Protein-based layer-by-layer films for biomedical applications

The surface engineering of biomaterials is crucial for their successful (bio)integration by the body, i.e. the colonization by the tissue-specific cell, and the prevention of fibrosis and/or bacterial colonization. Performed at room temperature in an aqueous medium, the layer-by-layer (LbL) coating method is based on the alternating deposition of macromolecules. Versatile and simple, this method allows the functionalization of surfaces with proteins, which play a crucial role in several biological mechanisms. Possessing intrinsic properties (cell adhesion, antibacterial, degradable, etc.), protein-based LbL films represent a powerful tool to control bacterial and mammalian cell fate. In this article, after a general introduction to the LbL technique, we will focus on protein-based LbL films addressing different biomedical issues/domains, such as bacterial infection, blood contacting surfaces, mammalian cell adhesion, drug and gene delivery, and bone and neural tissue engineering. We do not consider biosensing applications or electrochemical aspects using specific proteins such as enzymes.

Preparation of Gelatin-Quaternary Ammonium Salt Coating on Titanium Surface for Antibacterial/Osteogenic Properties

Titanium (Ti) and its alloys are widely used in medical treatment, engineering, and other fields because of their excellent properties including biological activity, an elastic modulus similar to that of human bones, and corrosion resistance. However, there are still many defects in the surface properties of Ti in practical applications. For example, the biocompatibility of Ti with bone tissue can be greatly reduced in implants due to a lack of osseointegration as well as antibacterial properties, which may lead to osseointegration failure. To address these problems and to take advantage of the amphoteric polyelectrolyte properties of gelatin, a thin layer of gelatin was prepared by electrostatic self-assembly technology. Diepoxide quaternary ammonium salt (DEQAS) and maleopimaric acid quaternary ammonium salt (MPA-N⁺) were then synthesized and grafted onto the thin layer. The cell adhesion and migration experiments demonstrated that the coating has excellent biocompatibility, and those grafted with MPA-N⁺ promoted cell migration. The bacteriostatic experiment showed that the mixed grafting with two ammonium salts had excellent bacteriostatic performance against Escherichia coli and Staphylococcus aureus, with bacteriostasis rates of 98.1 ± 1.0% and 99.2 ± 0.5%, respectively.

Natural Coatings and Surface Modifications on Magnesium Alloys for Biomedical Applications

Magnesium (Mg) alloys have great potential in biomedical applications due to their incomparable properties regarding other metals, such as stainless steels, Co-Cr alloys, and titanium (Ti) alloys. However, when Mg engages with body fluids, its degradation rate increases, inhibiting the complete healing of bone tissue. For this reason, it has been necessary to implement protective coatings to control the rate of degradation. This review focuses on natural biopolymer coatings used on Mg alloys for resorbable biomedical applications, as well as some modification techniques implemented before applying natural polymer coatings to improve their performance. Issues such as improving the corrosion resistance, cell adhesion, proliferation, and biodegradability of natural biopolymers are discussed through their basic comparison with inorganic-type coatings. Emphasis is placed on the expected biological behavior of each natural polymer described, to provide basic information as a reference on this topic.

Using a degradable three-layer sandwich-type coating to prevent titanium implant infection with the combined efficient bactericidal ability and fast immune remodeling property

Titanium (Ti) implant-associated infections are a challenge in orthopedic surgery, for which a series of antibacterial coatings have been designed and fabricated to reduce the risk of bacterial contamination. Herein, we created a degradable three-layer sandwich-type coating to achieve long-term antibacterial effects while simultaneously reconstructing the local immune microenvironment. The vancomycin (Van)-loaded vaterite coating constitutes the outer and inner layers, whereas Interleukin-12 (IL-12)-containing liposomes embedded in sodium alginate constitutes the middle layer. Van, released from the vaterite, demonstrated a favorable and rapid bactericidal ability against the representative methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains. The released IL-12 exhibited the desired immune reconstitution abilities, actively facilitating defenses against subsequent bacterial invasions. Furthermore, the biocompatibility and cell-binding feature of the multifunctional coating was beneficial for achieving solid interface intergradation. Overall, the benefits of the three-layer sandwich-type coating, including the convenient fabrication process, efficient antimicrobial activity, fast immune remodeling property, fine cell-binding feature, and biodegradability, highlight its promising translational potential in preventing implant infection. STATEMENT OF SIGNIFICANCE: To prevent titanium implant infections, researchers have designed various antibacterial coatings. However, most of these coatings focused only on killing the invading bacteria over a limited postoperative period. However, the local immune microenvironment is compromised during surgery. Local immune deflection impedes the ability of the local immune defenses to clear bacteria and limits immune memory building from active defense against long-term subsequent bacterial invasions. Furthermore, these coatings are usually nondegradable and differ substantially from bone components, thereby impairing the integration of the coating and bone interface and generating concerns about implant stability and bacterial contamination. In this work, we synthesized a degradable coating that provides sustained antibacterial activity, promotes immune reconstitution, and simultaneously achieves solid bone integration.

