**Abstract**

Bioactive glasses are very attractive materials, used for tissue engineering materials, usually to fill and restore bone defects. This category of biomaterials, show considerable potential for orthopaedic surgery because they can promote bone tissue regeneration. Many trace elements have been incorporated in the glass network, an example is metallic glasses to obtain the desired properties. Because of tolerable mechanical properties, and because they are able to bond to living bone and stimulate its regeneration, this bioactive glasses have a particular interest and are in a continuous research and improvement. The chapter presents the history of bioactive glasses, classification, include a summary of common fabrication methods, applications, surface coatings, applications and future trends in relation to human bone. This review highlight new trends and areas of future research for bioactive glasses.

**Keywords:** bioactive glasses, bioactivity, glass-ceramics, biodegradable, melt-derived glasses, bone, applications, tissue engineering

## **1. Introduction**

Research in the field of materials science and engineering has expanded greatly in recent decades, especially in the field of biocompatible materials. This is because, on the one hand, medicine is constantly looking for solutions to remedy many health problems, and on the other hand, certain classes of materials have already proven useful in alleviating or even curing certain human suffering [1, 2].

The development of biocompatible materials research is an evolving process driven by the increase in the number of accidents and many health problems, but also by the desire to increase the average life expectancy in humans. As research in the field of biomaterials science advances at the laboratory level, the incidence of serious diseases is increasing in the global human community. The World population is getting larger and the percent of elder persons is increasing and influencing the increase of chronic illness, like cancer or cardiovascular diseases. Next to this on large scale other infectious diseases are getting more common like: HIV/AIDS, tuberculosis or gastrointestinal

issues. On this reason the focus of the research in the field of medical materials and instruments should prepare for the request on the market [3].

While traditional biomaterials were based on polymers, ceramics and metals, now the latest generation of biomaterials incorporates biomolecules, therapeutic drugs and even living cells. At present, biomaterials are a special category of materials, indispensable for raising the quality of human life and extending its duration [4].

Biomaterials are generally intended to be implanted in a living organism to restore the shape and function of a part of a tissue destroyed by disease or trauma.

The introduction of a biomaterial into the human body determines an implant versus tissue interaction, which can generate conflicting reactions. They can be toxic, mechanical, and electrochemical biological. It can even lead to serious damage to the bone or adjacent tissue, or assembly used. Due to these phenomena, depending on the quality of the biomaterial, the place of implantation and other causes, corrosion occurs on the surface of the implant, with loss of quality his.

Depending on the medical application for which it is suitable, a biomaterial must have one or more of the properties presented in **Figure 1**. These factors are very important and have a close correlation between them: to be biologically compatible with the host tissue (for example, it does not have to causes rejection, inflammation and immune responses); Easily achieve direct bio-chemical attachment to the host tissue; The biodegradation time must be adjusted to suit the time of natural bone formation; Degradation mode: Surface or depth erosion; Ability to support the growth of germinal capillaries, tissues perivascular mesenchymal and osteoprogenitor cells from host in the three-dimensional structure of the graft that acts as a support; Needed to maximize space for grip and growth cellular, revascularization, proper nutrition and oxygen supply; For support in the process of cell growth and in the transport of nutrients and oxygen [5].

A material suitable for use in medicine must have, where appropriate, certain characteristics special and offer a number of advantages: mechanical integrity of the tissues acting as a support for growth living tissue; control of the biological response, by promoting dynamic interactions with tissues surrounding; behaving as a space for the survival of host cells, facilitating the transport of nutrients and metabolites, by maximizing the biological and / or pharmaceutical response; good biocompatibility / biodegradability, with adequate degradation kinetics; new tissue formation, thus minimizing both tissue and response toxicity systemic; feasibility in production [6, 7].

Of all the factors, biocompatibility is the most important feature to be taken into account consideration in the clinical applications of a biomaterial and which is related to

**Figure 1.** *The main characteristics of biomaterials.*

behavior biomaterials in various contexts. Biocompatibility is correlated with the appearance of a response weak immune system in contact with a particular biomaterial [8, 9].

The most complex unit is the human body, having many levels of tissues, organs and systems. If we speak about tissues these can be soft or hard, after that being classified in ones in contact with blood or not, in contact with the biomaterials or not [10].

On biomaterials the classification can vary, according to the composing materials and their use; the origin – natural or synthetic, simple or mixed composite and so on. Regarding the composition these can be metallic, ceramic, polymeric, composite and of natural origin.

