Bioartificial organs in the twenty-first century: nanobiological devices

Microphysiological Systems Evaluation: Experience of TEX-VAL Tissue Chip Testing Consortium

Much has been written and said about the promise and excitement of microphysiological systems, miniature devices that aim to recreate aspects of human physiology on a chip. The rapid explosion of the offerings and persistent publicity placed high expectations on both product manufacturers and regulatory agencies to adopt the data. Inevitably, discussions of where this technology fits in chemical testing paradigms are ongoing. Some end-users became early adopters, while others have taken a more cautious approach because of the high cost and uncertainties of their utility. Here, we detail the experience of a public-private collaboration established for testing of diverse microphysiological systems. Collectively, we present a number of considerations on practical aspects of using microphysiological systems in the context of their applications in decision-making. Specifically, future end-users need to be prepared for extensive on-site optimization and have access to a wide range of imaging and other equipment. We reason that cells, related reagents and the technical skills of the research staff, not the devices themselves, are the most critical determinants of success. Extrapolation from concentration-response effects in microphysiological systems to human blood or oral exposures, difficulties with replicating the whole organ, and long-term functionality remain as critical challenges. Overall, we conclude that it is unlikely that a rodent- or human-equivalent model is achievable through a finite number of microphysiological systems in the near future; therefore, building consensus and promoting the gradual incorporation of these models into tiered approaches for safety assessment and decision-making is the sensible path to wide adoption.

Honeycomb-like pH-responsive γ-cyclodextrin electrospun particles for highly efficient tumor therapy

We report here the tumor-implantable microparticles with a honeycomb-like porous structure. These microparticles were prepared by electrospinning using γ-cyclodextrin (γ-CD) conjugated with 3-(diethylamino)propylamine (DEAP, as a pH-responsive moiety), named γ-CD-DEAP. The resulting microparticles had pore channels (constructed using γ-CD-DEAP) extending into the deep compartment of the microparticles and allowing efficient paclitaxel (PTX, as a chemotherapeutic model drug) entrapment by a simple hole-filling encapsulation process. Importantly, the hydrophobic DEAP (at pH 7.4) in the γ-CD-DEAP microparticles changed to hydrophilic DEAP (at pH 6.8) because of its acidic pH-induced protonation. This phenomenon resulted in an acidic pH-activated particle destruction by a charge-charge repulsion between the protonated DEAP moieties and allowed a pH-triggered release of the encapsulated PTX from the collapsed microparticles. Consequently, γ-CD-DEAP microparticles implanted at the tumor site caused a significant enhancement of the in vitro/in vivo tumor cell ablation, suggesting their significant potential as a chemotherapeutic implant for tumor therapy.

Upregulation of Foreign Body Response in Obese Mice

OBJECTIVE

Obesity is a highly prevalent multifactorial metabolic condition in which the need for functional bioengineered substitutes (e.g., scaffolds for tissue engineering) is likely to occur. However, the adverse foreign body response (FBR) that invariably takes place adjacent to implant devices impairing their function is poorly characterized in this condition. This study investigated the influence of obesity on the host response to a synthetic matrix implanted subcutaneously in high-fat-fed obese mice.

METHODS

Histological analysis of 14-day-old implants was performed to identify collagen deposition, capsule thickness, fibroblast-like cells, foreign body giant cells, and mast cells. In addition, transforming growth factor β1 (TGF-β1) levels in the implants and serum were determined.

RESULTS

All fibrogenic markers (and TGF-β1 levels) increased in the implants of obese mice compared with their nonobese counterparts. Particularly relevant was the fibrous capsule thickness in implants of obese mice (234.2 ± 22.1 µm vs. 109.2 ± 13.4 µm in implants of nonobese animals).

CONCLUSIONS

The study results showing that obesity upregulates the main features of the FBR induced by subcutaneous implants in mice may be relevant in understanding biomaterial integration and performance in this condition. This is crucial to the development of strategies to maintain the integrity and function of implantable devices.

