Wojciech Chrzanowski

Magnesium incorporation into hydroxyapatite

The incorporation of Mg in hydroxyapatite (HA) was investigated using multinuclear solid state NMR, X-ray absorption spectroscopy (XAS) and computational modeling. High magnetic field (43)Ca solid state NMR and Ca K-edge XAS studies of a ∼10% Mg-substituted HA were performed, bringing direct evidence of the preferential substitution of Mg in the Ca(II) position. (1)H and (31)P solid state NMR show that the environment of the anions is disordered in this substituted apatite phase. Both Density Functional Theory (DFT) and interatomic potential computations of Mg-substituted HA structures are in agreement with these observations. Indeed, the incorporation of low levels of Mg in the Ca(II) site is found to be more favourable energetically, and the NMR parameters calculated from these optimized structures are consistent with the experimental data. Calculations provide direct insight in the structural modifications of the HA lattice, due to the strong contraction of the M⋯O distances around Mg. Finally, extensive interatomic potential calculations also suggest that a local clustering of Mg within the HA lattice is likely to occur. Such structural characterizations of Mg environments in apatites will favour a better understanding of the biological role of this cation.

The antimicrobial properties of light-activated polymers containing methylene blue and gold nanoparticles

We report the formation of polysiloxane polymers containing embedded methylene blue and gold nanoparticles incorporated by a swell-encapsulation-shrink method. These polymers show significant antimicrobial activity against methicillin-resistant Staphylococcus aureus and Escherichia coli with up to a 3.5 log(10) reduction in the viable count when exposed for 5 min to light from a low power 660 nm laser. The bacterial kill is due to the light-induced production of singlet oxygen and other reactive oxygen species by the methylene blue. Interestingly, the presence of 2 nm gold nanoparticles significantly enhanced the ability of the methylene blue to kill bacteria.

An elastomeric patch derived from poly(glycerol sebacate) for delivery of embryonic stem cells to the heart.

We hypothesize that a combinatorial approach of ventricle constraint and stem cell therapy would offer a greater benefit for the treatment of heart failure than either strategy alone. A heart patch would serve two therapeutic purposes: biomechanical support and cell delivery. In this study, we describe a hybrid heart patch engineered from a synthetic elastomer, poly(glycerol sebacate) (PGS), supplemented with cardiomyocytes differentiated from human embryonic stem cells (hESCs). In line with two therapeutically relevant considerations, i.e. biocompatibility and cell delivery efficiency, the PGS was (a) pre-conditioned in culture medium for 6 days, and (b) prepared without gelatin coatings to facilitate detachment and delivery of cardiomyocytes following patch implantation. Following pre-conditioning under physiological conditions, the PGS patch material without gelatin coating was found to satisfactorily support cardiomyocyte viability and attachment, with active cell beating for periods of longer than 3 months until interrupted. Dynamic culture studies revealed that cells detached more efficiently from the uncoated surface of PGS than from gelatin-coated PGS. No significant differences were detected between the beating rates of human embryonic stem cell-derived cardiomyocytes on tissue culture plate and the pre-conditioned and gelatin-uncoated PGS. PGS patches sutured over the left ventricle of rats in vivo remained intact over a 2 week period without any deleterious effects on ventricular function. We conclude that PGS is a suitable biomaterial for stem cell-based regeneration strategies to restore cardiomyocyte function, and the hybrid heart patch engineered under optimal conditions would be a promising support device for the cardiac repair.

Silica-based mesoporous nanoparticles for controlled drug delivery

Drug molecules with lack of specificity and solubility lead patients to take high doses of the drug to achieve sufficient therapeutic effects. This is a leading cause of adverse drug reactions, particularly for drugs with narrow therapeutic window or cytotoxic chemotherapeutics. To address these problems, there are various functional biocompatible drug carriers available in the market, which can deliver therapeutic agents to the target site in a controlled manner. Among the carriers developed thus far, mesoporous materials emerged as a promising candidate that can deliver a variety of drug molecules in a controllable and sustainable manner. In particular, mesoporous silica nanoparticles are widely used as a delivery reagent because silica possesses favourable chemical properties, thermal stability and biocompatibility. Currently, sol-gel-derived mesoporous silica nanoparticles in soft conditions are of main interest due to simplicity in production and modification and the capacity to maintain function of bioactive agents. The unique mesoporous structure of silica facilitates effective loading of drugs and their subsequent controlled release. The properties of mesopores, including pore size and porosity as well as the surface properties, can be altered depending on additives used to fabricate mesoporous silica nanoparticles. Active surface enables functionalisation to modify surface properties and link therapeutic molecules. The tuneable mesopore structure and modifiable surface of mesoporous silica nanoparticle allow incorporation of various classes of drug molecules and controlled delivery to the target sites. This review aims to present the state of knowledge of currently available drug delivery system and identify properties of an ideal drug carrier for specific application, focusing on mesoporous silica nanoparticles.

Curcumin as a wound healing agent.

Turmeric (Curcuma longa) is a popular Indian spice that has been used for centuries in herbal medicines for the treatment of a variety of ailments such as rheumatism, diabetic ulcers, anorexia, cough and sinusitis. Curcumin (diferuloylmethane) is the main curcuminoid present in turmeric and responsible for its yellow color. Curcumin has been shown to possess significant anti-inflammatory, anti-oxidant, anti-carcinogenic, anti-mutagenic, anti-coagulant and anti-infective effects. Curcumin has also been shown to have significant wound healing properties. It acts on various stages of the natural wound healing process to hasten healing. This review summarizes and discusses recently published papers on the effects of curcumin on skin wound healing. The highlighted studies in the review provide evidence of the ability of curcumin to reduce the bodys natural response to cutaneous wounds such as inflammation and oxidation. The recent literature on the wound healing properties of curcumin also provides evidence for its ability to enhance granulation tissue formation, collagen deposition, tissue remodeling and wound contraction. It has become evident that optimizing the topical application of curcumin through altering its formulation is essential to ensure the maximum therapeutical effects of curcumin on skin wounds.

