Topography-mediated immunomodulation in osseointegration; Ally or Enemy

Surface topography modulates initial platelet adhesion to titanium substrata

The clinical success of implanted biomaterials such as dental implants is largely determined by the molecular signaling that occurs at the tissue-implant interface. The modification of surface topography is a widely-employed strategy for optimizing tissue integration with dental implants. However, little is known regarding the direct, cellular-level effects of substratum topography on platelet signaling and adhesion, despite these cells being the first to encounter the implant surface during surgical placement. Here we compared platelet adhesion and secretion on four (4) different titanium surfaces, notably, the modifications applied to commercially available dental implants: smooth (S) titanium; acid-etched (AE), sandblasted (SB) and a combined acid-etching/sandblasting procedure (SLA). Platelets were isolated from human blood, washed, and seeded on to the 4 test surfaces; platelet adhesion was quantified by microscopy. In addition, the secretion of critical molecules stored in platelet granules (platelet factor 4, PF4; soluble P-selectin, sCD62P; transforming growth factor-beta1, TGF-β1; platelet-derived growth factor-AB, PDGF-AB) was measured by enzyme-linked immunosorbent assay (ELISA) analysis of the supernatants. There was greater platelet adhesion to the rougher AE and SB surfaces, however, the concentration of the secreted growth factors was comparable on all surfaces. We conclude that while surface topography can be engineered to modulate initial platelet adhesion, granule secretion is likely regulated as a separate and independent process.

Jaw osteoporosis: Challenges to oral health and emerging perspectives of treatment

Osteoporosis is a prevalent bone metabolic disease that poses a significant challenge to global human health. Jaw osteoporosis, characterized by microstructural damage of the jaw resulting from various factors, is one of the common manifestations of this condition. Recent studies have demonstrated that jaw osteoporosis has multifaceted effects on oral health and can negatively impact conditions such as periodontitis, oral implantation, orthodontic treatment, and wound healing. However, there are still some limitations in the conventional treatment of osteoporosis. For instance, while bisphosphonates can enhance bone quality, they may also lead to osteonecrosis of the jaw, which poses a potential safety hazard in oral diagnosis and treatment. In recent years, considerable attention has been focused on improving the pathological condition of jaw osteoporosis. Treatment strategies such as gut microbial regulation, extracellular vesicles, molecular targeted therapy, herbal medicine, mechanical stimulation are expected to enhance efficacy and minimize adverse reactions. Therefore, understanding these effects and exploring novel treatments for jaw osteoporosis may provide new insights for oral health maintenance and disease treatment. This article reviews the impact of jaw osteoporosis on oral health and describes the limitations associated with current methods. It also discusses emerging perspectives on treatment, offering a comprehensive overview of the challenges and future directions in managing jaw osteoporosis.

Preliminary study of the homeostatic regulation of osseointegration by nanotube topology

The ideal implant surface plays a substantial role in maintaining bone homeostasis by simultaneously promoting osteoblast differentiation and limiting overactive osteoclast activity to a certain extent, which leads to satisfactory dynamic osseointegration. However, the rational search for implant materials with an ideal surface structure is challenging and a hot research topic in the field of tissue engineering. In this study, we constructed titanium dioxide titanium nanotubes (TNTs) by anodic oxidation and found that this structure significantly promoted osteoblast differentiation and inhibited osteoclast formation and function while simultaneously inhibiting the total protein levels of proline-rich tyrosine kinase 2 (PYK2) and focal adhesion kinase (FAK). Knockdown of the PYK2 gene by siRNA significantly suppressed the number and osteoclastic differentiation activity of mouse bone marrow mononuclear cells (BMMs), while overexpression of PYK2 inhibited osteogenesis and increased osteoclastic activity. Surprisingly, we found for the first time that neither knockdown nor overexpression of the FAK gene alone caused changes in osteogenesis or osteoclastic function. More importantly, compared with deletion or overexpression of PYK2/FAK alone, coexpression or cosilencing of the two kinases accelerated the effects of TNTs on osteoclastic and osteogenic differentiation on the surface of cells. Furthermore, in vivo experiments revealed a significant increase in positiveexpression-PYK2 cells on the surface of TNTs, but no significant change in positiveexpression -FAK cells was observed. In summary, PYK2 is a key effector molecule by which osteoblasts sense nanotopological mechanical signals and maintain bone homeostasis around implants. These results provide a referable molecular mechanism for the future development and design of homeostasis-based regulatory implant biomaterials.

