Strontium-Doped Hydroxyapatite Coating Improves Osteo/Angiogenesis for Ameliorative Graft-Bone Integration via the Macrophage-Derived Cytokines-Mediated Integrin Signal Pathway

Polyethylene terephthalate (PET) artificial ligaments, renowned for their superior mechanical properties, have been extensively adopted in anterior cruciate ligament (ACL) reconstruction surgeries. However, the inherent bio-inertness of PET introduces formidable barriers to graft-bone integration, a critical aspect of rehabilitation. Previous interventions, ranging from surface roughening to chemical modifications, have aimed to address this challenge; however, consistently effective techniques for inducing graft-bone integration remain scarce. Our study employed advanced surface-coating methodologies to introduce strontium-doped hydroxyapatite (SrHA) onto PET ligaments. Detailed scanning electron microscopy (SEM) examinations revealed a uniform and integrative coating of SrHA on PET fibers. Furthermore, spectroscopic analysis confirmed the steady release of strontium ions from the coated surface under physiological conditions. In-depth cellular studies proved that extracellular strontium emanating from SrHA-coated PET (PET@SrHA) ligaments actively steers the M2 macrophage polarization. Additionally, macrophages (Mφs) manifested a heightened secretion of prohealing cytokines when exposed to PET@SrHA. Subsequent investigations showed that these cytokines acted as mediators, activating integrin signaling pathways among macrophages, vascular endothelial cells, and osteoblasts. As a direct consequence, an increased rate of angiogenesis and osteogenic differentiation was observed, vital for graft-bone integration following ACL reconstruction with PET@SrHA ligaments. From a biochemical standpoint, our results pinpoint strontium ions as influential immunomodulators, sculpting the graft-bone interface's immune environment. This insight presents the SrHA-coating technique as a viable therapeutic strategy, holding sound promise for improving angiogenesis and osseointegration outcomes during ACL reconstruction using PET-based grafts.

Physicochemical Properties and Simulation of Magnesium/Zinc Binary-Substituted Hydroxyapatite with Enhanced Biocompatibility and Antibacterial Ability

Ionic substitution can effectively activate the surface of hydroxyapatite (HA) for bone repair and regeneration processes. Therefore in this study, magnesium (Mg)-, zinc (Zn)-, and Mg/Zn-codoped HA was prepared by a hydrothermal method. The results of experimental and first-principles calculations verify the existence of Mg and Zn ions in the HA structure by altering cell parameters, crystallinity, and particle size. The results also showed that Mg and Zn are actively accommodated at the Ca(1) and Ca(2) positions, which not only inhibit HA formation but also promote calcium-deficient HA, and when the codoping content increased to 10%Mg and 10%Zn, the HA transformed completely to the whitlockite phase. Furthermore, the impact of codoping on biocompatibility was examined by employing MC3T3 cells. The in vitro study revealed that 5%Mg and 5%Zn single and -codoped HA promoted the proliferation of MC3T3 cells and 5%Mg-doped and -codoped HA stimulated MC3T3 cell differentiation, while 5%Zn-doped and -codoped HA revealed worthy antibacterial properties. Overall, the obtained results demonstrate that cosubstituted HA (5%Mg and 5%Zn) is promising, which not only eradicates bacteria (Escherichia coli and Staphylococcus aureus) but also induces bone regeneration. These findings suggest that 5%Mg and 5%Zn binary-substituted HA is a very promising biomaterial for hard tissue scaffolds and bone repair.

Cryogel Scaffolds for Tissue-Engineering: Advances and Challenges for Effective Bone and Cartilage Regeneration

Critical-sized bone defects and articular cartilage injuries resulting from trauma, osteonecrosis, or age-related degeneration can be often non-healed by physiological repairing mechanisms, thus representing a relevant clinical issue due to a high epidemiological incidence rate. Novel tissue-engineering approaches have been proposed as an alternative to common clinical practices. This cutting-edge technology is based on the combination of three fundamental components, generally referred to as the tissue-engineering triad: autologous or allogenic cells, growth-stimulating factors, and a scaffold. Three-dimensional polymer networks are frequently used as scaffolds to allow cell proliferation and tissue regeneration. In particular, cryogels give promising results for this purpose, thanks to their peculiar properties. Cryogels are indeed characterized by an interconnected porous structure and a typical sponge-like behavior, which facilitate cellular infiltration and ingrowth. Their composition and the fabrication procedure can be appropriately tuned to obtain scaffolds that match the requirements of a specific tissue or organ to be regenerated. These features make cryogels interesting and promising scaffolds for the regeneration of different tissues, including those characterized by very complex mechanical and physical properties, such as bones and joints. In this review, state-of-the-art fabrication and employment of cryogels for supporting effective osteogenic or chondrogenic differentiation to allow for the regeneration of functional tissues is reported. Current progress and challenges for the implementation of this technology in clinical practice are also highlighted.

