Advances in the scaffolds fabrication techniques using biocompatible polymers and their biomedical application: A technical and statistical review

With the advancement in tissue engineering, researchers are working hard on new techniques to fabricate more advanced scaffolds from biocompatible polymers with enhanced porosity, appropriate mechanical strength, diverse shapes and sizes for potential applications in biomedical field in general and tissue engineering in particular. These techniques include electrospinning, solution blow spinning, centrifugal spinning, particulate leaching (salt leaching), freeze-drying, lithography, self-assembly, phase separation, gas foaming, melt molding, 3-D printing, fiber mesh and solvent casting. In this article we have summarized the scaffold’s fabrication techniques from biocompatible polymers that are reported so far, the recent advances in these techniques, characterization of the physicochemical properties of scaffolds and their potential applications in the biomedical field and tissue engineering. The article will help both newcomers and experts working in the biomedical implant fabrication to not only find their desired information in one document but also understand the fabrication techniques and the parameters that control the success of biocompatible polymeric scaffolds. Furthermore, a static analysis of the work published in all forms on the most innovative techniques is also presented. The data is taken from Scopus, restricting the search to biomedical fields and tissue engineering.     

Fabrication of cellulose-based scaffold with microarchitecture using a leaching technique for biomedical applications

Providing a conclusive microenvironment for cell growth, proliferation and differentiation is a major developmental strategy in the tissue engineering and regenerative medicine. This is usually achieved in the laboratory by culturing cells in three-dimensional polymer-based scaffolding materials. Here, we describe the fabrication of a cellulose scaffold for tissue engineering purposes from cellulose fiber using a salt leaching method. The 1-n-allyl-3-methylimidazolium chloride (AmimCl) IL was used as a solvent for cellulose. The leaching methodology used in this study offers the unique advantage of providing effective control of scaffold porosity by simply varying cellulose concentration. Morphologic testing of the scaffolds produced revealed pore sizes of 200–500 μm. In addition, the scaffolds had high water adsorption rates and slow degradation rates. To further investigate the suitability of these scaffolds for tissue engineering applications, biocompatibility was checked using an MTT assay and confirmed by Live/Dead^® viability testing. In addition, scanning electron microscopy and DAPI studies and in vivo experiment demonstrated the ability of cells to attach to scaffold surfaces, and a biocompatibility of matrices with cells, respectively. The authors describe the environmentally friendly fabrication of a novel cellulose-based tissue engineering scaffold.     

可降解聚氨酯型组织工程多孔支架材料的制备

本文在可降解型聚氨酯分子设计,聚氨酯型组织工程支架制备方法,可降解聚氨酯多孔支架的生物学性能及可降解聚氨酯多孔支架在组织工程中的应用等几个方面对可降解聚氨酯型组织工程支架的最新研究进展作了综述。重点讨论了静电纺丝、冷冻干燥、相分离等几种聚氨酯多孔支架制备方法以及聚氨酯型组织工程支架的生物降解性质、生长因子嵌入、生物力学性能、生物相容性等生物学性能。目前的研究表明通过聚氨酯分子设计与各种支架制备方法结合可制得满足各种生物学性能的支架材料且这类材料已被证实在血管、软骨、硬质骨等各类组织工程中有重要的应用价值。但如何进一步提高聚氨酯支架材料的力学强度以使其能更好地与硬组织的力学性能相匹配以及如何降低或消除聚氨酯对人体的毒性仍是需要进一步研究的问题。     

Novel 3D Neuron Regeneration Scaffolds Based on Synthetic Polypeptide Containing Neuron Cue

Neural tissue engineering has become a potential technology to restore the functionality of damaged neural tissue with the hope to cure the patients with neural disorder and to improve their quality of life. This paper reports the design and synthesis of polypeptides containing neuron stimulate, glutamic acid, for the fabrication of biomimetic 3D scaffold in neural tissue engineering application. The polypeptides are synthesized by efficient chemical reactions. Monomer γ‐benzyl glutamate‐N‐carboxyanhydride undergoes ring‐opening polymerization to form poly(γ‐benzyl‐l ‐glutamate), then hydrolyzes into poly(γ‐benzyl‐l ‐glutamate)‐r‐poly(glutamic acid) random copolymer. The glutamic acid amount is controlled by hydrolysis time. The obtained polymer molecular weight is in the range of 200 kDa for good quality of fibers. The fibrous 3D scaffolds of polypeptides are fabricated using electrospinning techniques. The scaffolds are biodegradable and biocompatible. The biocompatibility and length of neurite growth are improved with increasing amount of glutamic acid in scaffold. The 3D scaffold fabricated from aligned fibers can guide anisotropic growth of neurite along the fiber and into 3D domain. Furthermore, the length of neurite outgrowth is longer for scaffold made from aligned fibers as compared with that of isotropic fibers. This new polypeptide has potential for the application in the tissue engineering for neural regeneration.     

