Compritol solid lipid nanoparticle formulations enhance the protective effect of betulinic acid derivatives in human Müller cells against oxidative injury.

Müller cells maintain homeostatic functions in the retina. Their dysfunction leads to irreversible retinal diseases. Oxidative injury is a leading cause of retinal cytotoxicity. Our previous studies reported several betulinic acid (BA) derivatives can protect Müller cells from oxidative injury but achieving pharmacologically effective concentrations in the Müller cells could be a limitation. To optimise cellular delivery, we encapsulated the BA analogues H3, H5 and H7 into the clinically approved Compritol 888 and HD5 ATO solid lipid nanoparticles (SLNs) using the micro-emulsion method. The cytoprotective effects of these SLN-formulations were determined in human MIO-M1 cells. We found cytoprotection by H3 and H5 SLN-formulations was significantly enhanced, which was evident at concentrations much lower than those required with the free agents. Both SLN-formulations prolonged the duration of action of these agents. The most effective agent H5 delivered in 888 ATO SLNs attenuated glutamate-induced ROS formation and the associated necrosis in MIO-M1 cells. Overall, SLNs have emerged as promising delivery carriers for BA derivatives enhancing their protective effects against oxidative injury in human Müller cells. Our study is the first to show SLNs can be a viable route to delivery agents with improved efficacy and stability into human Müller cells favoring the treatment/prevention of retinal diseases.

Nanoscale Probing of Liposome Encapsulating Drug Nanocrystal Using Atomic Force Microscopy-Infrared Spectroscopy.

Use of liposomes encapsulating drug nanocrystals for the treatment of diseases like cancer and pulmonary infections is gaining attention. The potential therapeutic benefit of these engineered formulations relies on maintaining the physical integrity of the liposomes and the stability of the encapsulated drug. With the significant advancement in the microscopic and analytical techniques, analysis of the size and size distribution of these nanosized vesicles is possible. However, due to the limited spatial resolution of conventional vibrational spectroscopy techniques, the chemical composition of individual nanosized liposome cannot be resolved. To address this limitation, we applied atomic force microscopy infrared spectroscopy (AFM-IR) to assess the chemical composition of individual liposomes encapsulating ciprofloxacin in dissolved and nanocrystalline form. Spatially resolved AFM-IR spectra acquired from individual liposomes confirmed the presence of peaks related to N-H bending vibration, C-N stretching and symmetric, and asymmetric vibration of the carboxyl group present in the ciprofloxacin. Our results further demonstrated the effectiveness of AFM-IR in differentiating the liposome containing ciprofloxacin in dissolved or nanocrystalline form. Spectra acquired from dissolved ciprofloxacin had peaks related to the ionised carboxyl group, i.e., at 1576 and 1392 cm-1, which were either absent or far weaker in intensity in the spectra of liposomal sample containing ciprofloxacin nanocrystals. These findings are highly significant for pharmaceutical scientists to ascertain the stability and physicochemical composition of individual liposomes and will facilitate the design and development of liposomes with greater therapeutic benefits.

Gentamicin-Loaded Polysaccharide Membranes for Prevention and Treatment of Post-operative Wound Infections in the Skeletal System.

PURPOSE: To develop polysaccharide-based membranes that allow controlled and localized delivery of gentamicin for the treatment of post-operative bone infections. METHODS: Membranes made of gellan gum (GUM), sodium alginate (ALG), GUM and ALG crosslinked with calcium ions (GUM + Ca and ALG + Ca, respectively) as well as reference collagen (COL) were produced by freeze-drying. Mechanical properties, drug release, antimicrobial activity and cytocompatibility of the membranes were assessed. RESULTS: The most appropriate handling and mechanical properties (Young's modulus, E = 92 ± 4 MPa and breaking force, F MAX  = 2.6 ± 0.1 N) had GUM + Ca membrane. In contrast, COL membrane showed F MAX  = 0.14 ± 0.02 N, E = 1.0 ± 0.3 MPa and was deemed to be unsuitable for antibiotic delivery. The pharmacokinetic data demonstrated a uniform and sustainable delivery of gentamicin from GUM + Ca (44.4 ± 1.3% within 3 weeks), while for COL, ALG and ALG + Ca membranes the most of the drug was released within 24 h (55.3 ± 1.9%, 52.5 ± 1.5% and 37.5 ± 1.8%, respectively). Antimicrobial activity against S. aureus and S. epidermidis was confirmed for all the membranes. GUM + Ca and COL membranes supported osteoblasts growth, whereas on ALG and ALG + Ca membranes cell growth was reduced. CONCLUSIONS: GUM + Ca membrane holds promise for effective treatment of bone infections thanks to favorable pharmacokinetics, bactericidal activity, cytocompatibility and good mechanical properties.