Enhanced properties of nickel-silver codoped hydroxyapatite for bone tissue engineering: Synthesis, characterization, and biocompatibility evaluation

Hydroxyapatite (HAp) is the most well-known bioceramic and widely utilized in bone tissue regeneration. Hydroxyapatite is biocompatible and bioactive however, it lacks osteogenesis, angiogenesis, and antibacterial properties. In the current study, we synthesized and evaluated a novel nickel (Ni) and silver (Ag) codoped hydroxyapatite (HAp) in comparison to undoped HAp and individually doped HAp samples. Extensive physicochemical characterizations like XRD, TEM, FE-SEM/EDS, FTIR, Raman spectroscopy, and TGA were performed, confirming the crystal structure and morphology of the synthesized HAp samples. All HAp samples exhibited elongated spherical-like nanoparticle morphologies with lengths between 34 and 44 nm and widths between 21 and 26 nm. The presence of dopant atoms, Ag and Ni, were observed in the doped/codoped HAp samples by EDS elemental mapping. Biocompatibility assessments using pre-osteoblast cells indicated high cell viability for all the doped and undoped HAp samples. Osteoinduction potential through alkaline phosphatase (ALP) activity measurements and alizarin red S (ARS) staining revealed enhanced calcium deposition in the presence of Ni-Ag codoped HAp compared to other HAp samples and control groups. This highlights the importance of Ni-Ag co-doping in promoting osteogenesis, surpassing the effects of silver doped HAp and nickel doped HAp. The potential of this novel Ni-Ag codoped HAp to induce osteogenesis in pre-osteoblast cells makes it a promising material for various applications in bone tissue engineering.

Preparation and Properties of Antibacterial Silk Fibroin Scaffolds

The development of a wound dressing with both antibacterial and healing-guiding functions is a major concern in the treatment of open and infected wounds. In this study, poly(hexamethylene biguanide) hydrochloride (PHMB) was loaded into a 3D silk fibroin (SF) scaffold based on electrostatic interactions between PHMB and SF, and PHMB/SF hybrid scaffolds were prepared via freeze-drying. The effects of the PHMB/SF ratio on the antibacterial activity and cytocompatibility of the hybrid scaffold were investigated. The results of an agar disc diffusion test and a bacteriostasis rate examination showed that when the mass ratio of PHMB/SF was greater than 1/100, the scaffold exhibited obvious antibacterial activity against E. coli and S. aureus. L-929 cells were encapsulated in the PHMB/SF scaffolds and cultured in vitro. SEM, laser scanning confocal microscopy, and CCK-8 assay results demonstrated that hybrid scaffolds with a PHMB/SF ratio of less than 2/100 significantly promoted cell adhesion, spreading, and proliferation. In conclusion, a hybrid scaffold with a PHMB/SF ratio of approximately 2/100 not only effectively inhibited bacterial reproduction but also showed good cytocompatibility and is expected to be usable as a functional antibacterial dressing for wound repair.

Designing Biomimetic Conductive Gelatin-Chitosan-Carbon Black Nanocomposite Hydrogels for Tissue Engineering

Conductive nanocomposites play a significant role in tissue engineering by providing a platform to support cell growth, tissue regeneration, and electrical stimulation. In the present study, a set of electroconductive nanocomposite hydrogels based on gelatin (G), chitosan (CH), and conductive carbon black (CB) was synthesized with the aim of developing novel biomaterials for tissue regeneration application. The incorporation of conductive carbon black (10, 15 and 20 wt.%) significantly improved electrical conductivity and enhanced mechanical properties with the increased CB content. We employed an oversimplified unidirectional freezing technique to impart anisotropic morphology with interconnected porous architecture. An investigation into whether any anisotropic morphology affects the mechanical properties of hydrogel was conducted by performing compression and cyclic compression tests in each direction parallel and perpendicular to macroporous channels. Interestingly, the nanocomposite with 10% CB produced both anisotropic morphology and mechanical properties, whereas anisotropic pore morphology diminished at higher CB concentrations (15 and 20%), imparting a denser texture. Collectively, the nanocomposite hydrogels showed great structural stability as well as good mechanical stability and reversibility. Under repeated compressive cyclic at 50% deformation, the nanocomposite hydrogels showed preconditioning, characteristic hysteresis, nonlinear elasticity, and toughness. Overall, the collective mechanical behavior resembled the mechanics of soft tissues. The electrical impedance associated with the hydrogels was studied in terms of the magnitude and phase angle in dry and wet conditions. The electrical properties of the nanocomposite hydrogels conducted in wet conditions, which is more physiologically relevant, showed a decreasing magnitude with increased CB concentrations, with a resistive-like behavior in the range 1 kHz-1 MHz and a capacitive-like behavior for frequencies <1 kHz and >1 MHz. Overall, the impedance of the nanocomposite hydrogels decreased with increased CB concentrations. Together, these nanocomposite hydrogels are compositionally, morphologically, mechanically, and electrically similar to native ECMs of many tissues. These gelatin-chitosan-carbon black nanocomposite hydrogels show great promise for use as conducting substrates for the growth of electro-responsive cells in tissue engineering.

