Sustained release of plasmid DNA using lipid microtubules and agarose hydrogel

Preparation of konjac glucomannan hydrogels as DNA-controlled release matrix

In this study, hydrogels for DNA-controlled release was prepared with konjac glucomannan (KGM), a water-soluble non-ionic polysaccharide, by means of deacetylated reaction and physically cross-linking method under mild conditions. The properties of the KGM hydrogels were analyzed by FTIR spectra and scanning electron microscopy (SEM). The integrality of the released DNA was investigated by circular dichroism (CD). The DNA release kinetics was performed using the DNA-loaded KGM gels in buffer solutions of pH 7.4 at 37+/-0.5 degrees C. Peppas model and Higuchi model were used to analysis the DNA release mechanism; the data indicated that the DNA release can be controlled by changing the preparation conditions and the structure parameters of the gels. This study suggested that the KGM hydrogels have a potential use for advanced controlled release.

Heterogeneous and anomalous diffusion inside lipid tubules

Self-assembled lipid tubules with crystalline bilayer walls are promising candidates for controlled drug delivery vehicles on the basis of their ability to release preloaded biological molecules in a sustained manner. While a previous study has shown that the release rate of protein molecules from lipid tubules depends on the associated molecular mass, suggesting that the pertinent diffusion follows the well-known Stokes-Einstein relationship, only a few attempts have been made toward investigating the details of molecular diffusion in the tubule interior. Herein, we have characterized the diffusion rates of several molecules encapsulated in lipid tubules formed by 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) using the techniques of fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS). Our results show that the mobility of these molecules depends not only on their positions in the DC8,9PC tubules but also on their respective concentrations. While the former indicates that the interior of the DC8,9PC tubules is heterogeneous in terms of diffusion, the latter further highlights the possibility of engineering specific conditions for achieving sustained release of a "drug molecule" over a targeted period of time. In addition, our FCS results indicate that the molecular diffusions inside the crystalline bilayer walls of the DC8,9PC tubules strongly deviate from the normal, stochastic processes, with features characterizing not only anomalous subdiffusions but also motions that are superdiffusive in nature.

Soluble sustained release gene delivery system

Delivery of genetic substance to target cells remains an obstacle for efficient utilization of gene therapy approaches. In this study, we describe a formulation of methacrylate acid copolymer carrier of DNA, in which the release rate of the gene can be controlled by pH. Plasmid release was coupled with the polymer's dissolution, which was accelerated in alkali conditions. The released plasmid was intact and bioactive, although alteration from closed circular supercoil to relaxed conformation was observed. Confocal laser scanning microscopy detected the plasmid DNA along the central layers of the polymeric film. Gene delivery systems controlled by the dissolution of the polymeric films offer flexibility in quantity and size of the incorporated DNA, and therefore could have a potential for in vivo use.

Differences between the effect of anisotropic and isotropic laminin and nerve growth factor presenting scaffolds on nerve regeneration across long peripheral nerve gaps

Anisotropic scaffolds of agarose hydrogels containing gradients of laminin-1 (LN-1) and nerve growth factor (NGF) molecules were used to promote sciatic nerve regeneration across a challenging 20mm nerve gap in rats. Step and continuous gradient anisotropic scaffolds were fabricated and characterized, and regeneration was compared to that in isotropic scaffolds with uniform concentrations of LN-1 and NGF and sciatic nerve grafts harvested from syngenic rats. Polysulfone tubular guidance channels were used to present the agarose-based scaffolds to the nerve stumps. Four months after implantation, regenerating axons were observed in animals implanted with anisotropic scaffolds with gradients of both LN-1 and NGF molecules and nerve grafts, but not in animals with isotropic scaffold implants. Also, the scaffolds with gradients of either LN-1 or NGF, with the other component being uniformly distributed in the scaffold, did not elicit axonal regeneration. The total number of myelinated axons was similar for the anisotropic scaffold and the nerve graft conditions, with the anisotropic scaffolds having a higher density of axons than the nerve grafts. Axonal diameter distribution was similar for the anisotropic scaffolds and the nerve grafts. The nerve grafts and anisotropic scaffolds resulted in better functional outcome compared to isotropic scaffolds as measured by the relative gastrocnemius muscle weight (RGMW). Additionally the state of neuromuscular junctions as assessed by pre- and post-synaptic staining revealed that both the anisotropic scaffolds performed as well as nerve grafts.

