Microfabricated biocapsules provide short-term immunoisolation of insulinoma xenografts

An arteriovenous mock circulatory loop and accompanying bond graph model for in vitro study of peripheral intravascular bioartificial organs

BACKGROUND

Silicon nanopore membrane-based implantable bioartificial organs are dependent on arteriovenous implantation of a mechanically robust and biocompatible hemofilter. The hemofilter acts as a low-resistance, high-flow network, with blood flow physiology similar to arteriovenous shunts commonly created for hemodialysis access. A mock circulatory loop (MCL) that mimics shunt physiology is an essential tool for refinement and durability testing of arteriovenous implantable bioartificial organs and silicon blood-interfacing membranes. We sought to develop a compact and cost-effective MCL to replicate flow conditions through an arteriovenous shunt and used data from the MCL and swine to inform a bond graph mathematical model of the physical setup.

METHODS

Flow physiology through bioartificial organ prototypes was obtained in the MCL and during extracorporeal attachment to swine for biologic comparison. The MCL was tested for stability overtime by measuring pressurewave variability over a 48-h period. Data obtained in vitro and extracorporeally informed creation of a bond graph model of the MCL.

RESULTS

The arteriovenous MCL was a cost-effective, portable system that reproduced flow rates and pressures consistent with a pulsatile arteriovenous shunt as measured in swine. MCL performance was stable over prolonged use, providing a cost-effective simulator for enhanced testing of peripherally implanted bioartificial organ prototypes. The corresponding bond graph model recapitulates MCL and animal physiology, offering a tool for further refinement of the MCL system.

Feasibility of an implantable bioreactor for renal cell therapy using silicon nanopore membranes

The definitive treatment for end-stage renal disease is kidney transplantation, which remains limited by organ availability and post-transplant complications. Alternatively, an implantable bioartificial kidney could address both problems while enhancing the quality and length of patient life. An implantable bioartificial kidney requires a bioreactor containing renal cells to replicate key native cell functions, such as water and solute reabsorption, and metabolic and endocrinologic functions. Here, we report a proof-of-concept implantable bioreactor containing silicon nanopore membranes to offer a level of immunoprotection to human renal epithelial cells. After implantation into pigs without systemic anticoagulation or immunosuppression therapy for 7 days, we show that cells maintain >90% viability and functionality, with normal or elevated transporter gene expression and vitamin D activation. Despite implantation into a xenograft model, we find that cells exhibit minimal damage, and recipient cytokine levels are not suggestive of hyperacute rejection. These initial data confirm the potential feasibility of an implantable bioreactor for renal cell therapy utilizing silicon nanopore membranes.

Artificial Cell Encapsulation for Biomaterials and Tissue Bio-Nanoengineering: History, Achievements, Limitations, and Future Work for Potential Clinical Applications and Transplantation

Pancreatic β-cell loss and failure with subsequent deficiency of insulin production is the hallmark of type 1 diabetes (T1D) and late-stage type 2 diabetes (T2D). Despite the availability of parental insulin, serious complications of both types are profound and endemic. One approach to therapy and a potential cure is the immunoisolation of β cells via artificial cell microencapsulation (ACM), with ongoing promising results in human and animal studies that do not depend on immunosuppressive regimens. However, significant challenges remain in the formulation and delivery platforms and potential immunogenicity issues. Additionally, the level of impact on key metabolic and disease biomarkers and long-term benefits from human and animal studies stemming from the encapsulation and delivery of these cells is a subject of continuing debate. The purpose of this review is to summarise key advances in this field of islet transplantation using ACM and to explore future strategies, limitations, and hurdles as well as upcoming developments utilising bioengineering and current clinical trials.

Real-Time Monitoring of Doxorubicin Release from Hybrid Nanoporous Anodic Alumina Structures

This work demonstrates an advanced approach to fabricate Hybrid nanoporous anodic alumina gradient-index filters (Hy-NAA-GIFs) through a heterogeneous anodization process combining sinusoidal current-density anodization and constant potential anodization. As a result, the hybrid structure obtained reveals a single photonic stopband (PSB), which falls within the absorption region of the drug molecule and the intensity of the spectrum that are far from such absorption range. The prepared structures were loaded with the doxorubicin (DOX) drug through the drop-casting method, which allows for evaluating the maximum reflectance of the relative height of the PSB with the average reflectance of the spectrum intensity. Thereafter, this property has been applied in a flow cell setup connected to a reflectance spectrophotometer where different drug-loaded samples were placed to study the behavior and kinetics of the drug release in real-time by varying two parameters, i.e., different pore length and flow rates. As such, obtained results were analyzed with a model that includes a sum of two inverted exponential decay functions with two different characteristic time releases. Overall, this study opens up several possibilities for the Hy-NAA-GIFs to study the drug kinetics from nanoporous structures.

Stem Cell Therapies for Treating Diabetes: Progress and Remaining Challenges

Restoration of insulin independence and normoglycemia has been the overarching goal in diabetes research and therapy. While whole-organ and islet transplantation have become gold-standard procedures in achieving glucose control in diabetic patients, the profound lack of suitable donor tissues severely hampers the broad application of these therapies. Here, we describe current efforts aimed at generating a sustainable source of functional human stem cell-derived insulin-producing islet cells for cell transplantation and present state-of-the-art efforts to protect such cells via immune modulation and encapsulation strategies.