Effect of plasma immersion ion implantation on polycaprolactone with various molecular weights and crystallinity.

Polycaprolactone with five different molecular weights was spin-coated on silicon wafers and plasma immersion ion implanted (PIII) with ion fluence in the range 5 × 1014-2 × 1016 ions/cm2. The effects of PIII treatment on the optical properties, chemical structure, crystallinity, morphology, gel fraction formation and wettability were investigated. As in the case of a number of previously studied polymers, oxidation and hydrophobic recovery of the PIII treated PCL follow second order kinetics. CAPA 6250, which has the lowest molecular weight and the highest degree of crystallinity of the untreated PCL films studied, has the highest carbonization of the modified layer after PIII treatment. Untreated medical grade PCL films, mPCL PC12 (Perstorp) and mPCL OsteoporeTM have similar chemical structures and crystallinity. Accordingly, the chemical and structural transformations caused by PIII treatment and post-treatment oxidation are almost identical for these two polymers. In general, PIII treatment destroys the nano-scale lamellar structure and results in a reduction of PCL crystallinity. Examination after washing PIII treated PCL films in toluene confirmed our hypothesis that cross-linking due to PIII treatment is significantly higher in semi-crystalline PCL as compared with amorphous polymers.

Lorentz contact resonance spectroscopy for nanoscale characterisation of structural and mechanical properties of biological, dental and pharmaceutical materials.

Scanning probe microscopy has been widely used to obtain topographical information and to quantify nanostructural properties of different materials. Qualitative and quantitative imaging is of particular interest to study material-material interactions and map surface properties on a nanoscale (i.e. stiffness and viscoelastic properties). These data are essential for the development of new biomedical materials. Currently, there are limited options to map viscoelastic properties of materials at nanoscale and at high resolutions. Lorentz contact resonance (LCR) is an emerging technique, which allows mapping viscoelasticity of samples with stiffness ranging from a few hundred Pa up to several GPa. Here we demonstrate the applicability of LCR to probe and map the viscoelasticity and stiffness of 'soft' (biological sample: cell treated with nanodiamond), 'medium hard' (pharmaceutical sample: pMDI canister) and 'hard' (human teeth enamel) specimens. The results allowed the identification of nanodiamond on the cells and the qualitative assessment of its distribution based on its nanomechanical properties. It also enabled mapping of the mechanical properties of the cell to demonstrate variability of these characteristics in a single cell. Qualitative imaging of an enamel sample demonstrated variations of stiffness across the specimen and precise identification of enamel prisms (higher stiffness) and enamel interrods (lower stiffness). Similarly, mapping of the pMDI canister wall showed that drug particles were adsorbed to the wall. These particles showed differences in stiffness at nanoscale, which suggested variations in surface composition-multiphasic material. LCR technique emerges as a valuable tool for probing viscoelasticity of samples of varying stiffness's.

Bioactive nanocomposite PLDL/nano-hydroxyapatite electrospun membranes for bone tissue engineering.

