Multilayered coating of titanium implants promotes coupled osteogenesis and angiogenesis in vitro and in vivo

Surface Functionalization of Titanium-Based Implants with a Nanohydroxyapatite Layer and Its Impact on Osteoblasts: A Systematic Review

This study aims to evaluate the influence of a nanohydroxyapatite layer applied to the surface of titanium or titanium alloy implants on the intricate process of osseointegration and its effect on osteoblast cell lines, compared to uncoated implants. Additionally, the investigation scrutinizes various modifications of the coating and their consequential effects on bone and cell line biocompatibility. On the specific date of November 2023, an exhaustive electronic search was conducted in esteemed databases such as PubMed, Web of Science, and Scopus, utilizing the meticulously chosen keywords ((titanium) AND ((osteoblasts) and hydroxyapatite)). Methodologically, the systematic review meticulously adhered to the PRISMA protocol. Initially, a total of 1739 studies underwent scrutiny, with the elimination of 741 duplicate records. A further 972 articles were excluded on account of their incongruence with the predefined subjects. The ultimate compilation embraced 26 studies, with a predominant focus on the effects of nanohydroxyapatite coating in isolation. However, a subset of nine papers delved into the nuanced realm of its modifiers, encompassing materials such as chitosan, collagen, silver particles, or gelatine. Across many of the selected studies, the application of nanohydroxyapatite coating exhibited a proclivity to enhance the osseointegration process. The modifications thereof showcased a positive influence on cell lines, manifesting in increased cellular spread or the attenuation of bacterial activity. In clinical applications, this augmentation potentially translates into heightened implant stability, thereby amplifying the overall procedural success rate. This, in turn, renders nanohydroxyapatite-coated implants a viable and potentially advantageous option in clinical scenarios where non-modified implants may not suffice.

Engineering tunable dual peptide hybrid coatings promote osseointegration of implants

Utilizing complementary bioactive peptides is a promising surface engineering strategy for bone regeneration on osteogenesis. In this study, we designed block peptides, (Lysine)6-capped RGD (K6-(linker-RGD)3) and OGP (K6-linker-(YGFGG)2), which were mildly grafted onto PC/Fe-MPNs through supramolecular interactions between K6 and PC residues on the MPNs surface to form a dual peptide coating, named PC/Fe@K6-RGD/OGP. The properties of the block peptides coating, including mechanics, hydrophilicity, chemical composition, etc., were detailly characterized by various techniques (ellipsometry, quartz crystal microbalance, X-ray photoelectron spectroscopy, water contact angle, scanning electronic microscopy and atomic force microscopy). Importantly, the RGD/OGP ratio can be well adjusted, which allowed optimizing the RGD/OGP ratio to endow significantly enhanced osteogenic activity of MC3T3-E1 cells through the Wnt/β-catenin pathway, while also promoting cell adhesion, immune regulation, inhibiting osteoclast differentiation and oxidative stress reduction. In vivo, the optimized RGD/OGP coatings promoted bone regeneration and osseointegration around implants in rats with bone defects. In conclusion, rationally designed PC/Fe@K6-RGD/OGP coating integrated RGD and OGP bioactivities, providing a convenient approach to enhance bioinert implant surfaces for bone regeneration.

Marriage of High-Throughput Gradient Surface Generation With Statistical Learning for the Rational Design of Functionalized Biomaterials

Functional biomaterial is already an important aspect in modern therapeutics; yet, the design of novel multi-functional biomaterial is still a challenging task nowadays. When several biofunctional components are present, the complexity that arises from their combinations and interactions will lead to tedious trial-and-error screening. In this work, a novel strategy of biomaterial rational design through the marriage of gradient surface generation with statistical learning is presented. Not only can parameter combinations be screened in a high-throughput fashion, but also the optimal conditions beyond the experimentally tested range can be extrapolated from the models. The power of the strategy is demonstrated in rationally designing an unprecedented ternary functionalized surface for orthopedic implant, with optimal osteogenic, angiogenic, and neurogenic activities, and its optimality and the best osteointegration promotion are confirmed in vitro and in vivo, respectively. The presented strategy is expected to open up new possibilities in the rational design of biomaterials.

Synergistic effect of hierarchical topographic structure on 3D-printed Titanium scaffold for enhanced coupling of osteogenesis and angiogenesis

The significance of the osteogenesis-angiogenesis relationship in the healing process of bone defects has been increasingly emphasized in recent academic research. Surface topography plays a crucial role in guiding cellular behaviors. Metal-organic framework (MOF) is an innovative biomaterial with nanoscale structural and topological features, enabling the modulation of scaffold physicochemical properties. This study involved the loading of varying quantities of UiO-66 nanocrystals onto alkali-heat treated 3D-printed titanium scaffolds, resulting in the formation of hierarchical micro/nano topography named UiO-66/AHTs. The physicochemical properties of these scaffolds were subsequently characterized. Furthermore, the impact of these scaffolds on the osteogenic potential of BMSCs, the angiogenic potential of HUVECs, and their intercellular communication were investigated. The findings of this study indicated that 1/2UiO-66/AHT outperformed other groups in terms of osteogenic and angiogenic induction, as well as in promoting intercellular crosstalk by enhancing paracrine effects. These results suggest a promising biomimetic hierarchical topography design that facilitates the coupling of osteogenesis and angiogenesis.

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

Biomaterials combined with ADSCs for bone tissue engineering: current advances and applications

In recent decades, bone tissue engineering, which is supported by scaffold, seed cells and bioactive molecules (BMs), has provided new hope and direction for treating bone defects. In terms of seed cells, compared to bone marrow mesenchymal stem cells, which were widely utilized in previous years, adipose-derived stem cells (ADSCs) are becoming increasingly favored by researchers due to their abundant sources, easy availability and multi-differentiation potentials. However, there is no systematic theoretical basis for selecting appropriate biomaterials loaded with ADSCs. In this review, the regulatory effects of various biomaterials on the behavior of ADSCs are summarized from four perspectives, including biocompatibility, inflammation regulation, angiogenesis and osteogenesis, to illustrate the potential of combining various materials with ADSCs for the treatment of bone defects. In addition, we conclude the influence of additional application of various BMs on the bone repair effect of ADSCs, in order to provide more evidences and support for the selection or preparation of suitable biomaterials and BMs to work with ADSCs. More importantly, the associated clinical case reports and experiments are generalized to provide additional ideas for the clinical transformation and application of bone tissue engineering loaded with ADSCs.

