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In orchestrating the wound healing process, the immune system plays a critical role. Hence, controlling the immune system to repair skin defects is an attractive approach. The highly complex immune system includes the coordinated actions of several immune cells, which can produce various inflammatory and antiinflammatory cytokines and affect the healing of skin wounds. This process can be optimized using biomaterials, bioactive molecules, and cell delivery. The present review discusses various immunomodulation strategies for supporting the healing of chronic wounds. In this regard, following the evolution of the immune system and its role in the wound healing mechanism, the interaction between the extracellular mechanism and immune cells for acceleration wound healing will be firstly investigated. Consequently, the immune-based chronic wounds will be briefly examined and the mechanism of progression, and conventional methods of their treatment are evaluated. In the following, various biomaterials-based immunomodulation strategies are introduced to stimulate and control the immune system to treat and regenerate skin defects. Other effective methods of controlling the immune system in wound healing which is the release of bioactive agents (such as antiinflammatory, antigens, and immunomodulators) and stem cell therapy at the site of injury are reviewed.

The California Institute for Regenerative Medicine (CIRM) has a mission to accelerate stem cell treatments to patients with unmet medical needs. This perspective describes successful examples of work funded by CIRM's New Cell Lines and Tools and Technologies Initiatives, which were developed to address bottlenecks to stem cell research and translation. The tools developed through these programs evolved from more discovery‐oriented technologies, such as disease models, differentiation processes, and assays, to more translation focused tools, including scalable good manufacturing processes, animal models, and tools for clinical cell delivery. These tools are available to the research community and many are facilitating translation of regenerative therapeutics today., Focused efforts to develop novel tools and technologies have advanced regenerative medicine from discovery to development. Key CIRM investments have included methods to scale up and manufacture stem cells and differentiated derivatives in xeno‐free conditions; novel disease and preclinical models; tools for safe and efficacious delivery of cell therapies; and new methods to engineer and deliver genes for therapeutic applications.

Self-healing injectable hydrogel biomaterials uniquely enable precise therapeutic deposition and deployment at specific bodily locations through versatile and minimally invasive processes that can preserve cargo integrity and cell viability. Despite the distinct advantages that injectable hydrogels offer in tissue engineering and therapeutic delivery, exceptionally few have been created using components naturally present in the cellular niche. In this work, we introduce a shear-thinning hydrogel based on guest-host complexation of gelatin. As a biocompatible, biodegradable, and non-immunogenic biopolymer derived from the most abundant extracellular matrix protein (collagen), gelatin offers great utility as the structural component of biomaterials. Taking advantage of reversible guest-host interactions between β-cyclodextrin (CD) and adamantane (AD) on modified gelatins, we report the first strategy to afford a self-healing material based solely on a functionalized extracellular matrix (ECM) protein. By varying the initial material formulation, hydrogels were synthesized with variable moduli and shear-thinability across a broad range. Gels were demonstrated to exhibit shear-thinning and self-healing properties, supporting protection of clinically relevant stem-cell-derived cardiomyocytes during injection. These materials are expected to expand clinical opportunities in cell delivery for in vivo tissue regeneration.

Neural precursor/stem cell transplantation therapies promote regeneration in neurological injuries, but current cell delivery methods have drawbacks. These include risks with surgical microinjection (e.g., hemorrhage, embolism) and high cell loss with systemic delivery/passage through fine gauge needles. Aerosolized cell delivery offers significant benefits including rapid and minimally invasive cell delivery, and ease of delivery to end users. To develop this approach, it is necessary to prove that 1) aerosolization does not have detrimental effects on transplant cells and 2) suitable media can be identified to support cell delivery. To achieve these aims, cells are sprayed using a commercial spray device or stored in Hibernate‐A, a CO2‐independent nutrient solution. Histological assessments consist of cell viability analysis, immunocytochemistry, and EdU labeling. It is shown that a major neural precursor transplant population—oligodendrocyte precursor cells (OPCs)—survive following aerosolized delivery and retain their capacity for proliferation and differentiation (key to their repair function). Hibernate‐A can support OPCs’ survival without specialized maintenance conditions, with no detrimental impact on cell fate. It is considered that this data supports the concept of a novel class of advanced medical spray devices to facilitate transport and delivery of transplant populations in neural cell therapy.

