Thermally produced biodegradable scaffolds for cartilage tissue engineering

A novel process was developed to fabricate biodegradable polymer scaffolds for tissue engineering applications, without using organic solvents. Solvent residues in scaffolds fabricated by processes involving organic solvents may damage cells transplanted onto the scaffolds or tissue near the transplantation site. Poly(L-lactic acid) (PLLA) powder and NaCl particles in a mold were compressed and subsequently heated at 180 degrees C (near the PLLA melting temperature) for 3 min. The heat treatment caused the polymer particles to fuse and form a continuous matrix containing entrapped NaCl particles. After dissolving the NaCl salts, which served as a porogen, porous biodegradable PLLA scaffolds were formed. The scaffold porosity and pore size were controlled by adjusting the NaCl/PLLA weight ratio and the NaCl particle size. The characteristics of the scaffolds were compared to those of scaffolds fabricated using a conventional solvent casting/particulate leaching (SC/PL) process, in terms of pore structure, pore-size distribution, and mechanical properties. A scanning electron microscopic examination showed highly interconnected and open pore structures in the scaffolds fabricated using the thermal process, whereas the SC/PL process yielded scaffolds with less interconnected and closed pore structures. Mercury intrusion porosimetry revealed that the thermally produced scaffolds had a much more uniform distribution of pore sizes than the SC/PL process. The utility of the thermally produced scaffolds was demonstrated by engineering cartilaginous tissues in vivo. In summary, the thermal process developed in this study yields tissue-engineering scaffolds with more favorable characteristics, with respect to, freedom from organic solvents, pore structure, and size distribution than the SC/PL process. Moreover, the thermal process could also be used to fabricate scaffolds from polymers that are insoluble in organic solvents, such as poly(glycolic acid). Cartilage tissue regenerated from thermally produced PLLA scaffold.     

Synthetic biodegradable functional polymers for tissue engineering: a brief review

Scaffolds play a crucial role in tissue engineering. Biodegradable polymers with great processing flexibility are the predominant scaffolding materials. Synthetic biodegradable polymers with well-defined structure and without immunological concerns associated with naturally derived polymers are widely used in tissue engineering. The synthetic biodegradable polymers that are widely used in tissue engineering, including polyesters, polyanhydrides, polyphosphazenes, polyurethane, and poly (glycerol sebacate) are summarized in this article. New developments in conducting polymers, photoresponsive polymers, amino-acid-based polymers, enzymatically degradable polymers, and peptide-activated polymers are also discussed. In addition to chemical functionalization, the scaffold designs that mimic the nano and micro features of the extracellular matrix (ECM) are presented as well, and composite and nanocomposite scaffolds are also reviewed.     

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.     

Novel photopolymerizable biodegradable triblock polymers for tissue engineering scaffolds: synthesis and characterization

For use in micro-patterned scaffolds in tissue engineering, novel diacrylated triblock macromers (PLA-b-PCL-b-PLA, PGA-b-PCL-b-PGA and PCL-b-PEO-b-PCL) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). All diacrylated polymers were designed as triblock copolymers and involved biodegradable blocks of relatively non-polar epsilon-caprolactone (CL) and polar monomers such as glycolide (GA), lactide (LA) or ethylene oxide (EO). All triblock polymers were prepared in molecular weights of a few kilo daltons via the anionic ring-opening polymerization (ROP) of the corresponding lactide, glycolide or caprolactone using stannous octoate [Sn(Oct)(2)] as catalyst. The polymers had low polydispersity indices, ranging from 1.23 to 1.56. Biodegradable polymeric networks were prepared with conversions of 72-84% via photopolymerization of the triblock diacrylated polymers with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. PLA-b-PCL-b-PLA copolymers crumbled easily and were not suitable for micro-patterning. PGA-b-PCL-b-PGA copolymers had higher water contact angles than PCL-b-PEO-b-PCL and were also cytocompatible with Fibroblasts 3T3.     

Non-bioengineered silk fibroin protein 3D scaffolds for potential biotechnological and tissue engineering applications

This paper describes a new source for fabricating high-strength, non-bioengineered silk gland fibroin 3D scaffolds from Indian tropical tasar silkworm, Antheraea mylitta using SDS for dissolution. The scaffolds were fabricated by freeze drying at different prefreezing temperatures for pore size and porosity optimization. Superior mechanical properties with compressive strength in the range of 972 kPa were observed. The matrices were degraded by proteases within 28 d of incubation. Biocompatibility was assessed by feline fibroblast culture in vitro and confocal microscopy further confirmed adherence, spreading, and proliferation of primary dermal fibroblasts. Results indicate nonmulberry 3D silk gland fibroin protein as an inexpensive, high-strength, slow biodegradable, biocompatible, and alternative natural biomaterial. [Figure: see text].     