Surface Topography Steer Soft Tissue Response and Antibacterial Function at the Transmucosal Region of Titanium Implant

Metallic dental implants have been extensively used in clinical practice due to their superior mechanical properties, biocompatibility, and aesthetic outcomes. However, their integration with the surrounding soft tissue at the mucosal region remains challenging and can cause implant failure due to the peri-implant immune microenvironment. The soft tissue integration of dental implants can be ameliorated through different surface modifications. This review discussed and summarized the current knowledge of topography-mediated immune response and topography-mediated antibacterial activity in Ti dental implants which enhance soft tissue integration and their clinical performance. For example, nanopillar-like topographies such as spinules, and spikes showed effective antibacterial activity in human salivary biofilm which was due to the lethal stretching of bacterial membrane between the nanopillars. The key findings of this review were (I) cross-talk between surface nanotopography and soft tissue integration in which the surface nanotopography can guide the perpendicular orientation of collagen fibers into connective tissue which leads to the stability of soft tissue, (II) nanotubular array could shift the macrophage phenotype from pro-inflammatory (M1) to anti-inflammatory (M2) and manipulate the balance of osteogenesis/osteoclasia, and (III) surface nanotopography can provide specific sites for the loading of antibacterial agents and metallic nanoparticles of clinical interest functionalizing the implant surface. Silver-containing nanotubular topography significantly decreased the formation of fibrous encapsulation in per-implant soft tissue and showed synergistic antifungal and antibacterial properties. Although the Ti implants with surface nanotopography have shown promising in targeting soft tissue healing in vitro and in vivo through their immunomodulatory and antibacterial properties, however, long-term in vivo studies need to be conducted particularly in osteoporotic, and diabetic patients to ensure their desired performance with immunomodulatory and antibacterial properties. The optimization of product development is another challenging issue for its clinical translation, as the dental implant with surface nanotopography must endure implantation and operation inside the dental microenvironment. Finally, the sustainable release of metallic nanoparticles could be challenging to reduce cytotoxicity while augmenting the therapeutic effects.

Designer Micro-/Nanocrumpled MXene Multilayer Coatings Accelerate Osteogenesis and Regulate Macrophage Polarization

Effective tissue regeneration and immune responses are essential for the success of biomaterial implantation. Although the interaction between synthetic materials and biological systems is well-recognized, the role of surface topographical cues in regulating the local osteoimmune microenvironment─specifically, their impact on host tissue and immune cells, and their dynamic interactions─remains underexplored. This study addresses this gap by investigating the impact of surface topography on osteogenesis and immunomodulation. We fabricated MXene/hydroxyapatite (HAP)-coated surfaces with controlled 2.5D nano-, submicro-, and microscale topographical patterns using our custom bottom-up patterning method. These engineered surfaces were employed to assess the behavior of osteoblast precursor cells and macrophage polarization. Our results demonstrate that MXene/HAP-coated surfaces with microscale crumpled topography significantly influence osteogenic activity and macrophage polarization: these surfaces notably enhanced osteoblast precursor cell spreading, proliferation, and differentiation and facilitated a shift in macrophages toward an anti-inflammatory, prohealing M2 phenotype. The observed cell responses indicate that the physical cues from the crumpled topographies, combined with the chemical cues from the MXene/HAP coatings, synergistically create a favorable osteoimmune microenvironment. This study presents the first evidence of employing MXene/HAP-multilayer coated surfaces with finely crumpled topography to concurrently facilitate osteogenesis and immunomodulation for improved implant-to-tissue integration. The tunable topographic patterns of these coatings coupled with a facile and scalable fabrication process make them widely applicable for various biomedical purposes. Our results highlight the potential of these multilayer coatings with controlled topography to improve the in vivo performance and fate of implants by modulating the host response at the material interface.

Hierarchically porous surface of HA-sandblasted Ti implant screw using the plasma electrolytic oxidation: Physical characterization and biological responses

The surface topological features of bioimplants are among the key indicators for bone tissue replacement because they directly affect cell morphology, adhesion, proliferation, and differentiation. In this study, we investigated the physical, electrochemical, and biological responses of sandblasted titanium (SB-Ti) surfaces with pore geometries fabricated using a plasma electrolytic oxidation (PEO) process. The PEO treatment was conducted at an applied voltage of 280 V in a solution bath consisting of 0.15 mol L-1 calcium acetate monohydrate and 0.02 mol L-1 calcium glycerophosphate for 3 min. The surface chemistry, wettability, mechanical properties and corrosion behavior of PEO-treated sandblasted Ti implants using hydroxyapatite particles (PEO-SB-Ti) were improved with the distribution of calcium phosphorous porous oxide layers, and showed a homogeneous and hierarchically porous surface with clusters of nanopores in a bath containing calcium acetate monohydrate and calcium glycerophosphate. To demonstrate the efficacy of PEO-SB-Ti, we investigated whether the implant affects biological responses. The proposed PEO-SB-Ti were evaluated with the aim of obtaining a multifunctional bone replacement model that could efficiently induce osteogenic differentiation as well as antibacterial activities. These physical and biological responses suggest that the PEO-SB-Ti may have a great potential for use an artificial bone replacement compared to that of the controls.

