Tissue engineered biomaterials : biological and mechanical characteristics

One must see a severely burned patient in an emergency ward to fully grasp the severity and the multisystemic nature of this trauma. Depending on the age and previous medical condition of these burn victims, the definition of severe may vary. However, most burn specialists agree that, when more than 20-30% of the total body surface has been injured with third-degree and/or second-degree burns, the consequences far exceed the local lesions to the skin [1-5]. These notions of multiple insults on different organs of the body go well beyond the scope of the present chapter of this encyclopedia. However, it must be understood that the diagnosis and treatment of burn wounds, with all their complications, demand the interaction and cooperation of various specialists: burn surgeons, burn nurses, chest specialists, infectious diseases specialists, anesthetists, cardiologists, internists, etc. One must also envision the formidable surgical task that has to be accomplished during the next weeks after the trauma. The larger the body area involved, the more difficult and complex will this surgical approach he. These clinical facts can be summed up in a simple statement since the only definitive classic therapy for burn wound coverage is the patient’s own skin taken from spared sites (called donor sites): The more a patient is burned, the fewer donor sites there are for long-term remedy [6-9]. Consequently, burn survival is, among other parameters, directly related to the total wound surface [7,10,11]. The clinical situation described by this statement used to be of a particularly ominous nature when the burned area was over 70% of the total body surface. The preceding sentences can explain quite readily the need for an additional therapeutic option such as the one offered by tissue engineered epidermis. However, other less evident advantages of such a tissue reconstruction approach are expanded upon later in this chapter (see Sec. II.C). One must also be aware of the very complex nature of the healing processes involved in the recovery of these patients. Thus, the treatment of burn patients cannot be seen as a simple mechanical coverage, but as a complicated biological phenomenon that is always imperfect. In other words, although minor skin injuries will heal with a minimum of defects such as scarring, large burn wounds are invariably accompanied by many disruptive phenomena, which seem to have most of their origin in the dermal cells [12—16]. Thus, the pattern of normal healing in these large wounds frequently leads to hypertrophic scarring and contracture [2-4, 12-14]. These quite mechanical events must be countered by what is also a very physical approach : pressure garments. Carefully fitted garments are the only method for minimizing these inaropirate healing processes, which otherwise may lead to unsightly scars [13, 17]. This unfortunate sequence of events is also another reason for trying to find new therapeutic modalities. Tissue engineering of epidermis and skin seems to offer such valid therapeutic 0ptions. However, each of these tissue engineered organs has its advantages and pitfalls as, we shall submit to the reader in the following paragraphs. Also, in reSponse to the previously described clinical concerns related to wound coverage and appropriate healing processes, it can be stated immediately that the tissue engineered skin equivalent should be a better therapeutic option. However, this logical affirmation may have to be tempered by some sobering clinical conditions and evaluation, as we describe in this chapter.