In vitro and in vivo evaluation of structurally-controlled silk fibroin coatings for orthopedic infection and in-situ osteogenesis

The Effect of Antibacterial-Osteogenic Surface Modification on the Osseointegration of Titanium Implants: A Static and Dynamic Strategy

Titanium (Ti) and its alloys are widely used biomaterials in bone repair. Although these biomaterials possess stable properties and good biocompatibility, the high elastic modulus and low surface activity of Ti implants have often been associated with infection, inflammation, and poor osteogenesis. Therefore, there is an urgent need to modify the surface of Ti implants, where changes in surface morphology or coatings loading can confer specific functions to help them adapt to the osseointegration formation phase and resist bacterial infection. This can further ensure a healthy microenvironment for bone regeneration as well as the promotion of immunomodulation, angiogenesis, and osteogenesis. Therefore, in this review, we evaluated various functional Ti implants after surface modification, both in terms of static modifications and dynamic response strategies, mainly focusing on the synergistic effects of antimicrobial activities and functionalized osteogenic. Finally, the current challenges and future perspectives are summarized to provide innovative and effective solutions for osseointegration and bone defect repair.

Biomedical Applications of Electro-Initiated Polymerisation on Ti6Al4 V Titanium Alloy using Silk Fibroin Coatings for Antibiotic Delivery and Improved Cell Metabolism

Silk fibroin interactions with metallic surfaces can provide utility for medical materials and devices. Toward this goal, titanium alloy (Ti6Al4 V) was covalently grafted with polyacrylamide via electrochemically reducing 4-nitrobenzene diazonium salt in the presence of acrylamide. Analysis of the modified surfaces with FT-IR spectra, SEM and AFM were consistent with surface grafting. Functionalised titanium samples with a silk fibroin membrane, with and without impregnated therapeutics, were used to assess cytocompatibility and drug delivery. Initial cytocompatibility experiments using fibroblasts showed that the functionalised samples, both with and without silk fibroin coatings, supported significant increases between 72-136 % in cell metabolism, compared to the controls after 7 days. A 7-days release profiling showed consistent bacterial inhibition through gentamicin release with average inhibition zones of 239 mm2. Over a 5-week period, silk fibroin coated samples, both with and without growth factors, supported better human mesenchymal stem cell metabolism with increases reaching 1031 % and 388 %, respectively, compared to samples without the silk fibroin coating with.

Incorporating bioactive glass nanoparticles in silk fibroin/bacterial nanocellulose composite scaffolds improves their biological and osteogenic properties for bone tissue engineering applications

Blend polymers composed of natural polymers are a ubiquitous biomaterial class due to their suitable mechanical and biological characterization. In the present study, composite scaffolds based on bacterial cellulose (BC)/silk fibroin (SF) with bioactive glass nanoparticles (BGNPs) were developed to enhance osteogenesis in human adipose derived stem cells (hASCs). The scanning electron microscopy (SEM) results of BGNPs indicated a spherical morphology and size ranging from 15 to 30 nm. The presence of BC and BGNPs reduced the pore diameter of SF scaffolds to about 210 ± 10 μm and 205 ± 10 μm, respectively, while increasing their compressive strength and compressive modulus. FTIR analyses proved the presence of BGNPs, BC and SF in the scaffolds. Flow cytometry data confirmed the surface markers for hASCs. The results also showed that BC and BGNPs addition to BC/SF scaffolds decreased degradation and swelling rate. The gene expression (Runx2, alkaline phosphatase and osteocalcin) studies signified the osteogenic potential of BGNPs in BC/SF scaffolds on hASCs. Eventually, the increased cell adhesion, viability and differentiation in the BC/SF and BC/SF/BGNPs composite scaffolds drawn from MTT, SEM, Alizarin red staining and alkaline phosphatase activity confirmed that these scaffolds promise to serve as a therapeutic candidate for bone defects.

