Linker-free covalent attachment of the extracellular matrix protein tropoelastin to a polymer surface for directed cell spreading

Transcriptome analysis reveals hepatotoxicity in zebrafish induced by cyhalofop‑butyl

Cyhalofop‑butyl is a highly effective aryloxyphenoxypropionate herbicide and widely used for weed control in paddy fields. With the increasing residue of cyhalofop‑butyl, it poses a threat to the survival of aquatic organisms. Here, we investigated the effect of cyhalofop‑butyl on zebrafish to explore its potential hepatotoxic mechanism. The results showed that cyhalofop‑butyl induced hepatocyte degeneration, vacuolation and necrosis of larvae after embryonic exposure for 4 days and caused liver atrophy after 5 days. Meanwhile, the activities of enzymes related to liver function were significantly increased by 0.2 mg/L cyhalofop‑butyl and higher, such as alanine transaminase (ALT) and aspartate transaminase (AST). And the contents of triglyceride (TG) involved in lipid metabolism were significantly decreased by 0.4 mg/L cyhalofop-buty. The expression of genes related to liver development was also significantly down-regulated. Furthermore, transcriptome results showed that the pathways involved in metabolism, immune system and endocrine system were significantly impacted, which may be related to hepatoxicity. To sum up, the present study demonstrated the hepatoxicity caused by cyhalofop-buty and its underlying mechanism. The results may provide new insights for the risk of cyhalofop‑butyl to aquatic organisms and new horizons for the pathogenesis of hepatotoxicity.

Effect of Recombinant Human Perlecan Domain V Tethering Method on Protein Orientation and Blood Contacting Activity on Polyvinyl Chloride

Surface modification of biomaterials is a promising approach to control biofunctionality while retaining the bulk biomaterial properties. Perlecan is the major proteoglycan in the vascular basement membrane that supports low levels of platelet adhesion but not activation. Thus, perlecan is a promising bioactive for blood-contacting applications. This study furthers the mechanistic understanding of platelet interactions with perlecan by establishing that platelets utilize domains III and V of the core protein for adhesion. Polyvinyl chloride (PVC) is functionalized with recombinant human perlecan domain V (rDV) to explore the effect of the tethering method on proteoglycan orientation and bioactivity. Tethering of rDV to PVC is achieved via either physisorption or covalent attachment via plasma immersion ion implantation (PIII) treatment. Both methods of rDV tethering reduce platelet adhesion and activation compared to the pristine PVC, however, the mechanisms are unique for each tethering method. Physisorption of rDV on PVC orientates the molecule to hinder access to the integrin-binding region, which inhibits platelet adhesion. In contrast, PIII treatment orientates rDV to allow access to the integrin-binding region, which is rendered antiadhesive to platelets via the glycosaminoglycan (GAG) chain. These effects demonstrate the potential of rDV biofunctionalization to modulate platelet interactions for blood contacting applications.

Covalent Biofunctionalization of the Inner Surfaces of a Hollow-Fiber Capillary Bundle Using Packed-Bed Plasma Ion Implantation

Hollow-fiber capillary bundles are widely used in the production of medical devices for blood oxygenation and purification purposes such as in cardiopulmonary bypass, hemodialysis, and hemofiltration, but the blood interfacing inner surfaces of these capillaries provide poor hemocompatibility. Here, we present a novel method of packed-bed plasma ion implantation (PBPII) for the modification of the inner surfaces of polymeric hollow-fiber bundles enclosed in a cassette. The method is simple and can be performed on an intact hollow-fiber bundle cassette by the placement of a hollow cylindrical electrode, connected to a negative high-voltage pulse generator, around the cassette. The method does not require the insertion of electrodes inside the capillaries or the cassette. Nitrogen gas is fed into the capillaries inside the cassette by connecting the inlet of the cassette to a gas source. Upon the application of negative high-voltage bias pulses to the electrode, plasma is ignited inside the cassette, achieving the surface modification of both the internal and external surfaces of the capillaries. Fourier transform infrared-attenuated total reflectance spectroscopy of the PBPII-treated capillaries revealed the formation of aromatic C═C bonds, indicating the progressive carbonization of the capillary surfaces. The PBPII treatment was found to be uniform along the capillaries and independent of the radial position in the cassette. Atomic force microscopy of cross sections through the capillaries revealed that the increased stiffness associated with the carbonized layer on the inner surface of the PBPII-treated capillary has a depth (∼40 nm) consistent with that expected for ions accelerated by the applied bias voltage. The modified internal surfaces of the capillary bundle showed a greatly increased wettability and could be biofunctionalized by covalently immobilizing protein directly from the buffer solution. The direct, reagent-free protein immobilization was demonstrated using tropoelastin as an example protein. Covalent binding of the protein was confirmed by its resistance to removal by hot sodium dodecyl sulfate detergent washing, which is known to disrupt physical binding.