Soft organisms such as earthworms can access confined, narrow spaces, inspiring scientists to fabricate soft robots for in vivo manipulation of cells or tissues and minimally invasive surgery. We report a super-soft and super-elastic magnetic DNA hydrogel-based soft robot (DNA robot), which presents a shape-adaptive property and enables magnetically driven navigational locomotion in confined and unstructured space. The DNA hydrogel is designed with a combinational dynamic and permanent crosslinking network through chain entanglement and DNA hybridization, resulting in shear-thinning and cyclic strain properties. DNA robot completes a series of complex magnetically driven navigational locomotion such as passing through narrow channels and pipes, entering grooves and itinerating in a maze by adapting and recovering its shape. DNA robot successfully works as a vehicle to deliver cells in confined space by virtue of the 3D porous networked structure and great biocompatibility.

Chemical protein synthesis and biorthogonal modification chemistries allow production of unique proteins for a range of biological studies. Bond-forming reactions for site-selective protein labeling are commonly used in these endeavors. Selective bond-cleavage reactions, however, are much less explored and still pose a great challenge. In addition, most of studies with modified proteins prepared by either total synthesis or semisynthesis have been applied mainly for in vitro experiments with very limited extension to live cells. Reported here is an approach for studying uniquely modified proteins containing a traceless cell delivery unit and palladium-based cleavable element for chemical activation, and monitoring the effect of these proteins in live cells. This approach is demonstrated for the synthesis of a caged ubiquitin-aldehyde, which was decaged for the inhibition of deubiquitinases in live cells.

Live-cell labeling, super-resolution microscopy, single-molecule applications, protein localization, or chemically induced assembly are emerging approaches, which require specific and very small interaction pairs. The minimal disturbance of protein function is essential to derive unbiased insights into cellular processes. Herein, we define a new class of hexavalent N-nitrilotriacetic acid (hexaNTA) chelators, displaying the highest affinity and stability of all NTA-based small interaction pairs described so far. Coupled to bright organic fluorophores with fine-tuned photophysical properties, the super-chelator probes were delivered into human cells by chemically gated nanopores. These super-chelators permit kinetic profiling, multiplexed labeling of His6 - and His12 -tagged proteins as well as single-molecule-based super-resolution imaging.

Stem cell therapies have emerged as promising treatments for injuries and diseases in regenerative medicine. Yet, delivering stem cells therapeutically can be complicated by invasive administration techniques, heterogeneity in the injection media, and/or poor cell retention at the injection site. Despite these issues, traditional administration protocols using bolus injections in a saline solution or surgical implants of cell‐laden hydrogels have highlighted the promise of cell administration as a treatment strategy. To address these limitations, we have designed an injectable polymer–nanoparticle (PNP) hydrogel platform exploiting multivalent, noncovalent interactions between modified biopolymers and biodegradable nanoparticles for encapsulation and delivery of human mesenchymal stem cells (hMSCs). hMSC‐based therapies have shown promise due to their broad differentiation capacities and production of therapeutic paracrine signaling molecules. In this work, the fundamental hydrogel mechanical properties that enhance hMSC delivery processes are elucidated using basic in vitro models. Further, in vivo studies in immunocompetent mice reveal that PNP hydrogels enhance hMSC retention at the injection site and retain administered hMSCs locally for upwards of 2 weeks. Through both in vitro and in vivo experiments, we demonstrate a novel scalable, synthetic, and biodegradable hydrogel system that overcomes current limitations and enables effective cell delivery.

