Sustained release of plasmid DNA using lipid microtubules and agarose hydrogel

Fabrication of 3D Printed, Core-and-Shell Implants as Controlled Release Systems for Local siRNA Delivery

The development and clinical translation of small interfering RNA (siRNA) therapies remains challenging owing to their poor pharmacokinetics. 3D printing technology presents a great opportunity to fabricate personalized implants for local and sustained delivery of siRNA. Hydrogels can mimic the mechanical properties of tissues, avoiding the problems associated with rigid implants. Herein, a thermoresponsive composite hydrogel suitable for extrusion 3D-printing is formulated to fabricate controlled-release implants loaded with siRNA-Lipofectamine RNAiMAX complexes. A hydrogel matrix mainly composed of uncharged agarose to protect siRNA from decomplexation is selected. Additionally, pluronic F127 and gelatin are added to improve the printability, degradation, and cell adhesion to the implants. To avoid exposing siRNA to thermal stress during the printing process, a core-and-shell design is set up for the implants in which a core of siRNA-complexes loaded-pluronic F127 is printed without heat and enclosed with a shell comprising the thermoresponsive composite hydrogel. The release profile of siRNA-complexes is envisioned to be controlled by varying the printing patterns. The results reveal that the implants sustain siRNA release for one month. The intactness of the released siRNA-complexes is proven until the eighth day. Furthermore, by changing the printing patterns, the release profiles can be tailored.

Fabrication, modification and application of lipid nanotubes

The potential application of high aspect-ratio nanomaterials motivates the development of the fabrication and modification of lipid nanotubes(LNTs). To date, diverse fabricate processes and elaborate template procedures have produced suitable tubular architectures with definite dimensions and complex structures for expected functions and applications. Herein, we comprehensively summarize the fabrication of LNTs in vitro and discuss the progress made on the micro/nanomaterials fabrication using LNTs as a template, as well as the functions and possible application of a wide range of LNTs as fundamental or derivative material. In addition, the characteristics, advantages, and disadvantages of different fabrication, modification methods, and development prospects of LNTs were briefly summarized.

A Novel Strategy to Coat Dopamine-Functionalized Titanium Surfaces With Agarose-Based Hydrogels for the Controlled Release of Gentamicin

Introduction

The use of spinal implants for the treatment of back disorders is largely affected by the insurgence of infections at the implantation site. Antibacterial coatings have been proposed as a viable solution to limit such infections. However, despite being effective at short-term, conventional coatings lack the ability to prevent infections at medium and long-term. Hydrogel-based drug delivery systems may represent a solution controlling the release of the loaded antibacterial agents while improving cell integration. Agarose, in particular, is a biocompatible natural polysaccharide known to improve cell growth and already used in drug delivery system formulations. In this study, an agarose hydrogel-based coating has been developed for the controlled release of gentamicin (GS).

Methods

Sand blasted Ti6Al4V discs were grafted with dopamine (DOPA) solution. After, GS loaded agarose hydrogels have been produced and additioned with tannic acid (TA) and calcium chloride (CaCl₂) as crosslinkers. The different GS-loaded hydrogel formulations were deposited on Ti6Al4V-DOPA surfaces, and allowed to react under UV irradiation. Surface topography, wettability and composition have been analyzed with profilometry, static contact angle measurement, XPS and FTIR spectroscopy analyses. GS release was performed under pseudo-physiological conditions up to 28 days and the released GS was quantified using a specific ELISA test. The cytotoxicity of the produced coatings against human cells have been tested, along with their antibacterial activity against S. aureus bacteria.

Results

A homogeneous coating was obtained with all the hydrogel formulations. Moreover, the coatings presented a hydrophilic behavior and micro-scale surface roughness. The addition of TA in the hydrogel formulations showed an increase in the release time compared to the normal GS-agarose hydrogels. Moreover, the GS released from these gels was able to significantly inhibit S. aureus growth compared to the GS-agarose hydrogels. The addition of CaCl₂ to the gel formulation was able to significantly decrease cytotoxicity of the TA-modified hydrogels.