Performance and Structure Evaluation of Gln-Lys Isopeptide Bond Crosslinked USYK-SPI Bioplastic Film Derived from Discarded Yak Hair

To reduce the waste from yak hair and introduce resource recycling into the yak-related industry, an eco-friendly yak keratin-based bioplastic film was developed. We employed yak keratin (USYK) from yak hair, soy protein isolate (SPI) from soybean meal as a film-forming agent, transglutaminase (EC 2.3.2.13, TGase) as a catalytic crosslinker, and glycerol as a plasticizer for USYK-SPI bioplastic film production. The structures of the USYK-SPI bioplastic film were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-Ray diffraction (XRD). The mechanical properties, the thermal behavior, light transmittance performance, and water vapor permeability (WVP) were measured. The results revealed that the added SPI possibly acted as a reinforcement. The formation of Gln-Lys isopeptide bonds and hydrophobic interactions led to a stable crosslinking structure of USYK-SPI bioplastic film. The thermal and the mechanical behaviors of the USYK-SPI bioplastic film were improved. The enhanced dispersion and formation of co-continuous protein matrices possibly produced denser networks that limited the diffusion of water vapor and volatile compounds in the USYK-SPI bioplastic films. Moreover, the introduction of SPI prompted the relocation of hydrophobic groups on USYK molecules, which gave the USYK-SPI bioplastic film stronger surface hydrophobicity. The SPI and USYK molecules possess aromatic amino residuals (tyrosine, phenylalanine, tryptophan), which can absorb ultraviolet radiation. Thus, the USYK-SPI bioplastic films were shown to have an excellent UV barrier. The synergy effect between USYK and SPI is not only able to improve rigidity and the application performance of keratin-based composite film but can also reduce the cost of the keratin-based composite film through the low-cost of the SPI alternative which partially replaces the high-cost of keratin. The data obtained from this research can provide basic information for further research and practical applications of USYK-SPI bioplastic films. There is an increasing demand for the novel USYK-SPI bioplastic film in exploit packaging material, biomedical materials, eco-friendly wearable electronics, and humidity sensors.

Improved Osteogenesis by Mineralization Combined With Double-Crosslinked Hydrogel Coating for Proliferation and Differentiation of Mesenchymal Stem Cells

In consideration of improving the interface problems of poly-L-lactic acid (PLLA) that hindered biomedical use, surface coatings have been explored as an appealing strategy in establishing a multi-functional coating for osteogenesis. Though the layer-by-layer (LBL) coating developed, a few studies have applied double-crosslinked hydrogels in this technique. In this research, we established a bilayer coating with double-crosslinked hydrogels [alginate–gelatin methacrylate (GelMA)] containing bone morphogenic protein (BMP)-2 [alginate-GelMA/hydroxyapatite (HA)/BMP-2], which displayed great biocompatibility and osteogenesis. The characterization of the coating showed improved properties and enhanced wettability of the native PLLA. To evaluate the biosafety and inductive ability of osteogenesis, the behavior (viability, adherence, and proliferation) and morphology of human bone mesenchymal stem cells (hBMSCs) on the bilayer coatings were tested by multiple exams. The satisfactory function of osteogenesis was verified in bilayer coatings. We found the best ratios between GelMA and alginate for biological applications. The Alg70-Gel30 and Alg50-Gel50 groups facilitated the osteogenic transformation of hBMSCs. In brief, alginate-GelMA/HA/BMP-2 could increase the hBMSCs’ early transformation of osteoblast lineage and promote the osteogenesis of bone defect, especially the outer hydrogel layer such as Alg70-Gel30 and Alg50-Gel50.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

