Lifeng Kang

Micro- and nanoscale technologies for tissue engineering and drug discovery applications

Micro- and nanoscale technologies are emerging as powerful enabling tools for tissue engineering and drug discovery. In tissue engineering, micro- and nanotechnologies can be used to fabricate biomimetic scaffolds with increased complexity and vascularization. Furthermore, these technologies can be used to control the cellular microenvironment (i.e., cell–cell, cell–matrix and cell–soluble factor interactions) in a reproducible manner and with high temporal and spatial resolution. In drug discovery, miniaturized platforms based on micro- and nanotechnology can be used to precisely control the fluid flow, enable high-throughput screening, and minimize sample or reagent volumes. In addition, these systems enhance reproducibility and significantly reduce reaction times. This paper reviews the recent developments in the field of micro- and nanoscale technology and gives examples of their tissue engineering and drug discovery applications.

Iron Oxide Filled Magnetic Carbon Nanotube–Enzyme Conjugates for Recycling of Amyloglucosidase: Toward Useful Applications in Biofuel Production Process

Biofuels are fast advancing as a new research area to provide alternative sources of sustainable and clean energy. Recent advances in nanotechnology have sought to improve the efficiency of biofuel production, enhancing energy security. In this study, we have incorporated iron oxide nanoparticles into single-walled carbon nanotubes (SWCNTs) to produce magnetic single-walled carbon nanotubes (mSWCNTs). Our objective is to bridge both nanotechnology and biofuel production by immobilizing the enzyme, Amyloglucosidase (AMG), onto mSWCNTs using physical adsorption and covalent immobilization, with the aim of recycling the immobilized enzyme, toward useful applications in biofuel production processes. We have demonstrated that the enzyme retains a certain percentage of its catalytic efficiency (up to 40%) in starch prototype biomass hydrolysis when used repeatedly (up to ten cycles) after immobilization on mSWCNTs, since the nanotubes can be easily separated from the reaction mixture using a simple magnet. The enzyme loading, activity, and structural changes after immobilization onto mSWCNTs were also studied. In addition, we have demonstrated that the immobilized enzyme retains its activity when stored at 4 °C for at least one month. These results, combined with the unique intrinsic properties of the nanotubes, pave the way for greater efficiency in carbon nanotube-enzyme bioreactors and reduced capital costs in industrial enzyme systems.

Effect of Microneedle Geometry and Supporting Substrate on Microneedle Array Penetration into Skin

Microneedles are being fast recognized as a useful alternative to injections in delivering drugs, vaccines, and cosmetics transdermally. Owing to skins inherent elastic properties, microneedles require an optimal geometry for skin penetration. In vitro studies, using rat skin to characterize microneedle penetration in vivo, require substrates with suitable mechanical properties to mimic human skins subcutaneous tissues. We tested the effect of these two parameters on microneedle penetration. Geometry in terms of center-to-center spacing of needles was investigated for its effect on skin penetration, when placed on substrates of different hardness. Both hard (clay) and soft (polydimethylsiloxane, PDMS) substrates underneath rat skin and full-thickness pig skin were used as animal models and human skins were used as references. It was observed that there was an increase in percentage penetration with an increase in needle spacing. Microneedle penetration with PDMS as a support under stretched rat skin correlated better with that on full-thickness human skin, while penetration observed was higher when clay was used as a substrate. We showed optimal geometries for efficient penetration together with recommendation for a substrate that could better mimic the mechanical properties of human subcutaneous tissues, when using microneedles fabricated from poly(ethylene glycol)-based materials.

Cell confinement in patterned nanoliter droplets in a microwell array by wiping

Cell patterning is useful for a variety of biological applications such as tissue engineering and drug discovery. In particular, the ability to localize cells within distinct fluids is beneficial for a variety of applications ranging from microencapsulation to high-throughput analysis. However, despite much progress, cell immobilization and maintenance within patterned microscale droplets remains a challenge. In particular, no method currently exists to rapidly seed cells into microwell arrays in a controllable and reliable manner. In this study, we present a simple wiping technique to localize cells within arrays of polymeric microwells. This robust method produces cell seeding densities that vary consistently with microwell geometry and cell concentration. Moreover, we develop a simple theoretical model to accurately predict cell seeding density and seeding efficiency in terms of the design parameters of the microwell array and the cell density. This short-term cell patterning approach is an enabling tool to develop new high-throughput screening technologies that utilize microwell arrays containing cells for screening applications.