Regenerated silk fibroin coating stable liquid metal nanoparticles enhance photothermal antimicrobial activity of hydrogel for wound infection repair

The integration of liquid metal (LM) and regenerated silk fibroin (RSF) hydrogel holds great potential for achieving effective antibacterial wound treatment through the LM photothermal effect. However, the challenge of LM's uncontrollable shape-deformability hinders its stable application. To address this, we propose a straightforward and environmentally-friendly ice-bath ultrasonic treatment method to fabricate stable RSF-coated eutectic gallium indium (EGaIn) nanoparticles (RSF@EGaIn NPs). Additionally, a double-crosslinked hydrogel (RSF-P-EGaIn) is prepared by incorporating poly N-isopropyl acrylamide (PNIPAAm) and RSF@EGaIn NPs, leading to improved mechanical properties and temperature sensitivity. Our findings reveal that RSF@EGaIn NPs exhibit excellent stability, and the use of near-infrared (NIR) irradiation enhances the antibacterial behavior of RSF-P-EGaIn hydrogel in vivo. In fact, in vivo testing demonstrates that wounds treated with RSF-P-EGaIn hydrogel under NIR irradiation completely healed within 14 days post-trauma infection, with the formation of new skin and hair. Histological examination further indicates that RSF-P-EGaIn hydrogel promoted epithelialization and well-organized collagen deposition in the dermis. These promising results lay a solid foundation for the future development of drug release systems based on photothermal-responsive hydrogels utilizing RSF-P-EGaIn.

Smart stimuli-responsive strategies for titanium implant functionalization in bone regeneration and therapeutics

With the increasing and aging of global population, there is a dramatic rise in the demand for implants or substitutes to rehabilitate bone-related disorders which can considerably decrease quality of life and even endanger lives. Though titanium and its alloys have been applied as the mainstream material to fabricate implants for load-bearing bone defect restoration or temporary internal fixation devices for bone fractures, it is far from rare to encounter failed cases in clinical practice, particularly with pathological factors involved. In recent years, smart stimuli-responsive (SSR) strategies have been conducted to functionalize titanium implants to improve bone regeneration in pathological conditions, such as bacterial infection, chronic inflammation, tumor and diabetes mellitus, etc. SSR implants can exert on-demand therapeutic and/or pro-regenerative effects in response to externally applied stimuli (such as photostimulation, magnetic field, electrical and ultrasound stimulation) or internal pathology-related microenvironment changes (such as decreased pH value, specific enzyme secreted by bacterial and excessive production of reactive oxygen species). This review summarizes recent progress on the material design and fabrication, responsive mechanisms, and in vitro and in vivo evaluations for versatile clinical applications of SSR titanium implants. In addition, currently existing limitations and challenges and further prospective directions of these strategies are also discussed.

Silver/Graphene Oxide Nanostructured Coatings for Modulating the Microbial Susceptibility of Fixation Devices Used in Knee Surgery

Exploring silver-based and carbon-based nanomaterials' excellent intrinsic antipathogenic effects represents an attractive alternative for fabricating anti-infective formulations. Using chemical synthesis protocols, stearate-conjugated silver (Ag@C18) nanoparticles and graphene oxide nanosheets (nGOs) were herein obtained and investigated in terms of composition and microstructure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations revealed the formation of nanomaterials with desirable physical properties, while X-ray diffraction (XRD) analyses confirmed the high purity of synthesized nanomaterials. Further, laser-processed Ag@C18-nGO coatings were developed, optimized, and evaluated in terms of biological and microbiological outcomes. The highly biocompatible Ag@C18-nGO nanostructured coatings proved suitable candidates for the local modulation of biofilm-associated periprosthetic infections.

Choosing the right animal model for osteomyelitis research: Considerations and challenges

Osteomyelitis is a debilitating bone disorder characterized by an inflammatory process involving the bone marrow, bone cortex, periosteum, and surrounding soft tissue, which can ultimately result in bone destruction. The etiology of osteomyelitis can be infectious, caused by various microorganisms, or noninfectious, such as chronic nonbacterial osteomyelitis (CNO) and chronic recurrent multifocal osteomyelitis (CRMO). Researchers have turned to animal models to study the pathophysiology of osteomyelitis. However, selecting an appropriate animal model that accurately recapitulates the human pathology of osteomyelitis while controlling for multiple variables that influence different clinical presentations remains a significant challenge. In this review, we present an overview of various animal models used in osteomyelitis research, including rodent, rabbit, avian/chicken, porcine, minipig, canine, sheep, and goat models. We discuss the characteristics of each animal model and the corresponding clinical scenarios that can provide a basic rationale for experimental selection. This review highlights the importance of selecting an appropriate animal model for osteomyelitis research to improve the accuracy of the results and facilitate the development of novel treatment and management strategies.