In vitro evaluation of bone cell response to novel 3D-printable nanocomposite biomaterials for bone reconstruction

Critically-sized segmental bone defects represent significant challenges requiring grafts for reconstruction. 3D-printed synthetic bone grafts are viable alternatives to structural allografts if engineered to provide appropriate mechanical performance and osteoblast/osteoclast cell responses. Novel 3D-printable nanocomposites containing acrylated epoxidized soybean oil (AESO) or methacrylated AESO (mAESO), polyethylene glycol diacrylate, and nanohydroxyapatite (nHA) were produced using masked stereolithography. The effects of volume fraction of nHA and methacrylation of AESO on interactions of differentiated MC3T3-E1 osteoblast (dMC3T3-OB) and differentiated RAW264.7 osteoclast cells with 3D-printed nanocomposites were evaluated in vitro and compared with a control biomaterial, hydroxyapatite (HA). Higher nHA content and methacrylation significantly improved the mechanical properties. All nanocomposites supported dMC3T3-OB cells' adhesion and proliferation. Higher amounts of nHA enhanced cell adhesion and proliferation. mAESO in the nanocomposites resulted in greater adhesion, proliferation, and activity at day 7 compared with AESO nanocomposites. Excellent osteoclast-like cells survival, defined actin rings, and large multinucleated cells were only observed on the high nHA fraction (30%) mAESO nanocomposite and the HA control. Thus, mAESO-based nanocomposites containing higher amounts of nHA have better interactions with osteoblast-like and osteoclast-like cells, comparable with HA controls, making them a potential future alternative graft material for bone defect repair.

Bacteroid cerium oxide particles promote macrophage polarization to achieve early vascularization and subsequent osseointegration around implants

The establishment of an osseointegration is crucial for the long-term stability and functionality of implant materials, and early angiogenesis is the key to successful osseointegration. However, the bioinertness of titanium implants affects osseointegration, limiting their clinical application. In this study, inspired by the rapid polarization of macrophages following the phagocytosis of bacteria, we developed bacteroid cerium oxide particles; these particles were composed of CeO2 and had a size similar to that of Bacillus (0.5 μ m). These particles were constructed on the implant surfaces using a hydrothermal method. In vitro experiments demonstrated that the particles effectively decreased the reactive oxygen species (ROS) levels in macrophages (RAW264.7). Furthermore, these particles exerted effects on M1 macrophage polarization, enhanced nitric oxide (NO) secretion to promote vascular regeneration, and facilitated rapid macrophage transition to the M2 phenotype. Subsequently, the particles facilitated human umbilical vein endothelial cell (HUVEC) migration. In vivo studies showed that these particles rapidly stimulated innate immune responses in animal models, leading to enhanced angiogenesis around the implant and improved osseointegration. In summary, the presence of bacteroid cerium oxide particles on the implant surface regulated and accelerated macrophage polarization, thereby enhancing angiogenesis during the immune response and improving peri-implant osseointegration.

Ion-incorporated titanium implants for staged regulation of antibacterial activity and immunoregulation-mediated osteogenesis

Antibacterial properties and osteogenic activity are considered as two crucial factors for the initial healing and long-term survivability of orthopedic implants. For decades, various drug-loaded implants to enhance biological activities have been investigated extensively. More importantly, to control the drug release timing is equally significant due to the sequential biological processes after implantation. Hence, developing a staged regulation system on the titanium surface is practically significant. Here, we prepared TiO2 nanotubes (TiO2 NTs) on the titanium surface by anodization, followed by the incorporation of zinc (Zn) and strontium (Sr) sequentially through a hydrothermal process. Surface characterization confirmed the successful fabrication of Zn and Sr-incorporated TiO2 NTs (Zn-Sr/TiO2) on the titanium surface. The ion release results exhibited the differential release characteristic of Zn and Sr, which meant the early-stage release of Zn and the long-term release of Sr. It was exactly in accord with  the biological process after implantation, laying the basis of staged regulation after implantation. Zn-Sr/TiO2 showed favorable anti-early infection properties both in vitro and in vivo. Its inhibition effect on bacterial biofilm formation was attributed to the resistance against bacteria's initial adhesion and the killing effect on planktonic bacteria. Additionally, the release of Sr could alleviate infection-induced damage via immunoregulation. The biocompatibility and osteogenic activity mediated by M2 macrophage activation were confirmed with in vitro and in vivo studies. Therefore, it exhibited great potential in staged regulation for antibacterial activity in the early stage and the M2 activation-mediated osteogenic activity in the late stage. The staged regulation process was based on the differential release of Zn and Sr to achieve the early antibacterial effect and the long-term immune-induced osteogenic activity, to prevent implant-related infection and achieve better osseointegration. These two kinds of ions played their roles synergistically and complement mutually. This work is expected to provide an innovative idea for realizing sequential regulation after implantation.

Calcitonin gene-related peptide-modulated macrophage phenotypic alteration regulates angiogenesis in early bone healing

OBJECTIVES

This study aimed to investigate the effect of calcitonin gene-related peptide (CGRP) on the temporal alteration of macrophage phenotypes and macrophage-regulated angiogenesis duringearlybonehealing and preliminarily elucidate the mechanism.