New nanocomposite membranes with high bioactivity were fabricated using the electrospinning. These nanocomposites combine a degradable polymer poly(L/DL)-lactide and bone cell signaling carbonate nano-hydroxyapatite (n-HAp). Chemical and physical characterization of the membranes using scanning electron microscopy, Fourier transform infrared spectroscopy and the wide angle X-ray diffraction evidenced that nanoparticles were successfully incorporated into the fibers and membrane structure. The incorporation of the n-HAp into the structure increased significantly the mineralization of the membrane in vitro. It has been demonstrated that after a 3-day incubation of composite membrane in the Simulated Body Fluid a continuous compact apatite layer was formed. In vitro experiments demonstrated that the incorporation of n-HAp significantly improved cell attachment, upregulated cells proliferation and stimulated cell differentiation quantified using Alkaline Phosphatase and OsteoImage tests. In conclusion, the results demonstrated that the addition of n-HAp provided chemical cues that were a key factor that regulated osteoblastic differentiation.

Recent advances and prospects for lipid-based nanoparticles as drug carriers in the treatment of human retinal diseases.

The delivery of cures for retinal diseases remains problematic. There are four main challenges: passing through multiple barriers of the eye, the delivery to particular retinal cell types, the capability to carry different forms of therapeutic cargo and long-term therapeutic efficacy. Lipid-based nanoparticles (LBNPs) are potent to overcome these challenges due to their unique merits: amphiphilic nanoarchitectures to pass biological barriers, vary modifications with specific affinity to target cell types, flexible capacity for large and mixed types of cargos and slow-release formulations for long-term treatment. We have reviewed the latest research on the applications of LBNPs for treating retinal diseases and categorized them by different payloads. Furthermore, we identified technical barriers and discussed possible future development for LBNPs to expand the therapeutic potential in treating retinal diseases.

Antimicrobial and Anti-inflammatory Gallium-Defensin Surface Coatings for Implantable Devices.

Emerging and re-emerging infections are a global threat driven by the development of antimicrobial resistance due to overuse of antimicrobial agents and poor infection control practices. Implantable devices are particularly susceptible to such infections due to the formation of microbial biofilms. Furthermore, the introduction of implants into the body often results in inflammation and foreign body reactions. The antimicrobial and anti-inflammatory properties of gallium (Ga) have been recognized but not yet utilized effectively to improve implantable device integration. Furthermore, defensin (De, hBD-1) has potent antimicrobial activity in vivo as part of the innate immune system; however, this has not been demonstrated as successfully when used in vitro. Here, we combined Ga and De to impart antimicrobial activity and anti-inflammatory properties to polymer-based implantable devices. We fabricated polylactic acid films, which were modified using Ga implantation and subsequently functionalized with De. Ga-ion implantation increased surface roughness and increased stiffness. Ga implantation and defensin immobilization both independently and synergistically introduced antimicrobial activity to the surfaces, significantly reducing total live bacterial biomass. We demonstrated, for the first time, that the antimicrobial effects of De were unlocked by its surface immobilization. Ga implantation of the surface also resulted in reduced foreign body giant cell formation and expression of proinflammatory cytokine IL-1ß. Cumulatively, the treated surfaces were able to kill bacteria and reduce inflammation in comparison to the untreated control. These innovative surfaces have the potential to prevent biofilm formation without inducing cellular toxicity or inflammation, which is highly desired for implantable device integration.

Probing the calcium and sodium local environment in bones and teeth using multinuclear solid state NMR and X-ray absorption spectroscopy.

Despite the numerous studies of bone mineral, there are still many questions regarding the exact structure and composition of the mineral phase, and how the mineral crystals become organised with respect to each other and the collagen matrix. Bone mineral is commonly formulated as hydroxyapatite, albeit with numerous substitutions, and has previously been studied by (31)P and (1)H NMR, which has given considerable insight into the complexity of the mineral structure. However, to date, there has been no report of an NMR investigation of the other major component of bone mineral, calcium, nor of common minority cations like sodium. Here, direct analysis of the local environment of calcium in two biological apatites, equine bone (HB) and bovine tooth (CT), was carried out using both (43)Ca solid state NMR and Ca K-edge X-ray absorption spectroscopy, revealing important structural information about the calcium coordination shell. The (43)Ca delta(iso) in HB and CT is found to correlate with the average Ca-O bond distance measured by Ca K-edge EXAFS, and the (43)Ca NMR linewidths show that there is a greater distribution in chemical bonding around calcium in HB and CT, compared to synthetic apatites. In the case of sodium, (23)Na MAS NMR, high resolution 3Q-MAS NMR, as well as (23)Na{(31)P} REDOR and (1)H{(23)Na} R(3)-HMQC correlation experiments give the first direct evidence that some sodium is located inside the apatite phase in HB and CT, but with a greater distribution of environments compared to a synthetic sodium substituted apatite (Na-HA).