Cooperative Interactions between Different Classes of Disordered Proteins Play a Functional Role in the Nuclear Pore Complex of Baker's Yeast

Nucleocytoplasmic transport is highly selective, efficient, and is regulated by a poorly understood mechanism involving hundreds of disordered FG nucleoporin proteins (FG nups) lining the inside wall of the nuclear pore complex (NPC). Previous research has concluded that FG nups in Baker's yeast (S. cerevisiae) are present in a bimodal distribution, with the "Forest Model" classifying FG nups as either di-block polymer like "trees" or single-block polymer like "shrubs". Using a combination of coarse-grained modeling and polymer brush modeling, the function of the di-block FG nups has previously been hypothesized in the Di-block Copolymer Brush Gate (DCBG) model to form a higher-order polymer brush architecture which can open and close to regulate transport across the NPC. In this manuscript we work to extend the original DCBG model by first performing coarse grained simulations of the single-block FG nups which confirm that they have a single block polymer structure rather than the di-block structure of tree nups. Our molecular simulations also demonstrate that these single-block FG nups are likely cohesive, compact, collapsed coil polymers, implying that these FG nups are generally localized to their grafting location within the NPC. We find that adding a layer of single-block FG nups to the DCBG model increases the range of cargo sizes which are able to translocate the pore through a cooperative effect involving single-block and di-block FG nups. This effect can explain the puzzling connection between single-block FG nup deletion mutants in S. cerevisiae and the resulting failure of certain large cargo transport through the NPC. Facilitation of large cargo transport via single-block and di-block FG nup cooperativity in the nuclear pore could provide a model mechanism for designing future biomimetic pores of greater applicability.

Diversification and enrichment of clinical biomaterials inspired by Darwinian evolution

Regenerative medicine and biomaterials design are driven by biomimicry. There is the essential requirement to emulate human cell, tissue, organ and physiological complexity to ensure long-lasting clinical success. Biomimicry projects for biomaterials innovation can be re-invigorated with evolutionary insights and perspectives, since Darwinian evolution is the original dynamic process for biological organisation and complexity. Many existing human inspired regenerative biomaterials (defined as a nature generated, nature derived and nature mimicking structure, produced within a biological system, which can deputise for, or replace human tissues for which it closely matches) are without important elements of biological complexity such as, hierarchy and autonomous actions. It is possible to engineer these essential elements into clinical biomaterials via bioinspired implementation of concepts, processes and mechanisms played out during Darwinian evolution; mechanisms such as, directed, computational, accelerated evolutions and artificial selection contrived in the laboratory. These dynamos for innovation can be used during biomaterials fabrication, but also to choose optimal designs in the regeneration process. Further evolutionary information can help at the design stage; gleaned from the historical evolution of material adaptations compared across phylogenies to changes in their environment and habitats. Taken together, harnessing evolutionary mechanisms and evolutionary pathways, leading to ideal adaptations, will eventually provide a new class of Darwinian and evolutionary biomaterials. This will provide bioengineers with a more diversified and more efficient innovation tool for biomaterial design, synthesis and function than currently achieved with synthetic materials chemistry programmes and rational based materials design approach, which require reasoned logic. It will also inject further creativity, diversity and richness into the biomedical technologies that we make. All of which are based on biological principles. Such evolution-inspired biomaterials have the potential to generate innovative solutions, which match with existing bioengineering problems, in vital areas of clinical materials translation that include tissue engineering, gene delivery, drug delivery, immunity modulation, and scar-less wound healing.

STATEMENT OF SIGNIFICANCE

Evolution by natural selection is a powerful generator of innovations in molecular, materials and structures. Man has influenced evolution for thousands of years, to create new breeds of farm animals and crop plants, but now molecular and materials can be molded in the same way. Biological molecules and simple structures can be evolved, literally in the laboratory. Furthermore, they are re-designed via lessons learnt from evolutionary history. Through a 3-step process to (1) create variants in material building blocks, (2) screen the variants with beneficial traits/properties and (3) select and support their self-assembly into usable materials, improvements in design and performance can emerge. By introducing biological molecules and small organisms into this process, it is possible to make increasingly diversified, sophisticated and clinically relevant materials for multiple roles in biomedicine.