Conclusions

Due to their surface properties, low cytotoxicity and high antibacterial effects, the hereby proposed gentamicin-loaded agarose-hydrogels provide new insight, and represent a promising approach for the surface modification of spinal implants, greatly impacting their application in the orthopedic surgical scenario.

Size-dependent thermo-mechanical vibration of lipid supramolecular nano-tubules via nonlocal strain gradient Timoshenko beam theory

Nowadays, nanostructured lipid carriers are used as carrier systems to control the release of drug molecules and promote their physicochemical stability. A better understanding of the dynamic behavior of lipid nano-tubules can facilitate a better drug delivery and other relevant applications. The dynamic behaviors of these lipid nano-tubules are susceptible to temperature variations. Hence, a deeper insight into these effects, as mentioned above, is necessary to ensure higher analysis efficiency. However, the models used in previous researches did not take into account these effects. The lipid nano-tubules often possess a small length-to-width ratio and as a result, the use of the Euler-Bernoulli beam theory for modeling them will significantly reduce the accuracy of calculations, in which Timoshenko beam model is used to increase the accuracy of the model. The main objective of the current study is to investigate the bending vibrations of lipid nano-tubules by considering the temperature effects based on nonlocal strain gradient theory. To this end, based on Hamilton's principle, the governing equations of a dynamical system were extracted by taking into account the temperature effects. The equations were solved using the Navier solution method. Moreover, the dimensionless natural frequency and critical temperature of the lipid nano-tubules were calculated. Our findings demonstrate that the critical temperature is a function of the nonlocal parameter and length-scale parameter variations. It is also observed that at a certain interval of the length scale parameter, increasing the value of the nonlocal parameter results in intensification of the hardening behavior of lipid nano-tubules. Based on our findings, the proposed model indicates good accuracy and prediction.

Agarose-based biomaterials for advanced drug delivery

Agarose is a prominent marine polysaccharide representing reversible thermogelling behavior, outstanding mechanical properties, high bioactivity, and switchable chemical reactivity for functionalization. As a result, agarose has received particular attention in the fabrication of advanced delivery systems as sophisticated carriers for therapeutic agents. The ever-growing use of agarose-based biomaterials for drug delivery systems resulted in rapid growth in the number of related publications, however still, a long way should be paved to achieve FDA approval for most of the proposed products. This review aims at a classification of agarose-based biomaterials and their derivatives applicable for controlled/targeted drug delivery purposes. Moreover, it attempts to deal with opportunities and challenges associated with the future developments ahead of agarose-based biomaterials in the realm of advanced drug delivery. Undoubtedly, this class of biomaterials needs further advancement, and a lot of critical questions have yet to be answered.

Soft-Matter Nanotubes: A Platform for Diverse Functions and Applications

Self-assembled organic nanotubes made of single or multiple molecular components can be classified into soft-matter nanotubes (SMNTs) by contrast with hard-matter nanotubes, such as carbon and other inorganic nanotubes. To date, diverse self-assembly processes and elaborate template procedures using rationally designed organic molecules have produced suitable tubular architectures with definite dimensions, structural complexity, and hierarchy for expected functions and applications. Herein, we comprehensively discuss every functions and possible applications of a wide range of SMNTs as bulk materials or single components. This Review highlights valuable contributions mainly in the past decade. Fifteen different families of SMNTs are discussed from the viewpoints of chemical, physical, biological, and medical applications, as well as action fields (e.g., interior, wall, exterior, whole structure, and ensemble of nanotubes). Chemical applications of the SMNTs are associated with encapsulating materials and sensors. SMNTs also behave, while sometimes undergoing morphological transformation, as a catalyst, template, liquid crystal, hydro-/organogel, superhydrophobic surface, and micron size engine. Physical functions pertain to ferro-/piezoelectricity and energy migration/storage, leading to the applications to electrodes or supercapacitors, and mechanical reinforcement. Biological functions involve artificial chaperone, transmembrane transport, nanochannels, and channel reactors. Finally, medical functions range over drug delivery, nonviral gene transfer vector, and virus trap.