Potential of Membranes Surrounding the Fetus as Immunoprotective Cell-Carriers for Allogeneic Transplantations

Background

Membranes surrounding the fetus play a crucial role in providing a physical and immunological barrier between a semiallogeneic fetus and mother during pregnancy. In this study, we tested whether cotransplantation of fetal membranes (FMs) and allogeneic donor cells would improve the retention and function of allografts in mice.

Methods

Intact and enzyme-digested membranes obtained from E18-E19 pregnant mice were subcutaneously cotransplanted with 10F7MN hybridoma cells that are of BALB/cByJ (Balb) origin and secrete anti-human CD235a antibody. Cells were transplanted into C57BL/6J (B6, allogeneic), Balb (syngeneic), and FVB/NJ (third-party) mice. Serum was collected after 1 and 3 weeks of cell transplantation and tested using flow cytometry for the presence of anti-human CD235a antibody. Immunosuppressive functions of membranes were further investigated by analyzing the cytokine profile of supernatants collected from allo-reactive mixed lymphocyte reactions (MLRs) using a multiplex cytokine assay.

Results

B6 mice transplanted with 10F7MN cells along with membranes syngeneic to the host had significantly higher levels of CD235a antibody when compared to B6 mice that received cells without membranes, allogenic membranes, or third-party membranes. Syngeneic membranes significantly inhibited T-cell proliferation in the presence of allogeneic stimuli and suppressed the release of Th1-cytokines such as IFNγ, TNFα, and IL-2 in MLRs. Additionally, increases in the levels of Th2-cytokines were found in MLRs containing membrane-derived cells.

Conclusions

Our study highlights the potential use of syngeneic FMs to act as potent cell-carriers that could improve graft retention as well as graft-specific immunoprotection during allograft transplantation.

Comparative cytocompatibility of multiple candidate cell types to photoencapsulation in PEGNB/PEGDA macroscale or microscale hydrogels

The encapsulation of live cells into photopolymerized hydrogel scaffolds has the potential to augment or repair tissue defects, establish versatile regenerative medicine strategies, and be developed as well-defined, yet tunable microenvironments to study fundamental cellular behavior. However, hydrogel fabrication limitations constrain most studies to macroscale hydrogel scaffolds encapsulating millions of cells. These macroscale materials possess regions of heterogeneous photopolymerization conditions and are therefore poor platforms to identify the response of individual cells to encapsulation. Recently, microfluidic droplet-based hydrogel miniaturization and cell encapsulation offers high-throughput, reproducible, and continuous fabrication. Reports of post-encapsulation cell viability, however, vary widely among specific techniques. Furthermore, different cell types often exhibit different level of tolerance to photoencapsulation-induced toxicity. Accordingly, we evaluate the cellular tolerance of various encapsulation techniques and photopolymerization parameters for four mammalian cell types, with potential applications in tissue regeneration, using polyethylene glycol diacrylate or polyethylene glycol norbornene (PEGNB) hydrogels on micro- and macro-length scales. We found PEGNB provides excellent cellular tolerance and supports long-term cell survival by mitigating the deleterious effects of acrylate photopolymerization, which are exacerbated at diminishing volumes. PEGNB, therefore, is an excellent candidate for hydrogel miniaturization. PEGNB hydrogel properties, however, were found to have variable effects on encapsulating different cell candidates. This study could provide guidance for cell encapsulation practices in tissue engineering and regenerative medicine research.

Nanoporous Noninvasive Cellular Electrical Activity-Based Analysis Devices

In recent years, rapid advancements have been made in the biomedical applications of microtechnology and nanotechnology. While the focus of such technologies have been primarily on in vitro analytical and diagnostic tools, more recently in vivo therapeutic and sensing applications have gained attention. The long-term integration of cells with inorganic materials provides the basis for novel sensing platforms. The work presented here focuses on the ability to maintain cells long-term in nanoporous silicon-based microenvironments. This paper describes the creation of nanoporous, biocompatible, alumina membranes as a platform for incorporation into a cell-based device targeted for in situ recording of cellular electrical activity variations due to the changes associated with the surrounding microenvironments. Studies described herein focus on the interaction of nanoporous alumina substrates embedded in silicon patterned with cells of interest. The fidelity of such a system is demonstrated in terms of viability, proliferation, and functionality. The capability of such microfabricated nanoporous membranes, as in vitro for cell-based assays for sensing and drug delivery applications, is also demonstrated. It has potential in vivo application for therapeutic immunoisolation.

