Antibacterial hyaluronic acid/chitosan multilayers onto smooth and micropatterned titanium surfaces

Addressing the challenges of infectious bone defects: a review of recent advances in bifunctional biomaterials

Infectious bone defects present a substantial clinical challenge due to the complex interplay between infection control and bone regeneration. These defects often result from trauma, autoimmune diseases, infections, or tumors, requiring a nuanced approach that simultaneously addresses infection and promotes tissue repair. Recent advances in tissue engineering and materials science, particularly in nanomaterials and nano-drug formulations, have led to the development of bifunctional biomaterials with combined osteogenic and antibacterial properties. These materials offer an alternative to traditional bone grafts, minimizing complications such as multiple surgeries, high antibiotic dosages, and lengthy recovery periods. This review examines the repair mechanisms in the infectious microenvironment and highlights various bifunctional biomaterials that foster both anti-infective and osteogenic processes. Emerging design strategies are also discussed to provide a forward-looking perspective on treating infectious bone defects with clinically significant outcomes.

The impact of hyaluronic acid coating on polyether ether ketone dental implant surface: An in vitro analysis

Objective

Polyether ether ketone (PEEK), a biocompatible polymer, is being explored as an alternative to metallic alloys for dental implants due to its aesthetic and mechanical properties. This study aimed to enhance the surface biofunctionality through evaluating human MG-63 osteoblastic cell survival, proliferation, differentiation, and mineralization.

Method

Following the sandblasting and plasma treatment of the 3D-printed PEEK discs, a layer of hyaluronic acid (Hya) was coated onto the PEEK surface. Osteoblast cells were seeded onto the discs. The groups consisted of Hya-coated PEEK, uncoated PEEK, and a control group. Cell viability, proliferation, differentiation, and mineralization potential were examined after seven and twenty-one days of cell seeding using the MTT test, DAPI staining technique, alkaline phosphatase activity (ALP), and alizarin red staining.

Results

Hya-coated PEEK increased cell viability (1.48 ± 0.13, 1.49 ± 0.09) compared to the uncoated group (1.19 ± 0.06, 1.26 ± 0.07) and control group (0.98 ± 0.04, 1.00 ± 0.07) after 7 and 21 days. Proliferation rates of coated group (60.50 ± 3.08) were greater than the uncoated (50.33 ± 2.58) and control group (38.33 ± 4.88) at 21 days, respectively. Additionally, the ALP activity on Hya-coated PEEK disks (5.55 ± 0.65, 7.54 ± 0.64) was notably higher than that of the uncoated group (1.08 ± 0.49, 2.59 ± 0.68), and control group (0.16 ± 0.09, 0.34 ± 0.18) at both time periods. Alizarin red staining in the Hya-coated PEEK group (1.81 ± 0.23, 1.97 ± 0.20) was significantly greater in comparison with uncoated group (1.12 ± 0.17, 1.14 ± 0.19) and control group (0.99 ± 0.10, 0.98 ± 0.05) at both time intervals.

Conclusion

Hya's surface coating has enhanced the biofunctional properties of PEEK implant material, as demonstrated by improved cell survival, proliferation, differentiation, and mineralization potential.

Multifunctional curcumin-based polymer coating: A promising platform against bacteria, inflammation and coagulation

The extensive use of polymers in the medical field has facilitated the development of various devices and implants, contributing to the restoration of organ function. However, despite their advantages such as biocompatibility and robustness, these materials often face challenges like bacterial contamination and subsequent inflammation, leading to implant-associated infections (IAI). Integrating implants effectively is crucial to prevent bacterial colonization and reduce inflammatory responses. To overcome these major issues, surface chemical modifications have been extensively explored. Indeed, click chemistry, and particularly, copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has emerged as a promising approach for surface functionalization without affecting material bulk properties. Curcumin, known for its diverse biological activities, suffers from low solubility and stability. To enhance its bioavailability, bioconjugation strategy has garnered attention in recent years. This study represents pioneering work in immobilizing curcumin derivative onto polyethylene terephthalate (PET) surfaces, aiming to combat bacterial adhesion, inflammation and coagulation. Before curcumin derivative bioconjugation, a fluorophore, dansyl derivative, was employed in order to monitor and determine the efficiency of the proposed methodology. Previous surface chemical modifications were required for the immobilization of both dansyl and curcumin derivatives. Ultraviolet-Visible (UV-Vis) demonstrated the amidation functionalization of PET surface. Other surface characterization techniques including X-ray Photoelectron Spectroscopy (XPS), Attenuated Total Reflectance Fourier Transformed Infrared (ATR-FTIR), Scanning Electron Microscopy (SEM) and contact angle, among others, confirmed also the conjugation of both dansyl and curcumin derivatives. On the other hand, different biological assays corroborated that curcumin derivative immobilized PET surfaces do not exhibit cytotoxicity effect. Additionally, corresponding inflammation test were performed, indicating that these polymeric surfaces do not produce inflammation and, when curcumin derivative is immobilized, they decrease the inflammation marker level (IL-6). Moreover, the bacterial growth of both Gram positive and Gram negative bacteria were measured, demonstrating that the immobilization of curcumin derivative on PET provided antibacterial properties to the material. Finally, hemolysis rate analysis and whole blood clotting assay demonstrated the antithrombogenic effect of PET-Cur surfaces as well as no hemolysis concern in the fabricated functional surfaces.

pH-response of protein-polysaccharide multilayers adsorbed on a flat gold surface: A surface plasmon resonance study

Polysaccharide-protein multilayers (PPMLs) consisting of bovine serum albumin (BSA) and chondroitin sulfate (CS) are assembled in acidic solution (pH 4.2) via layer-by-layer deposition method. The formation of PPMLs on gold surface and their responsiveness to pH change from 4.2 to 7 is investigated by Surface Plasmon Resonance Spectroscopy. The buildup of the multilayer at pH 4.2 exhibits non-linear growth while the formation of the first layers is strongly affected by the physicochemical properties of the gold surface. Neutral solution (pH 7) affects the interactions between the biopolymers and results in a partially disassemble (disintegration) of the multilayer film. On one hand, the single pair of layers, BSA-CS and the double pair of layers, (BSA-CS)2, assemblies are stable in neutral pH, a result that will be of interest for biomedical applications. On the other hand, multilayer films consisting of more than four layers that is (BSA-CS)2 Collapse

Key Words

• layer‐by‐layer
• multilayer
• pH‐responsiveness
• protein‐polysaccharide
• surface plasmon

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MESH Headings

• Gold/chemistry
• Surface Plasmon Resonance/methods
• Hydrogen-Ion Concentration
• Serum Albumin, Bovine/chemistry
• Adsorption
• Chondroitin Sulfates/chemistry
• Surface Properties
• Cattle
• Animals
• Polysaccharides/chemistry

