Heejae Yang

A novel hydrogel-collagen composite improves functionality of an injectable extracellular matrix

Cellular transplantation is now closer to becoming a practical clinical strategy to repair, regenerate or restore the function of skin, muscle, nerves and pancreatic islets. In this study we sought to develop a simple injectable collagen matrix that would preserve the normal cellular organization of skin cells. Three different scaffolds were created and compared: collagen-glycosaminoglycan (GAG) scaffolds, crosslinked collagen-GAG scaffolds without polyvinyl alcohol (PVA) and crosslinked collagen-GAG scaffolds containing PVA hydrogel. Importantly, all scaffolds were found to be non-cytotoxic. PVA-containing gels exhibited a higher tensile strength (P<0.05), faster fibril formation (P<0.001) and reduced collagenase digestion (P<0.01) compared with other gels. Free floating fibroblast-populated, PVA-borate scaffolds resisted contraction over a 10 day period (P<0.001). The fibroblast-populated scaffolds containing PVA demonstrated a 3-fold reduction in cellularity over 10 days compared with the control gels (P<0.001). Multicellular skin substitutes containing PVA-borate networks display a linear cellular organization, reduced cellularity and the formation of a keratinized epidermis that resembles normal skin. In conclusion, these data underscore the multifunctionality of a simple PVA-borate-collagen matrix as an injectable composite for tissue engineering or cell transplantation.

Emulsion Electrospinning of a Collagen‐Like Protein/PLGA Fibrous Scaffold: Empirical Modeling and Preliminary Release Assessment of Encapsulated Protein

The effectiveness of a multifunctional scaffold produced by the electrospinning of emulsions composed of organic PLGA and aqueous collagen-like protein (denoted as Fol-8Col) solutions is demonstrated. The resultant Fol-8Col/PLGA fibrous scaffolds with homogeneous morphology have mean fiber diameters from 600 to 2,000 nm. A uniform distribution of encapsulated Fol-8Col in the fibers is observed by fluorescence microscopy. TEM is used to clarify the representative core/sheath structure of emulsion electrospun Fol-8Col/PLGA fibers. Preliminary release assessment of encapsulated Fol-8Col shows results of sustained release for more than one month from the Fol-8Col/PLGA fibrous mats. The cytocompatibility of fibroblast cell line L929 with the fibrous composite seems promosing.

Postelectrospinning modifications for alginate nanofiber-based wound dressings

Alginate nanofibers have been attractive for potential tissue regeneration applications due to a combination of their moisture retention ability and large surface area available in a nonwoven nanofiber form. This study aims to address several challenges in alginate nanofiber application, including the lack of structural stability in aqueous environment and limited cell attachment as compared to commercial wound dressings, via examining crosslinking techniques. In addition to the commonly performed divalent ion crosslinking, a glutaraldehyde double-crosslinking step and polylysine addition were applied to an electrospun alginate nanofiber nonwoven mat. With optimization of the electrospinning solution, nanofiber morphology was maintained after the two-stage crosslinking process. Extensibility of the nanofiber mat reduced after the crosslinking process. However, both aqueous stability and cell attachment improved after the postspinning modifications, as shown through degradation tests in phosphate buffered saline solutions and fibroblast cell culture studies, respectively.

Changes in Structural-Mechanical Properties and Degradability of Collagen during Aging-associated Modifications

Background: Extracellular matrix (ECM) alterations during aging contribute to various pathological phenotypes. Results: Collagen fibrils, fibers, and bone alter their structural integrity and susceptibility toward degradation by cathepsin K when age-modified. Conclusion: Age-related modifications of collagen affect its biomechanics and proteolytic stability. Significance: Our research reveals how matrix modifications may increase the risk of ECM disorders. During aging, changes occur in the collagen network that contribute to various pathological phenotypes in the skeletal, vascular, and pulmonary systems. The aim of this study was to investigate the consequences of age-related modifications on the mechanical stability and in vitro proteolytic degradation of type I collagen. Analyzing mouse tail and bovine bone collagen, we found that collagen at both fibril and fiber levels varies in rigidity and Youngs modulus due to different physiological changes, which correlate with changes in cathepsin K (CatK)-mediated degradation. A decreased susceptibility to CatK-mediated hydrolysis of fibrillar collagen was observed following mineralization and advanced glycation end product-associated modification. However, aging of bone increased CatK-mediated osteoclastic resorption by ∼27%, and negligible resorption was observed when osteoclasts were cultured on mineral-deficient bone. We observed significant differences in the excavations generated by osteoclasts and C-terminal telopeptide release during bone resorption under distinct conditions. Our data indicate that modification of collagen compromises its biomechanical integrity and affects CatK-mediated degradation both in bone and tissue, thus contributing to our understanding of extracellular matrix aging.