METHODS

In vivo, the rat mandibular defect models were established with inferior alveolar nerve transection (IANT) or CGRP receptor antagonist injection. Radiographicandhistologic assessments for osteogenesis, angiogenesis, and macrophage phenotypic alteration within bone defects were performed. In vitro, the effect and mechanism of CGRP on macrophage polarization and phenotypic alteration were analyzed. Then the conditioned medium (CM) from CGRP-treated M1 or M2 macrophages was used to culture human umbilical vein endothelial cells (HUVECs), and the CGRP's effect on macrophage-regulated angiogenesis was detected.

RESULTS

Comparable changes following IANT and CGRP blockade within bone defects were observed, including the suppression of early osteogenesis and angiogenesis, the prolonged M1 macrophage infiltration and the prohibited transition toward M2 macrophages around vascular endothelium. In vitro experiments showed that CGRP promoted M2 macrophage polarization while upregulating the expression of interleukin 6 (IL-6), a major cytokine that facilitates the transition from M1 to M2-dominant stage, in M1 macrophages via the activation of Yes-associated protein 1. Moreover, CGRP-treated macrophage-CM showed an anabolic effect on HUVECs angiogenesis compared with macrophage-CM and might prevail over the direct effect of CGRP on HUVECs.

CONCLUSIONS

Collectively, our results reveal the effect of CGRP on M1 to M2 macrophage phenotypic alteration possibly via upregulating IL-6 in M1 macrophages, and demonstrate the macrophage-regulated pro-angiogenic potential of CGRP in early bone healing.

Biomimetic Therapeutics for Bone Regeneration: A Perspective on Antiaging Strategies

Advances in modern medicine and the significant reduction in infant mortality have steadily increased the population's lifespan. As more and more people in the world grow older, incidence of chronic, noncommunicable disease is anticipated to drastically increase. Recent studies have shown that improving the health of the aging population is anticipated to provide the most cost-effective and impactful improvement in quality of life during aging-driven disease. In bone, aging is tightly linked to increased risk of fracture, and markedly decreased regenerative potential, deeming it critical to develop therapeutics to improve aging-driven bone regeneration. Biomimetics offer a cost-effective method in regenerative therapeutics for bone, where there are numerous innovations improving outcomes in young models, but adapting biomimetics to aged models is still a challenge. Chronic inflammation, accumulation of reactive oxygen species, and cellular senescence are among three of the more unique challenges facing aging-induced defect repair. This review dissects many of the innovative biomimetic approaches research groups have taken to tackle these challenges, and discusses the further uncertainties that need to be addressed to push the field further. Through these research innovations, it can be noted that biomimetic therapeutics hold great potential for the future of aging-complicated defect repair.

Synergistic Amelioration of Osseointegration and Osteoimmunomodulation with a Microarc Oxidation-Treated Three-Dimensionally Printed Ti-24Nb-4Zr-8Sn Scaffold via Surface Activity and Low Elastic Modulus

Biomaterial scaffolds, including bone substitutes, have evolved from being primarily a biologically passive structural element to one in which material properties such as surface topography and chemistry actively direct bone regeneration by influencing stem cells and the immune microenvironment. Ti-6Al-4V(Ti6Al4V) implants, with a significantly higher elastic modulus than human bone, may lead to stress shielding, necessitating improved stability at the bone-titanium alloy implant interface. Ti-24Nb-4Zr-8Sn (Ti2448), a low elastic modulus β-type titanium alloy devoid of potentially toxic elements, was utilized in this study. We employed 3D printing technology to fabricate a porous scaffold structure to further decrease the structural stiffness of the implant to approximate that of cancellous bone. Microarc oxidation (MAO) surface modification technology is then employed to create a microporous structure and a hydrophilic oxide ceramic layer on the surface and interior of the scaffold. In vitro studies demonstrated that MAO treatment enhances the proliferation, adhesion, and osteogenesis capabilities on the scaffold surface. The chemical composition of the MAO-Ti2448 oxide layer is found to enhance the transcription and expression of osteogenic genes in bone mesenchymal stem cells (BMSCs), potentially related to the enrichment of Nb2O5 and SnO2 in the oxide layer. The MAO-Ti2448 scaffold, with its synergistic surface activity and low stiffness, significantly activates the anti-inflammatory macrophage phenotype, creating an immune microenvironment that promotes the osteogenic differentiation of BMSCs. In vivo experiments in a rabbit model demonstrated a significant improvement in the quantity and quality of the newly formed bone trabeculae within the scaffold under the contact osteogenesis pattern with a matched elastic modulus. These trabeculae exhibit robust connections to the external structure of the scaffold, accelerating the formation of an interlocking structure between the bone and implant and providing higher implantation stability. These findings suggest that the MAO-Ti2448 scaffold has significant potential as a bone defect repair material by regulating osteoimmunomodulation and osteogenesis to enhance osseointegration. This study demonstrates an optional strategy that combines the mechanism of reducing the elastic modulus with surface modification treatment, thereby extending the application scope of β-type titanium alloy.