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Grants Collapse

Affiliation(s)

Nikolitsa Katsenou Department of Physics, University of Patras, Patras, Greece
Nikolaos Spiliopoulos Department of Physics, University of Patras, Patras, Greece
Dimitrios L Anastassopoulos Department of Physics, University of Patras, Patras, Greece
Aristeidis Papagiannopoulos Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens, Greece
Chris Toprakcioglu Department of Physics, University of Patras, Patras, Greece

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Microbial corrosion of metallic biomaterials in the oral environment

A wide variety of microorganisms have been closely linked to metal corrosion in the form of adherent surface biofilms. Biofilms allow the development and maintenance of locally corrosive environments and/or permit direct corrosion including pitting corrosion. The presence of numerous genetically distinct microorganisms in the oral environment poses a threat to the integrity and durability of the surface of metallic prostheses and implants used in routine dentistry. However, the association between oral microorganisms and specific corrosion mechanisms is not clear. It is of practical importance to understand how microbial corrosion occurs and the associated risks to metallic materials in the oral environment. This knowledge is also important for researchers and clinicians who are increasingly concerned about the biological activity of the released corrosion products. Accordingly, the main goal was to comprehensively review the current literature regarding oral microbiologically influenced corrosion (MIC) including characteristics of biofilms and of the oral environment, MIC mechanisms, corrosion behavior in the presence of oral microorganisms and potentially mitigating technologies. Findings included that oral MIC has been ascribed mostly to aggressive metabolites secreted during microbial metabolism (metabolite-mediated MIC). However, from a thermodynamic point of view, extracellular electron transfer mechanisms (EET-MIC) through pili or electron transfer compounds cannot be ruled out. Various MIC mitigating methods have been demonstrated to be effective in short term, but long term evaluations are necessary before clinical applications can be considered. Currently most in-vitro studies fail to simulate the complexity of intraoral physiological conditions which may either reduce or exacerbate corrosion risk, which must be addressed in future studies. STATEMENT OF SIGNIFICANCE: A thorough analysis on literature regarding oral MIC (microbiologically influenced corrosion) of biomedical metallic materials has been carried out, including characteristics of oral environment, MIC mechanisms, corrosion behaviors in the presence of typical oral microorganisms and potential mitigating methods (materials design and surface design). There is currently a lack of mechanistic understanding of oral MIC which is very important not only to corrosion researchers but also to dentists and clinicians. This paper discusses the significance of biofilms from a biocorrosion perspective and summarizes several aspects of MIC mechanisms which could be caused by oral microorganisms. Oral MIC has been closely associated with not only the materials research but also the dental/clinical research fields in this work.

Biomaterials science and surface engineering strategies for dental peri-implantitis management

Peri-implantitis is a bacterial infection that causes soft tissue inflammatory lesions and alveolar bone resorption, ultimately resulting in implant failure. Dental implants for clinical use barely have antibacterial properties, and bacterial colonization and biofilm formation on the dental implants are major causes of peri-implantitis. Treatment strategies such as mechanical debridement and antibiotic therapy have been used to remove dental plaque. However, it is particularly important to prevent the occurrence of peri-implantitis rather than treatment. Therefore, the current research spot has focused on improving the antibacterial properties of dental implants, such as the construction of specific micro-nano surface texture, the introduction of diverse functional coatings, or the application of materials with intrinsic antibacterial properties. The aforementioned antibacterial surfaces can be incorporated with bioactive molecules, metallic nanoparticles, or other functional components to further enhance the osteogenic properties and accelerate the healing process. In this review, we summarize the recent developments in biomaterial science and the modification strategies applied to dental implants to inhibit biofilm formation and facilitate bone-implant integration. Furthermore, we summarized the obstacles existing in the process of laboratory research to reach the clinic products, and propose corresponding directions for future developments and research perspectives, so that to provide insights into the rational design and construction of dental implants with the aim to balance antibacterial efficacy, biological safety, and osteogenic property.

Biomimetic Coatings in Implant Dentistry: A Quick Update

Biomimetic dental implants are regarded as one of the recent clinical advancements in implant surface modification. Coatings with varying thicknesses and roughness may affect the dental implant surface's chemical inertness, cell adhesion, and antibacterial characteristics. Different surface coatings and mechanical surface changes have been studied to improve osseointegration and decrease peri-implantitis. The surface medication increases surface energy, leading to enhanced cell proliferation and growth factors, and, consequently, to a rise in the osseointegration process. This review provides a comprehensive update on the numerous biomimetic coatings used to improve the surface characteristics of dental implants and their applications in two main categories: coating to improve osseointegration, including the hydroxyapatite layer and nanocomposites, growth factors (BMPs, PDGF, FGF), and extracellular matrix (collagen, elastin, fibronectin, chondroitin sulfate, hyaluronan, and other proteoglycans), and coatings for anti-bacterial performance, covering drug-coated dental implants (antibiotic, statin, and bisphosphonate), antimicrobial peptide coating (GL13K and human beta defensins), polysaccharide antibacterial coatings (natural chitosan and its coupling agents) and metal elements (silver, zinc, and copper).

Overview of strategies to improve the antibacterial property of dental implants

The increasing number of peri-implant diseases and the unsatisfactory results of conventional treatment are causing great concern to patients and medical staff. The effective removal of plaque which is one of the key causes of peri-implant disease from the surface of implants has become one of the main problems to be solved urgently in the field of peri-implant disease prevention and treatment. In recent years, with the advancement of materials science and pharmacology, a lot of research has been conducted to enhance the implant antimicrobial properties, including the addition of antimicrobial coatings on the implant surface, the adjustment of implant surface topography, and the development of new implant materials, and significant progress has been made in various aspects. Antimicrobial materials have shown promising applications in the prevention of peri-implant diseases, but meanwhile, there are some shortcomings, which leads to the lack of clinical widespread use of antimicrobial materials. This paper summarizes the research on antimicrobial materials applied to implants in recent years and presents an outlook on the future development.