Microbial production and recovery of hybrid biopolymers from wastes for industrial applications- a review

Agro-industrial wastes to be a global concern since agriculture and industrial processes are growing exponentially with the fast increase of the world population. Biopolymers are complex molecules produced by living organisms, but also found in many wastes or derived from wastes. The main drawbacks for the use of polymers are the high costs of the polymer purification processes from waste and the scale-up in the case of biopolymer production by microorganisms. However, the use of biopolymers at industrial scale for the development of products with high added value, such as food or biomedical products, not only can compensate the primary costs of biopolymer production, but also improve local economies and environmental sustainability. The present review describes some of the most relevant aspects related to the synthesis of hybrid materials and nanocomposites based on biopolymers for the development of products with high-added value.

Simple ultrasonic-assisted approach to prepare polysaccharide-based aerogel for cell research and histocompatibility study

Salecan, a water-soluble microbial polysaccharide with attractive biocompatible characteristics, is very suitable for aerogel fabrication. However, the practical application of salecan-based aerogels for cell culture was limited by complicated preparation method, lack of cell anchorage signals, and the ability to modulate this properly. Here, a smart aerogel was designed by ultrasonic-assisted self-assembly of salecan and cationic starch (CAS) without any organic and toxic crosslinkers. The ultrasound waves generated a marked impact on self-assemble process by means of ultrasonic cavitation. Aerogel network was produced by strong electrostatic attractions between the polysaccharides. Especially, salecan/CAS ratio can be precisely modulated to tailor the hydrophilicity, mechanical stiffness, and morphologic property. The specific surface area of the aerogels gradually increased with the increase in salecan/CAS ratio. These aerogels were non-cytotoxic, and the incorporation of salecan into them promoted cell-matrix interactions by directionally supporting cell adhesion and proliferation. Most strikingly, in vivo experiment revealed that the histological features in the main organs of the mice were similar to those observed in the PBS-treated control group, and no sign of the histopathological abnormality or tissue destruction was observed, indicating the excellent histocompatibility of the aerogels. This study offered a new and powerful avenue to fabricate functional biomaterial.

Advances in the synthesis and application of self-assembling biomaterials

The present study scrutinized some of the crucial advancements in the synthesis and functionalisation of self-assembling biomaterials for application in biomedicine. The basic concept of self-organization was discussed along with the mechanisms and methods involved in its implementation with biomaterials. Further, several recent applications of this technology in the biological and medical domain, and the avenues for future research and development were presented. This study brought to focus the vast potential of basic and applied research involved, especially in the context of hybrids and composites, as well as the difference in pace of new developments for different types of biomolecular materials. As nanobiotechnology matures, the tools and techniques available for developing and controlling self-assembled biomaterials as well as studying their interaction with biological tissue, will grow exponentially. Presently, self-assembly remains a potent tool for the synthesis of functional biomaterials.

Tanfloc/heparin polyelectrolyte multilayers improve osteogenic differentiation of adipose-derived stem cells on titania nanotube surfaces

In this study, a surface modification strategy using natural biopolymers on titanium is proposed to improve bone healing and promote rapid and successful osseointegration of orthopedic implants. Titania nanotubes were fabricated via an anodization process and the surfaces were further modified with polyelectrolyte multilayers (PEMs) based on Tanfloc (a cationic tannin derivative) and glycosaminoglycans (heparin and hyaluronic acid). Scanning electron microscopy (SEM), water contact angle measurements, and X-ray photoelectron spectroscopy were used to characterize the surfaces. Adipose-derived stem cells (ADSCs) were seeded on the surfaces, and the cell viability, adhesion, and proliferation were investigated. Osteogenesis was induced and osteogenic differentiation of human ADSCs on the surfaces was evaluated via mineralization and protein expression assays, immunofluorescent staining, and SEM. The Tanfloc/heparin PEMs on titania nanotubes improved the rate of osteogenic differentiation of ADSCs as well as the bone mineral deposition, and is therefore a promising approach for use in orthopedic implants.

