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Biomedical subjects

Frank K Ko

Publications and source records attributed to Frank K Ko.

9 recordsLinked to original sources

Co-electrospun poly(lactide-co-glycolide), gelatin, and elastin blends for tissue engineering scaffolds.

In this study, we describe composite scaffolds composed of synthetic and natural materials with physicochemical properties suitable for tissue engineering applications. Fibrous scaffolds were co-electrospun from a blend of a synthetic biodegradable polymer (poly(lactic-co-glycolic acid), PLGA, 10% solution) and two natural proteins, gelatin (denatured collagen, 8% solution) and alpha-elastin (20% solution) at ratios of 3:1:2 and 2:2:2 (v/v/v). The resulting PLGA-gelatin-elastin (PGE) fibers were homogeneous in appearance with an average diameter of 380 +/- 80 nm, which was considerably smaller than fibers made under identical conditions from the starting materials (PLGA, 780 +/- 200 nm; gelatin, 447 +/- 123 nm; elastin, 1060 +/- 170 nm). Upon hydration, PGE fibers swelled to an average fiber diameter of 963 +/- 132 nm, but did not disintegrate. Importantly, PGE scaffolds were stable in an aqueous environment without crosslinking and were more elastic than those made of pure elastin fibers. To investigate the cytocompatibility of PGE, we cultured H9c2 rat cardiac myoblasts and rat bone marrow stromal cells (BMSCs) on fibrous PGE scaffolds. We found that myoblasts grew equally as well or slightly better on the scaffolds than on tissue-culture plastic. Microscopic evaluation confirmed that myoblasts reached confluence on the scaffold surfaces while simultaneously growing into the scaffolds. Histological characterization of the PGE constructs indicated that BMSCs penetrated into the center of scaffolds and began proliferating shortly after seeding. Our results suggest that fibrous scaffolds made of PGE and similar biomimetic blends of natural and synthetic polymers may be useful for engineering soft tissues, such as heart, lung, and blood vessels.

Animals↗

Evaluation of the anterior cruciate ligament, medial collateral ligament, achilles tendon and patellar tendon as cell sources for tissue-engineered ligament.

This study investigated four different connective tissue cell types to determine which cell type should be the source for seeding a tissue-engineered anterior cruciate ligament (ACL) replacement. Cells derived from the ACL, medial collateral ligament (MCL), achilles tendon (AT), and patellar tendon (PT) of New Zealand White rabbits were isolated and cultured. Each cell type was cultured in vitro after seeding on three-dimensional (3-D) braided polymer scaffolds and on tissue culture polystyrene that served as a control. Samples were evaluated and compared for their morphology, proliferation, and gene expression of fibronectin, type I and type III collagen. Scanning electron microscopy (SEM) photomicrographs verified cell attachment of all four types of connective tissue fibroblasts to the scaffolds. Preliminary results comparing proliferation indicate that cells obtained from the PT and AT have the fastest proliferation. Whereas gene expression of the phenotypic markers measured using real-time reverse transcription polymerase chain reaction (RT-PCR) indicates ACL cells have the highest gene expression for the matrix markers. This leads to the question of which cell type should be the cell source for tissue-engineering of ligament, the highly proliferating cells or the differentiated matrix producing cells. This study would suggest that ACL differentiated matrix producing cells are the most suitable cells for further study and development of a tissue-engineered ligament.

Achilles Tendon↗

Anterior cruciate ligament regeneration using braided biodegradable scaffolds: in vitro optimization studies.