Three-dimensional printed polymeric system to encapsulate human mesenchymal stem cells differentiated into islet-like insulin-producing aggregates for diabetes treatment

Diabetes is one of the most prevalent, costly, and debilitating diseases in the world. Pancreas and islet transplants have shown success in re-establishing glucose control and reversing diabetic complications. However, both are limited by donor availability, need for continuous immunosuppression, loss of transplanted tissue due to dispersion, and lack of vascularization. To overcome the limitations of poor islet availability, here, we investigate the potential of bone marrow–derived mesenchymal stem cells differentiated into islet-like insulin-producing aggregates. Islet-like insulin-producing aggregates, characterized by gene expression, are shown to be similar to pancreatic islets and display positive immunostaining for insulin and glucagon. To address the limits of current encapsulation systems, we developed a novel three-dimensional printed, scalable, and potentially refillable polymeric construct (nanogland) to support islet-like insulin-producing aggregates’ survival and function in the host body. In vitro studies showed that encapsulated islet-like insulin-producing aggregates maintained viability and function, producing steady levels of insulin for at least 4 weeks. Nanogland—islet-like insulin-producing aggregate technology here investigated as a proof of concept holds potential as an effective and innovative approach for diabetes cell therapy.

Silicon nanopore membrane (SNM) for islet encapsulation and immunoisolation under convective transport

Problems associated with islet transplantation for Type 1 Diabetes (T1D) such as shortage of donor cells, use of immunosuppressive drugs remain as major challenges. Immune isolation using encapsulation may circumvent the use of immunosuppressants and prolong the longevity of transplanted islets. The encapsulating membrane must block the passage of host’s immune components while providing sufficient exchange of glucose, insulin and other small molecules. We report the development and characterization of a new generation of semipermeable ultrafiltration membrane, the silicon nanopore membrane (SNM), designed with approximately 7 nm-wide slit-pores to provide middle molecule selectivity by limiting passage of pro-inflammatory cytokines. Moreover, the use of convective transport with a pressure differential across the SNM overcomes the mass transfer limitations associated with diffusion through nanometer-scale pores. The SNM exhibited a hydraulic permeability of 130 ml/hr/m²/mmHg, which is more than 3 fold greater than existing polymer membranes. Analysis of sieving coefficients revealed 80% reduction in cytokines passage through SNM under convective transport. SNM protected encapsulated islets from infiltrating cytokines and retained islet viability over 6 hours and remained responsive to changes in glucose levels unlike non-encapsulated controls. Together, these data demonstrate the novel membrane exhibiting unprecedented hydraulic permeability and immune-protection for islet transplantation therapy.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

Biomaterials as carrier, barrier and reactor for cell-based regenerative medicine

Cell therapy has achieved tremendous success in regenerative medicine in the past several decades. However, challenges such as cell loss, death and immune-rejection after transplantation still persist. Biomaterials have been designed as carriers to deliver cells to desirable region for local tissue regeneration; as barriers to protect transplanted cells from host immune attack; or as reactors to stimulate host cell recruitment, homing and differentiation. With the assistance of biomaterials, improvement in treatment efficiency has been demonstrated in numerous animal models of degenerative diseases compared with routine free cell-based therapy. Emerging clinical applications of biomaterial assisted cell therapies further highlight their great promise in regenerative therapy and even cure for complex diseases, which have been failed to realize by conventional therapeutic approaches.

Membranes to achieve immunoprotection of transplanted islets

Transplantation of islet or beta cells is seen as the cure for type 1 diabetes since it allows physiological regulation of blood glucose levels without requiring any compliance from the patients. In order to circumvent the use of immunosuppressive drugs (and their side effects), semipermeable membranes have been developed to encapsulate and immunoprotect transplanted cells. This review presents the historical developments of immunoisolation and provides an update on the current research in this field. A particular emphasis is laid on the fabrication, characterization and performance of membranes developed for immunoisolation applications.

Vascularization and cellular isolation potential of a novel electrospun cell delivery vehicle

A clinical need exists for a cell delivery device that supports long-term cell viability, cell retention within the device and retrieval of delivered cells if necessary. Previously, cell isolation devices have been based on hollow fiber membranes, porous polymer scaffolds, alginate systems, or micro-machined membranes. We present the development and characterization of a novel dual porosity electrospun membrane based device, which supports cellular infiltration and vascularization of its outer porous layer and maintains cellular isolation within a lumen bounded by an inner low porosity layer. Electrospinning conditions were initially established to support electrospun fiber deposition onto nonconductive silicone surfaces. With these parameters established, devices for in vivo evaluations were produced using nylon as a nonconductive scaffold for deposition of dual porosity electrospun fibers. The outer porous layer supported the development of a penetrating microcirculation and the membrane supported the transfer of insulin from encapsulated sustained release pellets for 4 weeks. Viable cells implanted within the device could be identified after 2 weeks of implantation. Through the successful demonstration of survival and cellular isolation of human epithelial cells within the implanted devices and the ability to use the device to deliver insulin, we have established the utility of this device toward localized cell transplantation. The cell delivery device establishes a platform to test the feasibility of approaches to cell dose control and cell localization at the site of implantation in the clinical use of modified autologous or allogeneic cells.