Application of silk fibroin coatings for biomaterial surface modification: a silk road for biomedicine

Silk fibroin (SF) as a natural biopolymer has become a popular material for biomedical applications due to its minimal immunogenicity, tunable biodegradability, and high biocompatibility. Nowadays, various techniques have been developed for the applications of SF in bioengineering. Most of the literature reviews focus on the SF-based biomaterials and their different forms of applications such as films, hydrogels, and scaffolds. SF is also valuable as a coating on other substrate materials for biomedicine; however, there are few reviews related to SF-coated biomaterials. Thus, in this review, we focused on the surface modification of biomaterials using SF coatings, demonstrated their various preparation methods on substrate materials, and introduced the latest procedures. The diverse applications of SF coatings for biomedicine are discussed, including bone, ligament, skin, mucosa, and nerve regeneration, and dental implant surface modification. SF coating is conducive to inducing cell adhesion and migration, promoting hydroxyapatite (HA) deposition and matrix mineralization, and inhibiting the Notch signaling pathway, making it a promising strategy for bone regeneration. In addition, SF-coated composite scaffolds can be considered prospective candidates for ligament regeneration after injury. SF coating has been proven to enhance the mechanical properties of the substrate material, and render integral stability to the dressing material during the regeneration of skin and mucosa. Moreover, SF coating is a potential strategy to accelerate nerve regeneration due to its dielectric properties, mechanical flexibility, and angiogenesis promotion effect. In addition, SF coating is an effective and popular means for dental implant surface modification to promote osteogenesis around implants made of different materials. Thus, this review can be of great benefit for further improvements in SF-coated biomaterials, and will undoubtedly contribute to clinical transformation in the future.

Porous surface with fusion peptides embedded in strontium titanate nanotubes elevates osteogenic and antibacterial activity of additively manufactured titanium alloy

It is still a big challenge in orthopedics to treat infected bone defects properly using medical metals. The use of three-dimensional (3D) scaffold materials that simultaneously mimic the skeletal hierarchy and induce sustainable osteogenic and antibacterial functions are a promising solution with an increasing appeal. In this study, we first designed a bifunctional fusion peptide (HHC36-RGD, HR) by linking antimicrobial peptide (HHC36) and arginine-glycine-aspartate (RGD) peptide via 6-aminohexanoic acid. Then the 3D scaffold was fabricated by additive manufacturing, and the strontium titanate nanotube structure (3D-STN) was constructed on its surface. Finally, the HR was anchored to the 3D-STN with the aid of polydopamine (PDA, P), forming the 3D-STN-P-HR scaffold. The results showed that the scaffold exhibited an ordered 3D porous structure, and that the surface was covered by a dense HHC36-RGD layer. Expectedly, the adsorption of PDA effectively slowed down the release of HR. Moreover, the functionalized scaffold had a significant inhibitory effect on Staphylococcus aureus and Escherichia coli, and its antibacterial rate could reach more than 95%. The results of in vitro cell culture experiments demonstrated that the 3D-STN-P-HR scaffold possessed excellent cytocompatibility and could promote the transcription of osteogenic differentiation-related genes and the expression of related proteins. In conclusion, the functionally modified 3D porous titanium alloy scaffold (3D-STN-P-HR) has a balanced antibacterial and osteogenic function, which bodes well for future potential in the customized functional reconstruction of complex-shaped infected bone defects.

Biomimetic AgNPs@antimicrobial peptide/silk fibroin coating for infection-trigger antibacterial capability and enhanced osseointegration

Endowing implant surfaces with combined antibacterial and osteogenic properties by drug-loaded coatings has made great strides, but how to achieve the combined excellence of infection-triggered bactericidal and in vivo-proven osteogenic activities without causing bacterial resistance still remains a formidable challenge. Herein, antimicrobial peptides (AMPs) with osteogenic fragments were designed and complexed on the surface of silver nanoparticle (AgNP) through hydrogen bonding, and the collagen structure-bionic silk fibroin (SF) was applied to carry AgNPs@ AMPs to achieve infection-triggered antibacterial and osteointegration. As verified by TEM, AMPs contributed to the dispersion and size-regulation of AgNPs, with a particle size of about 20 nm, and a clear protein corona structure was observed on the particle surface. The release curve of silver ion displayed that the SF-based coating owned sensitive pH-responsive properties. In the antibacterial test against S.aureus for up to 21 days, the antibacterial rate had always remained above 99%. Meanwhile, the underlying mechanism was revealed, originating from the destruction of the bacterial cell membranes and ROS generation. The SF-based coating was conducive to the adhesion, diffusion, and proliferation of bone marrow stem cells (BMSCs) on the surface, and promoted the expression of osteogenic genes and collagen secretion. The in vivo implantation results showed that compared with the untreated Ti implants, SF-based coating enhanced osseointegration at week 4 and 8. Overall, the AgNPs@AMPs-loaded SF-based coating presented the ability to synergistically inhibit bacteria and promote osseointegration, possessing tremendous potential application prospects in bone defects and related-infection treatments.

