Special Issue "Coating Deposition and Surface Functionalization of Implants for Biomedical Applications"

Guest Editor
Dr. Antonella Sola
Dipartimento di Ingegneria dei Materiali e dell'Ambiente, Universita' di Modena e Reggio Emilia, Via Vignolese 905 - 41125 Modena, Italy
Website: http://ilo.unimo.it/Show/People.aspx?Action=Data&IdUniversity=1&IdDepartment=29&IdPeople=995&IdPeopleDept=1014&IdLanguage=2
E-Mail: antonella.sola@unimore.it
Phone: +39 059 2056233
Fax: +39 059 2056243

Dear Colleagues,

The human body is able to promote spontaneous healing phenomena to face the adverse consequences of diseases, aging processes or traumatic events. However such natural reactions are not always sufficient to recover extensive functional losses and, in that case, medical or surgical interventions are required. For this reason, the demand for new biomaterials to support or restore the role of damaged tissues is a major clinical and socioeconomic need. The deposition of a proper coating or the chemicophysical treatment of the surface may boost the performance of implant devices, conveying site-specific properties to the substrate material. The apposition of glass-based glazes which resemble the original enamel of tooth, the chemical modification of titanium to activate the bone-bonding ability or the deposition of calcium-phosphate layers on metal substrates to elicit the surface development of hydroxyapatite are just a few examples of the new approaches to improve the behaviour of medical grafts by means of biocoatings and surface functionalization methods.

Dr. Antonella Sola
Guest Editor

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• biocoatings
• functionalization
• surface treatments
• coating deposition methods
• implant materials

Title: The Use of Sonication to Completely Decellularize Aortic Tissue for Biomaterials
Author: Azran Azhim
Affiliation: Frontier Research & Development Center, Tokyo Denki University, Ishizaka, Hatoyama, Saitama 350-0394, Japan; E-Mail: azran@frontier.dendai.ac.jp
Abstract: We have developed a novel sonication decellularization system to prepare completely decellularized bioscaffolds in a short treatment time. The aim of the study is to investigate the sonication decellularization efficiency and its relation with ultrasonic power output and dissolved oxygen (DO) concentration in different detergent solution. In the study, we used aorta samples to evaluate sonication decellularization efficiency, which assessed treatment duration, washing treatment after decellularization, SDS detergent with/without saline. The treated samples were evaluated histologically by Hematoxylin Eosin (HE) and diamidino-2-phenylindol (DAPI) stains. The concentration of DO was monitored to identify the effect of sonication on cavitation-related DO concentration in the solution. The sonication decellularization efficiency was better than the other preparation methods. There were less than 2.0% of DNA remains after sonication decellularization treatment. The efficiency increased significantly which treated by sonication in SDS without saline as its DO value smaller compared with treatment in SDS with that. In conclusion, we conclude that sonication treatment is capable to use for preparation of the complete decellularized scaffolds in short treatment time.

Title: Calcium Orthophosphate Coatings, Films and Layers and their Biomedical Applications
Author: Sergey V. Dorozhkin
Affiliation: Kudrinskaja Square 1-155, Moscow 123242, Russia; E-Mail: sedorozhkin@yandex.ru
Abstract: In surgical disciplines, where bones have to be repaired, augmented or improved, bone substitutes are essential. Although bone banks are founded to supply such substitutes, natural bones are not always adequate. Therefore, an interest has dramatically increased in application of synthetic bone grafts. As various interactions among cells, surrounding tissues and implanted biomaterials always occur at the tissue/implant interfaces; the surface properties of implants play the major role in determining both the biological response to implants and the material response to the physiological conditions. Hence, a surface engineering of biomaterials is aimed to modify both the biomaterials themselves and biological responses through introducing desirable changes in the surface properties but still maintaining the bulk mechanical properties of the implants. To fulfill these requirements, a special class of artificial bone grafts has been introduced. It is composed of various mechanically stable (therefore, suitable for load bearing applications) biomaterials and/or bio-devices with calcium orthophosphate coatings, films and layers on their surfaces to both improve interactions with the surrounding tissues and provide bone bonding. Many production techniques of calcium orthophosphate coatings, films and layers have been already invented and new promising techniques are continuously investigated. These specialized coatings films and layers used to improve the surface properties of various types of implants are the topic of this review.

Title: A Method for Determining the Specific Growth Rate and Quantification of Biofilms
Authors: Maria Strömme
Affiliaion: Department of Engineering Sciences, Division of Nanotechnology and Functional Materials, Uppsala University, The Ångström Laboratory, Box 534, SE-751 21 Uppsala, Sweden; E-Mail: Maria.Stromme@Angstrom.uu.se
Abstract: Quantification of viable bacteria in a biofilm is a difficult task compared to quantifying viable planktonic bacteria. Methods that work well for planktonic bacteria have serious limitations when used on biofilms and produce erroneous results, primarily because it is difficult to separate the bacteria from the biofilm matrix without influencing bacterial viability. In this study we present a scheme for determining the specific growth rate of a biofilm from a series of metabolic assays. This information can subsequently be used to quantify the effect of, for example, antibacterial treatments of implant related infections. Existing metabolic assays for quantifying viable bacteria in biofilms usually utilize calibration curves derived from planktonic bacteria, which can introduce large errors due to significant differences in the metabolic and/or growth rates of bacteria in biofilms in comparison to their planktonic counterparts. In the presented method we derive the specific growth rate of Streptococcus mutans bacteria biofilm from a series of metabolic assays using the pH indicator phenol red, and show that this information could be used to more accurately quantify the relative number of viable bacteria in a biofilm. We found that the specific growth rate of S. mutans in biofilm mode of growth was 0.70 h⁻¹, compared to 1.09 h⁻¹ in planktonic growth. This method should be applicable for other types of bacterial biofilms on a broad range of functional surfaces such as medical implants.

Title: Surface Chemical Treatments of Ti and Ti Alloys as Biomedical Devices
Author: Deepak K. Pattanayak
Affiliation: Ceramics Research Laboratory, Nagoya Institute of Technology, 3-101-1, Honmachi, Tajimi, Gifu, 507-0033, Japan; E-Mails: deepak@crl.nitech.ac.jp or deepak_pattanayak@rediffmail.com
Abstract: Metals such as titanium (Ti) and Ti alloys are popularly used as hard tissue replacement materials due to their superior mechanical strength, high fracture toughness, high corrosion resistance and good biocompatibility. Further, in order to obtain the modulus of metallic materials comparable to that of human bone, porous Ti and Ti-Nb-Zr-Ta alloys are recently being developed. Although Ti and Ti alloys are popularly used as biocompatible implants, their direct contact between bone and implant is low and take longer time to develop new bones on their surfaces. Therefore, in order to improve the bone-bonding ability, various kinds of surface chemical treatments are proposed. Among them, alkali or acid or alkali following acid treatments are widely discussed in the literatures. Results showed that, surface modification of Ti and Ti alloys by chemical treatments not only improve the osteointegration and also enhance the direct bone formation in the living body. Surface topography and surface phase composition can be controlled by controlling the concentration of alkali or acid solutions or treatment temperatures or pH of exposed solution which intern affect the bioactivity of the implant. Also mechanism of bioactivity of different kinds of chemically treated Ti metals is different. In the present paper, various kinds of surface chemical treatment methods applied to Ti and Ti alloys are reviewed. This includes discussion on effect of surface morphology, surface phase on in vitro bioactivity and in vivo bone formation, and, development of chemically treated Ti and Ti alloys as bone substitutes and dental devices.
Keywords: surface modification; Ti and Ti alloys; bioactivity; medical devices