Controlled delivery of antimicrobial gallium ions from phosphate-based glasses

Gallium-doped phosphate-based glasses (PBGs) have been recently shown to have antibacterial activity. However, the delivery of gallium ions from these glasses can be improved by altering the calcium ion concentration to control the degradation rate of the glasses. In the present study, the effect of increasing calcium content in novel gallium (Ga2O3)-doped PBGs on the susceptibility of Pseudomonas aeruginosa is examined. The lack of new antibiotics in development makes gallium-doped PBG potentially a highly promising new therapeutic agent. The results show that an increase in calcium content (14, 15 and 16 mol.% CaO) cause a decrease in degradation rate (17.6, 13.5 and 7.3 microg mm(-2) h(-1)), gallium ion release and antimicrobial activity against planktonic P. aeruginosa. The most potent glass composition (containing 14 mol.% CaO) was then evaluated for its ability to prevent the growth of biofilms of P. aeruginosa. Gallium release was found to reduce biofilm growth of P. aeruginosa with a maximum effect (0.86 log(10) CFU reduction compared to Ga2O3-free glasses) after 48 h. Analysis of the biofilms by confocal microscopy confirmed the anti-biofilm effect of these glasses as it showed both viable and non-viable bacteria on the glass surface. Results of the solubility and ion release studies show that this glass system is suitable for controlled delivery of Ga3+. 71Ga NMR and Ga K-edge XANES measurements indicate that the gallium is octahedrally coordinated by oxygen atoms in all samples. The results presented here suggest that PBGs may be useful in controlled drug delivery applications, to deliver gallium ions in order to prevent infections due to P. aeruginosa biofilms.

Anti-bacterial surfaces: natural agents, mechanisms of action, and plasma surface modification

Strategies that confine antibacterial and/or antifouling property to the surface of the implant, by modifying the surface chemistry and morphology or by encapsulating the material in an antibiotic-loaded coating, are most promising as they do not alter bulk integrity of the material. Among them, plasma-assisted modification and catechol chemistry stand out for their ability to modify a wide range of substrates. By controlling processing parameters, plasma environment can be used for surface nano structuring, chemical activation, and deposition of biologically active and passive coatings. Catechol chemistry can be used for material-independent, highly-controlled surface immobilisation of active molecules and fabrication of biodegradable drug-loaded hydrogel coatings. In this article, we comprehensively review the role plasma-assisted processing and catechol chemistry can play in combating bacterial colonisation on medically relevant coatings, and how these strategies can be coupled with the use of natural antimicrobial agents to produce synthetic antibiotic-free antibacterial surfaces.

Effect of increasing titanium dioxide content on bulk and surface properties of phosphate-based glasses

There is an ingoing need for more effective and less costly bone substitute materials. In a previous study, addition of titanium dioxide (TiO2) up to 5 mol.% was shown to be effective in controlling glass degradation, and this was reflected in enhanced gene expression and bone-forming capacity of phosphate-based glasses. In the current study, incorporation of the maximum possible amount of TiO2 has been attempted in order to further improve the biological response of these glasses. This report describes the physical, surface properties and short-term response of an osteoblast cell line (MG63) on phosphate glasses doped with the maximum possible TiO2 content. The results showed that a maximum of 15 mol.% TiO2 can be incorporated into the ternary formulations while maintaining their amorphous nature; such incorporation was associated with a significant increase in density and glass transition temperature. On crystallization, X-ray diffraction analysis showed the presence of TiP2O7 and NaCa(PO3)3 as the main phases for all TiO2-containing glasses, while beta-(CaP2O6) was only detected for 10 and 15 mol.% TiO2 glasses. The degradation rate, however, was significantly reduced by an order of magnitude with incorporation of 10 and 15 mol.% TiO2, and this was reflected in the released ions. This change in the bulk properties, produced with TiO2 incorporation, was also associated with a significant change in the hydrophilicity and surface reactivity of these glasses. Even though the addition of TiO2 reduced the hydrophilicity and the surface free energy of these glasses compared to TiO2 free composition, TiO2-containing glasses still have a significantly reactive surface layer compared to Thermanox. Generally glasses with 5-15 mol.% TiO2 supported MG63 cell growth and maintained high cell viability for up to 7 days culture, which is comparable to Thermanox. Based on the results obtained from this study, TiO2-containing phosphate glasses are promising substrates for bone tissue engineering applications.

A DNA Nanostructure for the Functional Assembly of Chemical Groups with Tunable Stoichiometry and Defined Nanoscale Geometry

Herein we describe a new approach which merges DNA-based nanostructures and the chemical modification of DNA.We show that tetrahedron-shaped nanostructures can act asscaffoldstoassembleamultitudeofdifferentchemicalgroupsat tunable stoichiometry and at geometrically defined sites.The resulting molecular entities exhibit functional propertiesbeneficial in biosensing and diagnostics. Our new strategy forassembling chemical groups at the nanoscale may beexpanded to endow other DNA structures with rationallydesigned functions.DNA tetrahedra, as intoduced by Goodman et al, arenanostructures with edges composed of double-strandedDNA (dsDNA; Figure 1a).

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.