According to every biomaterial, the advantages and disadvantages can influence their use, being induced by the characteristics of biomaterials and by the functional requirements of implants.

Bioglass (BGs) is a chemical compound that is part of a compositional family known to have the best bioactivity properties. This are osteoconductive and osteoinductive as well biocompatible and highly bioactive, as demonstrated by the connection with living tissues in a short time to just a few hours [11].

This new class of biomaterials, based on an amorphous mixture of oxides (SiO2- Na2O-K2O-CaOMgO-P2O5), was patented in 1968 by Larry Hench by preparing the well-known Bioglass 45S5.

Depending on the percentage of SiO2 mainly, these biomaterials can be bioinert, bioactive or bioresorbable. Hench and Clark were the first researchers to observe the bioactivity of this material in vitro and in vivo and demonstrated its osteointegrative potential [12].

At the same time, the antimicrobial and anti-inflammatory properties and the possibility to easily control the crystallinity by applying heat treatments corresponding to the glassy phase present in the bioglass structure were noted. All these are additional arguments for this class of biomaterials to be a first objective in research in the field [13].

L.L. Hench developed the concept of using a material based on silicon dioxide, calcium oxide and phosphorus pentoxide, in a proportion similar to that of natural bone, to make implants, which have the property of developing a bond with the bone. In **Figure 2** is presented the Hench Diagram. The level of biocompatibility of a material can be correlated with the time in which it was performed bone binding for more than 50% of implant surface (t0.5bb) [15].

#### **Figure 2.**

*Hench diagram [14]. \*notations: A - bioactive materials, B - inert materials, C - absorbable materials, D - cannot be obtain bioglasses, la = 0 the limit of the compositions that allow the binding to the hard tissues, la = 8 is the limit of the compositions that allow the binding of soft tissues.*

The bioactivity index is defined by the following formula:

$$I\_{\beta} = \frac{\mathbf{100}}{t\_{0.5bb}}\tag{1}$$

Because some studies show that the GBs are fragile and exhibit poor mechanical properties, this limiting the involvement in load-bearing applications, another way to represent a feasible solution, is to incorporate the bioactive glasses into gelatine matrices and to fabricate composites [16, 17].

## **2. History - current level of development**

Although 40 years have passed since the patenting of this material, until now it has been intensively used only in the form of large diameter particles (~ 100 μm), grouped in blocks with different geometries, with applications in regenerative orthopedic surgery (bone fillers).

Enamel-glazing and flame / plasma spray are used as commercial methods to obtain bioglass thin films at the commercial level, and in recent years' intensive research has been carried out in many biomaterials research laboratories to find alternative methods to the traditional ones, which lead to thick coatings with low mechanical strength.

Although their superficial properties are interesting, their development is limited due to: high fragility and reduced mechanical resistance to static fatigue. However, they are used to make middle ear bones, alveolar reconstructions, dental implants, films for total coverage of prostheses (alumina or titanium alloy), for modern cancer treatments.

For all these applications, the bioglasess have seen a spectacular development, as shown in **Table 1**.

Due to the high fragility and low mechanical strength of bioglasses as well as the toxicity of metal ions that can occur from metal alloys used in internal prostheses, the study of metal orthopedic prostheses coated with thin bioglasses films was studied.

Their use is motivated, among other things, by the porosity characteristics of the bioglasses, which allow a very intimate propagation of the tissues, thus ensuring a perfect connection with the implant. Thus, these structures have the advantage of combining the bioactive properties of the coating material with the mechanical strength of the support (**Figure 3**).

Bioglasses are superficially active, they have the property of binding mechanically or biochemically to bone tissue or collagen fibers in contact with soft, living tissue.

It has been shown that the connection between the bioglass and the bone is achieved by the formation of a superficially active interface based on hydroxyapatite, which further determines the reconstruction action of the tissue cells; such a mechanism is stimulated by a slightly basic pH, caused by ion exchanges between the bioglass and the tissue.

Materials with limited reactivity, such as dense hydroxyapatite, have a weaker effect than biosticles in the healing process of bone tissue.

All classes of the biomaterials are used throughout the human body, for this purpose, physical, chemical and biological properties of materials are exploited, often new or improved properties, and the resulting structures can interact faster at the biomolecular level, both on the surface and inside the cell.

*New Trends in Bioactive Glasses for Bone Tissue: A Review DOI: http://dx.doi.org/10.5772/intechopen.100567*


#### **Table 1.**

*Stages of development of bioglass and glass-ceramics [4, 5, 15].*

**Figure 3.** *Multilayer structure [9].*