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee, and limitations in existing reconstruction grafts have prompted an interest in tissue engineered solutions. Previously, we reported on a tissue-engineered ACL scaffold fabricated using a novel, three-dimensional braiding technology. A critical factor in determining cellular response to such a graft is material selection. The objective of this in vitro study was to optimize the braided scaffold, focusing on material composition and the identification of an appropriate polymer. The selection criteria are based on cellular response, construct degradation, and the associated mechanical properties. Three compositions of poly-alpha-hydroxyester fibers, namely polyglycolic acid (PGA), poly-L-lactic acid (PLLA), and polylactic-co-glycolic acid 82:18 (PLAGA) were examined. The effects of polymer composition on scaffold mechanical properties and degradation were evaluated in physiologically relevant solutions. Prior to culturing with primary rabbit ACL cells, scaffolds were pre-coated with fibronectin (Fn, PGA-Fn, PLAGA-Fn, PLLA-Fn), an important protein which is upregulated during ligament healing. Cell attachment and growth were examined as a function of time and polymer composition. While PGA scaffolds measured the highest tensile strength followed by PLLA and PLAGA, its rapid degradation in vitro resulted in matrix disruption and cell death over time. PLLA-based scaffolds maintained their structural integrity and exhibited superior mechanical properties over time. The response of ACL cells was found to be dependent on polymer composition, with the highest cell number measured on PLLA-Fn scaffolds. Surface modification of polymer scaffolds with Fn improved cell attachment efficiency and effected the long-term matrix production by ACL cells on PLLA and PLAGA scaffolds. Therefore based on the overall cellular response and its temporal mechanical and degradation properties in vitro, the PLLA braided scaffold pre-coated with Fn was found to be the most suitable substrate for ACL tissue engineering.

Absorbable Implants↗

Fiber-based tissue-engineered scaffold for ligament replacement: design considerations and in vitro evaluation.

The anterior cruciate ligament (ACL) is the major intraarticular ligamentous structure of the knee, which functions as a joint stabilizer. It is the most commonly injured ligament of the knee, with over 150,000 ACL surgeries performed annually in the United States. Due to limitations associated with current grafts for ACL reconstruction, there is a significant demand for alternative graft systems. We report here the development of a biodegradable, tissue-engineered ACL graft. Several design parameters including construct architecture, porosity, degradability, and cell source were examined. This graft system is based on polymeric fibers of polylactide-co-glycolide 10:90, and it was fabricated using a novel, three-dimensional braiding technology. The resultant micro-porous scaffold exhibited optimal pore diameters (175-233 microm) for ligament tissue ingrowth, and initial mechanical properties of the construct approximate those of the native ligament.

Absorbable Implants↗

Electrospun protein fibers as matrices for tissue engineering.

Electrospinning has recently emerged as a leading technique for generating biomimetic scaffolds made of synthetic and natural polymers for tissue engineering applications. In this study, we compared collagen, gelatin (denatured collagen), solubilized alpha-elastin, and, as a first, recombinant human tropoelastin as biopolymeric materials for fabricating tissue engineered scaffolds by electrospinning. In extending previous studies, we optimized the shape and size (diameter or width) of the ensuing electrospun fibers by varying important parameters of the electrospinning process, such as solute concentration and delivery rate of the polymers. Our results indicate that the average diameter of gelatin and collagen fibers could be scaled down to 200-500 nm without any beads, while the alpha-elastin and tropoelastin fibers were several microns in width. Importantly, and contrary to any hitherto reported structures of electrospun polymers, fibers composed of alpha-elastin, especially tropoelastin, exhibited "quasi-elastic" wave-like patterns at increased solution delivery rates. The periodicity of these wave-like tropoelastin fibers was partly affected by the delivery rate. Atomic force microscopy was utilized to profile the topography of individual electrospun fibers and microtensile testing was performed to measure their mechanical properties. Cell culture studies confirmed that the electrospun engineered protein scaffolds support attachment and growth of human embryonic palatal mesenchymal (HEPM) cells.

Animals↗

Bioresorbable nanofiber-based systems for wound healing and drug delivery: optimization of fabrication parameters.

