Biomimetic fabrication of antibacterial calcium phosphates mediated by polydopamine

Silver-Containing Biomaterials for Biomedical Hard Tissue Implants

Bacterial infection caused by biomaterials is a very serious problem in the clinical treatment of implants. The emergence of antibiotic resistance has prompted other antibacterial agents to replace traditional antibiotics. Silver is rapidly developing as an antibacterial candidate material to inhibit bone infections due to its significant advantages such as high antibacterial timeliness, high antibacterial efficiency, and less susceptibility to bacterial resistance. However, silver has strong cytotoxicity, which can cause inflammatory reactions and oxidative stress, thereby destroying tissue regeneration, making the application of silver-containing biomaterials extremely challenging. In this paper, the application of silver in biomaterials is reviewed, focusing on the following three issues: 1) how to ensure the excellent antibacterial properties of silver, and not easy to cause bacterial resistance; 2) how to choose the appropriate method to combine silver with biomaterials; 3) how to make silver-containing biomaterials in hard tissue implants have further research. Following a brief introduction, the discussion focuses on the application of silver-containing biomaterials, with an emphasis on the effects of silver on the physicochemical properties, structural properties, and biological properties of biomaterials. Finally, the review concludes with the authors' perspectives on the challenges and future directions of silver in commercialization and in-depth research.

Can Differently Stabilized Silver Nanoparticles Modify Calcium Phosphate Precipitation?

Calcium phosphates (CaPs) composites with silver nanoparticles (AgNPs) attract attention as a possible alternative to conventional approaches to combating orthopedic implant-associated infections. Although precipitation of calcium phosphates at room temperatures was pointed out as an advantageous method for the preparation of various CaP-based biomaterials, to the best of our knowledge, no such study exists for the preparation of CaPs/AgNP composites. Motivated by this lack of data in this study we investigated the influence of AgNPs stabilized with citrate (cit-AgNPs), poly(vinylpyrrolidone) (PVP-AgNPs), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT-AgNPs) in the concentration range 5-25 mg dm^-3 on the precipitation of CaPs. The first solid phase to precipitate in the investigated precipitation system was amorphous calcium phosphate (ACP). The effect of AgNPs on ACP stability was significant only in the presence of the highest concentration of AOT-AgNPs. However, in all precipitation systems containing AgNPs, the morphology of ACP was affected, as gel-like precipitates formed in addition to the typical chain-like aggregates of spherical particles. The exact effect depended on the type of AgNPs. After 60 min of reaction time, a mixture of calcium-deficient hydroxyapatite (CaDHA) and a smaller amount of octacalcium phosphate (OCP) formed. PXRD and EPR data point out that the amount of formed OCP decreases with increasing AgNPs concentration. The obtained results showed that AgNPs can modify the precipitation of CaPs and that CaPs properties can be fine-tuned by the choice of stabilizing agent. Furthermore, it was shown that precipitation can be used as a simple and fast method for CaP/AgNPs composites preparation which is of special interest for biomaterials preparation.

Calcium Phosphate Delivery Systems for Regeneration and Biomineralization of Mineralized Tissues of the Craniofacial Complex

Calcium phosphate (CaP)-based materials have been extensively used for mineralized tissues in the craniofacial complex. Owing to their excellent biocompatibility, biodegradability, and inherent osteoconductive nature, their use as delivery systems for drugs and bioactive factors has several advantages. Of the three mineralized tissues in the craniofacial complex (bone, dentin, and enamel), only bone and dentin have some regenerative properties that can diminish due to disease and severe injuries. Therefore, targeting these regenerative tissues with CaP delivery systems carrying relevant drugs, morphogenic factors, and ions is imperative to improve tissue health in the mineralized tissue engineering field. In this review, the use of CaP-based microparticles, nanoparticles, and polymer-induced liquid precursor (PILPs) amorphous CaP nanodroplets for delivery to craniofacial bone and dentin are discussed. The use of these various form factors to obtain either a high local concentration of cargo at the macroscale and/or to deliver cargos precisely to nanoscale structures is also described. Finally, perspectives on the field using these CaP materials and next steps for the future delivery to the craniofacial complex are presented.

Polydopamine, harness of the antibacterial potentials-A review

Antibiotic resistance is one of the major causes of morbidity and mortality, triggered by the adhesion of microbes and to some extent the formation of biofilms. This condition has been quite challenging in the health and industrial sector. Conditions and processes required to foil these infectious and resistance are of much concern. The synthesis of PDA material, inspired by the Mytilus edulis foot protein (MEFP)5 possesses unique characteristics that allow for, adhesion, photothermal therapy, synergistic effects with other materials, biocompatibility process, etc. Therefore, their usage holds great potential for dealing with both the infectious nature and the antibiotic resistance processes. Hence, this review provides an overview of the mechanism involved in accomplishing and eradicating bacteria, the recently harnessed antibacterial effect of the PDA through other properties they possess, a way forward in tapping the benefit embedded in the PDA, and the future perspective.

