Cell microencapsulation with synthetic polymers

Droplet-based microfluidics: an efficient high-throughput portable system for cell encapsulation

One of the goals of tissue engineering and regenerative medicine is restoring primary living tissue function by manufacturing a 3D microenvironment. One of the main challenges is protecting implanted non-autologous cells or tissues from the host immune system. Cell encapsulation has emerged as a promising technique for this purpose. It involves entrapping cells in biocompatible and semi-permeable microcarriers made from natural or synthetic polymers that regulate the release of cellular secretions. In recent years, droplet-based microfluidic systems have emerged as powerful tools for cell encapsulation in tissue engineering and regenerative medicine. These systems offer precise control over droplet size, composition, and functionality, allowing for creating of microenvironments that closely mimic native tissue. Droplet-based microfluidic systems have extensive applications in biotechnology, medical diagnosis, and drug discovery. This review summarises the recent developments in droplet-based microfluidic systems and cell encapsulation techniques, as well as their applications, advantages, and challenges in biology and medicine. The integration of these technologies has the potential to revolutionise tissue engineering and regenerative medicine by providing a precise and controlled microenvironment for cell growth and differentiation. By overcoming the immune system's challenges and enabling the release of cellular secretions, these technologies hold great promise for the future of regenerative medicine.

Current Challenges in Microcapsule Designs and Microencapsulation Processes: A Review

Microencapsulation is an advanced methodology for the protection, preservation, and/or delivery of active materials in a wide range of industrial sectors, such as pharmaceuticals, cosmetics, fragrances, paints, coatings, detergents, food products, and agrochemicals. Polymeric materials have been extensively used as microcapsule shells to provide appropriate barrier properties to achieve controlled release of the encapsulated active ingredient. However, significant limitations are associated with such capsules, including undesired leaching and the nonbiodegradable nature of the typically used polymers. In addition, the energy cost of manufacturing microcapsules is an important factor to be considered when designing microcapsule systems and the corresponding production processes. Recent factors linked to UN sustainability goals are modifying how such microencapsulation systems should be designed in pursuit of "ideal" microcapsules that are efficient, safe, cost-effective and environmentally friendly. This review provides an overview of advances in microencapsulation, with emphasis on sustainable microcapsule designs. The key evaluation techniques to assess the biodegradability of microcapsules, in compliance with recently evolving European Union requirements, are also described. Moreover, the most common methodologies for the fabrication of microcapsules are presented within the framework of their energy demand. Recent promising microcapsule designs are also highlighted for their suitability toward meeting current design requirements and stringent regulations, tackling the ongoing challenges, limitations, and opportunities.

Chitosan-taurine nanoparticles cross-linked carboxymethyl chitosan hydrogels facilitate both acute and chronic diabetic wound healing

Wound dressing diligently facilitate healing by fostering hemostasis, immunoregulation, the angiogenesis, and collagen deposition. Our methodology entails fabricating chitosan-taurine nanoparticles (CS-Tau) through an ionic gelation method. The morphology of CS-Tau was observed utilizing Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Dynamic Light Scattering (DLS). The nanoparticles are subsequently incorporated into carboxymethyl chitosan hydrogels for crosslinking by EDC-NHS, yielding hydrogel dressings (CMCS-CS-Tau) designed to extend the duration of taurine release. In vitro investigations confirmed that these innovative compound dressings displayed superior biodegradation, biocompatibility, cytocompatibility, and non-toxicity, in addition to possessing anti-inflammatory properties, and stimulating the proliferation and mobility of human umbilical vein endothelial cells (HUVECs). Experiments conducted on mice models with full-thickness skin removal demonstrated that CMCS-CS-Tau efficaciously aided in wound healing by spurring angiogenesis, and encouraging collagen deposition. CMCS-CS-Tau can also minimize inflammation and promote collagen deposition in chronic diabetic wound. Hence, CMCS-CS-Tau promotes both acute and chronic diabetic wound healing. Furthermore, the sustained release mechanism of CMCS-CS-Tau on taurine reveals promising potential for extending its clinical utility in relation to various biological effects of taurine.

Influence of High Strain Dynamic Loading on HEMA-DMAEMA Hydrogel Storage Modulus and Time Dependence

Hydrogels have been extensively studied for biomedical applications such as drug delivery, tissue-engineered scaffolds, and biosensors. There is a gap in the literature pertaining to the mechanical properties of hydrogel materials subjected to high-strain dynamic-loading conditions even though empirical data of this type are needed to advance the design of innovative biomedical designs and inform numerical models. For this work, HEMA-DMAEMA hydrogels are fabricated using a photopolymerization approach. Hydrogels are subjected to high-compression oscillatory dynamic mechanical loading at strain rates equal to 50%, 60%, and 70%, and storage and loss moduli are observed over time, e.g., 72 h and 5, 10, and 15 days. As expected, the increased strains resulted in lower storage and loss moduli, which could be attributed to a breakdown in the hydrogel network attributed to several mechanisms, e.g., increased network disruption, chain scission or slippage, and partial plastic deformation. This study helps to advance our understanding of hydrogels subjected to high strain rates to understand their viscoelastic behavior, i.e., strain rate sensitivity, energy dissipation mechanisms, and deformation kinetics, which are needed for the accurate modeling and prediction of hydrogel behavior in real-world applications.

Pancreatic islet transplantation: current advances and challenges

Diabetes is a prevalent chronic disease that traditionally requires severe reliance on medication for treatment. Oral medication and exogenous insulin can only temporarily maintain blood glucose levels and do not cure the disease. Most patients need life-long injections of exogenous insulin. In recent years, advances in islet transplantation have significantly advanced the treatment of diabetes, allowing patients to discontinue exogenous insulin and avoid complications.Long-term follow-up results from recent reports on islet transplantation suggest that they provide significant therapeutic benefit although patients still require immunotherapy, suggesting the importance of future transplantation strategies. Although organ shortage remains the primary obstacle for the development of islet transplantation, new sources of islet cells, such as stem cells and porcine islet cells, have been proposed, and are gradually being incorporated into clinical research. Further research on new transplantation sites, such as the subcutaneous space and mesenteric fat, may eventually replace the traditional portal vein intra-islet cell infusion. Additionally, the immunological rejection reaction in islet transplantation will be resolved through the combined application of immunosuppressant agents, islet encapsulation technology, and the most promising mesenchymal stem cells/regulatory T cell and islet cell combined transplantation cell therapy. This review summarizes the progress achieved in islet transplantation, and discusses the research progress and potential solutions to the challenges faced.