Nanoscaled Titanium Oxide Layer Provokes Quick Osseointegration on 3D-Printed Dental Implants: A Domino Effect Induced by Hydrophilic Surface

Three-dimensional printing is a revolutionary strategy to fabricate dental implants. Especially, 3D-printed dental implants modified with nanoscaled titanium oxide layer (H-SLM) have impressively shown quick osseointegration, but the accurate mechanism remains elusive. Herein, we unmask a domino effect that the hydrophilic surface of the H-SLM facilitates blood wetting, enhances the blood shear rate, promotes blood clotting, and changes clot features for quick osseointegration. Combining computational fluid dynamic simulation and biological verification, we find a blood shear rate during blood wetting of the hydrophilic H-SLM 1.2-fold higher than that of the raw 3D-printed implant, which activates blood clot formation. Blood clots formed on the hydrophilic H-SLM demonstrate anti-inflammatory and pro-osteogenesis effects, leading to a 1.5-fold higher bone-to-implant contact and a 1.8-fold higher mechanical anchorage at the early stage of osseointegration. This mechanism deepens current knowledge between osseointegration speed and implant surface characteristics, which is instructive in surface nanoscaled modification of multiple 3D-printed intrabony implants.

GL13K-modified titanium regulates osteogenic differentiation via the NF-κB pathway

The osteoimmune response plays a crucial regulatory role in the osseointegration of dental implants. Previous studies found the antimicrobial peptide coating (GL13K) could activate the immunomodulatory potential of macrophages (Raw 264.7) and promote osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). To further investigate the mechanism of interaction between immunomodulation and differentiation, a co-culture model of the representative cells (Raw 264.7 and BMSCs) was constructed to mimic the immune microenvironment. In this system, GL13K coating of titanium implant effectively inhibited the polarization of the inflammatory M1 type and promoted the polarization of the anti-inflammatory M2 type. Furthermore, the inhibited NF-κB signaling pathway and Mip-2 gene expression were found and validated by bioinformatics analysis and virus-induced gene silencing, which significantly affected the tissue repair process. It can be concluded that the GL13K coating had the potential to establish a localized immune microenvironment conducive to osteogenic differentiation through cellular interactions. Subsequent investigations would be dedicated to a thorough examination of the osseointegration effects of GL13K coating.

Evaluation of nanoscale versus hybrid micro/nano surface topographies for endosseous implants

We examined the effect of a nanoscale titanium surface topography (D) versus two hybrid micro/nanoscale topographies (B and OS) on adherent mesenchymal stem cells (MSCs) and bone marrow derived macrophages (BMMs) function in cell culture and in vivo. In the in vitro study, compared to OS and B surfaces, D surface induced earlier and greater cell spreading, and earlier and profound mRNA expression of RUNX2, Osterix and BMP2 in MSCs. D surface induced earlier and higher expression of RUNX2 and BMP2 and lower expression of inflammatory genes in implant adherent cells in vivo. Measurement of osteogenesis at implant surfaces showed greater bone-to-implant contact at D versus OS surfaces after 21 days. We explored the cell population on the D and OS implant surfaces 24 h after placement using single-cell RNA sequencing and identified distinct cell clusters including macrophages, neutrophils and B cells. D surface induced lower expression and earlier reduction of inflammatory genes expression in BMMs in vitro. BMMs on D, B and OS surfaces demonstrated a marked increase of BMP2 expression after 1 and 3 days, and this increase was significantly higher on D surface at day 3. Our data implicates a dynamic process that may be influenced by nanotopography at multiple stages of osseointegration including initial immunomodulation, recruitment of MSCs and later osteoblastic differentiation leading to bone matrix production and mineralization. The results suggest that a nanoscale topography (D) favorably modulates adherent macrophage polarization toward anti-inflammatory and regenerative phenotypes and promotes the osteoinductive phenotype of adherent mesenchymal stem cells. STATEMENT OF SIGNIFICANCE: Our manuscript contains original data developed to define effects of a novel nanotopography on the process of osseointegration at the cell and tissue level.  Few studies have compared the effects of a nanoscale surface versus the more typical hybrid micro/nano-scale surfaces used today. We have utilized single-cell RNA sequencing for the first time to identify earliest cell populations on implant surfaces in vivo. We provide data indicating that the nanoscale surface acts upon both osteoprogenitor and immune cell (macrophages) to alter the process of bone formation in a surface-specific manner. This work represents new observations regarding osseointegration and immunomodulation.

Functionally Tailored Metal-Organic Framework Coatings for Mediating Ti Implant Osseointegration

Owing to their mechanical resilience and non-toxicity, titanium implants are widely applied as the major treatment modality for the clinical intervention against bone fractures. However, the intrinsic bioinertness of Ti and its alloys often impedes the effective osseointegration of the implants, leading to severe adverse complications including implant loosening, detachment, and secondary bone damage. Consequently, new Ti implant engineering strategies are urgently needed to improve their osseointegration after implantation. Remarkably, metalorganic frameworks (MOFs) are a class of novel synthetic material consisting of coordinated metal species and organic ligands, which have demonstrated a plethora of favorable properties for modulating the interfacial properties of Ti implants. This review comprehensively summarizes the recent progress in the development of MOF-coated Ti implants and highlights their potential utility for modulating the bio-implant interface to improve implant osseointegration, of which the discussions are outlined according to their physical traits, chemical composition, and drug delivery capacity. A perspective is also provided in this review regarding the current limitations and future opportunities of MOF-coated Ti implants for orthopedic applications. The insights in this review may facilitate the rational design of more advanced Ti implants with enhanced therapeutic performance and safety.