Effect of calcium phosphate particle shape and size on their antibacterial and osteogenic activity in the delivery of antibiotics in vitro

Powders composed of four morphologically different calcium phosphate particles were prepared by precipitation from aqueous solutions: flaky, brick-like, elongated orthogonal, and spherical. The particles were then loaded with either clindamycin phosphate as the antibiotic of choice or fluorescein, a model molecule used to assess the drug release properties. A comparison was carried out of the effect of such antibiotic-releasing materials on: sustained drug release profiles; Staphylococcus aureus growth inhibition; and osteogenic propensities in vitro. Raman spectroscopic analysis indicated the presence of various calcium phosphate phases, including monetite (flaky and elongated orthogonal particles), octacalcium phosphate (brick-shaped particles), and hydroxyapatite (spherical particles). Testing the antibiotic-loaded calcium phosphate powders for bacterial growth inhibition demonstrated satisfying antibacterial properties both in broths and on agar plates. All four calcium-phosphate-fluorescein powders exhibited sustained drug release over 21 days. The calcium phosphate sample with the highest specific surface area and the smallest, spherical particle size was the most effective in both drug loading and release, consequently having the highest antibacterial efficiency. Moreover, the highest cell viability, the largest gene expression upregulation of three different osteogenic markers--osteocalcin, osteopontin, and Runx2--as well as the least disrupted cell cytoskeleton and cell morphologies were also noticed for the calcium phosphate powder composed of the smallest, spherical nanosized particles. Still, all four powders exerted a viable effect on osteoblastic MC3T3-E1 cells in vitro, as evidenced by both morphological assessments on fluorescently stained cells and measurements of their mitochondrial activity. The obtained results suggest that the nanoscale particle size and the corresponding coarseness of the surface of particle conglomerates as the cell attachment points may present a favorable starting point for the development of calcium-phosphate-based osteogenic drug delivery devices.

Size-controlled insulin-secreting cell clusters

The search for an effective cure for type I diabetes from the transplantation of encapsulated pancreatic β-cell clusters has so far produced sub-optimal clinical outcomes. Previous efforts have not controlled the size of transplanted clusters, a parameter implicated in affecting long-term viability and the secretion of therapeutically sufficient insulin. Here we demonstrate a method based on covalent attachment of patterned laminin for fabricating uniformly size-controlled insulin-secreting cell clusters. We show that cluster size within the range 40-120μm in diameter affects a variety of therapeutically relevant cellular responses including insulin expression, content and secretion. Our studies elucidate two size-dependent phenomena: (1) as the cluster size increases from 40μm to 60μm, glucose stimulation results in a greater amount of insulin produced per cell; and (2) as the cluster size increases beyond 60μm, sustained glucose stimulation results in a greater amount of insulin secreted per cell. Our study describes a method for producing uniformly sized insulin-secreting cell clusters, and since larger cluster sizes risk nutrient availability limitations, our data suggest that 100-120μm clusters may provide optimal viability and efficacy for encapsulated β-cell transplants as a treatment for type I diabetes and that further in vivo evaluation is warranted.

A portrait of nanomedicine and its bioethical implications

This review addresses the current and future potential of nanomedicine, and its ethical considerations within the comprehensive framework of the four dimensions of medical ethics: Beneficence, Non-Maleficence, Respect, and Justice. From this perspective, the ethical considerations for nanomedicine are not novel, but have been addressed by precedents throughout the history of medicine. While these ethical challenges are not unique to nanomedicine, some require additional consideration, given the envisioned pervasive impact of nanomedicine on society.

Enhancing clinical islet transplantation through tissue engineering strategies

Clinical islet transplantation (CIT), the infusion of allogeneic islets within the liver, has the potential to provide precise and sustainable control of blood glucose levels for the treatment of type 1 diabetes. The success and long-term outcomes of CIT, however, are limited by obstacles such as a nonoptimal transplantation site and severe inflammatory and immunological responses to the transplant. Tissue engineering strategies are poised to combat these challenges. In this review, emerging methods for engineering an optimal islet transplantation site, as well as novel approaches for improving islet cell encapsulation, are discussed.

Enabling individualized therapy through nanotechnology

Individualized medicine is the healthcare strategy that rebukes the idiomatic dogma of 'losing sight of the forest for the trees'. We are entering a new era of healthcare where it is no longer acceptable to develop and market a drug that is effective for only 80% of the patient population. The emergence of "-omic" technologies (e.g. genomics, transcriptomics, proteomics, metabolomics) and advances in systems biology are magnifying the deficiencies of standardized therapy, which often provide little treatment latitude for accommodating patient physiologic idiosyncrasies. A personalized approach to medicine is not a novel concept. Ever since the scientific community began unraveling the mysteries of the genome, the promise of discarding generic treatment regimens in favor of patient-specific therapies became more feasible and realistic. One of the major scientific impediments of this movement towards personalized medicine has been the need for technological enablement. Nanotechnology is projected to play a critical role in patient-specific therapy; however, this transition will depend heavily upon the evolutionary development of a systems biology approach to clinical medicine based upon "-omic" technology analysis and integration. This manuscript provides a forward looking assessment of the promise of nanomedicine as it pertains to individualized medicine and establishes a technology "snapshot" of the current state of nano-based products over a vast array of clinical indications and range of patient specificity. Other issues such as market driven hurdles and regulatory compliance reform are anticipated to "self-correct" in accordance to scientific advancement and healthcare demand. These peripheral, non-scientific concerns are not addressed at length in this manuscript; however they do exist, and their impact to the paradigm shifting healthcare transformation towards individualized medicine will be critical for its success.