Nuclear pore complex protein sequences determine overall copolymer brush structure and function

The transport of cargo across the nuclear membrane is highly selective and accomplished by a poorly understood mechanism involving hundreds of nucleoporins lining the inside of the nuclear pore complex (NPC). Currently, there is no clear picture of the overall structure formed by this collection of proteins within the pore, primarily due to their disordered nature. We perform coarse-grained simulations of both individual nucleoporins and grafted rings of nups mimicking the in vivo geometry of the NPC and supplement this with polymer brush modeling. Our results indicate that different regions or blocks of an individual NPC protein can have distinctly different forms of disorder and that this property appears to be a conserved functional feature. Furthermore, this block structure at the individual protein level is critical to the formation of a unique higher-order polymer brush architecture that can exist in distinct morphologies depending on the effective interaction energy between the phenylalanine glycine (FG) domains of different nups. Because the interactions between FG domains may be modulated by certain forms of transport factors, our results indicate that transitions between brush morphologies could play an important role in regulating transport across the NPC, suggesting novel forms of gated transport across membrane pores with wide biomimetic applicability.

DNA hydrogel-based supercapacitors operating in physiological fluids

DNA nanostructures have been attractive due to their structural properties resulting in many important breakthroughs especially in controlled assemblies and many biological applications. Here, we report a unique energy storage device which is a supercapacitor that uses nanostructured DNA hydrogel (Dgel) as a template and layer-by-layer (LBL)-deposited polyelectrolyte multilayers (PEMs) as conductors. Our device, named as PEM-Dgel supercapacitor, showed excellent performance in direct contact with physiological fluids such as artificial urine and phosphate buffered saline without any need of additional electrolytes, and exhibited almost no cytotoxicity during cycling tests in cell culture medium. Moreover, we demonstrated that the PEM-Dgel supercapacitor has greater charge-discharge cycling stability in physiological fluids than highly concentrated acid electrolyte solution which is normally used for supercapacitor operation. These conceptually new supercapacitors have the potential to be a platform technology for the creation of implantable energy storage devices for packageless applications directly utilizing biofluids.

Evaluation of single-cell force spectroscopy and fluorescence microscopy to determine cell interactions with femtosecond-laser microstructured titanium surfaces

One goal in biomaterials research is to limit the formation of connective tissue around the implant. Antiwetting surfaces are known to reduce ability of cells to adhere. Such surfaces can be achieved by special surface structures (lotus effect). Aim of the study was to investigate the feasibility for creating antiwetting surface structures on titanium and to characterize their effect on initial cell adhesion and proliferation. Titanium microstructures were generated using femtosecond- (fs-) laser pulses. Murine fibroblasts served as a model for connective tissue cells. Quantitative investigation of initial cell adhesion was performed using atomic force microscopy. Fluorescence microscopy was used for the characterization of cell-adhesion pattern, cell morphology, and proliferation. Water contact angle (WCA) measurements evinced antiwetting properties of laser-structured surfaces. However, the WCA was decreased in serum-containing medium. Initial cell adhesion to microstructured titanium was significantly promoted when compared with polished titanium. Microstructures did not influence cell proliferation on titanium surfaces. However, on titanium microstructures, cells showed a flattened morphology, and the cell orientation was biased according to the surface topography. In conclusion, antiwetting properties of surfaces were absent in the presence of serum and did not hinder adhesion and proliferation of NIH 3T3 fibroblasts.

Role of biomaterials, therapeutic molecules and cells for hepatic tissue engineering

Current liver transplantation strategies face severe shortcomings owing to scarcity of donors, immunogenicity, prohibitive costs and poor survival rates. Due to the lengthy list of patients requiring transplant, high mortality rates are observed during the endless waiting period. Tissue engineering could be an alternative strategy to regenerate the damaged liver and improve the survival and quality of life of the patient. The development of an ideal scaffold for liver tissue engineering depends on the nature of the scaffold, its architecture and the presence of growth factors and recognition motifs. Biomimetic scaffolds can simulate the native extracellular matrix for the culture of hepatocytes to enable them to exhibit their functionality both in vitro and in vivo. This review highlights the physiology and pathophysiology of liver, the current treatment strategies, use of various scaffolds, incorporation of adhesion motifs, growth factors and stem cells that can stabilize and maintain hepatocyte cultures for a long period.