The Intraoperative Use of Defensive Antibacterial Coating (DAC®) in the Form of a Gel to Prevent Peri-Implant Infections in Orthopaedic Surgery: A Clinical Narrative Review

Periprosthetic joint infections (PJIs) in arthroplasty and osteosynthesis-associated infections (OAIs) in reconstructive surgery still represent a challenging complication in orthopaedics and traumatology causing a burden worsening the patient's quality of life, for caregiver and treating physicians, and for healthcare systems. PJIs and OAIs are the result of bacterial adhesion over an implant surface with subsequent biofilm formation. Therefore, the clinical pathological outcome is a difficult-to-eradicate persistent infection. Strategies to treat PJIs and OAIs involve debridement, the replacement of internal fixators or articular prostheses, and intravenous antibiotics. However, long treatments and surgical revision cause discomfort for patients; hence, the prevention of PJIs and OAIs represents a higher priority than treatment. Local antibiotic treatments through coating-release systems are becoming a smart approach to prevent this complication. Hydrophilic coatings, loaded with antibiotics, simultaneously provide a barrier effect against bacterial adhesion and allow for the local delivery of an antibiotic. The intraoperative use of a hyaluronan (HY)-derivative coating in the form of a gel, loaded with antibiotics to prevent PJI, has recently raised interest in orthopaedics. Current evidence supports the use of this coating in the prophylaxis of PJI and IRIs in terms of clinical outcomes and infection reduction. Thus, the purpose of this narrative review is to assess the use of a commercially available HY derivative in the form of a gel, highlighting the characteristics of this biomaterial, which makes it attractive for the management of PJIs and IRIs in orthopaedics and traumatology.

Antibacterial coatings on orthopedic implants

With the aging of population and the rapid improvement of public health and medical level in recent years, people have had an increasing demand for orthopedic implants. However, premature implant failure and postoperative complications frequently occur due to implant-related infections, which not only increase the social and economic burden, but also greatly affect the patient's quality of life, finally restraining the clinical use of orthopedic implants. Antibacterial coatings, as an effective strategy to solve the above problems, have been extensively studied and motivated the development of novel strategies to optimize the implant. In this paper, a variety of antibacterial coatings recently developed for orthopedic implants were briefly reviewed, with the focus on the synergistic multi-mechanism antibacterial coatings, multi-functional antibacterial coatings, and smart antibacterial coatings that are more potential for clinical use, thereby providing theoretical references for further fabrication of novel and high-performance coatings satisfying the complex clinical needs.

Multifunctionalized carbon-fiber-reinforced polyetheretherketone implant for rapid osseointegration under infected environment

Carbon fiber reinforced polyetheretherketone (CFRPEEK) possesses a similar elastic modulus to that of human cortical bone and is considered as a promising candidate to replace metallic implants. However, the bioinertness and deficiency of antibacterial activities impede its application in orthopedic and dentistry. In this work, titanium plasma immersion ion implantation (Ti-PIII) is applied to modify CFRPEEK, achieving unique multi-hierarchical nanostructures and active sites on the surface. Then, hybrid polydopamine (PDA)@ZnO-EDN1 nanoparticles (NPs) are introduced to construct versatile surfaces with improved osteogenic and angiogenic properties and excellent antibacterial properties. Our study established that the modified CFRPEEK presented favorable stability and cytocompatibility. Compared with bare CFRPEEK, improved osteogenic differentiation of rat mesenchymal stem cells (BMSCs) and vascularization of human umbilical vein endothelial cells (HUVECs) are found on the functionalized surface due to the zinc ions and EDN1 releasing. In vitro bacteriostasis assay confirms that hybrid PDA@ZnO NPs on the functionalized surface provided an effective antibacterial effect. Moreover, the rat infected model corroborates the enhanced antibiosis and osteointegration of the functionalized CFRPEEK. Our findings indicate that the multilevel nanostructured PDA@ZnO-EDN1 coated CFRPEEK with enhanced antibacterial, angiogenic, and osteogenic capacity has great potential as an orthopedic/dental implant material for clinical application.

Fabrication of succinate-alginate xerogel films for in vitro coupling of osteogenesis and neovascularization

The osseointegration of metallic implants is reliant on a cascade of molecular interactions and the delivery of macromolecules to the implant environment that occurs before substantial bone formation. Early blood vessel formation is a requisite first step in the healing timeline for osteoid formation, where vascular development can be accelerated as a result of controlled hypoxic conditioning. In this study, alginate-derived xerogel films containing varied concentrations of disodium succinate salt which has been shown to induce pseudohypoxia (short-term hypoxic effects while maintaining an oxygenated environment) were developed. Xerogels were characterized for their morphology, succinate release over time and cellular response with osteoblast-mimicking Saos-2 and human umbilical vein endothelial cells (HUVEC). Scanning electron microscopy revealed a multiscale topography that may favour osseointegration and alamarBlue assays indicated no cytotoxic effects during in vitro proliferation of Saos-2 cells. pH measurements of eluted succinate reach 95 % of peak value after 7 h of immersion for all gels containing 10 mM of succinate or less, and 60 % within the first 40 min. In vitro exposure of HUVECs to succinate-conditioned media increased the net concentration of total proteins measured by bicinchoninic acid (BCA) assay and maintains stable vascular endothelial growth factor (VEGF) and extracellular platelet-derived growth factor (PDGF) for vessel formation through comparison of enzyme-linked immunosorbent assays (ELISAs) of the culture media and cell lysate. Tube formation assays also showed a sustained increase in tube diameter across the first 48 h of HUVEC culture when succinate concentrations of 1 and 10 μM in the xerogel. Overall, the succinate-alginate films serve as a prospective organic coating for bone-interfacing implant materials which may induce temporary pseudohypoxic conditions favourable for early angiogenesis and bone regeneration in vivo at succinate concentrations of 1 or 10 μM.

Polydopamine and hyaluronic acid immobilisation on vancomycin-loaded titanium nanotube for prophylaxis of implant infections

Titanium nanotube (Ti-NT) is an attractive substrate for local drug delivery, however, it is difficult to control the burst drug release and achieve sustained release from these nanotubes. In the present study, we investigated the feasibility of controlling drug release from Ti-NT within polydopamine and hyaluronic acid films, to achieve antibacterial activity and osteogenic promotion. Vancomycin was loaded into the Ti-NT by lyophilisation. Dopamine and hyaluronic acid were immobilized on the vancomycin-loaded Ti-NT surface through alternate deposition technique. The anti-infective and osteogenic abilities of the polydopamine and hyaluronic acid-modified Ti-NT were then investigated. Our results demonstrated that polydopamine and hyaluronic acid-modified Ti-NT exhibited improved drug loading and release control for 7 days. Compared with the vancomycin-loaded Ti-NT, the polydopamine and hyaluronic acid-modified Ti-NT exhibited better antibacterial ability, and the hyaluronic acid-modified Ti-NT promoted the osteogenic differentiation of rat bone marrow stem cells. Our results demonstrated that Ti-NT biofunctionalized with polydopamine and hyaluronic acid can help overcome the limitations of Ti-NT, by improving drug loading, antibacterial activity and osteogenic ability.