Agarose-based biomaterials for tissue engineering

Agarose is a natural polysaccharide polymer having unique characteristics that give reason to consider it for tissue engineering applications. Special characteristics of agarose such as its excellent biocompatibility, thermo-reversible gelation behavior and physiochemical features support its use as a biomaterial for cell growth and/or controlled/localized drug delivery. The resemblance of this natural carbohydrate polymer to the extracellular matrix results in attractive features that bring about a strong interest in its usage in the field. The scope of this review is to summarize the extensive researches addressing agarose-based biomaterials in order to provide an in-depth understanding of its tissue engineering-related applications.

Engineered Hydrogels for Local and Sustained Delivery of RNA-Interference Therapies

It has been nearly two decades since RNA-interference (RNAi) was first reported. While there are no approved clinical uses, several phase II and III clinical trials suggest the great promise of RNAi therapeutics. One challenge for RNAi therapies is the controlled localization and sustained presentation to target tissues, to both overcome systemic toxicity concerns and to enhance in vivo efficacy. One approach that is emerging to address these limitations is the entrapment of RNAi molecules within hydrogels for local and sustained release. In these systems, nucleic acids are either delivered as siRNA conjugates or within nanoparticles. A plethora of hydrogels has been implemented using these approaches, including both traditional hydrogels that have already been developed for other applications and new hydrogels developed specifically for RNAi delivery. These hydrogels have been applied to various applications in vivo, including cancer, bone regeneration, inflammation and cardiac repair. This review will examine the design and implementation of such hydrogel RNAi systems and will cover the most recent applications of these systems.

Enhanced therapeutic neovascularization by CD31-expressing cells and embryonic stem cell-derived endothelial cells engineered with chitosan hydrogel containing VEGF-releasing microtubes

Various stem cells and their progeny have been used therapeutically for vascular regeneration. One of the major hurdles for cell-based therapy is low cell retention in vivo, and to improve cell survival several biomaterials have been used to encapsulate cells before transplantation. Vascular regeneration involves new blood vessel formation which consists of two processes, vasculogenesis and angiogenesis. While embryonic stem cell (ESC)-derived endothelial cells (ESC-ECs) have clearer vasculogenic potency, adult cells exert their effects mainly through paracrine angiogenic activities. While these two cells have seemingly complementary advantages, there have not been any studies to date combining these two cell types for vascular regeneration. We have developed a novel chitosan-based hydrogel construct that encapsulates both CD31-expressing BM-mononuclear cells (BM-CD31(+) cells) and ESC-ECs, and is loaded with VEGF-releasing microtubes. This cell construct showed high cell survival and minimal cytotoxicity in vitro. When implanted into a mouse model of hindlimb ischemia, it induced robust cell retention, neovascularization through vasculogenesis and angiogenesis, and efficiently induced recovery of blood flow in ischemic hindlimbs. This chitosan-based hydrogel encapsulating mixed adult and embryonic cell derivatives and containing VEGF can serve as a novel platform for treating various cardiovascular diseases.

Hydrogels and Cell Based Therapies in Spinal Cord Injury Regeneration

Spinal cord injury (SCI) is a central nervous system- (CNS-) related disorder for which there is yet no successful treatment. Within the past several years, cell-based therapies have been explored for SCI repair, including the use of pluripotent human stem cells, and a number of adult-derived stem and mature cells such as mesenchymal stem cells, olfactory ensheathing cells, and Schwann cells. Although promising, cell transplantation is often overturned by the poor cell survival in the treatment of spinal cord injuries. Alternatively, the therapeutic role of different cells has been used in tissue engineering approaches by engrafting cells with biomaterials. The latter have the advantages of physically mimicking the CNS tissue, while promoting a more permissive environment for cell survival, growth, and differentiation. The roles of both cell- and biomaterial-based therapies as single therapeutic approaches for SCI repair will be discussed in this review. Moreover, as the multifactorial inhibitory environment of a SCI suggests that combinatorial approaches would be more effective, the importance of using biomaterials as cell carriers will be herein highlighted, as well as the recent advances and achievements of these promising tools for neural tissue regeneration.