Insights from Syzygium aromaticum Essential Oil: Encapsulation, Characterization, and Antioxidant Activity

Alginate encapsulates loaded with clove essential oil (CEO) were prepared by ionic gelation, with subsequent freeze-drying. The objective of the present work was to develop a product with the ability to protect CEO against its easy volatility and oxidation. The following techniques were used to characterize the formulations: eugenol release, degree of swelling, GC/MS, TGA/DSC, and SEM. The alginate solution (1.0%) containing different concentrations of CEO (LF1: 1.0%; LF2: 0.5%; LF3: 0.1%) was dropped into a 3.0% CaCl2 solution. After lyophilization, the encapsulated samples were wrinkled and rigid, with high encapsulation power (LF3: 76.9% ± 0.5). Three chemical components were identified: eugenol (the major one), caryophyllene, and humulene. The antioxidant power (LF1: DPPH IC50 18.1 µg mL-1) was consistent with the phenol content (LF1: 172.2 mg GAE g-1). The encapsulated ones were thermally stable, as shown by analysis of FTIR peaks, eugenol molecular structure was kept unaltered. The degree of swelling was 19.2% (PBS). The release of eugenol (92.5%) in the PBS solution was faster than in the acidic medium. It was concluded that the low-cost technology used allows the maintenance of the content and characteristics of CEO in the three concentrations tested, offering a basis for further research with essential oil encapsulates.

Encapsulated cell technology: Delivering cytokines to treat posterior ocular diseases

Encapsulated cell technology (ECT) is a targeted delivery method that uses the genetically engineered cells in semipermeable polymer capsules to deliver cytokines. Thus far, ECT has been extensively utilized in pharmacologic research, and shows enormous potentials in the treatment of posterior segment diseases. Due to the biological barriers within the eyeball, it is difficult to attain effective therapeutic concentration in the posterior segment through topical administration of drug molecules. Encouragingly, therapeutic cytokines provided by ECT can cross these biological barriers and achieve sustained release at the desired location. The encapsulation system uses permeable materials that allow growth factors and cytokines to diffuse efficiently into retinal tissue. Moreover, the ECT based treatment can be terminated timely when we need to retrieve the implant, which makes the therapy reversible and provides a safer alternative for intraocular gene therapy. Meanwhile, we also place special emphasis on optimizing encapsulation materials and enhancing preservation techniques to achieve the stable release of growth factors and cytokines in the eyeball. This technology holds great promise for the treatment of patients with dry AMD, RP, glaucoma and MacTel. These findings would enrich our understandings of ECT and promote its future applications in treatment of degenerative retinopathy. This review comprises articles evaluating the exactness of artificial intelligence-based formulas published from 2000 to March 2024. The papers were identified by a literature search of various databases (PubMed/MEDLINE, Google Scholar, Cochrane Library and Web of Science).

The microspheres/hydrogels scaffolds based on the proteins, nucleic acids, or polysaccharides composite as carriers for tissue repair: A review

There are many studies on specific macromolecules and their contributions to tissue repair. Macromolecules have supporting and protective effects in organisms and can help regrow, reshape, and promote self-repair and regeneration of damaged tissues. Macromolecules, such as proteins, nucleic acids, and polysaccharides, can be constructed into hydrogels for the preparation of slow-release drug agents, carriers for cell culture, and platforms for gene delivery. Hydrogels and microspheres are fabricated by chemical crosslinking or mixed co-deposition often used as scaffolds, drug carriers, or cell culture matrix, provide proper mechanical support and nutrient delivery, a well-conditioned environment that to promote the regeneration and repair of damaged tissues. This review provides a comprehensive overview of recent developments in the construction of macromolecules into hydrogels and microspheres based on the proteins, nucleic acids, polysaccharides and other polymer and their application in tissue repair. We then discuss the latest research trends regarding the advantages and disadvantages of these composites in repair tissue. Further, we examine the applications of microspheres/hydrogels in different tissue repairs, such as skin tissue, cartilage, tumor tissue, synovial, nerve tissue, and cardiac repair. The review closes by highlighting the challenges and prospects of microspheres/hydrogels composites.

Advanced cryopreservation engineering strategies: the critical step to utilize stem cell products

With the rapid development of stem cell-related therapies and regenerative medicine, the clinical application of stem cell products is on the rise. However, ensuring the effectiveness of these products after storage and transportation remains a challenge in the transformation to clinical trials. Cryopreservation technology allows for the long-term storage of cells while ensuring viability, making it a top priority for stem cell preservation. The field of cryopreservation-related engineering technologies is thriving, and this review provides an overview of the background and basic principles of cryopreservation. It then delves into the main bioengineering technologies and strategies used in cryopreservation, including photothermal and electromagnetic rewarming, microencapsulation, and synergetic ice inhibition. Finally, the current challenges and future prospects in the field of efficient cryopreservation of stem cells are summarized and discussed.

Progress in the application of 3D-printed sodium alginate-based hydrogel scaffolds in bone tissue repair

In recent years, hydrogels have been widely used in the biomedical field as materials with excellent bionic structures and biological properties. Among them, the excellent comprehensive properties of natural polymer hydrogels represented by sodium alginate have attracted the great attention of researchers. At the same time, by physically blending sodium alginate with other materials, the problems of poor cell adhesion and mechanical properties of sodium alginate hydrogels were directly improved without chemical modification of sodium alginate. The composite blending of multiple materials can also improve the functionality of sodium alginate hydrogels, and the prepared composite hydrogel also has a larger application field. In addition, based on the adjustable viscosity of sodium alginate-based hydrogels, sodium alginate-based hydrogels can be loaded with cells to prepare biological ink, and the scaffold can be printed out by 3D printing technology for the repair of bone defects. This paper first summarizes the improvement of the properties of sodium alginate and other materials after physical blending. Then, it summarizes the application progress of sodium alginate-based hydrogel scaffolds for bone tissue repair based on 3D printing technology in recent years. Moreover, we provide relevant opinions and comments to provide a theoretical basis for follow-up research.

Encapsulation of stem-cell derived β-cells: A promising approach for the treatment for type 1 diabetes mellitus

Type 1 diabetes mellitus is an auto-immune disease causing the T-cell mediated destruction of insulin-producing β-cells, resulting in chronic hyperglycemia. Current treatments such as insulin replacement therapy or the transplantation of pancreas or pancreatic islets present major disadvantages such as the constant need of drugs, as well as a shortage of donor organs. In this review, we discuss a sustainable solution to overcome these limitations combining the use of β-cells, derived from stem cells, and their encapsulation within a protective matrix. This article provides an exhaustive overview of currently investigated stem cell sources including embryonic, mesenchymal as well as induced pluripotent stem cells in combination with various up to date encapsulation methods allowing the formation of immuno-protective devices. In order to identify current limitations of this interdisciplinary therapeutic approach and to find sustainable solutions, it is essential to consider key aspects from all involved domains. This includes biological parameters such as the stem cell origin but also the different aspects of the encapsulation process, the used materials and their physico-chemical properties such as elasticity, porosity and permeability cut-off as well as the best implantation sites allowing efficient and self-autonomous control of glycemia by the transplanted encapsulated cells.

