Bactericidal activity of gallium-doped chitosan coatings against staphylococcal infection.

AIMS: The aim of this study was to develop a new class of gallium (Ga)-doped chitosan (CS) coatings fabricated by electrophoretic deposition (EPD) in staphylococcal infection therapy. METHODS AND RESULTS: Biofilm formation on EPD CS/Ga coatings by Staphylococcus epidermidis and Staphylococcus aureus, which are the main strains involved in postarthroplasty infections, was assessed. The codeposition of an antibacterial agent was effective; Ga loaded into CS matrix reduces biofilm viability by up to 86% and 80% for S. epidermidis and S. aureus strains respectively. Lastly, the influence of pulsed electromagnetic field (PEMF) on the bactericidal activity of CS/Ga coatings was investigated in vitro. To this end, the coatings were incubated with S. epidermidis and S. aureus and exposed to the PEMF using two different frequencies and times. Biofilm viability for S. epidermidis was decreased by 35-40% in the presence of low-frequency (LF) and high-frequency (HF) PEMF respectively. Biofilm viability by S. aureus was not further reduced in the presence of LF PEMF, but decreased by 38% at HF PEMF. CONCLUSIONS: This study has established that a combination of PEMFs with the antibacterial agent improves bactericidal activity of Ga against S. epidermidis strain 14990 and S. aureus strain 12600. SIGNIFICANCE AND IMPACT OF THE STUDY: This new integrated approach could reduce the incidence of infection in orthopaedic implant applications. It also clearly demonstrates that the combination of Ga treatment with PEMF could aid biofilm-associated infection therapy due to improved Ga efficiency.

Programmed cell delivery from biodegradable microcapsules for tissue repair.

Injectable and resorbable hydrogels are an extremely attractive class of biomaterials. They make it possible to fill tissue defects accurately with an undoubtedly minimally invasive approach and to locally deliver cells that support repair or regeneration processes. However, their use as a cell carrier is often hindered by inadequate diffusion in bulk. A possible strategy for overcoming this transport limitation might be represented by injection of rapidly degradable cell-loaded microcapsules, so that maximum material thickness is limited by sphere radius. Here, the possibility of achieving programmable release of viable cells from alginate-based microcapsules was explored in vitro, by evaluating variations in material stability resulting from changes in hydrogel composition and assessing cell viability after encapsulation and in vitro release from microcapsules. Degradation of pure alginate microspheres was varied from a few days to several weeks by varying sodium alginate and calcium chloride concentrations. The addition of poloxamer was also found to accelerate degradation significantly, with capsule breakdown almost complete by two weeks, while chitosan was confirmed to strengthen alginate cross-linking. The presence of viable cells inside microspheres was revealed after encapsulation, and released cells were observed for all the formulations tested after a time interval dependent on bead degradation speed. These findings suggest that it may be possible to fine tune capsule breakdown by means of simple changes in material formulation and regulate, and eventually optimize, cell release for tissue repair.

Skin-derived stem cells transplanted into resorbable guides provide functional nerve regeneration after sciatic nerve resection.

The regeneration in the peripheral nervous system is often incomplete and the treatment of severe lesions with nerve tissue loss is primarily aimed at recreating nerve continuity. Guide tubes of various types, filled with Schwann cells, stem cells, or nerve growth factors are attractive as an alternative therapy to nerve grafts. In this study, we evaluated whether skin-derived stem cells (SDSCs) can improve peripheral nerve regeneration after transplantation into nerve guides. We compared peripheral nerve regeneration in adult rats with sciatic nerve gaps of 16 mm after autologous transplantation of GFP-labeled SDSCs into two different types of guides: a synthetic guide, obtained by dip coating with a L-lactide and trimethylene carbonate (PLA-TMC) copolymer and a collagen-based guide. The sciatic function index and the recovery rates of the compound muscle action potential were significantly higher in the animals that received SDSCs transplantation, in particular, into the collagen guide, compared to the control guides filled only with PBS. For these guides the morphological and immunohistochemical analysis demonstrated an increased number of myelinated axons expressing S100 and Neurofilament 70, suggesting the presence of regenerating nerve fibers along the gap. GFP positive cells were found around regenerating nerve fibers and few of them were positive for the expression of glial markers as S-100 and glial fibrillary acidic protein. RT-PCR analysis confirmed the expression of S100 and myelin basic protein in the animals treated with the collagen guide filled with SDSCs. These data support the hypothesis that SDSCs could represent a tool for future cell therapy applications in peripheral nerve regeneration.

Nanostructured surfaces for biomedical applications. Part I: nanotopography.

