Micro- and nanotechnologies for intelligent and responsive biomaterial-based medical systems

Bioactive hydrogels demonstrate mediated release of a chromophore by chymotrypsin

A model system, α-chymotrypsin (Cht) (a protease) and a cleavable peptide-chromogen (pro-drug) covalently incorporated into a hydrogel, was investigated to understand the mechanisms of covalent loading and release by enzymatic cleavage in bio-responsive delivery systems. Using EDC and Sulfo-NHS, terminal carboxyl groups of N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide, a cleavable chromogen, were conjugated to primary amines of a hydrated poly(HEMA)-based hydrogel. Hydrogel disks were incubated in buffered Cht causing enzyme-mediated cleavage of the peptide and concomitant release of the chromophore for monitoring. To investigate substrate loading and the effects of hydrogel morphology on the system, the concentration of the amino groups (5, 10, 20, and 30 mol%) and the cross-linked density (1, 5, 7, 9 and 12 mol%) were independently varied. Loading-Release Efficiency of the chromogen was shown to exhibit a positive relation to increasing amino groups (AEMA). The release rates demonstrated a negative relation to increasing cross-linked density attributed to decreasing void fractions and increasing tortuosities. The diffusion coefficient of Cht, D(0,Cht), was determined to be 6.9±0.5×10(-7)cm(2)s(-1), and the range of D(eff) of Cht for 1 to 12 mol% TEGDA was determined to be 6.9×10(-8) to 0.1×10(-8)cm(2)s(-1). We show how these parameters may be optimized and used to achieve programmed release rates in engineered bio-responsive systems.

Molecularly imprinted polymers in drug delivery: state of art and future perspectives

INTRODUCTION

Molecularly imprinted polymers (MIPs) are synthetic receptors, characterized by a high selectivity for the selected template. Among the different applications of MIPs, their use as controlled/sustained drug delivery devices has been extensively explored, even though the optimization of such devices needs to be performed before they are applied in clinical practice.

AREAS COVERED

Within drug delivery, one of the most promising fields is the possibility to modulate the drug release profile in response to a specific external stimulus; MIPs represent potentially suitable vehicles, because of the possibility to insert a stimuli-responsive co-monomer in their structure. This review discusses recent advances in the use of external stimuli to modulate drug release, as well as the synthetic strategies devoted to increase the water compatibility of these systems, which is a base requirement for their application in biomedicine.

EXPERT OPINION

Although it is easy to imagine imprinted polymers for biomedical applications, several aspects have to be further investigated, such as the in vivo studies, efficiency and biocompatibility. However, we think that in the next few years it will possible to see unprecedented progress in the preparation of such systems and the translational application of these intelligent structures in medicine.

NANO/MICROSCALE TECHNOLOGIES FOR DRUG DELIVERY

Nano- and microscale technologies have made a marked impact on the development of drug delivery systems. The loading efficiency and particle size of nano/micro particles can be better controlled with these new technologies than conventional methods. Moreover, drug delivery systems are moving from simple particles to smart particles and devices with programmable functions. These technologies are also contributing to in vitro and in vivo drug testing, which are important to evaluate drug delivery systems. For in vitro tests, lab-on-a-chip models are potentially useful as alternatives to animal models. For in vivo test, nano/micro-biosensors are developed for testing chemicals and biologics with high sensitivity and selectivity. Here, we review the recent development of nanoscale and microscale technologies in drug delivery including drug delivery systems, in vitro and in vivo tests.

Responsive theranostic systems: integration of diagnostic imaging agents and responsive controlled release drug delivery carriers

For decades, researchers and medical professionals have aspired to develop mechanisms for noninvasive treatment and monitoring of pathological conditions within the human body. The emergence of nanotechnology has spawned new opportunities for novel drug delivery vehicles capable of concomitant detection, monitoring, and localized treatment of specific disease sites. In turn, researchers have endeavored to develop an imaging moiety that could be functionalized to seek out specific diseased conditions and could be monitored with conventional clinical imaging modalities. Such nanoscale detection systems have the potential to increase early detection of pathophysiological conditions because they can detect abnormal cells before they even develop into diseased tissue or tumors. Ideally, once the diseased cells are detected, clinicians would like to treat those cells simultaneously. This idea led to the concept of multifunctional carriers that could target, detect, and treat diseased cells. The term "theranostics" has been created to describe this promising area of research that focuses on the combination of diagnostic detection agents with therapeutic drug delivery carriers. Targeted theranostic nanocarriers offer an attractive improvement to disease treatment because of their ability to execute simultaneous functions at targeted diseased sites. Research efforts in the field of theranostics encompass a broad variety of drug delivery vehicles, imaging contrast agents, and targeting modalities for the development of an all-in-one, localized detection and treatment system. Nanotheranostic systems that utilize metallic or magnetic imaging nanoparticles can also be used as thermal therapeutic systems. This Account explores recent advances in the field of nanotheranostics and the various fundamental components of an effective theranostic carrier.

