Review article
Applications of knitted mesh fabrication techniques to scaffolds for tissue engineering and regenerative medicine

https://doi.org/10.1016/j.jmbbm.2011.04.009Get rights and content

Abstract

Knitting is an ancient and yet, a fresh technique. It has a history of no less than 1,000 years. The development of tissue engineering and regenerative medicine provides a new role for knitting. Several meshes knitted from synthetic or biological materials have been designed and applied, either alone, to strengthen materials for the patching of soft tissues, or in combination with other kinds of biomaterials, such as collagen and fibroin, to repair or replace damaged tissues/organs. In the latter case, studies have demonstrated that knitted mesh scaffolds (KMSs) possess excellent mechanical properties and can promote more effective tissue repair, ligament/tendon/cartilage regeneration, pipe-like-organ reconstruction, etc. In the process of tissue regeneration induced by scaffolds, an important synergic relationship emerges between the three-dimensional microstructure and the mechanical properties of scaffolds. This paper presents a comprehensive overview of the status and future prospects of knitted meshes and its KMSs for tissue engineering and regenerative medicine.

Graphical abstract

Highlights

► A knitted mesh improves the mechanical strength of combined or hybrid scaffolds. ► Mechanical properties maintain the microstructure of scaffolds. ► The microstructure induces tissue reconstruction/regeneration.

Introduction

Tissue-engineered scaffolds can be the artificial equivalents of natural extracellular matrices (ECMs) that are used to induce tissue regeneration or replace damaged tissues/organs (Langer and Vacanti, 1993, Griffith and Naughton, 2002). Although the requirements of scaffolds for tissue engineering are multifaceted and specific to the structure and function of the tissue of interest (Yang et al., 2001), ideal scaffolds should have good biocompatibility and biodegradability, highly porous and interconnected microstructures, and suitable mechanical support (Hutmacher, 2000, Yang et al., 2002, Wang et al., 2007). Comparatively, the processing and bioactivity of scaffolds have been paid more attention than others (Harley et al., 2007). Naturally derived materials such as collagen have been used extensively to prepare scaffolds due to their good biocompatibility, hydrophilicity and cell affinity. However, scaffolds constructed entirely of collagen sponge or gel possess poor strength to resist mechanical forces (Bell et al., 1979, Young et al., 1998, Awad et al., 1999, Ng et al., 2004, Nirmalanandhan et al., 2007, Mao et al., 2009). Nowadays, for tissue-engineered scaffolds, the importance of three-dimensional (3D) porous structures has been confirmed to allow in vitro cell adhesion, ingrowth and reorganisation, and provide the necessary space for neovascularisation in vivo (Schmidt and Baier, 2000, O’Brien et al., 2005, Puppi et al., 2010). The role of mechanical properties is being increasingly recognised to provide temporary mechanical support and proper mechanical cues (Leong et al., 2008), and to maintain space for cell ingrowth and matrix formation (Puppi et al., 2010), and rapidly restore tissue biomechanical function (Gloria et al., 2010). Some researchers state that constructing a scaffold that simultaneously possesses optimal mechanical properties, a porous structure and a biocompatible microenvironment, is a more intriguing orientation (Chen et al., 2002, Chen et al., 2008).

A knitted mesh possesses highly ordered loop structures (Wintermantel et al., 1996) and versatile mechanical properties (Quaglini et al., 2008, Yeoman et al., 2010) that can provide sufficient internal connective space for tissue ingrowth (Ouyang et al., 2003). As a unique method of material processing, knitting has shown the potential to provide tissue engineering with many kinds of knitted meshes, or participate in the construction of tissue-engineered scaffolds (Chen et al., 2002). Nowadays, well-designed knitted meshes manufactured from synthetic or biological materials such as polylactide-co-glycolide (PLGA) (Ouyang et al., 2003) and silk (Chen et al., 2008) commonly have unique mechanical properties and have been used to provide improved physical support, either alone to strengthen materials for the patching of soft tissues Clave et al. (2010), or in combination with other types of biomaterials, for the construction of knitted mesh scaffolds (KMSs) (Tatekawa et al., 2010).

Given increasing reports about the applications of a knitted mesh, this review presents a comprehensive overview of the status and future prospects of knitted meshes and KMSs for tissue engineering and regenerative medicine.

The knitted mesh mentioned in the different papers cited may be associated with different names, e.g. knitted mesh, mesh, network or fabric. Meanwhile, KMSs may also have different terms used by the researchers, e.g. hybrid scaffold (Munirah et al., 2008, Urita et al., 2008, Dai et al., 2010), hybrid construct (Ananta et al., 2009), combined scaffold (Liu et al., 2008, Fan et al., 2009), composite web scaffold (Chen et al., 2003a), composite vascular graft (Xu et al., 2010), composite or 3D scaffold (Pu et al., 2010), etc. The inclusion criteria are based on the knitted structure described in detail in the cited articles.

Section snippets

Fundamentals of knitting

Knitting as an ancient and yet, a fresh technique, has a history of at least 1000 years. The basics of knitting, upon which most of this section is based, have been well documented (Spencer, 1983, Hatch, 1993, Leong et al., 2000). The structure of a knitted mesh is often defined as a highly ordered arrangement of interlocking loops (Wintermantel et al., 1996). The general categories and characteristics of textiles according to the structures and processing are summarised in Table 1. Knitting

Ways to fabricate knitted mesh scaffolds

Theoretically, a knitted mesh can be designed and knitted into many specific shapes to suit the target tissues/organs (Chen et al., 2003a, Dai et al., 2010). To date, many methods have been developed to integrate a mesh into a scaffold; chief among these are one-step moulding and assembly.

Properties of knitted mesh scaffolds

Proper mechanical support has been under essential consideration for the construction of scaffolds (Ng et al., 2005, Leong et al., 2008). Especially for naturally derived materials, various methods have been developed to improve the mechanical performance of scaffolds (Ruijgrok et al., 1994, Ulubayram et al., 2002, Powell and Boyce, 2006, Rezwan et al., 2006, Hillberg et al., 2009). Universally, the mechanical strength should maintain enough spaces for cell ingrowth and functionalisation in

Patches for soft tissues

Various knitted meshes made from synthetic materials, commonly regarded as prosthetic materials such as polypropylene, poly(ethylene terephthalate), and polylactic acid have been designed for the treatment of hernia (Boukerrou et al., 2007), pelvic organ prolapse (Ganj et al., 2009), pelvic floor dysfunctions (Clave et al., 2010), body wall defects (Lamb et al., 1983, Tyrell et al., 1989), and so on. In addition to good mechanical properties, for this kind of application, all of the materials

Conclusion and perspectives

For decades, knitted meshes have been applied surgically to reinforce frail tissues such as hernia (Boukerrou et al., 2007, Clave et al., 2010). Initially, the biomaterials constituting the knitted mesh were regarded as inert (Clave et al., 2010). Gradually, the biocompatibility and tissue-inducing regeneration of biomaterials have become recognised as important characteristics (Silva and Mooney, 2004). The mechanical properties of scaffolds have been shown to significantly affect cell

Acknowledgements

The authors sincerely acknowledge Dr. Fergal J. O’Brien, Department of Anatomy, Royal College of Surgeons in Ireland & Trinity Centre for Bioengineering, Trinity College Dublin, for his constructive suggestions. This work was financially supported by the Major State Basic Program of China (2005CB623902) and the Major Science and Technology Project of Zhejiang, China (2007C13040).

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