The natural cell environment provides a variety of chemical, topographical and mechanical stimuli that contribute in regulating cell behavior and function. If considerable effort has been traditionally dedicated to exploring the chemical side of cell regulation, it was more recently demonstrated that topographic cues might be equally important. Cell substratum interactions are particularly crucial in determining the reaction of cells to biomaterials, which was also shown to be strongly determined by topographical cues. A significant acceleration in investigating this aspect came from the availability of techniques for microstructured surfaces, and is now well known that cells can react to topographical features at their own scale (1-100 micron). Nevertheless, cells possess many nanoscaled features such as filopodia and a cytoskeleton, and the extracellular matrix (ECM) itself possess quite a few nanoscale details. Therefore, the capability of controlling the surface structure of materials in the nanoscale has offered the possibility of adding another level in the hierarchical understanding of cell/biomaterial interactions. Nanofabrication methods, mainly developed out of the semiconductor industries, are a technological driver for addressing the nanotopography related aspects of cell behavior. General concepts regarding some of the more widely utilized techniques that enable the achievement of ordered and well-defined nanoscale features for the investigation of cell reaction to topography are presented together with a few examples of the practical applications available in the literature.

Physical-chemical and biological characterization of silk fibroin-coated porous membranes for medical applications.

Membranes in artificial organs and scaffolds for tissue engineering are often coated with biomimetic molecules (e.g., collagen) to improve their biocompatibility and promote primary cell adhesion and differentiation. However, animal proteins are expensive and may be contaminated with prions. Silk fibroin (SF) made by Bombyx Mori silk worms, used as a scaffold or grafted to other polymers, reportedly promotes the adhesion and growth of many human cell types. This paper describes how commercial porous membranes were physically coated with SF, and their physical-chemical properties were characterized by SEM, AFM, tensile stress analysis and dynamic contact angle measurements. The effect of the SF coating on membrane biocompatibility and resistance to bacterial colonization is also examined. The proposed technique yields SF coats of different thickness that strengthen the membranes and make their surface remarkably more wettable. The SF coat is not cytotoxic, and promotes the adhesion and proliferation of an immortalized fibroblast cell line. Similarly to collagen, SF-coated membranes also exhibit a much better resistance to the adhesion of S. epidermidis bacteria than uncoated membranes. These preliminary results suggest that SF is a feasible alternative to collagen as a biomimetic coating for 3D scaffolds for tissue engineering or bioartificial (as well as artificial) prosthesis.

Bioabsorbable scaffold for in situ bone regeneration.

A non-porous poly-DL-lactide tubular chamber filled by demineralised bone matrix (DBM) and bone marrow stromal cells (BMSC) in combination, was evaluated as a scaffold for guided bone regeneration (GBR) in an experimental model using the rabbit radius. The tubular chamber had an internal diameter of 4.7 mm, a wall thickness of 0.4 mm and a length of 18 mm. Autologous BMSC were obtained, under general anaesthesia from rabbit iliac crest and isolated by centrifugation technique. Allogenic DBM was obtained from cortico-cancellous bone of rabbits. In general anaesthesia, a 10-mm defect was bilaterally created in the radii of 10 rabbits. On the right side (experimental side) the defect was bridged with the chamber filled with both BMSC and DBM. On the left side (control side) the defect was treated by positioning DBM and BMSC between the two stumps. At an experimental time of 4 months histology and histomorphometry demonstrated that the presence of a tubular chamber significantly improved bone regrowth in the defect The mean thickness of newly-formed bone inside the chamber was about 56.7+/-3.74% of the normal radial cortex, in comparison with 46.7+/-10.7% when DBM and BMSC without the chamber were placed in the defect, P<0.05). These results confirmed the effectiveness of the chamber as a container for factors promoting bone regeneration.

Microspheres leaching for scaffold porosity control.

Scaffold morphology plays a key role in the development of tissue engineering constructs. The control of pore size, shape and interconnection is needed to achieve adequate nutrient transport and cell ingrowth. Several techniques are available for scaffold manufacturing, but none allows easy control of morphology and is, at the same time, applicable to a wide variety of materials. To investigate the possibility of processing a wide range polymers by solvent casting/particulate leaching with accurate control of scaffold morphology, three different porogens (gelatin microspheres, paraffin microspheres and sodium chloride crystals) were used to fabricate scaffolds from commonly employed biodegradable polymers. The outcome of processing was evaluated in terms of scaffold morphology and structure/properties relationships. Highly porous scaffolds were obtained with all porogens and well defined spherical pores resulted from microspheres leaching. Furthermore, scaffolds with spherical pores showed better mechanical performance and lower flow resistance. Cytocompatibility tests performed showed no evidence of processing residuals released from the scaffolds. Solvent casting/microspheres leaching, particularly gelatin microspheres leaching, can be used to process a large number of polymers and enables to tailor scaffold pore size, shape and interconnection, thus providing a powerful tool for material selection and optimization of scaffold morphology.

[Carotid sinus syndrome. Description of a case treated by surgical denervation]. / Sindrome del seno carotideo. Descrizione di un caso trattato con denervazione chirurgica.

A 43 years old man suffering from syncopal attacks and episodes of dizziness was found as affected by right carotid sinus syndrome causing cardioinhibition. Excluding all possible specific causes of carotid sinus hypersensitivity and, by means of electrophysiological study, any intrinsic cardiac pathology, was settled that the long pauses of asystole that produce syncopal attacks were of extrinsic vagal nature. Considering the young age of the patient an operation of surgical denervation of the right carotid sinus was decided upon. This simple and riskless treatment allowed the case to be solved without resorting to permanent pacemaker implantation.