Mechanical and biological properties of chitin/polylactide (PLA)/hydroxyapatite (HAP) composites cast using ionic liquid solutions.

This research investigates the potential development of lobster shell waste-derived chitin reinforced with poly(lactic acid) (PLA) and nano-hydroxyapatite (nHAP) into new materials with potentially superior mechanical and thermal properties for biomedical applications. The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) was used as a solvent to prepare chitin/PLA/nHAP composites. The effect of variation of the polymer concentrations on the conduct of the resulting composite was explored. The detailed physico-mechanical, thermal and surface morphology properties were evaluated with different thermal and optical characterization techniques. When the concentration of PLA in the composite was increased from 20 to 80 wt%, the tensile strength improved by ~77% while the elongation at break and the toughness of the material decreased significantly. The addition of hydroxyapatite was observed to improve strength of the composites up to 140% with an increase in elongation at break up to 465%. Cell growth study show that the composite materials support the growth and proliferation of Ocy 454 osteocyte cells. The materials were shown to have no effect on osteocyte gene expression, as well as minimal cytotoxicity and biodegradability. These results reveal that the biocomposites would be suitable candidates for use in bone regeneration that are not exposed to excessive forces.

pH-responsive drug release from functionalized electrospun poly(caprolactone) scaffolds under simulated in vivo environment.

The difference in the tumor environment from the normal healthy tissue can be therapeutically exploited to develop new strategies for controlled and site-specific drug delivery. In the present study, a continuous flow system is designed to represent the in vivo environment of a tumor tissue and drug release is studied at different pH that represents normal tissue pH, tumor tissue pH, and stomach pH. The results obtained from these experiments were translated to a human embryonic kidney cell culture system and the effect of drug released from these functionalized PCL scaffolds on cell viability was studied. A significant decrease in cell viability was observed with the doxorubicin hydrochloride concentration that would be released at acidic pH, either present as a result of tumor extracellular environment or could be achieved via fabrication of a composite scaffold with a polyvinyl alcohol hydrogel containing acid. In the end, a study using zebrafish as an animal model is also undertaken in order to study the drug release from the scaffolds in vivo.

Zebrafish acvr2a and acvr2b exhibit distinct roles in craniofacial development.

To examine the roles of activin type II receptor signaling in craniofacial development, full-length zebrafish acvr2a and acvr2b clones were isolated. Although ubiquitously expressed as maternal mRNAs and in early embryogenesis, by 24 hr postfertilization (hpf), acvr2a and acvr2b exhibit restricted expression in neural, hindbrain, and neural crest cells (NCCs). A morpholino-based targeted protein depletion approach was used to reveal discrete functions for each acvr2 gene product. The acvr2a morphants exhibited defects in the development of most cranial NCC-derived cartilage, bone, and pharyngeal tooth structures, whereas acvr2b morphant defects were largely restricted to posterior arch structures and included the absence and/or aberrant migration of posterior NCC streams, defects in NCC-derived posterior arch cartilages, and dysmorphic pharyngeal tooth development. These studies revealed previously uncharacterized roles for acvr2a and acvr2b in hindbrain and NCC patterning, in NCC derived pharyngeal arch cartilage and joint formation, and in tooth development.

Maternal alk8 promoter fragment directs expression in early oocytes.

Zebrafish Alk8 is a novel type I TGFbeta family member receptor that functions in Bmp signaling pathways to direct dorsoventral patterning of the early embryo. Both alk8 mRNA and protein is expressed in a variety of tissues, including teeth, eye, heart, blood, notochord, muscle, neural tissues, and neural crest cells (NCC's). Previous functional analyses, performed by microinjection of constitutively active (CA) and dominant negative (DN) alk8 mRNAs, revealed early developmental requirements for alk8. The alk8 gene is expressed ubiquitously as a maternal mRNA, and later exhibits more restricted zygotic gene expression. To identify regulatory elements directing the temporospatial expression of alk8, we characterized fluorescence in transgenic zebrafish lines containing alk8 promoter/green fluorescent protein (GFP) reporter constructs. This approach identified transgenic alk8(2.6):GFP lines that first expressed GFP in early stage 1A oocytes, and maintained GFP expression throughout the embryo only for the first 72 hours of development. Analysis of the nucleotide sequence of the 2.6 kb alk8 promoter element provides insight into the regulation of maternal alk8 gene expression. Significantly, the identified maternal alk8 promoter is one of only two maternal-specific promoter elements that have been described to date.