**1. Introduction**

Bone defects are a serious illness that can result after a pathological process has de‐ stroyed vital components of the bone. Most commonly the causative event is extensive trauma and subsequent infection. It can be also osteomyelitis that destroys the bone and leaves non-vital bone sequesters along the length of the bone. This damage to the bone and soft tissues heals slowly and restitution can be only expected after some time of rest and procedures of debridement.

#### **1.1. Bone defects**

Bone defect by definition is a lack of bone tissue in a body area, where bone should normally be. Lack of bone tissue results in a pseudarthrosis, artificial joint that has no physiological importance. In that area, two parts of diseased bone are joined with a fibrous tissue. That area also lacks appropriate vascularization and is usually covered with scarred or fibrotic skin [1].

Bone defects can be treated by various surgical methods. One is always constrained with fibrosis that healed a wound or the site of infection [2]. Often there are factors that impair bone healing like diabetes mellitus [3, 4], immunosuppressive therapy [5, 6], poor locomotory status and others that one has to take in account when a procedure is planned.

There are some common methods of bone defect reconstruction, like decortication, excision and fixation, cancellous bone grafting [7] and the Ilizarov intercalary bone transport method [1]. The application of these methods results in successful final outcomes as far as the bone restitution is concerned.

© 2013 Smrke et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

However, one must consider repeated surgical procedures and often long hospitalization time or frequent outpatient visits for these patients. It is also common for patients to have prolonged ambulatory impairment with suboptimal functional and aesthetic results [8, 9].

#### **1.2. Tissue bioengineering**

Tissue engineering involves the restoration of tissue structure or function through the use of living cells. The general process consists of cell isolation and proliferation, followed by a reimplantation procedure in which a scaffold material is used. Cell sources can be autologous or allogenic cells. Autologous cells are usually the better choice, because the allogenic cells could incite immune rejection by the recipient. Mesenchymal stem cells provide a good alternative to cells from mature tissue and have a number of advantages as a cell source for bone and cartilage tissue regeneration [10].

Some authors report that most tissue engineering applications in the head and neck area would probably involve the use of chondrocytes and osteoblasts along with some type of scaffold material because of the importance of initial support and shaping [11].

Theoretically, the ideal bone graft substitutes should be osteogenic, biocompatible, bioabsorb‐ able, able to provide structural support, easy to use clinically and cost-effective. A composite graft combines an osteoconductive matrix with bioactive agents that provide osteoinductive and osteogenic properties [12].

Novel techniques have been studied recently, many involving growth enhancers with varying results. These have been used for healing wounds, ulcers, fractures, and in maxillofacial settings. Such biological enhancers are autologous platelet rich plasma (PRP) in the form of activated platelet gel and recombinant bone morphogenetic proteins (rBMP) [11, 13-23]. An animal study showed enhanced bone growth when autologous bone was combined with platelet-rich plasma [24, 25].

The healing effects of platelet rich gel were attributed to the numerous growth factors (GFs) released by the platelets after activation [19, 26]. Some of those identified are: the platelet derived growth factor (PDGF), TGF-α and β (transforming growth factor alpha and beta), EGF (epidermal growth factor), FGF (fibroblast growth factor), IGF (insulin growth factor), PDEGF (platelet derived epidermal growth factor), PDAF (platelet derived angiogenesis factor), IL-8 (interleukin-8), TNF-α (tumour necrosis factor alpha), CTGR (connective tissue growth factor), GM-CSF (granulocyte macrophage colony stimulating factor), KGF (keratinocyte growth factor), and Ang-2 (angiopoetin), as reviewed by several authors [26, 27]. The inductive potential of platelet gel in tissue regeneration could also be attributed to its significant antimicrobial activity [28].

#### **1.3. Clinical experiments**

Recent studies on patients for the regeneration of long bone and foot and ankle defects have provided promising clinical results when using platelets as a source of GFs [10]. Some studies demonstrated that with the use of platelet gel a better and stronger bone yield was achieved as compared to reconstruction with conventional methods [29]. X-ray images of treated bones showed increased density early in follow up and in-growth of treated area was enhanced [30].

In the majority of clinical experiments, authors have applied autologous platelets obtained by preoperative apheresis from the peripheral blood of the patient undergoing surgery. However, this may not always be the best solution. In cases of diabetes it has been shown that the release of platelet GFs is decreased in experimental diabetic animals [31]. If allogeneic platelet rich plasma was used as a source of additional GFs, healing of tissues in diabetic patients can considerably improve [32].

Allogenic single donor platelet units are easy to obtain, since they are a standard blood bank product. They are highly standardized in terms of platelet content and residual leukocyte and red blood cell content is low. All of this is due to proven centrifugal forces used for their isolation, temperature of centrifugation, techniques of separation and processing and compo‐ sition of preservative solution. Also, they are available in large quantities and considered safe. Autologous platelet preparations, on the other hand, are subject to enormous variability, which hinders serious studies of their clinical efficacy [33].

We used for our procedures the standard blood bank platelet concentrates. We prepared a graft composed of allogeneic platelet gel mixed with autologous cancellous bone in order to improve the healing conditions in bone defects, which was successfully demonstrated in our pilot clinical case [34].

In our case study, we showed that the healing potential of the gel GFs obtained from a high number of allogeneic platelets could be combined with the bone forming potential of autolo‐ gous osteogenic and other stem cells from the cancellous bone. We employed the plasticity of the resulting graft mixture for the modeling and all of this contributed to a successful clinical outcome.
