The selection of biomaterials for biomedical application is a significant challenge. In the last few decades, various bioabsorbable and stable biopolymers have been applied for use as biomedical devices in orthopedic applications. Ultra-high molecular weight polyethylene (UHMWPE) has been extensively used in medical implants, notably in the bearings of hip, knee, and other joint prostheses, owing to its biocompatibility and high wear resistance. For the ACL graft, synthetic UHMWPE is an ideal candidate due to its biocompatibility and its extremely high tensile strength. Despite the appeal of new advanced materials such as carbon fiber, poly-ether-ether ketone, and other load-bearing materials, UHMWPE remains a primary load-bearing candidate material for ACL reconstructions because of its extremely high strength, the simplicity of the fabrication process, its biocompatibility, and low friction. However, some significant problems are observed in UHMWPE based implants, such as wear debris, and oxidative degradation due to the generation of free radicals when exposed to irradiation with gamma rays for grafting or sterilization. Various innovative methodologies have been developed to resolve those problems and enhance the properties of UHMWPE. In this review, we will explore in detail the methods for surface functionalization of UHMWPE and will apply these findings to the case study of UHMWPE for Anterior Cruciate Ligament repair.

The selection of biomaterials as biomedical implants is a significant challenge. Ultra-high molecular weight polyethylene (UHMWPE) and composites of such kind have been extensively used in medical implants, notably in the bearings of the hip, knee, and other joint prostheses, owing to its biocompatibility and high wear resistance. For the Anterior Cruciate Ligament (ACL) graft, synthetic UHMWPE is an ideal candidate due to its biocompatibility and extremely high tensile strength. However, significant problems are observed in UHMWPE based implants, such as wear debris and oxidative degradation. To resolve the issue of wear and to enhance the life of UHMWPE as an implant, in recent years, this field has witnessed numerous innovative methodologies such as biofunctionalization or high temperature melting of UHMWPE to enhance its toughness and strength. The surface functionalization/modification/treatment of UHMWPE is very challenging as it requires optimizing many variables, such as surface tension and wettability, active functional groups on the surface, irradiation, and protein immobilization to successfully improve the mechanical properties of UHMWPE and reduce or eliminate the wear or osteolysis of the UHMWPE implant. Despite these difficulties, several surface roughening, functionalization, and irradiation processing technologies have been developed and applied in the recent past. The basic research and direct industrial applications of such material improvement technology are very significant, as evidenced by the significant number of published papers and patents. However, the available literature on research methodology and techniques related to material property enhancement and protection from wear of UHMWPE is disseminated, and there is a lack of a comprehensive source for the research community to access information on the subject matter. Here we provide an overview of recent developments and core challenges in the surface modification/functionalization/irradiation of UHMWPE and apply these findings to the case study of UHMWPE for ACL repair.

Anterior cruciate ligament rupture is more common nowadays and it can lead to cartilage degeneration and osteoarthritis [1]. Anterior cruciate ligament reconstruction is frequent [2] and one of the challenging work in tissue engineering [3]. Anterior cruciate ligament is important for maintenance of knee movement [4]. ACL do not heal itself because of its intrinsically poor healing potential and surgical mediation is usually required [5,6]. Allograft and autograft were used for ACL reconstruction [7,8]. Due to several drawbacks of allograft and autograft synthetic grafts are the main option for ACL reconstruction [9]. Ligaments are made of bands of strong collagenous connective tissue. These paralleled collagen bundles attached to each other by crosslinking [10]. Mesenchymal cells produce this type of tissue; it can diferentiate into ibroblast cells. These ibroblast cells again diferentiate into ibrocytes cells. After maturation of ibrocytes they become inactive and produce ligaments. Ligaments attach two bones together at a joint, prevent dislocations of the joints, and restrain the movements of the joints. Ligaments contain two-thirds water and one-third solid. Collagen is the solid component of the ligament basically collagen types I and rests of the types are III, VI, XI and XIV. To maintain a considerable range of mechanical and biological properties of soft tissues, related organ systems, and bone collagen plays a vital role [11]. Structure of ACL ACL is not isometric [12]. ACL is made of collagen bundles which are paralleled and cross linked to each other. These bundles vary the tension among the ibers of the ligament [13]. Fibroblasts are joined to the bundles individually. It can produce new