Advanced surface engineering of titanium materials for biomedical applications: From static modification to dynamic responsive regulation

Titanium (Ti) and its alloys have been widely used as orthopedic implants, because of their favorable mechanical properties, corrosion resistance and biocompatibility. Despite their significant success in various clinical applications, the probability of failure, degradation and revision is undesirably high, especially for the patients with low bone density, insufficient quantity of bone or osteoporosis, which renders the studies on surface modification of Ti still active to further improve clinical results. It is discerned that surface physicochemical properties directly influence and even control the dynamic interaction that subsequently determines the success or rejection of orthopedic implants. Therefore, it is crucial to endow bulk materials with specific surface properties of high bioactivity that can be performed by surface modification to realize the osseointegration. This article first reviews surface characteristics of Ti materials and various conventional surface modification techniques involving mechanical, physical and chemical treatments based on the formation mechanism of the modified coatings. Such conventional methods are able to improve bioactivity of Ti implants, but the surfaces with static state cannot respond to the dynamic biological cascades from the living cells and tissues. Hence, beyond traditional static design, dynamic responsive avenues are then emerging. The dynamic stimuli sources for surface functionalization can originate from environmental triggers or physiological triggers. In short, this review surveys recent developments in the surface engineering of Ti materials, with a specific emphasis on advances in static to dynamic functionality, which provides perspectives for improving bioactivity and biocompatibility of Ti implants.

Biological Effects of New Titanium Surface Coatings Based on Ionic Liquids and HMGB1: A Cellular and Molecular Characterization in Lewis Rats

High Mobility Group Box 1 (HMGB1) is a redox-sensitive molecule that plays dual roles in tissue healing and inflammation. We previously demonstrated that HMGB1 is stable when anchored by a well-characterized imidazolium-based ionic liquid (IonL), which serves as a delivery vehicle for exogenous HMGB1 to the site of injury and prevents denaturation from surface adherence. However, HMGB1 exists in different isoforms [fully reduced HMGB1 (FR), a recombinant version of FR resistant to oxidation (3S), disulfide HMGB1 (DS), and inactive sulfonyl HMGB1(SO)] that have distinct biological functions in health and disease. Thus, the goal of this study was to evaluate the effects of different recombinant HMGB1 isoforms on the host response using a rat subcutaneous implantation model. A total of 12 male Lewis rats (12-15 weeks) were implanted with titanium discs containing different treatments (n = 3/time point; Ti, Ti-IonL, Ti-IonL-DS, Ti-IonL-FR, and Ti-IonL-3S) and assessed at 2 and 14 days. Histological (H&E and Goldner trichrome staining), immunohistochemistry, and molecular analyses (qPCR) of surrounding implant tissues were employed for analysis of inflammatory cells, HMGB1 receptors, and healing markers. Ti-IonL-DS samples resulted in the thickest capsule formation, increased pro-inflammatory, and decreased anti-inflammatory cells, while Ti-IonL-3S samples demonstrated suitable tissue healing similar to uncoated Ti discs, as well as an upregulation of anti-inflammatory cells at 14 days compared to all other treatments. Thus, results from this study demonstrated that Ti-IonL-3S are safe alternatives for Ti biomaterials. Future studies are necessary to investigate the healing potential of Ti-IonL-3S in osseointegration scenarios.

Surface Modification and Functionalities for Titanium Dental Implants

Dental implants have become the mainstream strategy for oral restoration, and implant materials are the most important research hot spot in this field. So far, Ti implants dominate all kinds of implants. The surface properties of the Ti implant play decisive roles in osseointegration and antibacterial performance. Surface modifications can significantly change the surface micro/nanotopography and composition of Ti implants, which will effectively improve their hydrophilicity, mechanical properties, osseointegration performance, antibacterial performance, etc. These optimizations will thus improve implant success and service life. In this paper, the latest surface modification techniques of Ti dental implants are systematically and comprehensively reviewed. The various biomedical functionalities of surface modifications are discussed in-depth. Finally, a profound comment on the challenges and opportunities of this frontier is proposed, and the most promising directions for the future were explored.