Nanotechnology and human health: risks and benefits

Nanotechnology is expected to be promising in many fields of medical applications, mainly in cancer treatment. While a large number of very attractive exploitations open up for the clinics, regulatory agencies are very careful in admitting new nanomaterials for human use because of their potential toxicity. The very active research on new nanomaterials that are potentially useful in medicine has not been counterbalanced by an adequate knowledge of their pharmacokinetics and toxicity. The different nanocarriers used to transport and release the active molecules to the target tissues should be treated as additives, with potential side effects of themselves or by virtue of their dissolution or aggregation inside the body. Only recently has a systematic classification of nanomaterials been proposed, posing the basis for dedicated modeling at the nanoscale level. The use of in silico methods, such as nano-QSAR and PSAR, while highly desirable to expedite and rationalize the following stages of toxicological research, are not an alternative, but an introduction to mandatory experimental work.

Biomaterials/tissue interactions: possible solutions to overcome foreign body response

In recent years, a variety of biomaterial implantable devices has been developed. Of particular significance to pharmaceutical sciences is the progress made on the development of drug/implantable device combination products. However, the clinical application of these devices is still a critical issue due to the host response, which results from both the tissue trauma during implantation and the presence of the device in the body. Accordingly, the in vivo functionality and durability of any implantable device can be compromised by the body response to the foreign material. Numerous strategies to overcome negative body reactions have been reported. The aim of this review is to outline some key issues of biomaterial/tissue interactions such as foreign body response and biocompatibility and biocompatibility assessment. In addition, general approaches used to overcome the in vivo instability of implantable devices are presented, including (a) biocompatible material coatings, (b) steroidal and nonsteroidal anti-inflammatory drugs, and (c) angiogenic drugs. In particular, strategies to overcome host response to glucose biosensors are summarized.

A review of the biocompatibility of implantable devices: current challenges to overcome foreign body response

In recent years, a variety of devices (drug-eluting stents, artificial organs, biosensors, catheters, scaffolds for tissue engineering, heart valves, etc.) have been developed for implantation into patients. However, when such devices are implanted into the body, the body can react to these in a number of different ways. These reactions can result in an unexpected risk for patients. Therefore, it is important to assess and optimize the biocompatibility of implantable devices. To date, numerous strategies have been investigated to overcome body reactions induced by the implantation of devices. This review focuses on the foreign body response and the approaches that have been taken to overcome this. The biological response following device implantation and the methods for biocompatibility evaluation are summarized. Then the risks of implantable devices and the challenges to overcome these problems are introduced. Specifically, the challenges used to overcome the functional loss of glucose sensors, restenosis after stent implantation, and calcification induced by implantable devices are discussed.

Bacterial outer membrane protein analysis by electrophoresis and microchip technology

Outer membrane proteins are indispensable components of bacterial cells and participate in several relevant functions of the microorganisms. Changes in the outer membrane protein composition might alter antibiotic sensitivity and pathogenicity. Furthermore, the effects of various factors on outer membrane protein expression, such as antibiotic treatment, mutation, changes in the environment, lipopolysaccharide modification and biofilm formation, have been analyzed. Traditionally, the outer membrane protein profile determination was performed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Converting this technique to capillary electrophoresis format resulted in faster separation, lower sample consumption and automation. Coupling capillary electrophoresis with mass spectrometry enabled the fast identification of bacterial proteins, while immediate quantitative analysis permitted the determination of up- and downregulation of certain outer membrane proteins. Adapting capillary electrophoresis to microchip format ensured a further ten- to 100-fold decrease in separation time. Application of different separation techniques combined with various sensitive detector systems has ensured further opportunities in the field of high-throughput bacterial protein analysis. This review provides an overview using selected examples of outer membrane proteins and the development and application of the electrophoretic and microchip technologies for the analysis of these proteins.

