Hyeongjin Lee

Three-dimensional hierarchical composite scaffolds consisting of polycaprolactone, β-tricalcium phosphate, and collagen nanofibers: fabrication, physical properties, and in vitro cell activity for bone tissue regeneration.

β-Tricalcium phosphate (β-TCP) and collagen have been widely used to regenerate various hard tissues, but although Bioceramics and collagen have various biological advantages with respect to cellular activity, their usage has been limited due to β-TCPs inherent brittleness and low mechanical properties, along with the low shape-ability of the three-dimensional collagen. To overcome these material deficiencies, we fabricated a new hierarchical scaffold that consisted of a melt-plotted polycaprolactone (PCL)/β-TCP composite and embedded collagen nanofibers. The fabrication process was combined with general melt-plotting methods and electrospinning. To evaluate the capability of this hierarchical scaffold to act as a biomaterial for bone tissue regeneration, physical and biological assessments were performed. Scanning electron microscope (SEM) micrographs of the fabricated scaffolds indicated that the β-TCP particles were uniformly embedded in PCL struts and that electrospun collagen nanofibers (diameter = 160 nm) were well layered between the composite struts. By accommodating the β-TCP and collagen nanofibers, the hierarchical composite scaffolds showed dramatic water-absorption ability (100% increase), increased hydrophilic properties (20%), and good mechanical properties similar to PCL/β-TCP composite. MTT assay and SEM images of cell-seeded scaffolds showed that the initial attachment of osteoblast-like cells (MG63) in the hierarchical scaffold was 2.2 times higher than that on the PCL/β-TCP composite scaffold. Additionally, the proliferation rate of the cells was about two times higher than that of the composite scaffold after 7 days of cell culture. Based on these results, we conclude that the collagen nanofibers and β-TCP particles in the scaffold provide good synergistic effects for cell activity.

Designed hybrid scaffolds consisting of polycaprolactone microstrands and electrospun collagen-nanofibers for bone tissue regeneration

Biomedical scaffolds used in bone tissue engineering should have various properties including appropriate bioactivity, mechanical strength, and morphologically optimized pore structures. Collagen has been well known as a good biomaterial for various types of tissue regeneration, but its usage has been limited due to its low mechanical property and rapid degradation. In this work, a new hybrid scaffold consisting of polycaprolactone (PCL) and collagen is proposed for bone tissue regeneration. The PCL enhances the mechanical properties of the hybrid scaffold and controls the pore structure. Layered collagen nanofibers were used to enhance the initial cell attachment and proliferation. The results showed that the hybrid scaffold yielded better mechanical properties of pure PCL scaffold as well as enhanced biological activity than the pure PCL scaffold did. The effect of pore size on bone regeneration was investigated using two hybrid scaffolds with pore sizes of 200 ± 20 and 300 ± 27 μm. After post-seeding for 7 days, the cell proliferation with pore size, 200 ± 20 μm, was greater than that with pore size, 300 ± 27 μm, due to the high surface area of the scaffold.

Cells (MC3T3-E1)-Laden Alginate Scaffolds Fabricated by a Modified Solid-Freeform Fabrication Process Supplemented with an Aerosol Spraying

In this study, we propose a new cell encapsulation method consisting of a dispensing method and an aerosol-spraying method. The aerosol spray using a cross-linking agent, calcium chloride (CaCl(2)), was used to control the surface gelation of dispensed alginate struts during dispensing. To show the feasibility of the method, we used preosteoblast (MC3T3-E1) cells. By changing the relationship between the various dispensing/aerosol-spraying conditions and cell viability, we could determine the optimal cell-dispensing process: a nozzle size (240 μm) and an aerosol spray flow rate (0.93 ± 0.12 mL min(-1)), 10 mm s(-1) nozzle moving speed, a 10 wt % concentration of CaCl(2) in the aerosol solution, and 2 wt % concentration of CaCl(2) in the second cross-linking process. Based on these optimized process conditions, we successfully fabricated a three-dimensional, pore-structured, cell-laden alginate scaffold of 20 × 20 × 4.6 mm(3) and 84% cell viability. During long cell culture periods (16, 25, 33, and 45 days), the preosteoblasts in the alginate scaffold survived and proliferated well.