Inorganic nanoporous membranes for immunoisolated cell-based drug delivery

Materials advances enabled by nanotecbnology have brought about promising approaches to improve the encapsulation mechanism for immunoisolated cell-based drug delivery. Cell-based drug delivery is a promising treatment for many diseases but has thus far achieved only limited clinical success. Treatment of insulin dependent diabetes mellitus (IDDM) by transplantation of pancreatic beta-cells represents the most anticipated application ofcell-based drug delivery technology. This review outlines the challenges involved with maintaining transplanted cell viability and discusses how inorganic nanoporous membranes may be useful in achieving clinical success.

Cell culture on MEMS platforms: a review

Microfabricated systems provide an excellent platform for the culture of cells, and are an extremely useful tool for the investigation of cellular responses to various stimuli. Advantages offered over traditional methods include cost-effectiveness, controllability, low volume, high resolution, and sensitivity. Both biocompatible and bio-incompatible materials have been developed for use in these applications. Biocompatible materials such as PMMA or PLGA can be used directly for cell culture. However, for bio-incompatible materials such as silicon or PDMS, additional steps need to be taken to render these materials more suitable for cell adhesion and maintenance. This review describes multiple surface modification strategies to improve the biocompatibility of MEMS materials. Basic concepts of cell-biomaterial interactions, such as protein adsorption and cell adhesion are covered. Finally, the applications of these MEMS materials in Tissue Engineering are presented.

A novel 3-D model for cell culture and tissue engineering

A novel method of making microcapsules in a macrocapsule is demonstrated as a 3-D culture system in this article. Mouse embryonic stem (mES) cells as model cells were used in the 3-D culture space, and the cell viability and histological observation were conducted. Furthermore, Oct4 gene expression was evaluated for the undifferentiated status of mES cells in this 3-D model. The results showed that mES cells can grow in this 3-D model and retain their normal viability and morphology. This 3-D model allows mES cells to stay in the undifferentiated state better than 2-D culture systems. This work demonstrates a new 3-D tissue model which can provide an in vivo like microenvironment for non-differentiated mES cells with good immunoisolation. This approach may bridge the gap between traditional 2-D cell culture and animal models.

A biodegradable, immunoprotective, dual nanoporous capsule for cell-based therapies

To demonstrate the transplantation of drug-secreting cells with immunoprotection, a biodegradable delivery device combining two nanoporous capsules is developed using secretory alkaline phosphatase gene (SEAP) transfected mouse embryonic stem (mES) cells as a model system. The outer capsule is a poly (ethylene glycol) (PEG)-coated poly (epsilon-caprolactone) (PCL) chamber covered with a PEG grafted PCL nanoporous membrane made by phase inversion technique. SEAP gene transfected mES cells encapsulated in alginate-poly-L-lysine (AP) microcapsules are placed in the PCL capsule. Both nanoporous capsules showed good immunoprotection in the IgG solution. In microcapsules, mES cells could form a spheroid embryonic body (EB) and grow close to the microcapsule size. The secreted SEAP from encapsulated mES cells increased gradually to a maximum value before reaching a steady level, following the cell growth pattern in the microcapsule. Without microcapsules, mES cells only formed a monolayer in the large PCL capsule. The secreted SEAP release was very low. The integrated device showed a similar cell growth pattern to that in microcapsules alone, while the SEAP release rate could be regulated by the pore size of the large capsule. This integrated device can achieve multi-functionalities for cell-based therapy, i.e. a 3-D microenvironment provided by microcapsules for cell growth, superior immunoprotection and controllable release performance provided by the two nanoporous membranes, and good fibrosis prevention by PEG surface modification of the large capsule.

Nanoporous noninvasive cellular electrical activity-based analysis devices

In recent years, rapid advancements have been made in the biomedical applications of microtechnology and nanotechnology. While the focus of such technologies have been primarily on in vitro analytical and diagnostic tools, more recently in vivo therapeutic and sensing applications have gained attention. The long-term integration of cells with inorganic materials provides the basis for novel sensing platforms. The work presented here focuses on the ability to maintain cells long-term in nanoporous silicon-based microenvironments. This article describes the creation of nanoporous, biocompatible, alumina membranes as a platform for incorporation into a cell-based device targeted for in situ recording of cellular electrical activity variations due to the changes associated with the surrounding microenvironments. Studies described herein focus on the interaction of nanoporous alumina substrates embedded in silicon patterned with cells of interest. The fidelity of such a system is demonstrated in terms of viability, proliferation, and functionality. The capability of such microfabricated nanoporous membranes, as in vitro for cell-based assays for sensing and drug delivery applications, is also demonstrated. It has potential in vivo application for therapeutic immunoisolation.