Correlation between Surface Properties of Polystyrene and Polylactide Materials and Fibroblast and Osteoblast Cell Line Behavior: A Critical Overview of the Literature

Bone reconstruction remains an important challenge today in several clinical situations, notably regarding the control of the competition occurring during proliferation of osteoblasts and fibroblasts. Polystyrene and polylactide are reference materials in the biomedical field. Therefore, it could be expected from the literature that clear correlations have been already established between the behavior of fibroblasts or osteoblasts and the surface characteristics of these materials. After an extensive analysis of the literature, although general trends could be established, our critical review has highlighted the need to develop a more in-depth analysis of the surface properties of these materials. Moreover, the large variation noticed in the experimental conditions used for in vitro animal cell studies impairs comparison between studies. From our comprehensive review on this topic, we have suggested several parameters that would be valuable to standardize to integrate the data from the literature and improve our knowledge on the cell-material interactions.

Evaluation of the developmental toxicity of 2,7-dibromocarbazole to zebrafish based on transcriptomics assay

Polyhalogenated carbazoles (PHCZs), which have the similar structure of dioxin, have been reported ubiquitous in the environments and drawn wide concerns. However, their potential ecological and health risks are still poorly understood. Here, wildtype zebrafish embryos were used to evaluate the environmental risks of 2,7-dibromocarbazole (2,7-DBCZ), 3,6-dibromocarbazole (3,6-DBCZ), and 3,6-dichlorocarbazole (3,6-DCCZ). 2,7-DBCZ was the most toxic compound with the 96-h LC₅₀ value of 581.8 ± 29.3 μg·L^-1 and the EC₅₀ value of 201.5 ± 6.5 μg·L^-1 for pericardial edema. The teratogenic effects of 2,7-DBCZ were tested using transgenic zebrafish larvae. The transcriptomic analysis revealed that 90 genes in zebrafish expressed differently after exposure to 2,7-DBCZ, and many pathways were related to aryl hydrocarbon receptor (AhR) activation. The qRT-PCR also showed that expression levels of AhR1 and CYP1 A in zebrafish were significantly up-regulated after exposure to 2,7-DBCZ. In conclusion, 2,7-DBCZ exhibited more potent toxicity and cardiac teratogenic effects, and presented developmental toxicity partially consistent with AhR activation. Our results will be of great help to the risk assessment and regulation-making of PHCZs. Meanwhile, further studies should be promoted to illustrate the potential mechanism between PHCZs and AhR in the near future.

Plasma ion implantation enabled bio-functionalization of PEEK improves osteoblastic activity