Combining cell therapy and nanotechnology

Cell transplantation to treat diseases characterised by tissue and cell dysfunction, ranging from diabetes to spinal cord injury, has made great strides preclinically and towards clinical efficacy. In order to enhance clinical outcomes, research needs to continue in areas including the development of a universal cell source that can be differentiated into specific cellular phenotypes, methods to protect the transplanted allogeneic or xenogeneic cells from rejection by the host immune system, techniques to enhance cellular integration of the transplant within the host tissue, strategies for in vivo detection and monitoring of the cellular implants, and new techniques to deliver genes to cells without eliciting a host immune response. Overcoming these obstacles will be of considerable benefit, as it allows understanding, visualising and controlling cellular interactions at a submicron level. Nanotechnology is a multidisciplinary field that allows us to manipulate materials, tissues, cells and DNA at the level of and within the individual cell. As such, nanotechnology may be well suited to optimise the generally encouraging results already achieved in cell transplantation. This review presents some of the ways that nanotechnology can directly contribute to cell transplantation.

Toward the Emergence of Nanoneurosurgery: Part III—Nanomedicine: Targeted Nanotherapy, Nanosurgery, and Progress Toward the Realization of Nanoneurosurgery

The notion of nanotechnology has evolved since its inception as a fantastic conceptual idea to its current position as a mainstream research initiative with broad applications among all divisions of science. In the first part of this series, we reviewed the structures and principles that comprise the main body of knowledge of nanoscience and nanotechnology. In the second part, we discussed applications of nanotechnology to the emerging field of nanomedicine, with specific attention on medical diagnostics and imaging. This article further explores the applications of nanotechnology to nanomedicine. Specific attention is given to developments in therapeutic modalities, including advanced drug delivery systems and targeted nanotherapy, which will form the basis for the treatment arm of mature nanomedicine. A variety of modalities are discussed, including polymeric nanoparticles, micelles, liposomes, dendrimers, fullerenes, hydrogels, nanoshells, and smart surfaces. Applications of nanotechnology to nanosurgery and nanoneurosurgery are presented. Femtosecond laser systems, nanoneedles, and nanotweezers are presented as technologies that are operational at the nanoscale level and have the potential to revolutionize the practice of neurosurgery in a profound and momentous way.

DNA and microfluidics: Building molecular electronics systems

The development of molecular electronics using DNA molecules as the building blocks and using microfluidics to build nanowire arrays is reviewed. Applications of DNA conductivity to build sensors and nanowire arrays, and DNA conjugation with other nanostructures, offers an exciting opportunity to build extremely small analytical devices that are suitable for single-molecule detection and also target screening.

Biofabrication: using biological materials and biocatalysts to construct nanostructured assemblies

Emerging opportunities are placing greater demands on device fabrication: next-generation microelectronics will need minimum features of less than 100 nm, high-throughput drug screening will require facile methods to incorporate sensitive biological components into microelectromechanical systems (MEMS), and implantable devices will need to be built from biocompatible materials. Increasingly, these emerging demands are being addressed by combining traditional microfabrication methods with 'biofabrication': namely, the use of biologically derived materials and biocatalysts. Recent fabrication techniques are using biological construction materials as process aids or structural components, and enzymes are being considered for their potential to fabricate devices with high selectivity under mild conditions. If incompatibilities between biology and microfabrication can be eliminated, then biofabrication will be poised to emerge as the standard for nanoscale construction.

