Engineering Fibrous Tissues and Their Interfaces with Bone - Structural Interfaces and Attachments in Biology - page 319

Fig. 15.2 Typical stress-strain curve for bovine patellar tendon. A tendon stress-strain curve
exhibits behavior representing the toe region, the linear elastic region, the yield point, and the
failure region (plot courtesy of Dr. Yongzhi Qiu)
Acute and chronic injuries are caused by both intrinsic and extrinsic factors.
Intrinsic factors include age, gender, biomechanics, systemic diseases, (e.g., rheu-
matoid arthritis), and genetic factors [ 51 ]. Extrinsic factors are external stimuli,
such as, physical load, environment, occupation, and training [ 51 ].
15.3.2 Healing
Understanding the events of healing in tendons and ligaments is important because
tissue engineering techniques attempt to mimic or promote the environment and
events of this process. Healing of tendon and ligaments after traumatic injury
occurs in three overlapping phases: inflammatory, proliferation, and remodeling
[ 28 , 52 ]. The inflammatory phase occurs immediately after the injury. A hematoma
is formed and erythrocytes and leukocytes are recruited. Within the first 24 hours,
monocytes and macrophages release pro-inflammatory chemicals to increase vas-
cular permeability, initiate angiogenesis, and attract fibroblasts at the site of injury.
An increase in water, collagen type III, glycosaminoglycans, and fibronectin is
observed, which stabilizes the formation of new ECM [ 3 ].