Slow appositional growth of bone in vivo is a major problem associated with polyether ether ketone (PEEK) based orthopaedic implants. Early stage promotion of osteoblast activity, particularly bone nodule formation, would help to improve contact between PEEK implantable materials and the surrounding bone tissue. To improve interactions with bone cells, we explored here the use of plasma immersion ion implantation (PIII) treatment of PEEK to covalently immobilize biomolecules to the surface. In this study, a single step process was used to covalently immobilize tropoelastin on the surface of PIII modified PEEK through reactions with radicals generated by the treatment. Improved bioactivity was observed using the human osteoblast-like cell line, SAOS-2. Cells on surfaces that were PIII-treated or tropoelastin-coated exhibited improved attachment, spreading, proliferation, and bone nodule formation compared to cells on untreated samples. Surfaces that were both PIII-treated and tropoelastin-coated triggered the most favorable osteoblast-like responses. Surface treatment or tropoelastin coating did not alter alkaline phosphatase gene expression and activity of bound cells but did influence the expression of other bone markers including osteocalcin, osteonectin, and collagen I. We conclude that the surface modification of PEEK improves osteoblast interactions, particularly with respect to bone apposition, and enhances the orthopedic utility of PEEK.

Mechanically Robust Plasma-Activated Interfaces Optimized for Vascular Stent Applications

The long-term performance of many medical implants is limited by the use of inherently incompatible and bioinert materials. Metallic alloys, ceramics, and polymers commonly used in cardiovascular devices encourage clot formation and fail to promote the appropriate molecular signaling required for complete implant integration. Surface coating strategies have been proposed for these materials, but coronary stents are particularly problematic as the large surface deformations they experience in deployment require a mechanically robust coating interface. Here, we demonstrate a single-step ion-assisted plasma deposition process to tailor plasma-activated interfaces to meet current clinical demands for vascular implants. Using a process control-feedback strategy which predicts crucial coating growth mechanisms by adopting a suitable macroscopic plasma description in combination with noninvasive plasma diagnostics, we describe the optimal conditions to generate highly reproducible, industry-scalable stent coatings. These interfaces are mechanically robust, resisting delamination even upon plastic deformation of the underlying material, and were developed in consideration of the need for hemocompatibility and the capacity for biomolecule immobilization. Our optimized coating conditions combine the best mechanical properties with strong covalent attachment capacity and excellent blood compatibility in initial testing with plasma and whole blood, demonstrating the potential for improved vascular stent coatings.

Mechanical Properties of Plasma Immersion Ion Implanted PEEK for Bioactivation of Medical Devices

Plasma immersion ion implantation (PIII) is used to modify the surface properties of polyether ether ketone for biomedical applications. Modifications to the mechanical and chemical properties are characterized as a function of ion fluence (treatment time) to determine the suitability of the treated surfaces for biological applications. Young's modulus and elastic recovery were found to increase with respect to treatment time at the surface from 4.4 to 5.2 MPa and from 0.49 to 0.68, respectively. The mechanical properties varied continuously with depth, forming a graded layer where the mechanical properties returned to untreated values deep within the layer. The treated surface layer exhibited cracking under cyclical loads, associated with an increased modulus due to dehydrogenation and cross-linking; however, it did not show any sign of delamination, indicating that the modified layer is well integrated with the substrate, a critical factor for bioactive surface coatings. The oxygen concentration remained unchanged at the surface; however, in contrast to ion implanted polymers containing only carbon and hydrogen, the oxygen concentration within the treated layer was found to decrease. This effect is attributed to UV exposure and suggests that PIII treatments can modify the surface to far greater depths than previously reported. Protein immobilization on PIII treated surfaces was found to be independent of treatment time, indicating that the surface mechanical properties can be tuned for specific applications without affecting the protein coverage. Our findings on the mechanical properties demonstrate such treatments render PEEK well suited for use in orthopedic implantable devices.

Tropoelastin: a versatile, bioactive assembly module

Elastin provides structural integrity, biological cues and persistent elasticity to a range of important tissues, including the vasculature and lungs. Its critical importance to normal physiology makes it a desirable component of biomaterials that seek to repair or replace these tissues. The recent availability of large quantities of the highly purified elastin monomer, tropoelastin, has allowed for a thorough characterization of the mechanical and biological mechanisms underpinning the benefits of mature elastin. While tropoelastin is a flexible molecule, a combination of optical and structural analyses has defined key regions of the molecule that directly contribute to the elastomeric properties and control the cell interactions of the protein. Insights into the structure and behavior of tropoelastin have translated into increasingly sophisticated elastin-like biomaterials, evolving from classically manufactured hydrogels and fibers to new forms, stabilized in the absence of incorporated cross-linkers. Tropoelastin is also compatible with synthetic and natural co-polymers, expanding the applications of its potential use beyond traditional elastin-rich tissues and facilitating finer control of biomaterial properties and the design of next-generation tailored bioactive materials.

