Nanoscience and Nanotechnology

Advances and Developments in Nano-sized Materials

Marcel Van de Voorde, Marcel Van de Voorde

• Publisher: De Gruyter
• Year: 2018
• ISBN:
  9783110547290
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Clinical Chemistry

Innovations in Nanoscience and Nanotechnology summarizes the state of the art in nano-sized materials. The authors focus on innovation aspects and highlight potentials for future developments and applications in health care, including pharmaceutics, dentistry, and cosmetics; information and communications; energy; and chemical engineering. The chapters are written by leading researchers in nanoscience, chemistry, pharmacy, biology, chemistry, physics, engineering, medicine, and social science. The authors come from a range of backgrounds including academia, industry, and national and international laboratories around the world.

This book is ideally suited for researchers and students in chemistry, physics, biology, engineering, materials science, and medicine and is a useful guide for industrialists. It aims to provide inspiration for scientists, new ideas for developers and innovators in industry, and guidelines for toxicologists. It also provides guidelines for agencies and government authorities to establish safe working conditions.

Part I:Nanotechnology Innovations for Health

Bert Müller

1Nanomedicine at a glance

1.1Introduction

Medical doctors can efficiently diagnose and treat patients because of the broad experience available. Generally, the medical experts have hardly any deep understanding of nanoscience and nanotechnology. In some cases, however, they apply nanotechnology-based drugs, implants, and devices to reach the envisioned success. In our everyday life, we do make similar experiences, as we are using toothpaste and sun protection; both rely on nanometer-sized ingredients, without realizing that nanomedicine is employed. Nanomedicine, however, is a term often related to some danger for our health. Although there is no proof, people believe that nanotechnology could become harmful and the application should be better avoided. This chapter, therefore, summarizes selected examples, which elucidate the potential of nanoscience and nanotechnology for the treatment of common diseases, including caries, incontinence, and cardiovascular diseases.

Here, nanomedicine is defined as the science and technology of diagnosing, treating, and preventing diseases and traumatic injuries; of relieving pain; and of preserving and improving health using the nanometer-sized components [1]. Boisseau and Loubaton have introduced the term nanotechnology-enabled medicine, which might be the better choice compared to the simple word nanomedicine [2]. Recent publications prefer the term nanoscience and nanotechnology for human health, which covers the entire interdisciplinary field without pronouncing medicine [3].

1.2Nanoscience and Nanotechnology for Oral Health

It should be noted that the subject has been covered in previous books [4–6]. Therefore, the following part is based on the knowledge already available.

1.2.1Natural Nanomaterials Within the Oral Cavity

The human tissues consist of anisotropic and hierarchically ordered nanostructures. For example, the crowns of the 32 teeth embrace the hardest tissue of the human body – the enamel. It consists of nanometer-sized, ordered hydroxyapatite crystals. This natural material is about three times tougher than the geological hydroxyapatite and much less brittle than the hydroxyapatite sintered at elevated temperatures [7]. The unique mechanical properties stem from the organization of the crystallites in an ordered fibrous continuum in three-dimensional space, where the needle-like crystallites are aligned to form microscopic bundles or rods, sheeted by organic material. These are in return oriented in specific directions depending on their location within the crown. The design is not only restricted to the enamel but also includes the dentin located below the enamel, which is composed of a mineralized collagenous matrix more akin to bone. The softer dentin counteracts the enamel’s high brittleness. The result is a high-performance composite structure that maintains its functionality – mastication – over decades under heavy cyclical loads and adverse chemical conditions [8]. Where these two materials meet, they gradually merge in a complex interplay of highly mineralized and collagen-rich regions [9]. Although many research activities have been devoted to understand the impact of the dentin–enamel junction on the mechanical properties of the crown, the role of this complex interface in the tooth’s functionality is still under discussion [9, 10]. Especially the organization on the nanometer level seems to play a critical role [11]. Whereas the hydroxyapatite crystals in the enamel are oriented toward the crown surface and the dentin–enamel junction, in the dentin they are oriented parallel to the junction. The orientation of the enamel’s crystallites at the crown surface permits an effective way to remineralize the top layer of the crown after the food-related demineralization phase. Such a mineralization cycle occurs for several times during day and, if balanced, the natural teeth last healthy for several decades. An imbalance toward the acidic conditions within the oral cavity, however, leads to destruction within short periods of time. Currently, no engineering process to biomimetically repair or ex vivo recreate the human crowns has been identified. Nevertheless, the state-of-the-art nanoimaging allows for the identification of the design rules to build bioinspired dental fillings [12].

1.2.2Dental Fillings

The restoration of teeth has been significantly improved during the last century. Many of us do remember the gold crowns and the amalgam fillings, which have been replaced during the twenty-first century by zirconia crowns and polymer-based composites, respectively. Although the restoration materials and related procedures for crown repair have been steadily improved, their life span is limited and does not reach the level of the natural tissue [13, 14]. This means that after about two decades the fillings have to be replaced by larger ones or even by inlays or artificial crowns. The treatment of the root canal is usually the next step, before posts and dental implants become necessary. The costs involved are significant, and alternatives are desirable. One possible approach consists in the development of anisotropic restoration materials that mimic the complex ultrastructure of human teeth [12]. Ideally, such materials will improve bonding to the tooth material as well as better match physical properties, including Young’s and shear moduli as well as the thermal expansion of the tooth’s components, providing longer life span of the restoration.

1.2.3Dental Implants

Dental implants are inserted into the jaw and form a stable interface with the surrounding bony tissue. This part of the implant’s surface is made rough by means of sand-blasting and etching to reach osseointegration. Here, the roughness on the micro-and nanometer scales is equally important. It has been demonstrated that the nanostructures are especially vital to avoid the inflammatory reactions [15–17].

The other part of the implant is usually smooth and serves for the artificial crown fixation on top. The only current main challenge is the formation of a satisfactory interface between the crown and the soft tissue of the gingiva.

In general, the currently available dental implants remain stable with a success rate close to 100%, and further breakthroughs in nanostructured implants are not expected any more.

Before placing an implant, it is necessary to check for the bone volume and quality. In the case of insufficient bone availability, the bone has to be augmented to guarantee the stability of the implant. A variety of calcium phosphate-based bone graft materials of well-established suppliers are on the market [18], which are used to strengthen the jawbone within months and subsequently allow for a proper fixation of the implant. These calcium phosphate phases should be upgraded to accelerate the jawbone formation.

1.2.4Challenges of Nanotechnology in Oral Health

Depending on the pH value within the oral cavity, cyclic de- and remineralization of the enamel surface region takes place through diffusion of ions, maintaining tooth crowns in an intact state (see Figure 1.1). If a disequilibrium between the two processes occurs in favor of demineralization, tooth decay occurs. Conversely, artificially supporting the remineralization process can result in tooth repair. The biomimetic repair of the damaged crowns, however, is hardly solved and understood. Ion delivery is a concentration-mediated dynamic process, and such a material flow is more evasive to classical pharmaceutical approaches. In everyday life, we use a more or less nanotechnology-based toothpaste together with a more or less sophisticated brush mainly to clean the crowns usually twice a day. The toothpaste often also provides nanometer-sized species, which promote the remineralization of the crown’s surface, and thus, the regeneration processes. Therefore, the small damages that are optically invisible can be repaired. The penetration depth of these species is, however, limited, restricting their efficiency to surface incipient lesions. For slightly larger damages, termed white spots, which are visible because of their few hundred mic...