Cell(MC3T3-E1)-printed poly(ϵ-caprolactone)/alginate hybrid scaffolds for tissue regeneration.

A new cell-printed scaffold consisting of poly(ϵ-caprolactone) (PCL) and cell-embedded alginate struts is designed. The PCL and alginate struts are stacked in an interdigitated pattern in successive layers to acquire a three-dimensional (3D) shape. The hybrid scaffold exhibits a two-phase structure consisting of cell (MC3T3-E1)-laden alginate struts able to support biological activity and PCL struts able to provide controllable mechanical support of the cell-laden alginate struts. The hybrid scaffolds exhibit an impressive increase in tensile modulus and maximum strength compared to pure alginate scaffolds. Laden cells are homogeneously distributed throughout the alginate struts and the entire scaffold, resulting in cell viability of approximately 84%.

Three-dimensional plotted PCL/β-TCP scaffolds coated with a collagen layer: preparation, physical properties and in vitro evaluation for bone tissue regeneration

Poly(e-caprolactone)(PCL)/β-tricalcium phosphate (β-TCP) composite scaffolds, which can be fabricated using a rapid-prototyping process, have been used for bone tissue regeneration. However, one of the main defects of the three-dimensional (3D) PCL/β-TCP scaffold is the highly hydrophobic surface of the micro-sized PCL/β-TCP strands, which can cause poor initial cell attachment and proliferation. To overcome this problem, we propose a new and simple coating process supplemented with collagen solution. Three-dimensionally plotted PCL/β-TCP scaffolds simply coated with various concentrations (0.5, 2, 4 wt%) of collagen solution were studied in terms of water contact angle, water-absorption ability, mechanical properties and in vitro culturing of MG63 cells. Scanning electron microscope images demonstrated that the scaffolds were well coated with collagen solution, and the designed pore size (300 µm) and complete pore-interconnectivity of the scaffolds were well sustained. The scaffolds coated with collagen showed very good hydrophilic properties (0° at 3 min) with improved cell attachment and cell-viability, without any loss of mechanical property relative to the PCL/β-TCP scaffold.

A new hybrid scaffold constructed of solid freeform-fabricated PCL struts and collagen struts for bone tissue regeneration: fabrication, mechanical properties, and cellular activity

We propose a new technique for the fabrication of hybrid scaffolds using melt-plotting and a low temperature plate. This method is useful for the fabrication of a scaffold composed of heterogeneous biomaterials. We applied the new technique to collagen and polycaprolactone (PCL), which are stacked in interdigitated struts in successive layers to acquire a three-dimensional (3D) shape. The fabricated scaffolds exhibited a two-phase structure consisting of collagen struts to enhance the biological activity and PCL struts to increase the mechanical stability. They also exhibited a pore size under 100% pore interconnectivity appropriate for bone tissue regeneration. The fabricated hybrid scaffolds were assessed not only for mechanical properties, but also for biological capabilities by culturing osteoblast-like cells (MG63) on pure PCL, collagen, and hybrid scaffolds. Compared with the pure PCL scaffold, the hybrid scaffold exhibited higher biological activity, such as cell viability (an increase of about 27% at 7 days), alkaline phosphatase (ALP) activity (an increase of about 36% at 14 days), and calcium deposition. The pure collagen exhibited the highest value for most biological activities studied. In addition, the hybrid scaffolds exhibited a dramatic increase of Youngs modulus compared to those of pure collagen scaffolds. These results suggest that this hybrid scaffold is potentially useful as a biomedical scaffold for bone tissue regeneration.