An electrospun macrodevice for durable encapsulation of human cells with consistent secretion of therapeutic antibodies

Frequent subcutaneous or intravenous administrations of therapeutic biomolecules can be costly and inconvenient for patients. Implantation of encapsulated recombinant cells represents a promising approach for the sustained delivery of biotherapeutics. However, foreign body and fibrotic response against encapsulation materials results in drastically reduced viability of encapsulated cells, presenting a major engineering challenge for biocompatibility. Here, we show that the multi-laminate electrospun retrievable macrodevice (Bio-Spun) protects genetically modified human cells after subcutaneous implant in mice. We describe here a biocompatible nanofiber device that limits fibrosis and extends implant survival. For more than 150 days, these devices supported human cells engineered to secrete the antibodies: vedolizumab, ustekinumab, and adalimumab, while eliciting minimal fibrotic response in mice. The porous electrospun cell chamber allowed secretion of the recombinant antibodies into the host bloodstream, and prevented infiltration of host cells into the chamber. High plasma levels (>50 μg/mL) of antibody were maintained in the optimized devices for more than 5 months. Our findings demonstrate that macrodevices constructed from electrospun materials are effective in protecting genetically engineered cells for the sustained administration of recombinant therapeutic antibodies.

Olfactory ensheathing cells and neuropathic pain

Damage to the nervous system can lead to functional impairment, including sensory and motor functions. Importantly, neuropathic pain (NPP) can be induced after nerve injury, which seriously affects the quality of life of patients. Therefore, the repair of nerve damage and the treatment of pain are particularly important. However, the current treatment of NPP is very weak, which promotes researchers to find new methods and directions for treatment. Recently, cell transplantation technology has received great attention and has become a hot spot for the treatment of nerve injury and pain. Olfactory ensheathing cells (OECs) are a kind of glial cells with the characteristics of lifelong survival in the nervous system and continuous division and renewal. They also secrete a variety of neurotrophic factors, bridge the fibers at both ends of the injured nerve, change the local injury microenvironment, and promote axon regeneration and other biological functions. Different studies have revealed that the transplantation of OECs can repair damaged nerves and exert analgesic effect. Some progress has been made in the effect of OECs transplantation in inhibiting NPP. Therefore, in this paper, we provided a comprehensive overview of the biology of OECs, described the possible pathogenesis of NPP. Moreover, we discussed on the therapeutic effect of OECs transplantation on central nervous system injury and NPP, and prospected some possible problems of OECs transplantation as pain treatment. To provide some valuable information for the treatment of pain by OECs transplantation in the future.

Advances in polymer-based cell encapsulation and its applications in tissue repair

Cell microencapsulation is a more widely accepted area of biological encapsulation. In most cases, it involves fixing cells in polymer scaffolds or semi-permeable hydrogel capsules, providing the environment for protecting cells, allowing the exchange of nutrients and oxygen, and protecting cells against the attack of the host immune system by preventing the entry of antibodies and cytotoxic immune cells. Hydrogel encapsulation provides a three-dimensional (3D) environment similar to that experienced in vivo, so it can maintain normal cellular functions to produce tissues similar to those in vivo. Embedded cells can be genetically modified to release specific therapeutic products directly at the target site, thereby eliminating the side effects of systemic treatments. Cellular microcarriers need to meet many extremely high standards regarding their biocompatibility, cytocompatibility, immunoseparation capacity, transport, mechanical, and chemical properties. In this article, we discuss the biopolymer gels used in tissue engineering applications and the brief introduction of cell encapsulation for therapeutic protein production. Also, we review polymer biomaterials and methods for preparing cell microcarriers for biomedical applications. At the same time, in order to improve the application performance of cell microcarriers in vivo, we also summarize the main limitations and improvement strategies of cell encapsulation. Finally, the main applications of polymer cell microcarriers in regenerative medicine are summarized.

Tissue engineering approaches and generation of insulin-producing cells to treat type 1 diabetes

Tissue engineering (TE) has become a new effective solution to a variety of medical problems, including diabetes. Mesenchymal stem cells (MSCs), which have the ability to differentiate into endodermal and mesodermal cells, appear to be appropriate for this function. The purpose of this review was to evaluate the outcomes of various researches on the insulin-producing cells (IPCs) generation from MSCs with TE approaches to increase efficacy of type 1 diabetes treatments. The search was performed in PubMed/Medline, Scopus and Embase databases until 2021. Studies revealed that MSCs could also differentiate into IPCs under certain conditions. Therefore, a wide range of protocols have been used for this differentiation, but their effectiveness is very different. Scaffolds can provide a microenvironment that enhances the MSCs to IPCs differentiation, improves their metabolic activity and up-regulate pancreatic-specific transcription factors. They also preserve IPCs architecture and enhance insulin production as well as protect against cell death. This systematic review offers a framework for prospective research based on data. In vitro and in vivo evidence suggests that scaffold-based TE can improve the viability and function of IPCs.

Genipin-crosslinked fibrin seeded with oxidized alginate microbeads as a novel composite biomaterial strategy for intervertebral disc cell therapy

Discectomy procedures alleviate disability caused by intervertebral disc (IVD) herniation, but do not repair herniation-induced annulus fibrosus (AF) defects. Cell therapy shows promise for IVD repair, yet cell delivery biomaterials capable of sealing AF defects and restoring biomechanical function have poor biological performance. To balance the biomechanical and biological demands of IVD cell delivery biomaterials, we engineered an injectable composite biomaterial using cell-laden, degradable oxidized alginate (OxAlg) microbeads (MBs) to deliver AF cells within high-modulus genipin-crosslinked fibrin (FibGen) hydrogels (FibGen + MB composites). Conceptually, the high-modulus FibGen would immediately stabilize injured IVDs, while OxAlg MBs would protect and release cells required for long-term healing. We first showed that AF cells microencapsulated in OxAlg MBs maintained high viability and, upon release, displayed phenotypic AF cell morphology and gene expression. Next, we created cell-laden FibGen + MB composites and demonstrated that OxAlg MBs functionalized with RGD peptides (MB-RGD) minimized AF cell apoptosis and retained phenotypic gene expression. Further, we showed that cell-laden FibGen + MB composites are biomechanically stable and promote extracellular matrix (ECM) synthesis in long-term in vitro culture. Lastly, we evaluated cell-laden FibGen + MB-RGD composites in a long-term bovine caudal IVD organ culture bioreactor and found that composites had low herniation risk, provided superior biomechanical and biological repair to discectomy controls, and retained anabolic cells within the IVD injury space. This novel injectable composite hydrogel strategy shows promise as an IVD cell delivery sealant with potentially broad applications for its capacity to balance biomechanical and biological performance.