Recent Progress on Bioinspired Antibacterial Surfaces for Biomedical Application

Surface bacterial fouling has become an urgent global challenge that calls for resilient solutions. Despite the effectiveness in combating bacterial invasion, antibiotics are susceptible to causing microbial antibiotic resistance that threatens human health and compromises the medication efficacy. In nature, many organisms have evolved a myriad of surfaces with specific physicochemical properties to combat bacteria in diverse environments, providing important inspirations for implementing bioinspired approaches. This review highlights representative natural antibacterial surfaces and discusses their corresponding mechanisms, including repelling adherent bacteria through tailoring surface wettability and mechanically killing bacteria via engineering surface textures. Following this, we present the recent progress in bioinspired active and passive antibacterial strategies. Finally, the biomedical applications and the prospects of these antibacterial surfaces are discussed.

The Construction of a Self-assembled Coating with Chitosan-Grafted Reduced Graphene Oxide on Porous Calcium Polyphosphate Scaffolds for Bone Tissue Engineering

Bone regeneration in large bone defects remains one of the major challenges in orthopedic surgery. Calcium polyphosphate (CPP) scaffolds possess excellent biocompatibility and exhibits good bone ingrowth. However, the present CPP scaffolds lack enough osteoinductive activity to facilitate bone regeneration at bone defects that exceed the critical size threshold. To endow CPP scaffolds with improved osteoinductive activity for better bone regeneration, in this study, a self-assembled coating with chitosan-grafted reduced graphene oxide (CS-rGO) sheets was successfully constructed onto the surface of CPP scaffolds through strong electrostatic interaction and hydrogen bonds. Our results showed that the obtained CPP/CS-rGO composite scaffolds exhibited highly improved biomineralization and considerable antibacterial activity. More importantly, CPP/CS-rGO composite scaffolds could drive osteogenic differentiation of BMSCs and significantly up-regulate the expression of osteogenesis-related proteins in vitro. Meanwhile, the CS-rGO coating could inhibit aseptic loosening and improve interfacial osseointegration through stimulating BMSCs to secrete more OPG and lesser RANKL. Overall, the CS-rGO coating adjusts CPP scaffolds' biological environment interface and endows CPP scaffolds with more bioactivity.

Antimicrobial coating strategy to prevent orthopaedic device-related infections: recent advances and future perspectives

The rapid development of multidrug-resistant (MDR) bacteria and biofilm-related infections (BRIs) has urgently called for new strategies to combat severe orthopaedic device-related infections (ODRIs). Antimicrobial coating has emerged as a promising strategy in halting the incidence of ODRIs and treating ODRIs in long term. With the advancement of material science and biotechnology, numerous antimicrobial coatings have been reported in literature, showing superior antimicrobial and osteogenic functions. This review has specifically discussed the currently developed antimicrobial coatings in the perspective of drug release from the coating system, focusing on their realization of controlled and on demand antimicrobial agents release, as well as multi-functionality. Acknowledging the multidisciplinary nature of antimicrobial coating, the conceptual design, the deposition method and the therapeutic effect of the antimicrobial coatings have been described in detail and discussed critically. Particularly, the challenges and opportunities on the way toward the clinical translation of antimicrobial coatings have been highlighted.

"Dual-functional" strontium titanate nanotubes designed based on fusion peptides simultaneously enhancing anti-infection and osseointegration

Currently, there is an increasing clinical demand for implants that effectively resist bacterial infections while promoting osseointegration. In this study, the fusion peptide technology was used to linearly fuse the antimicrobial peptide (AMP, HHC36) and the bone-promoting peptide (RGD), so that the titanium (Ti)-based implant modified by the polypeptide had the dual function of "antibacterial-promoting bone". Firstly, self-organized vertically-oriented strontium-doped titanium dioxide nanotubes (STN) were manufactured by anodizing and hydrothermal synthesis methods. Secondly, the fusion peptide (HHC36-RGD) was loaded into the tubular structure by a simple vacuum-assisted physical adsorption method. Finally, STN loaded with HHC36-RGD (H-R-STN) was obtained. The characterization results demonstrated that the surface of the H-R-STN had a roughness and hydrophilicity that promoted cell adhesion. Additionally, electrochemical tests showed that H-R-STN coating can reduce the corrosion rate of pure Ti. The fusion peptide and Sr²⁺ in H-R-STN were released in the initial fast and subsequent slow kinetic model. Expected, H-R-STN can kill more than 99% of clinically common pathogenic bacteria (Staphylococcus aureus and Escherichia coli), and significantly inhibit the formation of bacterial biofilms. Simultaneously, under the synergistic effect of RGD in the fusion peptide and strontium in STN, H-R-STN markedly promoted the adhesion and proliferation of mouse osteoblasts, and significantly promoted osteogenic markers (alkaline phosphatase, runt-related transcription, collagen, mineralization) expression. In summary, the bifunctional titanium-based implant constructed by H-R-STN in this article can effectively prevent bacterial infections and promote early osseointegration. The main advantage of the titanium surface treatment method of the study was that its simplicity, low cost, especially its versatility made it a promising anti-infective bone repair material.

Bioactive Coatings on Titanium: A Review on Hydroxylation, Self-Assembled Monolayers (SAMs) and Surface Modification Strategies

Titanium (Ti) and its alloys have been demonstrated over the last decades to play an important role as inert materials in the field of orthopedic and dental implants. Nevertheless, with the widespread use of Ti, implant-associated rejection issues have arisen. To overcome these problems, antibacterial properties, fast and adequate osseointegration and long-term stability are essential features. Indeed, surface modification is currently presented as a versatile strategy for developing Ti coatings with all these challenging requirements and achieve a successful performance of the implant. Numerous approaches have been investigated to obtain stable and well-organized Ti coatings that promote the tailoring of surface chemical functionalization regardless of the geometry and shape of the implant. However, among all the approaches available in the literature to functionalize the Ti surface, a promising strategy is the combination of surface pre-activation treatments typically followed by the development of intermediate anchoring layers (self-assembled monolayers, SAMs) that serve as the supporting linkage of a final active layer. Therefore, this paper aims to review the latest approaches in the biomedical area to obtain bioactive coatings onto Ti surfaces with a special focus on (i) the most employed methods for Ti surface hydroxylation, (ii) SAMs-mediated active coatings development, and (iii) the latest advances in active agent immobilization and polymeric coatings for controlled release on Ti surfaces.