Effects of PEGylation on the physicochemical properties and in vivo distribution of organic nanotubes

Application of organic nanotubes (ONTs) into drug nanocarriers ultimately requires validation in live animals. For improving the dispersibility in biological media and in vivo distribution, the outer surface of an ONT was functionalized with polyethylene glycol (PEG) via the coassembly of an ONT-forming lipid with 5-20 mol% of a PEG-tethered lipid analogue (PEG-lipid). Firstly, the effect of PEGylation on the psysicochemical properties of ONTs, such as morphology and dispersibility, was investigated. PEGylation of ONTs slightly reduced the average length and effectively prevented the aggregation in phosphate-buffered saline (PBS). The PEGylated ONTs even showed high thermal stability in aqueous dispersion at least up to 95°C. Secondly, differential scanning calorimetry and powder X-ray diffraction indicated that ~10 mol% of PEG-lipid was completely incorporated into the ONTs, while 20 mol% of PEG-lipid encountered a partial phase separation during coassembly. In the heating differential scanning calorimetry runs, the resultant PEGylated ONTs with 5 mol% PEG-lipid showed no sign of phase separation up to 180°C under lyophilized condition, while those with 10 mol% and 20 mol% PEG-lipid showed some phase separation of the PEG-lipid above 120°C. Finally, PEGylation significantly affected the tissue distribution and prolonged the persistence time in the blood in mice. Non-PEGylated ONTs was quickly cleared from the circulation after intravenous infusion and preferentially accumulated in the lung, while PEGylated ONTs was mainly trapped in the liver and could circulate in the blood up to 24 hours. This study provided valuable information of physicochemical properties and the in vivo distribution behavior of PEGylated ONTs for their potential application into drug nanocarriers.

Gene delivery from polymer scaffolds for tissue engineering

The combination of gene therapy with tissue engineering offers the potential to direct progenitor cell proliferation and differentiation into functional tissue replacements. Many approaches to engineering tissue replacements feature a polymer scaffold to create and maintain a space, support cell adhesion, and organize tissue formation. Polymer scaffolds, either natural, synthetic, or a combination of the two, have also been adapted to serve as delivery vehicles for viral and nonviral vectors, which can induce the expression of tissue inductive factors. Gene delivery is a versatile approach, capable of targeting any cellular process through localized expression of tissue inductive factors. The design and application of tissue engineering scaffolds for localized gene transfer are reviewed. Scaffolds are designed either to release the vector into the local tissue environment or maintain the vector at the polymer surface, which is regulated by the effective affinity of the vector for the polymer. Polymeric delivery can enhance gene transfer locally, promote and extend transgene expression, avoid vector distribution to distant tissues, and reduce the immune response to the vector. Scaffolds capable of controlled DNA delivery can provide a fundamental tool for directing progenitor cell function, which has applications with the engineering of numerous types of tissue. The utility of this approach will increase with the development of design parameters that correlate release and transgene expression, and with continued research into the biology of tissue formation.

Immersive polymer assembly on immobilized particles for automated capsule preparation

We report a versatile approach for polymer capsule preparation using immobilized particles, which are immersed into polymer solutions either manually or by using an automated robotic dipping machine. This technique produces polyelectrolyte capsules with improved retention over conventionally prepared capsules. Additionally, responsive hydrogel capsules of different diameter can be prepared simultaneously.

Realizing the potential of gene-based molecular therapies in bone repair

A better understanding of osteogenesis at genetic and biochemical levels is yielding new molecular entities that can modulate bone regeneration and potentially act as novel therapies in a clinical setting. These new entities are motivating alternative approaches for bone repair by utilizing DNA-derived expression systems, as well as RNA-based regulatory molecules controlling the fate of cells involved in osteogenesis. These sophisticated mediators of osteogenesis, however, pose unique delivery challenges that are not obvious in deployment of conventional therapeutic agents. Viral and nonviral delivery systems are actively pursued in preclinical animal models to realize the potential of the gene-based medicines. This article will summarize promising bone-inducing molecular agents on the horizon as well as provide a critical review of delivery systems employed for their administration. Special attention was paid to synthetic (nonviral) delivery systems because they are more likely to be adopted for clinical testing because of safety considerations. We present a comparative analysis of dose-response relationships, as well as pharmacokinetic and pharmacodynamic features of various approaches, with the purpose of clearly defining the current frontier in the field. We conclude with the authors' perspective on the future of gene-based therapy of bone defects, articulating promising research avenues to advance the field of clinical bone repair.

