Ligaments and tendons are fibrous tissues with poor vascularity and limited regeneration capacity. Currently, a ligament/tendon injury often require a surgical procedure using auto-or allografts that present some limitations. These inadequacies combined with the significant economic and health impact have prompted the development of tissue engineering approaches. Several natural and synthetic biodegradable polymers as well as composites, blends and hybrids based on such materials have been used to produce tendon and ligament scaffolds. Given the complex structure of native tissues, the production of fiber-based scaffolds has been the preferred option for tendon/ligament tissue engineering. Electrospinning and several textile methods such as twisting, braiding and knitting have been used to produce these scaffolds. This review focuses on the developments achieved in the preparation of tendon/ ligament scaffolds based on different biodegradable polymers. Several examples are overviewed and their processing methodologies, as well as their biological and mechanical performances, are discussed. Fig. 20 a 3D view of the theoretical designed PLA screw-like scaffold structure. b The prepared PLA screw-like scaffold. c The SEM image of the PLA scaffold surface with well-defined orthogonal structure (Reprinted with permission from [114])
Despite the significant efforts in the synthesis of new polymers, the mechanical properties of polymer matrices can be considered modest in most cases, which limits their application in demanding areas. The isolation of graphene and evaluation of its outstanding properties, such as high thermal conductivity, superior mechanical properties, and high electronic transport, have attracted academic and industrial interest, and opened good perspectives for the integration of graphene as a filler in polymer matrices to form advanced multifunctional composites.Graphene-based nanomaterials have prompted the development of flexible nanocomposites for emerging applications that require superior mechanical, thermal, electrical, optical, and chemical performance. These multifunctional nanocomposites may be tailored to synergistically combine the characteristics of both components if proper structural and interfacial organization is achieved. The investigations carried out in this aim have combined graphene with different polymers, leading to a variety of graphene-based nanocomposites. The extensive research on graphene and its functionalization, as well as polymer graphene composites, aiming at applications in the biomedical field, are reviewed in this paper. An overview of the polymer matrices adequate for the biomedical area and the production techniques of graphene composites is presented. Finally, the applications of such nanocomposites in the biomedical field, particularly in drug delivery, wound healing, and biosensing, are discussed. KEYWORDS biomedical applications, graphene, polymer nanocomposites 1 | INTRODUCTION Polymer nanocomposites are multiphase solid materials formed by 1 or more polymer matrices and nanometric reinforcing phases having 1, 2, or 3 dimensions below 100 nm. 1 Commonly, composite materials involve polymer matrices due to their ease of processing and shaping, and because they present reasonable mechanical properties and allow to control surface and interfacial chemistry. Typical fillers encompass fibers, filaments, flakes, or other particles with high stiffness, or specific properties such as electrical or thermal conductivity, in order to overcome the polymer matrix weaknesses. 2-4 The recent use of nanoscale fillers takes advantage of their large specific area, enhancing the interface between filler and matrix, and reaching superior composite properties at low reinforcement loads. The principle of the fabrication of composite materials is to synergistically combine the strengths of various components and optimize the primary mechanical properties. 2 Thus, the obtained polymer nanocomposites are expected to reach substantial property enhancement, with significant improvement of strength and other specific functional properties (eg, thermal or electrical conductivity), 2,5,6 as well as controlled interfacial interactions. 7Carbon-based nanomaterials (carbon black, exfoliated graphite, carbon nanotubes) have been frequently used in the preparation of polymer composites as reinforcement. The isolati...
Additive manufacturing techniques established a new paradigm in the manufacture of composite materials providing a simple solution to build complex, custom designed shapes. In the biomedical field, 3D printing enabled the production of scaffolds with patient-specific requirements, controlling product architecture and microstructure, and have been proposed to regenerate a variety of tissues such as bone, cartilage, or the nervous system. Polymers reinforced with graphene or graphene derivatives have demonstrated potential interest for applications that require electrical and mechanical properties as well as enhanced cell response, presenting increasing interest for applications in the biomedical field. The present review focuses on graphene-based polymer nanocomposites developed for additive manufacturing fabrication, provides an overview of the manufacturing techniques available to reach the different biomedical applications, and summarizes relevant results obtained with 3D printed graphene/polymer scaffolds and biosensors.
Graphene and its derivatives are promising as reinforcement for polymer nanocomposites. Additionally to their inherent outstanding mechanical properties, these nanoparticles may be functionalized to enhance their compatibility with the polymeric matrix and provide specific chemical and physical properties. In this work, new freestanding films (FS) based on chitosan (CHI), alginate (ALG) and functionalized graphene were developed using the layer-by-layer assembly. Suspensions of functionalized graphene nanoflakes (f-GF) and nanoribbons (f-GNR) were prepared from expanded graphite (EG) and multiwalled carbon nanotubes (MWNTs), respectively. The graphene nanoflakes and MWNTs were covalently functionalized using a 1,3-dipolar cycloaddition reaction that allowed the nanoparticles exfoliation. f-GNR and f-GF suspensions were characterized to demonstrate that graphene nanoflakes and MWNTs were successfully functionalized and exfoliated. Then, the layer-by-layer deposition of CHI, ALG and both types of functionalized graphene was investigated and FS films were produced. The morphology, thermal and mechanical characteristics of the produced FS films were assessed. Their degradation and swelling profiles as well as their biological behavior were evaluated. The incorporation of f-GF resulted in smoother films while the incorporation of f-GNR resulted in rougher films. When compared with the CHI/ALG bi-component films. Both graphene containing films remained hydrophobic. The graphene incorporation in the multilayered FS was estimated to be 1.7 wt% for f-GF and 2.5 wt% for f-GNR. The presence of functionalized graphene did not affect the thermal stability of the films, it increased the storage modulus and the dynamic mechanical response at 1 Hz and 37 C, and decreased the electrical resistivity. The biological assays revealed cytocompatibility towards L929 cells when both f-GF and f-GNR were incorporated in the CHI/ALG matrix. In conclusion, these new f-GF and f-GNR reinforced FS films present great potential for use in biomedical applications such as films for wound healing or cardiac and bone engineering.
The anterior cruciate ligament (ACL) is one of the most prone to injury in the human body. Due to its insufficient vascularization and low regenerative capacity, surgery is often required when it is ruptured. Most of the current tissue engineering (TE) strategies are based on scaffolds produced with fibers due to the natural ligament’s fibrous structure. In the present work, composite filaments based on poly(L-lactic acid) (PLA) reinforced with graphite nanoplatelets (PLA+EG) as received, chemically functionalized (PLA+f-EG), or functionalized and decorated with silver nanoparticles [PLA+((f-EG)+Ag)] were produced by melt mixing, ensuring good filler dispersion. These filaments were produced with diameters of 0.25 mm and 1.75 mm for textile-engineered and 3D-printed ligament scaffolds, respectively. The resulting composite filaments are thermally stable, and the incorporation of graphite increases the stiffness of the composites and decreases the electrical resistivity, as compared to PLA. None of the filaments suffered significant degradation after 27 days. The composite filaments were processed into 3D scaffolds with finely controlled dimensions and porosity by textile-engineered and additive fabrication techniques, demonstrating their potential for ligament TE applications.
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