Microencapsulation-based cell therapies

Mapping a new therapeutic route can be fraught with challenges, but recent developments in the preparation and properties of small particles combined with significant improvements to tried and tested techniques offer refined cell targeting with tremendous translational potential. Regenerating new cells through the use of compounds that regulate epigenetic pathways represents an attractive approach that is gaining increased attention for the treatment of several diseases including Type 1 Diabetes and cardiomyopathy. However, cells that have been regenerated using epigenetic agents will still encounter immunological barriers as well as limitations associated with their longevity and potency during transplantation. Strategies aimed at protecting these epigenetically regenerated cells from the host immune response include microencapsulation. Microencapsulation can provide new solutions for the treatment of many diseases. In particular, it offers an advantageous method of administering therapeutic materials and molecules that cannot be substituted by pharmacological substances. Promising clinical findings have shown the potential beneficial use of microencapsulation for islet transplantation as well as for cardiac, hepatic, and neuronal repair. For the treatment of diseases such as type I diabetes that requires insulin release regulated by the patient's metabolic needs, microencapsulation may be the most effective therapeutic strategy. However, new materials need to be developed, so that transplanted encapsulated cells are able to survive for longer periods in the host. In this article, we discuss microencapsulation strategies and chart recent progress in nanomedicine that offers new potential for this area in the future.

The Role of 3D Printing Technology in Microengineering of Microneedles

Microneedles (MNs) are minimally invasive devices, which have gained extensive interest over the past decades in various fields including drug delivery, disease diagnosis, monitoring, and cosmetics. MN geometry and shape are key parameters that dictate performance and therapeutic efficacy, however, traditional fabrication methods, such as molding, may not be able to offer rapid design modifications. In this regard, the fabrication of MNs using 3D printing technology enables the rapid creation of complex MN prototypes with high accuracy and offers customizable MN devices with a desired shape and dimension. Moreover, 3D printing shows great potential in producing advanced transdermal drug delivery systems and medical devices by integrating MNs with a variety of technologies. This review aims to demonstrate the advantages of exploiting 3D printing technology as a new tool to microengineer MNs. Various 3D printing methods are introduced, and representative MNs manufactured by such approaches are highlighted in detail. The development of advanced MN devices is also included. Finally, clinical translation and future perspectives for the development of MNs using 3D printing are discussed.

Method to Isolate Dormant Cancer Cells from Heterogeneous Populations

Cancer recurrence is responsible for a high percentage of cancer-related deaths. Primary tumor removal, chemotherapy, and radiotherapy often leave behind cancer cells that are clinically undetectable. Recent evidence has shown that subpopulations of these residual cancer cells enter into a prolonged dormant state, remaining quiescent for months to years, and eventually lead to metastases and relapse (Sosa et al. Nat Rev Cancer 14:611-622, 2014). Identifying the presence of and isolating these dormancy-capable cells (DCCs) from resected tumors or bodily fluids may therefore provide an opportunity to understand their biology and develop personalized treatments for patients at risk for relapse. Physical confinement in a stiff and porous 3D matrix, which inhibits proliferation, migration, and growth of the immobilized cells, has been shown to isolate DCC populations (Preciado et al. Technology 05:1-10, 2017; Reátegui et al. J Mater Chem B 2:7440-7448, 2014). Isolated DCCs can then be recovered from the gel and analyzed. Here we describe this immobilization method that can be used to isolate DCCs from heterogeneous cell populations that may also include dormancy-incapable cancer cells and host cells.

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.

Pharmaceutical formulation and polymer chemistry for cell encapsulation applied to the creation of a lab-on-a-chip bio-microsystem

Microencapsulation of formulation designs further expands the field and offers the potential for use in developing bioartificial organs via cell encapsulation. Combining formulation design and encapsulation requires ideal excipients to be determined. In terms of cell encapsulation, an environment which allows growth and functionality is paramount to ensuring cell survival and incorporation into a bioartificial organ. Hence, excipients are examined for both individual properties and benefits, and compatibility with encapsulated active materials. Polymers are commonly used in microencapsulation, offering protection from the immune system. Bile acids are emerging as a tool to enhance delivery, both biologically and pharmaceutically. Therefore, this review will focus on bile acids and polymers in formulation design via microencapsulation, in the field of bioartificial organ development.

Chemotherapy-induced hearing loss: the applications of bio-nanotechnologies and bile acid-based delivery matrices

Advancement in the prevention of chemotherapy-induced hearing loss has proposed new nano-based delivery matrices that can target inner ear regions most damaged by chemotherapy. Chemotherapy agents (e.g., cisplatin) induce increased reactive oxygen species formation in the inner ear that damage sensory hair cells and result in irreversible hearing impairment. Exogenous antioxidants (e.g., Probucol and metformin) have been shown to block the formation of these reactive oxygen species. Delivery of these drugs in effective concentrations remains a challenge. Microencapsulation in combination with drug excipients provides one technique to effectively deliver these drugs. This paper investigates the use of probucol and metformin in combination with drug excipients for novel, inner ear, delivery.

Carbon nanomaterial properties help to enhance xylanase production from recombinant Kluyveromyces lactis through a cell immobilization method

Carbon nanomaterials, due to their catalytic activity and high surface area, have potential as cell immobilization supports to increase the production of xylanase. Recombinant Kluyveromyces lactis used for xylanase production was integrated into a polymeric gel network with carbon nanomaterials. Carbon nanomaterials were pretreated before cell immobilization with hydrochloric acid (HCl) treatment and glutaraldehyde (GA) crosslinking, which contributes to cell immobilization performance. Carbon nanotubes (CNTs) and graphene oxide (GO) were further screened using a Plackett-Burman experimental design. Cell loading and agar concentration were the most important factors in xylanase production with low cell leakage. Under optimized conditions, xylanase production was increased by more than 400% compared to free cells. Immobilized cell material containing such high cell densities may exhibit new and unexplored beneficial properties because the cells comprise a large fraction of the component. The use of carbon nanomaterials as a cell immobilization support along with the entrapment method successfully enhances the production of xylanase, providing a new route to improved bioprocessing, particularly for the production of enzymes. KEY POINTS: • Carbon nanomaterials (CNTs, GO) have potential as cell immobilization supports. • Entrapment in a polymeric gel network provides space for xylanase production. • Plackett-Burman design screen for the most important factor for cell immobilization.

Evaluation of Microfluidic Approaches to Encapsulate Cells into PEGDA Microparticles

Purpose

Polyethylene glycol diacrylate (PEGDA) is increasingly used to microencapsulate cells via a vortex-induced water-in-oil emulsion process. Herein, we evaluated methods to encapsulate cells into microparticles using microfluidic methods.

Methods

PEGDA prepolymer solution with or without cells was photopolymerized with white light under varying microfluidic parameters to form empty microspheres or cell-laden microparticles. Microparticles and entrapped cells were assessed for size and viability.