3D micropattern force triggers YAP nuclear entry by transport across nuclear pores and modulates stem cells paracrine

Biophysical cues of the cellular microenvironment tremendously influence cell behavior by mechanotransduction. However, it is still unclear how cells sense and transduce the mechanical signals from 3D geometry to regulate cell function. Here, the mechanotransduction of human mesenchymal stem cells (MSCs) triggered by 3D micropatterns and its effect on the paracrine of MSCs are systematically investigated. Our findings show that 3D micropattern force could influence the spatial reorganization of the cytoskeleton, leading to different local forces which mediate nucleus alteration such as orientation, morphology, expression of Lamin A/C and chromatin condensation. Specifically, in the triangular prism and cuboid micropatterns, the ordered F-actin fibers are distributed over and fully transmit compressive forces to the nucleus, which results in nuclear flattening and stretching of nuclear pores, thus enhancing the nuclear import of YES-associated protein (YAP). Furthermore, the activation of YAP significantly enhances the paracrine of MSCs and upregulates the secretion of angiogenic growth factors. In contrast, the fewer compressive forces on the nucleus in cylinder and cube micropatterns cause less YAP entering the nucleus. The skin repair experiment provides the first in vivo evidence that enhanced MSCs paracrine by 3D geometry significantly promotes tissue regeneration. The current study contributes to understanding the in-depth mechanisms of mechanical signals affecting cell function and provides inspiration for innovative design of biomaterials.

Adipogenesis-Related Metabolic Condition Affects Shear-Stressed Endothelial Cells Activity Responding to Titanium

PURPOSE

Obesity has increased around the world. Obese individuals need to be better assisted, with special attention given to dental and medical specialties. Among obesity-related complications, the osseointegration of dental implants has raised concerns. This mechanism depends on healthy angiogenesis surrounding the implanted devices. As an experimental analysis able to mimic this issue is currently lacking, we address this issue by proposing an in vitro high-adipogenesis model using differentiated adipocytes to further investigate their endocrine and synergic effect in endothelial cells responding to titanium.

MATERIALS AND METHODS

Firstly, adipocytes (3T3-L1 cell line) were differentiated under two experimental conditions: Ctrl (normal glucose concentration) and High-Glucose Medium (50 mM of glucose), which was validated using Oil Red O Staining and inflammatory markers gene expression by qPCR. Further, the adipocyte-conditioned medium was enriched by two types of titanium-related surfaces: Dual Acid-Etching (DAE) and Nano-Hydroxyapatite blasted surfaces (nHA) for up to 24 h. Finally, the endothelial cells (ECs) were exposed in those conditioned media under shear stress mimicking blood flow. Important genes related to angiogenesis were then evaluated by using RT-qPCR and Western blot.

RESULTS

Firstly, the high-adipogenicity model using 3T3-L1 adipocytes was validated presenting an increase in the oxidative stress markers, concomitantly with an increase in intracellular fat droplets, pro-inflammatory-related gene expressions, and also the ECM remodeling, as well as modulating mitogen-activated protein kinases (MAPKs). Additionally, Src was evaluated by Western blot, and its modulation can be related to EC survival signaling.

CONCLUSION

Our study provides an experimental model of high adipogenesis in vitro by establishing a pro-inflammatory environment and intracellular fat droplets. Additionally, the efficacy of this model to evaluate the EC response to titanium-enriched mediums under adipogenicity-related metabolic conditions was analyzed, revealing significant interference with EC performance. Altogether, these data gather valuable findings on understanding the reasons for the higher percentage of implant failures in obese individuals.

Circulating MiRNA-21-enriched extracellular vesicles promote bone remodeling in traumatic brain injury patients

Fracture combined with traumatic brain injury (TBI) is one of the most common and serious types of compound trauma in the clinic and is characterized by dysfunction of cellular communication in injured organs. Our prior studies found that TBI was capable of enhancing fracture healing in a paracrine manner. Exosomes (Exos), as small extracellular vesicles, are important paracrine vehicles for noncell therapy. However, whether circulating Exos derived from TBI patients (TBI-Exos) regulate the prohealing effects of fractures remains unclear. Thus, the present study aimed to explore the biological effects of TBI-Exos on fracture healing and reveal the potential molecular mechanism. TBI-Exos were isolated by ultracentrifugation, and the enriched miR-21-5 p was identified by qRT‒PCR analysis. The beneficial effects of TBI-Exos on osteoblastic differentiation and bone remodeling were determined by a series of in vitro assays. Bioinformatics analyses were conducted to identify the potential downstream mechanisms of the regulatory effect of TBI-Exos on osteoblasts. Furthermore, the role of the potential signaling pathway of TBI-Exos in mediating the osteoblastic activity of osteoblasts was assessed. Subsequently, a murine fracture model was established, and the effect of TBI-Exos on bone modeling was demonstrated in vivo. TBI-Exos can be internalized by osteoblasts, and in vitro, suppression of SMAD7 promoted osteogenic differentiation, whereas knockdown of miR-21-5 p in TBI-Exos strongly inhibited this bone-beneficial effect. Similarly, our results confirmed that preinjection of TBI-Exos led to enhanced bone formation, whereas knockdown of exosomal miR-21-5 p substantially impaired this bone-beneficial effect in vivo.

Effects of Nitrurized Titanium on Microhardness and Human Dental Pulp Stem Cell Adhesion and Differentiation

To compare the Vickers microhardness, surface roughness, initial adhesion, and osteogenic differentiation on titanium (Ti) and nitrurized titanium (NTi) plates were treated by UV irradiation and chitosan. Each plate was subjected to Vickers hardness with a pressure of 2.9 N for 10 seconds and roughness evaluation by atomic force microscope (AFM) analysis. Three groups of each type of plates were tested: control (C), ultraviolet irradiation (UV), and chitosan (Q). The UV group was exposed to UV-irradiation for 20 min at 253.7 nm (52 μW/cm2). The Q group was coated with 1% chitosan, and the C group had no treatment. The osteoblasts (2 × 106 cells/mL) were inoculated in each group for 60 min and their viability was determined by the MTT bioassay. Osteogenic differentiation was performed over 4 weeks and determined by alizarin red staining. The mean was analyzed with the Shapiro-Wilks, Kruskall-Wallis, and Mann-Whitney U tests of normality (n = 9/gp). The NTi plates hardness (125.1 ± 4.01 HV) was higher (P = 0.026) than the Ti plates (121.3 ± 2.23 HV). The surface topography was: NTi (Ra = 0.098 μm) and Ti (Ra = 0.212 μm). The quantification of cell adhesion was: Ti + Q = 123 ± 4.9% (P < 0.05) < NTi + Q = 107 ± 3.3% < Ti = 100 ± 10.7% < NTi = 72 ± 6.8% < NTi + UV = 71 ± 4.4% < Ti + UV = 69 ± 3.5%, regardless the plates, the presence of chitosan induce a faster osteogenic differentiation. The Ti + Q plates tested the highest cell attachment and osteogenic adhesion suggesting their potential use of chitosan for cell-implant interaction.

