Adhesion aspects in biomaterials and medical devices

The goal of this special issue is to provide material scientists and engineers with an appreciation of the fundamental aspects of adhesion phenomena in biomaterials and medical devices, as well as their interaction with human cells and tissue.

There is a wide range of biomaterials and medical devices used for different medical applications, from metallic alloys to ceramics and from polymers to hybrid composites.

Surface properties play an important role in discussions about adhesion phenomena and have a significant role in the inflammatory and wound healing responses to biomaterials and medical devices in vivo. Studies related to protein adhesion on the biomaterials surface gained a lot of interest in the past few decades because these interactions are fundamentally responsible for biocompatibility of the materials.

This special issue is focused on the new frontiers in research studies dedicated to the use of biomaterials in different forms, for biomedical applications in dentistry and related clinical investigations.

Based on the requirements of the modern biomedical technology, the novel research strategies in biomaterials field are nowadays directed toward biomaterials endowed with surface properties, controlled adhesion, and for the controlled release of active principles, especially against infections.

In this view, several research groups have been invited to contribute to this special issue with their original research papers that could stimulate efforts of comprehensive knowledge of adhesion aspects in biomaterials and medical devices. This special issue is divided into two categories based on the following keywords: biomaterials and medical devices.

In the category of adhesion in biomaterials, polymers and composite materials with polymeric matrix have attracted a significant attention being widely used in medical devices. Synthetic polymers are used as biomaterials for many medical devices due to their properties more appropriate to the properties of human tissues. A limitation of synthetic polymers is the lack of biological cues that can promote cell adhesion, proliferation, and tissue recovery. In order to improve these properties and to enhance their interactions with cells, different composite biomaterials with polymeric matrix were developed. In order to explain the adhesion mechanism at interface and the roles played by the two phases in the composites, some theories have been developed.

It is important to mention that none of them is being able yet to fully explain the nature of interfacial adhesion phenomenon and all the process. In addition, different surface modifications or coatings are the ways to improve biological properties of medical devices using the minimization of protein adhesion onto the surface of medical devices.

Development of new antimicrobial composite materials represents an important topic for research in biomaterials during the last years. The filler integration as well as their effect on the composite properties are a key factor.

In this regard, Dumitriu et al. (this issue) investigated the influence of silver nanoparticles presence and of the dispersion composition on the rheological properties, microstructure of polyurethane (PU)/biopolymers-based dispersions and on the morphology of the solvent cast membranes obtained. Nanocomposite dispersions from polyester-type PU and mixtures of the PU with various biopolymers such as hydrolyzed collagen, k-elastin, chondroitin sulfate, or hyaluronic acid containing different concentrations of in situ generated silver nanoparticles were prepared and studied for application as antimicrobial materials or coatings. The rheological properties study, focused on crossover point changes and relaxation time spectra investigation, showed the effect of both Ag NPs content and dispersion composition. It was evidenced a complex viscoelastic response determined by chain rearrangements within macromolecules under flow disturbances. The results obtained revealed the increased rigidity of the PU structure by adding Ag NPs, leading to increased relaxation times compared with neat PU coupled with significant changes in the shape of relaxation time spectra. PU/biopolymers dispersions with higher Ag NPs content presented a more solid-like response and lower relaxation times than suspensions without Ag NPs.

Râpă et al. (this issue) reported the obtaining and characterization of some new materials obtained after modification of random polypropylene (PPR) by melt mixing technique with different thermoplastic elastomers: (poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) and poly(styrene-b-butadiene-b-styrene) (SBS) at various content ratios. Structural modifications of polypropylene with block-copolymers were investigated by determination of the elastomer content influence on density, crystallinity index, melting temperature, degree of crystallinity, crystallite size, and morphology. By increasing the elastomer content, a lower melting point and degree of crystallinity of blends were obtained. Average crystallite size and morphology of investigated blends were depending on the content and type of elastomer used. The obtained results revealed that SEBS was the most efficient and compatible elastomer with polymeric matrix. These properties could be responsible for mechanical and biological properties required for medical devices with certain applications.

