Induced Biological Response in Contact with Ag-and Cu-Doped Carbon Coatings for Potential Orthopedic Applications

Facile One-Step Electrospinning Process to Prepare AgNPs-Loaded PLA and PLA/PEO Mats with Antibacterial Activity

Nanofibers can play an important role in developing new kinds of medical applications. Poly(lactic acid) (PLA) and PLA/poly(ethylene oxide) (PEO) antibacterial mats containing silver nanoparticles (AgNPs) were prepared by a simple one-step electrospinning method that allows AgNPs to be synthesized simultaneously with the preparation of the electrospinning solution. The electrospun nanofibers were characterized by scanning electron microscopy, transmission electron microscopy and thermogravimetry, while silver release over time was monitored by inductively coupled plasma/optical emission spectroscopy. The antibacterial activity was tested against Staphylococcus epidermidis and Escherichia coli by colony forming unit (CFU) count on agar after 15, 24 and 48 h of incubation. AgNPs were found to be mainly concentrated in the PLA nanofiber core, and the mats showed steady but slow Ag release in the short term; in contrast, AgNPs were uniformly distributed in the PLA/PEO nanofibers, which released up to 20% of their initial silver content in 12 h. A significant (p < 0.05) antimicrobial effect towards both tested bacteria, highlighted by a reduction in the CFU/mL counts, was observed for the nanofibers of PLA and PLA/PEO embedded with AgNPs, with a stronger effect exerted by the latter, confirming the more efficient silver release from these samples. The prepared electrospun mats may have good potential for use in the biomedical field, particularly in wound dressing applications, where a targeted delivery of the antimicrobial agent is highly desirable to avoid infections.

Interactive Effects of Copper-Doped Urological Implants with Tissue in the Urinary Tract for the Inhibition of Cell Adhesion and Encrustation in the Animal Model Rat

The insertion of a ureteral stent provides acute care by restoring urine flow and alleviating urinary retention or dysfunction. The problems of encrustation, bacterial colonization and biofilm formation become increasingly important when ureteral stents are left in place for a longer period of time. One way to reduce encrustation and bacterial adherence is to modify the stent surface with a diamond-like carbon coating, in combination with copper doping. The biocompatibilities of the Elastollan^® base material and the a-C:H/Cu-mulitilayer coating were tested in synthetic urine. The copper content in bladder tissue was determined by atomic absorption spectroscopy and in blood and in urine by inductively coupled plasma mass spectrometry. Encrustations on the materials were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. A therapeutic window for copper ions of 0.5–1.0 mM was determined to kill bacteria without affecting human urothelial cells. In the rat animal model, it was found that copper release did not reach toxic concentrations in the affecting tissue of the urinary tract or in the blood. The encrustation behavior of the surfaces showed that the roughness of the amorphous carbon layer with the copper doping is probably the causal factor for the higher encrustation.

Current Knowledge on Biomaterials for Orthopedic Applications Modified to Reduce Bacterial Adhesive Ability

A significant challenge in orthopedics is the design of biomaterial devices that are able to perform biological functions by substituting or repairing various tissues and controlling bone repair when required. This review presents an overview of the current state of our recent research into biomaterial modifications to reduce bacterial adhesive ability, compared with previous reviews and excellent research papers, but it is not intended to be exhaustive. In particular, we investigated biomaterials for replacement, such as metallic materials (titanium and titanium alloys) and polymers (ultra-high-molecular-weight polyethylene), and biomaterials for regeneration, such as poly(ε-caprolactone) and calcium phosphates as composites. Biomaterials have been designed, developed, and characterized to define surface/bulk features; they have also been subjected to bacterial adhesion assays to verify their potential capability to counteract infections. The addition of metal ions (e.g., silver), natural antimicrobial compounds (e.g., essential oils), or antioxidant agents (e.g., vitamin E) to different biomaterials conferred strong antibacterial properties and anti-adhesive features, improving their capability to counteract prosthetic joint infections and biofilm formation, which are important issues in orthopedic surgery. The complexity of biological materials is still far from being reached by materials science through the development of sophisticated biomaterials. However, close interdisciplinary work by materials scientists, engineers, microbiologists, chemists, physicists, and orthopedic surgeons is indeed necessary to modify the structures of biomaterials in order to achieve implant integration and tissue regeneration while avoiding microbial contamination.

Novel Silver-Functionalized Poly(ε-Caprolactone)/Biphasic Calcium Phosphate Scaffolds Designed to Counteract Post-Surgical Infections in Orthopedic Applications

In this study, we designed and developed novel poly(ε-caprolactone) (PCL)-based biomaterials, for use as bone scaffolds, through modification with both biphasic calcium phosphate (BCP), to impart bioactive/bioresorbable properties, and with silver nitrate, to provide antibacterial protection against Staphylococcus aureus, a microorganism involved in prosthetic joint infections (PJIs). Field emission scanning electron microscopy (FESEM) showed that the samples were characterized by square-shaped macropores, and energy dispersive X-ray spectroscopy analysis confirmed the presence of PCL and BCP phases, while inductively coupled plasma-mass spectrometry (ICP-MS) established the release of Ag+ in the medium (~0.15-0.8 wt% of initial Ag content). Adhesion assays revealed a significant (p < 0.0001) reduction in both adherent and planktonic staphylococci on the Ag-functionalized biomaterials, and the presence of an inhibition halo confirmed Ag release from enriched samples. To assess the potential outcome in promoting bone integration, preliminary tests on sarcoma osteogenic-2 (Saos-2) cells indicated PCL and BCP/PCL biocompatibility, but a reduction in viability was observed for Ag-added biomaterials. Due to their combined biodegrading and antimicrobial properties, the silver-enriched BCP/PCL-based scaffolds showed good potential for engineering of bone tissue and for reducing PJIs as a microbial anti-adhesive tool used in the delivery of targeted antimicrobial molecules, even if the amount of silver needs to be tuned to improve osteointegration.

Overview on the Antimicrobial Activity and Biocompatibility of Sputtered Carbon-Based Coatings

Due to their outstanding properties, carbon-based structures have received much attention from the scientific community. Their applications are diverse and include use in coatings on self-lubricating systems for anti-wear situations, thin films deposited on prosthetic elements, catalysis structures, or water remediation devices. From these applications, the ones that require the most careful testing and improvement are biomedical applications. The biocompatibility and antibacterial issues of medical devices remain a concern, as several prostheses still fail after several years of implantation and biofilm formation remains a real risk to the success of a device. Sputtered deposition prevents the introduction of hazardous chemical elements during the preparation of coatings, and this technique is environmentally friendly. In addition, the mechanical properties of C-based coatings are remarkable. In this paper, the latest advances in sputtering methods and biocompatibility and antibacterial action for diamond-based carbon (DLC)-based coatings are reviewed and the greater outlook is then discussed.