaffolds containing 10 wt% ZnO has suitable mechanical and biological properties. After that, an analytical model is developed to predict the nonlinear instability and vibration responses of an axially loaded sandwich plate-type implants made of the fabricated n-HA-ZnO bio-nanocomposites coated by GN-IBO thin film corresponding to various weight fractions of ZnO nanoparticles. It is found that ZnO peaks in the positions of 2θ are equal to 31.6°, 33.6°, 34°, 46.4°, and 62°, which represent the crystalline characteristics. Also, it is revealed that through addition of ZnO nanoparticles, the hardness and elastic modulus as well as the bone formation and biodegradation rate of the bio-nanocomposite scaffold enhance, while its drug release in the phosphate buffer solution detected with UV spectrum reduces. It is found that by increasing the ZnO weight fraction, the critical axial buckling load of the sandwich bio-nanocomposite implant enhances, and it buckles at lower axial shortening. However, it is seen that for higher value of wt% ZnO, its influence on the critical buckling load decreases.

Biomimetic Scaffolds for Bone Tissue Engineering

The use of biomimetic scaffolds for bone tissue engineering has been studied for a long time. Biomimetic scaffolds can assist and accelerate bone regeneration that is similar to that of authentic tissue, which represents the environment of cells in a living organism. Currently, numerous biomaterials have been reported for use as a biomimetic scaffold. This review focuses on the design of biomimetic scaffolds, kinds of biomaterials and methods used to fabricate biomimetic scaffolds, growth factors used with biomimetic scaffold for bone regeneration, mobilization of biological agents into biomimetic scaffolds, and studies on (pre)clinical bone regeneration from biomimetic scaffolds. Then, future prospects for biomimetic scaffolds are discussed.