Effects of an avidin-biotin binding system on chondrocyte adhesion and growth on biodegradable polymers

Cell adhesion to a scaffold is a prerequisite for tissue engineering. Many studies have been focused on enhancing cell adhesion to synthetic materials that are used for scaffold fabrication. In this study, we applied an avidin-biotin binding system to enhance chondrocyte adhesion to biodegradable polymers. Biotin molecules were conjugated to the cell membrane of chondrocytes, and mediated cell adhesion to avidin-coated surfaces. We demonstrated that immobilization of biotin molecules to chondrocyte surfaces enhanced cell adhesion to avidin-coated biodegradable polymers such as poly(L-lactic acid), poly(D,L-lactic acid), and polycaprolactone, compared to the adhesion of normal chondrocytes to the same type of biodegradable polymer. The biotinylated chondrocytes still maintained their proliferation ability. This study showed the promise of applying the avidin-biotin system in cartilage tissue engineering. [diagram in text].     

Horizons of modern molecular dynamics simulation in digitalized solid freeform fabrication with advanced materials

Our ability to shape and finish a component by combined methods of fabrication including (but not limited to) subtractive, additive, and/or no theoretical mass-loss/addition during the fabrication is now popularly known as solid freeform fabrication (SFF). Fabrication of a telescope mirror is a typical example where grinding and polishing processes are first applied to shape the mirror, and thereafter, an optical coating is usually applied to enhance its optical performance. The area of nanomanufacturing cannot grow without a deep knowledge of the fundamentals of materials and consequently, the use of computer simulations is now becoming ubiquitous. This article is intended to highlight the most recent advances in the computation benefit specific to the area of precision SFF as these systems are traversing through the journey of digitalization and Industry-4.0. Specifically, this article demonstrates that the application of the latest materials modelling approaches, based on techniques such as molecular dynamics, are enabling breakthroughs in applied precision manufacturing techniques.     

Recent Strategies in Fabrication of Gradient Hydrogels for Tissue Engineering Applications

Hydrogels are widely used as scaffold in tissue engineering field because of their ability to mimic the cellular microenvironment. However, mimicking a completely natural cellular environment is complicated due to the differences in various physical and chemical properties of cellular environments. Recently, gradient hydrogels provide excellent heterogeneous environment to mimic the different cellular microenvironments. To create hydrogels with an anisotropic distribution, gradient hydrogels have been widely developed by adopting several gradient generation techniques. Herein, the various gradient hydrogel fabrication techniques, including dual syringe pump systems, microfluidic device, photolithography, diffusion, and bio‐printing are summarized. As the effects of gradient 3D hydrogels with stems have been reviewed elsewhere, this review focuses principally on gradient hydrogel fabrication for multi‐model tissue regeneration. This review provides new insights into the key points for fabrication of gradient hydrogels for multi‐model tissue regeneration.     

Reinforcement of electrospun polycaprolacton scaffold using KIT-6 to improve mechanical and biological performance

Electrospinning has been extensively accepted as one of most important techniques for fabrication of scaffolds for bone tissue engineering. Polycaprolactone is one of the most applied electro-spinned scaffolds. Since low mechanical strength of polycaprolactone scaffold leads to the limitation of its applications, composition of polycaprolactone with ceramic particles is of great interest. Several studies have been conducted on fabrication and characterization of polycaprolactone nanocomposite scaffolds, but none of these researches has used mesoporous silica particles (KIT-6). In this project, a high-strength and bioactive nanocomposite scaffold has been developed which consists of polycaprolactone and mesoporous silica particles. Results showed that increase of KIT-6 particles percentages up to 5% leads to the enhancement of tensile strength of scaffold from 1.8 ± 0.2 to 2.9 ± 1.0 MPa. Although wettability of scaffolds in presence of particles was totally lower than pure PCL scaffold, but increase of particles percentages led to enhancement of wettability and water absorption of scaffolds. On the other hand presence of KIT-6 particles increased specific surface area and also bioactivity of scaffold was increased by enhancement of ion exchange between surface and simulated body fluid. Finally it was concluded that PCL-KIT-6 scaffolds are a suitable candidate for application in tissue engineering.     

