Assoc Prof Behnam Akhavan

Current synthetic bioceramic scaffolds often lack bioinstructive ability for effective bone regeneration. We have selected magnesium-doped baghdadite (Mg-BAG) scaffolds, known for their promising osteoinductive and mechanical properties, as the base material and fabricated them using a liquid crystal display 3D printing technique. Building on this foundation, we have advanced the application of ion-assisted plasma polymerization (IAPP) technology, adapted for 3D structures, to develop homogeneous bioinstructive interfaces on these scaffolds for enhanced osteoinductive properties. The IAPP coatings formed under energetic ion bombardment maintained a strong attachment to the Mg-BAG scaffolds after 1 month of incubation at 37 °C in cell culture media. We provided evidence that such robustness of the interfaces is regulated by the coating's growth mechanism on a nanoscale, transitioning from initial island formation to a stable, smooth structure. The coatings enhanced the release of silicon ions from the scaffolds and significantly slowed the release of bone morphogenetic protein 2 (BMP2) over a period of 45 days. In the presence of lower soluble BMP2 concentrations, the biofunctionalized scaffolds demonstrated superior biocompatibility and osteoinductivity compared to those with physisorbed BMP2, as evidenced by sustained cell proliferation and elevated levels of osteogenic gene expression observed in human osteoblast-like cells (HOBs). This research highlights a key evolution of IAPP from traditional 2D substrates to more complex 3D structures and the excellent potential of IAPP bioceramic scaffolds as a next generation of cell-free constructs for bone regeneration applications and beyond.

Spontaneous and directional droplet transport has attracted considerable attention for its potential applications such as self-cleaning surfaces and microfluidics. Previous studies on the droplet motion between rigid or parallel flexible channels established that the movement direction can be predetermined by the initial channel configuration and wettability. However, in this study, we experimentally show that the direction of droplet movement in nonparallel deformable channels can be carefully tuned, even under the same geometric and wetting conditions. This advanced feature arises from the interplay between initial system conditions and the subsequent solid-liquid interaction, depending on the initial channel configuration, channel flexibility, droplet conditions, wettability, and contact angle hysteresis. Combining the capillary pressure determined from the Young-Laplace equation with the structural deformation described by Euler-Bernoulli beam theory, we developed a general mathematical model capable of accurately predicting the droplet movement direction under a wide range of conditions. The model does not need any fitting parameters and is validated by our experiments. Additionally, our results lead to the identification of a phase diagram encompassing three distinct modes of droplet movement: toward the free end, toward the fixed end, and a stationary state. The proposed phase diagram serves as a predictive tool, offering new insights into controlling the direction of spontaneous droplet motion in flexible channels, with applications in the design and optimization of microfluidic devices.

Polymeric nanoparticles (PNPs) have evolved over the past few decades as promising vehicles to deliver drugs to treat cancer. However, their clinical application remains limited mainly due to several biological obstacles. These include rapid clearance from the bloodstream, complex hemorheological dynamics, suboptimal biodistribution, limited tumor accumulation and extravasation, inefficient cellular internalization and trafficking, and offsite toxicity. How can we carefully tune the physicochemical properties of PNPs to break these barriers? This review answers this question by comprehensively and critically examining recent advances and trends in engineering the physicochemical properties of PNPs to enhance their efficacy in cancer drug delivery. It sheds light on the underpinning mechanisms regulated by size, shape, and surface chemistry critical in overcoming heterogeneous biological barriers. Synergistic effects and the interplay between these physicochemical properties are discussed in detail. The types of PNPs, based on form, morphology, and fabrication strategies, are critically reviewed and evaluated according to their physicochemical properties, which directly impact the efficacy of the drug delivery systems and their fate upon administration. The review concludes by proposing design principles and future research directions to enhance the clinical translation of PNPs and their advancement towards more effective cancer treatments.

A thermally triggered, on demand, surface modification method was exploited using carbon fibers (CFs). Bisdiazomethanes undergo thermal activation to generate extremely reactive carbene intermediates, able to react with the CF surface. Herein, the surface modification of continuous CFs is demonstrated by dipping the fibers in a solution of bisdiazomethane at three different concentrations of 1 mmol, 5 mmol, and 10 mmol, followed by air drying and heating at 120 °C. Tensile strength and Young's Modulus values were preserved in the treated fibers, while the interfacial shear strength (IFSS) values showed significant improvement. The highest IFSS improvement was found (189 %) for the fibers dipped in the 5 mmol solution, with significant increases noted for the 1 and 10 mmol modifications, of 54 % and 97 %, respectively. When the thermal modification was repeated with parameters analogous to a sizing application used in CF manufacture (30 s dip, 2-min heating), 74¿79 % improvements in IFSS resulted. Hence, this approach can serve as a simple, scalable, and tunable surface modification method for discontinuous CFs that promotes their use in high value applications.

Long-term antibacterial effects and favourable biocompatibility are crucial to sustaining the long-term application of medical devices such as cardiac implantable devices, orthopedic devices, hernia meshes, and catheters. This study reports the development of sodium carboxymethyl cellulose/polydopamine films on Ti[sbnd]Cu coatings (TiCu-CMC/PDA) with long-term antimicrobial effects and cytocompatibility for surface engineering of implants. The TiCu-CMC/PDA coatings demonstrate sustained antimicrobial efficacy, maintaining bacterial inhibition rates above 99.6 % after aging in simulated body fluid (SBF) at 37 °C for 60 days. This remarkable antibacterial performance is primarily driven by the controlled release of copper ions during aging, complemented by surface copper's contribution to antimicrobial effects. Further, the TiCu-CMC/PDA coatings exhibit high cell viability and proliferation with negligible cytotoxicity, attributed to the regulated copper ion release. However, the endothelial cell viability on TiCu-CMC/PDA coatings decreased with aging due to the formation of copper ion complexes and CuO/Cu(OH)2, as well as increased surface roughness and hydrophilicity over time. The technology offers a simple and controllable approach to fabricating TiCu-CMC/PDA coatings, providing a pathway for the design of long-term antibacterial biomedical devices, including cardiovascular and orthopedic implants.

