Development of chitosan-vancomycin antimicrobial coatings on titanium implants

Chitosan-based materials for dental implantology: A comprehensive review

Chitosan, a versatile biopolymer, has gained recognition in the discipline of dental implantology due to possessing salient properties. This comprehensive review explores the potential of chitosan in dental implants, focusing on its biocompatibility, bioactivity, and the various chitosan-based materials that have been utilized for dental implant therapy. The review also highlights the importance of surface treatment in dental implants to enhance osseointegration and inhibit bacterial biofilm formation. Additionally, the chemical structure, properties, and sources of chitosan are described, along with its different structural forms. The characteristics of chitosan particularly color, molecular weight, viscosity, and degree of deacetylation are discussed about their influence on its applications. This review provides valuable insights into the promising utilization of polymeric chitosan in enhancing the success and functionality of dental implants. This study highlights the potential applications of chitosan in oral implantology. Chitosan possesses various advantageous properties, including muco-adhesiveness, hemostatic action, biocompatibility, biodegradability, bioactivity, and antibacterial and antifungal activities, which enhance its uses in dental implantology. However, it has limited aqueous solubility at the physiological pH, which sometimes restricts its biological application, but this problem can be overcome by using modified chitosan or chitosan derivatives, which have also shown encouraging results. Recent research suggests that chitosan may act as a promising material for coating titanium-based implants, improving osteointegration together with antibacterial properties.

Towards Polycaprolactone-Based Scaffolds for Alveolar Bone Tissue Engineering: A Biomimetic Approach in a 3D Printing Technique

The alveolar bone is a unique type of bone, and the goal of bone tissue engineering (BTE) is to develop methods to facilitate its regeneration. Currently, an emerging trend involves the fabrication of polycaprolactone (PCL)-based scaffolds using a three-dimensional (3D) printing technique to enhance an osteoconductive architecture. These scaffolds are further modified with hydroxyapatite (HA), type I collagen (CGI), or chitosan (CS) to impart high osteoinductive potential. In conjunction with cell therapy, these scaffolds may serve as an appealing alternative to bone autografts. This review discusses research gaps in the designing of 3D-printed PCL-based scaffolds from a biomimetic perspective. The article begins with a systematic analysis of biological mineralisation (biomineralisation) and ossification to optimise the scaffold's structural, mechanical, degradation, and surface properties. This scaffold-designing strategy lays the groundwork for developing a research pathway that spans fundamental principles such as molecular dynamics (MD) simulations and fabrication techniques. Ultimately, this paves the way for systematic in vitro and in vivo studies, leading to potential clinical applications.

Effect of electrochemical oxidation and drug loading on the antibacterial properties and cell biocompatibility of titanium substrates

A combination of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{ TiO}}_{2}$$\end{document}TiO2 nanotube array (TON) and controlled drug release system is employed to provide enhanced surface properties of titanium implants. Electrochemical anodization process is used to generate TON for introducing, vancomycin, an effective antibacterial drug against Staphylococcusaureus. TON loaded vancomycin is then coated with a number of layers of 10% gelatin using spin coating technique. The gelatin film is reinforced with graphene oxide (GO) nanoparticles to improve the surface bioactivity. The surface of the samples is characterized by field emission electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and contact angle measurement. The results illustrate that the TON was constructed and vancomycin molecules are successfully loaded. The drug release study shows that the amount of released vancomycin is controlled by the thickness of gelatin layers. With an increase in gelatin film layers from 3 to 7, the release of vancomycin in the burst release phase decreased from 58 to 31%, and sustained release extended from 10 to 17 days. The addition of GO nanoparticles seems to reduce drug release in from 31 to 22% (burst release phase) and prolonged drug release (from 17 to 19 days). MTT assay indicates that samples show no cytotoxicity, and combination of GO nanoparticles with gelatin coating could highly promote MG63 cell proliferation. Soaking the samples in SBF solution after 3 and 7 days demonstrates that hydroxy apatite crystals were deposited on the TON surface with GO-gelatin coating more than surface of TON with gelatin. Moreover, based on the results of disc diffusion assay, both samples (loaded with Vancomycin and coated with gelatin and gelatin-GO) with the inhibition zones equaled to 20 mm show effective antibacterial properties against S. aureus. The evidence demonstrates that titania nanotube loaded with vancomycin and coated with gelatin-GO has a great potential for general applicability to the orthopedic implant field.

Latest Trends in Surface Modification for Dental Implantology: Innovative Developments and Analytical Applications

An increase in the world population and its life expectancy, as well as the ongoing concern about our physical appearance, have elevated the relevance of dental implantology in recent decades. Engineering strategies to improve the survival rate of dental implants have been widely investigated, focusing on implant material composition, geometry (usually guided to reduce stiffness), and interface surrounding tissues. Although efforts to develop different implant surface modifications are being applied in commercial dental prostheses today, the inclusion of surface coatings has gained special interest, as they can be tailored to efficiently enhance osseointegration, as well as to reduce bacterial-related infection, minimizing peri-implantitis appearance and its associated risks. The use of biomaterials to replace teeth has highlighted the need for the development of reliable analytical methods to assess the therapeutic benefits of implants. This literature review considers the state-of-the-art strategies for surface modification or coating and analytical methodologies for increasing the survival rate for teeth restoration.