Artificial pancreas to treat type 1 diabetes mellitus

Substitution of diseased organ/tissues with totally artificial machines or transplantable biohybrid devices where functionally competent cells are enveloped within immunoprotective artificial membranes could represent one of the future goals in medicine. In particular, artificial or, closer to feasibility, biohybrid artificial pancreas (BHAP) could replace the function of pancreatic islet beta-cells that have been destroyed by autoimmunity, thereby obviating the need to treat patients with type 1 diabetes mellitus (TIDM) with multiple daily insulin injections. State-of-the-art diabetes therapy and perspectives in the use of BHAP, with special regard to islet-cell-containing microcapsules fabricated with alginate-based polymers, including applications to experimental animal models according to different chemical procedures, are reviewed. Special emphasis has been given to preparation methods, immunoprotection strategies, and biocompatibility of the islet-cell-containing microbarriers, as well as to approaches to ameliorate these features. Currently available BHAP prototypes have been critically reviewed to define expectations about the next generation devices targeting the final cure of TIDM.

Microfabricated nanochannel implantable drug delivery devices: trends, limitations and possibilities

This is a review of the application of microfabrication technologies, borrowed from the semiconductor industry, to drug delivery implants incorporating structures in the nanometer dimension. In the futuristic ideal, these systems would involve the implantation of precisely microfabricated drug delivery systems with nanopores, nanochannels and/or nanoreservoirs fabricated from silicon, coupled with electronic sensing and actuator systems, for the precise, timed and/or targeted delivery of drugs. After more than a decade in conceptualisation and experimentation, four systems that have commercial potential are discussed: i) implantable microchips with on-demand microdosage for one or more therapeutic agents under internal control or external control using a wireless link; ii) nanopore pumps, implantable titanium pumps, consisting of a drug reservoir with a nanopore-release membrane, capable of delivering potent small or macromolecules at constant serum levels for sustained periods of time; iii) nanocages, microfabricated nanopore immunoisolation chambers for cellular implants, capable of natural feedback-controlled delivery of proteins and peptides; and iv) nanobuckets, micromachined silicon porous particles with drug-loading capacity and targeting ligands for localised delivery. Each of the systems, along with future trends in microfabrication manufacturing, limitations and possibilities, are discussed.

Development of nanostructured biomedical micro-drug testing device based on in situ cellular activity monitoring

Integration of micro and nanofabrication techniques with biotechnology has resulted in the development of in vitro analytical and diagnostic tools for biomedical applications. The focus of such technology has primarily been on therapeutic and sensing applications. The long-term integration of cells with inorganic materials provides the basis for novel sensing platforms. This paper describes the creation of, nanoporous, biocompatible, alumina membranes as a platform for incorporation into a cell based device targeted for in situ recording of cellular electrical activity variations due to the changes associated with the surrounding microenvironments more specifically due to the effect of therapeutic drugs. Studies described herein focus on the interaction of nanoporous alumina substrates embedded in silicon, patterned with cells of interest. The cells that have been used to develop the in vitro test platform are primary hippocampal neurons. Demonstrated here, is the fidelity of such a system in terms of determination of cell viability, proliferation, and functionality. The response of the cells to the "drug" molecules is electro-optically characterized in an in situ manner. The capability of such, micro fabricated nanoporous membranes as in vitro drug testing platforms, is first theoretically estimated using two dimensional finite element modeling of the diffusion of the molecules of interest through the nanoporous substrate using CFDRC. It is then experimentally established, using glucose and immunoglobulin G (IgG).

Cancer nanotechnology: opportunities and challenges

Nanotechnology is a multidisciplinary field, which covers a vast and diverse array of devices derived from engineering, biology, physics and chemistry. These devices include nanovectors for the targeted delivery of anticancer drugs and imaging contrast agents. Nanowires and nanocantilever arrays are among the leading approaches under development for the early detection of precancerous and malignant lesions from biological fluids. These and other nanodevices can provide essential breakthroughs in the fight against cancer.

Release of Biologically Functional Interferon-Alpha from a Nanochannel Delivery System

Metastatic melanoma lesions often are unresectable due to their size and/or location near critical structures. These lesions represent a significant challenge for the oncologist, because radiation therapy and chemotherapy are infrequently successful in halting tumor growth. Of primary concern is the fact that these lesions are usually painful and present a cosmetic dilemma. We hypothesized that the development of a silicon-based nano-device capable of delivering antitumor compounds (e.g. immune modulators), locally, at a constant rate, to the tumor microenvironment could avoid the toxicity of systemic administration and the inconvenience of frequent clinic visits for local injections. Because of its diminutive size, such a device could be implanted using a minimally invasive procedure in close proximity to unresectable melanoma lesions. The current report uses interferon alpha-2b (IFN-alpha) as a model antitumor agent, since it is commonly used in the treatment of malignant melanoma and metastatic renal cell carcinoma. In this system, IFN-alpha is delivered directly to the tumor microenvironment by a novel nanochannel delivery system (nDS) that is capable of zero order release of small molecules. We have demonstrated that the IFN-alpha released from the nDS is functionally active on both host immune cells and a human melanoma cell line in vitro. This drug delivery platform could be used to develop alternative strategies for the treatment of unresectable tumors.