An attractive alternative method to add new functionalities such as biocompatibility due to the micro- and nanoscaled modification of surfaces is given by UV-modified polymers.

Drobota et al. [1] evaluated the effect of the UV light functionalization on two polymers poly(ethylene terephthalate) (PET) and PU films by means of atomic force microscopy (AFM), Fourier transform infrared–attenuated total reflectance (FTIR–ATR) and contact angle measurements. The UV-irradiation activates the polymer surface by breaking some chemical bonds and generation of new functional groups on the surfaces. These can interact with the adsorbing protein molecules via hydrogen bonding, electrostatic, or van der Waals interactions. Static contact angle measurements demonstrate the increase in the hydrophilicity with the irradiation time due to the appearance at the surfaces of some polar groups or radicals, and AFM analysis of the adsorbed layers showed the presence of collagen structures at the surface of both polymer films. This study shows that the UV treatment proved a suitable surface modification technique to functionalize/activate the polymeric films without affecting the bulk properties and these polymeric supports could be utilized as patches in various biomedical applications.

As was mentioned previously, the interaction between biomaterials surface and cells are crucial for better functionality of medical devices.

Stoica et al. [2] investigated a polyimide based on alicyclic units, such as epiclon (5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride) from the point of view of its surface features to check their suitability for cell culture applications. AFM data revealed fractal and isotropic surfaces with nanoscale roughness and peaks placed at much smaller distances comparing to the cell size scale, favoring a good compatibility of the synthesized material with the biological medium, particularly after plasma treatment. Surface tension properties were determined in order to evaluate the interactions at the bio-interface affecting the adherence behavior of cell-binding proteins to the sample surface. In vitro experiments regarding the cytocompatibility and population tendency reveal that polyimide allows cells to adhere and to proliferate onto the surface. They conclude that the studied epiclon-based polyimide is not cytotoxic and could be recommended as good candidate for cell culture substrate in tissue engineering, especially after plasma treatment.

In the category of adhesion in medical devices, all papers debate subject from dentistry and prove that the adhesion represents one of the most important revolutions in modern dentistry.

From prosthetic restorations to the definitive cementation, the search for a strong bond has guided scientific studies so that nowadays, biomaterials with improved performance and with modified surface are used in clinical practice. Anyway, the continuous analysis and monitoring of the clinical results obtained after the use of the dental materials and deices represent a good way to establish new research directions and develop new solutions for the future.

Dental restorations represent just a part of biomaterial application in dentistry when the adhesion aspects and surface modifications influence strongly the functionality of the medical devices.

With this regard, Craciunescu et al. [3] evaluated the alterations of the shear bond strength between the zirconia core and the ceramic veneer, as produced by the first set of complete burning procedures and by the second correction burning of the dental restorations. The experimental in vitro study concluded that a second burning of the layering ceramic lowers significantly the shear bond strength value of the zirconium and layering ceramic interface. The ability to process the samples is another factor that has a strong impact on the adhesion force of the two materials. The weakest area proved constantly to be the interface one and not the ceramic added on the zirconium core. The authors concluded that the future work will focus on a comparison between the veneering layering technique and the pressed-on veneering technique, as new generations of pressed ceramic are being associated with zirconium oxide framework due to simplicity, time-saving, and defect-free structures.

In other study, Uzun et al. (this issue) evaluated the shear bond strength (SBS) of a new repairing material including zirconia primer to zirconia and veneering porcelain after various surface treatments. Authors consider that grinding with the green bur followed by the application of zirconia primer and adhesive was the most efficient method for improve the adhesion, giving the best results for zirconia and feldspathic ceramic. Also, they observe that Er-YAG laser irradiation is the least effective method to rough the zirconia surface but may be an alternative for conditioning of the feldspathic porcelain.

Esthetic dentistry imposes several demands on the artistic abilities of the dentist and knowledge of the underlying scientific principles of tooth color is essential.