Proteoglycans and Glycosaminoglycans in Stem Cell Homeostasis and Bone Tissue Regeneration

Stem cells maintain a subtle balance between self-renewal and differentiation under the regulatory network supported by both intracellular and extracellular components. Proteoglycans are large glycoproteins present abundantly on the cell surface and in the extracellular matrix where they play pivotal roles in facilitating signaling transduction and maintaining stem cell homeostasis. In this review, we outline distinct proteoglycans profiles and their functions in the regulation of stem cell homeostasis, as well as recent progress and prospects of utilizing proteoglycans/glycosaminoglycans as a novel glycomics carrier or bio-active molecules in bone regeneration.

Antimicrobial coatings based on chitosan to prevent implant-associated infections: A systematic review

Despite the advancements in material science and surgical techniques, the incidence of implant-associated infections (IAIs) has increased significantly. IAIs are mainly caused by microbial adhesion and biofilm formation on implant surfaces. In this study, we aimed to evaluate and critically discuss the antimicrobial efficacy of chitosan-based coatings to prevent the occurrence of IAIs. For this purpose, a PRISMA-oriented systematic review was conducted based on predefined criteria and forty studies were selected for qualitative analysis. Results indicated that chitosan (CS) association with enzymes and antimicrobial peptides improves its antimicrobial activity and extends its use in a broad range of physiological conditions. Likewise, CS association with polymers resulted in enhanced antimicrobial and anti-adhesive coatings with desirable properties, such as biocompatibility and durability, for implantable medical devices (IMDs). These findings can assist researchers in the design of new CS coatings for application in IMDs.

Dental Implant Nano-Engineering: Advances, Limitations and Future Directions

Titanium (Ti) and its alloys offer favorable biocompatibility, mechanical properties and corrosion resistance, which makes them an ideal material choice for dental implants. However, the long-term success of Ti-based dental implants may be challenged due to implant-related infections and inadequate osseointegration. With the development of nanotechnology, nanoscale modifications and the application of nanomaterials have become key areas of focus for research on dental implants. Surface modifications and the use of various coatings, as well as the development of the controlled release of antibiotics or proteins, have improved the osseointegration and soft-tissue integration of dental implants, as well as their antibacterial and immunomodulatory functions. This review introduces recent nano-engineering technologies and materials used in topographical modifications and surface coatings of Ti-based dental implants. These advances are discussed and detailed, including an evaluation of the evidence of their biocompatibility, toxicity, antimicrobial activities and in-vivo performances. The comparison between these attempts at nano-engineering reveals that there are still research gaps that must be addressed towards their clinical translation. For instance, customized three-dimensional printing technology and stimuli-responsive, multi-functional and time-programmable implant surfaces holds great promise to advance this field. Furthermore, long-term in vivo studies under physiological conditions are required to ensure the clinical application of nanomaterial-modified dental implants.

Nanoparticles in Dentistry: A Comprehensive Review

In recent years, nanoparticles (NPs) have been receiving more attention in dentistry. Their advantageous physicochemical and biological properties can improve the diagnosis, prevention, and treatment of numerous oral diseases, including dental caries, periodontal diseases, pulp and periapical lesions, oral candidiasis, denture stomatitis, hyposalivation, and head, neck, and oral cancer. NPs can also enhance the mechanical and microbiological properties of dental prostheses and implants and can be used to improve drug delivery through the oral mucosa. This paper reviewed studies from 2015 to 2020 and summarized the potential applications of different types of NPs in the many fields of dentistry.

Native Spider Silk-Based Antimicrobial Hydrogels for Biomedical Applications

Novel antimicrobial natural polymeric hybrid hydrogels based on hyaluronic acid (HA) and spider silk (Ss) were prepared using the chemical crosslinking method. The effects of the component ratios on the hydrogel characteristics were observed parallel to the primary physicochemical characterization of the hydrogels with scanning electron microscopic imaging, Fourier-transform infrared spectroscopy, and contact angle measurements, which confirmed the successful crosslinking, regular porous structure, exact composition, and hydrophilic properties of hyaluronic acid/spider silk-based hydrogels. Further characterizations of the hydrogels were performed with the swelling degree, enzymatic degradability, viscosity, conductivity, and shrinking ability tests. The hyaluronic acid/spider silk-based hydrogels do not show drastic cytotoxicity over human postnatal fibroblasts (HPF). Hydrogels show extraordinary antimicrobial ability on both gram-negative and gram-positive bacteria. These hydrogels could be an excellent alternative that aids in overcoming antimicrobial drug resistance, which is considered to be one of the major global problems in the biomedical industry. Hyaluronic acid/spider silk-based hydrogels are a promising material for collaborated antimicrobial and anti-inflammatory drug delivery systems for external use. The rheological properties of the hydrogels show shear-thinning properties, which suggest that the hydrogels could be applied in 3D printing, such as in the 3D printing of antimicrobial surgical meshes.

Antibacterial catechol-based hyaluronic acid, chitosan and poly (N-vinyl pyrrolidone) coatings onto Ti6Al4V surfaces for application as biomedical implant

Bacterial contamination in implanted biomedical devices is a critical daily concern. The most used material for permanent implant in biomedical field is Ti6Al4V alloy due to its beneficial mechanical properties and high biocompatibility. Accordingly, in this work different polymeric antibacterial coatings poly(N-vinyl pyrrolidone) (PVP), hyaluronic acid (HA) and chitosan (CHI) were developed and comparatively analysed for Ti6Al4V surface covering. The adhesion of these coatings to Ti6Al4V substrates were carried out after the conjugation of these polymers with the so well-known bioadhesive properties of catechol (CA) anchor group. These surface modifications were characterized by X-ray photoelectronic spectroscopy, contact angle measurements and atomic force microscopy. In addition, the stability of CA-conjugated polymeric coatings was compared with the coatings formed with unconjugated polymers. Finally, the cytocompatibility and antibacterial properties against gram-positive and gram-negative strains on coated Ti6Al4V substrates were assessed confirming the effectiveness of these polymeric coatings against bacterial infections for future applications in protecting biomedical implants.

Multifunctional natural polymer-based metallic implant surface modifications

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

Overview of Antibacterial Strategies of Dental Implant Materials for the Prevention of Peri-Implantitis

As dental implants have become one of the main treatment options for patients with tooth loss, the number of patients with peri-implant diseases has increased. Similar to periodontal diseases, peri-implant diseases have been associated with dental plaque formation on implants. Unconventional approaches have been reported to remove plaque from infected implants, but none of these methods can completely and permanently solve the problem of bacterial invasion. Fortunately, the constant development of antibacterial implant materials is a promising solution to this situation. In this review, the development and study of different antibacterial strategies for dental implant materials for the prevention of peri-implantitis are summarized. We hope that by highlighting the advantages and limitations of these antimicrobial strategies, we can assist in the continued development of oral implant materials.