Characterization and Evaluation of Silver Concentrations in Hydroxyapatite Powders

The goal of this study is to evaluate the influence of the concentration of silver on the structural and antimicrobial in vitro properties of silver-doped hydroxyapatite powders obtained using the precipitation method. Different concentrations of silver were evaluated to assess the antimicrobial properties. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), and dispersive energy spectroscopy (EDS) were used to characterize the powders. XRD and FTIR showed that the hydroxyapatite structure is not affected by the incorporation of silver; on the other hand, EDS showed the presence of silver in the powders. Antibacterial studies showed the efficiency of hydroxyapatite powders in inhibiting bacterial growth as silver concentration increases. According to the results, silver-doped hydroxyapatite powders are suggested for use in the prevention and treatment of infections in bone and dental tissues.

Antibacterial activity of silver doped hydroxyapatite toward multidrug-resistant clinical isolates of Acinetobacter baumannii

Bacteria Acinetobacter baumannii is a persistent issue in hospital-acquired infections due to its fast and potent development of multi-drug resistance. To address this urgent challenge, a novel biomaterial using silver (Ag⁺) ions within the hydroxyapatite (HAp) lattice has been developed to prevent infections in orthopedic surgery and bone regeneration applications without relying on antibiotics. The aim of the study was to examine the antibacterial activity of mono-substituted HAp with Ag⁺ ions and a mixture of mono-substituted HAps with Sr²⁺, Zn²⁺, Mg²⁺, SeO₃^2- and Ag⁺ ions against the A. baumannii. The samples were prepared in the form of powder and disc and analyzed by disc diffusion, broth microdilution method, and scanning electron microscopy. The results from the disc-diffusion method have shown a strong antibacterial efficacy of the Ag-substituted and mixture of mono-substituted HAps (Sr, Zn, Se, Mg, Ag) toward several clinical isolates. The Minimal Inhibitory Concentrations for the powdered HAp samples ranged from 32 to 42 mg/L (Ag⁺ substituted) and 83-167 mg/L (mixture of mono-substituted), while the Minimal Bactericidal Concentrations after 24 h of contact ranged from 62.5 (Ag⁺) to 187.5-292 mg/L (ion mixture). The lower substitution level of Ag⁺ ions in a mixture of mono-substituted HAps was the cause of lower antibacterial effects measured in suspension. However, the inhibition zones and bacterial adhesion on the biomaterial surface were comparable. Overall, the clinical isolates of A. baumannii were effectively inhibited by substituted HAp samples, probably in the same amount as by other commercially available silver-doped materials, and such materials may provide a promising alternative or supplementation to antibiotic treatment in the prevention of infections associated with bone regeneration. The antibacterial activity of prepared samples toward A. baumannii was time-dependent and should be considered in potential applications.

Advanced applications of strontium-containing biomaterials in bone tissue engineering

Strontium (Sr) and strontium ranelate (SR) are commonly used therapeutic drugs for patients suffering from osteoporosis. Researches have showed that Sr can significantly improve the biological activity and physicochemical properties of materials in vitro and in vivo. Therefore, a large number of strontium containing biomaterials have been developed for repairing bone defects and promoting osseointegration. In this review, we provide a comprehensive overview of Sr-containing biomaterials along with the current state of their clinical use. For this purpose, the different types of biomaterials including calcium phosphate, bioactive glass, and polymers are discussed and provided future outlook on the fabrication of the next-generation multifunctional and smart biomaterials.