The application of magnesium alloys in cardiovascular stents exhibits a rapid corrosion rate and insufficient biocompatibility, resulting in significant morbidity and mortality. Achieving an appropriate corrosion rate and biocompatibility for magnesium alloys is still a key research priority. Hydroxypropyl methylcellulose (HPMC) is an environment-friendly cellulosic polymer with excellent biocompatibility and corrosion-inhibiting properties. Here we present a simple and controllable coating method to enhance the corrosion protection and biocompatibility of HPMC coatings on Mg alloy for the first time for cardiovascular applications. The various thicknesses of HPMC coatings were deposited in the present study using a dip-coating method, followed by evaluations of surface physicochemical characteristics, corrosion behavior, and immersion tests including Mg2+ ion release, pH, and hydrogen evolution. Biocompatibility of the samples was assessed by hemolysis assay and endothelial cell cultures. HPMC coatings exhibit hydrophilic surfaces with strong tensile strength and robust adhesion to AZ31 Mg substrates. Electrochemical corrosion results reveal that at the high thickness of 3011.0 ± 100.0 nm, the HPMC coatings provide superior corrosion protection. In vitro cross-sectional and weight loss results revealed that the HPMC coatings reduce the corrosion rates, whilst immersion tests show reduced Mg2+ ion release, pH values, and hydrogen evolution compared to bare Mg alloy. The HPMC samples show a significantly reduced hemolysis ratio and enhanced cell viability and adhesion ascribed to their superior corrosion protection and moderate wettability. This study of HPMC coatings on Mg alloys provides insights into their potential future application for cardiovascular stents.

Sodium carboxymethylcellulose (CMC) is a biocompatible and biodegradable derivative of cellulose, making it a promising material for biomedical applications. However, its poor stability in aqueous environments has significantly limited its use in long-term biomedical devices. Here, we present for the first time a simple and controllable method to enhance the wet stability of CMC coatings by cross-linking of CMC and polydopamine (PDA) and self-polymerization of PDA for widespread applications in biomedical devices. A series of CMC/PDA coatings were fabricated on the initial PDA layers by using dip coating and subsequently heated at 200 °C. The performance of the CMC/PDA coatings and their chemical and structural stability in aqueous media have been systematically analyzed, and the mechanisms underpinning their robust performance have been revealed. FITR, X-ray photoelectron spectroscopy (XPS), and gel permeation chromatography (GPC) results showed that CMC/PDA coatings involved amidation and esterification reactions as well as self-polymerization of PDA. Degradation studies in phosphate-buffered saline (PBS) solution at 37 °C indicated degradation via ester and amide bond cleavage, with the stability of CMC/PDA coatings surpassing that of individual PDA and CMC coatings over a 30-day immersion period. The CMC/PDA coating with a CMC concentration of 15 mg/mL exhibited the highest adhesion strength in an aqueous environment, which was attributed to the high cross-linking of CMC and PDA, as well as the intrinsic stability of PDA. The CMC/PDA coatings demonstrated favorable viability, growth, and proliferation of endothelial cells. The stable and biocompatible biocellulose coatings can be easily applied from aqueous solutions onto almost any type of solid metal and ceramic material, providing a promising dimension for surface engineering of vascular scaffolds and tissue engineering constructs.

Bio-absorbable magnesium (Mg) alloys exhibit significant promise for implantable medical devices, particularly in orthopedic applications. However, their limited corrosion resistance and rapid degradation rates have hindered their clinical translation. To address this long-standing challenge, here we developed a composite coating system (PTMC-MAO) for Mg-alloys, seamlessly integrating Microarc oxidation (MAO) and Poly-(Trimethylene Carbonate) (PTMC) layers. Leveraging the synergistic effects between MAO coatings, generated through micro-arc oxidation, and PTMC coatings, synthesized via gradual dropwise addition, our approach effectively controls corrosion and degradation rates of a widely applied Mg-alloy (AZ31) both in terms of kinetics and thermodynamics. Compared with the uncoated AZ31, the PTMC-MAO coatings exhibited greater positive Ecorr of -1290 mV and lower icorr of 5.3 nA· cm-2 with a significant 851-fold reduction. The coatings reached up to a distinguished protection efficiency (¿) of 99.9 %, accompanying with the higher impedance |Z| of 4×105 O·cm2. The ¿pH change and the released Mg2+ concentration were 0.25 and 42 µg/ml, respectively, after 21 days of immersion. Both values were superior to those observed for the AZ31 substrate. These results highlight the transformational potential of PTMC-MAO composite coatings, indicating their feasibility as a new class of materials for engineering the surfaces of Mg-based degradable implants.

Carbon fiber electrodes were prepared by grafting anthraquinone molecules via a scalable electrochemical approach which simultaneously increased interfacial and electrochemical capacitance properties. In this work, anthraquinone diazonium salts were synthesized and grafted onto carbon fiber tows at various concentrations. These modified fibers were subsequently evaluated mechanically and electrochemically to analyze their suitability in structural supercapacitors. Compared to control fibers, the grafted anthraquinone groups resulted in a 30% increase in interfacial shear strength (IFSS) and 6.6× increase in specific capacitance. Industry application was also a focus thus carbon fibers were also modified with in-situ generated diazonium salts to determine the applicability to an in-line industrial process. Specifically, potentiostatic functionalization of fibers with in-situ generated diazonium salts AQ-1 and AQ-2, showed 3× and 4.3× increase in specific capacitance, respectively, relative to unmodified carbon fiber (CF). We expect that implementing a scalable method to introduce a conductive and electrochemically active covalently bound surface chemistry layer onto carbon fiber exhibits a higher specific capacitance than carbon fiber grafted with most other small molecules reported in literature. This will open new avenues for manufacturing multifunctional and high-performance fibers with tailored properties for specific/targeted applications.

