Electrokinetically driven concentration of particles and cells by dielectrophoresis with DC-offset AC electric field

Insulator-based dielectrophoresis (iDEP) has been successfully used for on-chip manipulations of biological samples. Despite its effectiveness, iDEP typically requires high DC voltages to achieve sufficient electric field; this is mainly due to the coupled phenomena among linear electrokinetics: electroosmosis (EO) and electrophoresis (EP) and nonlinear electrokinetics: dielectrophoresis (DEP). This paper presents a microfluidic technique using DC-offset AC electric field for electrokinetic concentration of particles and cells by repulsive iDEP. This technique introduces AC electric field for producing iDEP which is decoupled from electroosmosis (EO) and electrophoresis (EP). The repulsive iDEP is generated in a PDMS tapered contraction channel that induces non-uniform electric field. The benefits of introducing AC electric field component are threefold: (i) it contributes to DEP force acting on particles, (ii) it suppresses EO flow and (iii) it does not cause any EP motion. As a result, the required DC field component that is mainly used to transport particles on the basis of EO and EP can be significantly reduced. Experimental results supported by numerical simulations showed that the total DC-offset AC electric field strength required to concentrate 15-μm particles is significantly reduced up to 85.9% as compared to using sole DC electric field. Parametric experimental studies showed that the higher buffer concentration, larger particle size and higher ratio of AC-to-DC electric field are favorable for particle concentration. In addition, the proposed technique was demonstrated for concentration of yeast cells.     

Biological characteristic effects of human dental pulp stem cells on poly-ε-caprolactone-biphasic calcium phosphate fabricated scaffolds using modified melt stretching and multilayer deposition

Craniofacial bone defects such as alveolar cleft affect the esthetics and functions that need bone reconstruction. The advanced techniques of biomaterials combined with stem cells have been a challenging role for maxillofacial surgeons and scientists. PCL-coated biphasic calcium phosphate (PCL-BCP) scaffolds were created with the modified melt stretching and multilayer deposition (mMSMD) technique and merged with human dental pulp stem cells (hDPSCs) to fulfill the component of tissue engineering for bone substitution. In the present study, the objective was to test the biocompatibility and biofunctionalities that included cell proliferation, cell viability, alkaline phosphatase activity, osteocalcin, alizarin red staining for mineralization, and histological analysis. The results showed that mMSMD PCL-BCP scaffolds were suitable for hDPSCs viability since the cells attached and spread onto the scaffold. Furthermore, the constructs of induced hDPSCs and scaffolds performed ALP activity and produced osteocalcin and mineralized nodules. The results indicated that mMSMD PCL-BCP scaffolds with hDPSCs showed promise in bone regeneration for treatment of osseous defects.     

Microfluidic characterization and continuous separation of cells and particles using conducting poly(dimethyl siloxane) electrode induced alternating current-dielectrophoresis

This paper presents a poly(dimethyl siloxane) (PDMS) polymer microfluidic device using alternating current (ac) dielectrophoresis (DEP) for separating live cells from interfering particles of similar sizes by their polarizabilities under continuous flow and for characterizing DEP behaviors of cells in stagnant flow. The ac-DEP force is generated by three-dimensional (3D) conducting PDMS composite electrodes fabricated on a sidewall of the device main channel. Such 3D PDMS composite electrodes are made by dispersing microsized silver (Ag) fillers into PDMS gel. The sidewall AgPDMS electrodes can generate a 3D electric field that uniformly distributes throughout the channel height and varies along the channel lateral direction, thereby producing stronger lateral DEP effects over the entire channel. This allows not only easy observation of cell/particle lateral motion but also using the lateral DEP force for manipulation of cells/particles. The former feature is used to characterize the frequency-dependent DEP behaviors of Saccharomyces cerevisiae (yeast) and Escherichia coli (bacteria). The latter is utilized for continuous separation of live yeast and bacterial cells from similar-size latex particles as well as live yeast cells from dead yeast cells. The separation efficiency of 97% is achieved in all cases. The demonstration of these functions shows promising applications of the microfluidic device.     

Assessment of bone regeneration of a tissue-engineered bone complex using human dental pulp stem cells/poly(ε-caprolactone)-biphasic calcium phosphate scaffold constructs in rabbit calvarial defects

The objective of the present study was to investigate the effect of a fabricated combination of poly-?-caprolactone (PCL)–biphasic calcium phosphate (BCP) with the modified melt stretching and multilayer deposition (mMSMD) technique on human dental pulp stem cell (hDPSC) differentiation to be osteogenic like cells for bone regeneration of calvarial defects in rabbit models. hDPSCs extracted from human third molars were seeded onto mMSMD PCL-BCP scaffolds and the osteogenic gene expression was tested prior to implantation in vivo. Two standardized 11?mm in diameter circular calvarial defects were created in 18 adult male New Zealand white rabbits. The rabbits were divided into 4 groups: (1) hDPSCs seeded in mMSMD PCL-BCP scaffolds; (2) mMSMD PCL-BCP scaffolds alone, (3) empty defects and (4) autogenous bone (n?=?3 site/time point/groups). After two, four and eight weeks after the operation, the specimens were harvested for micro-CT including histological and histomorphometric analysis. The explicit results presented an interesting view of the bioengineered constructs of hDPSCs in PCL-BCP scaffolds that increased the newly formed bone compared to the empty defect and scaffold alone groups. The results demonstrated that hDPSCs combined with mMSMD PCL-BCP scaffolds may be an augmentation material for bony defect.     

Preparation and characterization of amphotericin B-loaded silk fibroin nanoparticles-in situ hydrogel composites for topical ophthalmic application

Journal of Materials Science - The objective of this study was to develop and characterize a novel combined systems of amphotericin B-loaded silk fibroin nanoparticles (AmB-FNPs) and in situ...     

Crosslinked fibroin nanoparticles using EDC or PEI for drug delivery: physicochemical properties,crystallinity and structure

A new silk fibroin-based nanoparticles (FNPs) have been successfully developed utilizing crosslinker EDC (EDC-FNPs) or cationic polymer poly(ethyleneimine) (PEI-FNPs). All developed crosslinked FNPs show a similar spherical particle size of ~?300 nm. Depending on the amount of EDC or the addition of PEI, the zeta potential could be controlled favorably and range from ??15 mV to +?30 mV. Particle structures and crystallinity index are determined and compared using different techniques; X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), differential scanning calorimetry and nuclear magnetic resonance (NMR). The most reliable crystallinity calculation methods are based on FT-IR and NMR. The degree of fibroin crystallinity increases with increasing EDC content, whereas PEI reduces it. Exceptionally, XRD shows a reverse order of crystallinity due to the inability to detect short-range ordered structures. Proposed schematic particle structures match all experimental data. In conclusion, the crosslinked fibroin-based nanoparticle properties could be manipulated by using carbodiimide or PEI crosslinkers. In addition, both EDC-FNPs and PEI-FNPs showed high potential as a drug delivery system.