Octacalcium phosphate: Innovative vehicle for the local biologically active substance delivery in bone regeneration

Disadvantages of conventional drug delivery systems (DDS), such as systemic circulation, interaction with physiochemical factors, reduced bioavailability, and insufficient drug concentration at bone defect site, have underlined the importance of developing efficacious local drug delivery systems. Octacalcium phosphate (OCP) is presumed to be the precursor of biologically formed apatite, owing to its similarity to hydroxyapatite (HAp) and readiness to convert to it. Specific crystal structure of OCP is constructed of compiled apatite layers and water layers, which make possible the incorporation of various ions in its structure, making it feasible to alter the overall effect OCP has in the system. Next to that intrinsic property, characteristics as high solubility, biodegradability and osteoconductivity have made it indispensable to tailor OCP as a carrier material. In this review, we present the main characteristics and progress done on utilizing OCP as an innovative vehicle and provide suggestions for possible research pathways and advantages for local drug delivery in bone tissue engineering. STATEMENT OF SIGNIFICANCE: Octacalcium phosphate (OCP), being a precursor to biologically formed apatite, has many assets when compared to other calcium phosphates. Owing to its highly pertinent structure, it is being used as a vehicle for biologically active substances or ions for bone regeneration. However, orchestrating drug delivery systems with OCP, in order to achieve the best possible outcome, is still a pioneering concept, and the all-encompassing data is still scarce. Although several articles have been published on this matter, to this date there is no systematic overview pointing out the benefits that OCP can bring in the field of drug delivery. Here we offer a comprehensive overview, starting from the OCP synthesis to its structure, morphology, and the biological significance OCP has.

Improved eradication efficacy of a combination of newly identified antimicrobial agents in C. albicans and S. aureus mixed-species biofilm

Candida albicans and Staphylococcus aureus are common human pathogens, frequently isolated independently or co-isolated from bloodstream infections, and able to form dense polymicrobial biofilms on various medical devices resulting in strong resistance to conventionally used antimicrobials. New and innovative approaches are therefore needed to ensure the successful management of biofilm related infections. In this study, a chalcone-based derivative and a polycyclic anthracene-maleimide adduct, previously ascertained by us as inhibitors of C. albicans and S. aureus growths, respectively, were reconsidered in a new perspective by evaluating the efficacy of a combined treatment against a polymicrobial biofilm. Both quantitative and qualitative analyses were carried out to delve into their inhibitory potential on the polymicrobial population. Our results indicate that these newly identified antimicrobials are effective in reducing the biomass of the mixed C. albicans-S. aureus biofilm and the viability of fungal-bacterial cells within the polymicrobial community; in addition, confocal laser scanning microscopy demonstrate that compounds 1 and 2 treatment thoroughly modifies the architecture of the dual-species biofilm.

Medicated Hydroxyapatite/Collagen Hybrid Scaffolds for Bone Regeneration and Local Antimicrobial Therapy to Prevent Bone Infections

Microbial infections occurring during bone surgical treatment, the cause of osteomyelitis and implant failures, are still an open challenge in orthopedics. Conventional therapies are often ineffective and associated with serious side effects due to the amount of drugs administered by systemic routes. In this study, a medicated osteoinductive and bioresorbable bone graft was designed and investigated for its ability to control antibiotic drug release in situ. This represents an ideal solution for the eradication or prevention of infection, while simultaneously repairing bone defects. Vancomycin hydrochloride and gentamicin sulfate, here considered for testing, were loaded into a previously developed and largely investigated hybrid bone-mimetic scaffold made of collagen fibers biomineralized with magnesium doped-hydroxyapatite (MgHA/Coll), which in the last ten years has widely demonstrated its effective potential in bone tissue regeneration. Here, we have explored whether it can be used as a controlled local delivery system for antibiotic drugs. An easy loading method was selected in order to be reproducible, quickly, in the operating room. The maintenance of the antibacterial efficiency of the released drugs and the biosafety of medicated scaffolds were assessed with microbiological and in vitro tests, which demonstrated that the MgHA/Coll scaffolds were safe and effective as a local delivery system for an extended duration therapy—promising results for the prevention of bone defect-related infections in orthopedic surgeries.