骨组织工程支架材料研究进展*

骨在组织工程中得到了非常广泛、深入的研究.支架材料与许多可降解材料一起也在进行探索性研究.用于骨组织工程的生物材料可以是三维多孔的刚硬材料,也可以是可注射材料.本文从聚合物角度综述了骨组织工程对支架材料的基本要求,用于骨组织工程的可降解生物材料、支架材料的设计和制备技术以及支架材料的表面修饰等方面的研究进展.     

Biochemical Characterization of a GH43 β-Xylosidase from <Emphasis Type="Italic">Bacteroides ovatus</Emphasis>

Cartilage tissue engineering is believed to provide effective cartilage repair post-injuries or diseases. Biomedical materials play a key role in achieving successful culture and fabrication of cartilage. The physical properties of a chitosan/gelatin hybrid hydrogel scaffold make it an ideal cartilage biomimetic material. In this study, a chitosan/gelatin hybrid hydrogel was chosen to fabricate a tissue-engineered cartilage in vitro by inoculating human adipose-derived stem cells (ADSCs) at both dynamic and traditional static culture conditions. A bioreactor that provides a dynamic culture condition has received greater applications in tissue engineering due to its optimal mass transfer efficiency and its ability to simulate an equivalent physical environment compared to human body. In this study, prior to cell-scaffold fabrication experiment, mathematical simulations were confirmed with a mass transfer of glucose and TGF-β2 both in rotating wall vessel bioreactor (RWVB) and static culture conditions in early stage of culture via computational fluid dynamic (CFD) method. To further investigate the feasibility of the mass transfer efficiency of the bioreactor, this RWVB was adopted to fabricate three-dimensional cell-hydrogel cartilage constructs in a dynamic environment. The results showed that the mass transfer efficiency of RWVB was faster in achieving a final equilibrium compared to culture in static culture conditions. ADSCs culturing in RWVB expanded three times more compared to that in static condition over 10 days. Induced cell cultivation in a dynamic RWVB showed extensive expression of extracellular matrix, while the cell distribution was found much more uniformly distributing with full infiltration of extracellular matrix inside the porous scaffold. The increased mass transfer efficiency of glucose and TGF-β2 from RWVB promoted cellular proliferation and chondrogenic differentiation of ADSCs inside chitosan/gelatin hybrid hydrogel scaffolds. The improved mass transfer also accelerated a dynamic fabrication of cell-hydrogel constructs, providing an alternative method in tissue engineering cartilage.     

Poly(vinyl alcohol)-Amino Acid Hydrogels Fabricated into Tissue Engineering Scaffolds by Colloidal Gas Aphron Technology

A new class of hydrogels made from poly(vinyl alcohol) (PVA) and amino acid was formed into porous tissue engineering scaffolds by the colloidal gas aphron (CGA) method. CGA microfoams are formed using high speed stirring to generate uniform, micrometer scale bubbles. CGAs offer several advantages over conventional scaffold fabrication techniques including room temperature processing, aqueous conditions and utilization of air bubbles to create uniform pores. This technique eliminates the need for toxic solvents and salt templates. In addition, the novel poly(vinyl alcohol) hydrogels are inherently strong, eliminating the need for crosslinkers.     

Recent Progress in Fabrication of Electrospun Nanofiber Membranes for Developing Physiological In Vitro Organ/Tissue Models

Nanofiber membranes (NFMs), which have an extracellular matrix-mimicking structure and unique physical properties, have garnered great attention as biomimetic materials for developing physiologically relevant in vitro organ/tissue models. Recent progress in NFM fabrication techniques immensely contributes to the development of NFM-based cell culture platforms for constructing physiological organ/tissue models. However, despite the significance of the NFM fabrication technique, an in-depth discussion of the fabrication technique and its future aspect is insufficient. This review provides an overview of the current state-of-the-art of NFM fabrication techniques from electrospinning techniques to postprocessing techniques for the fabrication of various types of NFM-based cell culture platforms. Moreover, the advantages of the NFM-based culture platforms in the construction of organ/tissue models are discussed especially for tissue barrier models, spheroids/organoids, and biomimetic organ/tissue constructs. Finally, the review concludes with perspectives on challenges and future directions for fabrication and utilization of NFMs.     