Results

PEGDA microparticles were easily formed when cells were absent; the introduction of cells resulted in aggregation that clogged microfluidic devices, resulting in a mix of empty polymer microparticles and cells that were not encapsulated. Cells that were successfully encapsulated had poor viability.

Conclusion

Microfluidic methods may work for low density microencapsulation of mammalian cells; however, when the cell density within each microparticle must be relatively high, emulsion-based methods are superior to microfluidic methods.

Lay Summary

The synthetic polymer polyethylene glycol diacrylate (PEGDA) has been increasingly used to encapsulate cells into micrometer-sized hydrogel spheres (microspheres). One method to microencapsulate cells has been to form a water-in-oil emulsion with liquid polymer containing cells and then expose the suspended droplets to white light, polymerizing them into PEGDA hydrogel microspheres. Although successful, this method has poor control over the process, resulting in polydisperse microsphere sizes with varying cell density. We evaluated microfluidic methods to form both empty and cell-laden PEGDA microspheres. Although microfluidic methods resulted in monodisperse microsphere sizes, the introduction of cells resulted in clogging of microfluidic devices, non-spherical microparticles, and poor cell viability.

Future Work

Because the microfluidic approach successfully formed cell-free microspheres, the effect of reducing cell aggregation will be examined. Specifically, the use of anti-aggregation agents as well as a reduced cell density in the liquid polymer phase and their effects on polymer formation will be explored.

Artificial cells for the treatment of liver diseases

Liver diseases have become an increasing health burden and account for over 2 million deaths every year globally. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they also suffer limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. Artificial cells have demonstrated advantages in long-term storage, targeting capability, and tuneable features. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment. First, the design of artificial cells and their biomimicking functions are summarized. Then, systems that mimic cell surface properties are introduced with two concepts highlighted: cell membrane-coated artificial cells and synthetic lipid-based artificial cells. Next, cell microencapsulation strategy is summarized and discussed. Finally, challenges and future perspectives of artificial cells are outlined. STATEMENT OF SIGNIFICANCE: Liver diseases have become an increasing health burden. Standard therapies including liver transplant and cell therapy offer a promising treatment for liver diseases, but they have limitations such as adverse immune reactions and lack of long-term efficacy. Artificial cells that mimic certain functions of a living cell have emerged as a new strategy to overcome some of the challenges that liver cell therapy faces at present. This article provides an overview of the recent progress in developing artificial cells and their potential applications in liver disease treatment, including the design of artificial cells and their biomimicking functions, two systems that mimic cell surface properties (cell membrane-coated artificial cells and synthetic lipid-based artificial cells), and cell microencapsulation strategy. We also outline the challenges and future perspectives of artificial cells.

Glycol Chitosan Functionalized with a Gd(III) Chelate as a Redox-responsive Magnetic Resonance Imaging Probe to Label Cell Embedding Alginate Capsules

One possibility for the non-invasive imaging of encapsulated cell grafts is to label the lumen of cell embedding capsules with a redox-responsive probe, as an increased extracellular reducing potential can be considered as a marker of hypoxia-induced necrosis. A Gd(III)-HPDO3A-like chelate has been conjugated to glycol-chitosan through a redox-responsive disulphide bond to obtain a contrast agent for Magnetic Resonance Imaging (MRI). Such a compound can be interspersed with fibroblasts within the lumen of alginate-chitosan capsules. Increasing reducing conditions within the extracellular microenvironment lead to the reductive cleavage of the disulphide bond and to the release of gadolinium in the form of a low molecular weight, non-ionic chelate. The efflux of such chelate from capsules is readily detected by a decrease of contrast enhancement in T₁ -weighted MR images.

Cell microencapsulation technologies for sustained drug delivery: Latest advances in efficacy and biosafety

The development of cell microencapsulation systems began several decades ago. However, today few systems have been tested in clinical trials. For this reason, in the last years, researchers have directed efforts towards trying to solve some of the key aspects that still limit efficacy and biosafety, the two major criteria that must be satisfied to reach the clinical practice. Regarding the efficacy, which is closely related to biocompatibility, substantial improvements have been made, such as the purification or chemical modification of the alginates that normally form the microspheres. Each of the components that make up the microcapsules has been carefully selected to avoid toxicities that can damage the encapsulated cells or generate an immune response leading to pericapsular fibrosis. As for the biosafety, researchers have developed biological circuits capable of actively responding to the needs of the patients to precisely and accurately release the demanded drug dose. Furthermore, the structure of the devices has been subject of study to adequately protect the encapsulated cells and prevent their spread in the body. The objective of this review is to describe the latest advances made by scientist to improve the efficacy and biosafety of cell microencapsulation systems for sustained drug delivery, also highlighting those points that still need to be optimized.

Induction of dormancy by confinement: An agarose-silica biomaterial for isolating and analyzing dormant cancer cells

The principal cause of cancer deaths is the residual disease, which eventually results in metastases. Certain metastases are induced by disseminated dormancy-capable single cancer cells that can reside within the body undetected for months to years. Awakening of the dormant cells starts a cascade resulting in the patient's demise. Despite its established clinical significance, dormancy research and its clinical translation have been hindered by lack of in vitro models that can identify, isolate, and analyze dormancy-capable cells. We have previously shown that immobilization of cells in a stiff microenvironment induces dormancy in dormancy-capable cell lines. In this communication, we present a novel biomaterial and an in vitro immobilization method to isolate, analyze, and efficiently recover dormancy-capable cancer cells. MCF-7, MDA-MB-231, and MDA-MB-468 cells were individually coated with agarose using a microfluidic flow-focusing device. Coated cells were then immobilized in a rigid and porous silica gel. Dormancy induction by this process was validated by decreased Ki-67 expression, increased p38/ERK activity ratio, and reduced expression of CDK-2, cyclins D1, and E1. We showed that we can reliably and repeatedly induce dormancy in dormancy-capable MCF-7 cells and enhance the dormancy-capable sub-population in MDA-MB-231 cells. As expected, dormancy-resistant MDA-MB-468 cells did not survive immobilization. The dormant cells could be awakened on demand, by digesting the agarose gel in situ, and efficiently recovered by magnetically separating the silica gel, making the cells available for downstream analysis and testing. The awakened cells were shown to regain motility immediately, proliferating, and migrating normally.

