Immunomodulatory Effects of Calcium and Strontium Co-Doped Titanium Oxides on Osteogenesis

A review of the advances in implant technology: accomplishments and challenges for the design of functionalized surface structures

Biomedical implants are extensively utilized to replace hard-tissue defects owing to their biocompatibility and remarkable tissue-affinity. The materials and functional design are selected based on the resultant osseointegration level and resistance to infection, and these considerations constitute the dominant research topic in this field. However, high rates of implantation failure and peri-implantitis have been reported. Current research on biomedical-implant design encompasses enhancement of the implant surface properties, such as the roughness, nano/micro topography, and hydrophilicity, along with the realization of advanced features including antibacterial properties and cell and immunomodulation regulation. This review considers the two achievements of contemporary implant manufacturing; namely, osseointegration and the realization of antibacterial properties. Present mainstream surface modifications and coatings are discussed, along with functional design technologies and achievements. The impacts of direct surface-treatment techniques and osteogenic functional coatings on osseointegration performance and antibacterial surface structures are elucidated, considering inorganic and organic coatings with antibacterial properties as well as antibiotic-releasing coatings. Furthermore, this review highlights recent advancements in physically driven antimicrobial strategies. Expanding upon existing research, future directions for implant studies are proposed, including the realization of comprehensive functionality that integrates osseointegration and antibacterial properties, as well as patient-specific design. Our study presents a comprehensive review and offers a novel perspective on the design of biomedical implants for enhanced versatility. An in-depth exploration of future research directions will also stimulate subsequent investigations.

Cell-Type-Specific ROS-AKT/mTOR-Autophagy Interplay-Should It Be Addressed in Periimplantitis?

Periimplantitis represents an inflammatory disease of the soft and hard tissues surrounding the osseointegrated dental implant, triggering progressive damage to the alveolar bone. Cumulative data have revealed that periimplantitis plays a crucial part in implant failure. Due to the strategic roles of autophagy and its upstream coordinator, the AKT/mTOR pathway, in inflammatory responses, the crosstalk between them in the context of periimplantitis should become a key research target, as it opens up an area of interesting data with clinical significance. Therefore, in this article, we aimed to briefly review the existing data concerning the complex roles played by ROS in the interplay between the AKT/mTOR signaling pathway and autophagy in periimplantitis, in each of the main cell types involved in periimplantitis pathogenesis and evolution. Knowing how to modulate specifically the autophagic machinery in each of the cellular types involved in the healing and osseointegration steps post implant surgery can help the clinician to make the most appropriate post-surgery decisions. These decisions might be crucial in order to prevent the occurrence of periimplantitis and ensure the proper conditions for effective osseointegration, depending on patients' clinical particularities.

A novel multifunctional nanocomposite hydrogel orchestrates the macrophage reprogramming-osteogenesis crosstalk to boost bone defect repair

Repairing bone defects is a complex cascade reaction process, as immune system regulation, vascular growth, and osteogenic differentiation are essential. Thus, developing a tissue-engineered biomaterial that caters to the complex healing process of bone regeneration remains a major clinical challenge. In the study, Ca2+-TA-rGO (CTAG)/GelMA hydrogels were synthesized by binding Ca2+ using metal chelation to graphene oxide (GO) nanosheets reduced by tannic acid (TA-rGO) and doping them into gelatin methacrylate (GelMA) hydrogels. TA and rGO exhibited biocompatibility and immunomodulatory properties in this composite, while Ca2+ promoted bone formation and angiogenesis. This novel nanocomposite hydrogel demonstrated good mechanical properties, degradability, and conductivity, and it could achieve slow Ca2+ release during bone regeneration. Both in vitro and in vivo experiments revealed that CTAG/GelMA hydrogel modulated macrophage reprogramming and induced a shift from macrophages to healing-promoting M2 macrophages during the inflammatory phase, promoted vascular neovascularization, and facilitated osteoblast differentiation during bone formation. Moreover, CTAG/GelMA hydrogel could downregulate the NF-κB signaling pathway, offering new insights into regulating macrophage reprogramming-osteogenic crosstalk. Conclusively, this novel multifunctional nanocomposite hydrogel provides a multistage treatment for bone and orchestrates macrophage reprogramming-osteogenic crosstalk to boost bone repair.

Advances in osteoimmunomodulation of biomaterials after intrabone implantation: focus on surface hydrophilicity

Biomaterials intended for intrabone implantation are extensively utilized in orthopedic and dental applications. Their surface properties, particularly hydrophilicity, significantly influence the biological interactions surrounding the implant, ultimately determining the implant's in vivo fate. Recently, the role of osteoimmunomodulation in these implantable biomaterials has been recognized for its importance in regulating biomaterial-mediated osteogenesis. Consequently, it is imperative to elucidate the correlation between hydrophilicity and the immune response for the development of osteoimmunomodulatory implants. Herein, this review highlights recent advances in osteoimmunomodulation of biomaterials after intrabone implantation from a novel perspective-surface hydrophilicity, and summarizes the series of immune reactions and subsequent bone remodeling that occur in response to hydrophilic implants, focusing on protein adsorption, the behaviors of major immune cells, and osteoimmunomodulation-enhanced angiogenesis and osteogenesis. Hydrophilic biomaterials have the capacity to alter the surrounding immune microenvironment and accelerate the process of material-tissue bonding, thereby facilitating the successful integration of biomaterials with tissue. Collectively, the authors hope that this article provides strategies for modulating hydrophilicity to achieve osteoimmunomodulatory performance and further promotes the development of novel implantable biomaterials for orthopedic and dental applications.

A Janus Microsphere Delivery System Orchestrates Immunomodulation and Osteoinduction by Fine-tuning Release Profiles

Bone regeneration is a well-orchestrated process synergistically involving inflammation, angiogenesis, and osteogenesis. Therefore, an effective bone graft should be designed to target multiple molecular events and biological demands during the bone healing process. In this study, a biodegradable gelatin methacryloyl (GelMA)-based Janus microsphere delivery system containing calcium phosphate oligomer (CPO) and bone morphogenetic protein-2 (BMP-2) is developed based on natural biological events. The exceptional adjustability of GelMA facilitates the controlled release and on-demand application of biomolecules, and optimized delivery profiles of CPO and BMP-2 are explored. The sustained release of CPO during the initial healing stages contributes to early immunomodulation and promotes mineralization in the late stage. Meanwhile, the administration of BMP-2 at a relatively high concentration within the therapeutic range enhances the osteoinductive property. This delivery system, with fine-tuned release patterns, induces M2 macrophage polarization and creates a conducive immuno-microenvironment, which in turn facilitates effective bone regeneration in vivo. Collectively, this study proposes a bottom-up concept, aiming to develop a user-friendly and easily controlled delivery system targeting individual biological events, which may offer a new perspective on developing function-optimized biomaterials for clinical use.

Applications of Bioactive Strontium Compounds in Dentistry

Divalent cations have captured the interest of researchers in biomedical and dental fields due to their beneficial effects on bone formation. These metallic elements are similar to trace elements found in human bone. Strontium is a divalent cation commonly found in various biomaterials. Since strontium has a radius similar to calcium, it has been used to replace calcium in many calcium-containing biomaterials. Strontium has the ability to inhibit bone resorption and increase bone deposition, making it useful in the treatment of osteoporosis. Strontium has also been used as a radiopacifier in dentistry and has been incorporated into a variety of dental materials to improve their radiopacity. Furthermore, strontium has been shown to improve the antimicrobial and mechanical properties of dental materials, promote enamel remineralization, alleviate dentin hypersensitivity, and enhance dentin regeneration. The objective of this review is to provide a comprehensive review of the applications of strontium in dentistry.