Enhanced osteogenesis of 3D printed β-TCP scaffolds with Cissus Quadrangularis extract-loaded polydopamine coatings

Growing demand in bone tissue replacement has shifted treatment strategy from pursuing traditional autogenous and allogeneic grafts to tissue replacement with bioactive biomaterials. Constructs that exhibit the ability to support the bone structure while encouraging tissue regeneration, integration, and replacement represent the future of bone tissue engineering. The present study aimed to understand the osteogenic and mechanical effects of binder jet 3D printed, porous β-tricalcium phosphate scaffolds modified with a natural polymer/drug coating of polydopamine and Cissus Quadrangularis extract. Compression testing was used to determine the effect the polydopamine coating process had on the mechanical strength of the scaffolds. 3D printed scaffolds with and without polydopamine coatings fractured at 3.88 ± 0.51 MPa and 3.84 ± 1 MPa, respectively, suggesting no detrimental effect on strength due to the coating process. The osteogenic potential of the extract-loaded coating was tested in vitro, under static and dynamic flow conditions, and in vivo in a rat distal femur model. Static osteoblast cultures indicated polydopamine-coated samples with and without the extract exhibited greater proliferation after 3 days (p < 0.05). Similarly, polydopamine resulted in increased proliferation and alkaline phosphatase expression under dynamic flow, but alkaline phosphatase expression was significantly enhanced (p < 0.05) only in samples treated with the extract. Histological analysis of implanted scaffolds showed substantially more new bone growth throughout the implant pores at 4 weeks post-op in polydopamine and extract-loaded implants compared to pure β-tricalcium phosphate. These results indicated that implants coated with polydopamine and Cissus Quadrangularis extract facilitated osteoblast proliferation and alkaline phosphatase production and improved early bone formation and ingrowth while maintaining mechanical strength.

Nanosized-Ag-doped porous β-tricalcium phosphate for biological applications

The treatment of infectious or potentially infective bone defects remains a major problem in clinical practice. Silver has the ability to potentiate antibiotics against resistant bacterial strains. In order to reduce the risk of long-term infections, it is necessary for the biomaterial scaffold to release Ag⁺ in a controlled manner during the entire healing process. In this study, given the antimicrobial characteristics of nanosized Ag (NSAg), we synthesized β-tricalcium phosphate (β-TCP) doped with 5 and 10 wt% NSAg (5 wt% NSAgTCP and 10 wt% NSAgTCP, respectively). The NSAgTCP composites exhibited similar macroporous structures to pure β-TCP. The NSAgTCP samples were examined by scanning electron microscopy at 10,000-times magnification, which revealed that silver was still present at the nanometer scale. X-ray diffraction revealed that silver does not change the crystalline properties of β-TCP. In addition, we observed that the mechanical strength of NSAgTCP increased with increasing amounts of added Ag. The antibacterial, physical, and chemical properties of NSAgTCP were investigated in vitro. We found that NSAgTCP is effective at inhibiting the growth of Staphylococcus aureus and Escherichia coli and is not cytotoxic to human bone marrow mesenchymal stem cells. Moreover, it does not hinder liver or kidney function when tested in vivo. As the bioceramic degrades, Ag ions are slowly released and new bone is formed. No significant cytotoxic effects were observed even when 10 wt% NSAgTCP was used. NSAgTCP has the ability to simultaneously repair bone defects and act as an anti-infective agent; hence, we expect that this material, with its good bone-repairing and anti-infective properties, will find wide spread use as a novel bone substitute.

Biomimetic Nanostructures with Compositional Gradient Grown by Combinatorial Matrix-Assisted Pulsed Laser Evaporation for Tissue Engineering

There is permanent progress with the fabrication of smart bioactive surfaces that could govern tissue regeneration. Thin coatings of two or more materials with compositional gradient allow the construction of arrays with different chemical and physical features on a solid substrate. With such intelligent bio-platforms, cells can be exposed to a tissue-like biomimetic micro-environment with precise characteristics that directs cells fate towards specific phenotypes. We have introduced combinatorial matrix-assisted pulsed laser evaporation (C-MAPLE) as an alternative approach for the fabrication in a single-step process of either organic or inorganic thin and nanostructured coatings with variable composition. A continuous reciprocal gradient of two biomolecules can be achieved by C-MAPLE with discrete areas exhibiting physicochemical specificity that modulates intracellular signaling events. Herein, we present a review of the current combinatorial laser strategies and methods for fabricating thin organic and inorganic films with compositional gradient with emphasis on the surface influence on cell responsiveness. In particular, the specific biological potential of surface functionalization with thin coatings of biopolymers, proteins and drugs will be discussed. Laser deposition combinatorial processes are considered an emerging unconventional technology that can be widely applied to produce composite multilayers and micro-patterns for faster cell colonization and tissue engineering.