Current Advances in 3D Dynamic Cell Culture Systems

The traditional two-dimensional (2D) cell culture methods have a long history of mimicking in vivo cell growth. However, these methods cannot fully represent physiological conditions, which lack two major indexes of the in vivo environment; one is a three-dimensional 3D cell environment, and the other is mechanical stimulation; therefore, they are incapable of replicating the essential cellular communications between cell to cell, cell to the extracellular matrix, and cellular responses to dynamic mechanical stimulation in a physiological condition of body movement and blood flow. To solve these problems and challenges, 3D cell carriers have been gradually developed to provide a 3D matrix-like structure for cell attachment, proliferation, differentiation, and communication in static and dynamic culture conditions. 3D cell carriers in dynamic culture systems could primarily provide different mechanical stimulations which further mimic the real in vivo microenvironment. In this review, the current advances in 3D dynamic cell culture approaches have been introduced, with their advantages and disadvantages being discussed in comparison to traditional 2D cell culture in static conditions.

Additive Manufacturing of Polymer/Mg-Based Composites for Porous Tissue Scaffolds

Due to their commercial availability, superior processability, and biocompatibility, polymers are frequently used to build three-dimensional (3D) porous scaffolds. The main issues limiting the widespread clinical use of monophasic polymer scaffolds in the bone healing process are their inadequate mechanical strength and inappropriate biodegradation. Due to their mechanical strength and biocompatibility, metal-based scaffolds have been used for various bone regenerative applications. However, due to the mismatch in mechanical properties and nondegradability, they lack integration with the host tissues, resulting in the production of fiber tissue and the release of toxic ions, posing a risk to the durability of scaffolds. Due to their natural degradability in the body, Mg and its alloys increasingly attract attention for orthopedic and cardiovascular applications. Incorporating Mg micro-nano-scale particles into biodegradable polymers dramatically improves scaffolds and implants' strength, biocompatibility, and biodegradability. Polymer biodegradable implants also improve the quality of life, particularly for an aging society, by eliminating the secondary surgery often needed to remove permanent implants and significantly reducing healthcare costs. This paper reviews the suitability of various biodegradable polymer/Mg composites for bone tissue scaffolds and then summarizes the current status and challenges of polymer/magnesium composite scaffolds. In addition, this paper reviews the potential use of 3D printing, which has a unique design capability for developing complex structures with fewer material waste at a faster rate, and with a personalized and on-site fabrication possibility.

Effect of bone-shaped nanotube-hydrogel drug delivery system for enhanced osseointegration

Anodic titanium dioxide nanotubes (TNT) have a range of beneficial theranostic properties. However, a lack of effective osseointegration is a problem frequently associated with the titanium dental implant surface. Here, we investigated whether bone-shaped nanotube titanium implants could enhance osseointegration via promoting initial release of vascular endothelial growth factor 165 (VEGF165) and dual release of recombinant human bone morphogenetic protein-2 (rhBMP-2). Thus, we generated cylindrical-shaped nanotubes (TNT1) and bone-shaped nanotubes (TNT2) through voltage-varying and time-varying electrochemical anodization methods, respectively. Additionally, we prepared rhBMP-2-loaded cylindrical-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F1) and rhBMP-2-loaded bone-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F2) drug delivery systems. We evaluated the characteristics and release kinetics of the drug delivery systems, and then analyzed the cytocompatibility and osteogenic differentiation of these specimens with mesenchymal stem cells (MSCs) in vitro. Finally, we utilized a rat femur defect model to test the bone formation capacity of nanotube-hydrogel drug delivery system in vivo. Among these different nanotubes structures, the bone-shaped one was the optimum structure for growth factor release.

Effects of Zinc Ions Released From Ti-NW-Zn Surface on Osteogenesis and Angiogenesis In Vitro and in an In Vivo Zebrafish Model

Zinc-modified titanium materials have been widely applied in oral implants. Among them, our previous studies have also successfully prepared a novel acid-etched microstructured titanium surface modified with zinc-containing nanowires (Ti-NW-Zn) and proved its excellent biocompatibility. It is well known that the functional regulation between angiogenesis and osteogenesis is of great importance for bone remodeling around implants. However, there are few reports concerning the biological safety of zinc ions released from materials and the appropriate concentration of released zinc ions which was more conducive to angiogenesis and bone regeneration. In this study, we investigated the effects of zinc ions released from Ti-NW-Zn surfaces on angiogenesis and osteogenesis using the zebrafish model and revealed the relationship between angiogenesis and osteogenesis via HUVECs and MC3T3-E1s in vitro. We found that the zinc ions released from Ti-NW-Zn surfaces, with a concentration lower than median lethal concentrations (LCs) of zebrafish, were biologically safe and promote osteogenesis and angiogenesis in vivo. Moreover, the proper concentration of zinc ions could induce the proliferation of HUVECs and osteogenic differentiation. The positive effects of the appropriate concentration of zinc ions on osteoblast behaviors might be regulated by activating the MAPK/ERK signaling pathway. These aspects may provide new sights into the mechanisms underlying zinc-modified titanium surfaces between osteogenesis and angiogenesis, to lay the foundation for further improving the materials, meanwhile, promoting the applications in dentistry.

Engineering the surfaces of orthopedic implants with osteogenesis and antioxidants to enhance bone formation in vitro and in vivo

Limited osteointegration of orthopedic implants with surrounding tissues has been the leading issue until the failure of orthopedic implants in the long term, which could be induced by multiple factors, including infection, limited abilities for bone formation and remodeling, and an overstressed reactive oxygen species (ROS) environment around implants. To address this challenge, a multifunctional coating composed of tannic acid (TA), nanohydroxyapatite (nHA) and gelatin (Gel) was fabricated by a layer-by-layer (LBL) technique, into which TA, nHA, and Gel were integrated, and their respective functions were utilized to synergistically promote osteogenesis. The fabrication process of (TA@nHA/Gel)_n coatings and related bio-multifunctionalities were thoroughly investigated by various techniques. We found that the (TA@nHA/Gel)_n coatings showed strong antioxidant activity and accelerated cellular attachment in the early stage and proliferation in the long term, largely enhancing osteogenesis in vitro and promoting bone formation in vivo. We believe our findings will guide the design of orthopedic implants in the future, and the strategy developed here could pave the way for multifunctional orthopedic implant coating and protein-related coatings with various potential applications, including biosensors, catalysis, tissue engineering, and life science.