Hybrid organic nanotubes with dual functionalities localized on cylindrical nanochannels control the release of doxorubicin

A method to control the release of the anti-cancer drug doxorubicin (Dox) from cylindrical nanocapsules, known as organic nanotubes (ONTs), is reported. Co-assembly of a tube-forming glycolipid and its hydrophobized analogue yield novel ONTs with both -COOH and hydrophobic benzyloxycarbonyl groups localized on cylindrical nanochannels. The hydrophobicity of the ONTs nanochannels is easily tunable by adjusting the mixing ratio of the two glycolipids in the co-assembly process. The resultant biologically stable ONTs are able to capture Dox with high efficiency into the cylindrical nanochannels via ion complexation between cationic Dox and anionic -COO(-) , and the release of Dox from hybrid ONTs is effectively controlled by tuning the electrostatic interaction and the hydrophobicity. This controlled release by tuning the hydrophobicity of the ONTs' nanochannels greatly reduces the cytotoxicity of Dox@ONTs for HeLa cells.

Nanostructured self assembled lipid materials for drug delivery and tissue engineering

Every living organism comprises of lipids as basic building blocks in addition to other components. Utilizing these lipids for pharmaceutical and biomedical applications can overcome biocompatibility and biodegradability issues. A well known example is liposomes (lipids arranged in lamellar structures), but other than that there are additional unique mesophasic structures of lipids formed as a result of lipid polymorphisms, which include cubic-, hexagonal- or sponge-phase structures. These structures provide the advantages of stability and production feasibility compared with liposomes. Cubosomes, which exist in a cubic structure, have improved stability, bioadhesivity and biocompatibility. Hexagonal phases or hexosomes exhibit hexagonal arrangements and can encapsulate different drugs with high stability. Lipids also forms tube-like structures known as tubules and ribbons that are also utilized in different biomedical applications, especially in tissue engineering. Immune stimulating complexes are nanocage-like structures formed as a result of interactions of lipid, antigen and Quillaja saponin. These lipidic mesophasic structures have been utilized for gene, vaccine and drug delivery. This article addresses lipid self-assembled supramolecular nanostructures, including cubosomes, hexosomes, tubules, ribbons, cochleates, lipoplexes and immune stimulating complexes and their biomedical applications.

Facile fabrication and magnetic properties of a one-dimensional magnetite peapod in a lipid nanotube

Magnetite nanoclusters (MNCs) were aligned one-dimensionally in the hollow cavity of a lipid nanotube (LNT) as a peapod using a simple mixing method in an aqueous solution. The electrostatic interaction of the two materials was considerable enough to allow the preparation of a densely packed MNC-LNT peapod composite. The composite was formed at a pH 5.4-6.8, i.e., near the isoelectric point of the MNCs. At a pH 5.4-6.8, there was neither a strong attractive nor repulsive electrostatic interaction between the surface of the MNC and the LNT. The MNCs-capped LNT composites were formed at basic conditions (above a pH 7.8) in which the MNCs and the LNT pushed each other because of their opposite surface charges. The magnetic property measurement revealed that the 1D aligned MNCs in the peapod structure had a much higher coercivity (10.6 Oe) than the bulk randomized MNCs (5.8 Oe).

Longitudinal zipping/unzipping of self-assembled organic tubes

Stimuli-responsive organic tubes are an attractive supramolecular assembly which has potential applications as a controlled release vehicle. We synthesize a smart organic tube by the coassembly of lithocholic acid (LCA) and taurolithocholic acid (TLCA) in aqueous solution. The coassembled LCA/TLCA tubes can be longitudinally unzipped into flat sheets by capillary force after being dehydrated on substrates. Consequently, the encapsulated guest molecules are released from the unzipping tubes. After the release of guest molecules, the flat sheets can be zipped back into hollow tubes upon hydration with aqueous solution. The zipping/unzipping LCA/TLCA tubes provide a new type of delivery vehicles, which may have potential for surface decontaminations.