Classification and research progress of implant surface antimicrobial techniques

Due to the good biocompatibility and ideal mechanical property, titanium implants have been widely used in dental clinic and orthopedic surgery. However, bacteria induced infection can cause per-implant inflammation and decrease the success rate of implant surgery. Therefore, developing antimicrobial techniques is essential to successful application of titanium implants. Many surface antimicrobial techniques, including antimicrobial coating and surface modifications, have been explored and they always exert antimicrobial effect by reducing bacterial adhesion, inhibiting their metabolism, or destructing cell structure. In this paper, different surface antimicrobial techniques and their recent research progress are reviewed to provide a brief insight on this area.

Titanium Implants and Local Drug Delivery Systems Become Mutual Promoters in Orthopedic Clinics

Titanium implants have always been regarded as one of the gold standard treatments for orthopedic applications, but they still face challenges such as pain, bacterial infections, insufficient osseointegration, immune rejection, and difficulty in personalizing treatment in the clinic. These challenges may lead to the patients having to undergo a painful second operation, along with increased economic burden, but the use of drugs is actively solving these problems. The use of systemic drug delivery systems through oral, intravenous, and intramuscular injection of various drugs with different pharmacological properties has effectively reduced the levels of inflammation, lowered the risk of endophytic bacterial infection, and regulated the progress of bone tumor cells, processing and regulating the balance of bone metabolism around the titanium implants. However, due to the limitations of systemic drug delivery systems-such as pharmacokinetics, and the characteristics of bone tissue in the event of different forms of trauma or disease-sometimes the expected effect cannot be achieved. Meanwhile, titanium implants loaded with drugs for local administration have gradually attracted the attention of many researchers. This article reviews the latest developments in local drug delivery systems in recent years, detailing how various types of drugs cooperate with titanium implants to enhance antibacterial, antitumor, and osseointegration effects. Additionally, we summarize the improved technology of titanium implants for drug loading and the control of drug release, along with molecular mechanisms of bone regeneration and vascularization. Finally, we lay out some future prospects in this field.

A Novel Strategy to Coat Dopamine-Functionalized Titanium Surfaces With Agarose-Based Hydrogels for the Controlled Release of Gentamicin

Introduction

The use of spinal implants for the treatment of back disorders is largely affected by the insurgence of infections at the implantation site. Antibacterial coatings have been proposed as a viable solution to limit such infections. However, despite being effective at short-term, conventional coatings lack the ability to prevent infections at medium and long-term. Hydrogel-based drug delivery systems may represent a solution controlling the release of the loaded antibacterial agents while improving cell integration. Agarose, in particular, is a biocompatible natural polysaccharide known to improve cell growth and already used in drug delivery system formulations. In this study, an agarose hydrogel-based coating has been developed for the controlled release of gentamicin (GS).

Methods

Sand blasted Ti6Al4V discs were grafted with dopamine (DOPA) solution. After, GS loaded agarose hydrogels have been produced and additioned with tannic acid (TA) and calcium chloride (CaCl₂) as crosslinkers. The different GS-loaded hydrogel formulations were deposited on Ti6Al4V-DOPA surfaces, and allowed to react under UV irradiation. Surface topography, wettability and composition have been analyzed with profilometry, static contact angle measurement, XPS and FTIR spectroscopy analyses. GS release was performed under pseudo-physiological conditions up to 28 days and the released GS was quantified using a specific ELISA test. The cytotoxicity of the produced coatings against human cells have been tested, along with their antibacterial activity against S. aureus bacteria.

Results

A homogeneous coating was obtained with all the hydrogel formulations. Moreover, the coatings presented a hydrophilic behavior and micro-scale surface roughness. The addition of TA in the hydrogel formulations showed an increase in the release time compared to the normal GS-agarose hydrogels. Moreover, the GS released from these gels was able to significantly inhibit S. aureus growth compared to the GS-agarose hydrogels. The addition of CaCl₂ to the gel formulation was able to significantly decrease cytotoxicity of the TA-modified hydrogels.

Conclusions

Due to their surface properties, low cytotoxicity and high antibacterial effects, the hereby proposed gentamicin-loaded agarose-hydrogels provide new insight, and represent a promising approach for the surface modification of spinal implants, greatly impacting their application in the orthopedic surgical scenario.