Development of brushite particles synthesized in the presence of acidic monomers for dental applications.

OBJECTIVES: To synthesize and characterize brushite particles in the presence of acidic monomers (acrylic acid/AA, citric acid/CA, and methacryloyloxyethyl phosphate/MOEP) and evaluate the effect of these particles on degree of conversion (DC), flexural strength/modulus (FS/FM) and ion release of experimental composites. METHODS: Particles were synthesized by co-precipitation with monomers added to the phosphate precursor solution and characterized for monomer content, size and morphology. Composites containing 20 vol% brushite and 40 vol% reinforcing glass were tested for DC, FS and FM (after 24 h and 60 d in water), and 60-day ion release. Data were subjected to ANOVA/Tukey tests (DC) or Kruskal-Wallis/Dunn tests (FS and FM, alpha: 5%). RESULTS: The presence of acidic monomers affected particle morphology. Monomer content on the particles was low (0.1-1.4% by mass). Composites presented similar DC. For FS/24 h, only the composite containing DCPD_AA was statistically similar to the composite containing 60 vol% of reinforcing glass (without brushite, "control"). After 60 days, all brushite-containing materials showed similar FS, statistically lower than the control composite (p<0.01). Composites containing DCPD_AA, DCPD_MOEP or DCPD_U ("unmodified") showed statistically similar FM/24 h, higher than the control composite. After prolonged immersion, all composites were similar to the control composite, except DCPD_AA. Cumulative ion release ranged from 21 ppm to 28 ppm (calcium) and 9 ppm to 17 ppm (phosphate). Statistically significant reductions in ion release between 15 and 60 days were detected only for the composite containing DCPD_MOEP. SIGNIFICANCE: Acidic monomers added to the synthesis affected brushite particle morphology. After 60-day storage in water, composite strength was similar among all brushite-containing composites. Ion release was sustained for 60 days and it was not affected by particle morphology.

Structure and properties of strontium-doped phosphate-based glasses.

Owing to similarity in both ionic size and polarity, strontium (Sr2+) is known to behave in a comparable way to calcium (Ca2+), and its role in bone metabolism has been well documented as both anti-resorptive and bone forming. In this study, novel quaternary strontium-doped phosphate-based glasses, containing 1, 3 and 5 mol% SrO, were synthesized and characterized. (31)P magic angle spinning (MAS) nuclear magnetic resonance results showed that, as the Sr2+ content is increased in the glasses, there is a slight increase in disproportionation of Q2 phosphorus environments into Q(1) and Q3 environments. Moreover, shortening and strengthening of the phosphorus to bridging oxygen distance occurred as obtained from FTIR. The general broadening of the spectral features with Sr2+ content is most probably due to the increased variation of the phosphate-cation bonding interactions caused by the introduction of the third cation. This increased disorder may be the cause of the increased degradation of the Sr-containing glasses relative to the Sr-free glass. As confirmed from elemental analysis, all Sr-containing glasses showed higher Na2O than expected and this also could be accounted for by the higher degradation of these glasses compared with Sr-free glasses. Measurements of surface free energy (SFE) showed that incorporation of strontium had no effect on SFE, and samples had relatively higher fractional polarity, which is not expected to promote high cell activity. From viability studies, however, the incorporation of Sr2+ showed better cellular response than Sr(2+)-free glasses, but still lower than the positive control. This unfavourable cellular response could be due to the high degradation nature of these glasses and not due to the presence of Sr2+.

Incorporation of vitamin E in poly(3hydroxybutyrate)/Bioglass composite films: effect on surface properties and cell attachment.