Covalent biofunctionalization of implant surfaces using anti microbial agents is a promising approach to reducing bone infection and implant failure. Radical-rich, ion-assisted plasma polymerized (IPP) coatings enable surface covalent biofunctionalization in a simple manner; but until now, they are limited to only 2D¿surfaces. Here a new technology is demonstrated to create homogenous IPP coatings on 3D¿materials using a rotating, conductive cage that is negatively biased while immersed in RF plasma. Evidence is provided that under controlled energetic ion bombardment, this technology enables the formation of highly robust and homogenous radical-rich coatings on 3D objects for subsequent covalent attachment of antimicrobial agents. To functionally apply this technology, the broad-spectrum antimicrobial CSA-90 is attached to the surfaces, where it retained potent antibacterial activity against Staphylococcus aureus. CSA-90 covalent functionalization of stainless-steel pins used in a murine model of orthopedic infection revealed the highly promising potential of this coating system to reduce S. aureus infection-related bone loss. This study takes the previous research on plasma-based covalent functionalization of 2D surfaces a step further, with important implications for ushering in a new dimension in the biofunctionalization of 3D structures for applications in bone implants and beyond.

The deposition of gold-colored titanium nitride films without applying substrate heating is of significant interest due to the increasing demand for decorative coatings on temperature-sensitive three-dimensional substrates. Here, the energetic impact of Nb1+ ions during the deposition of TiN was achieved within a bipolar high-power impulse magnetron sputtering discharge operating on a Nb target. A separate titanium target was operated with direct current magnetron sputtering in the same reactive argon-nitrogen mixture. This process aimed to achieve a dense titanium nitride with the assistance of the niobium ion bombardment. The niobium controlled the phase formation and structure of the resulting Nb-containing TiN coating without needing external heating. The niobium ion bombardment during deposition increases the density of the titanium nitride coatings, promoting the formation of the cubic phase favored for its gold color and excellent mechanical and tribological properties, including HF1-level adhesion. Energy-selective mass spectrometer investigations revealed an increase in the flux and the energy of titanium ions due to momentum transfer from niobium ions to titanium neutrals in the plasma generated between the targets and the substrate. The approach introduced here paves the way for the formation of the cubic phase of Nb-doped TiN films without external heating, producing coatings with combined decorative and protective properties.

Tungsten oxide (WO3) thin films have been of prime interest among electrochromic materials because of their chemical stability, strong adherence to various substrates, and high coloration efficiency. High-power impulse magnetron sputtering (HiPIMS) holds great potential in fabricating durable WO3-based electrochromic layers. However, the tungsten target¿plasma interactions in reactive-HiPIMS deposition of WO3 and their role in modulating the electrochromic function of the resulting WO3 coatings are yet to be understood. Herein, by controlling the HiPIMS pulse length, the stoichiometry of tungsten oxide structures can be tuned to optimize the transparency and electrochromic function of the coatings. X-ray photoelectron spectroscopy data shows that at pulse lengths shorter than 85 µs, the concentration of suboxide compounds is less than that of tungsten trioxide, while for pulse lengths longer than 100 µs, this balance is reversed. The average optical transparency of the coatings in the range of visible light is higher than 80%. The optical transmittance modulation (¿T) of 38.1, 36.2, and 34.3% and coloration efficiency of 41.3, 38.4, and 35.9 cm2 C-1 are measured for the WOx samples deposited at pulse lengths of 70, 85, and 100 µs, respectively. Tuning the HiPIMS pulse characteristics is a simple strategy to deposit tungsten oxide films with tuned electrochromic properties for an array of applications, from smart windows to wearable displays.

Many biological structures such as nerves, blood and lymphatic vessels, and muscle fibres exhibit longitudinal geometries with distinct cell types extending along both the length and width of internal linear axes. Modelling these three-dimensional structures in vitro is challenging: the best-defined stem-cell differentiation systems are monolayer cultures or organoids using pluripotent stem cells. Pluripotent stem cells can differentiate into functionally mature cells depending on the signals received, holding great promise for regenerative medicine. However, the integration of in vitro differentiated cell types into diseased tissue remains a challenge. Engineered scaffolds can bridge this gap if the appropriate signalling systems are incorporated into the scaffold. Here, we have taken a biomimicry approach to generate longitudinal structures in vitro. In this approach, mouse embryonic stem cells are directed to differentiate to specific cell types on the surface of polycaprolactone (PCL) fibres treated by plasma-immersion ion implantation and to which with lineage-specifying molecules have been covalently immobilised. We demonstrate the simplicity and utility of our method for efficiently generating high yields of the following cell types from these pluripotent stem cells: neurons, vascular endothelial cells, osteoclasts, adipocytes, and cells of the erythroid, myeloid, and lymphoid lineages. Strategically arranged plasma-treated scaffolds with differentiated cell types could ultimately serve as a means for the repair or treatment of diseased or damaged tissue.