The effect of coating chitosan on Porphyromonas gingivalis biofilm formation in the surface of orthodontic mini-implant

Infection is the main problem for the failure of orthodontic mini-implant. Modern prevention of infection is now focused on local antibacterial coatings on implant devices. Chitosan is biocompatible and has antibacterial properties. Azithromycin is a synthetic antibiotic with immunomodulatory properties in which it has an advantage over the rest of antibiotics. This study aimed to evaluate the effect coating chitosan on the orthodontic mini-implant in Porphyromonas gingivalis biofilm formation. This is an experimental study using 25 orthodontic mini-implants. Five samples were coated with chitosan, 5 samples were coated with chitosan-azithromycin, 5 samples were coated with azithromycin, 5 samples were uncoated, and 5 samples were uncoated and were not exposed to P. gingivalis. P. gingivalis biofilms on the surface of the orthodontic mini-implant were observed after 24 h of incubation. P. gingivalis biofilm mass inhibition was highest in the azithromycin-treated group, followed by chitosan + azithromycin and chitosan only. The one-way ANOVA statistic test and post hoc Bonferroni statistic test of P. gingivalis biofilm mass show a significant difference between and within groups of experiments (P < 0.05). The Pearson correlation test with a value of R = +0.88, indicated that the bacterial viability count and the biofilm mass have a strong positive correlation. In conclusion, orthodontic mini-implant coated with chitosan, chitosan with azithromycin, or azithromycin only effectively suppressed P. gingivalis biofilm formation.

A functional coating to enhance antibacterial and bioactivity properties of titanium implants and its performance in vitro

Bacterial infections and lack of osseointegration may negatively affect the success of titanium (Ti) implants. In the present study, a functional coating composed of chitosan (CS) microspheres and nano hydroxyapatite (nHA) was prepared to obtain antimicrobial Ti implants with enhanced bioactivity. First, the chitosan microspheres were fixed to Ti surfaces activated by alkali and heat treatment, then nHA coatings were precipitated onto these surfaces. Ciprofloxacin was loaded into the microspheres using two different procedures; encapsulation and diffusion. Scanning electron microscopy micrographs of the modified Ti surfaces showed that the coating was successfully deposited onto the Ti surfaces and stable for 30 days in PBS. The drug was completely released from free microspheres loaded by encapsulation in 21 days whereas only 89% release was observed after immobilization. The burst release also decreased from ca. 55% to ca. 35%. The release was further reduced following the nHA precipitation. The modified Ti surfaces showed antimicrobial activity based on the bacterial time-kill assay using S. aureus, but the efficiency was affected by both nHA precipitation and drug loading strategy. Highest antimicrobial activity was seen in the samples without nHA layer, and when the drug was loaded by diffusion. Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed that nHA on the surface enhanced HA growth in simulated body fluid for 3 weeks, showing increased osseointegration potential. Therefore, the proposed coating may be used to prevent Ti implant failure originated from bacterial infection and/or low bioactivity.

Electrophoretic Deposition of Gentamicin-Loaded ZnHNTs-Chitosan on Titanium

There is a need for titanium (Ti), an antimicrobial implant coating that provides sustained protection against bacterial infection. Chitosan (CS) coatings, combined with halloysite nanotubes (HNTs), are an attractive solution due to the inherent biocompatibility of halloysite, its ability to provide sustained drug release, and the antimicrobial properties of CS. In this study, the electrodeposition (EPD) method was used to coat titanium foil with CS blended with zinc-coated HNTs (ZnHNTs) and pre-loaded with the antibiotic gentamicin. The CS-ZnHNTs-gentamycin sulfate (GS) coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and UV-visible spectroscopy. The coatings were further examined for their ability to sustain GS release, resist bacterial colonization and growth, and prevent biofilm formation. The CS-ZnHNTs-GS coatings were cytocompatible, exhibited significant antimicrobial properties, and supported pre-osteoblast cell proliferation. Hydroxyapatite also formed on the coatings after immersion in simulated body fluid. While the focus in this study was on zinc-coated HNTs doped into CS, our design offers tunability, as different metals can be coated onto the HNT surface and different drugs or growth factors loaded into the HNT lumen. Our results, and the potential for customization, suggest that these coatings have potential in the construction of an array of infection-resistant implant coatings.

Antimicrobial Prosthetic Surfaces in the Oral Cavity-A Perspective on Creative Approaches

Replacement of missing teeth is an essential component of comprehensive dental care for patients suffering of edentulism. A popular option is implant-supported restorations. However, implant surfaces can become colonized with polymicrobial biofilms containing Candida species that may compromise peri-implant health. To prevent this, implant components may be treated with a variety of coatings to create surfaces that either repel the attachment of viable microorganisms or kill microorganisms on contact. These coatings may consist of nanoparticles of pure elements (more commonly silver, copper, and zinc), sanitizing agents and disinfectants (quaternary ammonium ions and chlorhexidine), antibiotics (cefalotin, vancomycin, and gentamicin), or antimicrobial peptides (AMPs). AMPs in bioactive coatings have a number of advantages. They elicit a protective action against pathogens, inhibit the formation of biofilms, are less toxic to host tissues, and do not prompt inflammatory responses. Furthermore, many of these coatings may involve unique delivery systems to direct their antimicrobial capacity against pathogens, but not commensals. Coatings may also contain multiple antimicrobial substances to widen antimicrobial activity across multiple microbial species. Here, we compiled relevant information about a variety of creative approaches used to generate antimicrobial prosthetic surfaces in the oral cavity with the purpose of facilitating implant integration and peri-implant tissue health.