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AMPs and AgNPs were complexed through hydrogen bonds to form a protein crowns structure.

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Silk fibroin matrix was able to maintain the activity of AMPs over 21 d and endow with the infection-trigger release.

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The functional coating achieved synergistic antibacterial properties by damaging membrane structure and generating ROS.

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The coating displayed acceptable osteogenic properties in vitro and observably promoted osteointegration in vivo.

Silk fibroin scaffolds: A promising candidate for bone regeneration

It remains a big challenge in clinical practice to repair large-sized bone defects and many factors limit the application of autografts and allografts, The application of exogenous scaffolds is an alternate strategy for bone regeneration, among which the silk fibroin (SF) scaffold is a promising candidate. Due to the advantages of excellent biocompatibility, satisfying mechanical property, controllable biodegradability and structural adjustability, SF scaffolds exhibit great potential in bone regeneration with the help of well-designed structures, bioactive components and functional surface modification. This review will summarize the cell and tissue interaction with SF scaffolds, techniques to fabricate SF-based scaffolds and modifications of SF scaffolds to enhance osteogenesis, which will provide a deep and comprehensive insight into SF scaffolds and inspire the design and fabrication of novel SF scaffolds for superior osteogenic performance. However, there still needs more comprehensive efforts to promote better clinical translation of SF scaffolds, including more experiments in big animal models and clinical trials. Furthermore, deeper investigations are also in demand to reveal the degradation and clearing mechanisms of SF scaffolds and evaluate the influence of degradation products.

Application of bioactive metal ions in the treatment of bone defects

The treatment of bone defects is an important problem in clinical practice. The rapid development of bone tissue engineering (BTE) may provide a new method for bone defect treatment. Metal ions have been widely studied in BTE and demonstrated a significant effect in promoting bone tissue growth. Different metal ions can be used to treat bone defects according to specific conditions, including promoting osteogenic activity, inhibiting osteoclast activity, promoting vascular growth, and exerting certain antibacterial effects. Multiple studies have confirmed that metal ions-modified composite scaffolds can effectively promote bone defect healing. By studying current extensive research on metal ions in the treatment of bone defects, this paper reviews the mechanism of metal ions in promoting bone tissue growth, analyzes the loading mode of metal ions, and lists some specific applications of metal ions in different types of bone defects. Finally, this paper summarizes the advantages and disadvantages of metal ions and analyzes the future research trend of metal ions in BTE. This article can provide some new strategies and methods for future research and applications of metal ions in the treatment of bone defects.

A concise review on implications of silver nanoparticles in bone tissue engineering

Skeletal disorders represent a variety of degenerative diseases that affect bone and cartilage homeostasis. The regenerative capacity of bone is affected in osteoporosis, osteoarthritis, rheumatoid arthritis, bone fractures, congenital defects, and bone cancers. There is no viable, non-invasive treatment option and bone regeneration requires surgical intervention with the implantation of bone grafts. Incorporating nanoparticles in bone grafts have improved fracture healing by providing fine structures for bone tissue engineering. It is currently a revolutionary finding in the field of regenerative medicine. Silver nanoparticles (AgNPs) have garnered particular attention due to their well-known anti-microbial and potential osteoinductive properties. In addition, AgNPs have been demonstrated to regulate the proliferation and differentiation of mesenchymal stem cells (MSCs) involved in bone regeneration. Furthermore, AgNPs have shown toxicity towards cancer cells derived from bone. In the last decade, there have been multiple studies focusing on the effect of nanoparticles on the proliferation and/or differentiation of MSCs and bone cancer cells; however, the specific studies with AgNPs are limited. Although the reported investigations show promising in vitro and in vivo potential of AgNPs for application in bone regeneration, more studies are required to ensure their implications in bone tissue engineering. This review aims to highlight the current advances related to the production of AgNPs and their effect on MSCs and bone cancer cells, which will potentiate their possible implications in orthopedics. Moreover, this review article evaluates the future of AgNPs in bone tissue engineering.