Tough Porous Silk Nanofiber-Derived Cryogels with Osteogenic and Angiogenic Capacity for Bone Repair

Tough porous cryogels with angiogenesis and osteogenesis features remain a design challenge for utility in bone regeneration. Here, building off of the recent efforts to generate tough silk nanofiber-derived cryogels with osteogenic activity, deferoxamine (DFO) is loaded in silk nanofiber-derived cryogels to introduce angiogenic capacity. Both the mechanical cues (stiffness) and the sustained release of DFO from the gels are controlled by tuning the concentration of silk nanofibers in the system, achieving a modulus above 400 kPa and slow release of the DFO over 60 days. The modulus of the cryogels and the released DFO induce osteogenic and angiogenic activity, which facilitates bone regeneration in vivo in femur defects in rat, resulting in faster regeneration of vascularized bone tissue. The tunable physical and chemical cues derived from these nanofibrous-microporous structures support the potential for silk cryogels in bone tissue regeneration.

Nanoparticles based composite coatings with tunable vascular endothelial growth factor and bone morphogenetic protein-2 release for bone regeneration

Bone healing is a complex cascade involving precisely coordinated spatiotemporal presentation of multiple growth factors (GFs), including osteogenic and angiogenic GFs, and each stage of bone healing requires varying types and content of GFs. In this study, we fabricated a composite nanocoating with tunable vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) that was coated on the surface of a polydopamine (PDA)-decorated tertiary calcium phosphate (TCP) scaffold using VEGF-loaded chitosan/bovine serum albumin nanoparticles (CS/BSA-NPs) and BMP-2-loaded poly-L-lysine/oxidized alginate nanoparticles (PLL/OALG-NPs). It was found that VEGF could be efficiently released to promote vascularization in early bone repair stages due to the rapid biodegradation of CS/BSA-NPs, while bone formation can be promoted by a sustained release of BMP-2 from the slowly degrading PLL/OALG-NPs. The composite coating and TCP scaffold can be conjugated due to the excellent adhesive property of PDA. The composite coating can achieve the rapid release of VEGF and sustained release of BMP-2, which can activate GFs for accelerating bone healing.

Designing Silk-Based Cryogels for Biomedical Applications

There is a need to develop the next generation of medical products that require biomaterials with improved properties. The versatility of various gels has pushed them to the forefront of biomaterials research. Cryogels, a type of gel scaffold made by controlled crosslinking under subzero or freezing temperatures, have great potential to address many current challenges. Unlike their hydrogel counterparts, which are also able to hold large amounts of biologically relevant fluids such as water, cryogels are often characterized by highly dense and crosslinked polymer walls, macroporous structures, and often improved properties. Recently, one biomaterial that has garnered a lot of interest for cryogel fabrication is silk and its derivatives. In this review, we provide a brief overview of silk-based biomaterials and how cryogelation can be used for novel scaffold design. We discuss how various parameters and fabrication strategies can be used to tune the properties of silk-based biomaterials. Finally, we discuss specific biomedical applications of silk-based biomaterials. Ultimately, we aim to demonstrate how the latest advances in silk-based cryogel scaffolds can be used to address challenges in numerous bioengineering disciplines.

Current Development in Biomaterials-Hydroxyapatite and Bioglass for Applications in Biomedical Field: A Review

Inorganic biomaterials, including different types of metals and ceramics are widely used in various fields due to their biocompatibility, bioactivity, and bioresorbable capacity. In recent years, biomaterials have been used in biomedical and biological applications. Calcium phosphate (CaPs) compounds are gaining importance in the field of biomaterials used as a standalone material or in more complex structures, especially for bone substitutes and drug delivery systems. The use of multiple dopants into the structure of CaPs compounds can significantly improve their in vivo and in vitro activity. Among the general information included in the Introduction section, in the first section of this review paper, the authors provided a background on the development of hydroxyapatite, methods of synthesis, and its applications. The advantages of using different ions and co-ions for substitution into the hydroxyapatite lattice and their influence on physicochemical, antibacterial, and biological properties of hydroxyapatite are also presented in this section of the review paper. Larry Hench's 45S5 Bioglass^®, commercially named 45S5, was the first bioactive glass that revealed a chemical bond with bone, highlighting the potential of this biomaterial to be widely used in biomedicine for bone regeneration. The second section of this article is focused on the development and current products based on 45S5 Bioglass^®, covering the historical evolution, importance of the sintering method, hybrid bioglass composites, and applications. To overcome the limitations of the original biomaterials, studies were performed to combine hydroxyapatite and 45S5 Bioglass^® into new composites used for their high bioactivity and improved properties. This particular type of combined hydroxyapatite/bioglass biomaterial is discussed in the last section of this review paper.

