Multifunctional Ti-xCu coatings for cardiovascular interfaces: Control of microstructure and surface chemistry

Advances in copper-containing biomaterials for managing bone-related diseases

Bone-related diseases pose a major challenge in contemporary society, with significant implications for both health and economy. Copper, a vital trace metal in the human body, facilitates a wide range of physiological processes by being crucial for the function of proteins and enzymes. Numerous studies have validated copper's role in bone regeneration and protection, particularly in the development and expansion of bone collagen. Owing to copper's numerous biological advantages, an increasing number of scientists are endeavoring to fabricate novel, multifunctional copper-containing biomaterials as an effective treatment strategy for bone disorders. This review integrates the current understanding regarding the biological functions of copper from the molecular and cellular levels, highlighting its potential for bone regeneration and protection. It also reviews the novel fabrication techniques for developing copper-containing biomaterials, including copper-modified metals, calcium phosphate bioceramics, bioactive glasses, bone cements, hydrogels and biocomposites. The fabrication strategies and various applications of these biomaterials in addressing conditions such as fractures, bone tumors, osteomyelitis, osteoporosis, osteoarthritis and osteonecrosis are carefully elaborated. Moreover, the long-term safety and toxicity assessments of these biomaterials are also presented. Finally, the review addresses current challenges and future prospects, in particular the regulatory challenges and safety issues faced in clinical implementation, with the aim of guiding the strategic design of multifunctional copper-based biomaterials to effectively manage bone-related diseases.

Recent advances in surface functionalization of cardiovascular stents

Cardiovascular diseases (CVD) are the leading global threat to human health. The clinical application of vascular stents improved the survival rates and quality of life for patients with cardiovascular diseases. However, despite the benefits stents bring to patients, there are still notable complications such as thrombosis and in-stent restenosis (ISR). Surface modification techniques represent an effective strategy to enhance the clinical efficacy of vascular stents and reduce complications. This paper reviews the development strategies of vascular stents based on surface functional coating technologies aimed at addressing the limitations in clinical application, including the inhibition of intimal hyperplasia, promotion of re-endothelialization. These strategies have improved endothelial repair and inhibited vascular remodeling, thereby promoting vascular healing post-stent implantation. However, the pathological microenvironment of target vessels and the lipid plaques are key pathological factors in the development of atherosclerosis (AS) and impaired vascular repair after percutaneous coronary intervention (PCI). Therefore, restoring normal physiological environment and removing the plaques are also treatment focuses after PCI for promoting vascular repair. Unfortunately, research in this area is limited. This paper reviews the advancements in vascular stents based on surface engineering technologies over the past decade, providing guidance for the development of stents.

Coatless modification of 3D-printed Ti6Al4V implants through tailored Cu ion implantation combined with UV photofunctionalization to enhance cell attachment, osteogenesis and angiogenesis

The three-dimensional-printed Ti6Al4V implant (3DTi) has been widely accepted for the reconstruction of massive bone defects in orthopedics owing to several advantages, such as its tailored shape design, avoiding bone graft and superior bone-implant interlock. However, the osteoinduction activity of 3DTi is inadequate when applied clinically even though it exhibits osteoconduction. This study developes a comprehensive coatless strategy for the surface improvement of 3DTi through copper (Cu) ion implantation and ultraviolet (UV) photofunctionalization to enhance osteoinductivity. The newly constructed functional 3DTi (UV/Ti-Cu) achieved stable and controllable Cu doping, sustained Cu2+ releasing, and increased surface hydrophilicity. By performing cellular experiments, we determined that the safe dose range of Cu ion implantation was less than 5×1016 ions/cm2. The implanted Cu2+ enhanced the ALP activity and the apatite formation ability of bone marrow stromal cells (BMSCs) while slightly decreasing proliferation ability. When combined with UV photofunctionalization, cell adhesion and proliferation were significantly promoted and bone mineralization was further increased. Meanwhile, UV/Ti-Cu was conducive to the migration and angiogenesis of human umbilical vein endothelial cells (HUVECs) in vitro, theoretically facilitating vascular coupling osteogenesis. In conclusion, UV/Ti-Cu is a novel attempt to apply two coatless techniques for the surface modification of 3DTi. In addition, it is considered a potential bone substrate for repairing bone defects.