Fucoidan- and carrageenan-based biosynthetic poly(vinyl alcohol) hydrogels for controlled permeation

Since the permeation of the inflammatory cytokines into hydrogel scaffolds has been shown to cause dysfunction of encapsulated cells, appropriate design strategies to circumvent this are essential. In the present work, it was hypothesized that highly crosslinked PVA-fucoidan and PVA-carrageenan hydrogels can control permeation of the trefoil-shaped inflammatory cytokine IL-1β while allowing the permeation of the globular protein albumin. PVA, fucoidan, and carrageenans were functionalized with methacrylate groups and the functionalized polymers were co-crosslinked by UV photopolymerization. The resultant hydrogels were characterized physicochemically and the release of fucoidan and carrageenans was quantified by developing a colorimetric assay, which was validated by XPS analysis. The permeability characteristics of the hydrogels were evaluated using bovine serum albumin (BSA), IgG, and IL-1β. The results demonstrated an increase in hydrogel swelling through the incorporation of the polysaccharides with minimal overall mass loss. The release studies showed hydrogel stability, where the formulations exhibited ~43% retention of fucoidan and ~60-80% retention of carrageenans consistently up to 7 days. The permeation data revealed very low permeation of IgG and IL-1β through the hydrogels, with <1% permeation after 24 h, while allowing >6% permeation of BSA. These data indicate that such hydrogels can be used as the basis for cytokine-protective implantable devices for clinical applications.

A Versatile Microencapsulation Platform for Hyaluronic Acid and Polyethylene Glycol

Cell microencapsulation is a rapidly expanding field with broad potential for stem cell therapies and tissue engineering research. Traditional alginate microspheres suffer from poor biocompatibility, and microencapsulation of more advanced hydrogels is challenging due to their slower gelation rates. We have developed a novel, noncytotoxic, nonemulsion-based method to produce hydrogel microspheres compatible with a wide variety of materials, called core-shell spherification (CSS). Fabrication of microspheres by CSS derived from two slow-hardening hydrogels, hyaluronic acid (HA) and polyethylene glycol diacrylate (PEGDA), was characterized. HA microspheres were manufactured with two different crosslinking methods: thiolation and methacrylation. Microspheres of methacrylated HA (MeHA) had the greatest swelling ratio, the largest average diameter, and the lowest diffusion barrier. In contrast, PEGDA microspheres had the smallest diameters, the lowest swelling ratio, and the highest diffusion barrier, while microspheres of thiolated HA had characteristics that were in between the other two groups. To test the ability of the hydrogels to protect cells, while promoting function, diabetic NOD mice received intraperitoneal injections of PEGDA or MeHA microencapsulated canine islets. PEGDA microspheres reversed diabetes for the length of the study (up to 16 weeks). In contrast, islets encapsulated in MeHA microspheres at the same dose restored normoglycemia, but only transiently (3-4 weeks). Nonencapsulated canine islet transplanted at the same dose did not restore normoglycemia for any length of time. In conclusion, CSS provides a nontoxic microencapsulation procedure compatible with various hydrogel types.

Cell microencapsulation technologies for sustained drug delivery: Clinical trials and companies

In recent years, cell microencapsulation technology has advanced, mainly driven by recent developments in the use of stem cells or the optimization of biomaterials. Old challenges have been addressed from new perspectives, and systems developed and improved for decades are now being transferred to the market by novel start-ups and consolidated companies. These products are mainly intended for the treatment of diabetes mellitus (DM), but also cancer, central nervous system (CNS) disorders or lysosomal diseases, among others. In this review, we analyze the results obtained in clinical trials to date and define the global key players that will lead the cell microencapsulation market to bring this technology to the clinic in the future.

A Low-Cost Open Source Device for Cell Microencapsulation

Microencapsulation is a widely studied cell therapy and tissue bioengineering technique, since it is capable of creating an immune-privileged site, protecting encapsulated cells from the host immune system. Several polymers have been tested, but sodium alginate is in widespread use for cell encapsulation applications, due to its low toxicity and easy manipulation. Different cell encapsulation methods have been described in the literature using pressure differences or electrostatic changes with high cost commercial devices (about 30,000 US dollars). Herein, a low-cost device (about 100 US dollars) that can be created by commercial syringes or 3D printer devices has been developed. The capsules, whose diameter is around 500 µm and can decrease or increase according to the pressure applied to the system, is able to maintain cells viable and functional. The hydrogel porosity of the capsule indicates that the immune system is not capable of destroying host cells, demonstrating that new studies can be developed for cell therapy at low cost with microencapsulation production. This device may aid pre-clinical and clinical projects in low- and middle-income countries and is lined up with open source equipment devices.

Polymer microcapsules and microbeads as cell carriers for in vivo biomedical applications

Polymer microcarriers are being extensively explored as cell delivery vehicles in cell-based therapies and hybrid tissue and organ engineering. Spherical microcarriers are of particular interest due to easy fabrication and injectability. They include microbeads, composed of a porous matrix, and microcapsules, where matrix core is additionally covered with a semipermeable membrane. Microcarriers provide cell containment at implantation site and protect the cells from host immunoresponse, degradation and shear stress. Immobilized cells may be genetically altered to release a specific therapeutic product directly at the target site, eliminating side effects of systemic therapies. Cell microcarriers need to fulfil a number of extremely high standards regarding their biocompatibility, cytocompatibility, immunoisolating capacity, transport, mechanical and chemical properties. To obtain cell microcarriers of specified parameters, a wide variety of polymers, both natural and synthetic, and immobilization methods can be applied. Yet so far, only a few approaches based on cell-laden microcarriers have reached clinical trials. The main issue that still impedes progress of these systems towards clinical application is limited cell survival in vivo. Herein, we review polymer biomaterials and methods used for fabrication of cell microcarriers for in vivo biomedical applications. We describe their key limitations and modifications aiming at improvement of microcarrier in vivo performance. We also present the main applications of polymer cell microcarriers in regenerative medicine, pancreatic islet and hepatocyte transplantation and in the treatment of cancer. Lastly, we outline the main challenges in cell microimmobilization for biomedical purposes, the strategies to overcome these issues and potential future improvements in this area.

Emergence of nanomaterials as potential immobilization supports for whole cell biocatalysts and cell toxicity effects

The traditional approach of fermentation by a free cell system has limitations of low productivity and product separation that need to be addressed for production enhancement and cost effectiveness. One of potential methods to solve the problems is cell immobilization. Microbial cell immobilization allows more efficient up-scaling by reducing the nonproductive growth phase, improving product yield and simplifying product separation. Furthermore, the emergence of nanomaterials such as carbon nanotubes, graphene, and metal-based nanomaterials with excellent functional properties provides novel supports for cell immobilization. Nanomaterials have catalytic properties that can provide specific binding site with targeted cells. However, the toxicity of nanomaterials towards cells has hampered its application as it affects the biological system of the cells, which cannot be neglected in any way. This gray area in immobilization is an important concern that needs to be addressed and understood by researchers. This review paper discusses an overview of nanomaterials used for cell immobilization with special focus on its toxicological challenges and how by understanding physicochemical properties of nanomaterials could influence the toxicity and biocompatibility of the cells.