Microelement strontium and human health: comprehensive analysis of the role in inflammation and non-communicable diseases (NCDs)

Strontium (Sr), a trace element with a long history and a significant presence in the Earth's crust, plays a critical yet often overlooked role in various biological processes affecting human health. This comprehensive review explores the multifaceted implications of Sr, especially in the context of non-communicable diseases (NCDs) such as cardiovascular diseases, osteoporosis, hypertension, and diabetes mellitus. Sr is predominantly acquired through diet and water and has shown promise as a clinical marker for calcium absorption studies. It contributes to the mitigation of several NCDs by inhibiting oxidative stress, showcasing antioxidant properties, and suppressing inflammatory cytokines. The review delves deep into the mechanisms through which Sr interacts with human physiology, emphasizing its uptake, metabolism, and potential to prevent chronic conditions. Despite its apparent benefits in managing bone fractures, hypertension, and diabetes, current research on Sr's role in human health is not exhaustive. The review underscores the need for more comprehensive studies to solidify Sr's beneficial associations and address the gaps in understanding Sr intake and its optimal levels for human health.

Advancements in incorporating metal ions onto the surface of biomedical titanium and its alloys via micro-arc oxidation: a research review

The incorporation of biologically active metallic elements into nano/micron-scale coatings through micro-arc oxidation (MAO) shows significant potential in enhancing the biological characteristics and functionality of titanium-based materials. By introducing diverse metal ions onto titanium implant surfaces, not only can their antibacterial, anti-inflammatory and corrosion resistance properties be heightened, but it also promotes vascular growth and facilitates the formation of new bone tissue. This review provides a thorough examination of recent advancements in this field, covering the characteristics of commonly used metal ions and their associated preparation parameters. It also highlights the diverse applications of specific metal ions in enhancing osteogenesis, angiogenesis, antibacterial efficacy, anti-inflammatory and corrosion resistance properties of titanium implants. Furthermore, the review discusses challenges faced and future prospects in this promising area of research. In conclusion, the synergistic approach of micro-arc oxidation and metal ion doping demonstrates substantial promise in advancing the effectiveness of biomedical titanium and its alloys, promising improved outcomes in medical implant applications.

Ion incorporation into bone grafting materials

The use of biomaterials in regenerative medicine has expanded to treat various disorders caused by trauma or disease in orthopedics and dentistry. However, the treatment of large and complex bone defects presents a challenge, leading to a pressing need for optimized biomaterials for bone repair. Recent advances in chemical sciences have enabled the incorporation of therapeutic ions into bone grafts to enhance their performance. These ions, such as strontium (for bone regeneration/osteoporosis), copper (for angiogenesis), boron (for bone growth), iron (for chemotaxis), cobalt (for B12 synthesis), lithium (for osteogenesis/cementogenesis), silver (for antibacterial resistance), and magnesium (for bone and cartilage regeneration), among others (e.g., zinc, sodium, and silica), have been studied extensively. This review aims to provide a comprehensive overview of current knowledge and recent developments in ion incorporation into biomaterials for bone and periodontal tissue repair. It also discusses recently developed biomaterials from a basic design and clinical application perspective. Additionally, the review highlights the importance of precise ion introduction into biomaterials to address existing limitations and challenges in combination therapies. Future prospects and opportunities for the development and optimization of biomaterials for bone tissue engineering are emphasized.

The development of magnesium-based biomaterials in bone tissue engineering: A review

Bone regeneration is a vital clinical challenge in massive or complicated bone defects. Recently, bone tissue engineering has come to the fore to meet the demand for bone repair with various innovative materials. However, the reported materials usually cannot satisfy the requirements, such as ideal mechanical and osteogenic properties, as well as biocompatibility at the same time. Mg-based biomaterials have considerable potential in bone tissue engineering owing to their excellent mechanical strength and biosafety. Moreover, the biocompatibility and osteogenic activity of Mg-based biomaterials have been the research focuses in recent years. The main limitation faced in the applications of Mg-based biomaterials is rapid degradation, which can produce excessive Mg2+ and hydrogen, affecting the healing of the bone defect. In order to overcome the limitations, researchers have explored several ways to improve the properties of Mg-based biomaterials, including alloying, surface modification with coatings, and synthesizing other composite materials to control the degradation rate upon implantation. This article reviewed the osteogenic mechanism and requirement for appropriate degradation rate and focused on current progress in the biomedical use of Mg-based biomaterials to inspire more clinical applications of Mg in bone regeneration in the future.

A dual-functional strontium-decorated titanium implants that guides the immune response for osseointegration of osteoporotic rats

Due to the dynamic imbalance between osteogenesis and osteoclasis and the abnormal inflammatory microenvironment in situ, osteoporosis hampers the early osseointegration between implants and bones. To improve osseointegration with the osteoporosis, we first coated the titanium implants (Ti) with polydopamine (PDA) coating (Ti-PDA), followed by modification with strontium (Sr) to prepare the Ti-PDA-Sr implants. An osteoporotic rat model with femoral bone defect was verified to estimate the osseointegration of the implants. The Ti-PDA-Sr implants exhibited good biocompatibility with continuous release of Sr ions for up to 21 days. Ti-PDA-Sr implants promoted the osteogenesis of BMSCs and the polarization of BMMs to M2 phenotype compared to that of Ti and Ti-PDA implants, revealing the double-regulated effects in bone induction and immune regulation. According to the Micro-CT and histopathology results, Ti-PDA-Sr implants exhibited the most stable osseointegration between bone tissues and implants. According to the immunohistochemistry results, the Ti-PDA-Sr implants differentiated the BMMs to M2 phenotype, alleviating the abnormal inflammation in osteoporosis and preventing the consistent bone destruction between the implants and bone tissues. This study provides a practical and effective strategy in preparing bi-functional implants that can promote osseointegration with osteoporosis.

Development of a composite hydrogel incorporating anti-inflammatory and osteoinductive nanoparticles for effective bone regeneration

BACKGROUND

Bone tissue regeneration is regulated by complex events, including inflammation, osteoinduction, and remodeling. Therefore, to induce the complete restoration of defective bone tissue, biomaterials with the ability to regulate the collective bone regenerative system are beneficial. Although some studies conclude that reducing reactive oxygen species created a favorable environment for bone regeneration by controlling inflammation, biomaterials that can simultaneously promote osteogenesis and regulate inflammation have not been developed. Herein, we describe the development of a multi-functional nanoparticle and its hydrogel composite with osteoinductive, anti-inflammatory, and osteoclast-maturation regulatory functions for enhanced bone regeneration.

METHODS

Tannic acid-mineral nanoparticles (TMP) were prepared by self-assembly of tannic acid in an ion-rich simulated body fluid containing Ca2+ and PO43-. Particles with a diameter of 443 ± 91 nm were selected for their stable spherical morphology and minimal tendency to aggregate. The particles were homogeneously embedded within a gelatin-based cryogel (TMP/Gel) to be used in further experiments. The osteoinductive properties, anti-inflammatory and osteoclast-maturation regulatory functions in vitro were tested by culturing corresponding cells on either TMP/Gel or a gelatin-based cryogel without the particles (Gel). For in vivo analyses, a murine calvarial defect model was used. Statistical analyses were carried out using a Graphpad Prism 7 software (San Diego, CA, USA) to perform one-way analysis of variance ANOVA with Tukey's honest significant difference test and a Student's t-test (for two variables) (P < 0.05).

RESULTS

Excellent biocompatibility and radical scavenging abilities were exhibited by the TMP/Gel. The expression of osteogenic mRNA is significantly increased in human adipose-derived stem cells seeded on the TMP/Gel compared to those without the particles. Furthermore, RAW264.7 cells seeded on the TMP/Gel displayed significantly lower-than-normal levels of pro-inflammatory and osteoclastogenic genes. Finally, the in vivo results indicated that, compared with the cryogel with no anti-inflammatory effect, the TMP/Gel significantly enhanced both the quality and quantity of newly formed bone, demonstrating the importance of combining anti-inflammation with osteoinduction.

CONCLUSION

Collectively, these findings suggest our nanoparticle-hydrogel composite could be an effective tool to regulate complex events within the bone healing process.