Atmospheric pressure plasma jets (APPJs) are advancing as a versatile dry technology for creating biofunctional structures. Recently, reagent-free, single-step covalent immobilization of bioactive molecules onto surfaces was demonstrated. Despite this, the mechanisms governing the covalent attachment process remain obscure. Here, we studied morphological changes, concentrations of radicals, and the formation of reactive species on APPJ-treated polymers to shed light on the underlying mechanisms of covalent attachment. The APPJ-treated polyethylene surfaces, prepared either in air or with controlled ambient gas composition, were analyzed using Fourier transform infrared, X-ray photoelectron, electron spin resonance, and fluorescence spectroscopies, as well as atomic force microscopy. It was demonstrated that only non-radical reactive oxygen species (ROS) could explain the attachment. This attachment was also demonstrated on silicone (PDMS), broadening the range of possible applications. Finally, to identify reaction pathways, fluorinated carbon brushes were used, each presenting a specific functional group. Attachment data indicated that molecules with amine or thiol groups can be covalently bound to treated surfaces. As a result, reactions involving the ROS, hydroxyl, carbonyl, carboxyl, and peroxides are potential pathways. These findings provide a means of optimizing treatment features such as binding site density in future studies and applications, thereby expanding the capabilities of APPJ treatment within 3D bioprinters.

This study presents a direct electrochemical modification technique for incorporating two specific small molecules, phenol, and aniline into carbon fibre (CF) surface. These molecules have a strong hydrogen bonding for polyphenylene sulphide (PPS) and are intended to improve the friction and wear properties of PPS/CF composites. The tribological properties of PPS/CF composites were evaluated using a pin-on-disc. To get a more thorough comprehension of the working conditions of PPS/CF composites, a comparative examination of the composites' tribological characteristics was carried out by modifying the nature of the opposing surface while keeping the sliding speed of the applied force consistent. The results showed that the addition of 10 mM phenol to carbon fibre results in a significant reduction in the coefficient of friction (COF) compared to carbon fibre treated with 50 mM phenol and 6 mM aniline when in contact with a steel counter-face. When sliding against a polymer counter-face, the composites experienced a reduction in the COF due to the formation of a transfer film rich in PPS. Introducing aniline groups to the fibre surface reduced the wear rate by 57.5% to 46% with applied forces of 25 N compared to PPS and unmodified PPS/CF when sliding against the polymer counter-face. This study thoroughly discusses the synergistic process of chemical modification on the tribological performance of PPS/CF. It also analyses the surface microstructures of the worn surfaces of the composites. This study has the potential to provide new insights into the design and development of CF/polymer composites with enhanced friction and wear properties.

Adverse body reactions to blood-contacting medical devices endanger patient safety and impair device functionality, with events invariably linked to nonspecific protein adsorption due to suboptimal material biocompatibility. To improve the safety and durability of such devices, herein we propose a strategy for introducing stable zwitterionic grafts onto polymeric surfaces via plasma functionalization. The resulting zwitterion-grafted substrates exhibit long-lasting superhydrophilicity, enabling antifouling and anti-thrombogenic properties. We demonstrate the successful modification of the surface elemental composition, morphology, and hydrophilicity, while retaining the underlying mechanical properties of the polymeric substrate. Furthermore, we optimise the fabrication process to ensure long-lasting modifications at least three months after fabrication. This strategy decreases fibrinogen adsorption by approximately 9-fold, and thrombosis by almost 75% when applied to a commercial polyurethane. Moreover, this process is universally applicable to a wide range of polymeric materials, even those with stable chemistry such as polytetrafluoroethylene.

The multifunctionality of carbon fiber (CF) is being extensively explored. Herein, polyimide covalent organic frameworks (PI-COFs) are grafted bound to CF to enhance their mechanical and electrochemical properties. Here, a range of COF scaffolds are grafted to the surface of CFs via a two-step functionalization. First, melamine is tethered to the fiber surface to provide an anchoring point for the COFs followed by a "graft from" approach to grow three different sized PI-COFs utilizing three differently sized dianhydride, PMDA to form MA-PMDA, NTCDA to form MA-NTCDA, and PTCDA to form MA-PTCDA COFs. These COFs increase the capacitance of CF by a maximum of 2.9 F g-1 (480% increase) for the MA-PTCDA, this coincides with an increase in interfacial shear strength by 67.5% and 52% for MA-NTCDA and MA-PTCDA, respectively. This data represents that the first-time CF has been modified with PI-COFs and allows access to COF properties including their porosity and CO2 capture ability while being attached to a substrate. This may lead to additional high-value recyclability and second-life applications for CFs.

Current biomaterial-based strategies explored to treat articular cartilage defects have failed to provide adequate physico-chemical cues in order to guide functional tissue regeneration. Here, it is hypothesized that atmospheric-pressure plasma (APPJ) treatment and melt electrowriting (MEW) will produce microfiber support structures with covalently-immobilized transforming growth factor beta-1 (TGFß1) that can stimulate the generation of functional cartilage tissue. The effect of APPJ operational speeds to activate MEW polycaprolactone meshes for immobilization of TGFß1 is first investigated and chondrogenic differentiation and neo-cartilage production are assessed in vitro. All APPJ speeds test enhanced hydrophilicity of the meshes, with the slow treatment speed having significantly less C-C/C-H and more COOH than the untreated meshes. APPJ treatment increases TGFß1 loading efficiency. Additionally, in vitro experiments highlight that APPJ-based TGFß1 attachment to the scaffolds is more advantageous than direct supplementation within the medium. After 28 days of culture, the group with immobilized TGFß1 has significantly increased compressive modulus (more than threefold) and higher glycosaminoglycan production (more than fivefold) than when TGFß1 is supplied through the medium. These results demonstrate that APPJ activation allows reagent-free, covalent immobilization of TGFß1 on microfiber meshes and, importantly, that the biofunctionalized meshes can stimulate neo-cartilage matrix formation. This opens new perspectives for guided tissue regeneration.