Sustained delivery of activated Rho GTPases and BDNF promotes axon growth in CSPG-rich regions following spinal cord injury

BACKGROUND

Spinal cord injury (SCI) often results in permanent functional loss. This physical trauma leads to secondary events, such as the deposition of inhibitory chondroitin sulfate proteoglycan (CSPG) within astroglial scar tissue at the lesion.

METHODOLOGY/PRINCIPAL FINDINGS

We examined whether local delivery of constitutively active (CA) Rho GTPases, Cdc42 and Rac1 to the lesion site alleviated CSPG-mediated inhibition of regenerating axons. A dorsal over-hemisection lesion was created in the rat spinal cord and the resulting cavity was conformally filled with an in situ gelling hydrogel combined with lipid microtubes that slowly released constitutively active (CA) Cdc42, Rac1, or Brain-derived neurotrophic factor (BDNF). Treatment with BDNF, CA-Cdc42, or CA-Rac1 reduced the number of GFAP-positive astrocytes, as well as CSPG deposition, at the interface of the implanted hydrogel and host tissue. Neurofilament 160kDa positively stained axons traversed the glial scar extensively, entering the hydrogel-filled cavity in the treatments with BDNF and CA-Rho GTPases. The treated animals had a higher percentage of axons from the corticospinal tract that traversed the CSPG-rich regions located proximal to the lesion site.

CONCLUSION

Local delivery of CA-Cdc42, CA-Rac1, and BDNF may have a significant therapeutic role in overcoming CSPG-mediated regenerative failure after SCI.

Sustained delivery of thermostabilized chABC enhances axonal sprouting and functional recovery after spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs) are a major class of axon growth inhibitors that are up-regulated after spinal cord injury (SCI) and contribute to regenerative failure. Chondroitinase ABC (chABC) digests glycosaminoglycan chains on CSPGs and can thereby overcome CSPG-mediated inhibition. But chABC loses its enzymatic activity rapidly at 37 degrees C, necessitating the use of repeated injections or local infusions for a period of days to weeks. These infusion systems are invasive, infection-prone, and clinically problematic. To overcome this limitation, we have thermostabilized chABC and developed a system for its sustained local delivery in vivo, obviating the need for chronically implanted catheters and pumps. Thermostabilized chABC remained active at 37 degrees C in vitro for up to 4 weeks. CSPG levels remained low in vivo up to 6 weeks post-SCI when thermostabilized chABC was delivered by a hydrogel-microtube scaffold system. Axonal growth and functional recovery following the sustained local release of thermostabilized chABC versus a single treatment of unstabilized chABC demonstrated significant differences in CSPG digestion. Animals treated with thermostabilized chABC in combination with sustained neurotrophin-3 delivery showed significant improvement in locomotor function and enhanced growth of cholera toxin B subunit-positive sensory axons and sprouting of serotonergic fibers. Therefore, improving chABC thermostability facilitates minimally invasive, sustained, local delivery of chABC that is potentially effective in overcoming CSPG-mediated regenerative failure. Combination therapy with thermostabilized chABC with neurotrophic factors enhances axonal regrowth, sprouting, and functional recovery after SCI.

Buckling instability of lipid tubules with multibilayer walls under local radial indentation

The mechanical behavior of self-assembled lipid tubules is an important property which determines their suitability for technological applications. We study the instability of multibilayer lipid tubules (with wall thickness t and external radius R(ext)) beyond elastic response under local radial atomic force microscopy indentations. A discontinuity in force-distance curves associated with the buckling instability of lipid tubules is observed. The critical force at which lipid tubules undergo a buckling transition linearly scales as t/R(ext). In addition, a reduced critical buckling force is found to extend a distance of approximately 1 microm from the end of lipid tubules.

Sustained release of BMP-2 in a lipid-based microtube vehicle

Sustained release systems have been developed for the use of growth factors in tissue engineering applications. However, many of these systems continue to have limitations associated with low loading efficiencies and reduced biological activity after release. In this paper, we utilized a lipid-based microtube system for the sustained release of BMP-2. The lipid microtubes were fabricated using a self-assembly method, in order to avoid the use of harsh organic solvents that may damage the protein. BMP-2 was loaded into the microtubes by rehydrating dried microtubes in the protein solution. The loading efficiency and release kinetics of BMP-2 in the microtubes were measured using in vitro immunoassays. Loading efficiency was found to be dependent on microtube concentration. The potential for this system to deliver biologically active BMP-2 was assessed using the alkaline phosphatase assay and von Kossa staining on human mesenchymal stem cell cultures. The results demonstrate that the lipid microtube system is able to provide sustained delivery of biologically active BMP-2 and thereby induce osteogenic differentiation.