Diffusion characteristics of microfabricated silicon nanopore membranes as immunoisolation membranes for use in cellular therapeutics

OBJECTIVE

Immunoisolating membranes protect transplanted xenogeneic tissue by physically isolating them from the host. However, most are commercial filter membranes that do not possess all the features needed for immunoisolation. Silicon nanopore membranes are thin layers of silicon containing tens of thousands of nanometer-sized channels, which allow passive diffusion of small molecules. They are excellent size-selective barriers, and the objective of this study was to further characterize their immunoprotective properties and make comparisons with commercial filter membranes.

METHODS

Diffusion across membranes was studied using molecules of different sizes, including fluorescein isothiocyanate-dextrans (relative molecular sizes of 4.4 kDa, 20 kDa, and 70 kDa), glucose (0.18 kDa), insulin (6.1 kDa), and immunoglobulin G (IgG) (150 kDa). Protection from complement-mediated lysis was analyzed by a hemolysis assay. Comparative studies were done with filter membranes that have been reported as immunoisolation barriers. To evaluate if silicon nanopore membranes changed insulin response patterns for glucose-stimulated islets, macrocapsules were constructed with nanopore membranes and filled with pancreatic islets, and dynamic perifusion studies were performed.

RESULTS

Relative to commercial membranes, silicon nanopore membranes showed high rates of diffusion for glucose and insulin, and acted as efficient barriers to complement proteins and IgG. No other commercial membrane showed comparable diffusion and immunoisolating properties. Islets placed within the macrocapsule exhibited glucose-responsive insulin secretion in perifusion studies.

CONCLUSIONS

Silicon nanopore membranes possess unique and desirable diffusion properties as immunoisolation membranes and allow rapid response times for the stimulation of islets by glucose. These features are attributed to the physical properties of the membranes, namely, the straight channels, adequate porosity, and the 5 microm thickness.

Nanoporous microsystems for islet cell replacement

The inadequacy of conventional insulin therapy for the treatment of Type I diabetes has stimulated research on several therapeutic alternatives, including insulin pumps and controlled release systems for insulin. One of the most physiological alternatives to insulin injections is the transplantation of insulin-secreting cells. It is the beta cells of the islets that secrete insulin in response to increasing blood glucose concentrations. Ideally, transplantation of such cells (allografts or xenografts) could restore normoglycemia. However, as with most tissue or cellular transplants, the cellular grafts, particularly xenografts, are subjected to immunorejection in the absence of chronic immunosuppression. Thus, it is of great interest to develop new technologies that may be used for islet cell replacement. This research proposal describes a new approach to cellular delivery based on micro- and nanotechnology. Utilizing this approach, nanoporous biocapsules are bulk and surface micromachined to present uniform and well-controlled pore sizes as small as 7 nm, tailored surface chemistries, and precise microarchitectures, in order to provide immunoisolating microenvironments for cells. Such a design may overcome some of the limitations associated with conventional encapsulation and delivery technologies, including chemical instabilities, material degradation or fracture, and broad membrane pore sizes.

BioMEMS: state-of-the-art in detection, opportunities and prospects

In recent years, the biological and biomedical applications of micro- and nanotechnology (commonly referred to as Biomedical or Biological Micro-Electro-Mechanical Systems [BioMEMS]) have become increasingly prevalent and have found widespread use in a wide variety of applications such as diagnostics, therapeutics, and tissue engineering. While research and development activity in this field stays intense, some applications have also been commercialized. This article reviews the recent advances in this very exciting and important field and presents a summary of the state of the art in the area of BioMEMS focusing on diagnostics, sensing, and detection. The areas of therapeutics and hybrid bio/artificial devices will be presented in more detail elsewhere [Biomedical Nanotechnology, Vol. I-IV, Maruo Ferrari (Ed.), Kluwer Academic Publishers, 2004, in press.] and here are discussed briefly in terms of future directions and prospects.

Small-scale systems for in vivo drug delivery

Recent developments in the application of micro- and nanosystems for drug administration include a diverse range of new materials and methods. New approaches include the on-demand activation of molecular interactions, novel diffusion-controlled delivery devices, nanostructured 'smart' surfaces and materials, and prospects for coupling drug delivery to sensors and implants. Micro- and nanotechnologies are enabling the design of novel methods such as radio-frequency addressing of individual molecules or the suppression of immune response to a release device. Current challenges include the need to balance the small scale of the devices with the quantities of drugs that are clinically necessary, the requirement for more stable sensor platforms, and the development of methods to evaluate these new materials and devices for safety and efficacy.

Microfabricated drug delivery systems: from particles to pores

Microfabrication techniques which permit the creation of therapeutic delivery systems that possess a combination of structural, mechanical, and perhaps electronic features may surmount challenges associated with conventional delivery of therapy. In this review, delivery concepts are presented which capitalize on the strengths of microfabrication. Possible applications include micromachined silicon membranes to create implantable biocapsules for the immunoisolation of pancreatic islet cells-as a possible treatment for diabetes-and sustained release of injectable drugs needed over long time periods. Asymmetrical, drug-loaded microfabricated particles with specific ligands linked to the surface are proposed for improving oral bioavailability of peptide (and perhaps protein) drugs. In addition, microfabricated drug delivery systems ranging from transdermal microneedles to implantable microchips will be discussed.