This study investigated the possibility of incorporating alpha-tocopherol (vitamin E) into poly(3hydroxybutyrate) (P(3HB))/Bioglass composites, which are being developed for bone tissue engineering matrices. P(3HB) films with 20 wt% Bioglass and 10 wt% vitamin E were prepared using the solvent casting technique. Addition of vitamin E significantly improved the hydrophilicity of the composites along with increasing the total protein adsorption. The presence of protein adsorbed on the composite surface was further confirmed using X-ray photoelectron spectroscopy analysis. Preliminary cell culture studies using MG-63 human osteoblasts showed that the addition of vitamin E in the P(3HB)/20 wt% Bioglass films significantly increased cell proliferation. The results achieved in this study confirmed the possibility of incorporating vitamin E as a suitable additive in P(3HB)/Bioglass composites to engineer the surface of the composites by promoting higher protein adsorption and increasing the hydrophilicity.

Chemical, corrosion and topographical analysis of stainless steel implants after different implantation periods.

The aim of this work is to examine the corrosion properties, chemical composition, and material-implant interaction after different periods of implantation of plates used to correct funnel chest. The implants are made of 316L stainless steel. Examinations are carried out on three implants: new (nonimplanted) and two implanted for 29 and 35 months. The corrosion study reveals that in the potential range that could occur in the physiological condition the new bar has the lowest current density and the highest corrosion potential. This indicates that the new plate has the highest corrosion resistance and the corrosion resistance could be reduced during implantation by the instruments used during the operation. XPS analysis reveals changes in the surface chemistry. The longer the implantation time the more carbon and oxygen are observed and only trace of elements such as Cr, Mo are detected indicating that surface is covered by an organic layer. On some parts of the implants whitish tissue is observed: the thickness of which increased with the time of implantation. This tissue was identified as an organic layer; mainly attached to the surface on the areas close to where the implant was bent to attain anatomical fit and thus where the implant has higher surface roughness. The study indicates that the chest plates are impaired by the implantation procedure and contact with biological environment. The organic layer on the surface shows that the implant did not stay passive but some reactions at the tissue-implant interface occurred. These reactions should be seen as positive, as it indicates that the implants were accepted by the tissues. Nevertheless, if the implants react, they may continue to release chromium, nickel, and other harmful ions long term as indicated by lower corrosion resistance of the implants following implantation.

Plasma Ion Implantation of Silk Biomaterials Enabling Direct Covalent Immobilization of Bioactive Agents for Enhanced Cellular Responses.

Silk fibroin isolated from Bombyx mori cocoons is a promising material for a range of biomedical applications, but it has no inherent cell-interactive domains, necessitating functionalization with bioactive molecules. Here we demonstrate significantly enhanced cell interactions with silk fibroin biomaterials in the absence of biofunctionalization following surface modification using plasma immersion ion implantation (PIII). Further, PIII treated silk fibroin biomaterials supported direct covalent immobilization of proteins on the material surface in the absence of chemical cross-linkers. Surface analysis after nitrogen plasma and PIII treatment at 20 kV revealed that the silk macromolecules are significantly fragmented, and at the higher fluences of implanted ions, surface carbonization was observed to depths corresponding to that of the ion penetration. Consistent with the activity of radicals created in the treated surface layer, oxidation was observed on contact with atmospheric oxygen and the PIII treated surfaces were capable of direct covalent immobilization of bioactive macromolecules. Changes in thickness, amide and nitrile groups, refractive index, and extinction coefficient in the wavelength range 400-1000 nm as a function of ion fluence are presented. Reactions responsible for the restructuring of the silk surface under ion beam treatment that facilitate covalent binding of proteins and a significant improvement in cell interactions on the modified surface are proposed.

Tropoelastin Implants That Accelerate Wound Repair.

