Yurong Cai

Extraction of pectins with different degrees of esterification from mulberry branch bark

Pectins were extracted from mulberry branch bark, a byproduct of the sericulture industry. A single-factor experiment was used to optimize the production conditions. Under optimal conditions, the galacturonic acid yields from bark with and without epidermis were 61.73 + or - 1.39% and 35.12 + or - 0.24%, respectively. The extracted pectins mainly consisted of galacturonic acid with a trace amount of neutral sugars, and the total galacturonic acid content in the pectins extracted from the bark without epidermis reached 85.46 + or - 2.76%. Pectins extracted from bark without epidermis had a higher degree of esterification (71.13 + or - 1.67%) than those extracted from bark with epidermis (24.27 + or - 2.89%). Pectin solution from bark without epidermis showed higher apparent viscosity, suggesting its higher gelation ability. Thus, the mulberry branch bark is a potential source of pectin with different degrees of esterification.

Preparation and characterization of nano-hydroxyapatite/silk fibroin porous scaffolds

Novel tissue engineering scaffold materials of nano-hydroxyapatite (nHA)/silk fibroin (SF) biocomposite were prepared by freeze-drying. The needle-like nHA crystals of about 10 nm in diameter by 50–80 nm in length, which were uniformly distributed in the porous nHA/SF scaffolds, were prepared by a co-precipitation method with a size. The as-prepared nHA/SF scaffolds showed good homogeneity, interconnected pores and high porosity. XRD and FT-IR analysis suggested that the silk fibroin was in β-sheet structure, which usually provides outstanding mechanical properties for silk materials. In this work, composite scaffolds containing as high as 70% (w/w) nHA were prepared, which had excellent compressive modulus and strength, higher than the scaffolds at low nHA content level and other porous biodegradable polymeric scaffolds often considered in bone-related tissue engineering reported previously. The cell compatibility of composite scaffolds was evaluated through cell viability by MTT assay. All these results indicated that these nHA/SF scaffold materials may be a promising biomaterial for bone tissue engineering.

Bio-inspired mineralization of hydroxyapatite in 3D silk fibroin hydrogel for bone tissue engineering.

To fabricate hard tissue implants with bone-like structure using a biomimetic mineralization method is drawing much more attentions in bone tissue engineering. The present work focuses in designing 3D silk fibroin hydrogel to modulate the nucleation and growth of hydroxyapatite crystals via a simple ion diffusion method. The study indicates that Ca(2+) incorporation within the hydrogel provides the nucleation sites for hydroxyapatite crystals and subsequently regulates their oriented growth. The mineralization process is regulated in a Ca(2+) concentration- and minerlization time-dependent way. Further, the compressive strength of the mineralized hydrogels is directly proportional with the mineral content in hydrogel. The orchestrated organic/inorganic composite supports well the viability and proliferation of human osteoblast cells; improved cyto-compatibility with increased mineral content. Together, the present investigation reports a simple and biomimetic process to fabricate 3D bone-like biomaterial with desired efficacy to repair bone defects.

Silk fibroin membrane used for guided bone tissue regeneration

With the aim to develop a novel membrane with an appropriate mechanical property and degradation rate for guided bone tissue regeneration, lyophilized and densified silk fibroin membrane was fabricated and its mechanical behavior as well as biodegradation property were investigated. The osteoconductive potency of the silk fibroin membranes were evaluated in a defect rabbit calvarial model. Silk fibroin membrane showed the modulated biodegradable and mechanical properties via ethanol treatment with different concentration. The membrane could prevent soft tissue invasion from normal tissue healing, and the amounts of new bone and defect closure with silk fibroin membrane were similar to those of commercially available collagen membrane.

Silk sericin microcapsules with hydroxyapatite shells: protection and modification of organic microcapsules by biomimetic mineralization

Silk protein sericin based organic-inorganic hybrid microcapsules are fabricated by incubating sericin microcapsules with a supersaturated calcium phosphate solution containing citric acid. A mineral hydroxyapatite shell is formed on the surface of the microcapsules. The thickness of the mineralized shell is dependant on the mineralization time. The amylum as a model cargo is encapsulated into the microcapsules with/without the presence of a mineralized shell. The release behavior of amylum from the microcapsules is investigated under different external environments. The results show that the release speed of amylum from the hybrid microcapsules is slower than from the sericin microcapsules under different pH and ionic strength conditions. This indicates that the stability of the hybrid microcapsules is improved due to the presence of the hydroxyapatite shell. The mineral shell provides a good protection to the microcapsule structure and carries goods against external harsh environment. In addition, cell cultures show a good cytocompatibility of the hybrid microcapsules. The natural microcapsules having an inorganic mineral shell cover may potentially act as drug delivery and encapsulating bioactive molecule systems.