Microfabrication technology for pancreatic cell encapsulation

The inadequacy of conventional insulin therapy for the treatment of Type I diabetes has stimulated research on several therapeutic alternatives, including insulin pumps and controlled-release systems for insulin. One of the most physiological alternatives to insulin injections is the transplantation of insulin-secreting cells. It is the beta-cells of the islets that secrete insulin in response to increasing blood glucose concentrations. Ideally, transplantation of such cells (allografts or xenografts) could restore normoglycaemia. However, as with most tissue or cellular transplants, the cellular grafts, particularly xenografts, are subject to immunorejection in the absence of chronic immunosuppression. Thus, it is of great interest to develop new technologies that may be used for insulin delivery or pancreatic cell transplantation. This review describes a new approach to cellular delivery based on micro- and nanotechnology. Utilising this approach, nanoporous biocapsules are bulk and surface micromachined to present uniform and well-controlled pore sizes as small as 7 nm, tailored surface chemistries and precise microarchitectures, in order to provide immunoisolating microenvironments for cells. Such a design may overcome some of the limitations associated with conventional encapsulation and delivery technologies, including chemical instabilities, material degradation or fracture and broad membrane pore sizes.

Nanoporous biocapsules for the encapsulation of insulinoma cells: biotransport and biocompatibility considerations

This study investigates whether nanoporous micromachined biocapsules, with uniform membrane pore sizes of 24.5-nm, can be used to encapsulate insulin-secreting cells in vitro. This approach to cell encapsulation is based on microfabrication technology whereby immunoisolation membranes are bulk and surface micromachined to present uniform and well-controlled pore sizes as small as 10 nm, tailored surface chemistries, and precise microarchitectures. This study evaluates the behavior of insulinoma cells with micromachined membranes, the effect of matrix configurations within the biocapsule on cell behavior, as well as insulin and glucose transport through the biocapsule membranes.

Nanoporous anti-fouling silicon membranes for biosensor applications

The ability to create biocompatible well-controlled membranes has been an area of great interest over the last few years, particularly for biosensor applications. The present study describes the fabrication and characterization of novel nanoporous micromachined membranes that exhibit selective permeability and low biofouling. Results indicate that such membranes can be fabricated with uniform pore sizes capable of the simultaneous exclusion of albumin and diffusion of glucose. Compared to polymeric membranes of similar pore size, micromachined silicon membranes allowed more than twice the amount of glucose diffusion after 240 min and complete albumin exclusion. Moreover, membranes exhibit no morphological change or degradability in the presence of biological proteins and fluids at 37 degrees C. The results point to the potential of using such membranes for implantable biosensor applications. With monodisperse pores sizes as small as 10 nm, these membranes offer advantages in their reproducibility, stability, and ability to be integrated in silicon-based biosensing technology.

Artificial organs and vanishing boundaries

With the first clinical use of the artificial kidney over 5 decades ago, we entered into a new era of medicine-that of substitutive and replacement therapy. Yet it took nearly another 15 years until chronic treatment was possible and nearly another 15 years until widespread treatment was possible due to government support. The history of development and clinical use of other artificial organ technologies such as the artificial heart and heart valves, the artificial lung, artificial blood, joint replacements, the artificial liver, the artificial pancreas, immunologic, metabolic, and neurologic support, neurocontrol, and tissue substitutes have followed similar long development paths. Despite their relatively long time to be put into clinical use, the contributions of artificial organ technologies to the betterment of mankind have been unquestionably a major success. For example, modern day surgery would not be possible without heart-lung support, and the technologies for heart support have led to the development of various minimally invasive technologies. The powerful impact that artificial organ technologies presently has on our lives is seen through the statistic that in the U.S.A. nearly 1 in 10 persons is living with an implanted medical device. With the aging of our population and the improvements in technologies, these numbers will only increase.

Micromachined interfaces: new approaches in cell immunoisolation and biomolecular separation

As a novel therapeutic application of microfabrication technology, a micromachined membrane-based biocapsule is described for the transplantation of protein-secreting cells without the need for immunosuppression. This new approach to cell encapsulation is based on microfabrication technology whereby immunoisolation membranes are bulk and surface micromachined to present uniform and well-controlled pore sizes as small as 10 nm, tailored surface chemistries, and precise microarchitecture. Through its ability to achieve highly controlled microarchitectures on size scales relevant to living systems (from microm to nm), microfabrication technology offers unique opportunities to more precisely engineer biocapsules that allow free exchange of the nutrients, waste products, and secreted therapeutic proteins between the host (patient) and implanted cells, but exclude lymphocytes and antibodies that may attack foreign cells. Microfabricated inorganic encapsulation devices may provide biocompatibility, in vivo chemical and mechanical stability, tailored pore geometries, and superior immunoisolation for encapsulated cells over conventional encapsulation approaches. By using microfabrication techniques, structures can be fabricated with spatial features from the sub-micron range up to several millimeters. These multi-scale structures correspond well with hierarchical biological structures, from proteins and sub-cellular organelles to the tissue and organ levels.