A novel, pure, synthetic material is presented that promotes the repair of full-thickness skin wounds. The active component is tropoelastin and leverages its ability to promote new blood vessel formation and its cell recruiting properties to accelerate wound repair. Key to the technology is the use of a novel heat-based, stabilized form of human tropoelastin which allows for tunable resorption. This implantable material contributes a tailored insert that can be shaped to the wound bed, where it hydrates to form a conformable protein hydrogel. Significant benefits in the extent of wound healing, dermal repair, and regeneration of mature epithelium in healthy pigs are demonstrated. The implant is compatible with initial co-treatment with full- and split-thickness skin grafts. The implant's superiority to sterile bandaging, commercial hydrogel and dermal regeneration template products is shown. On this basis, a new concept for a prefabricated tissue repair material for point-of-care treatment of open wounds is provided.

Shape dependent cytotoxicity of PLGA-PEG nanoparticles on human cells.

We investigated the influence of nanoparticles' shape on the physiological responses of cells, when they were fed with spherical and needle-shaped PLGA-PEG nanoparticles (the volume of the nanoparticles had been chosen as the fixed parameter). We found that both types of NPs entered cells via endocytosis and upon internalization they stayed in membrane bounded vesicles. Needle-shaped, but not the spherical-shaped NPs were found to induce significant cytotoxicity in the cell lines tested. Our study evidenced that the cytotoxicity of needle-shaped NPs was induced through the lysosome disruption. Lysosome damage activated the signaling pathways for cell apoptosis, and eventually caused DNA fragmentation and cell death. The present work showed that physiological response of the cells can be very different when the shape of the fed nanoparticles changed from spherical to needle-like. The finding suggests that the toxicity of nanomaterials also depends on their shape.

Two-in-One Biointerfaces-Antimicrobial and Bioactive Nanoporous Gallium Titanate Layers for Titanium Implants.

The inhibitory effect of gallium (Ga) ions on bone resorption and their superior microbial activity are attractive and sought-after features for the vast majority of implantable devices, in particular for implants used for hard tissue. In our work, for the first time, Ga ions were successfully incorporated into the surface of titanium metal (Ti) by simple and cost-effective chemical and heat treatments. Ti samples were initially treated in NaOH solution to produce a nanostructured sodium hydrogen titanate layer approximately 1 µm thick. When the metal was subsequently soaked in a mixed solution of CaCl2 and GaCl3, its Na ions were replaced with Ca and Ga ions in a Ga/Ca ratio range of 0.09 to 2.33. 8.0% of the Ga ions were incorporated into the metal surface when the metal was soaked in a single solution of GaCl3 after the NaOH treatment. The metal was then heat-treated at 600 °C to form Ga-containing calcium titanate (Ga-CT) or gallium titanate (GT), anatase and rutile on its surface. The metal with Ga-CT formed bone-like apatite in a simulated body fluid (SBF) within 3 days, but released only 0.23 ppm of the Ga ions in a phosphate-buffered saline (PBS) over a period of 14 days. In contrast, Ti with GT did not form apatite in SBF, but released 2.96 ppm of Ga ions in PBS. Subsequent soaking in hot water at 80 °C dramatically enhanced apatite formation of the metal by increasing the release of Ga ions up to 3.75 ppm. The treated metal exhibited very high antibacterial activity against multidrug resistant Acinetobacter baumannii (MRAB12). Unlike other antimicrobial coating on titanium implants, Ga-CT and GT interfaces were shown to have a unique combination of antimicrobial and bioactive properties. Such dual activity is essential for the next generation of orthopaedic and dental implants. The goal of combining both functions without inducing cytotoxicity is a major advance and has far reaching translational perspectives. This unique dual-function biointerfaces will inhibit bone resorption and show antimicrobial activity through the release of Ga ions, while tight bonding to the bone will be achieved through the apatite formed on the surface.

Triple Hit with Drug Carriers: pH- and Temperature-Responsive Theranostics for Multimodal Chemo- and Photothermal Therapy and Diagnostic Applications.