Chitosan-based smart hybrid materials: a physico-chemical perspective

Chitosan is one of the most studied cationic polysaccharides. Due to its unique characteristics of being water soluble, biocompatible, biodegradable, and non-toxic, this macromolecule is highly attractive for a broad range of applications. In addition, its complex behavior and the number of ways it interacts with different components in a system result in an astonishing variety of chitosan-based materials. Herein, we present recent advances in the field of chitosan-based materials from a physico-chemical perspective, with focus on aqueous mixtures with oppositely charged colloids, chitosan-based thin films, and nanocomposite systems. In this review, we focus our attention on the physico-chemical properties of chitosan-based materials, including solubility, mechanical resistance, barrier properties, and thermal behaviour, and provide a link to the chemical peculiarities of chitosan, such as its intrinsic low solubility, high rigidity, large charge separation, and strong tendency to form intra- and inter-molecular hydrogen bonds.

Preparation and Antifouling Property of Polyurethane Film Modified by PHMG and HA Using Layer-by-Layer Assembly

To reduce the possibility of bacterial infection and implant-related complications, surface modification on polyurethane (PU) film is an ideal solution to endow hydrophobic PU with antibacterial and antifouling properties. In this work, a variety of polyhexamethylene guanidine/ hyaluronic acid (PHMG/HA) multilayer films were self-assembled layer-by-layer on PU films using polyanions, carboxyl-activated HA, and polycations PHMG by controlling the concentration of these polyelectrolytes as well as the number of layers self-assembled. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectra, water contact angle (WCA), and A Atomic force microscope (AFM) of PU and modified PU films were studied. Protein adsorption and bacterial adhesion as well as the cytotoxicity against L929 of the film on selected PU-(PHMG/HA)₅/5-5 were estimated. The results showed that PU-(PHMG/HA)₅/5-5 had the best hydrophilicity among all the prepared films, possessing the lowest level of protein adsorption. Meanwhile, this film showed efficient broad-spectrum antibacterial performance as well as significant resistance of bacterial adhesion of more than a 99.9% drop for the selected bacteria. Moreover, almost no influence on cell viability of L929 enhanced the biocompatibility of film. Therefore, the modified PU films with admirable protein absorption resistance, antimicrobial performance, and biocompatibility would have promising applications in biomedical aspect.

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.

Surface functionalization of chitosan as a coating material for orthopaedic applications: A comprehensive review

Metallic implants have dominated the biomedical implant industries for the past century for load-bearing applications, while the polymeric implants have shown great promise for tissue engineering applications. The surface properties of such implants are critical as the interaction of implant surfaces, and the body tissues may lead to unfavourable reactions. Desired implant properties are biocompatibility, corrosion resistance, and antibacterial activity. A polymer coating is an efficient and economical way to produce such surfaces. A lot of research has been carried out on chitosan (CS)-modified metallic and polymer scaffolds in the last decade. Different methods such as electrophoretic deposition, sol-gel methods, dip coating and spin coating, electrospinning, etc. have been utilized to produce CS coatings. However, a systematic review of chitosan coatings on scaffolds focussing on widely employed techniques is lacking. This review surveys literature concerning the current status of orthopaedic applications of CS for the purpose of coatings. In this review, the various preparation methods of coating, and the role of the surface functionalities in determining the efficiency of coatings are discussed. Effect of nanoparticle additions on the polymeric interfaces and in regulating the properties of surface coatings are also investigated in detail.

Hyaluronic acid as a bioactive component for bone tissue regeneration: Fabrication, modification, properties, and biological functions

Hyaluronic acid (HA) is widely distributed in the human body, and it is heavily involved in many physiological functions such as tissue hydration, wound repair, and cell migration. In recent years, HA and its derivatives have been widely used as advanced bioactive polymers for bone regeneration. Many medical products containing HA have been developed because this natural polymer has been proven to be nontoxic, noninflammatory, biodegradable, and biocompatible. Moreover, HA-based composite scaffolds have shown good potential for promoting osteogenesis and mineralization. Recently, many HA-based biomaterials have been fabricated for bone regeneration by combining with electrospinning and 3D printing technology. In this review, the polymer structures, processing, properties, and applications in bone tissue engineering are summarized. The challenges and prospects of HA polymers are also discussed.

Structure, morphology, adhesion and in vitro biological evaluation of antibacterial multi-layer HA-Ag/SiO2/TiN/Ti coatings obtained by RF magnetron sputtering for biomedical applications

Biocompatible and antibacterial multi-layer coatings of hydroxyapatite (HA)-Ag/SiO2/TiN/Ti were obtained on the Ti-6Al-4V alloy, by means of the magnetron sputtering technique. During characterization of the coatings, the chemical composition was evaluated by energy dispersive X-ray spectroscopy and the phase analysis was carried out by X-ray diffraction. The morphology of the coatings was observed by field emission scanning electron microscopy, while transmission electron microscopy was used to appreciate their structure. The adhesion of the coatings to the substrate was evaluated by micro scratch test. The in vitro biological response was evaluated in terms of cytotoxicity, adhesion and differentiation of mouse mesenchymal stem cells, as well as adhesion and bacterial viability of Staphylococcus aureus strain. Through the compositional study carried out, the deposition of the HA phase was verified, with a Ca/P ratio close to 1.67 and the characteristic diffraction peaks of this compound. The structural study of the coatings evidenced the obtention of multi-layer architectures. The use of an intermediate SiO2/TiN/Ti trilayer was found to improve adhesion between HA-Ag and the substrate by 84%. Finally, the in vitro biological tests carried out indicated a potentially non-toxic character in the coatings. Additionally, an antibacterial effect was registered at low concentrations of Ag (<0.25 mg/L).

Surface Modified Techniques and Emerging Functional Coating of Dental Implants

Dental implants are widely used in the field of oral restoration, but there are still problems leading to implant failures in clinical application, such as failed osseointegration, marginal bone resorption, and peri-implantitis, which restrict the success rate of dental implants and patient satisfaction. Poor osseointegration and bacterial infection are the most essential reasons resulting in implant failure. To improve the clinical outcomes of implants, many scholars devoted to modifying the surface of implants, especially to preparing different physical and chemical modifications to improve the osseointegration between alveolar bone and implant surface. Besides, the bioactive-coatings to promote the adhesion and colonization of ossteointegration-related proteins and cells also aim to improve the osseointegration. Meanwhile, improving the anti-bacterial performance of the implant surface can obstruct the adhesion and activity of bacteria, avoiding the occurrence of inflammation related to implants. Therefore, this review comprehensively investigates and summarizes the modifying or coating methods of implant surfaces, and analyzes the ossteointegration ability and anti-bacterial characteristics of emerging functional coatings in published references.