Synthetic ECM: Bioactive Synthetic Hydrogels for 3D Tissue Engineering

The specific microenvironment that cells reside in fundamentally impacts their broader function in tissues and organs. At its core, this microenvironment is composed of precise arrangements of cells that encourage homotypic and heterotypic cell-cell interactions, biochemical signaling through soluble factors like cytokines, hormones, and autocrine, endocrine, or paracrine secretions, and the local extracellular matrix (ECM) that provides physical support and mechanobiological stimuli, and further regulates biochemical signaling through cell-ECM interactions like adhesions and growth factor sequestering. Each cue provided in the microenvironment dictates cellular behavior and, thus, overall potential to perform tissue and organ specific function. It follows that in order to recapitulate physiological cell responses and develop constructs capable of replacing damaged tissue, we must engineer the cellular microenvironment very carefully. Many great strides have been made toward this goal using various three-dimensional (3D) tissue culture scaffolds and specific media conditions. Among the various 3D biomimetic scaffolds, synthetic hydrogels have emerged as a highly tunable and tissue-like biomaterial well-suited for implantable tissue-engineered constructs. Because many synthetic hydrogel materials are inherently bioinert, they minimize unintentional cell responses and thus are good candidates for long-term implantable grafts, patches, and organs. This review will provide an overview of commonly used biomaterials for forming synthetic hydrogels for tissue engineering applications and techniques for modifying them to with bioactive properties to elicit the desired cell responses.

Tissue-engineered parathyroid gland and its regulatory secretion of parathyroid hormone

Parathyroid glands (PTGs) are important endocrine organs being mainly responsible for the secretion of parathyroid hormone (PTH) to regulate the balance of calcium (Ca) /phosphorus (P) ions in the body. Once PTGs get injured or removed, their resulting defect or loss of PTH secretion should disturb the level of Ca/P in blood, thus damaging other related organs (bone, kidney, etc.) and even causing death. Recently, tissue-engineered PTGs (TE-PTGs) have attracted lots of attention as a potential treatment for the related diseases of PTGs caused by hypoparathyroidism and hyperparathyroidism, including tetany, muscle cramp, nephrolithiasis, nephrocalcinosis, and osteoporosis. Although great progress has been made in the establishment of TE-PTGs with an effective strategy to integrate the key factors of cells and biomaterials, its regulatory secretion of PTH to mimic its natural rhythms in the body remains a huge challenge. This review comprehensively describes an overview of PTGs from physiology and pathology to cytobiology and tissue engineering. The state of the arts in TE-PTGs and the feasible strategies to regulate PTH secretion behaviors are highlighted to provide an important foundation for further investigation.

Oligomeric collagen as an encapsulation material for islet/β-cell replacement: effect of islet source, dose, implant site, and administration format

Replacement of islets/β-cells that provide long-lasting glucose-sensing and insulin-releasing functions has the potential to restore extended glycemic control in individuals with type 1 diabetes. Unfortunately, persistent challenges preclude such therapies from widespread clinical use, including cumbersome administration via portal vein infusion, significant loss of functional islet mass upon administration, limited functional longevity, and requirement for systemic immunosuppression. Previously, fibril-forming type I collagen (oligomer) was shown to support subcutaneous injection and in situ encapsulation of syngeneic islets within diabetic mice, with rapid (<24 h) reversal of hyperglycemia and maintenance of euglycemia for beyond 90 days. Here, we further evaluated this macroencapsulation strategy, defining effects of islet source (allogeneic and xenogeneic) and dose (500 and 800 islets), injection microenvironment (subcutaneous and intraperitoneal), and macrocapsule format (injectable and preformed implantable) on islet functional longevity and recipient immune response. We found that xenogeneic rat islets functioned similarly to or better than allogeneic mouse islets, with only modest improvements in longevity noted with dosage. Additionally, subcutaneous injection led to more consistent encapsulation outcomes along with improved islet health and longevity, compared with intraperitoneal administration, whereas no significant differences were observed between subcutaneous injectable and preformed implantable formats. Collectively, these results document the benefits of incorporating natural collagen for islet/β-cell replacement therapies.

100th Anniversary of Macromolecular Science Viewpoint: Re-Engineering Cellular Interfaces with Synthetic Macromolecules Using Metabolic Glycan Labeling

Cell-surface functionality is largely programmed by genetically encoded information through modulation of protein expression levels, including glycosylation enzymes. Genetic tools enable control over protein-based functionality, but are not easily adapted to recruit non-native functionality such as synthetic polymers and nanomaterials to tune biological responses and attach therapeutic or imaging payloads. Similar to how polymer-protein conjugation evolved from nonspecific PEGylation to site-selective bioconjugates, the same evolution is now occurring for polymer-cell conjugation. This Viewpoint discusses the potential of using metabolic glycan labeling to install bio-orthogonal reactive cell-surface anchors for the recruitment of synthetic polymers and nanomaterials to cell surfaces, exploring the expanding therapeutic and diagnostic potential. Comparisons to conventional approaches that target endogenous membrane components, such as hydrophobic, protein coupling and electrostatic conjugation, as well as enzymatic and genetic tools, have been made to highlight the huge potential of this approach in the emerging cellular engineering field.

Nanopolyphenols: a review of their encapsulation and anti-diabetic effects

Polyphenols are believed to possess numerous health benefits and can be grouped as phenolic acids, flavonoids or non-flavonoids. Research involving the synthesis of nanopolyphenols has attracted interest in the areas of functional food, nutraceutical and pharmaceutical development. This is in an effort to overcome current challenges which limit the application of polyphenols such as their rapid elimination, low water-solubility, instability at low pH, and their particle size. In the synthesis of nanopolyphenols, the type of nanocarrier used, the nanoencapsulation technique employed and the type of polymers that constitute the drug delivery system are crucial. For this review, all mentioned factors which can influence the therapeutic efficacy of nanopolyphenols were assessed. Their efficacy as anti-diabetic agents was also evaluated in 33 publications. Among these were phenolic acid (1), flavonoids (13), non-flavonoids (17) and polyphenol-rich extracts (2). The most researched polyphenols were quercetin and curcumin. Nanoparticles were the main nanocarrier and the size of the nanopolyphenols ranged from 15 to 333 nm with encapsulation efficiency and drug loading capacities of 56–97.7% and 4.2–53.2%, respectively. The quantity of nanomaterial administered orally ranged from 1 to 300 mg/kg/day with study durations of 1–70 days. Most studies compared the effect of the nanopolyphenol to its free-form and, in all but three cases, significantly greater effects of the former were reported. Assessment of the polyphenol to understand its properties and the subsequent synthesis of its nanoencapsulated form using suitable nanocarriers, polymers and encapsulation techniques can result in effective therapeutic agents for the treatment of diabetes.