Molecular simulations of the interfacial properties in silk-hydroxyapatite composites

Biomineralization is a common strategy used in Nature to improve the mechanical strength and toughness of biological materials. This strategy, applied in materials like bone or nacre, serves as inspiration for materials scientists and engineers to design new materials for applications in healthcare, soft robotics or the environment. In this regard, composites consisting of silk and hydroxyapatite have been extensively researched for bone regeneration applications, due to their reported cytocompatibility and osteoinduction capacity that supports bone formation in vivo. Thus, it becomes relevant to understand how silk and hydroxyapatite interact at their interface, and how this affects the overall mechanical properties of these composites. This theoretical-experimental work investigates the interfacial dynamic and structural properties of silk in contact with hydroxyapatite, combining molecular dynamics simulations with analytical characterization. Our data indicate that hydroxyapatite decreases the β-sheets in silk, which are a key load-bearing element of silk. The β-sheets content can usually be increased in silk biomaterials via post-processing methods, such as water vapor annealing. However, the presence of hydroxyapatite appears to reduce also for the formation of β-sheets via water vapor annealing. This work sheds light into the interfacial properties of silk-hydroxyapatite composite and their relevance for the design of composite biomaterials for bone regeneration.

Silk fibroin-based biomaterials for cartilage/osteochondral repair

Osteoarthritis (OA) is a common joint disease with a high disability rate. In addition, OA not only causes great physiological and psychological harm to patients, but also puts great pressure on the social healthcare system. Pathologically, the disintegration of cartilage and the lesions of subchondral bone are related to OA. Currently, tissue engineering, which is expected to overcome the defects of existing treatment methods, had a lot of research in the field of cartilage/osteochondral repair. Silk fibroin (SF), as a natural macromolecular material with good biocompatibility, unique mechanical properties, excellent processability and degradability, holds great potential in the field of tissue engineering. Nowadays, SF had been prepared into various materials to adapt to the demands of cartilage/osteochondral repair. SF-based biomaterials can also be functionally modified to enhance repair performance further. In this review, the preparation methods, types, structures, mechanical properties, and functional modifications of SF-based biomaterials used for cartilage/osteochondral repair are summarized and discussed. We hope that this review will provide a reference for the design and development of SF-based biomaterials in cartilage/osteochondral repair field.

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.

Inorganic Nanoparticles in Bone Healing Applications

Modern biomedicine aims to develop integrated solutions that use medical, biotechnological, materials science, and engineering concepts to create functional alternatives for the specific, selective, and accurate management of medical conditions. In the particular case of tissue engineering, designing a model that simulates all tissue qualities and fulfills all tissue requirements is a continuous challenge in the field of bone regeneration. The therapeutic protocols used for bone healing applications are limited by the hierarchical nature and extensive vascularization of osseous tissue, especially in large bone lesions. In this regard, nanotechnology paves the way for a new era in bone treatment, repair and regeneration, by enabling the fabrication of complex nanostructures that are similar to those found in the natural bone and which exhibit multifunctional bioactivity. This review aims to lay out the tremendous outcomes of using inorganic nanoparticles in bone healing applications, including bone repair and regeneration, and modern therapeutic strategies for bone-related pathologies.

A Review on Antibacterial Silk Fibroin-based Biomaterials: Current State and Prospects

Bacterial contamination of biomaterials is a common problem and a serious threat to human health worldwide. Therefore, the development of multifunctional biomaterials that possess antibacterial properties and can resist infection is a continual goal for biomedical applications. Silk fibroin (SF), approved by U.S. Food and Drug Administration (FDA) as a biomaterial, is one of the most widely studied natural polymers for biomedical applications due to its unique mechanical properties, biocompatibility, tunable biodegradation, and versatile material formats. In the last decade, many methods have been employed for the development of antibacterial SF-based biomaterials (SFBs) such as physical loading or chemical functionalization of SFBs with different antibacterial agents and bio-inspired surface modifications. In this review, we first describe the current understanding of the composition and structure-properties relationship of SF as a leading-edge biomaterial. Then we demonstrate the different antibacterial agents and methods implemented for the development of bactericidal SFBs, their mechanisms of action, and different applications. We briefly address their fabrication methods, advantages, and limitations, and finally discuss the emerging technologies and future trends in this research area.

