Emerging Nanofibrous Polycaprolactone Vascular Grafts in Small and Large Animal Models: in vivo and in vitro Analyses

INTRODUCTION

Polycaprolactone (PCL)

Polycaprolactone is a biodegradable polyester having a low melting point of about 60 °C and a glass transition temperature of about −60 °C[1-3]. The most widespread public usage of PCL is in the manufacture of specialty polyurethanes (Table 1) [4-6].

Vascular Tissue Engineering

Vascular tissue damages resulting from defects, accidents, wounds or other kinds of injuries poses a significant challenge to human health [10].

However, in current years, the use of tissue engineering methods has become increasingly important in advancing the field of cardio-vascular biology and improving patient care [11-15]. The objective of vascular tissue engineering is to produce neo-vessels and neo-organ tissue using autologous cells through a biodegradable polymer like polycaprolactone (PCL) as a scaffold [16-18]. Fabrication of scaffolds with improved mechanical properties and promising cellular compatibility is essential for many tissue engineering applications [8,19-20]. Favorable scaffolds can be prepared via reinforcement with nanoparticles and hydrogels [21-23].

A proper vascular graft must reproduce the biomechanical specifications of blood vessels, as serving like a platform for cell attachment and proliferation [24-26]. It must exhibit nonthrombogenic, nonimmunogenic, biocompatible, and hemocompatible properties; biodegradability, suitable pore size, and elasticity are also important factors [27-29]. Therefore, this graft must aid the in vivo regeneration of a tissue-engineered vascular material after being implanted in a suitable location (Fig. 1 )[30-32].

Application of PCL Nanofibrous Grafts in the Vascular Regeneration

PCL nano-fibrous scaffolds possess substantial surface area–to-volume ratios and porosity that resemble the structure of protein fibers in native ECM [33-35]. The versatilities of polymer components, fiber structures, and functionalization have made feasible the fabrication of PCL nanofibrous scaffolds with appropriate mechanical strength, transparency, and biological specifications for vascular tissue engineering [17, 36].

Implantation of PCL Vascular Grafts

The fabrication of PCL nanofibrous scaffolds for cell cultivating serves as an important process for vascular tissue engineering method. Subsequently, implanting the PCL scaffold-cell matrix in an animal body is a main stage for vascular regeneration. One of the primary benefits of vascular engineered implants is that these tissues can grow, remodel, rebuild, and respond to damage [14, 37].

Implantation of PCL Scaffolds in the Blood Vessels

A blood vessel consists of three covers: intima (internal layer), media (central layer), and adventitia (external layer) (Fig. 2).

In the process of blood vessel tissue engineering, effective phases include cell sources, cell culture, scaffolds, vessel bio‑reactors, and implantation. Non immunogenic autologous endothelium cells and smooth muscle cells (tunica media area) are isolated from patients. These cells are optimal choices for vessel tissue engineering [15, 38].

Table 2 presents the results of PCL vascular implantation surgery in the blood vessels (abdominal aorta, carotid artery) of various animals (Rat, Rabbit, Sheep, Canine).

SEM OBSERVATION

Scanning electron microscopy (SEM), an easily acquired and widely applied image acquisition and analysis method [52, 53], has rarely been used to study the structure of PCL scaffolds after cell culture process. Fig. 3 exhibits the SEM images of cultured cells on PCL scaffolds for vascular regeneration.

CONCLUSIONS

In recent years, adapting tissue engineering methods is crucial for advancing the field of cardio-vascular biology and providing better patient care. PCL polymer has drawn significant attention amongst the biodegradable polymers as an appropriate vascular tissue engineering material.The authors propose an alternative strategy, namely “Ultraviolet/O₃ Irradiation,” on the PCL nanofibers (for increasing of cell adhesion on the scaffolds). This strategy is expected to improve the success of scaffold implantation.

CONFLICT OF INTEREST

The authors declare no conflicts of interest.

ACKNOWLEDGEMENT

This study was supported by the Applied Textile Research Center.