Hybrid membrane of flat silk cocoon and carboxymethyl chitosan formed through hot pressing promotes wound healing and repair in a rat model

Clinical wound management is always a relatively urgent problem. Moreover, wounds, especially severe wounds with excessive tension or excessive movement are prone to tissue infection, necrosis, and other negative effects during healing. Therefore, research has aimed to develop low-cost complementary treatments to address the urgent need for an innovative low-cost dressing that can adapt to high mechanical requirements and complex wound conditions. At present, tissue engineering to produce artificial skin with a structure similar to that of normal skin is one effective method to solve this challenge in the regeneration and repair of serious wounds. The present study hot pressed flat silk cocoons (FSC) with carboxymethyl chitosan (CMCS) to generate a cross-linked binding without enzymes or cross-linking agents that simulated the 3D structural composites of the skin cuticle. This hybrid membrane showed potential to reduce inflammatory cells and promote neovascularization in skin wound repair. After hot pressing at 130°C and 20 Mpa, the FSC/CMCS composite material was denser than FSC, showed strong light transmission, and could be arbitrarily cut. Simulating the normal skin tissue structure, the hybrid membrane overcame the poor mechanical properties of traditional support materials. Moreover, the combination of protein and polysaccharide simulated the extracellular matrix, thus providing better biocompatibility. The results of this study also demonstrated the excellent mechanical properties of the FSC/CMCS composite support material, which also provided a low-cost and environmentally friendly process for making dressings. In addition, the results of this study preliminarily reveal the mechanism by which the scaffolds promoted the healing of full-thickness skin defects on the back of SD rats. In vivo experiments using a full-thickness skin defect model showed that the FSC/CMCS membranes significantly promoted the rate of wound healing and also showed good effects on blood vessel formation and reduced inflammatory reactions. This bionic support structure, with excellent repair efficacy on deep skin defect wounds, showed potential to further improve the available biomaterial systems, such as skin and other soft tissues.

Biomimetic chitosan with biocomposite nanomaterials for bone tissue repair and regeneration

Biomimetic materials for better bone graft substitutes are a thrust area of research among researchers and clinicians. Autografts, allografts, and synthetic grafts are often utilized to repair and regenerate bone defects. Autografts are still considered the gold-standard method/material to treat bone-related issues with satisfactory outcomes. It is important that the material used for bone tissue repair is simultaneously osteoconductive, osteoinductive, and osteogenic. To overcome this problem, researchers have tried several ways to develop different materials using chitosan-based nanocomposites of silver, copper, gold, zinc oxide, titanium oxide, carbon nanotubes, graphene oxide, and biosilica. The combination of materials helps in the expression of ideal bone formation genes of alkaline phosphatase, bone morphogenic protein, runt-related transcription factor-2, bone sialoprotein, and osteocalcin. In vitro and in vivo studies highlight the scientific findings of antibacterial activity, tissue integration, stiffness, mechanical strength, and degradation behaviour of composite materials for tissue engineering applications.

Multifunctional chitosan/gelatin@tannic acid cryogels decorated with in situ reduced silver nanoparticles for wound healing

Background

Most traditional wound dressings only partially meet the needs of wound healing because of their single function. Patients usually suffer from the increasing cost of treatment and pain resulting from the frequent changing of wound dressings. Herein, we have developed a mutifunctional cryogel to promote bacterial infected wound healing based on a biocompatible polysaccharide.

Methods

The multifunctional cryogel is made up of a compositive scaffold of chitosan (CS), gelatin (Gel) and tannic acid (TA) and in situ formed silver nanoparticles (Ag NPs). A liver bleeding rat model was used to evaluate the dynamic hemostasis performance of the various cryogels. In order to evaluate the antibacterial properties of the prepared cryogels, gram-positive bacterium Staphylococcus aureus (S. aureus) and gram-negative bacterium Escherichia coli (E. coli) were cultured with the cryogels for 12 h. Meanwhile, S. aureus was introduced to cause bacterial infection in vivo. After treatment for 2 days, the exudates from wound sites were dipped for bacterial colony culture. Subsequently, the anti-inflammatory effect of the various cryogels was evaluated by western blotting and enzyme-linked immunosorbent assay. Finally, full-thickness skin defect models on the back of SD rats were established to assess the wound healing performances of the cryogels.

Results

Due to its porous structure, the multifunctional cryogel showed fast liver hemostasis. The introduced Ag NPs endowed the cryogel with an antibacterial efficiency of >99.9% against both S. aureus and E. coli. Benefited from the polyphenol groups of TA, the cryogel could inhibit nuclear factor-κB nuclear translocation and down-regulate inflammatory cytokines for an anti-inflammatory effect. Meanwhile, excessive reactive oxygen species could also be scavenged effectively. Despite the presence of Ag NPs, the cryogel did not show cytotoxicity and hemolysis. Moreover, in vivo experiments demonstrated that the biocompatible cryogel displayed effective bacterial disinfection and accelerated wound healing.