Customized Therapeutic Surface Coatings for Dental Implants

Dental implants are frequently used to support fixed or removable dental prostheses to replace missing teeth. The clinical success of titanium dental implants is owed to the exceptional biocompatibility and osseointegration with the bone. Therefore, the enhanced therapeutic effectiveness of dental implants had always been preferred. Several concepts for implant coating and local drug delivery had been developed during the last decades. A drug is generally released by diffusion-controlled, solvent-controlled, and chemical controlled methods. Although a range of surface modifications and coatings (antimicrobial, bioactive, therapeutic drugs) have been explored for dental implants, it is still a long way from designing sophisticated therapeutic implant surfaces to achieve the specific needs of dental patients. The present article reviews various interdisciplinary aspects of surface coatings on dental implants from the perspectives of biomaterials, coatings, drug release, and related therapeutic effects. Additionally, the various types of implant coatings, localized drug release from coatings, and how released agents influence the bone–implant surface interface characteristics are discussed. This paper also highlights several strategies for local drug delivery and their limitations in dental implant coatings as some of these concepts are yet to be applied in clinical settings due to the specific requirements of individual patients.

Synthesis and characterization of silica-chitosan hybrid materials as antibacterial coatings for titanium implants

To avoid dental implant-related infections and to promote the osseointegration of titanium implants, the application of silicon and chitosan containing coatings is proposed. Silicon is a well-known osteogenic element and chitosan was selected to confer the antibacterial properties. The synthesis of hybrid silica-chitosan coatings using the sol-gel process is presented and the characterization using ²⁹Si-NMR to verify the correct formation of the network is discussed. The ¹³C NMR spectroscopy was used to confirm the covalent union between chitosan and the silicon network. Hydrolytic degradation and silicon release studies showed the effective silicon release from the hybrids and, hence, the possibility to promote bone formation. The introduction of different amounts of chitosan and tetraethyl orthosilicate (TEOS) modulated the Si release. The analysis of cell cultures in vitro demonstrated that the hybrid coatings were not cytotoxic and promoted cell proliferation on their surfaces. The coatings containing 5%-10% chitosan had substantial antibacterial properties.

The immobilization of antibiotic-loaded polymeric coatings on osteoarticular Ti implants for the prevention of bone infections

Implant-associated infections in orthopaedic surgeries are very critical as they may hinder bone healing, cause implant failure and even progress to osteomyelitis. Drug-eluting implants for local delivery of antibiotics at surgical sites are thought to be promising in preventing infections. Herein, the antibiotic vancomycin was encapsulated in a poly(ethylene glycol) (PEG)-based hydrogel film that was covalently bound to Ti implants and subsequently covered by a PEG-poly(lactic-co-caprolactone) (PEG-PLC) membrane. Additionally, crosslinked starch (CSt) was mixed with the hydrogel because its porous microstructure is able to inhibit hydrogel swelling and thus slow down drug release. The release behavior could be regulated by the drug loading and the coating thickness. The vancomycin-loaded Ti implants showed no initial burst release, offering a sustained drug release for nearly 3 weeks in vitro and more than 4 weeks in vivo. In a rabbit model of S. aureus infection, the implants with a 4 mg vancomycin loading significantly reduced the inflammatory reaction and exhibited a good antimicrobial capability. The immobilization of the antibiotic-loaded polymeric coatings on orthopaedic implants can offer a sustainable drug release with no initial burst release and maintain an effective concentration for a longer time, so it is expected to be an effective strategy to treat and prevent local bone infections.

Marine polysaccharides: therapeutic efficacy and biomedical applications

The ocean contains numerous marine organisms, including algae, animals, and plants, from which diverse marine polysaccharides with useful physicochemical and biological properties can be extracted. In particular, fucoidan, carrageenan, alginate, and chitosan have been extensively investigated in pharmaceutical and biomedical fields owing to their desirable characteristics, such as biocompatibility, biodegradability, and bioactivity. Various therapeutic efficacies of marine polysaccharides have been elucidated, including the inhibition of cancer, inflammation, and viral infection. The therapeutic activities of these polysaccharides have been demonstrated in various settings, from in vitro laboratory-scale experiments to clinical trials. In addition, marine polysaccharides have been exploited for tissue engineering, the immobilization of biomolecules, and stent coating. Their ability to detect and respond to external stimuli, such as pH, temperature, and electric fields, has enabled their use in the design of novel drug delivery systems. Thus, along with the promising characteristics of marine polysaccharides, this review will comprehensively detail their various therapeutic, biomedical, and miscellaneous applications.

Retrospective comparison of postoperative infection and bone union between late and immediate intramedullary nailing of Gustilo grades I, II, and IIIA open tibial shaft fractures

Background

The optimal method of skeletal stabilization is still controversial. Therefore, we examined the clinical outcomes associated with late (L) versus immediate intramedullary nailing (IMN).

Methods

This was a retrospective comparative study of trauma registry data from an emergency medical care center (university hospital). We examined 85 open tibial shaft fractures (85 patients) treated with L or immediate (I) IMN from January 2004 to December 2010. The L and I groups comprised 37 (33 men, 4 women) and 48 (44 men, 4 women) patients, respectively. The postoperative infection rate, time to bone union, and delayed union/non-union were evaluated.