Ultra-filtration membranes based on electrospun poly(vinylidene fluoride) (PVDF) fibrous composite membrane scaffolds

In this study, electrospun TiO2–PVDF composite scaffolds coupled with different polymeric coatings were fabricated. TiO2 nanoparticles with an average diameter of 20 nm were used to improve the mechanical properties of the scaffold. It was found that the physical properties of ultrafiltration (UF) membranes could be adjusted by varying the type of polymeric coating used. The electrospun TiO2–PVDF membranes coupled with a thin PVDF coating showed benign mechanical properties but a low water permeability. Contrarily, the filter possessed good water permeability but weak mechanical properties when it was covered by two layers of coatings including both pure PVDF and chitosan–PEO. The breaking mechanism of the UF membrane coupled with different polymer coatings was analysed in detail, and corresponding models for this mechanism were provided.

Palladium-Zeolite nanofiber as an effective recyclable catalyst membrane for water treatment.

Zeolite is an exciting natural material due to its unique capability of ammonium nitrogen (NH3N) adsorption in water. In this study, multifunctional hybrid composites of zeolite/palladium (Ze/Pd) on polymer nanofiber membranes were fabricated and explored for sustainable contaminant removal. SEM and XRD demonstrated that zeolite and palladium nanoparticles were uniformly distributed and deposited on the nanofibers. NH3N recovery rate was increased from 23 to 92% when palladium coated zeolite was embedded on the nanofiber. Multifunctional nanofibers of Ze/Pd membranes were able to adsorb NH3N on the zeolites placed on the surface of fibers and palladium catalysts were capable of selective oxidation of NH3N to N2 gas. The cycling of NH3N adsorption-oxidation, high flux, hydrophilicity, and flexibility of the membrane makes it a strong candidate for water treatment.

Alternating magnetic field heat behaviors of PVDF fibrous mats filled with iron oxide nanoparticles

To study the magnetic heat behaviors, iron oxide nanoparticles (IONPs) and the polyvinylidene fluoride (PVDF) fibrous mats filled with IONPs were prepared by using coprecipitaion method and the electrospinning technique. The synthesized IONPs exhibited a magnetization of about 72 emu/g with average diameter of about 10 nm. The magnetizations of PVDF fibrous mats filled with IONPs showed 2.6 emu/g, 5.5 emu/g and 9.9 emu/g for 5 wt.%, 10 wt.% and 20 wt.% IONPs concentration, respectively. The heat of the magnetic fibrous mats were measured under various alternating magnetic fields (90, 128, and 167 Oe), frequencies (190, 250 and 355 kHz). The maximum saturated temperature showed up to 62 °C for 20 wt.% IONPs filled in PVDF fibrous mat under 167 Oe and 355 kHz.

Nanofibers for ligament and tendon tissue regeneration

Abstract Over the last decade, researchers have turned to nanofibrous ligament and tendon scaffolds as alternatives to autografting, due to the fibers’ desirable surface properties. In addition, the flexibility of material choice and fabrication route allows the creation of highly tailored scaffolds that support tissue generation while satisfying the stringent mechanical property requirements presented by musculoskeletal tissues. This chapter explores recent work on nanofibers and identifies ways in which nanofibers can address challenges posed by current treatments. We also discuss methods for translating nanofiber properties into three-dimensional scaffolds, based on existing and emerging textile composite fabrication techniques.

Effect of iron oxide nanoparticle size on electromagnetic properties of composite nanofibers

Electrically conductive and magnetically permeable carbon nanofiber-based composites were developed using the electrospinning with subsequent heat treatment. The composite nanofiber contains a variable composition of magnetite nanoparticles with two different size regimes, ranging from superparamagnetic (10–20 nm) to ferromagnetic (20–30 nm). The composite nanofibers are then characterized using Scanning/Transmission Electron Microscopy, X-Ray Diffractometry, Raman Spectroscopy, four-point probe, and a Superconducting Quantum Interference Device. Electromagnetic Interference Shielding Effectiveness of pristine carbon nanofibers as well as electromagnetic composite nanofibers are examined in the X-band frequency region. Higher degree of graphitization, electrical conductivity, and magnetic strength are obtained for nanocomposites containing larger magnetite nanoparticles (20–30 nm). A transition from superpartamagnetic to ferromagnetic characteristics is observed during nanocomposite processing. Electromagnetic Interference Shielding Effectiveness of as high as 68 dB (in the working frequency of 10.4 GHz) is observed for composite nanofibers fabricated with larger magnetite nanoparticles carbonized at 900℃.

The magnetic thermo-sensitive magnetite nanoparticles filled in electrospun fibrous

The authors describes the composite sheet with Fe₃O₄ particles as inclusions in polymer based nanofibers by using the electrospinning technique . The spinning dopes were prepared by sonication of the iron oxide nanoparticles in Dimethylformamide (DMF, Sigma-Aldrich) for 24 hrs . Polyvinylidene Fluoride (PVDF, Kynar) of 20 wt .% to DMF were then added to the prepared Fe₃O₄/DMF mixture . The solutions mixtures were stirred for 24 hrs with 5, 10 and 20 wt .% of Fe₃O₄ in PVDF before the electrospinning at 90 ⁰C, respectively . The spinning dope of 5 ml was transferred to a syringe for electrospinning.