Conclusions

The multifunctional cryogel, with fast hemostasis, antibacterial and anti-inflammation properties and the ability to promote cell proliferation could be widely applied as a wound dressing for bacterial infected wound healing.

Injectable shape memory hydroxyethyl cellulose/soy protein isolate based composite sponge with antibacterial property for rapid noncompressible hemorrhage and prevention of wound infection

Uncontrollable hemorrhage and subsequent wound infection are severe threats to life, especially for the deep noncompressible massive bleeding. However, traditional hemostatic materials are ineffective for extreme bleeding and subsequent wound infection. Here, we prepared an injectable shape memory hydroxyethyl cellulose/soy protein isolate based composite sponge (EHSS) for rapid noncompressible hemorrhage and prevention of wound infection. The nano silver (AgNPs)-loaded shape memory sponge (EHP@Ag) was fabricated by mussel-inspired polydopamine coating EHSS sponge, then reducing and immobilizing AgNPs in situ. The EHP@Ag sponges showed rapid blood-triggered shape recovery speed, which is beneficial for administering noncompressible hemorrhage. The results of the hemostatic experiment in vivo demonstrated that EHP@Ag sponge exhibited a desirable hemostasis effect (hemostasis time: 22.75 ± 3.86 s, blood loss: 285.25 ± 24.93 mg) compared to the commercial gelatin sponge (hemostasis time: 49.25 ± 3.30 s, blood loss: 755.50 ± 24.45 mg). Meanwhile, the EHP@Ag sponge has an efficient antibacterial property. Furthermore, the antibacterial experiment in vivo showed that the EHP@Ag sponges could kill bacteria effectively and reduce the bacteria-induced inflammatory response. In summary, the shape memory sponges can quickly control bleeding and avoid bacterial infection, which shows great potential for clinical application as a multifunctional hemostatic agent.

Macroporous Silk Nanofiber Cryogels with Tunable Properties

Cryogels are widely used in tissue regeneration due to their porous structures and friendly hydrogel performance. Silk-based cryogels were developed but failed to exhibit desirable tunable properties to adapt various biomedical applications. Here, amorphous short silk nanofibers (SSFs) were introduced to fabricate silk cryogels with versatile cues. Compared to previous silk cryogels, the SSF cryogels prepared under same conditions showed significantly enhanced mechanical properties. The microporous cryogels were achieved under lower silk concentrations, confirming better tunability. Versatile cryogels with the modulus in the range of 0.5-283.7 kPa were developed through adjusting silk concentration and crosslinking conditions, superior to previous silk cryogel systems. Besides better cytocompatibility, the SSF cryogels were endowed with effective mechanical cues to control osteogenetic differentiation behaviors of BMSCs. The mechanical properties could be further regulated finely through the introduction of β-sheet-rich silk nanofibers (SNFs), which suggested possible optimization of mechanical niches. Bioactive cargo-laden SNFs were introduced to the SSF cryogel systems, bringing biochemical signals without the compromise of mechanical properties. Versatile SNF-based cryogels with different physical and biological cues were developed here to facilitate the applications in various tissue engineering.

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.

Anisotropic expansion effect of Sr doping on the crystal structure of hydroxyapatite

The anisotropic expansion effect of Sr on the HA crystal structure is proposed where the relative expansion rate in the c-axis direction is about 2.22 times that in the a-axis direction.

Effects of bioactive strontium-substituted hydroxyapatite on osseointegration of polyethylene terephthalate artificial ligaments

The insufficient bioactivity of polyethylene terephthalate (PET) artificial ligaments severely weakens the ligament-bone healing in anterior cruciate ligament (ACL) reconstruction, while osteogenic modification is a prevailing method to enhance osseointegration of PET artificial ligaments. In the present study, strontium-substituted hydroxyapatite (SrHA) nanoparticles with different strontium (Sr) contents were synthesized via microwave-hydrothermal method and subsequently were coated on the surface of PET artificial ligaments. The results of XRD, FT-IR, TEM and ICP-OES revealed that the doping of Sr ions had no great influences on the phase composition, morphology and particle size of HA, but affected its chemical compositions and crystallinity. The SEM images showed that nanoparticles were successfully deposited on the surface of PET grafts, the surface hydrophilicity of which was significantly improved by the prepared coatings. The in vitro study revealed that the osteogenic activity of rat bone marrow mesenchymal stem cells (rBMSCs) was affected by varying concentrations of Sr ions in coatings and the optimal osteogenic differentiation was observed in the 2SrHA-PET group, which significantly up-regulated the expression of BMP-2, OCN, Col-I and VEGF. The enhanced osteogenic ability of the 2SrHA-PET group was further demonstrated through an in vivo study, which obviously promoted ligament-bone integration compared with that of PET and HA-PET groups, thus improving the biomechanical strength of the graft-bone complex. This study confirms that SrHA coatings can facilitate osseointegration in the repair of ligament injury in rabbits and thus offers a prospective method for ACL reconstruction by using Sr-containing biomaterial-modified PET artificial ligaments.