High entropy alloy (HEA) thin films have become increasingly popular because they exhibit favorable properties but with lower material consumption. Here, this research demonstrates that annealing of AlCoCrCu0.5FeNi thin films results in multiphase hardening and the formation of nanotwins. HEA thin films were atmospherically annealed at different temperatures (300 ¿ 700 °C) for 5 h. A thin dense oxide layer consisting of Al2O3 and Cr2O3 appeared at the top surface of the 700 °C annealed film. This oxide layer endows the HEA thin film with excellent antioxidant properties. As such, vacuum and inert gas might not be required for HEAs annealing process at up to 700 °C. A phase transformation was observed in the film annealed at 700 °C for 5 h from X-ray diffraction patterns. Results from transmission Kikuchi diffraction and energy dispersive X-ray spectroscopy mapping indicated the formation of three new phases, including the FeCo phase, Cr-rich phase and Cu nano-clusters. Variations also happened in HEA FCC matrix where two types of texture existed in the HEA FCC grains i.e., {012} <110> and {112} <110>. Of particular interest was that high-resolution transmission electron microscopy revealed a high density of annealing nanotwins among the HEA FCC grains, including lamellar and co-axial twins. The influence of these structural phenomena on mechanical properties was evaluated. The results showed that the hardness and modulus of 700 °C annealed HEA thin film increased by 25% and 24% to 8.4 ± 0.2 GPa and 149.4 ± 6.1 GPa when compared to the properties of as-deposited films.

High entropy alloy (HEA) films offer excellent mechanical properties due to their random solid solution structure. However, their large grain boundary volume fraction can cause thermal instability, resulting in phase decomposition that affects their high-temperature performance. Nevertheless, it remains an interesting question whether phase decomposition can be used as a processing tool to create new HEA materials. In this study, AlCrFeCoNiCu0.5 HEA thin films were fabricated and annealed at 500 °C for up to 72 h. The 72-hour annealed thin film exhibited a 30 % increase in mechanical properties, exceeding most other HEA thin films. Characterization using X-ray and electron microscopy revealed a decomposition-induced phase transformation, which produced four new phases, including Cu-rich FCC phase, Cr-rich BCC phase, and ordered B2 phase of AlNi and FeCo. The enhanced mechanical properties were due to back stress strengthening and BCC + B2 phase strengthening. The 72-hour annealed thin film also showed excellent thermal stability through a new round of annealing, exhibiting a low variation in microstructure and chemical composition after being annealed at 500 °C for 100 h.

One of the greatest trends currently revolutionizing healthcare is the introduction of advanced additive manufacturing techniques, also known as 3D printing, for personalized, regenerative, and accessible treatments. Bioactivity, as controlled by physical cues and biochemical signalling, is essential to this broad range of emerging treatments. In this review, we critically examine the current capabilities and limitations of biofunctionalization methods that have been used to immobilize biomolecules on 3D printed structures. A set of relevant considerations for determining the optimum biofunctionalization approach for an application is outlined, and common co-requisites are identified. Opportunities for expansion and improvement in relation to materials, biomolecules, cells, other immobilization methods and further applications are explored. The rapid expansion in the number of studies observed in recent years will likely accelerate due to the promising results to date.

Surface biofunctionalization aims to create cell-instructive surfaces that control the behavior of cells and modulate cellular interactions by incorporating cell signaling moieties at the materials-biosystem interface. Despite advances in developing bioinert and biocompatible materials, blood clotting, inflammation, and cell death continue to be observed upon the contact of foreign materials with living tissues leading to the materials' rejection. Specific examples include the application of foreign materials in implantable devices (e.g., bone implants, antimicrobial surfaces, and cardiovascular stents), biosensors, drug delivery, and 3D-bioprinting. Biofunctionalization of materials to date has been predominantly realized using wet chemical approaches. However, the complexity of wet chemistry, toxicity of reactants, waste disposal issues, reaction time, poor reproducibility, and scalability drive a need for a paradigm shift from wet chemical approaches to dry methods of surface biofunctionalization. Plasma-based technologies that enable covalent surface immobilization of biomolecules have emerged as dry, reagent-free, and single-step alternatives for surface biofunctionalization. This review commences by highlighting the need for bioinstructive surfaces and coatings for various biomedical applications such as bone implants, antimicrobial surfaces, biosensors, and 3D-bioprinted structures, followed by a brief review of wet chemical approaches for developing biofunctionalized surfaces and biomimetic devices. We then provide a comprehensive review of the development of plasma-based technologies for biofunctionalization, highlighting the plasma-surface interactions and underpinning mechanisms of biomolecule immobilization.

High entropy alloys (HEAs), as a novel material in the 21st century, possess several advantages, such as excellent corrosion & oxidation resistance and high mechanical properties. HEA thin films show these favourable properties with lower material costs than their bulk counterparts. Studying the HEA film-substrate interface represents challenges but is of extreme importance for the understanding of growth mechanisms with important implications for film adhesion. However, most HEA films were deposited on monocrystalline silicon substrates with limited practical applicability. Further, where commercial stainless steel, aluminium or titanium alloy substrates were used, the microstructure and chemistry at the interface were neglected. Here, we deposited AlCrFeCoNiCu0.5 HEA thin films on stainless steel 304 (SS304) substrates using cathodic arc deposition with different substrate biases. The crystallography and microstructure were investigated using an X-ray and electron-microscopy based chatacterization. A transition of an incoherent to semi-coherent interface was observed from 0 V to -50 V of the substrate bias. Energy dispersive spectroscopy demonstrated a transition of Cr2O3 to aluminum oxide across the interface. The nanoindentation tests revealed the significant improvement of mechanical properties of SS304 with HEA coatings. High-strength HEA (8.0 ± 0.2 GPa) thin films with semi-coherent interfaces were manufactured on SS304.