Solvent-assisted room-temperature compression molding approach to fabricate porous scaffolds for tissue engineering

This study investigated the room-temperature compression molding/particle leaching approach to fabricate three-dimensional porous scaffolds for tissue engineering. Scaffolds with anatomical shapes (ear, joint, tube, cylinder) were made from biodegradable poly(D,L-lactide) and poly[(D,L-lactide)-co-glycolide]. The utility of this room-temperature compression approach comes from the effect of solvent assistance, but the tendency for post-molding scaffold shrinkage is a problem unique to this method and is thus examined with emphasis in this paper. Scaffold shrinkage was found to be tolerable under normal fabrication conditions with high salt contents, which is just what the preparation of highly porous scaffolds requires. Furthermore, the resultant porosities after salt leaching were measured as well as the initial scaffold shrinkages after solvent evaporation, and the relation between them was revealed by theoretical analysis and confirmed by comparison with experimental measurements. The pores were interconnected, and porosity can exceed 90%. The effects of porosity on the mechanical properties of porous scaffolds were also investigated. This convenient fabrication approach is a prospective method for the tailoring of porous scaffolds for a variety of possible applications in tissue engineering and tissue reconstruction.     

Biodegradable elastomers for tissue engineering and cell-biomaterial interactions

Synthetic biomaterials serve as a cornerstone in the development of clinically focused regenerative medicine therapies that aim to reduce suffering and prolong life. Recent improvements in biodegradable elastomeric materials utilize natural extracellular matrix proteins as inspiration to yield a new class of materials with superior degradation kinetics, desirable biocompatibility profiles, and mechanical properties that closely match those of soft tissues. This review describes several classes of synthetic biodegradable elastomers and associated fabrication techniques that are relevant to scaffold development. The application of these materials to select tissue engineering models is also discussed.     

3D Plotted PCL Scaffolds for Stem Cell Based Bone Tissue Engineering

The ability to control the architecture and strength of a bone tissue engineering scaffold is critical to achieve a harmony between the scaffold and the host tissue. Rapid prototyping (RP) technique is applied to tissue engineering to satisfy this need and to create a scaffold directly from the scanned and digitized image of the defect site. Design and construction of complex structures with different shapes and sizes, at micro and macro scale, with fully interconnected pore structure and appropriate mechanical properties are possible by using RP techniques. In this study, RP was used for the production of poly(ε-caprolactone) (PCL) scaffolds. Scaffolds with four different architectures were produced by using different configurations of the fibers (basic, basic-offset, crossed and crossed-offset) within the architecture of the scaffold. The structure of the prepared scaffolds were examined by scanning electron microscopy (SEM), porosity and its distribution were analyzed by micro-computed tomography (µ-CT), stiffness and modulus values were determined by dynamic mechanical analysis (DMA). It was observed that the scaffolds had very ordered structures with mean porosities about 60%, and having storage modulus values about 1 × 10⁷ Pa. These structures were then seeded with rat bone marrow origin mesenchymal stem cells (MSCs) in order to investigate the effect of scaffold structure on the cell behavior; the proliferation and differentiation of the cells on the scaffolds were studied. It was observed that cell proliferation was higher on offset scaffolds (262000 vs 235000 for basic, 287000 vs 222000 for crossed structure) and stainings for actin filaments of the cells reveal successful attachment and spreading at the surfaces of the fibers. Alkaline phosphatase (ALP) activity results were higher for the samples with lower cell proliferation, as expected. Highest MSC differentiation was observed for crossed scaffolds indicating the influence of scaffold structure on cellular activities.     

Carbon nanotubes reinforced with natural/synthetic polymers to mimic the extracellular matrices of bone – a review

The persistent failure of conventional materials used in manufacturing orthopedic implants was due to the deficiency or poor integrations of implant materials to the juxtaposed bone and stress-strain imbalances between the interfaces of tissues and implant materials. Therefore, the fabrication of a suitable bioactive scaffold for bone tissue engineering is considered a vital requisite to mimic the extracellular bone matrix. Numerous researches were reported concerning the fabrication of a suitable bioactive scaffold to improve cell adhesion, proliferation, and differentiation so far. However, for the past two decades, the research on carbon nanotubes (CNTs)-reinforced composites employed in the biomedical field is increasing day-by-day because of its outstanding properties. Moreover, it is essential to choose a biocompatible polymer with greater affinity to act as an extracellular matrix as well as to attract CNTs and in facilitating the homogeneous distribution of CNTs in aqueous and organic solvents. The development of CNTs-based composites in bone tissue engineering is presented in this review based on the last 10 years of research. The detailed information about the structural-functions and defects of bone, and the importance of CNTs-functionalized natural and synthetic polymers, and their potential activity in bone regenerations and bone replacements have been reviewed.     