Titanium coating: introducing an antibacterial and bioactive chitosan-alginate film on titanium by spin coating

Coating of titanium (Ti) implants with biocompatible polymers were performed to improve bone healing. In this study, pure Ti implants were coated via chitosan and alginate by spin coating method at 1000, 4000, and 8000 rpm. The coating layer was cross-linked by calcium chloride. Their chemical structures were analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) evaluations. The morphology of the created coating was observed by scanning electron microscopy (SEM), and the best uniformity was observed in the prepared coating at 8000 rpm (6093× g) spinal speed. The adhesion strength of the coating layer on the substrate was evaluated by the adhesion pull-off test. Also, the best adhesion strength was achieved at an 8000 rpm (6093× g) coating rate. Bioactivity of the chitosan-alginate coating on Ti sheets was evaluated by soaking the samples in a simulated body fluid (SBF) solution. The apatite formation on prepared Ti sheets was investigated by SEM, XRD, and energy dispersive X-ray spectroscopy (EDS). A higher mineralization appeared on coated samples compared with pure Ti. The antibacterial behavior of the implants was analyzed by bacterial counting against Escherichia coli. The presence of chitosan and alginate on the Ti sheets resulted in a better antibacterial effect. In-vitro experiments, with L929 fibroblast cells, confirmed the biocompatibility of the implants. Coating the Ti implants with chitosan and alginate improved biomineralization and biological behavior of the implant especially at the spinal speed of 8000 rpm (6093× g). These implants can support osteoblast cell adhesion and facilitate bone regeneration.

Advances in biomolecule inspired polymeric material decorated interfaces for biological applications

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

Natural protein bioinspired materials for regeneration of hard tissues

This review describes the protein bioinspired materials for the repair of hard tissues such as enamel, dentin and bone.

The effect of hybrid coatings based on hydrogel, biopolymer and inorganic components on the corrosion behavior of titanium bone implants

Modification of titanium (Ti) bone implant materials with hybrid organic-inorganic coatings is a novel promising approach to improve the osteoconductivity and osteointegration of implants and prevent their failure after implantation. However, in these coatings, which are mostly hydrophilic, chemically active moieties capable of releasing oxidizing ions can have a significant influence on the corrosion resistance of Ti, which is critical for the Ti implant osteointegration behavior. In this research, in order to study the dependence of the change of the corrosion behavior of Ti on the composition of the coating, Ti surfaces were modified with various coatings: organic (alginate hydrogel crosslinked with Ca²⁺ ions (Alg), and dextran sulfate (DS)), inorganic (porous calcium carbonate CaCO₃), and composite organic-inorganic (Alg-CaCO₃, DS-CaCO₃). The morphology and composition of these materials before and after the corrosion experiment, performed in simulated body fluid (SBF), were followed by extensive characterization. Electrochemical impedance spectroscopy (EIS) was performed to study the corrosion behavior of the prepared materials in SBF. The characteristics obtained during the EIS measurements revealed the dependence of the variation of the corrosion resistance level on the composition of the coating. The bare Ti surface had the higher value of the total impedance compared with the modified surfaces, while the Ti surfaces modified with organic coatings demonstrated the best charge transfer resistance in comparison with the coatings containing the inorganic CaCO₃ component and uncoated Ti.

Approaches based on passive and active antibacterial coating on titanium to achieve antibacterial activity

Titanium (Ti) and its alloys are widely applied as orthopedic implants for hip and knee prosthesis, fixation, and dental implants. However, Ti and its alloys are bioinert and susceptible to bacteria and biofilm formation. Strategies for improving the antibacterial properties of Ti can be divided into two approaches, namely, passive coating and active coating on the Ti surface. Passive coating on Ti mainly kills the bacteria in contact but does not kill plankton or bacteria dwell in the bone tissue around the Ti implant. Active coating mainly involves the release of antibacterial agents to kill the bacteria, but this may result in the development of bacterial resistance. Both strategies include advantages and disadvantages. This article reviews the current and potential future approaches for improving antibacterial activity on Ti. We mainly focus on current approaches for fabricating antibacterial Ti and its limitations and countermeasures, and provide direction for further studies of biofunctionalization of Ti with antibacterial properties. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2531-2539, 2018.