In vitro platform establishes antigen-specific CD8+ T cell cytotoxicity to encapsulated cells via indirect antigen recognition

The curative potential of non-autologous cellular therapy is hindered by the requirement of anti-rejection therapy. Cellular encapsulation within nondegradable biomaterials has the potential to inhibit immune rejection, but the efficacy of this approach in robust preclinical and clinical models remains poor. While the responses of innate immune cells to the encapsulating material have been characterized, little attention has been paid to the contributions of adaptive immunity in encapsulated graft destabilization. Avoiding the limitations of animal models, we established an efficient, antigen-specific in vitro platform capable of delineating direct and indirect host T cell recognition to microencapsulated cellular grafts and evaluated their consequential impacts. Using ovalbumin (OVA) as a model antigen, we determined that alginate microencapsulation abrogates direct CD8⁺ T cell activation by interrupting donor-host interaction; however, indirect T cell activation, mediated by host antigen presenting cells (APCs) primed with shed donor antigens, still occurs. These activated T cells imparted cytotoxicity on the encapsulated cells, likely via diffusion of cytotoxic solutes. Overall, this platform delivers unique mechanistic insight into the impacts of hydrogel encapsulation on host adaptive immune responses, comprehensively addressing a long-standing hypothesis of the field. Furthermore, it provides an efficient benchtop screening tool for the investigation of new encapsulation methods and/or synergistic immunomodulatory agents.

Biomaterials for Personalized Cell Therapy

Cell therapy has already had an important impact on healthcare and provided new treatments for previously intractable diseases. Notable examples include mesenchymal stem cells for tissue regeneration, islet transplantation for diabetes treatment, and T cell delivery for cancer immunotherapy. Biomaterials have the potential to extend the therapeutic impact of cell therapies by serving as carriers that provide 3D organization and support cell viability and function. With the growing emphasis on personalized medicine, cell therapies hold great potential for their ability to sense and respond to the biology of an individual patient. These therapies can be further personalized through the use of patient-specific cells or with precision biomaterials to guide cellular activity in response to the needs of each patient. Here, the role of biomaterials for applications in tissue regeneration, therapeutic protein delivery, and cancer immunotherapy is reviewed, with a focus on progress in engineering material properties and functionalities for personalized cell therapies.

Novel therapeutic approaches of tissue engineering in male infertility

Male reproductive organ plays an important role in sperm production, maintenance and entry to the female reproductive tract, as well as generation and secretion of male sex hormones responsible for the health of male reproductive system. The purpose of this paper is to discuss the experimental and clinical evidence on the utilization of tissue engineering techniques in treating male infertility. Tissue engineering (TE) and regenerative medicine have developed new approaches to treat patients with reproductive disorders such as iatrogenic injuries, congenital abnormalities, and trauma. In some cases, including congenital defects and undescended testis or hypogonadism, the sperm samples are not retrieved. This makes TE a possible future strategy for restoration of male fertility. Here, we have summarized the recent advances in experimental and clinical application of cell-, tissue-, and organ-based regenerative medicine in male reproductive disorders.

Clinical Applications of Cell Encapsulation Technology

Cell encapsulation comprises immunoisolation three-dimensional systems for housing therapeutic cells that secrete bioactive compounds de novo and in a sustained manner. This allows transplantation of multiple allo- or xenogeneic cells without the aid of immunosuppressant drugs. Recent advances in the field have provided improvements to these cell-based drug delivery systems, which have gained the attention of the scientific community and inspired many biotechnological companies to develop their own product candidates. From micro- to macroencapsulation devices, this chapter describes some of the most important approaches that are being currently tested in late-stage clinical trials and are likely to reach the market as future game changers. Most studies involve the treatment of diabetes, eye disorders, and diseases of the central nervous system. However, many other pathologies are also amenable to benefit from this technology. Latest advances to overcome major pending challenges related to biosafety and efficacy are also discussed.

Bioactive nanoparticle embedded microcapsules for improving the efficacy of type I diabetes therapy

In order to overcome the side effects of pancreatic transplantation and insulin injection treatment for type I diabetes, we established a drug delivery system employing nanoparticle embedded microcapsules (NEMs). The system co-encapsulated chitosan nanoparticles with γ-aminobutyric acid and β-TC-6 cells for combined drug and cell therapy in diabetes mellitus (DM). The NEMs, which were formed via high-voltage electrostatic method, had an excellent sphericity with a smooth surface. The average size NEM was 245.52 ± 22.00 μm, which indicated a good size for cell encapsulation. Haemolysis rate of NEMs at concentrations of 100, 200 or 300 mg/mL were all below 5%. Relative viability rates of L929 cells with the same concentrations at 24, 48 or 72 h were all above 80%. We implanted bioactive NEMs into type 1 DM mice to evaluate the effect of the combined therapy. The level of blood glucose in the group receiving the combined therapy decreased during the first 2 weeks of treatment. During the next week, the level of blood glucose stayed in a safe range. Body weight continuously increased during the postoperative period after combined therapy group. Oral glucose tolerance test (OGTT) performed after 24 d showed that the level of blood glucose combined therapy reached the maximum peak of 13.04 mmol/L, lower than 16.56 mmol/L for the cell therapy group. This primary study indicated that microencapsulation technology and combined therapy are promising for the treatment of type I diabetes mellitus.

Polymeric Approaches to Reduce Tissue Responses Against Devices Applied for Islet-Cell Encapsulation

Immunoisolation of pancreatic islets is a technology in which islets are encapsulated in semipermeable but immunoprotective polymeric membranes. The technology allows for successful transplantation of insulin-producing cells in the absence of immunosuppression. Different approaches of immunoisolation are currently under development. These approaches involve intravascular devices that are connected to the bloodstream and extravascular devices that can be distinguished in micro- and macrocapsules and are usually implanted in the peritoneal cavity or under the skin. The technology has been subject of intense fundamental research in the past decade. It has co-evolved with novel replenishable cell sources for cure of diseases such as Type 1 Diabetes Mellitus that need to be protected for the host immune system. Although the devices have shown significant success in animal models and even in human safety studies most technologies still suffer from undesired tissue responses in the host. Here we review the past and current approaches to modulate and reduce tissue responses against extravascular cell-containing micro- and macrocapsules with a focus on rational choices for polymer (combinations). Choices for polymers but also choices for crosslinking agents that induce more stable and biocompatible capsules are discussed. Combining beneficial properties of molecules in diblock polymers or application of these molecules or other anti-biofouling molecules have been reviewed. Emerging are also the principles of polymer brushes that prevent protein and cell-adhesion. Recently also immunomodulating biomaterials that bind to specific immune receptors have entered the field. Several natural and synthetic polymers and even combinations of these polymers have demonstrated significant improvement in outcomes of encapsulated grafts. Adequate polymeric surface properties have been shown to be essential but how the surface should be composed to avoid host responses remains to be identified. Current insight is that optimal biocompatible devices can be created which raises optimism that immunoisolating devices can be created that allows for long term survival of encapsulated replenishable insulin-producing cell sources for treatment of Type 1 Diabetes Mellitus.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.