The immunomodulatory role of exosomal microRNA networks in the crosstalk between tumor-associated myeloid-derived suppressor cells and tumor cells

Myeloid-derived suppressor cells (MDSCs) are considered a heterogeneous group of immature myeloid cells engaging in aggressive tumor progression and metastasis in the tumor microenvironment (TME) of patients diagnosed with cancer, through downregulation of anti-tumor immune responses. Exosomes are small vesicles carrying specific cargos, including proteins, lipids, and MicroRNA (miRNAs). Such exosomal miRNAs delivered by MDSCs and tumor cells are short noncoding RNAs mediating some of the immunosuppressive characteristics of MDSCs in the TME. However, when it comes to cancer diseases, how these miRNAs interact with MDSCs and encourage MDSCs differentiation and function need further investigations. In this review, we discuss MDSC-derived exosomal miRNAs and those derived from tumor cells (TDE) could modulate anti-tumor immunity and regulate the interaction between tumor cells and MDSCs in the TME. Afterward, we focus on dividing miRNAs, as an important substance interacting with MDSCs and tumor cells in the TME, into those have an immunosuppressive or stimulating effect not only on MDSCs expansion, differentiation, and suppressive function but also on tumor evasion.

The Effect of Titanium Surface Topography on Adherent Macrophage Integrin and Cytokine Expression

Immunomodulatory biomaterials have the potential to stimulate an immune response able to promote constructive and functional tissue remodeling, as opposed to persistent inflammation and scar tissue formation. This study examined the effects of titanium surface modification on integrin expression and concurrent cytokine secretion by adherent macrophages in vitro in an attempt to delineate the molecular events involved in biomaterial-mediated immunomodulation. Non-polarised (M0) and inflammatory polarised (M1) macrophages were cultured on a relatively smooth (machined) titanium surface and two proprietary modified rough titanium surfaces (blasted and fluoride-modified) for 24 h. The physiochemical characteristics of the titanium surfaces were assessed by microscopy and profilometry, while macrophage integrin expression and cytokine secretion were determined using PCR and ELISA, respectively. After 24 h adhesion onto titanium, integrin α1 expression was downregulated in both M0 and M1 cells on all titanium surfaces. Expression of integrins α2, αM, β1 and β2 increased in M0 cells cultured on the machined surface only, whereas in M1 cells, expression of integrins α2, αM and β1 all increased with culture on both the machined and rough titanium surfaces. These results correlated with a cytokine secretory response whereby levels of IL-1β, IL-31 and TNF-α increased significantly in M1 cells cultured on the titanium surfaces. These results show that adherent inflammatory macrophages interact with titanium in a surface-dependent manner such that increased levels of inflammatory cytokines IL-1β, TNF-α and IL-31 secreted by M1 cells were associated with higher expression of integrins α2, αM and β1.

Tissue Engineering Supporting Regenerative Strategies to Enhance Clinical Orthodontics and Dentofacial Orthopaedics: A Scoping, Perspective Review

The personalized regenerative therapeutic strategies applicable in the structural and functional repair of maxillofacial/dental defects are expected to extend beyond the limits of what is currently possible in the management of dentofacial anomalies and treating malocclusions. The application of undifferentiated stem cells (SCs), including signaling molecule control and individualized tissue engineering based on targeted therapies, has been proposed to overcome therapeutic limitations and complications associated with treatments for craniofacial defects, including severe orthodontic discrepancies. This scoping, prospective review discusses comprehensively the current knowledge and prospects for improving clinical outcomes by the application of novel cell-required and cell-free regenerative strategies in biomedicine. The existing evidence, although scant, suggests that patients receiving an orthodontic treatment could benefit from precise tissue augmentation, allowing enhancement of tooth movement generated by orthognathic forces; faster, more predictable alignment of dental arches; optimal management of periodontal complications; and prevention of external root resorption. Ultimately, enriching orofacial tissues and “customizing” the repair of congenital/acquired defects in the craniofacial region can be vastly enhanced to provide a positive therapeutic outcome and improve patients’ quality of life.

Towards Controlling the Local Bone Tissue Remodeling-Multifunctional Injectable Composites for Osteoporosis Treatment

Alendronate (ALN) is the most commonly prescribed oral nitrogen-containing bisphosphonate for osteoporosis therapy. However, its administration is associated with serious side effects. Therefore, the drug delivery systems (DDS) enabling local administration and localized action of that drug are still of great importance. Herein, a novel multifunctional DDS system based on the hydroxyapatite-decorated mesoporous silica particles (MSP-NH₂-HAp-ALN) embedded into collagen/chitosan/chondroitin sulfate hydrogel for simultaneous osteoporosis treatment and bone regeneration is proposed. In such a system, the hydrogel serves as a carrier for the controlled delivery of ALN at the site of implantation, thus limiting potential adverse effects. The involvement of MSP-NH₂-HAp-ALN in the crosslinking process was established, as well as the ability of hybrids to be used as injectable systems. We have shown that the attachment of MSP-NH₂-HAp-ALN to the polymeric matrix provides a prolonged ALN release (up to 20 days) and minimizes the initial burst effect. It was revealed that obtained composites are effective osteoconductive materials capable of supporting the osteoblast-like cell (MG-63) functions and inhibiting osteoclast-like cell (J7741.A) proliferation in vitro. The purposely selected biomimetic composition of these materials (biopolymer hydrogel enriched with the mineral phase) allows their biointegration (in vitro study in the simulated body fluid) and delivers the desired physicochemical features (mechanical, wettability, swellability). Furthermore, the antibacterial activity of the composites in in vitro experiments was also demonstrated.