The use of plasma-activated covalent attachment of early domains of tropoelastin to enhance vascular compatibility of surfaces

All current metallic vascular prostheses, including stents, exhibit suboptimal biocompatibility. Improving the re-endothelialization and reducing the thrombogenicity of these devices would substantially improve their clinical efficacy. Tropoelastin (TE), the soluble precursor of elastin, mediates favorable endothelial cell interactions while having low thrombogenicity. Here we show that constructs of TE corresponding to the first 10 ("N10") and first 18 ("N18") N-terminal domains of the molecule facilitate endothelial cell attachment and proliferation equivalent to the performance of full-length TE. This N-terminal ability contrasts with the known role of the C-terminus of TE in facilitating cell attachment, particularly of fibroblasts. When immobilized on a plasma-activated coating ("PAC"), N10 and N18 retained their bioactivity and endothelial cell interactive properties, demonstrating attachment and proliferation equivalent to full-length TE. In whole blood assays, both N10 and N18 maintained the low thrombogenicity of PAC. Furthermore, these N-terminal constructs displayed far greater resistance to protease degradation by blood serine proteases kallikrein and thrombin than did full-length TE. When immobilized onto a PAC surface, these shorter constructs form a modified metal interface to establish a platform technology for biologically compatible, implantable cardiovascular devices.

Tropoelastin--a multifaceted naturally smart material

Tropoelastin dominates the physical performance of human elastic tissue as it is assembled to make elastin. Tropoelastin is increasingly appreciated as a protein monomer with a defined solution shape comprising modular, bridged regions that specialize in elasticity and cell attachment, which collectively participate in macromolecular assembly. This modular, multifaceted molecule is being exploited to enhance the physical performance and biological presentation of engineered constructs to augment and repair human tissues. These tissues include skin and vasculature, and emphasize how growing knowledge of tropoelastin can be powerfully adapted to add value to pre-existing devices like stents and novel, multi-featured biological implants.

Mechanisms for covalent immobilization of horseradish peroxidase on ion-beam-treated polyethylene

The surface of polyethylene was modified by plasma immersion ion implantation. Structure changes including carbonization and oxidation were observed. High surface energy of the modified polyethylene was attributed to the presence of free radicals on the surface. The surface energy decay with storage time after treatment was explained by a decay of the free radical concentration while the concentration of oxygen-containing groups increased with storage time. Horseradish peroxidase was covalently attached onto the modified surface by the reaction with free radicals. Appropriate blocking agents can block this reaction. All aminoacid residues can take part in the covalent attachment process, providing a universal mechanism of attachment for all proteins. The native conformation of attached protein is retained due to hydrophilic interactions in the interface region. The enzymatic activity of covalently attached protein remained high. The long-term activity of the modified layer to attach protein is explained by stabilisation of unpaired electrons in sp(2) carbon structures. A high concentration of free radicals can give multiple covalent bonds to the protein molecule and destroy the native conformation and with it the catalytic activity. The universal mechanism of protein attachment to free radicals could be extended to various methods of radiation damage of polymers.