Protective effects of curcumin against osteoporosis and its molecular mechanisms: a recent review in preclinical trials

Osteoporosis (OP) is one of the most common metabolic skeletal disorders and is commonly seen in the elderly population and postmenopausal women. It is mainly associated with progressive loss of bone mineral density, persistent deterioration of bone microarchitecture, and increased fracture risk. To date, drug therapy is the primary method used to prevent and treat osteoporosis. However, long-term drug therapy inevitably leads to drug resistance and specific side effects. Therefore, researchers are constantly searching for new monomer compounds from natural plants. As a candidate for the treatment of osteoporosis, curcumin (CUR) is a natural phenolic compound with various pharmacological and biological activities, including antioxidant, anti-apoptotic, and anti-inflammatory. This compound has gained research attention for maintaining bone health in various osteoporosis models. We reviewed preclinical and clinical studies of curcumin in preventing and alleviating osteoporosis. These results suggest that if subjected to rigorous pharmacological and clinical trials, naturally-derived curcumin could be used as a complementary and alternative medicine for the treatment of osteoporosis by targeting osteoporosis-related mechanistic pathways. This review summarizes the mechanisms of action and potential therapeutic applications of curcumin in the prevention and mitigation of osteoporosis and provides reference for further research and development of curcumin.

Angiogenic and immunomodulation role of ions for initial stages of bone tissue regeneration

It is widely known that bone has intrinsic capacity to self-regenerate after injury. However, the physiological regeneration process can be impaired when there is an extensive damage. One of the main reasons is due to the inability to establish a new vascular network that ensures oxygen and nutrient diffusion, leading to a necrotic core and non-junction of bone. Initially, bone tissue engineering (BTE) emerged to use inert biomaterials to just fill bone defects, but it eventually evolved to mimic bone extracellular matrix and even stimulate bone physiological regeneration process. In this regard, the stimulation of osteogenesis has gained a lot of attention especially in the proper stimulation of angiogenesis, being critical to achieve a successful osteogenesis for bone regeneration. Besides, the immunomodulation of a pro-inflammatory environment towards an anti-inflammatory one upon scaffold implantation has been considered another key process for a proper tissue restoration. To stimulate these phases, growth factors and cytokines have been extensively used. Nonetheless, they present some drawbacks such as low stability and safety concerns. Alternatively, the use of inorganic ions has attracted higher attention due to their higher stability and therapeutic effects with low side effects. This review will first focus in giving fundamental aspects of initial bone regeneration phases, focusing mainly on inflammatory and angiogenic ones. Then, it will describe the role of different inorganic ions in modulating the immune response upon biomaterial implantation towards a restorative environment and their ability to stimulate angiogenic response for a proper scaffold vascularization and successful bone tissue restoration. STATEMENT OF SIGNIFICANCE: The impairment of bone tissue regeneration when there is excessive damage has led to different tissue engineered strategies to promote bone healing. Significant importance has been given in the immunomodulation towards an anti-inflammatory environment together with proper angiogenesis stimulation in order to achieve successful bone regeneration rather than stimulating only the osteogenic differentiation. Ions have been considered potential candidates to stimulate these events due to their high stability and therapeutic effects with low side effects compared to growth factors. However, up to now, no review has been published assembling all this information together, describing individual effects of ions on immunomodulation and angiogenic stimulation, as well as their multifunctionality or synergistic effects when combined together.

The Inflammatory Contribution of B-Lymphocytes and Neutrophils in Progression to Osteoporosis

Osteoporosis is a bone disease characterized by structural deterioration and low bone mass, leading to fractures and significant health complications. In this review, we summarize the mechanisms by which B-lymphocytes and neutrophils contribute to the development of osteoporosis and potential therapeutics targeting these immune mediators to reduce the proinflammatory milieu. B-lymphocytes-typically appreciated for their canonical role in adaptive, humoral immunity-have emerged as critical regulators of bone remodeling. B-lymphocytes communicate with osteoclasts and osteoblasts through various cytokines, including IL-7, RANK, and OPG. In inflammatory conditions, B-lymphocytes promote osteoclast activation and differentiation. However, B-lymphocytes also possess immunomodulatory properties, with regulatory B-lymphocytes (Bregs) secreting TGF-β1 to restrain pathogenic osteoclastogenesis. Neutrophils, the body's most prevalent leukocyte, also contribute to the proinflammatory environment that leads to osteoporotic bone remodeling. In aged individuals, neutrophils display reduced chemotaxis, phagocytosis, and apoptosis. Understanding the delicate interplay between B-lymphocytes and neutrophils in the context of impaired bone metabolism is crucial for targeted therapies for osteoporosis.

Metal-phenolic networks acted as a novel bio-filler of a barrier membrane to improve guided bone regeneration via manipulating osteoimmunomodulation

A guided bone tissue regeneration membrane (GBRM) is traditionally viewed as an inert physical barrier to isolate soft tissue from the bone defect area. However, as a "foreign body", the implantation of a GBRM would inevitably modulate immune response and subsequently affect bone dynamics. Herein, we developed strontium ion (Sr²⁺)-based metal-phenolic network complexes (MPNs) as a novel type of bio-filler to manipulate the osteoimmunomodulation of the advanced GBRM. For controllable delivery of Sr²⁺ depending on the difference in affinity between phenolic ligands and Sr²⁺, tannic acid (TA), epigallocatechin gallate (EGCG), and epigallocatechin (EGC) were selected to chelate with Sr²⁺. The formed MPNs were incorporated into PCL nanofibrous membranes by blending electrospinning. Among them, TA/Sr based MPN particles displayed the most sustainable release profile of phenolic ligands and Sr²⁺. Further investigations demonstrated that Sr²⁺ could not only directly promote osteogenic differentiation of BMSCs, but also manipulate an anti-inflammatory osteoimmune microenvironment in a synergistic manner with TA, thus enhancing osteogenesis and inhibiting bone resorption. The rat alveolar bone defect model also confirmed that the TA/Sr nanoparticle modified membrane displayed better bone regeneration performance than the pure PCL membrane via inhibiting bone resorption. This work provides a new platform for controllable delivery of bioactive nutrient elements, and holds great promise for advancing multi-functional biocomposites.

Antibiotic delivery from bone-targeted mesoporous silica nanoparticles for the treatment of osteomyelitis caused by methicillin-resistant Staphylococcus aureus

Osteomyelitis is a hard-to-treat infection of the bone and bone marrow that is mainly caused by Staphylococcus aureus, with an increasing incidence of methicillin-resistant S. aureus (MRSA). Owing to the aggressiveness of these bacteria in colonizing and destroying the bone, systemic antibiotic treatments fail to eradicate the infection. Instead, it normally entails surgery to remove the dead or infected bone. In this work, we report bone-targeted mesoporous silica nanoparticles for the treatment of osteomyelitis. The nanoparticles have been engineered with a functional gelatine/colistin coating able to hamper premature release from the mesopores while effectively disaggregating the bacterial biofilm. Because antibiotic resistance is a global emergency, we have designed two sets of identical nanoparticles, carrying each of them a clinically relevant antibiotic, that have demonstrated to have synergistic effect. The bone-targeted nanoparticles have been thoroughly evaluated in vitro and in vivo, obtaining a notable reduction of the amount of bacteria in the bone in just 24 h after only one dose, and paving the way for localized, nanoparticle-mediated treatment of MRSA-caused osteomyelitis. STATEMENT OF SIGNIFICANCE: In this work, we propose the use of bone-targeted mesoporous silica nanoparticles to address S. aureus-caused osteomyelitis that render synergistic therapeutic effect via multidrug delivery. Because the bacterial biofilm is responsible for an aggressive surgical approach and prolonged antibiotic treatment, the nanoparticles have been functionalized with a functional coating able to both disaggregate the biofilm, hamper premature antibiotic release and protect the intact bone. These engineered nanoparticles are able to effectively target bone tissue both in vitro and in vivo, showing high biocompatibility and elevated antibacterial effect.