Surface Bio-engineered Polymeric Nanoparticles

Surface bio-engineering of polymeric nanoparticles (PNPs) has emerged as a cornerstone in contemporary biomedical research, presenting a transformative avenue that can revolutionize diagnostics, therapies, and drug delivery systems. The approach involves integrating bioactive elements on the surfaces of PNPs, aiming to provide them with functionalities to enable precise, targeted, and favorable interactions with biological components within cellular environments. However, the full potential of surface bio-engineered PNPs in biomedicine is hampered by obstacles, including precise control over surface modifications, stability in biological environments, and lasting targeted interactions with cells or tissues. Concerns like scalability, reproducibility, and long-term safety also impede translation to clinical practice. In this review, these challenges in the context of recent breakthroughs in developing surface-biofunctionalized PNPs for various applications, from biosensing and bioimaging to targeted delivery of therapeutics are discussed. Particular attention is given to bonding mechanisms that underlie the attachment of bioactive moieties to PNP surfaces. The stability and efficacy of surface-bioengineered PNPs are critically reviewed in disease detection, diagnostics, and treatment, both in vitro and in vivo settings. Insights into existing challenges and limitations impeding progress are provided, and a forward-looking discussion on the field's future is presented. The paper concludes with recommendations to accelerate the clinical translation of surface bio-engineered PNPs.

Dealloyed nano-porous TiCu coatings with controlled copper release for cardiovascular devices

TiCu coatings with controlled copper release and nano-porous structures were fabricated as biocompatible, blood-contacting interfaces through a two-step process. Initially, coatings with 58 % Cu were created using HiPIMS/DC magnetron co-sputtering, followed by immersion in a dilute HF solution for varying durations to achieve dealloying. The presence of Ti elements in the as-deposited TiCu coatings facilitated their dissolution upon exposure to the dilute HF solution, resulting in the formation of nanopores and increased nano-roughness. Dealloying treatment time correlated with higher Cu/(Ti + Cu) values, nanopore size, and nano-roughness in the dealloyed samples. The dealloyed TiCu coatings with 87 % Cu exhibited a controlled release of copper ions and displayed nanopores (approximately 80 nm in length and 31.0 nm in width) and nano-roughness (Ra roughness: 82 nm). These coatings demonstrated inhibited platelet adhesion and suppressed smooth muscle cell behavior, while supporting favorable endothelial cell viability and proliferation, attributed to the controlled release of copper ions and the extent of nanostructures. In contrast, the as-deposited TiCu coatings with 85 % Cu showed high copper ion release, leading to decreased viability and proliferation of endothelial cells and smooth muscle cells, as well as suppressed platelet adhesion. The TiCu coatings met medical safety standards, exhibiting hemolysis rates of <5 %. The technology presented here paves the way for the simple, controllable, and cost-effective fabrication of TiCu coatings, opening new possibilities for surface modification of cardiovascular devices such as vascular stents and inferior vena cava filters.

Corroded iron stent increases fibrin deposition and promotes endothelialization after stenting

Poststent restenosis is caused by insufficient endothelialization and is one of the most serious clinical complications of stenting. We observed a rapid endothelialization rate and increased fibrin deposition on the surfaces of the corroded iron stents. Thus, we hypothesized that corroded iron stents would promote endothelialization by increasing fibrin deposition on rough surfaces. To verify this hypothesis, we conducted an arteriovenous shunt experiment to analyze fibrin deposition in the corroded iron stents. We implanted a corroded iron stent in both the carotid and iliac artery bifurcations to elucidate the effects of fibrin deposition on endothelialization. Co-culture experiments were conducted under dynamic flow conditions to explore the relationship between fibrin deposition and rapid endothelialization. Our findings indicate that, from the generation of corrosion pits, the surface of the corroded iron stent was rough, and numerous fibrils were deposited in the corroded iron stent. Fibrin deposition in corroded iron stents facilitates endothelial cell adhesion and proliferation, which, in turn, promotes endothelialization after stenting. Our study is the first to elucidate the role of iron stent corrosion in endothelialization, pointing to a new direction for preventing clinical complications caused by insufficient endothelialization.