In vitro drug release and antibacterial activity evaluation of silk fibroin coated vancomycin hydrochloride loaded poly (lactic-co-glycolic acid) (PLGA) sustained release microspheres

Currently, the treatment of osteomyelitis poses a great challenge to clinical orthopedics. The use of biodegradable materials combined with antibiotics provides a completely new option for the treatment of osteomyelitis. In this study, vancomycin hydrochloride (VANCO) loaded poly (lactic-co-glycolic acid) (PLGA) microspheres were prepared by a double emulsion solvent evaporation method, and the in vitro drug release behaviors of the drug loaded microspheres were explored after coating with different concentrations of silk fibroin (SF). Drug loading, encapsulation efficiency, Scanning electron microscopy, particle size analysis, Fourier transform infrared spectroscopy, hydrophilicity, in vitro drug release, and in vitro antibacterial activity were evaluated. The results showed that the drug loading of vancomycin loaded PLGA microspheres was (24.11 ±1.72)%, and the encapsulation efficiency was (48.21 ±3.44)%. The in vitro drug release indicated that the drug loaded microspheres showed an obvious initial burst release, and the drug loaded microspheres coated with SF could alleviate the initial burst release in varying degrees. It also can reduce the amount of cumulative drug release, and the effect of microspheres coated with 0.1% concentration of SF is the best. The time of in vitro drug release in different groups of drug loaded microspheres can be up to 28 days. The microspheres coated with (0.1%SF) or without (0%SF) SF showed a cumulative release of (82.50±3.51)% and (67.70±3.81)%,respectively. Therefore, the surface coating with SF of vancomycin loaded microspheres can alleviate the initial burst release, reduce the cumulative drug release, potentially prolong the drug action time, and improve the anti-infection effect.

"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.

Biomimetic Inorganic Nanoparticle-Loaded Silk Fibroin-Based Coating with Enhanced Antibacterial and Osteogenic Abilities

Poor osseointegration and infection are the main reasons leading to the failure of hard tissue implants; especially, in recent years, the failure rate has been increasing every year owing to the continuously increasing conditions such as injury, trauma, diseases, or infections. Therefore, the development of a biomimetic surface coating of bone tissues with antibacterial function is an effective means to improve bone healing and inhibit bacterial infection. Mimicking the natural bone, in this study, we have designed a silk fibroin (collagen-like structure)-based coating inlaid with nanohydroxyapatite (nHA) and silver nanoparticles (AgNPs) for promoting antibacterial ability and osteogenesis, especially focusing on the bone mimetic structure for enhancing bone health. Observing the morphology and size of the composite nanoparticles by transmission electron microscope (TEM), nHA provided nucleation sites for the formation of AgNPs, forming an nHA/AgNP complex with a size of about 100-200 nm. Characterization of the nHA/Ag-loaded silk fibroin biomimetic coating showed an increased surface roughness with good density and compact performances. The silk fibroin-based coating loaded with uniformly distributed AgNPs and nHA could effectively inhibit the adhesion of Staphylococcus aureus on the surface and, at the same time, quickly kill planktonic bacteria, indicating their good antibacterial ability. In vitro cell experiments revealed that the biomimetic silk fibroin-based coating was beneficial to the adhesion, spreading, and proliferation of osteoblasts (MC3T3-E1). In addition, by characterizing LDH and ROS, it was found that the nHA/Ag complex could significantly reduce the cytotoxicity of AgNPs, and the osteoblasts on the coating surface maintained the structure intact.

[Progress in the application of silk fibroin in tissue engineered drug delivery system]

Objective

The properties and characteristics of different types of silk fibroin (SF) drug-loaded sustained-release carriers and their effects on the drug release behavior were reviewed, and the existing problems and development prospects of SF drug-loaded sustained-release carriers in tissue engineering drug delivery system were discussed.

Methods

The literatures about drug-loaded SF sustained-release carriers in recent years were extensively consulted, and the types of sustained-release carriers, characteristics of drug release, range of applications, advantages and disadvantages, and solutions were summarized and analyzed.