Results

The mean ages at the time of trauma in the L and I groups were 41.8 (18-79) and 42.0 (18-71) years, respectively; the mean follow-up periods were 15.0 (6-39) and 18.3 (8-36) months, respectively. A higher rate of postoperative infection was found in the L group than in the I group (p=0.004). Superficial/deep infection developed at a higher rate in the L group than in the I group (p=0.042 and 0.045, respectively). Among patients with Gustilo grade IIIA fractures, postoperative infection occurred at a higher rate in the L group than in the I group (p=0.008). However, the delayed union rate, non-union rate, and time to bone union were not significantly different between the groups.

Conclusions

Gustilo grade IIIA fractures had a high infection rate, which is likely due to various factors, including pin-site infection after external fixation. We think that I IMN is safer than L IMN, and it should be the treatment of choice.

Level of evidence

Retrospective comparative study, level III.

Reference positions for transosseous elements in femur: A cadaveric study

INTRODUCTION

During external fixator treatment, displacement of soft tissue at pin sites may cause infection and contracture. Due to surrounding soft tissue thickness, the femur is especially susceptible to severe complications. However, standard textbooks demonstrate only how major neurovascular bundles should be avoided. This study is the first cadaver study investigating which pin sites within safe zones exhibit minimal soft tissue displacement.

METHODS

To identify the clear direction of any pin, the femoral shaft was divided into eight levels, from I to VIII. The transverse sections at each level were further divided into 12 radial positions analogous to a clock face, where the anterior direction was assigned twelve o'clock, the medial three, etc. Fifteen adult cadavers were used. Twelve wires were aligned radially on the examined ring, and were dyed at each point toward the soft tissue. Each soft tissue displacement was measured by marking the surface before and after three particular joint motions, namely hip flexion (0-90°), abduction (0-45), and knee flexion (0-90). The same procedures were performed in three layers of soft tissue: skin, fascia, and muscle.

RESULTS

The average displacement was determined in 89 directions excluding the groin part, upon three joint motions. The three layers of skin, fascia, and muscle showed similar data curves. Greater displacements were seen at juxta-articular areas than at the mid-diaphyseal. The data curve exhibited a bimodal characteristic, with larger displacements at the extension and flexion directions. The amount of displacement at 6 o'clock was large at the levels near the hip joint, whereas at 12 o'clock, it was large near the knee joint.

DISCUSSION

"Reference positions" for transosseous elements were defined within zones absent neurovascular bundles, indicating 30 sites with minimal tissue displacement. Three or four directions at each level were chosen: I.9-11, II.9-11, III.8-11, IV.8-11, V.7-10, VI.3, 7-9, VII.3, 4, 8, 9, and VIII.3, 4, 8, 9. The anterolateral aspect near the hip joint and the posterolateral aspect near the knee tended to be chosen. They may prove useful in perioperative practice.

Improvement of tribological and anti-corrosive performance of titanium surfaces coated with dicationic imidazolium-based ionic liquids

In this work, dicationic imidazolium-based ionic liquids (ILs) with amino acid anionic moieties were employed as coatings for commercially pure titanium (Ti) surfaces.

Ionic Liquid Coatings for Titanium Surfaces: Effect of IL Structure on Coating Profile

Dicationic imidazolium-based ionic liquids (ILs) having bis(trifluoromethylsulfonyl)imide (NTf2) and amino acid-based (methionine and phenylalanine) anionic moieties were synthesized and used to coat titanium surfaces using a dip-coating technique. Dicationic moieties with varying alkyl chains (8 and 10 carbons) and anions with distinct characteristics were selected to understand the influence of IL structural features on deposition profile. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used in this study to help elucidate intermolecular interactions within ILs as well as between ILs and TiO2 surfaces and to investigate IL coating morphology. Charge concentration on IL moieties, as well as the presence of functional groups that can interact via hydrogen bond, such as carboxylate and amino groups, were observed to influence the deposition profile. ILs containing amino acids as the anionic moiety were observed to interact strongly with TiO2, which resulted in more pronounced changes in Ti 2p binding energy. The higher hydrophobicity of the IL having NTf2 as the anionic moiety resulted in higher adhesion strength between the IL coating and TiO2.

Chitosan coatings to control release and target tissues for therapeutic delivery

The natural biopolymer chitosan has versatile applications in therapeutic delivery. Coating drug delivery matrices or biomaterials with chitosan offers several advantages in drug delivery, including control of drug release, slowing degradation rate and improving biocompatibility. Advanced uses of chitosan in coating form include targeting drug delivery vehicles to specific tissue as well as providing a stimulus-controlled release response. The present review summarizes the current applications of chitosan coatings in the context of different biomaterial delivery technologies, as well as future directions of chitosan coatings for drug delivery technologies under development.

Novel Antibiotic-loaded Point-of-care Implant Coating Inhibits Biofilm

BACKGROUND

Orthopaedic biomaterials are susceptible to biofilm formation. A novel lipid-based material has been developed that may be loaded with antibiotics and applied as an implant coating at point of care. However, this material has not been evaluated for antibiotic elution, biofilm inhibition, or in vivo efficacy.

QUESTIONS/PURPOSES

(1) Do antibiotic-loaded coatings inhibit biofilm formation? (2) Is the coating effective in preventing biofilm in vivo?