One-pot, self-catalyzed synthesis of self-adherent hydrogels for photo-thermal, antimicrobial wound treatment

Self-adhering hydrogels are promising materials to be employed as wound dressings, because they can be used for wound healing without the necessity of additional stitching. However, micro-organisms can easily adhere to these hydrogels as well, which usually causes wound infections. Therefore, adhesive hydrogels are often combined with antibiotics. However, this introduces a risk of drug resistance, cytotoxicity and poor cell affinity. Consequently, recently, there has been great interest in developing non-antibiotic, antibacterial adhesive hydrogels. In this article, we present a simple one-pot synthesis procedure to prepare self-adhesive hydrogels composed of poly(acrylamide) (PAM), naturally derived chitosan (CS) and tannic acid/ferric ion chelates (TA@Fe³⁺). TA@Fe³⁺ enables self-catalysis of the polymerization reaction. In addition, due to its near infrared (NIR) photothermal responsiveness, TA@Fe³⁺ allows for eliminating the bacterial activity with up to 91.6% and 94.7% effectivity against Escherichia coli and Staphylococcus aureus, respectively. Mechanical and adhesion testing shows that the hydrogels are tough as well as flexible and will adhere repeatedly to many types of biological tissues, which can be attributed to the combination of physical and chemical bonding between TA@Fe³⁺ and PAM and CS, respectively. Moreover, in vitro and in vivo tests indicate that the NIR photothermally active hydrogel can effectively prevent bacterial infection and accelerate tissue regeneration, which demonstrates that these hydrogels are promising functional materials for wound healing applications.

An 'on-demand' photothermal antibiotic release cryogel patch: evaluation of efficacy on an ex vivo model for skin wound infection

A myriad of topical therapies and dressings are available to the clinicians for wound healing skin, but only a very few have shown their effectiveness in promoting wound repair due to challenges in controlling drug release. To address this issue, in this work, a near infrared (NIR)-light activable cryogel based on butyl methacrylate (BuMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) incorporated with reduced graphene oxide (rGO) was fabricated. The obtained cryogel provides the required hydrophilicity beneficial for wound treatment. The excellent photo-thermal properties of rGO allow for heating the cryogel, which results in subsequent swelling of the cryogel (CG) followed by release of the encapsulated drug load, cefepime in our case. Without photothermal activation, no release of payload was observed. The potential of this bandage for wound healing was examined using an ex vivo human skin model infected with Staphylococcus aureus (S. aureus). Apart from the efficacy of the cryogel based wound healing system, our results also suggest that the ex vivo wound model evaluated here provides a rapid and valuable tool to study superficial skin infections in humans and test the efficacy of antimicrobial agents.

Electro-mechanical and Polarization-Induced Antibacterial Response of 45S5 Bioglass-Sodium Potassium Niobate Piezoelectric Ceramic Composites

Besides the excellent osteoconductivity and biocompatibility of 45S5 bioglass (BG), poor mechanical and electrical properties as well as susceptibility toward bacterial adhesion limit its widespread clinical applications. In this context, the present study investigates the effect of addition of piezoelectric sodium potassium niobate (Na_0.5K_0.5NbO₃; NKN) on mechanical, dielectric, and antibacterial response of BG. BG-xNKN (x = 0, 10, 20, and 30 vol%) composites were synthesized at 800 °C for 30 min. The phase analyses using spectral techniques revealed the formation of the composite without any reaction between BG and piezoelectric ceramic NKN. The dielectric and electrical measurements were performed over a wide range of temperature (30-500 °C) and frequency (1 Hz-1 MHz) which suggests that space charge and dipolar polarizations are the dominant polarization mechanisms. The complex impedance analyses suggest that the average activation energies for grain and grain boundary resistances for BG-xNKN (x = 10, 20, and 30 vol%) composites are 0.59, 0.87, 0.94 and 0.76, 0.93, 1.06 eV, respectively. The issue of bacterial infection has been addressed by electrical polarization of the developed composite samples, at 20 kV for 30 min. Statistical analyses reveal that the viability of Gram-positive (S. aureus) and Gram-negative (E. coli) bacterial cells has been reduced significantly on positively and negatively charged BG-NKN composite samples, respectively. The qualitative analyses using the Kirby-Bauer test supports the above findings. Nitro blue tetrazolium and lipid peroxide assays were performed to understand the mechanism of such antibacterial response, which suggested that the combined effect of NKN addition and polarization significantly enhances the superoxide production, which kills the bacterial cells. Overall, incorporation of NKN in BG enhances the mechanical, electrical, and dielectric properties as well as improves the antibacterial response of polarized BG-xNKN composites.