Antibacterial Activity and Cytocompatibility of Electrospun PLGA Scaffolds Surface-Modified by Pulsed DC Magnetron Co-Sputtering of Copper and Titanium

Biocompatible poly(lactide-co-glycolide) scaffolds fabricated via electrospinning are having promising properties as implants for the regeneration of fast-growing tissues, which are able to degrade in the body. The hereby-presented research work investigates the surface modification of these scaffolds in order to improve antibacterial properties of this type of scaffolds, as it can increase their application possibilities in medicine. Therefore, the scaffolds were surface-modified by means of pulsed direct current magnetron co-sputtering of copper and titanium targets in an inert atmosphere of argon. In order to obtain different amounts of copper and titanium in the resulting coatings, three different surface-modified scaffold samples were produced by changing the magnetron sputtering process parameters. The success of the antibacterial properties’ improvement was tested with the methicillin-resistant bacterium Staphylococcus aureus. In addition, the resulting cell toxicity of the surface modification by copper and titanium was examined using mouse embryonic and human gingival fibroblasts. As a result, the scaffold samples surface-modified with the highest copper to titanium ratio show the best antibacterial properties and no toxicity against mouse fibroblasts, but have a toxic effect to human gingival fibroblasts. The scaffold samples with the lowest copper to titanium ratio display no antibacterial effect and toxicity. The optimal poly(lactide-co-glycolide) scaffold sample is surface-modified with a medium ratio of copper and titanium that has antibacterial properties and is non-toxic to both cell cultures.

Antibacterial Ti-Cu implants: A critical review on mechanisms of action

Titanium (Ti) has been widely used for manufacturing of bone implants because of its mechanical properties, biological compatibility, and favorable corrosion resistance in biological environments. However, Ti implants are prone to infection (peri-implantitis) by bacteria which in extreme cases necessitate painful and costly revision surgeries. An emerging, viable solution for this problem is to use copper (Cu) as an antibacterial agent in the alloying system of Ti. The addition of copper provides excellent antibacterial activities, but the underpinning mechanisms are still obscure. This review sheds light on such mechanisms and reviews how incorporation of Cu can render Ti-Cu implants with antibacterial activity. The review first discusses the fundamentals of interactions between bacteria and implanted surfaces followed by an overview of the most common engineering strategies utilized to endow an implant with antibacterial activity. The underlying mechanisms for antibacterial activity of Ti-Cu implants are then discussed in detail. Special attention is paid to contact killing mechanisms because the misinterpretation of this mechanism is the root of discrepancies in the literature.

A high-hydrophilic Cu2O-TiO2/Ti2O3/TiO coating on Ti-5Cu alloy: Perfect antibacterial property and rapid endothelialization potential

In order to make novel antibacterial Ti-Cu alloy more suitable for cardiovascular implant application, a Cu-containing oxide coating was manufactured on Ti-Cu alloy by plasma-enhanced oxidation deposition in plasma enhanced chemical vapor deposition (PECVD) equipment to further improve the antibacterial ability and the surface bioactivity. The results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and water contact angle indicated that a sustainably high-hydrophilic Cu₂O-TiO₂/Ti₂O₃/TiO coating with nano-morphology on Ti-5Cu was successfully constructed. The corrosion performance results showed that the coating enhanced the corrosion resistance while releasing more Cu²⁺, compared with Ti-5Cu. Antibacterial tests confirmed the perfect antibacterial property of the coating (R ≥ 99.9 %), superior to Ti-Cu alloy (R > 90 %). More delightfully, it was observed by phalloidin-FITC and DAPI staining that the coating improved the early adhesion of HUVEC cells mainly due to strong hydrophilicity and nano-morphology. It was demonstrated that the extract of the coated sample significantly promoted proliferation (RGR = 112 %-138 % after cultivation for 1 to 3 days) and migration of HUVEC cells due to the appropriate Cu²⁺ release concentration. Hemolysis assay and platelet adhesion results showed that the coating had excellent blood compatibility. All results suggested that the coating on Ti-Cu alloy might be a promising surface with the perfect antibacterial ability, blood compatibility and evident promoting endothelialization ability for the cardiovascular application.