Fabrication of cell-laden three-dimensional alginate-scaffolds with an aerosol cross-linking process

A modified dispensing method for fabricating three-dimensional (3D) cell-laden alginate scaffolds is presented that utilizes aerosolized calcium chloride solutions for crosslinking. To evaluate the process, preosteoblasts (MC3T3-E1) mixed with 3.5 wt% alginate were fabricated into a 3D matrix (20 × 20 × 4.5 mm3). The fabricated cell-laden structure was highly porous and had uniformly designed pore size and shape. We compared two different dispensing nozzle sizes (310 and 610 μm) by observing the cell distribution in the struts and determining the cell viability within the scaffolds. The scaffold-embedded cells were 85% viable compared to the initial cell viability, and the cell distribution was homogeneous. This innovative cell dispensing technique is likely to be a promising fabrication tool for obtaining functional 3D scaffolds for tissue regeneration.

Biocomposites electrospun with poly(ε-caprolactone) and silk fibroin powder for biomedical applications.

Biomedical synthetic polymers have been used in soft and hard tissue regeneration because of their good processability and biodegradability. However, biomaterials such as poly(ε-caprolactone) (PCL) have various shortcomings, including intrinsic hydrophobicity and lack of bioactive functional groups. The material must be reinforced with natural biomaterials to achieve good cellular and mechanical performance as biomedical material. We fabricated a biocomposite using PCL and silk fibroin (SF) powder, which has good biocompatibility and mechanical properties. The hydrophilicity, mechanical properties and cellular behavior of the PCL/SF fibers were analyzed. In addition, we obtained a highly oriented conduit of electrospun biocomposite fibers by modifying the rolling collector of the electrospinning system. As the alignment of micro/nanofibers increased, the orthotropic mechanical properties were improved. The biocompatibility of the biocomposite was evaluated in a culture of bone-marrow-derived rat mesenchymal stem cells. The cellular result demonstrated the potential usefulness of electrospun biocomposites for various biomedical conduit systems.

Recent cell printing systems for tissue engineering

Three-dimensional (3D) printing in tissue engineering has been studied for the bio mimicry of the structures of human tissues and organs. Now, it is being applied to 3D cell printing, which can position cells and biomaterials, such as growth factors, at desired positions in the 3D space. However, there are some challenges of 3D cell printing, such as cell damage during the printing process and the inability to produce a porous 3D shape owing to the embedding of cells in the hydrogel-based printing ink, which should be biocompatible, biodegradable, and non-toxic, etc. Therefore, researchers have been studying ways to balance or enhance the post-print cell viability and the print-ability of 3D cell printing technologies by accommodating several mechanical, electrical, and chemical based systems. In this mini-review, several common 3D cell printing methods and their modified applications are introduced for overcoming deficiencies of the cell printing process.

Combining a micro/nano-hierarchical scaffold with cell-printing of myoblasts induces cell alignment and differentiation favorable to skeletal muscle tissue regeneration.

Biomedical scaffolds must be used in tissue engineering to provide physical stability and topological/biochemical properties that directly affect tissue regeneration. In this study, a new cell-laden scaffold was developed that supplies micro/nano-topological cues and promotes efficient release of cells. The hierarchical structure consisted of poly(ε-caprolactone) macrosized struts for sustaining a three-dimensional structural shape, aligned nanofibers obtained with optimized electrospinning, and cell-printed myoblasts. Importantly, the printed myoblasts were fully safe and were efficiently released from the cell-laden struts to neighboring nanofiber networks. The incorporation of micro/nanofibers in the hierarchical scaffold significantly affected myoblast proliferation, alignment, and even facilitated the formation of myotubes. We observed that myosin heavy chain expression and the expression levels of various myogenic genes (MyoD, myogenin, and troponin T) were significantly affected by the fiber alignment achieved in our hierarchical cell-laden structure. We believe that the combination of cell-printing and a hierarchical scaffold that encourages fiber alignment is a highly promising technique for skeletal muscle tissue engineering.