Connection between Osteoarthritis and Nitric Oxide: From Pathophysiology to Therapeutic Target

Osteoarthritis (OA), a disabling joint inflammatory disease, is characterized by the progressive destruction of cartilage, subchondral bone remodeling, and chronic synovitis. Due to the prolongation of the human lifespan, OA has become a serious public health problem that deserves wide attention. The development of OA is related to numerous factors. Among the factors, nitric oxide (NO) plays a key role in mediating this process. NO is a small gaseous molecule that is widely distributed in the human body, and its synthesis is dependent on NO synthase (NOS). NO plays an important role in various physiological processes such as the regulation of blood volume and nerve conduction. Notably, NO acts as a double-edged sword in inflammatory diseases. Recent studies have shown that NO and its redox derivatives might be closely related to both normal and pathophysiological joint conditions. They can play vital roles as normal bone cell-conditioning agents for osteoclasts, osteoblasts, and chondrocytes. Moreover, they can also induce cartilage catabolism and cell apoptosis. Based on different conditions, the NO/NOS system can act as an anti-inflammatory or pro-inflammatory agent for OA. This review summarizes the studies related to the effects of NO on all normal and OA joints as well as the possible new treatment strategies targeting the NO/NOS system.

Antisclerostin Effect on Osseointegration and Bone Remodeling

Objective: This study reviewed the literature on local or systemic administration of antisclerostin, presenting results associated with osseointegration of dental/orthopedic implants and stimulation of bone remodeling. Materials and Methods: An extensive electronic search was conducted through MED-LINE/PubMed, PubMed Central, Web of Science databases and specific peer-reviewed journals to identify case reports, case series, randomized controlled trials, clinical trials and animal studies comparing either the systemic or local administration of antisclerostin and its effect in osseointegration and bone remodeling. Articles in English and with no restriction on period were included. Results: Twenty articles were selected for a full-text, and one was excluded. Finally, 19 articles were included in the study (16 animal studies and 3 randomized control trials). These studies were divided into two groups, which evaluated (i) osseointegration and (ii) bone remodeling potential. Initially 4560 humans and 1191 animals were identified. At least 1017 were excluded from the studies (981 humans and 36 animals), totaling 4724 subjects who completed (3579 humans and 1145 animals). (a) Osseointegration: 7 studies described this phenomenon; 4 reported bone-implant contact, which increased in all included studies. Similar results were found for bone mineral density, bone area/volume and bone thickness. (b) Bone remodeling: 13 studies were used for description. The studies reported an increase in BMD with sclerostin antibody treatment. A similar effect was found for bone mineral density/area/volume, trabecular bone and bone formation. Three biomarkers of bone formation were identified: bone-specific alkaline phosphatase (BSAP), osteocalcin and procollagen type 1 N-terminal Pro-peptide (P1NP); and markers for bone resorption were: serum C-telopeptide (sCTX), C-terminal telopeptides of type I collagen (CTX-1), β-isomer of C-terminal telopeptides of type I collagen (β-CTX) and tartrate-resistant acid phosphatase 5b (TRACP-5b). There were limitations: low number of human studies identified; high divergence in the model used (animal or human); the variance in the type of Scl-Ab and doses of administration; and the lack of reference quantitative values in the parameters analyzed by authors' studies (many articles only reported qualitative information). Conclusion: Within the limitations of this review and carefully observing all data, due to the number of articles included and the heterogeneity existing, more studies must be carried out to better evaluate the action of the antisclerostin on the osseointegration of dental implants. Otherwise, these findings can accelerate and stimulate bone remodeling and neoformation.

A Review of 3D Polymeric Scaffolds for Bone Tissue Engineering: Principles, Fabrication Techniques, Immunomodulatory Roles, and Challenges

Over the last few years, biopolymers have attracted great interest in tissue engineering and regenerative medicine due to the great diversity of their chemical, mechanical, and physical properties for the fabrication of 3D scaffolds. This review is devoted to recent advances in synthetic and natural polymeric 3D scaffolds for bone tissue engineering (BTE) and regenerative therapies. The review comprehensively discusses the implications of biological macromolecules, structure, and composition of polymeric scaffolds used in BTE. Various approaches to fabricating 3D BTE scaffolds are discussed, including solvent casting and particle leaching, freeze-drying, thermally induced phase separation, gas foaming, electrospinning, and sol-gel techniques. Rapid prototyping technologies such as stereolithography, fused deposition modeling, selective laser sintering, and 3D bioprinting are also covered. The immunomodulatory roles of polymeric scaffolds utilized for BTE applications are discussed. In addition, the features and challenges of 3D polymer scaffolds fabricated using advanced additive manufacturing technologies (rapid prototyping) are addressed and compared to conventional subtractive manufacturing techniques. Finally, the challenges of applying scaffold-based BTE treatments in practice are discussed in-depth.