Currently there is a strong need for new drug delivery systems, which enable targeted and controlled function in delivering drugs while satisfying highly sensitive imaging modality for early detection of the disease symptoms and damaged sites. To meet these criteria we develop a system that integrates therapeutic and diagnostic capabilities (theranostics). Importantly, therapeutic efficacy of the system is enhanced by exploiting synergies between nanoparticles, drug, and hyperthermia. At the core of our innovation is near-infrared (NIR) responsive gold nanorods (Au) coated with drug reservoirs--mesoporous silica shell (mSi)--that is capped with thermoresponsive polymer. Such design of theranostics allows the detection of the system using computed tomography (CT), while finely controlled release of the drug is achieved by external trigger, NIR light irradiation--ON/OFF switch. Doxorubicin (DOX) was loaded into mSi formed on the gold core (Au@mSi-DOX). Pores were then capped with the temperature-sensitive poly(N-isopropylacrylamide)-based N-butyl imidazolium copolymer (poly(NIPAAm-co-BVIm)) resulting in a hybrid system-Au@mSi-DOX@P. A 5 min exposure to NIR induces polymer transition, which triggers the drug release (pores opening), increases local temperature above 43 °C (hyperthermia), and upregulates particle uptake (polymer becomes hydrophilic). The DOX release is also triggered by drop in pH enabling localized drug release when particles are taken up by cancer cells. Importantly, the synergies between chemo- and photothermal therapy for DOX-loaded theranostics were confirmed. Furthermore, higher X-ray attenuation value of the theranostics was confirmed via X-ray CT test indicating that the nanoparticles act as contrast agent and can be detected by CT.

Injectable hybrid delivery system composed of gellan gum, nanoparticles and gentamicin for the localized treatment of bone infections.

OBJECTIVES: Bone infections are treated with antibiotics administered intravenously, antibiotic-releasing bone cements or collagen sponges placed directly in the infected area. These approaches render limited effectiveness due to the lack of site specificity and invasiveness of implanting cements and sponges. To address these limitations, we developed a novel polysaccharide hydrogel-based injectable system that enables controlled delivery of gentamicin (GENT). Its advantages are minimal invasiveness, and localized and finely regulated release of the drug. METHODS: GENT was incorporated both directly within the gellan gum hydrogel and into poly(L-lactide-co-glycolide) nanoparticles embedded into the hydrogel. RESULTS: We confirmed the injectability of the system and measured extrusion force was 15.6 ± 1.0 N, which is suitable for injections. The system set properly after the injection as shown by rheological measurements. Desired burst release of the drug was observed within the first 12 h and the dose reached ~27% of total GENT. Subsequently, GENT was released gradually and sustainably: ~60% of initial dose within 90 days. In vitro studies confirmed antimicrobial activity of the system against Staphylococcus spp. and cytocompatibility with osteoblast-like cells. CONCLUSIONS: Developed injectable system enables minimally invasive, local and sustained delivery of the pharmaceutically relevant doses of GENT to combat bone infections.

The future perspectives of natural materials for pulmonary drug delivery and lung tissue engineering.

INTRODUCTION: Search for new, functional biomaterials that can be used to synergistically deliver a drug, enhance its adsorption and stimulate the post-injury recovery of tissue function, is one of the priorities in biomedicine. Currently used materials for drug delivery fail to satisfy one or more of these functionalities, thus they have limited potential and new classes of materials are urgently needed. AREAS COVERED: Natural materials, due to their origin, physical and chemical structure can potentially fulfill these requirements and there is already strong evidence of their usefulness in drug delivery. They are increasingly utilized in various therapeutic applications due to the obvious advantages over synthetic materials. Particularly in pulmonary drug delivery, there have been limitations in the use of synthetic materials such as polymers and lipids, leading to an increase in the use of natural and protein-based materials such as silk, keratin, elastin and collagen. Literature search in each specialized field, namely, silk, keratin and collagen was conducted, and the benefits of each material for future application in pulmonary drug delivery are highlighted. EXPERT OPINION: The natural materials discussed in this review have been well established in their use for other applications, yet further studies are required in the application of pulmonary drug delivery. The properties exhibited by these natural materials seem positive for their application in lung tissue engineering, which may allow for more extensive testing for validation of pulmonary drug delivery systems.