Cell-Seeded Biomaterial Scaffolds: The Urgent Need for Unanswered Accelerated Angiogenesis

One of the most arduous challenges in tissue engineering is neovascularization, without which there is a lack of nutrients delivered to a target tissue. Angiogenesis should be completed at an optimal density and within an appropriate period of time to prevent cell necrosis. Failure to meet this challenge brings about poor functionality for the tissue in comparison with the native tissue, extensively reducing cell viability. Prior studies devoted to angiogenesis have provided researchers with some biomaterial scaffolds and cell choices for angiogenesis. For example, while most current angiogenesis approaches require a variety of stimulatory factors ranging from biomechanical to biomolecular to cellular, some other promising stimulatory factors have been underdeveloped (such as electrical, topographical, and magnetic). When it comes to choosing biomaterial scaffolds in tissue engineering for angiogenesis, key traits rush to mind including biocompatibility, appropriate physical and mechanical properties (adhesion strength, shear stress, and malleability), as well as identifying the appropriate biomaterial in terms of stability and degradation profile, all of which may leave essential trace materials behind adversely influencing angiogenesis. Nevertheless, the selection of the best biomaterial and cells still remains an area of hot dispute as such previous studies have not sufficiently classified, integrated, or compared approaches. To address the aforementioned need, this review article summarizes a variety of natural and synthetic scaffolds including hydrogels that support angiogenesis. Furthermore, we review a variety of cell sources utilized for cell seeding and influential factors used for angiogenesis with a concentrated focus on biomechanical factors, with unique stimulatory factors. Lastly, we provide a bottom-to-up overview of angiogenic biomaterials and cell selection, highlighting parameters that need to be addressed in future studies.

An improved osseointegration of metal implants by pitavastatin loaded multilayer films with osteogenic and angiogenic properties

An increasing number of works have highlighted the importance of metal implants surface modification in enhancing bone defect healing through the synergistic osteogenesis-angiogenesis regulation. Studies have shown that pitavastatin has the effect of promoting osteogenesis and angiogenesis. However, how to prepare pitavastatin functionalized implants and how pitavastatin regulates the synergies of osteogenesis and angiogenesis around implants as well as the related mechanisms remain unclear. In the present study, multilayer films with osteogenic and angiogenic properties were constructed on pure titanium substrates via the layer-by-layer assembly of pitavastatin-loaded β-cyclodextrin grafted chitosan and gelatin. In vitro experiments demonstrated that locally applied pitavastatin could dramatically enhance osteogenic potential of mesenchymal stem cells (MSCs) and angiogenic potential of endothelial cells (ECs). Moreover, pitavastatin loaded multilayer films could regulate the paracrine signaling mediated crosstalk between MSCs and ECs, and indirectly increase the angiogenic potential of MSCs and osteogenic potential of ECs via multiple paracrine signaling. The results of subcutaneous and femur implantation confirmed that locally released pitavastatin had potentially triggered a chain of biological events: mobilizing endogenous stem cells and ECs to the implant-bone interface, in turn facilitating coupled osteogenesis and angiogenesis, and eventually enhancing peri-implant osseointegration. This study enlarges the application scope of pitavastatin and provides an optional choice for developing a multifunctional bioactive coating on the surfaces of mental implants.

Mussel-inspired functionalization of electrospun scaffolds with polydopamine-assisted immobilization of mesenchymal stem cells-derived small extracellular vesicles for enhanced bone regeneration

Mesenchymal stem cells-derived small extracellular vesicles (MSCs-sEV) have shown promising prospects as a cell-free strategy for bone tissue regeneration. Here, a bioactive MSCs-sEV-loaded electrospun silk fibroin/poly(ε-caprolactone) (SF/PCL) scaffold was synthesized via a mussel-inspired immobilization strategy assisted by polydopamine (pDA). This pDA modification endowed the as-prepared scaffold with high loading efficiency and sustained release profile of sEV. In addition, the fabricated composite scaffold exhibited good physiochemical, mechanical, and biocompatible properties. In vitro cellular experiments indicated that the MSCs-sEV-loaded composite scaffold promoted the adhesion and spreading of preosteoblast and endothelial cells, as well as enhanced osteogenic differentiation and angiogenic activity. In vivo experiments showed that the functionalized electrospun scaffolds promoted bone regeneration in a rat calvarial bone defect model. Results suggest that the developed MSCs-sEV-anchored pDA-modified SF/PCL electrospun scaffolds possess high application potential in bone tissue engineering owing to their powerful pro-angiogenic and -osteogenic capacities, cell-free bioactivity, and cost effectiveness.

Co-culture of BMSCs and HUVECs with simvastatin-loaded gelatin nanosphere/chitosan coating on Mg alloy for osteogenic differentiation and vasculogenesis

Mg alloys are increasingly being investigated as a versatile and economical alternative for developing bone repair implants because of their high mechanical strength, wide availability, adjustable structure and properties. In this study, magnesium alloy WE43 is coated on both sides with gelatin nanosphere/chitosan (GNs/CTS), a coating enhanced by incorporating simvastatin (SIM). SIM-loaded GNs/CTS coated magnesium alloy can promote the osteogenic differentiation of bone mesenchymal stem cells (BMSCs). BMSCs and human umbilical vein endothelial cells (HUVECs) are co-cultured through transwell systems. The release of SIM from the coating is found to increase the secretion of chemokine and angiogenic factors from BMSCs, which promote the migration and tube formation of HUVECs, respectively. Bone morphogenetic protein secreted by HUVECs is seen to increase by the release of SIM from the coating, promoting the osteogenic differentiation of BMSCs. The secretion of chemokines from HUVECs promote the migration of BMSCs. The coated magnesium alloy substrate loaded with SIM is found to regulate the osteogenic differentiation of BMSCs. The study of the paracrine interaction between BMSCs and HUVECs proves that the applied coating promotes both osteogenic differentiation and vascularization, thus demonstrating a new approach for the design of bone repair materials based on magnesium alloys.

An ossifying landscape: materials and growth factor strategies for osteogenic signalling and bone regeneration

Breakthroughs in our understanding of the complex interplay between cellular nanoenvironment and biomolecular signalling pathways are facilitating development of targeted osteogenic platforms. As critical biomolecules for osteogenesis, growth factors stimulate osteogenesis by activating key genes and transcription factors. The first half of this review presents emerging interconnectedness and recent discoveries of osteogenic signalling pathways initiating from growth factors for example, bone morphogenetic protein 2 (BMP-2). To complement this, the second half of review proposes a number of strategies to induce osteogenesis which include metallic, organic implants, nanotopological environments as well as growth factor immobilization techniques. The drawbacks of traditional osteogenic implants and how these have been overcome by biomedical engineers in the recent years without producing side-effects have also been summarized.

Innovative Coatings of Metallic Alloys Used as Bioactive Surfaces in Implantology: A Review

Metallic implants are widely used in the field of implantology, but there are still problems leading to implant failures due to weak osseointegration, low mechanical strength for the implant, inadequate antibacterial properties, and low patient satisfaction. Implant failure can be caused by bacterial infections and poor osteointegration. To improve the implant functionalization, many researchers focus on surface modifications to prepare the proper physical and chemical conditions able to increase biocompatibility and osteointegration between implant and bone. Improving the antibacterial performance is also a key factor to avoid the inflammation in the human body. This paper is a brief review for the types of coatings used to increase osseointegration and biocompatibility for the successful use of metal alloys in the field of implantology.