Gene therapy used for tissue engineering applications

This review highlights the advances at the interface between tissue engineering and gene therapy. There are a large number of reports on gene therapy in tissue engineering, and these cover a huge range of different engineered tissues, different vectors, scaffolds and methodology. The review considers separately in-vitro and in-vivo gene transfer methods. The in-vivo gene transfer method is described first, using either viral or non-viral vectors to repair various tissues with and without the use of scaffolds. The use of a scaffold can overcome some of the challenges associated with delivery by direct injection. The ex-vivo method is described in the second half of the review. Attempts have been made to use this therapy for bone, cartilage, wound, urothelial, nerve tissue regeneration and for treating diabetes using viral or non-viral vectors. Again porous polymers can be used as scaffolds for cell transplantation. There are as yet few comparisons between these many different variables to show which is the best for any particular application. With few exceptions, all of the results were positive in showing some gene expression and some consequent effect on tissue growth and remodelling. Some of the principal advantages and disadvantages of various methods are discussed.

Delivery of DNA vaccines by agarose hydrogel implants facilitates genetic immunization in cattle

The present study demonstrates the interest of two slow-release systems as vaccination tools in cattle. Two experiments show that a first intradermal administration of one DNA vaccine dose combined with the slow-release of a second dose conduct to a priming of the bovine herpesvirus 1-specific immune response similar to the one generated by two discrete administrations 4 weeks apart. The first experiment demonstrates the efficacy of the slow-release system with well-characterized Alzet osmotic pumps, whereas the second experiment extends the same concept with innovative agarose hydrogel implants. These latter implants are cheaper and more convenient than the osmotic pumps or repeated intradermal administrations since they contribute to an efficient priming of the immune response in a single manipulation of the animals.

Surface adsorption of DNA to tissue engineering scaffolds for efficient gene delivery

Gene delivery from tissue engineering scaffolds has potential to promote localized transgene expression that can induce the formation of functional tissues. Substrate-mediated delivery, an alternative delivery strategy to sustained release, is based on immobilization of DNA complexes to the polymer surface for subsequent delivery to cells cultured on the substrate. We investigate polyethylenimine (PEI)/DNA complex immobilization and subsequent cellular transfection on tissue engineering scaffolds fabricated from poly(lactide-co-glycolide) (PLG). The properties of the substrate and the complex affect both immobilization and cellular transfection. PLG promotes binding of PEI/DNA complexes, with percent bound independent of the N/P ratio or the DNA dosage. The levels of transgene expression are similar to or greater than control studies based on bolus DNA delivery, with orders of magnitude less DNA. Immobilization also homogeneously distributes the DNA throughout the scaffold, resulting in large numbers of transfected cells (>60%) at low surface quantities (<50 ng). Importantly, this approach can be employed to transfect cells throughout a three-dimensional scaffold. Tissue engineering scaffolds that are prefabricated into various shapes from a range of materials could potentially employ this strategy for numerous applications.

Positioning and alignment of lipid tubules on patterned Au substrates

This paper presents a method for positioning and aligning self-assembled tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphochloline (DC(8,9)PC) by withdrawing a patterned Au substrate from tubule solution. The patterned Au substrates with alternating bare Au stripes and thiol monolayer stripes are formed by microcontact printing. We find that the lipid tubules selectively adsorb on the bare Au stripes but show no orientation order. By withdrawing the patterned Au substrates at the direction along the stripes from tubule solution, the lipid tubules are found to be aligned along the direction of the Au stripes. The angular distribution and the density of the aligned lipid tubules depend on the withdrawal rates and the adsorption time, respectively. We conclude that forces causing tubule alignment that originate in the surface tension associated with the moving meniscus dominate alignment forces exerted by the patterned Au substrates.