METHODS

Purified phosphatidylcholine was mixed with 25% amikacin or vancomycin or a combination of 12.5% of both. A 7-day elution study for coated titanium and stainless steel coupons was followed by turbidity and zone of inhibition assays against Staphylococcus aureus and Pseudomonas aeruginosa. Coupons were inoculated with bacteria and incubated 24 hours (N = 4 for each test group). Microscopic images of biofilm were obtained. After washing and vortexing, attached bacteria were counted. A mouse biofilm model was modified to include coated and uncoated stainless steel wires inserted into the lumens of catheters inoculated with a mixture of S aureus or P aeruginosa. Colony-forming unit counts (N = 10) and scanning electron microscopy imaging of implants were used to determine antimicrobial activity.

RESULTS

Active antibiotics with colony inhibition effects were eluted for up to 6 days. Antibiotic-loaded coatings inhibited biofilm formation on in vitro coupons (log-fold reductions of 4.3 ± 0.4 in S aureus and 3.1 ± 0 for P aeruginosa in phosphatidylcholine-only coatings, 5.6 ± 0 for S aureus and 3.1 ± 0 for P aeruginosa for combination-loaded coatings, 5.5 ± 0.3 for S aureus in vancomycin-loaded coatings, and 3.1 ± 0 for P aeruginosa for amikacin-loaded coatings (p < 0.001 for all comparisons of antibiotic-loaded coatings against uncoated controls for both bacterial strains, p < 0.001 for comparison of antibiotic-loaded coatings against phosphatidylcholine only for S aureus, p = 0.54 for comparison of vancomycin versus combination coating in S aureus, P = 0.99 for comparison of antibiotic- and unloaded phosphatidylcholine coatings in P aeruginosa). Similarly, antibiotic-loaded coatings reduced attachment of bacteria to wires in vivo (log-fold reduction of 2.54 ± 0; p < 0.001 for S aureus and 0.83 ± 0.3; p = 0.112 for P aeruginosa).

CONCLUSIONS

Coatings deliver active antibiotics locally to inhibit biofilm formation and bacterial growth in vivo. Future evaluations will include orthopaedic preclinical models to confirm therapeutic efficacy.

CLINICAL RELEVANCE

Clinical applications of local drug delivery coating could reduce the rate of implant-associated infections.

Chitosan/siRNA functionalized titanium surface via a layer-by-layer approach for in vitro sustained gene silencing and osteogenic promotion

Titanium surface modification is crucial to improving its bioactivity, mainly its bone binding ability in bone implant materials. In order to functionalize titanium with small interfering RNA (siRNA) for sustained gene silencing in nearby cells, the layer-by-layer (LbL) approach was applied using sodium hyaluronate and chitosan/siRNA (CS/siRNA) nanoparticles as polyanion and polycation, respectively, to build up the multilayered film on smooth titanium surfaces. The CS/siRNA nanoparticle characterization was analyzed first. Dynamic contact angle, atomic force microscopy, and scanning electron microscopy were used to monitor the layer accumulation. siRNA loaded in the film was quantitated and the release profile of film in phosphate-buffered saline was studied. In vitro knockdown effect and cytotoxicity evaluation of the film were investigated using H1299 human lung carcinoma cells expressing green fluorescent protein (GFP). The transfection of human osteoblast-like cell MG63 and H1299 were performed and the osteogenic differentiation of MG63 on LbL film was analyzed. The CS/siRNA nanoparticles exhibited nice size distribution. During formation of the film, the surface wettability, topography, and roughness were alternately changed, indicating successful adsorption of the individual layers. The scanning electron microscope images clearly demonstrated the hybrid structure between CS/siRNA nanoparticles and sodium hyaluronate polymer. The cumulated load of siRNA increased linearly with the bilayer number and, more importantly, a gradual release of the film allowed the siRNA to be maintained on the titanium surface over approximately 1 week. In vitro transfection revealed that the LbL film-associated siRNA could consistently suppress GFP expression in H1299 without showing significant cytotoxicity. The LbL film loading with osteogenic siRNA could dramatically increase the osteogenic differentiation in MG63. In conclusion, LbL technology can potentially modify titanium surfaces with specific gene-regulatory siRNAs to enhance biofunction.

Modulating the elution of antibiotics from nanospongy titanium surfaces with a pH-sensitive coating

Fraction of vancomycin eluted at 3 different pHs from bare nanospongy titanium (left) and from nanospongy titanium coated with uncross-linked (center, CH:PEG) and cross-linked (right, CH:PEG + GEN) chitosan–poly(ethylene glycol.