Metallic Antibacterial Surface Treatments of Dental and Orthopedic Materials

The oral cavity harbors complex microbial communities, which leads to biomaterial-associated infections (BAI) during dental and orthopedic treatments. Conventional antibiotic treatments have met great challenges recently due to the increasing emergency of drug-resistant bacteria. To tackle this clinical issue, antibacterial surface treatments, containing surface modification and coatings, of dental and orthopedic materials have become an area of intensive interest now. Among various antibacterial agents used in surface treatments, metallic agents possess unique properties, mainly including broad-spectrum antibacterial properties, low potential to develop bacterial resistance, relative biocompatibility, and chemical stability. Therefore, this review mainly focuses on underlying antibacterial applications and the mechanisms of metallic agents in dentistry and orthopedics. An overview of the present review indicates that much work remains to be done to deepen the understanding of antibacterial mechanisms and potential side-effects of metallic agents.

Fusion peptide engineered "statically-versatile" titanium implant simultaneously enhancing anti-infection, vascularization and osseointegration

Although antimicrobial titanium implants can prevent biomaterial-associated infection (BAI) in orthopedics, they display cytotoxicity and delayed osseointegration. Therefore, versatile implants are desirable for simultaneously inhibiting BAI and promoting osseointegration, especially "statically-versatile" ones with nonessential external stimulations for facilitating applications. Herein, we develop a "statically-versatile" titanium implant by immobilizing an innovative fusion peptide (FP) containing HHC36 antimicrobial sequence and QK angiogenic sequence via sodium borohydride reduction promoted Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC-SB), which shows higher immobilization efficiency than traditional CuAAC with sodium ascorbate reduction (CuAAC-SA). The FP-engineered implant exhibits over 96.8% antimicrobial activity against four types of clinical bacteria (S. aureus, E. coli, P. aeruginosa and methicillin-resistant S. aureus), being stronger than that modified with mixed peptides. This can be mechanistically attributed to the larger bacterial accessible surface area of HHC36 sequence. Notably, the implant can simultaneously enhance cellular proliferation, up-regulate expressions of angiogenesis-related genes/proteins (VEGF and VEGFR-2) of HUVECs and osteogenesis-related genes/proteins (ALP, COL-1, RUNX-2, OPN and OCN) of hBMSCs. In vivo assay with infection and non-infection bone-defect model reveals that the FP-engineered implant can kill 99.63% of S. aureus, and simultaneously promote vascularization and osseointegration. It is believed that this study presents an excellent strategy for developing "statically-versatile" orthopedic implants.

Pristine and Antibiotic-Loaded Nanosheets/Nanoneedles-Based Boron Nitride Films as a Promising Platform to Suppress Bacterial and Fungal Infections

In recent years, bacteria inactivation during their direct physical contact with surface nanotopography has become one of the promising strategies for fighting infection. Contact-killing ability has been reported for several nanostructured surfaces, e.g., black silicon, carbon nanotubes, zinc oxide nanorods, and copper oxide nanosheets. Herein, we demonstrate that Gram-negative antibiotic-resistant Escherichia coli (E. coli) bacteria are killed as a result of their physical destruction while contacting nanostructured h-BN surfaces. BN films, made of spherical nanoparticles formed by numerous nanosheets and nanoneedles with a thickness <15 nm, have been obtained through a reaction of ammonia with amorphous boron. The contact-killing bactericidal effect of BN nanostructures has been compared with a toxic effect of gentamicin released from them. For a wider protection against bacterial and fungal infection, the films have been saturated with a mixture of gentamicin and amphotericin B. Such BN films demonstrate a high antibiotic/antimycotic agent loading capacity and a fast initial and sustained release of therapeutic agents for 170-260 h depending on the loaded dose. The pristine BN films possess high antibacterial activity against E. coli K-261 strain at their initial concentration of 10⁴ cells/mL, attaining >99% inactivation of colony forming units after 24 h, same as gentamicin-loaded (150 μg/cm²) BN sample. The BN films loaded with a mixture of gentamicin (150 and 300 μg/cm²) and amphotericin B (100 μg/cm²) effectively inhibit the growth of E. coli K-261 and Neurospora crassa strains. During immersion in the normal saline solution, the BN film generates reactive oxygen species (ROS), which can lead to accelerated oxidative stress at the site of physical cell damage. The obtained results are valuable for further development of nanostructured surfaces having contact killing, ROS, and biocide release abilities.

Chitosan-based drug delivery systems: From synthesis strategy to osteomyelitis treatment - A review

Osteomyelitis is a complex disease in orthopedics mainly caused by bacterial pathogens invading bone or bone marrow. The treatment of osteomyelitis is highly difficult and it is a major challenge in orthopedic surgery. The long-term systemic use of antibiotics may lead to antibiotic resistance and has limited effects on eradicating local biofilms. Localized antibiotic delivery after surgical debridement can overcome the problem of antibiotic resistance and reduce systemic toxicity. Chitosan, a special cationic polysaccharide, is a product extracted from the deacetylation of chitin. It has numerous advantages, such as nontoxicity, biocompatibility, and biodegradability. Recently, chitosan has attracted significant attention in bacterial inhibition and drug delivery. Because chitosan contains many functional bioactive groups conducive to chemical reaction and modification, some chitosan-based biomaterials have been applied as the local antibiotic delivery systems in the treatment of osteomyelitis. This review aims to introduce recent advances in the biomedical applications of chitosan-based drug delivery systems in osteomyelitis treatment and to highlight the perspectives for further studies.

Hyaluronic Acid as a Component of Natural Polymer Blends for Biomedical Applications: A Review

In this review, we provide a report on recent studies in the field of research on the blends of hyaluronic acid with other natural polymers, namely collagen and chitosan. Hyaluronic acid has attracted significant interest in biomedical and cosmetic applications due to its interesting properties. In recent years, blends of hyaluronic acid with other polymers have been studied for new materials development. New materials may show improved properties that are important in the biomedical applications and in cosmetic preparations. In this review paper, the structure, preparation, and properties of hyaluronic acid blends with collagen and chitosan have been discussed and examples of new materials based on such blends have been presented. A comparison of the currently available information in the field has been shown. Future aspects in the field of hyaluronic acid blends and their applications in the biomedical and cosmetic industry have also been mentioned.