Wound healing is a complex process that often requires treatment with antibiotics. This article reports the initial development of a biodegradable polymeric nanofiber-based antibiotic delivery system. The functions of such a system would be (a) to serve as a biodegradable gauze, and (b) to serve as an antibiotic delivery system. The polymer used in this study was poly(lactide-co-glycolide) (PLAGA), and nanofibers of PLAGA were fabricated with the use of the electrospinning process. The objective of this study was to determine the effect of fabrication parameters: orifice diameter (needle gauge), polymer solution concentration, and voltage per unit length, on the morphology and diameter of electrospun nanofibers. The needle gauges studied were 16 (1.19 mm), 18 (0.84 mm), and 20 (0.58 mm), and the range of polymer solution concentration studied was from 0.10 g/mL to 0.30 g/mL. The effect of voltage was determined by varying the voltage per unit electrospinning distance, and the range studied was from 0.375 kV/cm to 1.5 kV/cm. In addition, the mass per unit area of the electrospun nanofibers as a function of time was determined and the feasibility of antibiotic (cefazolin) loading into the nanofibers was also studied. The results indicate that the diameter of nanofibers decreased with an increase in needle gauge (decrease in orifice diameter), and increased with an increase in the concentration of the polymer solution. The voltage study demonstrated that the average diameter of the nanofibers decreased with an increase in voltage. However, the effect of voltage on fiber diameter was less pronounced as compared to polymer solution concentration. The results of the areal density study indicated that the mass per unit area of the electrospun nanofibers increased linearly with time. Feasibility of drug incorporation into the nanofibers was demonstrated with the use of cefazolin, a broad-spectrum antibiotic. Overall, these studies demonstrated that PLAGA nanofibers can be tailored to desired diameters through modifications in processing parameters, and that antibiotics such as cefazolin can be incorporated into these nanofibers. Therefore, PLAGA nanofibers show potential as antibiotic delivery systems for the treatment of wounds.

Anti-Bacterial Agents↗

Position of single amino acid substitutions in the collagen triple helix determines their effect on structure of collagen fibrils.

Collagen II fibrils are a critical structural component of the extracellular matrix of cartilage providing the tissue with its unique biomechanical properties. The self-assembly of collagen molecules into fibrils is a spontaneous process that depends on site-specific binding between specific domains belonging to interacting molecules. These interactions can be altered by mutations in the COL2A1 gene found in patients with a variety of heritable cartilage disorders known as chondrodysplasias. Employing recombinant procollagen II, we studied the effects of R75C or R789C mutations on fibril formation. We determined that both R75C and R789C mutants were incorporated into collagen assemblies. The effects of the R75C and R789C substitutions on fibril formation differed significantly. The R75C substitution located in the thermolabile region of collagen II had no major effect on the fibril formation process or the morphology of fibrils. In contrast, the R789C substitution located in the thermostable region of collagen II caused profound changes in the morphology of collagen assemblies. These results provide a basis for identifying pathways leading from single amino acid substitutions in collagen II to changes in the structure of individual fibrils and in the organization of collagenous matrices.

Binding Sites↗

Electrospun nanofibrous structure: a novel scaffold for tissue engineering.

The architecture of an engineered tissue substitute plays an important role in modulating tissue growth. A novel poly(D,L-lactide-co-glycolide) (PLGA) structure with a unique architecture produced by an electrospinning process has been developed for tissue-engineering applications. Electrospinning is a process whereby ultra-fine fibers are formed in a high-voltage electrostatic field. The electrospun structure, composed of PLGA fibers ranging from 500 to 800 nm in diameter, features a morphologic similarity to the extracellular matrix (ECM) of natural tissue, which is characterized by a wide range of pore diameter distribution, high porosity, and effective mechanical properties. Such a structure meets the essential design criteria of an ideal engineered scaffold. The favorable cell-matrix interaction within the cellular construct supports the active biocompatibility of the structure. The electrospun nanofibrous structure is capable of supporting cell attachment and proliferation. Cells seeded on this structure tend to maintain phenotypic shape and guided growth according to nanofiber orientation. This novel biodegradable scaffold has potential applications for tissue engineering based upon its unique architecture, which acts to support and guide cell growth.

Animals↗

Modeling of mechanical properties and structural design of spider web.

With a unique combination of strength and toughness among materials, spider silk is the model for engineering materials. This paper presents the stress-strain behavior of Nephila clavipes spider silk under tension, transverse compression, and torsional deformation obtained by a battery of micro testing equipment. The experimental results showed significantly higher toughness than the state-of-the-art fibers in tension and in transverse compression. Higher shear modulus was also observed for the spider silk comparing to other liquid crystalline fibers such as aramid fibers. On the basis of the experimental results finite element analysis is used to simulate static and dynamic properties of spider web and to explore the role of both material properties and architectural design in its structural integrity and mechanical performance.

Animals↗