Introduction

Soft tissue in the anatomy usually contains the blood vessel, skin, subcutaneous shallow fascia, intervertebral disc, muscle, joint capsule, tendon, synovial sac, ligament, nerves, cornea, etc., which are used to connect, support or enclose the body structure and organs rather than hard tissue (E.g., bone). Soft tissue injury often

B. Pei (*) • W. Wang • X. Li

Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Biological Science and Medical Engineering, Beihang University, Beijing 100191, China e-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

X. Li (ed.), Tissue Repair, DOI 10.1007/978-981-10-3554-8_8

occurs in daily life, which mainly refers to a variety of acute trauma or chronic stress and its own disease, leading to the human body soft tissue pathological damage. Although scientists have found a variety of methods to repair damaged soft tissue, autologous implantation is still the main treatment of soft tissue repair and regeneration. However, autologous tissue is easily absorbed and quickly lost its volume, and only about 40-60% of the graft tissue can remain active [1-4]. As an emerging field of research, tissue engineering offers a novel approach to generate new or substituted tissues to repair or regenerate damaged soft tissues and organs, overcoming the limitations of current treatments. This technique mainly consists of in vitro culture of cells and the incorporation into temporary scaffolds with tissue morphologies. The scaffold acts as an artificial temporary tissue matrix that directs the formation of new tissue by modulating the interaction of cells-matrix or even cells-cells [5-7]. Therefore, scaffolds used in tissue engineering are usually made into an artificial ECM having a structure, function and ability similar to that of human tissue, and play a vital role in the process of soft tissue regeneration.

Natural ECM is mainly composed of polysaccharides and proteins or proteoglycans to form a complex network structure, support and connect tissue structure, regulate the occurrence of tissue and cell physiological activities. Extracellular matrix as part of animal tissue provides a suitable place for the survival and activity of cells and affects their shape, metabolism, function, migration, proliferation and differentiation through the mechanical forces and signal transduction system. Therefore, in addition to providing physical support for cell growth, soft-tissue engineering scaffolds should meet several requirements, namely, biocompatibility, mechanical stability, and proper morphology as well as chemically modulating signal and mechanical transduction [8-10]. In view of the above-mentioned factors, the scaffold is usually made of biocompatible, biodegradable and resorbable materials and developed into a new biological tissue through advanced manufacturing and culture methods. The current study of soft tissue have found that cell adhesion, proliferation and differentiation have a great relationship with micro-mechanical environment in which the cells are located [11-13]. When soft tissues have high mechanical activity, such as blood vessels, heart valves and corneas, it is particularly important that the scaffold has sufficient mechanical properties to effectively transfer the mechanical stimulus between the cells and scaffold [11, 14, 15]. In fact, the failure of the scaffold grafted in the blood vessel is usually caused by inti- mal hyperplasia due to compliance mismatch between graft stent and host vessel [16]. Also, studies of bladder tissue have shown that the mechanical properties of the membrane influence on cell growth, that is, the proliferation of cells in the membrane with the elastic modulus closer to the natural bladder tissue will be enhanced [5]. It is critical that the scaffold has good mechanical properties and is able to maintain relatively stable during the tissue growth phase to be successfully applied in soft tissue engineering. However, most of the scaffolds currently utilized in soft tissue engineering are not capable of satisfying the biomechanical properties of the microenvironment in cells and tissues throughout the implantation process.

Human soft tissues and organs have very complex components and microstructures. Elastin and collagen fibers are the most important constituents of most soft tissues. Elastin is the main component of elastic fibers. Elastic fibers are mainly present in ligaments and vessel walls. Elastic fibers and collagen fibers co-exist to provide flexibility and tensile capacity for soft tissues [17]. Collagen is the most important extracellular water-insoluble fibrin, used to form the skeleton of ECM [18]. Collagen in the ECM forms semi-crystalline fibers, provides cells with tension and elasticity and plays a role in the cell migration and development. These semicrystalline fibrils are arranged into fibers, that is, collagen fibers, which are widely distributed in various organs, especially in load carrying components such as skin, sclera and tendon [19]. Many soft tissue structures are that collagen fibers are encapsulated in the hydrogel-like elastin matrix, such as blood vessels [20], heart valves [21] and myocardium [22], and their biomechanical properties are jointly determined by the arrangement and composition of the two components. The fibers can directly affect the stiffness and strength of tissues under tension and shorten the time response of tissues under compression. Gel phase swelling can support and distribute compression loads through fluid pressurization [23, 24].

Therefore, we can often see in nature that soft tissue is supported by fibers to enhance mechanical properties. Articular cartilage is a typical example, that tough collagen fibrils are distributed in a soft proteoglycan matrix [25]. In addition, the bladder cytoskeleton is also composed of microtubules and intermediate fibers embedded in highly hydrogel-like cytoplasmic matrix [26]. In organisms, the structure of fiber- or tube- reinforced hydrogels is numerous. This concept has been successfully applied in the field of materials engineering, such as glass fiber, carbon fiber and carbon nanotube composite material [27-29]. The concept of scaffold with reinforcements also has a great potential advantage in the field of soft tissue regeneration. In fact, in recent years fiber- or tube- reinforced scaffolds have attracted considerable interest from investigators, and some of these findings have proven that reinforced scaffolds are an engineering material with high performance and utility for soft tissue engineering.

As the reinforcement material has greater controllability and moldability, the reinforced scaffold can better simulate the structure and composition of soft tissues. Fiber or tube-reinforced scaffolds that have been used in soft tissue repair and reconstruction significantly enhance tissue repair or regeneration, for they can provide sufficient mechanical strength for cell attachment, migration, differentiation and proliferation in the whole growth state, which means a reasonable micromechanical environment. And in most cases the reinforcement can improve the biocompatibility and biodegradability of the scaffold. Furthermore, recent studies have shown that the mechanical properties of the reinforced scaffold depend largely on the fiber or tube reinforcement’ properties, arrangement, volume content and aspect ratio, the combined manner of the matrix and fibers or tubes, and the matrix properties [1, 30-33].

This chapter describes the design and manufacture of novel fiber- or tube- reinforced scaffolds in soft tissue engineering. We discuss currently known fiber- or tube- reinforced scaffolds having been used in the field of soft tissue engineering, and how the fiber/tube influence structural characteristics, mechanical strength and biological activities in vitro and in vivo in repairing soft tissues. When the design and processing methods are reasonable, the reinforced scaffold will become a promising technology to produce bio-related microenvironments similar to the ECM of soft tissues and organs, and thus promote cell proliferation, migration, resulting in the final formation of new functional tissues.