Effect of strontium substituted ß-TCP associated to mesenchymal stem cells from bone marrow and adipose tissue on spinal fusion in healthy and ovariectomized rat

Despite alternatives to autogenous bone graft for spinal fusion have been investigated, it has been shown that osteoconductive materials alone do not give a rate of fusion comparable with autogenous bone. This study analyzed a strontium substituted ß-tricalcium phosphate (Sr-ßTCP) associated with syngeneic, unexpanded, and undifferentiated mesenchymal stem cells from bone marrow (BMSC) or adipose tissue (ADSC) as a new tissue engineering approach for spinal fusion procedures. A posterolateral fusion was performed in 15 ovariectomized (OVX) and 15 sham-operated (SHAM) Inbred rats. Both SHAM and OVX animals were divided into three groups: Sr-ßTCP, Sr-ßTCP + BMCSs, and Sr-ßTCP + ADSCs. Animals were euthanized 8 weeks after surgery and the spines evaluated by manual palpation, micro-CT, and histology. For both SHAM and OVX animals, the fusion tissue in the Sr-ßTCP + BMSCs group was more solid. This effect was significantly higher in OVX animals by comparing the Sr-ßTCP + BMCSs group with Sr-ßTCP + ADSCs. Radiographical score, based on micro-CT 2D image, highlighted that the Sr-ßTCP + BMCSs group presented a similar fusion to Sr-ßTCP and higher than Sr-ßTCP + ADSCs in both SHAM and OVX animals. Micro-CT 3D parameters did not show significant differences among groups. Histological score showed significantly higher fusion in Sr-ßTCP + BMSCs group than Sr-ßTCP and Sr-ßTCP + ADSCs, for both SHAM and OVX animals. In conclusion, our results suggest that addition of BMSCs to a Sr-ßTCP improve bone formation and fusion, both in osteoporotic and nonosteoporotic animal, whereas spinal fusion is not enhanced in rats treated with Sr-ßTCP + ADSCs. Thus, for conducting cells therapy in spinal surgery BMSCs still seems to be a better choice compared with ADSCs.

Studies on Cell Compatibility, Antibacterial Behavior, and Zeta Potential of Ag-Containing Polydopamine-Coated Bioactive Glass-Ceramic

Dopamine is a small molecule that mimics the adhesive component (L-DOPA) of marine mussels with a catecholamine structure. Dopamine can spontaneously polymerize to form polydopamine (PDA) in a mild basic environment. PDA binds, in principle, to all types of surfaces and offers a platform for post-modification of surfaces. In this work, a novel Ag-containing polydopamine coating has been developed for the functionalization of bioactive glass-ceramics. In order to study the interactions between the surface of uncoated and coated samples and the environment, we have measured the surface zeta potential. Results confirmed that PDA can interact with the substrate through different chemical groups. A strongly negative surface zeta potential was measured, which is desirable for biocompatibility. The dual function of the material, namely the capability to exhibit bioactive behavior while being antibacterial and not harmful to mammalian cells, was assessed. The biocompatibility of the samples with MG-63 (osteoblast-like) cells was determined, as well as the antibacterial behavior against Gram-positive Staphylococcus carnosus and Gram-negative Escherichia coli bacteria. During cell biology tests, uncoated and PDA-coated samples showed biocompatibility, while cell viability on Ag-containing PDA-coated samples was reduced. On the other hand, antibacterial tests confirmed the strong antimicrobial properties of Ag-containing PDA-coated samples, although tailoring of the silver release will be necessary to modulate the dual effect of PDA and silver.

Antimicrobial activity of commercial calcium phosphate based materials functionalized with vanillin

Infections represent one of the most frequent causes of arthroplasty revision. Thus, design of new antimicrobial scaffolds to reduce implant rejections, bone infections and associated medical costs is highly desired. In recent years, essential oil components (EOCs) have merged as compounds with significant antimicrobial activity that can be attached to specific surfaces to enhance and prolong their antimicrobial effect. Herein calcium phosphate CaP regenerative materials have been coated with a vanillin derivative to combine its original bone regeneration properties with antimicrobial action of EOCs. Materials in form of microparticles and blocks were prepared and fully characterized. Clonogenic viability tests demonstrated that low concentrations of material (10 mg·mL^-1) resulted effective to kill 100% of E. coli DH5α bacteria. Additionally, vanillin containing scaffolds did not display any toxic effect over cells, yet they preserve the ability to express alkaline phosphatase (ALPL), collagen type 1, chain α1 (COL1A1) and bone gamma-carboxyglutamic acid-containing protein or osteocalcin (BGLAP), which are genes typically expressed by osteoblasts. These results demonstrate that commercially available scaffolds can be functionalized with EOCs, achieving antimicrobial activity and open up a new approach for the treatment and prevention of infection. STATEMENT OF SIGNIFICANCE: During the last years, the interest in bone regenerative materials with antibiotic properties has increased, since prosthesis infection is one of the most usual complications in implant surgery. In this work, we report a hybrid system composed by a calcium phosphate material (powders and scaffolds) functionalized with the derivative of an essential oil component (EOC). Our purpose was to provide the calcium phosphate material with antimicrobial activity without harming its bone regenerative capability. The obtained results were encouraging, which opens up the possibility of developing new modified materials for the prevention and treatment of bone infection.