Enhancement of the skin-protective activities of Centella asiatica L. Urban by a nano-encapsulation process

Aqueous extracts of Centella asiatica L. Urban were encapsulated by an edible biopolymer, gelatin, which has no effect on their cosmetic activities. The nanoparticles were w/o-type spherical liposomes that had an average diameter of 115.0nm. The encapsulation efficiency was estimated to be approximately 67%, which was relatively high for these aqueous extracts. The nanoparticles showed lower cytotoxicity (10%) in human skin fibroblast cells than the unencapsulated crude extract (15%) at 1.0mg/ml, this was possibly because a smaller amount of the extract was present in the nanoparticles. The nanoparticles efficiently reduced the expression of matrix metalloproteinase (MMP)-1 in UV-irradiated cells from 136.1% to 77.6% (UV-irradiated control) and inhibited hyaluronidase expression (>60%) at a concentration of 0.5mg/ml, which was higher than the levels produced by the unencapsulated crude extracts. The nanoparticles had a very high flux through mouse skin and also remained at relatively large concentrations in the derma when compared to the unencapsulated crude extracts. These results clearly indicate that the skin-protective activities of C. asiatica were significantly improved through the nano-encapsulation process. These findings also imply that a crude extract can be used and have the same efficacy as purified compounds, which should reduce the purification process and production costs.

Advanced molecular design of biopolymers for transmucosal and intracellular delivery of chemotherapeutic agents and biological therapeutics

Hydrogels have been instrumental in the development of polymeric systems for controlled release of therapeutic agents. These materials are attractive for transmucosal and intracellular drug delivery because of their facile synthesis, inherent biocompatibility, tunable physicochemical properties, and capacity to respond to various physiological stimuli. In this contribution, we outline a multifaceted hydrogel-based approach for expanding the range of therapeutics in oral formulations from classical small-molecule drugs to include proteins, chemotherapeutics, and nucleic acids. Through judicious material selection and careful design of copolymer composition and molecular architecture, we can engineer systems capable of responding to distinct physiological cues, with tunable physicochemical properties that are optimized to load, protect, and deliver valuable macromolecular payloads to their intended site of action. These hydrogel carriers, including complexation hydrogels, tethered hydrogels, interpenetrating networks, nanoscale hydrogels, and hydrogels with decorated structures are investigated for their ability to respond to changes in pH, to load and release insulin and fluorescein, and remain non-toxic to Caco-2 cells. Our results suggest these novel hydrogel networks have great potential for controlled delivery of proteins, chemotherapeutics, and nucleic acids.

Controlled release of Fe3O4 nanoparticles in encapsulated microbubbles to tumor cells via sonoporation and associated cellular bioeffects

Fe(3)O(4) nanoparticles embedded in the shells of encapsulated microbubbles could be used therapeutically as in situ drug-delivery vehicles. Bioeffects on liver tumor cells SMMC-7721 due to the excitation of Fe(3)O(4) nanoparticles attached to microbubbles generated by ultrasound (US) are studied in an in vitro setting. The corresponding release phenomenon of Fe(3)O(4) nanoparticles from the shells of the microbubbles into the cells via sonoporation and related phenomena, including nanoparticle delivery efficiency, cell trafficking, cell apoptosis, cell cycle, and disturbed flow of intracellular calcium ions during this process, are also studied. Experimental observations show that Fe(3)O(4) nanoparticles embedded in the shells of microbubbles can be delivered into the tumor cells; the delivery rate can be controlled by adjusting the acoustic intensity. The living status or behavior of Fe(3)O(4) -tagged tumor cells can then be noninvasively tracked by magnetic resonance imaging (MRI). It is further demonstrated that the concentration of intracellular Ca(2+) in situ increases as a result of sonoporation. The elevated Ca(2+) is found to respond to the disrupted site in the cell membrane generated by sonoporation for the purpose of cell self-resealing. However, the excessive Ca(2+) accumulation on the membrane results in disruption of cellular Ca(2+) cycling that may be one of the reasons for the death of the cells at the G1 phase. The results also show that the Fe(3)O(4) -nanoparticle-embedded microbubbles have a lower effect on cell bioeffects compared with the non-Fe(3)O(4) -nanoparticle-embedded microbubbles under the same US intensity, which is beneficial for the delivery of nanoparticles and simultaneously maintains the cellular viability.

Application of smart nanostructures in medicine

Smart nanostructures are sensitive to various environmental or biological parameters. They offer great potential for numerous biomedical applications such as monitoring, diagnoses, repair and treatment of human biological systems. The present work introduces smart nanostructures for biomedical applications. In addition to drug delivery, which has been extensively reported and reviewed, increasing interest has been observed in using smart nanostructures to develop various novel techniques of sensing, imaging, tissue engineering, biofabrication, nanodevices and nanorobots for the improvement of healthcare.