Inductive tissue engineering with protein and DNA-releasing scaffolds

Cellular differentiation, organization, proliferation and apoptosis are determined by a combination of an intrinsic genetic program, matrix/substrate interactions, and extracellular cues received from the local microenvironment. These molecular cues come in the form of soluble (e.g. cytokines) and insoluble (e.g. ECM proteins) factors, as well as signals from surrounding cells that can promote specific cellular processes leading to tissue formation or regeneration. Recent developments in the field of tissue engineering have employed biomaterials to present these cues, providing powerful tools to investigate the cellular processes involved in tissue development, or to devise therapeutic strategies based on cell replacement or tissue regeneration. These inductive scaffolds utilize natural and/or synthetic biomaterials fabricated into three-dimensional structures. This review summarizes the use of scaffolds in the dual role of structural support for cell growth and vehicle for controlled release of tissue inductive factors, or DNA encoding for these factors. The confluence of molecular and cell biology, materials science and engineering provides the tools to create controllable microenvironments that mimic natural developmental processes and direct tissue formation for experimental and therapeutic applications.

In situ gelling hydrogels for conformal repair of spinal cord defects, and local delivery of BDNF after spinal cord injury

Permanent functional loss usually occurs after injury to the spinal cord. Currently, a clinical strategy to promote regeneration in the injured spinal cord does not exist. It has become evident that in order to promote regeneration, a growth permissive substrate at the injury site is critical. In this study, we report the utilization of an agarose scaffold that gels in situ, conformally filling an irregular, dorsal over-hemisection spinal cord defect in adult rats. Besides being growth permissive, the scaffolds also serve as carriers of trophic factors when embedded with BDNF releasing microtubules. We report that our thermo-reversible scaffolds are capable of supporting 3D neurite extension in vivo and are effective carriers of drug delivery vehicles for sustained local delivery of trophic factors. We demonstrate that BDNF encourages neurite growth into the scaffolds, and reduces further the minimal inflammatory response agarose gels generate in vivo as evidenced by quantitative analysis of the extent of NF-160 kDA positive neurons and axons, GFAP positive reactive astrocytes, and CS-56 positive chondroitin sulfate proteoglycan at the interface of the scaffold and host spinal cord. We suggest that these thermo-reversible scaffolds have great potential to serve as growth permissive 3D scaffolds, and to present neurotrophic factors and potentially anti-scar agents to the injury site and enhance regeneration after spinal cord injury.

Controlled release of plasmid DNA from photo-cross-linked pluronic hydrogels

Chemically cross-linked hydrogels composed of Pluronic, water-soluble tri-block copolymers of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), were synthesized by a photo-polymerization method to achieve controlled DNA release. Pluronic F127 was di-acrylated to form a macromer and cross-linked to form a hydrogel structure in the presence and absence of vinyl group-modified hyaluronic acid (HA). UV irradiation time and the presence of the vinyl group-modified HA affected the mechanical property of Pluronic hydrogels to a great extent. Swelling ratio, degradation, and rheological behaviors of Pluronic hydrogels were investigated. When plasmid DNA was loaded in the hydrogels for sustained delivery, various release profiles were attained by varying UV irradiation time and modified HA amounts. Entrapped DNA was gradually damaged with increasing the UV exposure time as evidenced by decreasing the transfection efficiency. The DNA fractions released from the HA/Pluronic hydrogels, however, exhibited considerable transfection efficiencies commensurate with the UV exposure time, suggesting that they were not chemically degraded during the release period and substantially maintained functional gene expression activities despite the UV irradiation.

Sustained in Vivo Gene Delivery from Agarose Hydrogel Prolongs Nonviral Gene Expression in Skin

Prolonging gene expression in skin using safe, nonviral gene delivery techniques could impact skin regeneration and wound healing, decrease infection, and potentially improve the success of tissue-engineered skin. To this end, an injectable, agarose-based delivery system was tested and shown to prolong nonviral gene expression in the skin. DNA was compacted with polylysine to improve DNA stability in the presence of nucleases. Up to 25 microg of compacted luciferase plasmid with or without agarose hydrogel was injected intradermally in rodents. Bioluminescence imaging was used for longitudinal, noninvasive monitoring of gene expression in vivo for 35 days. Injections of DNA in solution produced gene expression for only 5-7 days, whereas the sustained release of compacted DNA from the agarose system prolonged expression, with more than 500 pg (20% of day 1 levels) of luciferase per site for at least 35 days. Southern blotting confirmed that the agarose system extended DNA retention, with significant plasmid present through day 7, as compared with DNA in solution, which had detectable DNA only on day 1. Histology revealed that agarose invoked a wound-healing response through day 14. Tissue-engineering and wound-healing applications may benefit from the agarose gene delivery system.