Object-Oriented Design Tools for Supramolecular Devices and Biomedical Nanotechnology

Nanotechnology provides multifunctional agents for in vivo use that increasingly blur the distinction between pharmaceuticals and medical devices. Realization of such therapeutic nanodevices requires multidisciplinary effort that is difficult for individual device developers to sustain, and identification of appropriate collaborations outside ones own field can itself be challenging. Further, as in vivo nanodevices become increasingly complex, their design will increasingly demand systems level thinking. System engineering tools such as object-oriented analysis, object-oriented design (OOA/D) and unified modeling language (UML) are applicable to nanodevices built from biological components, help logically manage the knowledge needed to design them, and help identify useful collaborative relationships for device designers. We demonstrate the utility of these systems engineering tools by reverse engineering an existing molecular device (the bacmid molecular cloning system) using them, and illustrate how object-oriented approaches identify fungible components (objects) in nanodevices in a way that facilitates design of families of related devices, rather than single inventions. We also explore the utility of object-oriented approaches for design of another class of therapeutic nanodevices, vaccines. While they are useful for design of current nanodevices, the power of systems design tools for biomedical nanotechnology will become increasingly apparent as the complexity and sophistication of in vivo nanosystems increases. The nested, hierarchical nature of object-oriented approaches allows treatment of devices as objects in higher-order structures, and so will facilitate concatenation of multiple devices into higher-order, higher-function nanosystems.

Mortalin imaging in normal and cancer cells with quantum dot immuno-conjugates

Quantum dots are the nanoparticles that are recently emerging as an alternative to organic fluorescence probes in cell biology and biomedicine, and have several predictive advantages. These include their i) broad absorption spectra allowing visualization with single light source, ii) exceptional photo-stability allowing long term studies and iii) narrow and symmetrical emission spectrum that is controlled by their size and material composition. These unique properties allow simultaneous excitation of different size of quantum dots with a single excitation light source, their simultaneous resolution and visualization as different colors. At present there are only a few studies that have tested quantum dots in cellular imaging. We describe here the use of quantum dots in mortalin imaging of normal and cancer cells. Mortalin staining pattern with quantum dots in both normal and cancer cells mimicked those obtained with organic florescence probes and were considerably stable.

Nanotechnology: convergence with modern biology and medicine

The worldwide emergence of nanoscale science and engineering was marked by the announcement of the National Nanotechnology Initiative (NNI) in January 2000. Recent research on biosystems at the nanoscale has created one of the most dynamic science and technology domains at the confluence of physical sciences, molecular engineering, biology, biotechnology and medicine. This domain includes better understanding of living and thinking systems, revolutionary biotechnology processes, the synthesis of new drugs and their targeted delivery, regenerative medicine, neuromorphic engineering and developing a sustainable environment. Nanobiosystems research is a priority in many countries and its relevance within nanotechnology is expected to increase in the future.

Design and characterization of liposomes containing long-chain N-acylPEs for brain delivery: penetration of liposomes incorporating GM1 into the rat brain

PURPOSE

To develop a suitable liposomal carrier to encapsulate neu roactive compounds that are stable enough to carry them to the brain across the blood-brain barrier with the appropriate surface characteri tics for an effective targeting and for an active membrane transport.

METHODS

Liposomes containing glycosides and a fusogenic lipid were prepared by extrusion. Photon correlation spectroscopy, fluorescent spectroscopy, and differential scanning calorimetry were used to characterize liposomal preparations. Tissue distribution was determined by using 3H-cholesterylhexadecylether as a marker.

RESULTS

The incorporation of glycoside determinants and N-palmitoylphosphatidylethanolamine gives liposomes with similar in tial size, trapped volume, negative surface charge, bilayer fluidity, and melting temperature, except for monosialoganglioside-containing liposomes, which showed less negative surface charge and the highe size, trapped volume and melting temperature. All glycosilated formulations gave liposomes able to retain up to the 95% of encapsulated carboxyfluorescein after 90 min at physiologic temperature even in the presence of serum. Monosialoganglioside liposomes were recovered in the cortex, basal ganglia, and mesencephalon of both brain hemispheres. The liver uptake was higher for sulfatide- and glucose-liposomes, whereas the higher blood levels were observed for glucose- and mannose-liposomes.

CONCLUSIONS

These results show the suitability of such liposomal formulations to hold encapsulated drugs. Moreover, the brain uptake of monosialoganglioside liposomes makes them good candidates as drug delivery systems to the brain.