Starting from this, Mesaros et al. [4] reported the usefulness of some supervised classification and selection methods in the dental analysis domain into an experimental study conducted on extracted premolars from people who required orthodontic treatment. Data gathering was done using spectrophotometric recordings of tooth color parameters before and after accelerated bleaching, staining, and control procedures on extracted teeth on which was simulated orthodontic treatment. Based on the experimental data, they conclude also that fixed orthodontic treatment is associated with significant tooth color changes and statistically significant differences appear in tooth color change after fixed orthodontic treatment. In addition, the authors mention that the staining procedures on teeth undergoing orthodontic treatments are allowing a uniform staining, the permeability of orthodontic adhesives allowing the infiltration and for the staining agent to arrive to the enamel surface.

Manolea et al. (this issue) analyze how the adhesion to the dentine surfaces of the composite resins is influenced by the characteristics of the preparation mode of the surfaces to be covered by dental composite material and by the type of dental adhesive chosen. Thus, it has been studied the adhesion to dentine of three adhesive systems, two etch-and-rinse systems and one self-etch system, and also for three types of altered dental surfaces preparation with a diamond bur, a carbide bur, respectively, a polisher. From a clinical point of view, a standard ideal preparation with a perfectly polished surface would allow an intimate wetting of the enamel surface by the adhesive. Any changes made on this surface can bring disturbances in the quality of the adhesion. Therefore, pre-etching prior to application, even for a self-etch adhesive, should be used to provide an effective bonding without additional surface grinding. In addition, significant changes can occur when not enough attention is given to the intimate application of the adhesive on the tooth surface, its drying and proper light curing and the authors consider that a special attention should be paid on the technique of the application of the material on the tooth surface.

Fixed prosthetic restorations may generate periodontal irritation by various and complex mechanisms especially in the presence of the microbial factor, and different studies on patients wearing fixed denture show that those prosthetic structures facilitate plaque accumulation. Opri et al. [5] analyze the reaction of the periodontal tissue in contact with fixed prosthesis depending on the prosthetic material used following the effects of the fixed prostheses upon the marginal periodontium and show that the fixed prostheses determine a high retention of bacterial plaque. After the analysis of a total number of 102 fixed dental prosthesis from different materials (alloys based on copper, Cr–Ni alloys, Cr–Co alloys, gold alloys to stamping-made steel), they conclude that the gingival hypergrowth induced by the bacterial plaque is determined by the alteration of the tissue homeostasis. In addition, the histological study showed various morphological changes from one patient to another, depending on the intensity of the inflammatory and reparative response, the associated diseases (diabetes, dyslipidemia, cardiovascular diseases), and especially on the dental hygiene status. Fixed prosthesis, in the absence of a proper cervical adaptation and an adequate local hygiene, may act as an irritative thorn and may induce gingivitis and periodontitis phenomena. Authors prove that the adhesion phenomena play not just an important role in the functionality of the fixed dental prostheses but also in their effects on the human tissues.

By collecting these papers, we hope to enrich our readers and researchers in the field of adhesion phenomena in biomaterials and medical devices. Due to an unfortunate production error, five articles intended for this Special Issue were mistakenly assigned to earlier issues and the editors mention clearly these papers as references. We believe that novel surface modifications and improved understanding of the adhesion phenomena will be an important part of future biomaterials and medical devices with better functionality.

Iulian Antoniac
Materials Science and Engineering Faculty, Biomaterials Group, University Politehnica of Bucharest, Bucharest, Romania
[email protected]
Cosmin Sinescu
School of Dentistry, “Victor Babes” University of Medicine and Pharmacy of Timisoara, Timisoara, Romania
[email protected]
Aurora Antoniac
Materials Science and Engineering Faculty, Biomaterials Group, University Politehnica of Bucharest, Bucharest, Romania
[email protected]

Acknowledgments

We thank all the authors participating in the present Special Issue.