Plasma-based biofunctionalization of vascular implants

Polymeric and metallic materials are used extensively in permanently implanted cardiovascular devices and devices that make temporary but often prolonged contact with body fluids and tissues. Foreign body responses are typically triggered by host interactions at the implant surface, making surface modifications to increase biointegration desirable. Plasma-based treatments are extensively used to modify diverse substrates; modulating surface chemistry, wettability and surface roughness, as well as facilitating covalent biomolecule binding. Each aspect impacts on facets of vascular compatibility including endothelialization and blood contact. These modifications can be readily applied to polymers such as Dacron® and expanded polytetrafluoroethylene, which are widely used in bypass grafting and the metallic substrates of stents, valves and pacemaker components. Plasma modification of metals is more challenging given the need for coating deposition in addition to surface activation, adding the necessity for robust interface adhesion. This review examines the evolving plasma treatment technology facilitating the biofunctionalization of polymeric and metallic implantable cardiovascular materials.

Cell patterning via linker-free protein functionalization of an organic conducting polymer (polypyrrole) electrode

The interaction of proteins and cells with polymers is critical to their use in scientific and medical applications. In this study, plasma immersion ion implantation (PIII) was used to modify the surface of the conducting polymer, polypyrrole, which possesses electrical properties. PIII treatment enabled persistent, covalent binding of the cell adhesive protein, tropoelastin, without employing chemical linking molecules. In contrast tropoelastin was readily eluted from the untreated surface. Through this differential persistence of binding, surface bound tropoelastin supported cell adhesion and spreading on the PIII treated but not the untreated polypyrrole surface. The application of a steel shadow mask during PIII treatment allowed for spatial definition of tropoelastin exclusively to PIII treated regions. The general applicability of this approach to other extracellular matrix proteins was illustrated using collagen I, which displayed similar results to tropoelastin but required extended washing conditions. This approach allowed fine patterning of cell adhesion and spreading to tropoelastin and collagen, specifically on PIII treated polypyrrole regions. We therefore present a methodology to alter the functionality of polypyrrole surfaces, generating surfaces that can spatially control cellular interactions through protein functionalization with the potential for electrical stimulation.

Free radical functionalization of surfaces to prevent adverse responses to biomedical devices

Immobilizing a protein, that is fully compatible with the patient, on the surface of a biomedical device should make it possible to avoid adverse responses such as inflammation, rejection, or excessive fibrosis. A surface that strongly binds and does not denature the compatible protein is required. Hydrophilic surfaces do not induce denaturation of immobilized protein but exhibit a low binding affinity for protein. Here, we describe an energetic ion-assisted plasma process that can make any surface hydrophilic and at the same time enable it to covalently immobilize functional biological molecules. We show that the modification creates free radicals that migrate to the surface from a reservoir beneath. When they reach the surface, the radicals form covalent bonds with biomolecules. The kinetics and number densities of protein molecules in solution and free radicals in the reservoir control the time required to form a full protein monolayer that is covalently bound. The shelf life of the covalent binding capability is governed by the initial density of free radicals and the depth of the reservoir. We show that the high reactivity of the radicals renders the binding universal across all biological macromolecules. Because the free radical reservoir can be created on any solid material, this approach can be used in medical applications ranging from cardiovascular stents to heart-lung machines.

Binding of the cell adhesive protein tropoelastin to PTFE through plasma immersion ion implantation treatment

The interaction of proteins and cells with polymers is critical to their use in scientific and medical applications. In this study, plasma immersion ion implantation (PIII) was used to modify the surface of polytetrafluorethylene (PTFE), enabling the covalent binding of a cell adhesive protein, tropoelastin, without employing chemical linking molecules. Tropoelastin coating of untreated or PIII treated PFTE simultaneously promoted and blocked cell interactions respectively, i.e. PIII treatment of the PTFE surface completely inverses the cell interactive properties of bound tropoelastin. This activity persisted over long term storage of the PIII treated surfaces. The integrin binding C-terminus of tropoelastin was markedly less solvent exposed when bound to PIII treated PTFE than untreated PTFE, accounting for the modulation of cell adhesive activity. This presents a new methodology to specifically modulate cell behavior on a polymer surface using a simple one step treatment process, by adjusting the adhesive activity of a single extracellular matrix protein.