Fabrication of customized Ti6AI4V heterogeneous scaffolds with selective laser melting: Optimization of the architecture for orthopedic implant applications

Orthopedic implants with heterogeneous porous structures were known as ideal bone osteointegration. This research introduced the selective laser melting (SLM), finite element analysis (FEA), and a hydrothermal process (HT) for manufacturing a three-level heterogeneous porous structure. The macroporous structure was designed via CAD and micropores were tuned via laser power regulation. A nano-size layer of hydroxyapatite crystals was coated by an HT process. The mechanical properties were reinforced via a core-shell structure with core reinforcement. The existence of micropores and nano-hydroxyapatite coating enhanced the in vitro proliferation of preosteoblasts and osteogenic cellular behaviors of rBMSCs. Thus, the three-level heterogeneous porous titanium implants could inspire researchers with potential clue of cyto-implant interaction mechanism, therefore building ideal orthopedic implants with accelerated osteointegration. STATEMENT OF SIGNIFICANCE: Porous structures of titanium implants play an important role in bone tissue regeneration; The geometrical environment influence cell behaviour and bone tissue ingrowth in all macro-/micro-/nanoscale. In this study, a novel method to fabricate heterogeneous scaffolds and its macro-/micro-/nanoscopic structures were studied. A CAD model was used to obtain the macroscopic structure and the insufficient laser power was introduced for porous microstructure. Therefore, a layer of nano hydroxyapatite was coated via hydrothermal process. Cytoproliferation and cytodifferentiation results indicated that a integrity of regular/irregular, macro-/micro-/nanoscale porous structure had advance in recruiting stem cells and promoting differentiation. This research is beneficial to the development of bone implants with better bone regeneration ability.

Multifunctional natural polymer-based metallic implant surface modifications

High energy traumas could cause critical damage to bone, which will require permanent implants to recover while functionally integrating with the host bone. Critical sized bone defects necessitate the use of bioactive metallic implants. Because of bioinertness, various methods involving surface modifications such as surface treatments, the development of novel alloys, bioceramic/bioglass coatings, and biofunctional molecule grafting have been utilized to effectively integrate metallic implants with a living bone. However, the applications of these methods demonstrated a need for an interphase layer improving bone-making to overcome two major risk factors: aseptic loosening and peri-implantitis. To accomplish a biologically functional bridge with the host to prevent loosening, regenerative cues, osteoimmunomodulatory modifications, and electrochemically resistant layers against corrosion appeared as imperative reinforcements. In addition, interphases carrying antibacterial cargo were proven to be successful against peri-implantitis. In the literature, metallic implant coatings employing natural polymers as the main matrix were presented as bioactive interphases, enabling rapid, robust, and functional osseointegration with the host bone. However, a comprehensive review of natural polymer coatings, bridging and grafting on metallic implants, and their activities has not been reported. In this review, state-of-the-art studies on multifunctional natural polymer-based implant coatings effectively utilized as a bone tissue engineering (BTE) modality are depicted. Protein-based, polysaccharide-based coatings and their combinations to achieve better osseointegration via the formation of an extracellular matrix-like (ECM-like) interphase with gap filling and corrosion resistance abilities are discussed in detail. The hypotheses and results of these studies are examined and criticized, and the potential future prospects of multifunctional coatings are also proposed as final remarks.

Surface engineering of biomaterials in orthopedic and dental implants: Strategies to improve osteointegration, bacteriostatic and bactericidal activities

BACKGROUND

The success of biomedical implants in orthopedic and dental applications is usually limited due to insufficient bone-implant integration, and implant-related infections. Biointerfaces are critical in regulating their interactions and the desirable performance of biomaterials in biological environment. Surface engineering has been widely studied to realize better control of the interface interaction to further enhance the desired behavior of biomaterials.

PURPOSE AND SCOPE

This review aims to investigate surface coating strategies in hard tissue applications to address insufficient osteointegration and implant-related infection problems.

SUMMARY

We first focused on surface coatings to enhance the osteointegration and biocompatibility of implants by emphasizing calcium phosphate-related, nanoscale TiO₂ -related, bioactive tantalum-based and biomolecules incorporated coatings. Different coating strategies such as plasma spraying, biomimetic deposition, electrochemical anodization and LENS are discussed. We then discussed techniques to construct anti-adhesive and bactericidal surface while emphasizing multifunctional surface coating techniques that combine potential osteointegration and antibacterial activities. The effects of nanotopography via TiO₂ coatings on antibacterial performance are interesting and included. A smart bacteria-responsive titanium dioxide nanotubes coating is also attractive and elaborated.

CONCLUSION

Developing multifunctional surface coatings combining osteogenesis and antimicrobial activity is the current trend. Surface engineering methods are usually combined to obtain hierarchical multiscale surface structures with better biofunctionalization outcomes.

PI3K/AKT signaling drives titanium-induced angiogenic stimulus

Although osseointegration and clinical success of titanium (Ti)-implanted materials depend on neovascularization in the reactional peri-implant tissue, very little has been achieved considering the Ti-molecules release on the behavior of endothelial cells. To address this issue, we challenged endothelial cells (HUVECs) with Ti-enriched medium obtained from two types of commercial titanium surfaces [presenting or not dual-acid etching (DAE)] up to 72 h to allow molecular machinery analysis. Our data show that the Ti-enriched medium provokes significant stimulus of angiogenesis-related machinery in endothelial cells by upexpressing VEGFR1, VEGFR2, VEGF, eNOS, and iNOS genes, while the PI3K/Akt signaling pathway was also significantly enhanced. As PI3K/AKT signaling was related to angiogenesis in response to vascular endothelial growth factor (VEGF), we addressed the importance of PI3K/Akt upon Ti-enriched medium responses by concomitantly treating the cells with wortmannin, a well-known PI3K inhibitor. Wortmannin suppressed the angiogenic factors, because VEGF, VEGFR1, and eNOS genes were downregulated in those cells, highlighting the importance of PI3K/AKT signaling on driving angiogenic phenotype and angiogenesis performance within the peri-implant tissue reaction. In conjunction, these data reinforce that titanium-implantable devices modify the metabolism of surrounding cells, such as endothelial cells, probably coupling osteogenesis and angiogenesis processes in peri-implant tissue and then contributing to successfully osseointegration of biomedical titanium-based devices.