Sodium alginate/magnesium oxide nanocomposite scaffolds for bone tissue engineering

A simple 2‐step method, consisting of film casting and polyvinyl alcohol leaching, is proposed to prepare magnesium oxide (MO) nanoparticle‐reinforced sodium alginate scaffolds with right properties for bone tissue engineering. The cytocompatibility of the as‐prepared scaffolds was also evaluated using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium‐bromide yellow tetrazole assay test, wherein chondrocyte cells had been considered as target cells. According to the results, the ensuing sodium alginate nanocomposites, containing 4‐wt% MO nanoparticles, demonstrated the highest physical and mechanical properties after leaching step. The Young modulus of sodium alginate/4‐wt% MO was improved about 44%, in comparison with that of the pure alginate sample. Furthermore, incorporating MO nanoparticles up to 4 wt% controlled the liquid uptake capacity of scaffolds vis‐à‐vis the resultant pure sodium alginate sample. Moreover, with increasing the nanoparticle content, the antibacterial properties of scaffolds enhanced, but their degradation rates under in vitro conditions tapered off. With the introduction of 3‐ and 4‐wt% MO, the average diameter of the bacterial zone of the scaffold samples reduced to less than 10 mm², suggesting an insensitive antimicrobial performance, compared with the pure sodium alginate and the samples with 1‐ and 2‐wt% MO content, which exhibit antimicrobial sensitivity. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium‐bromide assay test also revealed the cultivated chondrocyte cells on the 4‐wt% MO nanoparticle‐reinforced scaffold possessed better interaction as well as appropriate cell attachment and proliferation than the pristine sodium alginate sample.     

Biomimetic polymer/apatite composite scaffolds for mineralized tissue engineering

The material surface must be considered in the design of scaffolds for bone tissue engineering so that it supports bone cells adhesion, proliferation and differentiation. A biomimetic approach has been developed as a 3D surface modification technique to grow partially carbonated hydroxyapatite (the bonelike mineral) in prefabricated, porous, polymer scaffolds using a simulated body fluid in our lab. For the rational design of scaffolding materials and optimization of the biomimetic process, this work focused on various materials and processing parameters in relation to apatite formation on 3D polymer scaffolds. The apatite nucleation and growth in the internal pores of poly(L-lactide) and poly(D,L-lactide) scaffolds were significantly faster than in those of poly(lactide-co-glycolide) scaffolds in simulated body fluids. The apatite distribution was significantly more uniform in the poly(L-lactide) scaffolds than in the poly(lactide-co-glycolide) scaffolds. After incubation in a simulated body fluid for 30 d, the mass of poly(L-lactide) scaffolds increased approximately 40%, whereas the mass of the poly(lactide-co-glycolide) scaffolds increased by about 15% (see Figure). A higher ionic concentration and higher pH value of the simulated body fluid enhanced apatite formation. The effects of surface functional groups on apatite nucleation and growth were found to be more complex in 3D scaffolds than on 2D films. Surprisingly enough, it was found that carboxyl groups significantly reduced the apatite formation, especially on the internal pore surfaces of 3D scaffolds. These findings are critically important in the rational selection of materials and surface design of 3D scaffolds for mineralized tissue engineering and may contribute to the understanding of biomineralization as well.SEM micrograph of a poly(L-lactide) scaffold.     

Production and characterization of chitosan fibers and 3-D fiber mesh scaffolds for tissue engineering applications

This study reports on the production of chitosan fibers and 3-D fiber meshes for the use as tissue engineering scaffolds. Both structures were produced by means of a wet spinning technique. Maximum strain at break and tensile strength of the developed fibers were found to be 8.5% and 204.9 MPa, respectively. After 14 d of immersion in simulated body fluid (SBF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and inductively coupled plasma emission (ICP) spectroscopy analyses showed that a bioactive Ca-P layer was formed on the surface of the fibers, meaning that they exhibit a bioactive behavior. The samples showed around 120% max. swelling in physiological conditions. The pore sizes of 3-D chitosan fiber mesh scaffolds were observed to be in the range of 100-500 microm by SEM. The equilibrium-swelling ratio of the developed scaffolds was found to be around 170% (w/w) in NaCl solution at 37 degrees C. Besides that, the limit swelling strain was less than 30%, as obtained by mechanical spectroscopy measurements in the same conditions. The viscoelastic properties of the scaffolds were also evaluated by both creep and dynamic mechanical tests. By means of using short-term MEM extraction test, both types of structures (fibers and scaffolds) were found to be non-cytotoxic to fibroblasts. Furthermore, osteoblasts directly cultured over chitosan fiber mesh scaffolds presented good morphology and no inhibition of cell proliferation could be observed.Osteoblast-like cells proliferating over chitosan based fibers after 7 d of culture.     