Results

At present, the SF drug-loaded sustained-release carriers are mainly divided into SF microparticles, SF scaffolds, SF membranes, SF hydrogels, SF nanofibers, SF sponges, and so on. These types of SF drug-loaded sustained-release carriers have their own advantages and problems, of which the most prominent problem is the burst release of drugs at the initial stage. While, the initial burst release of drugs can be effectively solved by improving the preparation process and adjusting the material ratio. Different types of drug-loaded sustained-release carriers can be prepared by combining different materials to achieve different application scopes and drug release behaviors under different conditions.

Conclusion

SF is a good drug-loaded carrier for tissue engineering, the burst release of drugs at the initial stage can be solved by improving the preparation process and changing the material structure; through the combination of the advantages of various types of SF drug-loaded sustained-release carriers, it is expected to prepare SF drug-loaded sustained-release carriers that meet different clinical needs.

Advancements in release-active antimicrobial biomaterials: A journey from release to relief

Escalating medical expenses due to infectious diseases are causing huge socioeconomic pressure on mankind globally. The emergence of antibiotic resistance has further aggravated this problem. Drug-resistant pathogens are also capable of forming thick biofilms on biotic and abiotic surfaces to thrive in a harsh environment. To address these clinical problems, various strategies including antibacterial agent delivering matrices and bactericidal coatings strategies have been developed. In this review, we have discussed various types of polymeric vehicles such as hydrogels, sponges/cryogels, microgels, nanogels, and meshes, which are commonly used to deliver antibiotics, metal nanoparticles, and biocides. Compositions of these polymeric matrices have been elaborately depicted by elucidating their chemical interactions and potential activity have been discussed. On the other hand, various implant/device-surface coating strategies which exploit the release-active mechanism of bacterial killing are discussed in elaboration. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Engineering a Bioactive Hybrid Coating for In Vitro Corrosion Control of Magnesium and Its Alloy

Magnesium (Mg) and its alloys are promising biodegradable metallic implant materials. However, their clinical applications are limited by their fast corrosion rate in the biological environment. In this work, with an outlook to improve the in vitro corrosion resistance of Mg and WE43 Mg alloy, a layer-by-layer interfacially engineered anticorrosive and bioactive coating consisting of a natural oxide lower layer, hydroxyapatite (HA) middle layer, and silk fibroin (SF) top layer was fabricated and investigated. Anodization was used to create natural oxide layer induced microroughness on substrates. The electrochemically deposited HA layer improved the surface microroughness and microhardness but significantly decreased Mg ion release, hydrogen gas evolution, and weight loss in simulated body fluid. The spin-coated SF layer further decreased hydrophilicity, in vitro degradation, and corrosion rate. The nonspecific and specific intermolecular interactions between fabricated layers along with their mechanical interlocking interface contributed to improved adhesion strength and integrity of the coating. The SF+HA-coated samples showed enhanced degradation and corrosion resistance due to a synergistic effect of the underlying HA layer, hindering the ingress of aggressive ions and the top hydrophobic SF layer, preventing the ingress of corrosive solution. The SF+HA-coated Mg and WE43 Mg alloy samples exhibited 50 and 26 times decreased corrosion rate, respectively, compared to uncoated samples. Moreover, in vitro cytotoxicity and cell culture studies using a mouse fibroblast cell showed that the SF+HA hybrid coating improved the cell viability, attachment, and proliferation, with cells exhibiting elongated morphology on coated samples as compared to a round shape on uncoated samples.

Polydopamine-assisted immobilization of silk fibroin and its derived peptide on chemically oxidized titanium to enhance biological activity in vitro

Biochemical modification can endow the surface of implants with superior biological activity. Herein, silk fibroin (SF) protein and its anionic derivative peptides (Cs) were covalently immobilized onto a titanium implant surface via a polydopamine layer. The successful conjugation of SF and Cs was revealed by X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and contact angle measurements. The addition of Cs prevented the conformational transition of silk fibroin to silk II. The deposition of apatite on its surface was significantly accelerated, and the bioactive composite coating was observed to enhance protein adsorption and cell proliferation. More importantly, it also promoted the osteogenic differentiation of bone marrow stem cells (BMSCs) for the quantitative and qualitative detection of alkaline phosphatase (ALP) and alizarin red (ARS). Overall, the stable performance and enhanced osteogenic property of the composite coating promote an extensive application for clinical titanium-based implants.