Bio-Activated PEEK: Promising Platforms for Improving Osteogenesis through Modulating Macrophage Polarization

The attention on orthopedic biomaterials has shifted from their direct osteogenic properties to their osteoimmunomodulation, especially the modulation of macrophage polarization. Presently, advanced technologies endow polyetheretherketone (PEEK) with good osteoimmunomodulation by modifying PEEK surface characteristics or incorporating bioactive substances with regulating macrophage polarization. Recent studies have demonstrated that the fabrication of a hydrophilic surface and the incorporation of bioactive substances into PEEK (e.g., zinc, calcium, and phosphate) are good strategies to promote osteogenesis by enhancing the polarization of M2 macrophages. Furthermore, the modification by other osteoimmunomodulatory composites (e.g., lncRNA-MM2P, IL-4, IL-10, and chitosan) and their controlled and desired release may make PEEK an optimal bio-activated implant for regulating and balancing the osteogenic system and immune system. The purpose of this review is to comprehensively evaluate the potential of bio-activated PEEK in polarizing macrophages into M2 phenotype to improve osteogenesis. For this objective, we retrieved and discussed different kinds of bio-activated PEEK regarding improving osteogenesis through modulating macrophage polarization. Meanwhile, the relevant challenges and outlook were presented. We hope that this review can shed light on the development of bio-activated PEEK with more favorable osteoimmunomodulation.

The effect of calcium-magnesium mixtures in sol-gel coatings on bone tissue regeneration

Calcium and magnesium are two elements essential for bone structure and metabolism. However, their synergistic or competitive effects on bone regeneration are often overlooked during biomaterial development. We examined the interactions between Ca and Mg in sol-gel coatings doped with mixtures of CaCl₂ (0.5%) and MgCl₂ (0.5, 1, and 1.5%). After physicochemical characterisation, the materials were incubated in vitro with MC3T3-E1 osteoblastic cells and RAW264.7 macrophages, and the protein adsorption was analysed using nLC-MS/MS. The incorporation of the ions did not lead to the formation of crystalline structures and did not affect the sol-gel network cross-linking. The release of the ions did not cause cytotoxic effects at any tested concentration. The proteomic analysis showed that adding the Ca and Mg ions elevated the adsorption of proteins associated with inflammatory response regulation (e.g., ALBU, CLUS, HPT, HPTR, A1AG1 and A1AG2) but decreased the adsorption of immunoglobulins. The CaMg coatings had reduced affinity to proteins associated with coagulation (e.g., FA9, FA10, FA11, FA12) but increased the adsorption of proteins involved in cell adhesion (DSG1, DESP, FBLN1, ZA2G). In vitro assays revealed that the cellular response was affected by changing the concentration of Mg. Moreover, our results show that these differences reflect the changes in the concentrations of both ions in the mix but are not a simple additive effect.

Strontium Functionalized in Biomaterials for Bone Tissue Engineering: A Prominent Role in Osteoimmunomodulation

With the development of bone tissue engineering bio-scaffold materials by adding metallic ions to improve bone healing have been extensively explored in the past decades. Strontium a non-radioactive element, as an essential osteophilic trace element for the human body, has received widespread attention in the medical field due to its superior biological properties of inhibiting bone resorption and promoting osteogenesis. As the concept of osteoimmunology developed, the design of orthopedic biomaterials has gradually shifted from “immune-friendly” to “immunomodulatory” with the aim of promoting bone healing by modulating the immune microenvironment through implanted biomaterials. The process of bone healing can be regarded as an immune-induced procedure in which immune cells can target the effector cells such as macrophages, neutrophils, osteocytes, and osteoprogenitor cells through paracrine mechanisms, affecting pathological alveolar bone resorption and physiological bone regeneration. As a kind of crucial immune cell, macrophages play a critical role in the early period of wound repair and host defense after biomaterial implantation. Despite Sr-doped biomaterials being increasingly investigated, how extracellular Sr²⁺ guides the organism toward favorable osteogenesis by modulating macrophages in the bone tissue microenvironment has rarely been studied. This review focuses on recent knowledge that the trace element Sr regulates bone regeneration mechanisms through the regulation of macrophage polarization, which is significant for the future development of Sr-doped bone repair materials. We will also summarize the primary mechanism of Sr²⁺ in bone, including calcium-sensing receptor (CaSR) and osteogenesis-related signaling pathways.

Immunomodulation and osseointegration activities of Na2TiO3 nanorods-arrayed coatings doped with different Sr content

To endow Ti-based orthopedic implants immunomodulatory capability and thus enhanced osseointegration, different amounts of Sr are doped in Na2TiO3 nanorods in the arrays with identical nanotopographic parameters (rod diameter, length and inter-rod spacing) by substitution of Na+ using hydrothermal treatment. The obtained arrays are denoted as STSr2, STSr4, and STSr7, where the arabic numbers indicate the incorporating amounts of Sr in Na2TiO3. The modulation effects of the Sr-doped nanorods arrays on macrophage polarization and osteogenetic functions of osteoblasts are investigated, together with the array without Sr (ST). Moreover, osseointegration of these arrays are also assayed in rat femoral condyles. Sr-doped nanorods arrays accelerate M1 (pro-inflammatory phenotype)-to-M2 (anti-inflammatory phenotype) transformation of the adhered macrophages, enhancing secretion of pro-osteogenetic cytokines and growth factors (TGF-β1 and BMP2), moreover, the Sr doped arrays directly enhance osteogenetic functions of osteoblasts. The enhancement of paracrine of M2 macrophages and osteogenetic function of osteoblasts is promoted with the increase of Sr incorporating amounts. Consequently, Sr doped arrays show significantly enhanced osseointegration in vivo compared to ST, and STSr7 exhibits the best performance. Our work sheds a new light on the design of surface chemical components and structures for orthopedic implants to enhance their osseointegration.

Lonafarnib Inhibits Farnesyltransferase via Suppressing ERK Signaling Pathway to Prevent Osteoclastogenesis in Titanium Particle-Induced Osteolysis

Wear debris after total joint arthroplasty can attract the recruitment of macrophages, which release pro-inflammatory substances, triggering the activation of osteoclasts, thereby leading to periprosthetic osteolysis (PPOL) and aseptic loosening. However, the development of pharmacological strategies targeting osteoclasts to prevent periprosthetic osteolysis has not been fruitful. In this study, we worked toward researching the effects and mechanisms of a farnesyltransferase (FTase) inhibitor Lonafarnib (Lon) on receptor activator of nuclear factor κB (NF-κB) ligand (RANKL)-induced osteoclastogenesis and bone resorption, as well as the impacts of Lon on titanium particle-induced osteolysis. To investigate the impacts of Lon on bone resorption and osteoclastogenesis in vitro, bone marrow macrophages were incubated and stimulated with RANKL and macrophage colony-stimulating factor (M-CSF). The influence of Lon on osteolysis prevention in vivo was examined utilizing a titanium particle-induced mouse calvarial osteolysis model. The osteoclast-relevant genes expression was explored by real-time quantitative PCR. Immunofluorescence was used to detect intracellular localization of nuclear factor of activated T cells 1 (NFATc1). SiRNA silence assay was applied to examine the influence of FTase on osteoclasts activation. Related signaling pathways, including NFATc1 signaling, NF-κB, mitogen-activated protein kinases pathways were identified by western blot assay. Lon was illustrated to suppress bone resorptive function and osteoclastogenesis in vitro, and it also reduced the production of pro-inflammatory substances and prevented titanium particle-induced osteolysis in vivo. Lon decreased the expression of osteoclast-relevant genes and suppressed NFATc1 nuclear translocation and auto-amplification. Mechanistically, Lon dampened FTase, and inhibition of FTase reduced osteoclast formation by suppressing ERK signaling. Lon is a promising treatment option for osteoclast-related osteolysis diseases including periprosthetic osteolysis by targeted inhibition of FTase through suppressing ERK signaling.