Fibers and 3D mesh scaffolds from biodegradable starch-based blends: production and characterization

The aim of this work is the production of fibers from biodegradable polymers to obtain 3D scaffolds for tissue engineering of hard tissues. The scaffolds required for this highly demanding application need to have, as well as the biological and mechanical characteristics, a high degree of porosity with suitable dimensions for cell seeding and proliferation. Furthermore, the open cell porosity should have adequate interconnectivity for a continuous flow of nutrients and outflow of cell metabolic residues as well as to allow cell growth into confluent layers. Blends of corn starch, a natural biodegradable polymer, with other synthetic polymers (poly(ethylene vinyl alcohol), poly(epsilon-caprolactone), poly(lactic acid)) were selected for this work because of their good balance of properties, namely biocompatibility, processability and mechanical properties. Melt spinning was used to produce fibers from all the blends and 3D meshes from one of the starch-poly(lactic acid) blends. The experimental characterization included the evaluation of the tensile mechanical properties and thermal properties of the fibers and the compression stiffness, porosity and degradation behavior of the 3D meshes. Light microscopy picture of 3D meshes.     

HPMC crosslinked chitosan/hydroxyapatite scaffolds containing Lemongrass oil for potential bone tissue engineering applications

The chitosan (CS), hydroxypropyl methyl cellulose (HPMC), hydroxyapatite (HAp and Lemon grass oil (LGO) based scaffolds was prepared by freeze gelation method. The composite formation was confirmed by FTIR (Fourier-transform infrared spectroscopy) analysis and surface morphology was evaluated by SEM (Scanning Electron Microscopy) analysis. The mechanical strength, biodegradation, swelling, porosity and antibacterial activity were evaluated on the basis of LGO contents. The scaffold structure was porous and the mechanical strength was enhanced as a function of LGO contents. The scaffold properties analysis revealed the biodegradation nature and swelling behavior of CS-HPMC-HAp-LGO was also affected significantly as a function of LGO contents. The cytotoxicity of CS-HPMC-HAp-LGO was studied against MC3T3-E1 cells and based on cell viability, no toxic sign was observed. The antimicrobial activity was evaluated against S. aureus and CS-HPMC-HAp-LGO scaffolds showed promising activity, which was varied as a function of LGO contents. The findings revealed that the CS-HPMC-HAp-LGO are biocompatible and have potential for bone tissue engineering.     

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.     

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.     

Magnesium-zinc-graphene oxide nanocomposite scaffolds for bone tissue engineering

The aim of this study was to fabricate and evaluate magnesium-zinc-graphene oxide nanocomposite scaffolds for bone tissue engineering. For this reason, Mg-6Zn, Mg-6Zn-1GO, and Mg-6Zn-2GO scaffolds were fabricated by the powder metallurgy method. The porosity level and also the pore size of the scaffolds were evaluated by SEM which varied from 40 to 46% and 200 to 500 μm, respectively. The chemical composition and microstructure of the scaffolds were characterized by XRD and SEM equipped with EDS; the presence of Mg, Zn, C, and O elements in the structure of the scaffolds was shown. Also, the elemental map confirmed the existence of magnesium, zinc, carbon, and oxygen in the structure of the scaffold. The mechanical properties of the scaffolds were investigated by the compression test; the results showed that by the addition of graphene oxide to the structure, the compressive strength of the samples increased from 5 to 8 MPa. Electrochemical corrosion polarization tests were conducted to evaluate the corrosion resistance of the samples immersed in simulated body fluid (SBF). Furthermore, the biodegradability of the scaffolds was determined by immersion of the samples in phosphate-buffered saline (PBS). The results demonstrated that the polarization resistance value and the corrosion rate for different formulations including Mg-6Zn, Mg-6Zn-1GO, and Mg-6Zn-2GO were 41.58, 35.48, and 55.40 Ω.cm² followed by 10.60, 14.83, and 9.06 mm.year^?1, respectively. Based on the results, the Mg-6Zn-2GO formulation presented the best corrosion resistance among the samples were investigated, which confirmed the results of the immersion test. Moreover, the MTT assay proved that the extract of Mg-6Zn-2GO scaffolds was not cytotoxic in contact with L-929 cells which validated the studied scaffolds for bone tissue applications.     