Layer-By-Layer Nanocoating of Antiviral Polysaccharides on Surfaces to Prevent Coronavirus Infections

In 2020, the world is being ravaged by the coronavirus, SARS-CoV-2, which causes a severe respiratory disease, Covid-19. Hundreds of thousands of people have succumbed to the disease. Efforts at curing the disease are aimed at finding a vaccine and/or developing antiviral drugs. Despite these efforts, the WHO warned that the virus might never be eradicated. Countries around the world have instated non-pharmaceutical interventions such as social distancing and wearing of masks in public to curb the spreading of the disease. Antiviral polysaccharides provide the ideal opportunity to combat the pathogen via pharmacotherapeutic applications. However, a layer-by-layer nanocoating approach is also envisioned to coat surfaces to which humans are exposed that could harbor pathogenic coronaviruses. By coating masks, clothing, and work surfaces in wet markets among others, these antiviral polysaccharides can ensure passive prevention of the spreading of the virus. It poses a so-called "eradicate-in-place" measure against the virus. Antiviral polysaccharides also provide a green chemistry pathway to virus eradication since these molecules are primarily of biological origin and can be modified by minimal synthetic approaches. They are biocompatible as well as biodegradable. This surface passivation approach could provide a powerful measure against the spreading of coronaviruses.

Hyaluronic Acid and Controlled Release: A Review

Hyaluronic acid (HA) also known as hyaluronan, is a natural polysaccharide—an anionic, non-sulfated glycosaminoglycan—commonly found in our bodies. It occurs in the highest concentrations in the eyes and joints. Today HA is used during certain eye surgeries and in the treatment of dry eye disease. It is a remarkable natural lubricant that can be injected into the knee for patients with knee osteoarthritis. HA has also excellent gelling properties due to its capability to bind water very quickly. As such, it is one the most attractive controlled drug release matrices and as such, it is frequently used in various biomedical applications. Due to its reactivity, HA can be cross-linked or conjugated with assorted bio-macromolecules and it can effectively encapsulate several different types of drugs, even at nanoscale. Moreover, the physiological significance of the interactions between HA and its main membrane receptor, CD44 (a cell-surface glycoprotein that modulates cell–cell interactions, cell adhesion and migration), in pathological processes, e.g., cancer, is well recognized and this has resulted in an extensive amount of studies on cancer drug delivery and tumor targeting. HA acts as a therapeutic but also as a tunable matrix for drug release. Thus, this review focuses on controlled or sustained drug release systems assembled from HA and its derivatives. More specifically, recent advances in controlled release of proteins, antiseptics, antibiotics and cancer targeting drugs from HA and its derivatives were reviewed. It was shown that controlled release from HA has many benefits such as optimum drug concentration maintenance, enhanced therapeutic effects, improved efficiency of treatment with less drug, very low or insignificant toxicity and prolonged in vivo release rates.

The application of hyaluronic acid in bone regeneration

Hyaluronic acid (HA) exists naturally as an important component of the extracellular matrix (ECM) in the human body. In recent decades, HA has been widely used in bone regeneration, and is currently a popular topic, particularly in the craniofacial and dental fields. From maxilla augmentation to craniofacial bone trauma, there is now a large demand for bone regenerative therapy. Serving as a cell-seeding scaffold or a carrier for bioactive components, hyaluronic acid-incorporated scaffolds and carriers in bone regeneration can be fabricated into either rigid or colloidal forms. Since the type of material used is a critical factor in the biological properties of a scaffold, HA derivatives or HA-incorporated composite scaffolds have shown excellent potential for improving osteogenesis and mineralization. Furthermore, in order to better enhance osteogenesis, local delivery carriers based on hyaluronic acid derivatives, rather than specifically serving as scaffolds, can be established by loading different osteoinductive or osteogenetic components and acquiring different release patterns. Such osteoinductive carriers immobilized on implant surfaces are also effective in improving osseointegration. Thus, as such a competent biomaterial, hyaluronic acid should be considered a promising tool in bone regeneration.

Antibacterial Coatings for Improving the Performance of Biomaterials

Biomedical devices have become essential in the health care. Every day, an enormous number of these devices are used or implanted in humans. In this context, the bacterial contamination that could be developed in implanted devices is critical since it is estimated that infections kill more people than other medical causes. Commonly, these infections are treated with antibiotics, but the biofilm formation on implant surfaces could significantly reduce the effectiveness of these antibiotics since bacteria inside the biofilm is protected from the drug. In some cases, a complete removal of the implant is necessary in order to overcome the infection. In this context, antibacterial coatings are considered an excellent strategy to avoid biofilm formation and, therefore, mitigate the derived complications. In this review, the main biomaterials used in biomedical devices, the mechanism of biofilm formation, and the main strategies for the development of antibacterial coatings, are reviewed. Finally, the main polymer-based strategies to develop antibacterial coatings are summarized, with the aim of these coatings being to avoid the bacteria proliferation by controlling the antibacterial mechanisms involved and enhancing long-term stability.

TiO2 doped chitosan/hydroxyapatite/halloysite nanotube membranes with enhanced mechanical properties and osteoblast-like cell response for application in bone tissue engineering

The current therapeutic strategies for healing bone defects commonly suffer from the occurrence of bacterial contamination on the graft, resulting in nonunion in the segmental bone defects and the requirement for secondary surgery to remove or sterilize the primary graft. A membrane with enhanced anti-bacterial efficacy, mechanical strength and osteoconductivity would represent an improvement in the therapeutic strategy for guided bone regeneration. The present study aims to optimize the content of halloysite nanotubes (HNTs) and TiO₂ in the polymer matrix of chitosan (CTS) with a constant amount of nano-hydroxyapatite (5%) with the objective of mimicking the mechanical and biological microenvironment of the natural bone extracellular matrix with enhanced anti-bacterial efficacy. HNTs are a low-cost alternative to MWNCTs for enhancing the mechanical properties and anti-bacterial efficacy of the composite. From the first stage of the study, it was concluded that the membranes possessed enhanced mechanical properties and optimum biological properties at 7.5% (w/w) loading of HNTs in the composite. In the second stage of this investigation, we studied the effect of the addition of TiO₂ nanoparticles (NPs) and TiO₂ nanotubes (NTs) in small amounts to the CTS/n-HAP/HNT nanocomposite at 7.5% HNT loading, with an aim to augment the anti-bacterial efficacy and osteoconductivity of this mechanically strong membrane. The study revealed a significant enhancement in the anti-bacterial efficacy, osteoblast-like MG-63 cell proliferation and ALP expression with the addition of TiO₂ NTs. The CHH-TiT membrane successfully inhibited the S. aureus and E. coli growth within 16 hours and simultaneously assisted the enhanced proliferation of osteoblast-like cells on its surface. The study supports the potential exploitation of CHH-TiT (7.5% HNT & 0.2% TiO₂ NT) membranes as a template for guided bone tissue regeneration.

This two-stage study aims to optimize the amount of halloysite nanotubes and TiO₂ in a chitosan/nano-hydroxyapatite composite to tailor the mechanical and biological properties for application in bone tissue engineering.