Immobilization of chitosan film containing semaphorin 3A onto a microarc oxidized titanium implant surface via silane reaction to improve MG63 osteogenic differentiation

Improving osseointegration of extensively used titanium (Ti) implants still remains a main theme in implantology. Recently, grafting biomolecules onto a Ti surface has attracted more attention due to their direct participation in the osseointegration process around the implant. Semaphorin 3A (Sema3A) is a new proven osteoprotection molecule and is considered to be a promising therapeutic agent in bone diseases, but how to immobilize the protein onto a Ti surface to acquire a long-term effect is poorly defined. In our study, we tried to use chitosan to wrap Sema3A (CS/Sema) and connect to the microarc oxidized Ti surface via silane glutaraldehyde coupling. The microarc oxidization could formulate porous topography on a Ti surface, and the covalently bonded coating was homogeneously covered on the ridges between the pores without significant influence on the original topography. A burst release of Sema3A was observed in the first few days in phosphate-buffered saline and could be maintained for >2 weeks. Coating in phosphate-buffered saline containing lysozyme was similar, but the release rate was much more rapid. The coating did not significantly affect cellular adhesion, viability, or cytoskeleton arrangement, but the osteogenic-related gene expression was dramatically increased and calcium deposition was also abundantly detected. In conclusion, covalent bonding of CS/Sema could strongly improve osteogenic differentiation of osteoblasts and might be applied for Ti implant surface biofunctionalization.

Similarities and differences in coatings for magnesium-based stents and orthopaedic implants

Magnesium (Mg)-based biodegradable materials are promising candidates for the new generation of implantable medical devices, particularly cardiovascular stents and orthopaedic implants. Mg-based cardiovascular stents represent the most innovative stent technology to date. However, these products still do not fully meet clinical requirements with regards to fast degradation rates, late restenosis, and thrombosis. Thus various surface coatings have been introduced to protect Mg-based stents from rapid corrosion and to improve biocompatibility. Similarly, different coatings have been used for orthopaedic implants, e.g., plates and pins for bone fracture fixation or as an interference screw for tendon-bone or ligament-bone insertion, to improve biocompatibility and corrosion resistance. Metal coatings, nanoporous inorganic coatings and permanent polymers have been proved to enhance corrosion resistance; however, inflammation and foreign body reactions have also been reported. By contrast, biodegradable polymers are more biocompatible in general and are favoured over permanent materials. Drugs are also loaded with biodegradable polymers to improve their performance. The key similarities and differences in coatings for Mg-based stents and orthopaedic implants are summarized.

Nanoporous titanium surfaces for sustained elution of proteins and antibiotics

Current medically relevant metals for prosthetic reconstructions enjoy a relatively good success rate, but their performance drops significantly in patients with compromised health status, and post-surgical infections still remain an important challenge. To address these problems, different nanotechnology-based strategies have been exploited to create implantable metals with an enhanced bioactivity and antibacterial capacities. Among these, oxidative nanopatterning has emerged as a very effective approach to engender nanoporous surfaces that stimulate and guide the activity of adhering cells. The resulting nanoporosity is also attractive because it offers nanoconfined volumes that can be exploited to load bioactive compounds and modulate their release over time. Such extended elution is needed since a single exposure to growth factors and/or antibiotics, for instance, may not be adequate to further sustain bone regeneration and/or to counteract bacterial colonization. In this article, we assessed the capacities of nanoporous titanium surfaces generated by oxidative nanopatterning to provide controlled and sustained elution of proteins and antibiotic molecules. To this end, we have selected bovine serum albumin (BSA) and vancomycin to reflect commonly used compounds, and investigated their adsorption and elution by Fourier-transform infrared (FT-IR) and ultraviolet-visible (UV-VIS) spectroscopy. Our results demonstrate that while the elution of albumin is not significantly affected by the nanoporosity, in the case of vancomycin, nanoporous surfaces provided an extended release. These findings were successively correlated to the establishment of interactions with the surface and physical-entrapment effects exerted by the nanopores, ultimately highlighting their synergistic contribution to the release profiles and thus their importance in the design of nanostructured eluting platforms for applications in medicine.

Vancomycin-chitosan composite deposited on post porous hydroxyapatite coated Ti6Al4V implant for drug controlled release

Through the hydrogen bonds and the deprotonation, the vancomycin-chitosan composite has been originally deposited on Ti4Al4V by electrochemical technology. However, the rapid destruction of the hydrogen bonding between them by polar water molecules during immersion tests revealed 80% drug burst in a few hours. In this study, the post porous hydroxyapatite (HA) coated Ti4Al4V is prepared for the subsequent electrolytic deposition of vancomycin-chitosan composite to control the drug release. As expected, the initial burst is reduced to 55%, followed by a steady release about 20% from day 1 to day 5 and a slower release of the retained 25% after day 6, resulting in bacterial inhibition zone diameter of 30 mm which can last for more than a month in antibacterial tests, compared with the coated specimen without HA gradually loosing inhibition zone after 21 days. Besides, the cell culture indicates that the vancomycin-chitosan/HA composite coated has enhanced the proliferation, the differentiation and the mineralization of the osteoblast-like cell. In general, it is helpful for the osteointegration on permanent implants. Consistently, it effectively provides the prophylaxis and therapy of osteomyelitis according to the results of the rabbit infection animal model.

Electrical signals guided entrapment and controlled release of antibiotics on titanium surface

Electrical signals are used to trigger the entrapment and release of antibiotics on the surface of titanium plate. The entrapment of antibiotics relies on the electrochemically induced pH gradient generated at the titanium surface that allows the gelation of an aminopolysaccharide chitosan and codeposition of vancomycin, a common antibiotic, within chitosan gel. The release of vancomycin is controlled by an anodic signal imposed to the titanium plate that causes a pH decrease and erosion of chitosan gel. We show that the on demand entrapment and release of vancomycin at the surface of titanium plate is fundamentally altered and controlled by voltage. We expect that this rapid, mild and facile electrochemical process for antibiotics loading and release will find applications in controlled drug release from titanium implants.