Biodegradable materials for bone defect repair

Compared with non-degradable materials, biodegradable biomaterials play an increasingly important role in the repairing of severe bone defects, and have attracted extensive attention from researchers. In the treatment of bone defects, scaffolds made of biodegradable materials can provide a crawling bridge for new bone tissue in the gap and a platform for cells and growth factors to play a physiological role, which will eventually be degraded and absorbed in the body and be replaced by the new bone tissue. Traditional biodegradable materials include polymers, ceramics and metals, which have been used in bone defect repairing for many years. Although these materials have more or fewer shortcomings, they are still the cornerstone of our development of a new generation of degradable materials. With the rapid development of modern science and technology, in the twenty-first century, more and more kinds of new biodegradable materials emerge in endlessly, such as new intelligent micro-nano materials and cell-based products. At the same time, there are many new fabrication technologies of improving biodegradable materials, such as modular fabrication, 3D and 4D printing, interface reinforcement and nanotechnology. This review will introduce various kinds of biodegradable materials commonly used in bone defect repairing, especially the newly emerging materials and their fabrication technology in recent years, and look forward to the future research direction, hoping to provide researchers in the field with some inspiration and reference.

Topography: A Biophysical Approach to Direct the Fate of Mesenchymal Stem Cells in Tissue Engineering Applications

Tissue engineering is a promising strategy to treat tissue and organ loss or damage caused by injury or disease. During the past two decades, mesenchymal stem cells (MSCs) have attracted a tremendous amount of interest in tissue engineering due to their multipotency and self-renewal ability. MSCs are also the most multipotent stem cells in the human adult body. However, the application of MSCs in tissue engineering is relatively limited because it is difficult to guide their differentiation toward a specific cell lineage by using traditional biochemical factors. Besides biochemical factors, the differentiation of MSCs also influenced by biophysical cues. To this end, much effort has been devoted to directing the cell lineage decisions of MSCs through adjusting the biophysical properties of biomaterials. The surface topography of the biomaterial-based scaffold can modulate the proliferation and differentiation of MSCs. Presently, the development of micro- and nano-fabrication techniques has made it possible to control the surface topography of the scaffold precisely. In this review, we highlight and discuss how the main topographical features (i.e., roughness, patterns, and porosity) are an efficient approach to control the fate of MSCs and the application of topography in tissue engineering.

Nanotechnology for angiogenesis: opportunities and challenges

Angiogenesis plays a critical role within the human body, from the early stages of life (i.e., embryonic development) to life-threatening diseases (e.g., cancer, heart attack, stroke, wound healing). Many pharmaceutical companies have expended huge efforts on both stimulation and inhibition of angiogenesis. During the last decade, the nanotechnology revolution has made a great impact in medicine, and regulatory approvals are starting to be achieved for nanomedicines to treat a wide range of diseases. Angiogenesis therapies involve the inhibition of angiogenesis in oncology and ophthalmology, and stimulation of angiogenesis in wound healing and tissue engineering. This review aims to summarize nanotechnology-based strategies that have been explored in the broad area of angiogenesis. Lipid-based, carbon-based and polymeric nanoparticles, and a wide range of inorganic and metallic nanoparticles are covered in detail. Theranostic and imaging approaches can be facilitated by nanoparticles. Many preparations have been reported to have a bimodal effect where they stimulate angiogenesis at low dose and inhibit it at higher doses.

Regulation of MSC and macrophage functions in bone healing by peptide LL-37-loaded silk fibroin nanoparticles on a titanium surface

Titanium-based materials have been long regarded as effective bone implants for clinical use, yet the corresponding osteointegration ability needs to be optimized. This challenge can be overcome by fabricating titanium (Ti) materials with physiological functions. In this study, peptide LL-37-loaded silk fibroin nanoparticles (SFNPs) were immobilized on a titanium surface to facilitate osteointegration by regulating the physiological functions of mesenchymal stem cells (MSCs) and macrophages. According to our results, the cell viability, recruitment and paracrine responses of MSCs and macrophages were improved by the modified Ti samples. MSC differentiation was promoted by the macrophages incubated on the modified Ti samples, and the phenotype switch of macrophages was also modulated by the MSCs incubated on the modified Ti samples. In vivo studies proved that the modified Ti implant induced MSC and macrophage recruitments to injury sites and the inflammatory response was positively regulated. Moreover, better bone formation was achieved around the modified Ti implant 28 days after surgery. This suggested that the immobilization of peptide LL-37-loaded SFNPs on a titanium surface improves osteointegration via the regulation of physiological functions of MSCs and macrophages.

Long-Term Efficacy of Biodegradable Metal-Polymer Composite Stents After the First and the Second Implantations into Porcine Coronary Arteries

A biodegradable coronary stent is expected to eliminate the adverse events of an otherwise eternally implanting material after vessel remodeling. Both biocorrodible metals and biodegradable polymers have been tried as the matrix of the new-generation stent. Herein, we utilized a metal-polymer composite material to combine the advantages of the high mechanical strength of metals and the adjustable degradation rate of polymers to prepare the biodegradable stent. After coating polylactide (PLA) on the surface of iron, the degradation of iron was accelerated significantly owing to the decrease of local pH resulting from the hydrolysis of PLA, etc. We implanted the metal-polymer composite stent (MPS) into the porcine artery and examined its degradation in vivo, with the corresponding metal-based stent (MBS) as a control. Microcomputed tomography (micro-CT), coronary angiography (CA), and optical coherence tomography (OCT) were performed to observe the stents and vessels during the animal experiments. The MPS exhibited faster degradation than MBS, and the inflammatory response of MPS was acceptable 12 months after implantation. Additionally, we implanted another MPS after 1-year implantation of the first MPS to investigate the result of the MPS in the second implantation. The feasibility of the biodegradable MPS in second implantation in mammals was also confirmed.

Microarc oxidation surface of titanium implants promote osteogenic differentiation by activating ERK1/2-miR-1827-Osterix

There has been a constant requirement from the clinic to develop biomedical titanium (Ti) implants with high osteogenic ability. In this study, we clarified a novel mechanism of how MAO (microarc oxidation) coating of Ti implants facilitates osteogenic differentiation of human bone marrow mesenchymal stem cells (hB-MSCs) by activating ERK1/2-miR-1827-Osterix signaling pathway in vitro. MAO surface of titanium implant was more favorable to promote osteogenic differentiation than SLA and AOS coating. Besides, titanium implants regulated hB-MSCs osteogenesis through the p38 MAPK pathway and ERK1/2 might be the most efficient target. Furthermore, MAO coating induced osteogenic differentiation though ERK1/2-miR-1827 pathway. Finally, we verified miR-1827 regulated osteogenic differentiation partially through Osterix. Our study reveals novel insights that MAO surface of titanium implant is a prior choice for biomedical trial and for its use in periprosthetic osteolysis (PIO) treatment in an evidence-based rationale.