Cubic multi-ions-doped Na2TiO3 nanorod-like coatings: Structure-stable, highly efficient platform for ions-exchanged release to immunomodulatory promotion on vascularized bone apposition

The dissolution-derived release of bioactive ions from ceramic coatings on metallic implants, despite improving osseointegration, renders a concern on the interfacial breakdown of the metal/coating/bone system during long-term service. Consequently, persistent efforts to seek alternative strategies instead of dissolution-derived activation are pressingly carrying out. Inspired by bone mineral containing ions as Ca²⁺, Mg²⁺, Sr²⁺ and Zn²⁺, here we hydrothermally grew the quadruple ions co-doped Na₂TiO₃ nanorod-like coatings. The co-doped ions partially substitute Na⁺ in Na₂TiO₃, and can be efficiently released from cubic lattice via exchange with Na⁺ in fluid rather than dissolution, endowing the coatings superior long-term stability of structure and bond strength. Regulated by the coatings-conditioned extracellular ions, TLR4-NFκB signalling is enhanced to act primarily in macrophages (MΦs) at 6 h while CaSR-PI3K-Akt1 signalling is potentiated to act predominately since 24 h, triggering MΦs in a M1 response early and then in a M2 response to sequentially secrete diverse cytokines. Acting on endothelial and mesenchymal stem cells with the released ions and cytokines, the immunomodulatory coatings greatly promote Type-H (CD31^hiEmcn^hi) angiogenesis and osteogenesis in vitro and in vivo, providing new insights into orchestrating insoluble ceramics-coated implants for early vascularized osseointegration in combination with long-term fixation to bone.

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Co-doped Ca²⁺, Mg²⁺, Sr²⁺ and Zn²⁺ in Na₂TiO₃ efficiently release via ion exchange.

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QID elevates extracellular concentrations of the ions and MΦ intracellular [Ca²⁺].

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Co-doped Na₂TiO₃ coatings promote immunomodulatory apposition of vascularized bone.

The Effects of Crocin on Bone and Cartilage Diseases

Crocin, the main biologically active carotenoid of saffron, generally is derived from the dried trifid stigma of Crocus sativus L. Many studies have demonstrated that crocin has several therapeutic effects on biological systems through its anti-oxidant and anti-inflammatory properties. The wide range of crocin activities is believed to be because of its ability to anchor to many proteins, triggering some cellular pathways responsible for cell proliferation and differentiation. It also has therapeutic potentials in arthritis, osteoarthritis, rheumatoid arthritis, and articular pain probably due to its anti-inflammatory properties. Anti-apoptotic effects, as well as osteoclast inhibition effects of crocin, have suggested it as a natural substance to treat osteoporosis and degenerative disease of bone and cartilage. Different mechanisms underlying crocin effects on bone and cartilage repair have been investigated, but remain to be fully elucidated. The present review aims to undertake current knowledge on the effects of crocin on bone and cartilage degenerative diseases with an emphasis on its proliferative and differentiative properties in mesenchymal stem cells.

Arabic gum plus colistin coated moxifloxacin-loaded nanoparticles for the treatment of bone infection caused by Escherichia coli

Osteomyelitis is an inflammatory process of bone and bone marrow that may even lead to patient death. Even though this disease is mainly caused by Gram-positive organisms, the proportion of bone infections caused by Gram-negative bacteria, such as Escherichia coli, has significantly increased in recent years. In this work, mesoporous silica nanoparticles have been employed as platform to engineer a nanomedicine able to eradicate E. coli- related bone infections. For that purpose, the nanoparticles have been loaded with moxifloxacin and further functionalized with Arabic gum and colistin (AG+CO-coated MX-loaded MSNs). The nanosystem demonstrated high affinity toward E. coli biofilm matrix, thanks to AG coating, and marked antibacterial effect because of the bactericidal effect of moxifloxacin and the disaggregating effect of colistin. AG+CO-coated MX-loaded MSNs were able to eradicate the infection developed on a trabecular bone in vitro and showed pronounced antibacterial efficacy in vivo against an osteomyelitis provoked by E. coli. Furthermore, AG+CO-coated MX-loaded MSNs were shown to be essentially non-cytotoxic with only slight effect on cell proliferation and mild hepatotoxicity, which might be attributed to the nature of both antibiotics. In view of these results, these nanoparticles may be considered as a promising treatment for bone infections caused by enterobacteria, such as E. coli, and introduce a general strategy against bone infections based on the implementation of antibiotics with different but complementary activity into a single nanocarrier. STATEMENT OF SIGNIFICANCE: In this work, we propose a methodology to address E.coli bone infections by using moxifloxacin-loaded mesoporous silica nanoparticles coated with Arabic gum containing colistin (AG+CO-coated MX-loaded MSNs). The in vitro evaluation of this nanosystem demonstrated high affinity toward E. coli biofilm matrix thanks to the Arabic gum coating, a disaggregating and antibacterial effect of colistin, and a remarkable antibiofilm action because of the bactericidal ability of moxifloxacin and colistin. This anti-E. coli capacity of AG+CO-coated MX-loaded MSNs was brought out in an in vivo rabbit model of osteomyelitis where the nanosystem was able to eradicate more than 90% of the bacterial load within the infected bone.

Icariin-loaded Sulfonated Polyetheretherketone with Osteogenesis Promotion and Osteoclastogenesis Inhibition Properties via Immunomodulation for Advanced Osseointegration

Preventing prosthesis loosening due to insufficient osseointegration is critical for patients with osteoporosis. Endowing implants with immunomodulatory function can effectively enhance osseointegration. In this work, we loaded icariin (ICA) onto...

The effect of polysaccharide-based hydrogels on the response of antigen-presenting cell lines to immunomodulators

Hydrogel presents as foreign material to the host and participates in immune responses, which skew the biofunctions of immunologic loads (antigen and adjuvants) during in situ DC priming. This study aims to investigate the effect of the hydrogel made from different polysaccharides on macrophage (RAW264.7) activation and DC (JAWSII) modulation. We adopted polysaccharides of different sugar chemistry to fabricate hydrogels. Hyaluronate (HA), glycol chitosan (GC) and dextran (DX) were functionalized with vinyl sulfone and chemically cross-linked with dithiothreitol via thiol-click chemistry. We found that HA reduced macrophage adhesion and activation on the hydrogel surface. GC and DX promoted M1 polarization in terms of higher CCR7 expression and TNF-α, IL-6 production. In terms of DC engagement, GC promoted antigen uptake by JAWSII and all hydrogels promoted antigen presentation on MHC-I molecules. GC and DX favoured the generation of immunogenic DC while accommodating immunostimulatory functions of IFN-γ and polyI:C or LPS during co-incubation. Particularly, the co-incubation of IP with GC promoted CCR7 expression on JAWSII. Conversely, HA was more appropriate for the construction of a tolerogenic DC priming platform. We observed that HA did not induce co-stimulatory markers expression on DC but suppressed the action of LPS in inducing TNF-α generation. Moreover, when immunosuppressive cytokines, IL-10 and TGF-β were added, cytokines' immunosuppressive action was amplified by hydrogel bedding, HA, GC and to a less extent DX in suppressing LPS-induced IL-6 generation from JAWSII. We concluded that HA is preferable for tolerogenic DC development while minimizing the macrophage response in conferring foreign body response, whereas DX and GC are more appropriate for immunogenic DC development. This study demonstrates the potential of polysaccharides in conferring in situ DC priming together with antigen and adjuvant loads while addressing the tradeoff between the foreign body responses and DC engagement by selecting appropriate polysaccharides for the hydrogel platform construction.