Molecular weight and pH effects of aminoethyl modified chitosan on antibacterial activity in vitro

Aminoethyl modified chitosan derivatives (AEMCSs) with different molecular weight (Mw) were synthesized by grafting aminoethyl group on different molecular weight chitosans and chitooligosaccharide. FTIR, (1)H NMR, (13)C NMR, elemental analysis and potentiometric titration results showed that branched polyethylimine chitosan was synthesized. Clinical Laboratory Standard Institute (CLSI) protocols were used to determine MIC for Gram-negative strain of Escherichia coli under different pH. The antibacterial activity of the derivatives was significantly improved compared with original chitosans, with MIC values against E. coli varying from 4 to 64 μg/mL depending on different Mw and pH. High molecular weight seems to be in favor of stronger antibacterial activity. At pH 7.4, derivatives with Mw above 27 kDa exhibited equivalent antibacterial activity (16 μg/mL), while oligosaccharide chitosan derivative with lower Mw (~1.4 kDa) showed decreased MIC of 64 μg/mL. The effect of pH on antibacterial activity is more complicated. An optimal pH for HAEMCS was found around 6.5 to give MIC as low as 4 μg/mL, while higher or lower pH compromised the activity. Cell integrity assay and SEM images showed evident cell disruption, indicating membrane disruption may be one possible mechanism for antibacterial activity.

Innovative antimicrobial coating of titanium implants with iodine

BACKGROUND

Postoperative infection associated with implants remains a serious complication in orthopedic surgery. Several biomaterial surface treatments have been proposed as a means of reducing the incidence of implant-associated infections. In this study, a clinical trial was performed using an iodine-supported titanium that suppresses the microbial activities.

METHODS

A total of 222 patients with postoperative infection or compromised status were treated using iodine-supported titanium implants. The mean age of the patients was 49.4 years (range 5-85 years). One hundred twenty-seven patients were male and 95 were female. In 158 patients, iodine-supported implants were used to prevent infection, such as compromised hosts and conditions, and in 64 patients to treat active infection. White blood cell (WBCs) and C-reactive protein (CRP) levels were measured pre- and postoperatively in all patients. To confirm whether iodine from the implant affected physiological functions, thyroid hormone levels in the blood were examined. Both examinations were conducted sequentially for a year. Radiological evaluations were performed regularly after the operation. The chronological changes of the iodine amount were evaluated using half pins removed after completion of external fixation.

RESULTS

The mean follow-up period was 18.4 months (range 3-44 months). Acute infection developed in three tumor cases among the 158 patients on preventive therapy. All three recovered without removal of the implants. Infection was cured in all 64 patients with infection. Median WBC levels were in the normal range, and median CRP levels returned to <0.5 within 4 weeks after surgery. Abnormalities of thyroid gland function were not detected. None of the patients experienced loosening of the implants. There were two patients with mechanical implant failure, which was treated by re-implantation. Excellent bone ingrowth and ongrowth were found around all hip and tumor prostheses. One year later, the amount of iodine on external fixation pins remained about 20-30%.

CONCLUSIONS

Iodine-supported titanium implants can be very effective for preventing and treating infections after orthopedic surgery. Cytotoxicity and adverse effects were not detected.

Antimicrobial activity of gentamicin palmitate against high concentrations of Staphylococcus aureus

The reduction of implant related infections plays a pivotal role in orthopaedic surgery as an increasing number of people require implants (up to 200,000 per year in the United States (source: Joint Implant Surgery & Research Foundation 2010)). The aim of the current study is to prevent and thus decrease the number of bacterial infections. Both pre and post operative systemic antibiotic treatment and gentamicin containing bone cements (polymethylmethacrylate, PMMA) are commonly used strategies to overcome infections. In this study, the antimicrobial efficacy of gentamicin sulfate loaded bone cement was compared with titan discs coated with a new form of gentamicin, gentamicin palmitate. Adherence prevention, killing rates and killing kinetics were compared in an in vitro model, using Staphylococcus aureus (S. aureus), which together with Staphylococcus epidermidis (S. epidermidis) represents 60% of bacteria found responsible for hip implant infections (An and Friedman, 1996, J Hosp Infect 33(2):93-108). In our experiments gentamicin, which was applied as gentamicin palmitate on the surface of the implants, showed a high efficacy in eliminating bacteria. In contrast to gentamicin sulfate containing bone cements, gentamicin palmitate is released over a shorter period of time thus not inducing antibiotic resistance. Another benefit for clinical application is that it achieves high local levels of active ingredient which fight early infections and minimize toxic side effects. Furthermore, the short term hydrophobic effect of gentamicin palmitate can successfully impede biofilm formation. Thus, the use of self-adhesive antibiotic fatty acid complexes like gentamicin palmitate represents a new option for the anti-infective coating of cementless titan implants.