The most attractive advantages of high entropy alloy (HEA) thin films are their excellent properties, such as high strength and high corrosion and oxidation resistance, with a lower material cost. However, the thermal stability of the HEA thin films is always controversial. This is critical since the thermal stability of metals and alloys is closely related to the material's performance at high temperatures and also determines the application field of the material. The question of how will the nanocrystalline high entropy alloy thin film perform in terms of thermal stability needs to be clarified urgently. In this research, the thermal stability of AlCrFeCoNiCu0.5 HEA thin film fabricated by cathodic arc deposition was investigated at 500 °C as a function of time during vacuum annealing. X-Ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HRTEM) and Transmission Kikuchi Diffraction (TKD) were applied to analyze the chemistry and microstructure of HEA thin films in detail. The results showed that there was no obvious change in the elemental compositions of the films after annealing, but the elemental distribution of the annealed films was different from the as-deposited film, especially at the film surface and film-substrate interface for the 24 h-annealed sample. The existence of the FeCo phase with B2 structure was a significant sign to demonstrate that the spinodal decomposition occurred in the single face-centered-cubic (FCC) phase matrix of the film during annealing. Simultaneously, the segregation of Cu and Cr near the film-substrate interface and the penetration of Ni and Cu towards the Si substrate were clearly observed. These unusual phenomena indicated that the thermal stability of HEA was not always excellent. Also, it was noticed that a few Kirkendall voids forming at the film-substrate interface after 24 h of annealing would affect the adhesion of the film. Additionally, heat recovery and recrystallization were achieved by 500 °C annealing, which were confirmed by the decrease of lattice parameter and the increase of grain size in the 24 h-annealed thin film. Furthermore, the hardness and elastic modulus of the thin films before and after annealing were measured by nanoindentation. The results showed all the thin films exhibited excellent mechanical properties, and the optimal hardness and elastic modulus of 7.7 ± 0.3 GPa and 183.9 ± 4.4 GPa were obtained after 3 h-annealing.

Amorphous carbon films were deposited by bipolar HiPIMS, as a function of negative and positive voltage pulse lengths (50-175 µs and 0-175 µs respectively), using argon as sputter gas. The deposition rate, compressive stress, sp3 fraction and mechanical properties of the films were investigated and the results compared with those of amorphous carbon films deposited by conventional unipolar HiPIMS. We found minimum threshold positive and negative lengths are required in bipolar HiPIMS to enhance the sp3 fraction above 45 % and reduce the argon content. In addition to increasing the flux and energy of depositing ions by electrostatic control, bipolar HiPIMS also increases the flux ratio of depositing ions to sputter ions and thus reduces the probability of sputter gas incorporation into the growing amorphous carbon layers. Reduced argon content in the coatings correlates with high residual stress, high hardness and evidently enhanced tool cutting functionality.

High entropy alloys (HEAs) are a novel class of materials exhibiting properties of high strength, high corrosion and oxidation resistance, and superb thermal stability. Cathodic arc deposition is an established physical vapor deposition (PVD) technology offering high deposition rate and high degrees of plasma ionization with controllable ion kinetic energy. Here we employed cathodic arc deposition to fabricate AlCrFeCoNiCu0.5 HEA thin films. To elucidate the growth mechanisms and microstructures of the HEA thin film microstructures, we varied arc and duct currents. The crystallography of the films was investigated using X-ray diffraction (XRD). The film chemistry and microstructure of the film-substrate interphase were comprehensively studied using transmission electron microscopy (TEM). Atomic force microscopy (AFM) was applied to study the surface morphology, and mechanical properties were evaluated using nanoindentation. It is demonstrated that the grain size in HEA thin films can be effectively controlled by the deposition rate, while the HEA film hardness and surface roughness are modulated by the grain size. The results presented here have important implications for the fabrication of HEA thin films using cathodic arc deposition as an industrially scalable technique.

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.

Complete and rapid endothelialization is critical to the long-term performance of synthetic vascular grafts. A fully formed endothelium is resistant to thrombosis and mitigates the development of neointimal hyperplasia, the dominant modes of acute and chronic graft failure, respectively. Significant research efforts aim to develop strategies which enhance graft endothelialization through the incorporation of surface ligands that promote the attachment and growth of endothelial cells. In native vessels these functions are regulated by the adhesion molecule vascular endothelial cadherin (VE-Cad). VE-Cad is exclusive to endothelial cells and possesses high self-affinity, forming homodimers with VE-Cad on adjacent endothelial cells. Leveraging this targeted binding ability, we developed a graft functionalization approach using a recombinant truncated form of VE-Cad (VEtr). VEtr contains only the domains responsible for self-interaction, recognition and adhesion. Using the plasma functionalization technique, plasma immersion ion implantation (PIII) technique we immobilize VEtr onto the surface of electrospun polycaprolactone (PCL). VEtr scaffolds achieved a nearly 2-fold increase in attachment and spreading, and a 2.5-fold increase in proliferation of human coronary artery endothelial cells (HCAECs) compared with control scaffolds in vitro. Following 14-day implantation in a mouse carotid artery model, VEtr grafts showed ~90% CD31-positive endothelial coverage. The benefits of this enhanced endothelialization included an ~88% reduction in fibrin deposition (early thrombosis) as well as ~63% reduction in macrophage recruitment (early neointimal hyperplasia). These findings highlight VEtr functionalization as a promising approach for rapid graft endothelialization which may potentially improve the long-term performance of synthetic vascular grafts.