A novel delivery nanobiotechnology: engineered miR-181b exosomes improved osteointegration by regulating macrophage polarization

Background

Many patients suffer from implant loosening after the implantation of titanium alloy caused by immune response to the foreign bodies and this could inhibit the following osteogenesis, which could possibly give rise to aseptic loosening and poor osteointegration while there is currently no appropriate solution in clinical practice. Exosome (Exo) carrying miRNA has been proven to be a suitable nanocarrier for solving this problem. In this study, we explored whether exosomes overexpressing miR-181b (Exo-181b) could exert beneficial effect on promoting M2 macrophage polarization, thus inhibiting inflammation as well as promoting osteogenesis and elaborated the underlying mechanism in vitro. Furthermore, we aimed to find whether Exo-181b could enhance osteointegration.

Results

In vitro, we firstly verified that Exo-181b significantly enhanced M2 polarization and inhibited inflammation by suppressing PRKCD and activating p-AKT. Then, in vivo, we verified that Exo-181b enhanced M2 polarization, reduced the inflammatory response and enhanced osteointegration. Also, we verified that the enhanced M2 polarization could indirectly promote the migration and osteogenic differentiation by secreting VEGF and BMP-2 in vitro.

Conclusions

Exo-181b could suppress inflammatory response by promoting M2 polarization via activating PRKCD/AKT signaling pathway, which further promoting osteogenesis in vitro and promote osteointegration in vivo.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01015-y.

Biomedical Implants with Charge-Transfer Monitoring and Regulating Abilities

Transmembrane charge (ion/electron) transfer is essential for maintaining cellular homeostasis and is involved in many biological processes, from protein synthesis to embryonic development in organisms. Designing implant devices that can detect or regulate cellular transmembrane charge transfer is expected to sense and modulate the behaviors of host cells and tissues. Thus, charge transfer can be regarded as a bridge connecting living systems and human-made implantable devices. This review describes the mode and mechanism of charge transfer between organisms and nonliving materials, and summarizes the strategies to endow implants with charge-transfer regulating or monitoring abilities. Furthermore, three major charge-transfer controlling systems, including wired, self-activated, and stimuli-responsive biomedical implants, as well as the design principles and pivotal materials are systematically elaborated. The clinical challenges and the prospects for future development of these implant devices are also discussed.

Strontium-doped gelatin scaffolds promote M2 macrophage switch and angiogenesis through modulating the polarization of neutrophils

The immune system mediates inflammation, vascularization and the first response to injuries or implanted biomaterials. Although the function of neutrophils in tissue repair has been extensively studied, its complete role in the tissue regeneration of biomaterials, specifically the resolution of inflammation and promotion of angiogenesis, is unclear. Here, we fabricate nanofibrous gelatin scaffolds containing 10% (w/w) strontium-hydroxyapatite (SrHA) via phase-separation methods to investigate Sr-mediated regulation of neutrophil polarization and, subsequently, the effects on angiogenesis and macrophage polarization. Compared with neutrophils cultured on pure gelatin or HA-incorporated gelatin scaffolds, neutrophils on SrHA-incorporated gelatin scaffolds show more N2 polarization in vitro and in vivo and significantly greater production of immunomodulatory and angiogenic factors. The Sr-induced immunomodulatory and proangiogenic functions of neutrophils are mediated through NF-κB pathway downregulation and increased STAT3 phosphorylation. Thus, neutrophils play a vital role in tissue engineering, and Sr-incorporated scaffolds efficiently promote neutrophil polarization to the N2 phenotype, enhancing resolution of inflammation and ultimately promoting angiogenesis and tissue regeneration. Thus, incorporation of neutrophils in analyses of the immune characteristics of scaffolds and the development of immunomodulatory biomaterials that can regulate neutrophils are novel and promising strategies in tissue engineering.

Inflammation and biomaterials: role of the immune response in bone regeneration by inorganic scaffolds

The regulatory role of the immune system in maintaining bone homeostasis and restoring its functionality, when disturbed due to trauma or injury, has become evident in recent years. The polarization of macrophages, one of the main constituents of the immune system, into the pro-inflammatory or anti-inflammatory phenotype has great repercussions for cellular crosstalk and the subsequent processes needed for proper bone regeneration such as angiogenesis and osteogenesis. In certain scenarios, the damaged osseous tissue requires the placement of synthetic bone grafts to facilitate the healing process. Inorganic biomaterials such as bioceramics or bioactive glasses are the most widely used due to their resemblance to the mineral phase of bone and superior osteogenic properties. The immune response of the host to the inorganic biomaterial, which is of an exogenous nature, might determine its fate, leading either to active bone regeneration or its failure. Therefore, various strategies have been employed, like the modification of structural/chemical features or the incorporation of bioactive molecules, to tune the interplay with the immune cells. Understanding how these particular modifications impact the polarization of macrophages and further osteogenic and osteoclastogenic events is of great interest in view of designing a new generation of osteoimmunomodulatory materials that support the regeneration of osseous tissue during all stages of bone healing.

Bioadaptation of implants to In vitro and In vivo oxidative stress pathological conditions via nanotopography-induced FoxO1 signaling pathways to enhance Osteoimmunal regeneration

Varieties of pathological conditions, including diabetes, are closely related to oxidative stress (OS), but the osseointegration or bioadaptation of implants to OS and the related mechanism remain poorly explored. In this study, the antioxidation and osteoimmune regeneration of titanium implants with micro/nanotopographies were evaluated under H₂O₂-, lipopolysaccharide (LPS)- and hyperglycemia-mediated cellular OS models and in diabetic rats as a representative animal model of OS. TiO₂ nanotube (TNT) coating on titanium implants directly induced superior osteogenic differentiation of bone mesenchymal stem cells (MSCs) and osseointegration compared with microscale sand blasted-acid etched topography (SLA) under OS, attributed to higher superoxide dismutase 2 activity, the neutralization of intracellular reactive oxygen species (ROS), and less apoptosis. Mechanistically, the oxidation resistance on TNT is driven by upregulated forkhead box transcription factor O1 (FoxO1), which is abolished after knockdown of FoxO1 via shRNA in MSCs. Indirectly, TNT also alleviates OS in macrophages, therefore inducing a higher portion of the M2 phenotype under OS with increased secretion of the anti-inflammatory cytokine IL-10, further promoting the osseoimmunity capacity compared with SLA. The current study not only suggests the potential application of TiO₂ nanotube-coated titanium implants in compromised conditions but also provides a systematic evaluation strategy for the future development of bone biomaterials.

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H₂O₂, lipopolysaccharide and hyperglycemia induced cellular oxidative stress models.

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TiO₂ nanotubes promote oxidation resistance and osteogenesis under oxidative stress.

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TiO₂ nanotubes activate forkhead box transcription factor O1 to enhance osteogenesis.

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TiO₂-nanotube-coated implants promote osseointegration in diabetic rats.

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TiO₂ nanotubes induce anti-inflammatory osteoimmunity under oxidative stress.

Synergistic effects of immunoregulation and osteoinduction of ds-block elements on titanium surface

Ds-block elements have been gaining increasing attention in the field of biomaterials modification, owing to their excellent biological properties, such as antibiosis, osteogenesis, etc. However, their function mechanisms are not well understood and conflicting conclusions were drawn by previous studies on this issue, which are mainly resulted from the inconsistent experimental conditions. In this work, three most widely used ds-block elements, copper, zinc, and silver were introduced on titanium substrate by plasma immersion ion implantation method to investigate the rule of ds-block elements in the immune responses. Results showed that the implanted samples could decrease the inflammatory responses compared with Ti sample. The trend of anti-inflammatory effects of macrophages on samples was in correlation with cellular ROS levels, which was induced by the implanted biomaterials and positively correlated with the number of valence electrons of ds-block elements. The co-culture experiments of macrophages and bone marrow mesenchymal stem cells showed that these two kinds of cells could enhance the anti-inflammation and osteogenesis of samples by the paracrine manner of PGE2. In general, in their steady states on titanium substrate (Cu2+, Zn2+, Ag), the ds-block elements with more valence electrons exhibit better anti-inflammatory and osteogenic effects. Moreover, molecular biology experiments indicate that the PGE2-related signaling pathway may contribute to the desired immunoregulation and osteoinduction capability of ds-block elements. These findings suggest a correlation between the number of valence electrons of ds-block elements and the relevant biological responses, which provides new insight into the selection of implanted ions and surface design of biomaterials.