Improved Blood Compatibility and Endothelialization of Titanium Oxide Nanotube Arrays on Titanium Surface by Zinc Doping

Titanium dioxide nanotube arrays are widely used in biomaterials due to their unique tubular structure and tunable biocompatibility. In the present study, titanium oxide nanotube arrays with different diameters were prepared on the titanium surface by anodization, followed by zinc doping using hydrothermal treatment to enhance the biocompatibility. Both the nanotube dimensions and zinc doping had obvious influences on the hydrophilicity, protein adsorption, blood compatibility, and endothelial cell behaviors of the titanium surface. The increase of the diameter and zinc doping can improve the hydrophilicity of the titanium surface. The increase of nanotube diameter could reduce the albumin adsorption while increasing the fibrinogen adsorption. However, zinc doping can simultaneously promote the adsorption of albumin and fibrinogen, and the effect was more obvious for albumin. Zinc doping can significantly improve the blood compatibility of the titanium oxide nanotubes because it cannot only increase the activity of cyclophosphate guanylate (cGMP) but also significantly reduce the platelets adhesion and hemolysis rate. Moreover, it was also found that both the smaller diameter and zinc doping nanotubes can enhance the endothelial cell adhesion and proliferation as well as up-regulate the expression of NO and VEGF. Therefore, the zinc doped titanium dioxide nanotube array can be used to simultaneously improve the blood compatibility and promote endothelialization of the titanium-based biomaterials and implants, such as intravascular stents.

Advances in biomolecule inspired polymeric material decorated interfaces for biological applications

With the development of surface modification technology, interface properties have great effects on the interaction between biomedical materials and cells and biomolecules, which significantly affects the biocompatibility and functionality of materials. As an orderly and perfect system, biological organisms in nature effectively integrate all kinds of bio-interfaces with physiological functions, which shed light on the importance of biomolecules in organisms. It gives birth to a bio-inspiration strategy to design and fabricate smart materials with specific functionalities, e.g. osteogenic and chondrocytic induced materials inspired by bone sialoprotein and chondroitin sulfate. Through this mimicking approach, various functional materials were utilized to decorate the interfaces and further optimize the performance of biomedical materials, which would widely expand their applications. In this review, followed by a summary and brief introduction of surface modification methods, we highlight recent advances in the fabrication of functional polymeric materials inspired by a range of biomolecules for decorating interfaces. Then, the other applications of biomolecule inspired materials including tissue engineering, diagnosis and treatment of diseases and physiological function regulation are presented and the future outlook is discussed as well.

A dynamic matrix potentiates mesenchymal stromal cell paracrine function via an effective mechanical dose

Compared to static conditions, MSCs in a dynamic matrix possess higher paracrine function as a result of collecting a mechanical dose through a cytoskeleton-YAP system.

PTH1-34 improves bone healing by promoting angiogenesis and facilitating MSCs migration and differentiation in a stabilized fracture mouse model

Objective

PTH_1-34 (parathyroid hormone 1–34) is the only clinical drug to promote osteogenesis. MSCs (mesenchymal stem cells) have multidirectional differentiation potential and are closely related to fracture healing. This study was to explore the effects of PTH_1-34 on proliferation and differentiation of endothelial cells and MSCs in vitro, and on angiogenesis, and MSCs migration during fracture healing in vivo.

Methods

Mice with stabilized fracture were assigned to 4 groups: CON, PTH (PTH_1-34 40 μg/kg/day), MSC (transplanted with 10⁵ MSCs), PTH+MSCs. Mice were sacrificed 14 days after fracture, and callus tissues were harvested for microCT scan and immunohistochemistry analysis. The effects of PTH_1-34 on angiogenesis, and MSCs differentiation and migration were assessed by wound healing, tube formation and immunofluorescence staining.

Results

Treatment with either PTH_1-34, or MSCs promoted bone healing and vascular formation in fracture callus. The callus bone mass, bone volume, and bone mineral density were all greater in PTH and/or MSC groups than they were in CON (p<0.05). PTH_1-34 increased small vessels formation (diameter ≤50μm), whereas MSCs increased the large ones (diameter >50μm). Expression of CD31 within calluses and trabecular bones were significantly higher in PTH_1-34 treated group than that of not (p<0.05). Expression of CD31, VEGFR, VEGFR2, and vWF was upregulated, and wound healing and tube formation were increased in MSCs treated with PTH_1-34 compared to that of control.

Conclusions

PTH_1-34 improved the proliferation and differentiation of endothelial cells and MSCs, enhancing migration of MSCs to bone callus to promote angiogenesis and osteogenesis, and facilitating fracture healing.

Applications of chitin and chitosan nanofibers in bone regenerative engineering

Promoting bone regeneration and repairing defects are urgent and critical challenges in orthopedic clinical practice. Research on bone substitute biomaterials is essential for improving the treatment strategies for bone regeneration. Chitin and its derivative, chitosan, are among the most abundant natural biomaterials and widely found in the shells of crustaceans. Chitin and chitosan are non-toxic, antibacterial, biocompatible, degradable, and have attracted significant attention in bone substitute biomaterials. Chitin/chitosan nanofibers and nanostructured scaffolds have large surface area to volume ratios and high porosities. These scaffolds can be fabricated by electrospinning, thermally induced phase separation and self-assembly, and are widely used in biomedical applications such as biological scaffolds, drug delivery, bacterial inhibition, and wound dressing. Recently, some chitin/chitosan-based nanofibrous scaffolds have been found structurally similar to bone's extracellular matrix and can assist in bone regeneration. This review outlines the biomedical applications and biological properties of chitin/chitosan-based nanofibrous scaffolds in bone tissue engineering.

Bioinspired surface modification of orthopedic implants for bone tissue engineering

Biomedical implants have been widely used in various orthopedic treatments, including total hip arthroplasty, joint arthrodesis, fracture fixation, non-union, dental repair, etc. The modern research and development of orthopedic implants have gradually shifted from traditional mechanical support to a bioactive graft in order to endow them with better osteoinduction and osteoconduction. Inspired by structural and mechanical properties of natural bone, this review provides a panorama of current biological surface modifications for facilitating the interaction between medical implants and bone tissue and gives a future outlook for fabricating the next-generation multifunctional and smart implants by systematically biomimicking the physiological processes involved in formation and functioning of bones.

Regeneration of large bone defects using mesoporous silica coated magnetic nanoparticles during distraction osteogenesis

Distraction osteogenesis (DO) represents an effective but undesirably lengthy treatment for large bone defects. Both magnetic nanoparticles and silicon have been shown to induce osteogenic differentiation of mesenchymal stem cells (MSCs), the key participant in bone regeneration. We herein synthesized mesoporous silica coated magnetic (Fe₃O₄) nanoparticles (M-MSNs) and evaluated its potential for acceleration of bone regeneration in a rat DO model. The M-MSNs exhibited good biocompatibility and remarkable capability in promoting the osteogenic differentiation of MSCs via the canonical Wnt/β-catenin pathway in vitro. More importantly, local injection of M-MSNs dramatically accelerated bone regeneration in a rat DO model according to the results of X-ray imaging, micro-CT, mechanical testing, histological examination, and immunochemical analysis. This study demonstrates the notable potential of M-MSNs in promoting bone regeneration during DO by enhancing the osteogenic differentiation of MSCs, paving the way for clinical translation of M-MSNs in DO to repair large bone defects.