Surface-functionalized polymeric nanoparticles have advanced the field of nanomedicine as promising constructs for targeted delivery of molecular cargo as well as diagnostics and therapeutics. Conventionally, the functionalization of polymeric nanoparticles incorporates tedious wet chemical methods that require complex, multistep protocols. Surface-active plasma-polymerized nanoparticles (PPNs) produced by a dry, low-pressure plasma process can be easily functionalized with multiple ligands in a simple step. However, plasma polymerization remains limited by the challenge of efficient collection of PPNs from low-pressure plasma reactors. Here, we demonstrate a simple method to overcome this limitation by delaying the inflow of the polymer-forming precursor gas, acetylene, into a nitrogen and argon plasma discharge. We provide evidence that this cutting-edge development in the plasma polymerization method drastically enhances the collection yield of nanoparticles by 2.5-fold, compared to the simultaneous inflow of the gases. COMSOL Multiphysics simulations support our experimental data and provide insights into the role of pressure gradients in regulating the forces controlling the collection of the particles. Surface characterization data revealed that changing the sequence of the precursor gas inflow had no significant effect on the physicochemical properties of the nanoparticles, as critically important for theranostic applications. A model, green fluorescent protein, was successfully conjugated to the surface of the PPNs via a reagent-free, one-step incubation process that immobilized the biomolecule while retaining its biological activity. Cytotoxicity of the particles was assessed by a lactate dehydrogenase (LDH) assay at concentrations of up to 5 × 105 nanoparticles per cell. Despite their high concentrations, the nanoparticles were remarkably well tolerated by the cells, demonstrating their superb potential for in vivo cellular uptake. This study advances previous research on plasma-polymerized nanoparticles, introducing a low-waste synthesis method that achieves higher yields. This sustainable technology has important implications for the production of multifunctional nanoparticles for drug delivery, tumor targeting, and medical imaging.

Three-dimensional (3D) bioprinting, where cells, hydrogels, and structural polymers can be printed layer by layer into complex designs, holds great promise for advances in medicine and the biomedical sciences. In principle, this technique enables the creation of highly patient-specific disease models and biomedical implants. However, an ability to tailor surface biocompatibility and interfacial bonding between printed components, such as polymers and hydrogels, is currently lacking. Here we demonstrate that an atmospheric pressure plasma jet (APPJ) can locally activate polymeric surfaces for the reagent-free covalent attachment of proteins and hydrogel in a single-step process at desired locations. Polyethylene and poly-¿-caprolactone were used as example polymers. Covalent attachment of the proteins and hydrogel was demonstrated by resistance to removal by rigorous sodium dodecyl sulfate washing. The immobilized protein and hydrogel layers were analyzed using Fourier transform infrared and X-ray photoelectron spectroscopy. Importantly, the APPJ surface activation also rendered the polymer surfaces mildly hydrophilic as required for optimum biocompatibility. Water contact angles were observed to be stable within a range where the conformation of biomolecules is preserved. Single and double electrode designs of APPJs were compared in their characteristics relevant to localized surface functionalization, plume length, and shape. As a proof of efficacy in a biological context, APPJ-treated polyethylene functionalized with fibronectin was used to demonstrate improvements in cell adhesion and proliferation. These results have important implications for the development of a new generation of 3D bioprinters capable of spatially patterned and tailored surface functionalization performed during the 3D printing process in situ.

Silk-based materials are widely used in biomaterial and tissue engineering applications due to their cytocompatibility and tunable mechanical and biodegradation properties. Aqueous-based processing techniques have enabled the fabrication of silk into a broad range of material formats, making it a highly versatile material platform across multiple industries. Utilizing the full potential of silk in biomedical applications frequently requires modification of silk's surface properties. Dry surface modification techniques, including irradiation and plasma treatment, offer an alternative to the conventional wet chemistry strategies to modify the physical and chemical properties of silk materials without compromising their bulk properties. While dry surface modification techniques are more prevalent in textiles and sterilization applications, the range of modifications available and resultant changes to silk materials all point to the utility of dry surface modification for the development of new, functional silk biomaterials. Dry surface treatment affects the surface chemistry, secondary structure, molecular weight, topography, surface energy, and mechanical properties of silk materials. This Review describes and critically evaluates the effect of physical dry surface modification techniques, including irradiation and plasma processes, on silk materials and discusses their utility in biomedical applications, including recent examples of modulation of cell/protein interactions on silk biomaterials, in vivo performance of implanted biomaterials, and applications in material biofunctionalization and lithographic surface patterning approaches.

Additive manufacturing has facilitated fabrication of complex and patient-specific metallic meta-biomaterials that offer an unprecedented collection of mechanical, mass transport, and biological properties as well as a fully interconnected porous structure. However, applying meta-biomaterials for addressing unmet clinical needs in orthopedic surgery requires additional surface functionalities that should be induced through tailor-made coatings. Here, we developed multi-functional layer-by-layer coatings to simultaneously prevent implant-associated infections and stimulate bone tissue regeneration. We applied multiple layers of gelatin- and chitosan-based coatings containing either bone morphogenetic protein (BMP)-2 or vancomycin on the surface of selective laser melted porous structures made from commercial pure Titanium (CP Ti) and designed using a triply periodic minimal surface (i.e., sheet gyroid). The additive manufacturing process resulted in a porous structure and met the the design values comparatively. X-ray photoelectron spectroscopy spectra confirmed the presence and composition of the coating layers. The release profiles showed a continued release of both vancomycin and BMP-2 for 2¿3 weeks. Furthermore, the developed meta-biomaterials exhibited a very strong antibacterial behavior with up to 8 orders of magnitude reduction in both planktonic and implant-adherent bacteria and no signs of biofilm formation. The osteogenic differentiation of mesenchymal stem cells was enhanced, as shown by two-fold increase in the alkaline phosphatase activity and up to four-fold increase in the mineralization of all experimental groups containing BMP-2. Eight-week subcutaneous implantation in vivo showed no signs of a foreign body response, while connective tissue ingrowth was promoted by the layer-by-layer coating. These results unequivocally confirm the superior multi-functional performance of the developed biomaterials.