Functionality-packed additively manufactured porous titanium implants

The holy grail of orthopedic implant design is to ward off both aseptic and septic loosening for long enough that the implant outlives the patient. Questing this holy grail is feasible only if orthopedic biomaterials possess a long list of functionalities that enable them to discharge the onerous task of permanently replacing the native bone tissue. Here, we present a rationally designed and additive manufacturing (AM) topologically ordered porous metallic biomaterial that is made from Ti-6Al-4V using selective laser melting and packs most (if not all) of the required functionalities into a single implant. In addition to presenting a fully interconnected porous structure and form-freedom that enables realization of patient-specific implants, the biomaterials developed here were biofunctionalized using plasma electrolytic oxidation to locally release both osteogenic (i.e. strontium) and antibacterial (i.e. silver ions) agents. The same single-step biofunctionalization process also incorporated hydroxyapatite into the surface of the implants. Our measurements verified the continued release of both types of active agents up to 28 days. Assessment of the antibacterial activity in vitro and in an ex vivo murine model demonstrated extraordinarily high levels of bactericidal effects against a highly virulent and multidrug-resistant Staphylococcus aureus strain (i.e. USA300) with total eradication of both planktonic and adherent bacteria. This strong antibacterial behavior was combined with a significantly enhanced osteogenic behavior, as evidenced by significantly higher levels of alkaline phosphatase (ALP) activity compared with non-biofunctionalized implants. Finally, we discovered synergistic antibacterial behavior between strontium and silver ions, meaning that 4-32 folds lower concentrations of silver ions were required to achieve growth inhibition and total killing of bacteria. The functionality-packed biomaterial presented here demonstrates a unique combination of functionalities that make it an advanced prototype of future orthopedic biomaterials where implants will outlive patients.

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

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

Perillyl alcohol has antibacterial effects and reduces ROS production in macrophages

Natural products have emerged as a rich source of bioactive compounds for adjunctive treatments of many infectious and inflammatory conditions, including periodontitis. Among the monoterpenes with significant biological properties, there is the perillyl alcohol (POH), which can be found in several essential oils and has shown immunomodulatory properties in recent studies, which may be interesting in the treatment of non-neoplastic inflammatory disorders.

Bioactive effects of strontium loading on micro/nano surface Ti6Al4V components fabricated by selective laser melting

Selective laser melting (SLM) titanium alloys require surface modification to achieve early bone-bonding. This study investigated the effects of solution and heat treatment to induce the sustained release of strontium (Sr) ions from SLM Ti6Al4V implants (Sr-S64). The results were compared with a control group comprising an untreated surface [SLM pure titanium (STi) and SLM Ti6Al4V (S64)] and a treated surface to induce the release of calcium (Ca) ions from SLM Ti6Al4V (Ca-S64). The surface-treated materials showed homogenous nanoscale network formation on the original micro-topographical surface and formed bone-like apatite on the surface in a simulated body fluid within 3 days. In vitro evaluation using MC3T3-E1 cells showed that the cells were viable on Sr-S64 surface, and Sr-S64 enhanced cell adhesion-related and osteogenic differentiation-related genes expression. In vivo rabbit tibia model, Sr-S64 provided significantly greater bone-bonding strength and bone-implant contact area than those in controls (STi and S64) in the early phase (2-4 weeks) after implantation; however, there was no statistical difference between Ca-S64 and controls. In conclusion, Sr solution and heat treatment was a safe and effective method to enhance early bone-bonding ability of S-64 by improving the surface characteristics and sustained delivery for Sr.

Effect of the nano/microscale structure of biomaterial scaffolds on bone regeneration

Natural bone is a mineralized biological material, which serves a supportive and protective framework for the body, stores minerals for metabolism, and produces blood cells nourishing the body. Normally, bone has an innate capacity to heal from damage. However, massive bone defects due to traumatic injury, tumor resection, or congenital diseases pose a great challenge to reconstructive surgery. Scaffold-based tissue engineering (TE) is a promising strategy for bone regenerative medicine, because biomaterial scaffolds show advanced mechanical properties and a good degradation profile, as well as the feasibility of controlled release of growth and differentiation factors or immobilizing them on the material surface. Additionally, the defined structure of biomaterial scaffolds, as a kind of mechanical cue, can influence cell behaviors, modulate local microenvironment and control key features at the molecular and cellular levels. Recently, nano/micro-assisted regenerative medicine becomes a promising application of TE for the reconstruction of bone defects. For this reason, it is necessary for us to have in-depth knowledge of the development of novel nano/micro-based biomaterial scaffolds. Thus, we herein review the hierarchical structure of bone, and the potential application of nano/micro technologies to guide the design of novel biomaterial structures for bone repair and regeneration.

Modulating the cobalt dose range to manipulate multisystem cooperation in bone environment: a strategy to resolve the controversies about cobalt use for orthopedic applications

The paradoxical effect of cobalt on biological processes has aroused controversy regarding the application of cobalt-based biomaterials in bone regeneration. Tuning the dose range of cobalt ions may be a valid strategy to resolve the controversies about cobalt use for orthopedic applications. Recent progress in bone biology has highlighted the effects of multisystem cooperation (especially of osteoimmune, skeletal, and vascular systems) on bone dynamics. Before the application of this dose-tuning strategy, a deeper understanding of its dose-dependent effect on the cooperation of osteoimmune, skeletal, and vascular systems is needed. However, due to the difficulties with investigating the interaction of multiple systems in vitro, the multimodal effects of cobalt on bone homeostasis were investigated here, in an in vivo scenario. Methods: In vitro CCK8 assay and cytoskeletal staining were preformed to detecte the cell cytotoxic reaction in response to 0.1-100 ppm cobalt stimulation. Blood clot containing 0.1 to 5 ppm of cobalt were implanted in the rat calvarium defect. The gene profile of osteoimmune, skeletal, and vascular system as well as the systemic toxicity were evaluated via RT-qPCR, histological analysis and inductively coupled plasma mass spectrometry. The bone regeneration, osteoclastogenesis and vascularization were assessed by micro-ct and histological analysis. Results: Cobalt concentration below 5 ppm did not cause cell toxicity in vitro. No systemic toxicity was observed in vivo at 0.1-5 ppm cobalt concentration. It was found that the early cytokine profiles of the multiple interacting systems were different in response to different cobalt doses. Most of the anti-inflammatory, osteogenic, and proangiogenic factors were upregulated in the 1 ppm cobalt group at the early stage. In the late stage, the 1ppm group was most superior in bone regenerative effect while the 5 ppm group displayed the strongest osteoclastogenesis activity. Conclusions: The 1 ppm concentration of cobalt yielded the most favorable cooperation of the osteoimmune, skeletal, and vascular systems and subsequently optimal bone regeneration outcomes. Tuning the cobalt dose range to manipulate the cooperation of osteoimmune, skeletal, and vascular systems could be a promising and valuable strategy to prevent paradoxical effects of cobalt while preserving its beneficial effects.

Magnetic lanthanum-doped hydroxyapatite/chitosan scaffolds with endogenous stem cell-recruiting and immunomodulatory properties for bone regeneration

Magnetic lanthanum hydroxyapatite/chitosan scaffolds can better repair bone defects through stem cell recruitment and immunomodulation.

