Advanced Materials Research Vols. 55-57

Abstract: Silk has been used commercially as biomedical sutures for decades. Recently silk fibroin, especially from Bombyx mori silkworm, has been explored for many tissue engineering applications such as bone and cartilage due to its impressive biological compatibility and mechanical properties. In Thailand, Thai native silkworms have been long cultivated. Distinct characteristics of cocoon Thai silk are its yellow color and coarse filament. There is more sericin in Thai silk than in other Bombyx mori silks. These characteristics provide Thai silk a unique texture for textile industry. It is therefore the aim of this study to develop three-dimensional silk fibroin-based scaffolds from Thai yellow cocoon “Nangnoi-Srisaket” of Bombyx mori silkworms using salt-leaching method. To enhance the biological properties, type A gelatin, the denature form of collagen having good biocompactibility, was used to conjugate with silk fibroin scaffolds. The pore size of salt-leached silk fibroin scaffold structure represented the size of salt crystals used (600-710µm). After gelatin conjugation, gelatin was partly formed fibers inside the pores of silk fibroin scaffolds resulting in fiber-like structure with highly interconnection. Gelatin conjugation enhanced the compressive modulus of silk fibroin scaffolds by 93%. The results on in vitro culture using mouse osteoblast-like cells (MC3T3-E1) showed that gelatin conjugation could promote the cell proliferation in silk fibroin scaffolds. Moreover, the observed morphology of cells proliferated inside the scaffold after 14 days of culture showed the larger spreading area of cells on conjugated gelatin/silk fibroin scaffolds, compared to round-shaped cells on silk fibroin scaffolds. The results implied that Thai silk fibroin looked promising to be applied in tissue engineering and gelatin conjugation on Thai silk fibroin scaffolds could enhance the biological properties of scaffolds.

Abstract: Incorporation of Iron into hydroxyapatite (HAp) has generated a novel material for which their properties differ from those of conventional HAp. Although XRD indicated that the as-prepared iron-substituted hydroxyapatite (HApFe) is of a single crystalline phase similar to that of HAp, we found that carbonate ions can incorporate in the HApFe structure 3 times better than in HAp. As results, HApFe possesses the Vickers microhardness about 1.5 times higher than that of HAp. Thermal behaviors and bioactivity of HApFe are discussed in comparison to those of HAp. Various experimental methods have been employed in this work including powder XRD, IR, SEM, DSC/TGA and Vickers Hardness testing.

Abstract: The bulk ring-opening copolymerisation of L-lactide (LL) and ε-caprolactone (CL) with an initial comonomer feed ratio of LL:CL = 75:25 mol % was carried out using stannous acetate as the initiator at 120 oC for 48 hrs. The copolymer was characterised by GPC, DSC and TGA. Due to its ability to biodegrade in the human body, this type of copolymer has potential for use as an absorbable surgical suture. The copolymer obtained was melt spun at 153 oC using a small-scale melt-spinning apparatus and extruded into ice-cooled water to produce an as-spun monofilament fibre which was largely if not completely amorphous. Alternate off-line hot-drawing and annealing (3 cycles) was carried out in order to develop the fibre’s oriented semi-crystalline morphology. To complete the processing operation, thermal treatment was necessary to stabilize the fibre morphology. It was found that fixed annealing at 60 oC followed by free annealing at 60 oC stabilized the fibre morphology as a result of molecular relaxation. In vitro hydrolytic degradation studied in a phosphate buffer saline (PBS) solution of pH 7.4 at 37.0 ± 0.1 oC indicated that, after 6 weeks immersion in the buffer, the fibre’s tensile strength decreased by approximately 50% whereas a commercial ‘PDS’ suture of similar size lost its strength completely after only 4 weeks.

Abstract: Mesenchymal stem cells are multipotential cells capable of differentiating into osteoblasts, chondrocytes, adipocytes, tenocytes, and myoblasts. Wharton’s jelly consists of stem cells that are a rich source of primitive multipotent mesenchymal cells. Demineralized bone matrix (DBM) has been widely utilized as a biomaterial to promote new bone formation. We isolate and characterize umbilical cord Wharton’s Jelly-derived mesenchymal stem (UCMS) cells derived from Wharton’s jelly and examine the biological activity of DBM in this cell line. Osteoblast differentiation of the UCMS cells was determined using alkaline phosphatase (ALP) activity assay. To examine differential gene expression during osteogenic differentiation, total RNA was isolated from UCMS cells in the absence or presence of DBM on day7 and analyzed using osteogenesis cDNA gene array. The selected genes were verified using reverse transcriptase-polymerase chain reaction (RT-PCR) analyses. Wharton’s jelly derived cells could differentiate along an osteogenic lineage after treatment of DBM. The ALP activity assay showed that human UCMS cells could differentiate into osteogenic lineage. Gene expression of human UCMS cells treated with DBM for 7 days was analyzed by using cDNA array and RT-PCR analyses. We found that expression of RUNX2 and SMAD2 was upregulated whereas SMAD7 expression was downregulated as confirmed by RT-PCR. UCMS cells from a Wharton’s jelly of human umbilical cord could express osteogenesis genes for treatment with DBM. Wharton’s jelly from umbilical cord is a new source of mesenchymal stem cells that are readily available for application to bone tissue engineering.