Electrospun nanofibrous polycaprolactone scaffolds for tissue engineering of annulus fibrosus

The annulus fibrosus comprises concentric lamellae that can be damaged due to intervertebral disc degeneration; to provide permanent repair of these acquired structural defects, one solution is to fabricate scaffolds that are designed to support the growth of annulus fibrosus cells. In this study, electrospun nanofibrous scaffolds of polycaprolactone are fabricated in random, aligned, and round-end configurations. Primary porcine annulus fibrosus cells are grown on the scaffolds and evaluated for attachment, proliferation, and production of extracellular matrix. The scaffold consisting of round-end nanofibers substantially outperforms the random and aligned scaffolds on cell adhesion; additionally, the scaffold with aligned nanofibers strongly affects the orientation of cells.     

Original method of imprinting pores in scaffolds for tissue engineering

Results of the preparation of biodegradable porous scaffolds using an original modification of a wet phase inversion method were presented. Influence of gelatin non‐woven as a non‐classic pore precursor and polyvinylpyrrolidone, Pluronic as classic pore precursors on the structure of obtained scaffolds was analyzed. It was shown that the addition of gelatin non‐wovens enables the preparation of scaffolds, which allow for the growth of cells (size, distribution, and shape of pores). Mechanical properties of the obtained cell scaffolds were determined. The influence of pore precursors on mass absorption of scaffolds against isopropanol and plasma was investigated. Interaction of scaffolds with a T‐lymphocyte line (Jurkat) and with fibroblasts (L929) was investigated. Obtained scaffolds are not cytotoxic and can be used as implants, for example, the regeneration of cartilage tissue.     

Microrobotics and MEMS-based fabrication techniques for scaffold-based tissue engineering

Scaffold based tissue engineering strategies use cells, biomolecules and a scaffold to promote the repair and regeneration of tissues. Although scaffold-based tissue engineering approaches are being actively developed, most are still experimental, and it is not yet clear what defines an ideal scaffold/cell construct. Solid free form fabrication (SFF) techniques can precisely control matrix architecture (size, shape, interconnectivity, branching, geometry and orientation). The SFF methods enable the fabrication of scaffolds with various designs and material compositions, thus providing a control of mechanical properties, biological effects and degradation kinetics. This paper reviews the application of micro-robotics and MEMS-based fabrication techniques for scaffold design and fabrication. It also presents a novel robotic technique to fabricate scaffold/cell constructs for tissue engineering by the assembly of microscopic building blocks.     

Three-dimensional scaffolds for tissue engineering: the importance of uniformity in pore size and structure

To validate the importance of uniformity in pore size and structure of a scaffold for tissue engineering, we fabricated two types of scaffolds with uniform (inverse opal scaffolds) and nonuniform pore sizes and structures, and then evaluated their properties in terms of diffusion of macromolecules, spatial distribution of fibroblasts, and differentiation of preosteoblasts. Our results confirmed the superior performance of the inverse opal scaffolds due to the uniform pore size, homogeneous environment, and high interconnectivity: a higher diffusion rate, a uniform distribution of cells, and a higher degree of differentiation. In addition, we found that both the differentiation of cells and secretion of extracellular matrix were dependent on the properties of the individual pore to which the cells were attached, rather than the bulk properties of a scaffold. Our results clearly indicate that inverse opal scaffolds could provide a better microenvironment for cells in comparison to a scaffold with nonuniform size and structure.     

Monolithic biocompatible and biodegradable scaffolds for tissue engineering

The state of the art in polymeric materials for tissue engineering as well as the needs and concerns for future medical applications are outlined and discussed and brought into relation to recent developments in polymer chemistry. Particularly, the recent developments in micro‐ and nano‐structured polymeric monoliths designed for these purposes will be discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2219–2227, 2009     

Biomimetic strengthening polylactide scaffold materials for bone tissue engineering

In this paper, a new polylactide (PLA)-based scaffold composite by biomimetic synthesis was designed. The novel composite mainly consists of nano-hydroxyapatite (n-HA), which is the main inorganic content in natural bone tissue for the PLA. The crystal degree of the n-HA in the composite is low and the crystal size is very small, which is similar to that of natural bone. The compressive strength of the composite is higher than that of the PLA scaffold. Using the osteoblast culture technique, we detected cell behaviors on the biomaterial in vitro by SEM, and the cell affinity of the composite was found to be higher than that of the PLA scaffold. The biomimetic three-dimensional porous composite can serve as a kind of excellent scaffold material for bone tissue engineering because of its microstructure and properties. Translated from Journal of Hunan University (Natural Sciences), 2006, 33(2) (in Chinese)