Biological applications of copper-containing materials

Copper is an indispensable trace metal element in the human body, which is mainly absorbed in the stomach and small intestine and excreted into the bile. Copper is an important component and catalytic agent of many enzymes and proteins in the body, so it can influence human health through multiple mechanisms. Based on the biological functions and benefits of copper, an increasing number of researchers in the field of biomaterials have focused on developing novel copper-containing biomaterials, which exhibit unique properties in protecting the cardiovascular system, promoting bone fracture healing, and exerting antibacterial effects. Copper can also be used in promoting incisional wounds healing, killing cancer cells, Positron Emission Tomography (PET) imaging, radioimmunological tracing and radiotherapy of cancer. In the present review, the biological functions of copper in the human body are presented, along with an overview of recent progress in our understanding of the biological applications and development of copper-containing materials. Furthermore, this review also provides the prospective on the challenges of those novel biomaterials for future clinical applications.

Polydopamine-Modified Copper-Doped Titanium Dioxide Nanotube Arrays for Copper-Catalyzed Controlled Endogenous Nitric Oxide Release and Improved Re-Endothelialization

The controllable release is necessary for ideal drug delivery technologies. Because of their high specific surface area and high porosity, titanium dioxide nanotubes (TNTs) have been widely used as drug carriers in medical devices. By loading copper as the catalyst, nitric oxide (NO) generation was facilitated by catalyzing the decomposition of renewable endogenous NO donors in vivo. Herein, the long-term controllable release profile of NO is highlighted owing to the multilayer polydopamine (PDA) cap structure. Different layers of PDA are used to adjust the NO release behavior, and the results show that three layers of PDA can not only effectively prevent the burst release of NO but also maintain long-term stable release of copper ion and NO. The bioactivity of the NO generated from three-layer PDA-modified copper-loaded TNTs (PDA-3L-NTCu2) and unmodified copper-loaded TNTs (NTCu2) are verified by our work, indicating effective inhibition of platelet activation, thrombosis, inflammation, and intimal hyperplasia. Importantly, the PDA-3L-NTCu2 show selectively promote the growth of endothelial cells in vitro and outstanding re-endothelialization for 4 weeks in vivo, as compared to NTCu2, TNTs, and 316L stain steel. This study suggests that copper-loaded with PDA modification helps us achieve controlled long-term stable local NO release with well-retained bioactivity and enhanced re-endothelialization.

Effect of ultrasonic micro-arc oxidation on the antibacterial properties and cell biocompatibility of Ti-Cu alloy for biomedical application

In order to improve antibacterial properties and cell biocompatibility of Ti-Cu alloy, an ultrasonic micro-arc oxidation (UMAO) has been applied to Ti-Cu alloy. The corrosion resistance, antibacterial activity and cell compatibility of Ti-Cu alloy before and after UMAO were studied in detail by means of electrochemical test, plate count method and CCK-8 test scanning electron microscopy (SEM) technology to evaluate the application possibilities of UMAO as a surface bio-modification method for Ti-Cu alloy. The surface microstructure characterisation showed that a typical porous coating with a pore diameter of 3-8 μm and a thickness of 5-15 μm was formed on the surface of the Ti-Cu alloy, which significantly improved the surface roughness and hydrophilicity. The plate count method demonstrated that UMAO coatings on Ti-Cu alloy showed strong antibacterial activity (≥99%) against Staphylococcus aureus (S. aureus) even after being immersed in a physiological saline for up to 20 days, indicating that UMAO-treated Ti-Cu alloy had very strong long-term antibacterial properties. It is believed that the strong long-term antimicrobial properties of Ti-Cu-UMAO samples were mainly due to the formation of Cu₂O and CuO in UMAO coatings. The results of cell compatibility evaluation showed that UMAO treatment did not bring about cytotoxicity but improved the early adhesion of MC3T3 cell.