Abstract: Currently, most commercialized peripheral nerve regenerative products are constructed from biodegradable polymers into hollow conduits. To speed up the regeneration rate, we proposed a development of a biocompatible protein-filled conduit for anastomosis amputated peripheral nerve with growth factor controlled release function. Glutaraldehyde-crosslinked protein sponges were tested for their abilities to controlled release of nerve growth factor (NGF) in vitro in our previous experiments. Type B gelatin sponges were able to limit diffusions of NGF due to electrostatic interactions between them. The rate of growth factor releases would be depended on degradation of the crosslinked gelatin. A nerve conduit model was produced using perfluoro alkoxy (PFA) tubes filled with gelatin which had been crosslinked using X-ray from Argon plasma treatment. This method of crosslinking provided 21.22±3.03 % degree of crosslinking. Hollow nerve conduits fabricated from poly(l-lactide-co-caprolactone) (PLCL) had a thicknesses and an inner diameters of 0.31±0.03 mm and 1.63±0.07 mm respectively. Average pore sizes of the inner surfaces and outer surfaces were 9.70±3.44 µm and 1.24±0.77 µm respectively. PLCL film supported growth of L929 mouse fibroblasts. For continuing works, we are testing the protein-filled conduits for peripheral nerve regeneration in animals.

Abstract: In various types of biomaterials used worldwide today, bioglass is one of the most interesting and a useful choice for research as it is unharmful or nontoxic to biological tissue. Binary or ternary phosphate-based glasses are also good candidates to be improved and used effectively. Glasses with 40 – 60 mol% of P2O5 incorporated at a constant mole-ratio of CaO: Na2O are studied in this experiment. Each batch of glasses is melted in an electric furnace at a temperature of about 1000 °C and splat-quenched at room temperature. Electrical properties such as conductivity and dielectric constant and microstructures of these glasses were investigated.

Abstract: A liposome is a spherical vesicle composed of phospholipids and cholesterol bilayer membrane and contains a core of aqueous solution. Liposomes are polymeric nanoparticles used for drug delivery due to their unique properties. It can carry both hydrophobic and hydrophilic molecules. In this study, we showed the benefit of using transmission electron microscope (TEM) with negative staining technique to investigate the morphology of liposomes produced by thin film method. At the same magnification of micrograph results, we could see the multilamellar vesicles of liposomes in various figures and different sizes.

Abstract: Cholesteryl cetyl carbonate (CCC) was synthesized from cetyl alcohol and cholesteryl chloroformate. Cholesteryl cetyl carbonate mixture (CCCM) was obtained from the reaction. CCCM was purified by liquid-liquid extraction and flash column chromatography. Thermotropic liquid crystal was formed in both pure CCC and CCCM. CCCM is composed of cholesterol, cetyl alcohol and CCC (30:20:50, weight ratio). FTIR and NMR were employed to confirm the functional groups of CCC. Thermal properties of CCC were determined by DSC and polarized light microscope. The phase transition from solid crystal to smectic appears at 42 °C, smectic to nematic appears at 54 °C and nematic to isotropic liquid appears at 73 °C. Indomethacin (IDM) could be incorporated into CCC and properties of CCC-IDM mixture stayed as liquid crystalline phase.

Abstract: Nanocomposite chitosan-based films incorporated with drug-loaded methoxy poly(ethylene glycol)-b-poly(D,L-lactide-co-glycolide) diblock copolymers (MPEG-b-PDLLG) nanoparticles were prepared by forming drug-loaded nanoparticles in chitosan solution before suspension-solution film casting. Salicylic acid was used as a poorly-water soluble model drug. The nanocomposite films with DLL/G ratios of 100/0 and 85/15 mol% and chitosan/diblock copolymer/drug ratios of 80/1/1, 80/2/2 and 80/4/4 (w/w) were prepared and investigated. The sizes of drug-loaded nanoparticles into the chitosan films were approximate or less than 100 nm. Nanopores were observed in the resulted chitosan films incorporated with drug-loaded nanoparticles when the diblock copolymer ratio was increased up to 2. Number and size of the nanopores increased as increasing the diblock copolymer ratio. Only the nanocomposite films with chitosan/diblock copolymer/drug ratio of 80/1/1 (w/w) showed slower drug release than the chitosan film.

Abstract: Nanoporous silk fibroin (SF) films were prepared as SF film loaded with methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) nanoparticles by film casting of MPEG-b-PDLL nanoparticle suspension-SF solution. Nanoporous structures of the SF films were formed due to self-condensation and nanophase separation of nanoparticles from SF film matrix during drying process. The films with SF/MPEG-b-PDLL ratios of 20/1, 20/2 and 20/3 (w/w) were prepared and investigated. The MPEG-b-PDLL nanoparticles can be observed on film surface and cross-section with 100-300 nm in size. The size of interconnected nanopore was in the range of 20 – 300 nm. The number and size of nanopores increased as increasing the MPEG-b-PDLL ratio. Thermal stability of the films studied from differential thermogravimetric (DTG) thermogram found that the nanoparticles dispersed into the SF films could improve thermal stability of each component. This indicated strong hydrogen bond interactions between SF and MPEG-b-PDLL were existed. Film transparency of the SF nanoporous films decreased when the MPEG-b-PDLL ratio was increased.