Novel engineered systems for oral, mucosal and transdermal drug delivery

Abstract Technological advances in drug discovery have resulted in increasing number of molecules including proteins and peptides as drug candidates. However, how to deliver drugs with satisfactory therapeutic effect, minimal side effects and increased patient compliance is a question posted before researchers, especially for those drugs with poor solubility, large molecular weight or instability. Microfabrication technology, polymer science and bioconjugate chemistry combine to address these problems and generate a number of novel engineered drug delivery systems. Injection routes usually have poor patient compliance due to their invasive nature and potential safety concerns over needle reuse. The alternative non-invasive routes, such as oral, mucosal (pulmonary, nasal, ocular, buccal, rectal, vaginal), and transdermal drug delivery have thus attracted many attentions. Here, we review the applications of the novel engineered systems for oral, mucosal and transdermal drug delivery.

A simple method of microneedle array fabrication for transdermal drug delivery

Abstract The outermost layer of skin, stratum corneum, being lipophilic limits the passive transport of hydrophilic and large molecular weight drugs. Microfabrication technology has been adapted to fabricate micron scale needles, which are minimally invasive, yet able to deliver the drugs across this barrier layer. In this study, we fabricated microneedles from a biocompatible polymer, namely, poly (ethylene glycol) diacrylate. A simple lithographical approach was developed for microneedle array fabrication. Several factors including polymerization time, ultraviolet light intensity and distance from light source were studied for their effects on microneedle formation. The microneedle length and tip diameter can be controlled by varying these factors. The microneedles were shown to be able to penetrate cadaver pig skin. Model drug rhodamine B was encapsulated in the range of 50 µg to 450 µg per microneedle array. The fabricated microneedles containing rhodamine B increased the permeability by four times than the control. Altogether, we demonstrated that the microneedle arrays can be fabricated through a simple single-step process and needles were mechanically strong to penetrate skin, increasing the permeability of encapsulated drug through skin.

Protein encapsulation in polymeric microneedles by photolithography

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Microneedle integrated transdermal patch for fast onset and sustained delivery of lidocaine.

Lidocaine as an analgesic is of particular interest in both acute and chronic pain conditions and is used via injections or transdermal patches. While injections are associated with problems such as patient incompliance, topical administration of lidocaine using patches is less efficient due to variability of drug absorption among individuals, slower drug permeation through the skin, and hence a resultant undesirable delay in analgesic effects. To address this clinical problem, we developed a microneedle integrated transdermal patch (MITP), using a photolithography based process, in which microneedles create micrometer-sized channels in the skin to deliver lidocaine rapidly, while the reservoir patch holding the bulk of the drug enables higher drug loading and carries on to release the drug for prolonged periods. We demonstrated a new approach of drug delivery using microneedles, where drugs diffuse out of microneedles through the porous channels left by dissolving drug particles. MITP was shown to be able to encapsulate up to 70 mg of lidocaine. In vitro permeation through rat skin demonstrated that MITP delivered a significantly higher amount of lidocaine than a commercial patch and with a faster onset of drug permeation.

Physicochemical effects of terpenes on organogel for transdermal drug delivery

It is accepted that terpenes are effective penetration enhancers to promote the passage of drugs or chemicals through the human skin barrier. However the physical and chemical changes of a pharmaceutical vehicle induced by the incorporation of terpenes have not been explored. Thus, this study examines the effects of three terpenes (linalool, cineole, limonene) on the rheology and chemical stability of an organogel composed of dibutyllauroylglutamide (GP1) and propylene glycol (PG). At a given GP1 concentration, oxygen-containing linalool and cineole decreased gel moduli (elastic and viscous) and brittleness, and the reverse was obtained for hydrocarbon limonene. Probably, linalool and cineole interfered with hydrogen bonding between GP1 molecules while limonene could have initiated a phase separation-mediated gelation, changing the gel morphology. Microcalorimetry detected minute heat endotherms for gels (with and without terpenes) subjected to accelerated heat testing. These heat changes could arise from a small degree of structural disruption of the gel network. Heat endotherms normalized with respect to GP1 content were used to assess gel chemical stability. Although the terpenes altered rheology, they did not significantly affect the chemical stability of the gels. This is the first in the literature that reports the effect of penetration enhancers, such as terpenes, on the physical, rheological and chemical characteristics of a model pharmaceutical formulation for topical and transdermal drug delivery.

Microfabricated particulate drug-delivery systems.

Micro‐ and nanoparticulate drug‐delivery systems (DDSs) play a significant role in formulation sciences. Most particulate DDSs are scaffold‐free, although some particles are encapsulated inside other biomaterials for controlled release. Despite rapid progress in recent years, challenges still remain in controlling the homogenicity of micro‐/nanoparticles, especially for two crucial factors in particulate DDSs: the size and shape of the particles. Recent approaches make use of microfabrication techniques to generate micro‐/nanoparticles with highly controllable architectures free of scaffolds. This review presents an overview of a burgeoning field of DDSs, which can potentially overcome some drawbacks of conventional techniques for particle fabrication and offer better control of particulate DDSs.