Silk Biomaterials for Bone Tissue Engineering

Silk is a natural fibrous polymer with application potential in regenerative medicine. Increasing interest remains for silk materials in bone tissue engineering due to their characteristics in biocompatibility, biodegradability and mechanical properties. Plenty of the in vitro and in vivo studies confirmed the advantages of silk in accelerating bone regeneration. Silk is processed into scaffolds, hydrogels, and films to facilitate different bone regenerative applications. Bioactive factors such as growth factors and drugs, and stem cells are introduced to silk-based matrices to create friendly and osteogenic microenvironments, directing cell behaviors and bone regeneration. The recent progress in silk-based bone biomaterials is discussed and focused on different fabrication and functionalization methods related to osteogenesis. The challenges and potential targets of silk bone materials are highlighted to evaluate the future development of silk-based bone materials.

An In Vitro Evaluation of the Hierarchical Micro/Nanoporous Structure of a Ti3Zr2Sn3Mo25Nb Alloy after Surface Dealloying

A process to dealloy a Ti-3Zr-2Sn-3Mo-25Nb (TLM) titanium alloy to create a porous surface structure has been reported in this paper aiming to enhance the bioactivity of the alloy. A simple nanoporous topography on the surface was produced through dealloying the as-solution treated TLM alloy. In contrast, dealloying the as-cold rolled alloy created a hierarchical micro/nanoporous topography. SEM and XPS were performed to characterize the topography and element chemistry of both porous structures. The roughness, hydrophilicity, protein adsorption, cell adhesion, proliferation, and osteogenic differentiation were tested. The elements of Zr, Mo, Sn, and Nb were depleted at the nanoporous TLM surface with a diameter of 15.6 ± 2.3 nm. Dissolving the microscale α phase from the alloy surface contributed to the formation of the microscale grooves on the surface. The simple nanoporous topographical surface exhibited hydrophilicity and higher protein adsorption ability, which facilitated the early adhesion of osteoblasts compared with the hierarchical micro/nanoporous surface. On the other hand, the hierarchical micro/nanoporous surface improved cell proliferation and differentiation and still retained the contact guidance function, which implied good bonding for osseointegration. This research revealed the effect of phase composition on the surface morphology of dealloying titanium alloy and the synergistic effect of micron and nanometer topography on the function of osteoblasts. This paper therefore provides insights into the surface topological design of titanium-based biomaterials with improved biocompatibility.

Review on Silver Nanoparticles as a Novel Class of Antibacterial Solutions

Nanomaterials represent a promising novel class of materials to be used as antibacterial solutions. Inhomogeneity of synthesis and characterization methods, as well as resulting variate physical and chemical properties make selection of proper nanostructure difficult when designing antimicrobial experiments. Present study focuses on the already existing evidence regarding silver nanoparticles and their antibacterial applications, with focus on various modulatory factors of reported antimicrobial efficiency. Present paper focuses on synthesis and characterization methods, factors modulating antibacterial efficiency, laboratory quantification procedures, as well as up–to-date knowledge on mechanisms of antibacterial action for silver nanoparticles. Moreover, challenges and future prospects for antimicrobial applications of silver nanoparticles are reviewed and discussed.

An Updated Review on Silver Nanoparticles in Biomedicine

Silver nanoparticles (AgNPs) represent one of the most explored categories of nanomaterials for new and improved biomaterials and biotechnologies, with impressive use in the pharmaceutical and cosmetic industry, anti-infective therapy and wound care, food and the textile industry. Their extensive and versatile applicability relies on the genuine and easy-tunable properties of nanosilver, including remarkable physicochemical behavior, exceptional antimicrobial efficiency, anti-inflammatory action and antitumor activity. Besides commercially available and clinically safe AgNPs-based products, a substantial number of recent studies assessed the applicability of nanosilver as therapeutic agents in augmented and alternative strategies for cancer therapy, sensing and diagnosis platforms, restorative and regenerative biomaterials. Given the beneficial interactions of AgNPs with living structures and their nontoxic effects on healthy human cells, they represent an accurate candidate for various biomedical products. In the present review, the most important and recent applications of AgNPs in biomedical products and biomedicine are considered.