An ideal surface of a cardiovascular device, such as a stent, must be multifunctional: promoting endothelialization to regenerate the vessel's natural endothelial cell (EC) lining; inhibiting the proliferation of smooth muscle cells that occlude vessels; and simultaneously mitigating thrombosis that leads to the spontaneous formation of blood clots. Here it is reported on Ti¿Cu interfaces that demonstrate this required multifunctionality through the controlled release of copper ions that induce the catalytic formation of nitric oxide (NO). Ti¿Cu coatings, deposited on stainless steel substrates via direct current magnetron sputtering, demonstrate a significantly higher NO-release catalytic activity compared to Ti coatings due to release of copper ions. Ti¿Cu surfaces that stimulate optimum catalytic formation of NO significantly decrease smooth muscle cell proliferation, inhibit platelet adhesion, and improve endothelial cell EC compatibility. The development of such catalytic surfaces through a simple sputtering method holds great promise for the fabrication of advanced multifunctional cardiovascular devices such as stents and coronary implants.

Surface functionalization of an implantable device with bioactive molecules can overcome adverse biological responses by promoting specific local tissue integration. Bioactive peptides have advantages over larger protein molecules due to their robustness and sterilizability. Their relatively small size presents opportunities to control the peptide orientation on approach to a surface to achieve favourable presentation of bioactive motifs. Here we demonstrate control of the orientation of surface-bound peptides by tuning electric fields at the surface during immobilization. Guided by computational simulations, a peptide with a linear conformation in solution is designed. Electric fields are used to control the peptide approach towards a radical-functionalized surface. Spontaneous, irreversible immobilization is achieved when the peptide makes contact with the surface. Our findings show that control of both peptide orientation and surface concentration is achieved simply by varying the solution pH or by applying an electric field as delivered by a small battery.

Competition between target erosion and compound layer formation during pulse cycles in reactive HiPIMS opens up the possibility of tuning discharge conditions and the properties of deposited films by varying the duty cycle in situ without altering the reactive gas mixture. Three different reactive systems, hafnium in oxygen, tungsten in oxygen, and tungsten in oxygen/nitrogen, are studied in which amorphous films of hafnium oxide (HfO2), tungsten oxide (WO3), and tungsten oxynitride (WOxNy) are deposited. We show that the cyclic evolution of the target surface composition depends on the properties of the target including its affinity for the reactive gas mix and the compound layer melting point and volatility. We find that pulse length variations modulate the target compound layer and hence the discharge chemistry and properties of the films deposited. The refractive indices of HfO2 and WO3 were progressively reduced with the duty cycle, whereas that of WOxNy increased. These variations were found to be due to changes in the chemical composition and/or densification. We present and validate a phenomenological model that explains these findings in terms of a compound layer on the target surface that undergoes evolution during each pulse resulting in a cyclic equilibrium. The end points of the composition of the target surface depend on the duty cycle. Tuning the pulse characteristics holds great promise for the fabrication of multilayer films with through thickness graded properties.

Plasma polymerization is traditionally recognized as a homogeneous film-forming technique. It is nevertheless reasonable to ask whether micrometer thick plasma polymerized structures are really homogeneous across the film thickness. Studying the properties of the interfacial, near-the-substrate (NTS) region in plasma polymer films represents particular experimental challenges due to the inaccessibility of the buried layers. In this investigation, a novel non-destructive approach has been utilized to evaluate the homogeneity of plasma polymerized acrylic acid (PPAc) and 1,7-octadiene (PPOD) films in a single measurement. Studying the variations of refractive index throughout the depth of the films was facilitated by a home-built surface plasmon resonance (SPR)/optical waveguide (OWG) spectroscopy setup. It has been shown that the NTS layer of both PPAc and PPOD films exhibits a significantly lower refractive index than the bulk of the film that is believed to indicate a higher concentration of internal voids. Our results provide new insights into the growth mechanisms of plasma polymer films and challenge the traditional view that considers plasma polymers as homogeneous and continuous structures.

Although plasma polymerization is traditionally considered as a substrate-independent process, we present evidence that the propensity of a substrate to form carbide bonds regulates the growth mechanisms of plasma polymer (PP) films. The manner by which the first layers of PP films grow determines the adhesion and robustness of the film. Zirconium, titanium, and silicon substrates were used to study the early stages of PP film formation from a mixture of acetylene, nitrogen, and argon precursor gases. The correlation of initial growth mechanisms with the robustness of the films was evaluated through incubation of coated substrates in simulated body fluid (SBF) at 37° for 2 months. It was demonstrated that the excellent zirconium/titanium-PP film adhesion is linked to the formation of metallic carbide and oxycarbide bonds during the initial stages of film formation, where a 2D-like, layer-by-layer (Frank-van der Merwe) manner of growth was observed. On the contrary, the lower propensity of the silicon surface to form carbides leads to a 3D, island-like (Volmer-Weber) growth mode that creates a sponge-like interphase near the substrate, resulting in inferior adhesion and poor film stability in SBF. Our findings shed light on the growth mechanisms of the first layers of PP films and challenge the property of substrate independence typically attributed to plasma polymerized coatings.