Biomaterials for the central nervous system

Biomaterials are widely used to help treat neurological disorders and/or improve functional recovery in the central nervous system (CNS). This article reviews the application of biomaterials in (i) shunting systems for hydrocephalus, (ii) cortical neural prosthetics, (iii) drug delivery in the CNS, (iv) hydrogel scaffolds for CNS repair, and (v) neural stem cell encapsulation for neurotrauma. The biological and material requirements for the biomaterials in these applications are discussed. The difficulties that the biomaterials might face in each application and the possible solutions are also reviewed in this article.

Controllable biomolecule release from self-assembled organic nanotubes with asymmetric surfaces: pH and temperature dependence

The release behavior of fluorescent dyes, oligo DNAs and spherical proteins from self-assembled organic nanotubes having 7-9 nm inner diameters has been studied in terms of novel nanocontainers with high-axial ratios. Both much smaller inner diameters and asymmetric inner and outer surfaces are characteristic of the nanotubes. The acid-dissociation constant (pKa) of the amino groups located at the inner surface and the thermal phase transition temperature (Tg-l) of the nanotube were evaluated based on the pH titration and variable-temperature circular dichroism (CD) spectroscopic experiments, respectively. Each guest was slowly released from both open ends of the nanotube under weak alkaline conditions (pH 8.5), as a result of the decrease in electrostatic attraction between the inner surface and the guests. Elevated temperatures above the obtained Tg-l converted the monolayer membrane of the nanotube from a solid state to a fluid one, promoting the remarkably fast release of the guests. The unique release properties of the nanotube as a nanocontainer with two terminal open ends were compared with those of liposomes that posses a closed hollow space covered with fluid bilayer membranes.

Radial elasticity of self-assembled lipid tubules

Self-assembled lipid tubules with crystalline bilayer walls represent useful supramolecular architectures which hold promise as vehicles for the controlled release of preloaded drugs and templates for the synthesis of one-dimensional inorganic materials. We study the local elasticity of lipid tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine by radial atomic force microscope indentation, coupled with finite element analysis. A reduced stiffness is found to extend a distance of approximately 600 nm from the ends of lipid tubules. The middle section of lipid tubules is homogeneous in terms of their radial elasticity with a Young's modulus of approximately 703 MPa. The inhomogeneous radial elasticity likely arises from the variation of lipid packing density near the tubule ends.

Engineering lipid tubules using nano-sized building blocks: the combinatorial self-assembly of vesicles

Nano-sized lipid vesicles with tailored properties have been used as building blocks to generate lipid tubules between two glass surfaces. The tubules formed not only have defined orientation, width, and length, but they can also grow to be as long as 13 mm under ambient conditions, without externally supplied flow, temperature control, or catalyzing agents. Tubule membrane and its internal aqueous content can be manipulated by controlling the combination of different vesicle's lipid composition and aqueous entrapment. This self-assembly process opens up new pathways for generating complicated and flexible architectures for use in biocompatible molecular and supramolecular engineering. We demonstrated these possibilities by generating tubules encapsulated with siRNA, tubules with multiple branches, and polymerized fluorescent tubules in a single-throughput self-assembly process.

An optimized β-tricalcium phosphate and agarose scaffold fabrication technique

Biodegradable scaffolds composed of beta-tricalcium phosphate, and a natural hydrogel, agarose, were prepared by a shaping method based on the thermal gelation of the polymeric component. This technique was modified to facilitate the inclusion, during the scaffold preparation stage, of therapeutic agents that could improve the graft performance. Vancomycin was included in materials containing different amounts of agarose and ceramic without affecting the scaffold consolidation process. These materials, easily injectable, behave like a reinforced hydrogel whose swelling behavior and drug release rate depend on their composition.