Synthesis and swelling behavior of temperature responsive κ-carrageenan nanogels

Crosslinked κ-carrageenan hydrogel nanoparticles (nanogels) with an average size smaller than 100 nm were prepared using reverse microemulsions combined with thermally induced gelation. The size of the nanogels varied with biopolymer concentration at a constant water/surfactant concentration ratio. The nanogels were found to be thermo-sensitive in a temperature range acceptable for living cells (37-45°C) undergoing reversible volume transitions in response to thermal stimuli. This opens the possibility to explore the application of these nanogels in smart therapeutics such as thermo-sensitive drug carriers. As such, the sustained release of methylene blue from the nanogels was evaluated in in vitro conditions as proof of concept experiments and the release rate was found to be controlled with temperature.

Modified Gellan Gum hydrogels with tunable physical and mechanical properties

Gellan Gum (GG) has been recently proposed for tissue engineering applications. GG hydrogels are produced by physical crosslinking methods induced by temperature variation or by the presence of divalent cations. However, physical crosslinking methods may yield hydrogels that become weaker in physiological conditions due to the exchange of divalent cations by monovalent ones. Hence, this work presents a new class of GG hydrogels crosslinkable by both physical and chemical mechanisms. Methacrylate groups were incorporated in the GG chain, leading to the production of a methacrylated Gellan Gum (MeGG) hydrogel with highly tunable physical and mechanical properties. The chemical modification was confirmed by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR-ATR). The mechanical properties of the developed hydrogel networks, with Young's modulus values between 0.15 and 148 kPa, showed to be tuned by the different crosslinking mechanisms used. The in vitro swelling kinetics and hydrolytic degradation rate were dependent on the crosslinking mechanisms used to form the hydrogels. Three-dimensional (3D) encapsulation of NIH-3T3 fibroblast cells in MeGG networks demonstrated in vitro biocompatibility confirmed by high cell survival. Given the highly tunable mechanical and degradation properties of MeGG, it may be applicable for a wide range of tissue engineering approaches.

Surface patterning strategies for microfluidic applications based on functionalized poly-p-xylylenes

Microfluidic systems require precise surface modification in order to tailor the interfacial properties. For instance, in lab-on-a-chip research, defined surface chemistry is key to minimizing contamination and to increasing signal-to-noise ratios for bioconjugation schemes. Device efficiency and analytical output can also be maximized with devices that have defined surfaces. Similarly, minimizing biofouling is also crucial to suppress background noise and ensure device functions. Once defined, surface properties have been engineered, microstructuring of surfaces can provide defined microenvironments for cell-based culture systems. In this report, we highlight the use of functionalized poly-p-xylylenes for surface modification with a specific focus on microfluidic systems. Functionalized poly-p-xylylenes constitute a versatile group of reactive coatings that can provide a defined chemical makeup of substrate surfaces irrespective of underlying bulk material properties. Recent advances using reactive coatings for surface modification of microfluidics are introduced, including use as nonfouling coatings, fabrication of patterned surfaces, functionalization of previously assembled devices, as well as device-bonding applications.

Conjugation of methacrylamide groups to a model protein via a reducible linker for immobilization and subsequent triggered release from hydrogels

An efficient strategy is reported to introduce methacrylamide groups on the lysine residues of a model protein (lysozyme) for immobilization and triggered release from a hydrogel network. A novel spacer unit was designed, containing a disulfide bond, such that the release of the protein can be triggered by reduction. The modified proteins were characterized by MALDI-TOF MS, titration of free NH(2) residues and spectral analysis. The modification reaction is well controlled, and the number of introduced functions can be tailored by changing the reaction conditions. Gel electrophoresis experiments showed that the methacrylamide modified protein can be immobilized in a polyacrylamide hydrogel and subsequently released by reduction of the spacer by which the protein was grafted to the polymeric network.

Synthesis of magnetic molecularly imprinted poly(ethylene-co-vinyl alcohol) nanoparticles and their uses in the extraction and sensing of target molecules in urine

Superparamagnetic nanoparticles are of great current interest for biomedical applications in both diagnostics and treatment. Magnetic nanoparticles (MNP) can be manipulated by magnetic fields, so that when functionalized, they can be used for the purification and separation of biomolecules and even whole cells. Here we report combining the separation capabilities of MNPs with the functional (binding) capability of molecularly imprinted polymers. Albumin- creatinine-, lysozyme-, and urea-imprinted polymer nanoparticles were synthesized from poly(ethylene-co-ethylene alcohol) via phase inversion, with both target molecules and hydrophobic magnetic nanoparticles mixed within the polymer solution. Several ethylene:ethylene alcohol mole ratios were studied. The rebinding capacities for those three target molecules varied from 0.76 +/- 0.02 to 5.97 +/- 0.04 mg/g of molecularly imprinted magnetic nanoparticles. Lastly, the composite nanoparticles were used for separation and sensing of template molecules (e.g., human serum albumin) in real samples (urine) and results were compared with a commercial ARCHITECT ci 8200 system.