Air-plasma treatment promotes bone-like nano-hydroxylapatite formation on protein films for enhanced in vivo osteogenesis

Introducing hydroxylapatite (HAp) into biomolecular materials is a promising approach to improve their bone regenerative capability. Thus a facile method needs to be developed to achieve this goal. Here we show that a simple air-plasma treatment of silk fibroin (SF) films for 5 min induced the formation of bone-like plate-shaped nano-HAp (nHAp) on their surface and the resultant material efficiently enhanced in vivo osteogenesis. The air-plasma-treated SF films (termed A-SF) presented surface nano-pillars and enhanced hydrophilicity compared to the pristine SF films (termed SF), making the A-SF and SF films induce the formation of plate-shaped/more-crystalline and needle-like/less-crystalline nHAp, respectively. The mineralized A-SF and SF films (termed A-SF-nHAp and SF-nHAp, respectively) and their non-mineralized counterparts were seeded with rat mesenchymal stem cells and subcutaneously implanted into the rat models. The A-SF-nHAp and A-SF films exhibited more efficient bone formation than the SF-nHAp and SF films in 4 weeks due to their unique nanotopography, with the A-SF-nHAp films being more efficient than the A-SF films. This work shows that a combination of the air-plasma treatment and the subsequent nHAp mineralization most efficiently promotes bone formation. Our plasma-based method is an attractive approach to enhance the bone regenerative capacity of protein-based biomaterials.

3-dimensional visualization of implant-tissue interface with the polyethylene glycol associated solvent system tissue clearing method

OBJECTIVES

Dental implants are major treatment options for restoring teeth loss. Biological processes at the implant-tissue interface are critical for implant osseointegration. Superior mechanical properties of the implant constitute a major challenge for traditional histological techniques. It is imperative to develop new technique to investigate the implant-tissue interface.

MATERIALS AND METHODS

Our laboratory developed the polyethylene glycol (PEG)-associated solvent system (PEGASOS) tissue clearing method. By immersing samples into various chemical substances, bones and teeth could be turned to transparent with intact internal structures and endogenous fluorescence being preserved. We combined the PEGASOS tissue clearing method with transgenic mouse line and other labelling technique to investigate the angiogenesis and osteogenesis processes occurring at the implant-bone interface.

RESULTS

Clearing treatment turned tissue highly transparent and implant could be directly visualized without sectioning. Implant, soft/hard tissues and fluorescent labels were simultaneously imaged in decalcified or non-decalcified mouse mandible samples without disturbing their interfaces. Multi-channel 3-dimensional image stacks at high resolution were acquired and quantified. The processes of angiogenesis and osteogenesis surrounding titanium or stainless steel implants were investigated.

CONCLUSIONS

Both titanium and stainless steel implants support angiogenesis at comparable levels. Successful osseointegration and calcium precipitation occurred only surrounding titanium, but not stainless steel implants. PEGASOS tissue clearing method provides a novel approach for investigating the interface between implants and hard tissue.

Critical Areas of Proliferation of Single Cells on Micropatterned Surfaces and Corresponding Cell Type Dependence

Material cues to influence cell proliferation are a fundamental issue in the fields of biomaterials, cell biology, tissue engineering, and regenerative medicine. This paper aims to investigate the proliferation of single mammal cells on micropatterned material surfaces. To this end, we prepared cell-adhesive circular microislands with 20 areas on the nonfouling background and systematically examined adhesion and proliferation behaviors of different kinds of single cells (primary stem and nonstem cells, cancer and normal cell lines) on micropatterns. On the basis of the analysis of experimental data, we found two critical areas about cell proliferation: (1) the critical spreading area of cells from almost no proliferation to confined proliferation, denoted as A_P and (2) the critical spreading area of cells from confined proliferation to almost free proliferation, denoted as A_FP. We further summarized the relative size relationship between these two critical areas and the characteristic areas of cell adhesion on both patterned and nonpatterned surfaces. While proliferation of single primary cells was affected by cell spreading, those cell lines, irrespective of normal and cancer cells, did not exhibit significant cell-spreading effects. As a result, this study reveals that proliferation of single cells is dependent upon spreading area, in particular for primary cells on material surfaces.

Intravital Imaging for Tracking of Angiogenesis and Cellular Events Around Surgical Bone Implants

IMPACT STATEMENT

These new experimental methods allow us to image, and quantify, angiogenesis and perivascular cell dynamics in the endosseous healing compartment. As such, the method is capable of providing a new perspective on, and unique information regarding, healing that occurs around orthopedic and dental implants.

PLGA-amoxicillin-loaded layer formed on anodized Ti alloy as a hybrid material for dental implant applications

In this paper, the preparation of a functional hybrid coating loaded with a drug (amoxicillin) on a promising titanium alloy - Ti-15Mo alloy is presented. The titanium alloy surface was anodized in solution with bioactive compounds to obtain a porous oxide layer favorable for MG-63 osteoblast-like cell adhesion. Then, a poly(lactide-co-glycolide) (PLGA) loaded with amoxicillin layer was formed using a dip-coating technique to cover the oxide layer, without filling in all of the pores. The morphology of the surface was evaluated using scanning electron microscopy supported by 3D Roughness Reconstruction software. The surface treatment of the Ti-15Mo alloy surface caused the surface roughness to increase up to 1.71 μm. The anodization process caused the Ti-15Mo alloy surface to become slightly more hydrophilic; however, the formation of the PLGA layer loaded with drug increased the contact angle to 96.5° ± 2.2°, respectively. After 4 weeks of polymer layer degradation, the registered signals on the ¹H NMR spectrum were identical to the signals registered for lactic acid (LAc), which confirms that the polymer layer was degraded within a short period of time. The concentration of drug released into the artificial saliva was investigated using high-performance liquid chromatography (HPLC) up to 12 h of coatings immersion. During the first hour of coating degradation in artificial saliva, and the concentration of the drug (13 μg/ml) was enough to inhibit bacterial growth of S. aureus and S. epidermidis. These results were confirmed by agar plate diffusion method and evaluation of the minimal inhibitory concentration (MIC). The cytocompatibility of the materials was determined using the osteoblast-like cells MG-63, and the viability and cell morphology (live/dead staining) were also evaluated. The results showed that amoxicillin influences the osteoblast-like MG-63 cells' behavior during cell culture, especially for the first few hours. The influence on the type of surface treatment on MG-63 cell behavior during 7 days of culture is discussed in this paper. To the best of our knowledge, this is the first time that a fast-degrading layer with amoxicillin has been deposited on previously anodized Ti surface. The formation of functional coating may find application as a cytocompatible coating to prevent bacterial adhesion on long-term implant surfaces.