Elastin-based materials

Elastin is a versatile elastic protein that dominates flexible tissues capable of recoil, and facilitates commensurate cell interactions in these tissues in all higher vertebrates. Elastin's persistence and insolubility hampered early efforts to construct versatile biomaterials. Subsequently the field has progressed substantially through the adapted use of solubilized elastin, elastin-based peptides and the increasing availability of recombinant forms of the natural soluble elastin precursor, tropoelastin. These interactions allow for the formation of a sophisticated range of biomaterial constructs and composites that benefit from elastin's physical properties of innate assembly and elasticity, and cell interactive properties as discussed in this tutorial review.

Plasma modified surfaces for covalent immobilization of functional biomolecules in the absence of chemical linkers: towards better biosensors and a new generation of medical implants

Plasma modification and plasma polymer deposition are valuable technologies for the preparation of surfaces for the covalent binding of biomolecules for applications such as biosensors, medical prostheses, and diagnostic devices as well as surfaces for enzyme-mediated reactions. Covalency is conveniently tested by the ability of the surface to retain the attached molecules after vigorous washing with sodium dodecyl sulphate (SDS). Covalency is indicated if the fraction of protein retained lies above the curve characteristic of physisorption. Confidence in covalency is strengthened when the washing protocol is aggressive enough to remove all adsorbed protein from a control significantly more hydrophobic than the test surface. The use of linker chemistry to space the molecules from the surface is in some cases beneficial. However, the use of linker chemistry is not necessary to retain molecular function for long periods when the polymer surface is modified by energetic bombardment. The energetic bombardment retains hydrophilicity of the surface by crosslinking the subsurface, and this appears to facilitate retention of protein function. Energetic bombardment also increases the functional life of molecules immobilized and then freeze dried on plasma-modified surfaces. Analysis of the surfaces shows that the covalent binding mechanism is related to the presence of free radicals on the surface and in the subsurface regions. The unpaired electrons associated with the radicals appear to be mobile within the modified region and can diffuse to the surface to take part in binding interactions. Proactive implantable devices can make use of these principles of covalent attachment by seeding the surface of an implant with a biomolecule that elicits the desired interaction with cells and prevents undesirable responses.

Engineered tropoelastin and elastin-based biomaterials

Elastin is a key mammalian extracellular matrix protein that is critical to the elasticity, compliance, and resilience of a range of tissues including the vasculature, skin, and lung. In addition to providing mechanical integrity to tissues, elastin also has critical functions in the regulation of cell behavior and may help to modulate the coagulation cascade. The high insolubility of elastin has limited its use to researchers, while soluble derivatives of elastin including elastin peptides, digested elastins, and tropoelastin have much broader applications. Recombinantly produced tropoelastin, the soluble monomer of elastin, has been shown to exhibit many of the properties intrinsic to the mature biopolymer. As such, recombinant human tropoelastin provides a versatile building block for the manufacture of biomaterials with potential for diverse applications in elastic tissues. One of the major benefits of soluble elastins is that they can be engineered into a range of physical forms. As a dominant example, soluble elastins including tropoelastin can form hydrogels when they are chemically cross-linked. These self-organized constructs swell when transferred from a saline to aqueous environment and are highly elastic; these tunable responses are dependent on the types of cross-linker and elastin used. Soluble elastins can also be drawn into fine fibers using electrospinning. The morphology of these fibers can be altered by modifying spinning parameters that include delivery flow rate and the starting protein concentration. The resulting fibers then accumulate to form porous scaffolds, and can be wound around mandrils to create conduits for vascular applications. Electrospun scaffolds retain the elasticity and cell-interactive properties inherent in the tropoelastin precursor. Additionally, soluble elastins serve as versatile biomaterial coatings, enhancing cellular interactions and modulating the blood compatibility of polymer- and metal-based prostheses. Soluble elastins, and in particular tropoelastin, have highly favorable intrinsic physical and cell-interactive properties, warranting their adaption through incorporation into biomaterials and modification of implantable devices. The multiple choices of ways to produce elastin-based biomaterials mean that they are well suited to the tailoring of elastic biomaterials and hybrid constructs.