Imaging and Manipulation of Extracellular Traps by Atomic Force Microscopy

Neutrophil extracellular traps (NETs) are part of an immunological response and one of the mechanisms by which neutrophils protect the host from pathogen invasion and proliferation. Notwithstanding their protective role, NETs have also been linked to the development of a variety of disorders, including cardiovascular and autoimmune diseases. Since the first reports on NETs in 2004 it has been possible to image NETs by a variety of imaging techniques. Despite this, such reports seldomly include contact probe methods, and therefore lack the unique insights such techniques typically provide. In fact, more than 10 years have passed since the discovery of NETs, and although their importance as part of a unique cellular response mechanism has become very clear, studies that attempt to address them by atomic force microscopy (AFM) remain very limited. Particularly striking is the almost absent information on the mechanical properties of NETs, and factors that may influence them. The fact that NETs are a particularly adhesive network of filaments poses a considerable technical challenge for contact probe methods and can limit advances involving either imaging or manipulation of NETs by AFM. The current set of protocols aims at aiding a knowledgeable AFM operator to obtain AFM images and to perform force spectroscopy experiments with such samples. A variety of different topics, including sample preparation and data analysis, are discussed.

Self-assembly of collagen-based biomaterials: preparation, characterizations and biomedical applications

By combining regulatory parameters with characterization methods, researchers can selectively fabricate collagenous biomaterials with various functional responses for biomedical applications.

Bio-functionalization of grade V titanium alloy with type I human collagen for enhancing and promoting human periodontal fibroblast cell adhesion - an in-vitro study

Surface modification of medical grade V titanium alloy (Ti-6Al-4V) with biomolecules is an important and vital step for tailoring it for various biomedical applications. Present study investigates theinfluence of type I human collagen (T1HC) bio-conjugation through a three stage process. Polished grade V titanium alloy discs were functionalizedwith free OH group by means of controlled heat and alkali treatment followed by coating of 3-aminopropyltriethoxy (APTES) silane couplingagent. T1HC were bio-conjugated through 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride N-hydroxysuccinimide (EDCNHS)coupling reaction. At each stage, grade V titanium alloy surfaces were characterized by atomic force microscopy (AFM), scanning electronmicroscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Xrayphotoelectron spectroscopy (XPS). FTIR and XPS studies confirms thecovalent attachment of APTES with titanium alloy surface while terminalamine groups of APTES remained free for further attachment of T1HCthrough covalent bond. Aqueous stability of bio-conjugated titanium discsat various pH and time intervals (i.e. at pH of 5.5, 6.8 and 8.0 at timeinterval of 27 and 48h) confirmed the stability of T1HC bioconjugated collagen on titanium surface. Further human periodontalfibroblast cell line (HPdlF) culture revealed enhanced adhesion on theT1HC bio-conjugated surface compared to the polystyrene and polishedgrade V titanium alloy surfaces.

Sugar-sensitive dendrimer films as a sacrificial layer for the preparation of freestanding multilayer films

Multilayer thin films composed of poly(vinyl alcohol) (PVA) and phenylboronic acid-bearing poly(amidoamine) dendrimer (PBA-PAMAM) were used as a sacrificial layer for constructing freestanding polyelectrolyte films consisting of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). Freestanding (PSS/PAH)₁₅ films were successfully released from substrate by exposing composite (PVA/PBA-PAMAM)_n/(PSS/PAH)₁₅ films (n=5 and 10) to sorbitol solutions under mild conditions at pH7.0-9.0. The film release was accelerated in solutions of higher sorbitol concentrations at pH9.0 as well as in solutions with lower concentration of NaCl. The results were rationalized based on the scission of boronate ester bonds between PBA-PAMAM and PVA in the (PVA/PBA-PAMAM)_n layer due to a competitive binding of sorbitol to PBA-PAMAM.

Regulation of local bone remodeling mediated by hybrid multilayer coating embedded with hyaluronan-alendronate/BMP-2 nanoparticles on Ti6Al7Nb implants

Hyaluronate-alendronate/BMP-2 nanoparticles were inserted into Gel/Chi multilayers on Ti6Al7Nb for enhancing BMP-2 stability and promoting local osteogenesis under osteoporosis.

Effects of magnesium silicate on the mechanical properties, biocompatibility, bioactivity, degradability, and osteogenesis of poly(butylene succinate)-based composite scaffolds for bone repair

The m-MS/PBSu scaffolds, with a hierarchical porous structure, could promote cell proliferation in vitro and bone regeneration in vivo.