Biomimetic synthesis of sericin and silica hybrid colloidosomes for stimuli-responsive anti-cancer drug delivery systems

Colloidosomes are becoming popular due to their significant flexibility with respect to microcapsule functionality. This study reports a facile approach for synthesizing silica colloidosomes by using sericin microcapsule as the matrix in an environment-friendly method. The silica colloid arrangement on the sericin microcapsules are orchestrated by altering the reaction parameters. Doxorubicin (DOX), used as a hydrophilic anti-cancer drug model, is encapsulated into the colloidosomes in a mild aqueous solution and becomes stimuli-responsive to different external environments, including pH values, protease, and ionic strength are also observed. Colloidosomes with sub-monolayers, close-packed monolayers, and close-packed multi-layered SiO2 colloid shells can be fabricated under the optimized reaction conditions. A flexible DOX release from colloidosomes can be obtained via modulating the SiO2 colloid layer arrangement and thickness. The close-packed and multi-layered SiO2 colloid shells can best protect the colloidosomes and delay the rapid cargo release. MG-63 cells are killed when doxorubicin is released from the microcapsules due to degradation in the microenvironment of cancer cells. The drug release period is prolonged as SiO2 shell thickness and integrity increase. This work suggests that the hybrid colloidosomes can be effective in a bioactive molecule delivery system.

Degradation pattern of porous CaCO3 and hydroxyapatite microspheres in vitro and in vivo for potential application in bone tissue engineering.

Despite superior clinical handling, excellent biocompatibility, biodegradation property of calcium phosphate needs to be improved to coincide with the rate of new bone formation. In this study, spherical CaCO3 are fabricated in the presence of the silk sericin and then transformed into porous hydroxyapatite (HAP) microspheres via hydrothermal method. The degradation behavior of obtained CaCO3, HAP and their mixture is first investigated in vitro. The result demonstrates that the weight loss of HAP microspheres are almost 24.3% after immersing in pH 7.40 Tris-HCl buffer solution for 12 weeks, which is far slower than that of spherical CaCO3 (97.5%). The degradation speed of the mixtures depends on the proportion of CaCO3 and HAP. The mixture with higher content of CaCO3 possesses a quicker degradation speed. The obtained CaCO3 and HAP microspheres are injected into subcutaneous tissue of ICR mice with the assistance of sodium alginate. The result in vivo also shows an obvious difference of degradation speed between the obtained CaCO3 and HAP microspheres, implying it is feasible to modulate the degradation property of the mixture through changing the proportion of CaCO3 and HAP The good cytocompatibility of the two kinds of microspheres is proved and a mild inflammation response is observed only at early stage of implantation. The job offers a simple method to modify the degradation properties of biomaterial for potential use in bone tissue engineering.

Controlled degradation pattern of hydroxyapatite/calcium carbonate composite microspheres.

Hydroxyapatite (HAP) is widely used in clinic due to its good biocompatibility and osteoconductivity except for its slow degradation speed. In the present study, spherical calcium carbonate (CaCO3) is fabricated in the presence of silk protein sericin, which is transmuted into HAP microsphere in phosphate solution with the assistance of microwave irradiation. The effect of reaction conditions on the conversion of CaCO3 is investigated including reaction time, chemical composition of phosphate solution, and microwave power to get a series of HAP/CaCO3 composites. The degradation property of the composites is evaluated in vitro. Results show the degradation speed of the composite with higher HAP content is slower. The degradation rate of the composite could be changed effectively by modulating the proportion of HAP and CaCO3. This work provides a feasible method for the preparation of spherical HAP/CaCO3 composite with controllable degradability. The composite thus obtained may be an ideal material for bone tissue engineering application. Microsc. Res. Tech. 79:518–524, 2016.

One-Step Synthesis of Natural Silk Sericin-Based Microcapsules with Bionic Structures

Different techniques are being developed for fabricating microcapsules; it is still a challenge to fabricate them in an efficient and environment-friendly process. Here, a one-step green route to synthesize silk protein sericin-based microcapsules without any assistance of organic solvents is reported. By carefully changing the concentration of calcium ions accompanied with stirring, the morphology of the microcapsules can easily be regulated to form either discoidal, biconcave, cocoon-like, or tubular structures. The chelation of Ca(2+) and shearing force from agitation may induce the conformational transformation of sericin, which possibly results in the formation of microcapsules through the self-assembly of the protein subsequently. The as-prepared cocoon-like microcapsules exhibit pH-dependent stability. A potential application of microcapsules being fabricated from natural water-soluble silk protein sericin for controlled bioactive molecules loading and release system by a pH-triggered manner is quite feasible.

Fabrication and characterization of absorbent and antibacterial alginate fibers loaded with sulfanilamide

Absorbent alginate fibers were fabricated using wet spinning technique and a broad-spectrum antibacterial and anti-inflammatory agent sulfanilamide was loaded from co-dissolving solution. The drug entrapment in the fibers during the processing was confirmed by optical microscope, SEM and FTIR. The water absorbency, in vitro drug release and antibacterial activities were performed to evaluate the potential application of the sulfanilamide-loaded alginate fibers for wound dressing. The results indicated that sulfanilamide was successfully encapsulated into the alginate fibers, and this system was stable in terms of high loading content and effectiveness in release. The in vitro release experiment showed a sustained and controlled release pattern of the drug from the fibers. And in vitro activity substantiated the fact that sulfanilamide was delivered in its active state and exhibited better antibacterial activities in comparison with the pure alginate fibers. Therefore the present investigation indicated that the sulfanilamide-loaded alginate fibers have potential application as ideal wound dressing.