Micro/nano-structured TiO2 surface with dual-functional antibacterial effects for biomedical applications

Implant-associated infections are generally difficult to cure owing to the bacterial antibiotic resistance which is attributed to the widespread usage of antibiotics. Given the global threat and increasing influence of antibiotic resistance, there is an urgent demand to explore novel antibacterial strategies other than using antibiotics. Recently, using a certain surface topography to provide a more persistent antibacterial solution attracts more and more attention. However, the clinical application of biomimetic nano-pillar array is not satisfactory, mainly because its antibacterial ability against Gram-positive strain is not good enough. Thus, the pillar array should be equipped with other antibacterial agents to fulfill the bacteriostatic and bactericidal requirements of clinical application. Here, we designed a novel model substrate which was a combination of periodic micro/nano-pillar array and TiO2 for basically understanding the topographical bacteriostatic effects of periodic micro/nano-pillar array and the photocatalytic bactericidal activity of TiO2. Such innovation may potentially exert the synergistic effects by integrating the persistent topographical antibacterial activity and the non-invasive X-ray induced photocatalytic antibacterial property of TiO2 to combat against antibiotic-resistant implant-associated infections. First, to separately verify the topographical antibacterial activity of TiO2 periodic micro/nano-pillar array, we systematically investigated its effects on bacterial adhesion, growth, proliferation, and viability in the dark without involving the photocatalysis of TiO2. The pillar array with sub-micron motif size can significantly inhibit the adhesion, growth, and proliferation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Such antibacterial ability is mainly attributed to a spatial confinement size-effect and limited contact area availability generated by the special topography of pillar array. Moreover, the pillar array is not lethal to S. aureus and E. coli in 24 h. Then, the X-ray induced photocatalytic antibacterial property of TiO2 periodic micro/nano-pillar array in vitro and in vivo will be systematically studied in a future work. This study could shed light on the direction of surface topography design for future medical implants to combat against antibiotic-resistant implant-associated infections without using antibiotics.

Mussel-Inspired Electroactive and Antioxidative Scaffolds with Incorporation of Polydopamine-Reduced Graphene Oxide for Enhancing Skin Wound Healing

Wound repair and tissue regeneration are complex processes that involve many physiological signals. Thus, employing novel wound dressings with potent biological activity and physiological signal response ability to accelerate wound healing is a possible solution. Herein, inspired by mussel chemistry, we developed a polydopamine (PDA)-reduced graphene oxide (pGO)-incorporated chitosan (CS) and silk fibroin (SF) (pGO-CS/SF) scaffold with good mechanical, electroactive, and antioxidative properties as an efficient wound dressing. First, pGO with good dispersibility and cell affinity was obtained upon reduction by PDA under alkali conditions. Second, pGO was dispersed into a CS/SF mixture, and then CS and SF chains were dual-cross-linked by poly(ethylene glycol) diglycidyl ether and glutaraldehyde to obtain a pGO-incorporated gel. Finally, the gel underwent a freeze-dry process to obtain the pGO-CS/SF scaffold. Owing to PDA reduction and functionalization, pGO in the scaffold plays important roles for the performances of the scaffolds. First, the pGO acts as nanoreinforcement to enhance the mechanical properties of the scaffold by combining the dual-cross-linked CS/SF network. Second, the uniformly distributed pGO in the scaffolds comprises a well-connected electric pathway, which can provide a channel for the transmission of electrical signals in the scaffold. Moreover, pGO in the scaffolds serves as an antioxidant agent to scavenge reactive oxygen species (ROS) and therefore terminates excessive ROS oxidation. In vitro studies show that electroactive pGO-CS/SF scaffolds can respond to electrical signals and promote cytological behavior. In addition, the pGO-CS/SF scaffolds can reduce cellular oxidation by removing excessive ROS. The in vivo full-thickness skin defect model demonstrates that the electroactive and antioxidative pGO-CS/SF scaffold can efficiently enhance wound healing. In summary, the pGO-CS/SF scaffold is a promising wound dressing because of its ability to promote physiological electrical signal transmission for cell growth and reduce ROS oxidation, resulting in an improved wound regeneration effect.