Biodegradable highly porous interconnected poly(ε-caprolactone)/poly(L-lactide-co-ε-caprolactone) scaffolds by supercritical foaming for small-diameter vascular tissue engineering

Biodegradable ?4 mm tubular porous poly(ε-caprolactone)/poly(L-lactide-co-ε-caprolactone) (PCL/PLCL) scaffolds are fabricated successfully via one-step microcellular supercritical carbon dioxide foaming process. The effect of blending ratio on the rheology, pore structures, mechanical property, wettability, and biocompatibility of PCL/PLCL blends tubular scaffold are reported. Rheological results show that PCL matrix and PLCL dispersed phase has good compatibility. The melt strength of PCL can be enhanced obviously by adding PLCL. With an increase of PLCL content from 10 to 30 wt%, the pore size increases from 7.6 to 24.9 μm due to the homogeneous nucleation effect. The maximum open-cell content can reach 77% for PCL/PLCL foamed sample. Cyclical tensile and compliance tests show that few content of dispersed PLCL (10–20 wt%) improves the flexibility and recoverability. Cell viability results demonstrate that human umbilical vein endothelial cells (HUVECs) cultured on all PCL/PLCL porous scaffolds exhibit a typical spindle-like cell morphology. Moreover, HUVECs have a higher density and spreading areas on surface of 10% PLCL scaffold. The results gathered in this paper may open a new perspective for the fabrication of small-diameter vascular tissue engineering scaffold.     

Biodegradable Polyesters for Tissue Engineering

Summary: Paper describes basic characteristics of synthesis and properties of aliphatic polyesters used for tissue engineering. Described is also synthesis of polyester containing block copolymers suitable for surface modification. Described are methods used for scaffold fabrication with required porosity. In particular, presented are methods according to which scaffolds are made from prefabricated polyester micro- and nanoparticles.     

Development of porous,antibacterial and biocompatible GO/n-HAp/bacterial cellulose/β-glucan biocomposite scaffold for bone tissue engineering

Due to their potential renewable materials-based tissue engineering scaffolds has gained more attention. Therefore, researchers are looking for new materials to be used as a scaffold. In this study, we have focused on the development of a nanocomposite scaffold for bone tissue engineering (using bacterial cellulose (BC) and β-glucan (β-G)) via free radical polymerization and freeze-drying technique. Hydroxyapatite nanoparticles (n-HAp) and graphene oxide (GO) were added as reinforcement materials. The structural changes, surface morphology, porosity, and mechanical properties were investigated through spectroscopic and analytical techniques like Fourier transformation infrared (FT-IR), scanning electron microscope (SEM), Brunauer–Emmett-Teller (BET), and universal testing machine Instron. The scaffolds showed remarkable stability, aqueous degradation, spongy morphology, porosity, and mechanical properties. Antibacterial activities were performed against gram -ive and gram + ive bacterial strains. The BgC-1.4 scaffold was found more antibacterial compared to BgC-1.3, BgC-1.2, and BgC-1.1. The cell culture and cytotoxicity were evaluated using the MC3T3-E1 cell line. More cell growth was observed onto BgC-1.4 due to its uniform interrelated pores distribution, surface roughness, better mechanical properties, considerable biochemical affinity towards cell adhesion, proliferation, and biocompatibility. These nanocomposite scaffolds can be potential biomaterials for fractured bones in orthopedic tissue engineering.     

Organ weaving: woven threads and sheets as a step towards a new strategy for artificial organ development

The concept of "organ weaving" is presented, a fabrication technique that can be an attractive option for the development of artificial tissues and organs. "Living threads" are created by immersing threads that are soaked in a CaCl(2) solution into a sodium-alginate-loaded cell suspension bath, encapsulating the cells and creating a bio-friendly, easily manageable starting material for building up larger scaffold structures. Such living threads have the advantage of being a particularly mild culturing medium for mammalian cells, protecting the cells during subsequent processing steps from dehydration and other rapid changes in the chemistry of the surrounding environment. Connecting different types of threads into 3D objects gives unique opportunities to address tissue engineering challenges.