Curcumin has immunomodulatory effects on RANKL-stimulated osteoclastogenesis in vitro and titanium nanoparticle-induced bone loss in vivo

Wear particle‐stimulated inflammatory bone destruction and the consequent aseptic loosening remain the primary causes of artificial prosthesis failure and revision. Previous studies have demonstrated that curcumin has a protective effect on bone disorders and inflammatory diseases and can ameliorate polymethylmethacrylate‐induced osteolysis in vivo. However, the effect on immunomodulation and the definitive mechanism by which curcumin reduces the receptor activators of nuclear factor‐kappa B ligand (RANKL)‐stimulated osteoclast formation and prevents the activation of osteoclastic signalling pathways are unclear. In this work, the immunomodulation effect and anti‐osteoclastogenesis capacities exerted by curcumin on titanium nanoparticle‐stimulated macrophage polarization and on RANKL‐mediated osteoclast activation and differentiation in osteoclastic precursor cells in vitro were investigated. As expected, curcumin inhibited RANKL‐stimulated osteoclast maturation and formation and had an immunomodulatory effect on macrophage polarization in vitro. Furthermore, studies aimed to identify the potential molecular and cellular mechanisms revealed that this protective effect of curcumin on osteoclastogenesis occurred through the amelioration of the activation of Akt/NF‐κB/NFATc1 pathways. Additionally, an in vivo mouse calvarial bone destruction model further confirmed that curcumin ameliorated the severity of titanium nanoparticle‐stimulated bone loss and destruction. Our results conclusively indicated that curcumin, a major biologic component of Curcuma longa with anti‐inflammatory and immunomodulatory properties, may serve as a potential therapeutic agent for osteoclastic diseases.

Lithium chloride with immunomodulatory function for regulating titanium nanoparticle-stimulated inflammatory response and accelerating osteogenesis through suppression of MAPK signaling pathway

Background

Wear particle-induced inflammatory osteolysis and the consequent aseptic loosening constitute the leading reasons for prosthesis failure and revision surgery. Several studies have demonstrated that the macrophage polarization state and immune response play critical roles in periprosthetic osteolysis and tissue repair, but the immunomodulatory role of lithium chloride (LiCl), which has a protective effect on wear particle-induced osteolysis by suppressing osteoclasts and attenuating inflammatory responses, has never been investigated.

Methods

In this work, the immunomodulatory capability of LiCl on titanium (Ti) nanoparticle-stimulated transformation of macrophage phenotypes and the subsequent effect on osteogenic differentiation were investigated. We first speculated that LiCl attenuated Ti nanoparticle-stimulated inflammation responses by driving macrophage polarization and generating an immune micro-environment to improve osteogenesis. Furthermore, a metal nanoparticle-stimulated murine air pouch inflammatory model was applied to confirm this protective effect in vivo.

Results

The results revealed that metal nanoparticles significantly activate M1 phenotype (proinflammatory macrophage) expression and increase proinflammatory cytokines secretions in vitro and in vivo, whereas LiCl drives macrophages to the M2 phenotype (anti-inflammatory macrophage) and increases the release of anti-inflammatory and bone-related cytokines. This improved the osteogenic differentiation capability of rat bone marrow mesenchymal stem cells (rBMSCs). In addition, we also provided evidence that LiCl inhibits the phosphorylation of the p38 mitogen-activated protein kinase (p38) and extracellular signal-regulated kinase (ERK) pathways in wear particle-treated macrophages.

Conclusion

LiCl has the immunomodulatory effects to alleviate Ti nanoparticle-mediated inflammatory reactions and enhance the osteogenic differentiation of rBMSCs by driving macrophage polarization. Thus, LiCl may be an effective therapeutic alternative for preventing and treating wear debris-induced inflammatory osteolysis.

Enhanced cell functions on graphene oxide incorporated 3D printed polycaprolactone scaffolds

For tissue engineering applications, a porous scaffold with an interconnected network is essential to facilitate the cell attachment and proliferation in a three dimensional (3D) structure. This study aimed to fabricate the scaffolds by an extrusion-based 3D printer using a blend of polycaprolactone (PCL), and graphene oxide (GO) as a favorable platform for bone tissue engineering. The mechanical properties, morphology, biocompatibility, and biological activities such as cell proliferation and differentiation were studied concerning the two different pore sizes; 400 μm, and 800 μm, and also with two different GO content; 0.1% (w/w) and 0.5% (w/w). The compressive strength of the scaffolds was not significantly changed due to the small amount of GO, but, as expected scaffolds with 400 μm pores showed a higher compressive modulus in comparison to the scaffolds with 800 μm pores. The data indicated that the cell attachment and proliferation were increased by adding a small amount of GO. According to the results, pore size did not play a significant role in cell proliferation and differentiation. Alkaline Phosphate (ALP) activity assay further confirmed that the GO increase the ALP activity and further Elemental analysis of Calcium and Phosphorous showed that the GO increased the mineralization compared to PCL only scaffolds. Western blot analysis showed the porous structure facilitate the secretion of bone morphogenic protein-2 (BMP-2) and osteopontin at both day 7 and 14 which galvanizes the osteogenic capability of PCL and PCL + GO scaffolds.

Crocin inhibits titanium particle-induced inflammation and promotes osteogenesis by regulating macrophage polarization

Wear particle-induced periprosthetic inflammatory osteolysis and resultant aseptic loosening are major causes of orthopedic implant failure, for which there are no effective treatments other than revision surgery. Crocin, a carotenoid compound derived from crocus flowers, has anti-inflammatory properties, but its immunomodulatory function and role in particle-induced osteolysis are not well characterized. Here we report the effect of crocin on titanium (Ti) particle-induced macrophage polarization and osteogenic differentiation. We found that crocin induced anti-inflammatory (M2) macrophage polarization and attenuated Ti particle-induced inflammation by promoting the expression of anti-inflammatory cytokines in vitro as well as in vivo in a mouse air-pouch model. Additionally, crocin pre-treated macrophages promoted osteogenic differentiation of co-cultured mouse bone mesenchymal stem cells (BMSCs). These effects were mediated via inhibition of p38 and c-Jun N-terminal kinase signaling. Our results indicate that crocin suppresses Ti particle-induced inflammation and enhances osteogenic differentiation of BMSCs by inducing M2 macrophage polarization, highlighting its therapeutic potential for preventing wear particle-induced osteolysis.

Macrophage polarization following three-dimensional porous PEEK

Macrophages play an important role in foreign body reaction (FBR), and exhibit a detrimental or beneficial function in tissue repair while polarized into different phenotypes. The objective of this work is to evaluate the effect of three-dimensional (3D) porous polyetheretherketone (PEEK) on macrophage polarization through sulfonating PEEK and establishing a mouse air pouch model. The in vivo results show that the sulfonated PEEK induced higher levels of anti-inflammatory cytokine together with lower levels of pro-inflammatory cytokine. In addition, it was found that a relatively mild infiltration of inflammatory cells was caused and there were more M2 macrophages and less M1 ones when compared with PEEK. It indicates that 3D porous PEEK induces a shift to M2 macrophages and has large potential in regenerative medicine application.

Nanostructural Surfaces with Different Elastic Moduli Regulate the Immune Response by Stretching Macrophages

A proper immune response is key for the successful implantation of biomaterials, and designing and fabricating biomaterials to regulate immune responses is the future trend. In this work, three different nanostructures were constructed on the surface of titanium using a hydrothermal method, and through a series of in vitro and in vivo experiments, we found that the aspect ratio of nanostructures can affect the elastic modulus of a material surface and further regulate immune cell behaviors. This work demonstrates that nanostructures with a higher aspect ratio can endow a material surface with a lower elastic modulus, which was confirmed by experiments and theoretical analyses. The deflection of nanostructures under the cell adsorption force is a substantial factor in stretching macrophages to enhance cell adhesion and spreading, further inducing macrophage polarization toward the M1 phenotype and leading to intense immune responses. In contrast, a nanostructure with a lower aspect ratio on a material surface leads to a higher surface elastic modulus, making deflection of the material difficult and creating a surface that is not conducive to macrophage adhesion and spreading, thus reducing the immune response. Moreover, molecular biology experiments indicated that regulation of the immune response by the elastic modulus is primarily related to the NF-κB signaling pathway. These findings suggest that the immune response can be regulated by constructing nanostructural surfaces with the proper elastic modulus through their influence on cell adhesion and spreading, which provides new insights into the surface design of biomaterials.