Microrobots with simultaneously improved degradability and mechanical strength are highly demanded in performing in vivo delivery tasks in clinical applications. The properties of degradability and mechanical strength are contradictory for many materials used to make microrobots. This article proposes a new design that can result in 3D cell culture microrobots with improved degradability and mechanical strength from the following perspectives. First, the mechanical strength of a microrobot is improved using triangle patterns to replace hexagon pattern in the microrobot structure, which can provide more supporting grids to obtain increased mechanical strength. Second, the relationship between structural design and material composition in relation to the mechanical strength of microrobot is investigated. The study reveals that triangle‐patterned microrobots have increased mechanical strength compared with hexagon‐patterned microrobots, thereby allowing high composition of degradable material that leads to the fast degradation of the microrobot. It is also shown that the triangle‐patterned microrobots can maintain the same structural integrity and cell capacity as hexagon‐patterned microrobots. Finally, the demonstration shows that the triangle‐patterned microrobot can be precisely navigated in microfluidic channels. This article successfully demonstrates that the degradability and mechanical strength can be improved simultaneously through the microrobot structural design.

For many cellular therapies being evaluated in preclinical and clinical trials, the mechanisms behind their therapeutic effects appear to be the secretion of growth factors and cytokines, also known as paracrine activity. Often, delivered cells are transient, and half-lives of the growth factors that they secrete are short, limiting their long-term effectiveness. The goal of this study was to optimize a hydrogel system capable of in situ cell delivery that could sequester and release growth factors secreted from those cells after the cells were no longer present. Here, we demonstrate the use of a fast photocross-linkable heparin-conjugated hyaluronic acid (HA-HP) hydrogel as a cell delivery vehicle for sustained growth factor release, which extends paracrine activity. The hydrogel could be modulated through cross-linking geometries and heparinization to support sustained release proteins and heparin-binding growth factors. To test the hydrogel in vivo, we used it to deliver amniotic fluid-derived stem (AFS) cells, which are known to secrete cytokines and growth factors, in full thickness skin wounds in a nu/nu murine model. Despite transience of the AFS cells in vivo, the HA-HP hydrogel with AFS cells improved wound closure and reepithelialization and increased vascularization and production of extracellular matrix in vivo. These results suggest that HA-HP hydrogel has the potential to prolong the paracrine activity of cells, thereby increasing their therapeutic effectiveness in wound healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1986-2000, 2017.

Hydrogels with adhesive properties have potential for numerous biomedical applications. Here, the design of a novel, intrinsically adhesive hydrogel and its use in developing internal therapeutic bandages is reported. The design involves incorporation of "triple hydrogen bonding clusters" (THBCs) as side groups into the hydrogel matrix. The THBC through a unique "load sharing" effect and an increase in bond density results in strong adhesions of the hydrogel to a range of surfaces, including glass, plastic, wood, poly(tetrafluoroethylene) (PTFE), stainless steel, and biological tissues, even without any chemical reaction. Using the adhesive hydrogel, tissue-adhesive bandages are developed for either targeted and sustained release of chemotherapeutic nanodrug for liver cancer treatment, or anchored delivery of pancreatic islets for a potential type 1 diabetes (T1D) cell replacement therapy. Stable adhesion of the bandage inside the body enables almost complete tumor suppression in an orthotopic liver cancer mouse model and ≈1 month diabetes correction in chemically induced diabetic mice.

Background Translation of cell therapies to the clinic is accompanied by numerous challenges, including controlled and targeted delivery of the cells to their site of action, without compromising cell viability and functionality. Objectives To explore the use of hollow microneedle devices (to date only used for the delivery of drugs and vaccines into the skin and for the extraction of biological fluids) to deliver cells into skin in a minimally-invasive, user-friendly and targeted fashion. Methods Melanocyte, keratinocyte and mixed epidermal cell suspensions were passed through various types of microneedles and subsequently delivered into the skin. Results Cell viability and functionality is maintained after injection through hollow microneedles with a bore size ≥75 μm. Healthy cells are delivered into skin at clinically relevant depths. Conclusions Hollow microneedles provide an innovative and minimally-invasive method for delivering functional cells into the skin. Microneedle cell delivery represents a potential new treatment option for cell therapy approaches including skin re-pigmentation, wound repair, scar and burn remodelling, immune therapies, and cancer vaccines.

Cell replacement therapy is emerging as a promising treatment platform for many endocrine disorders and hormone deficiency diseases. The survival of cells within delivery devices is, however, often limited due to low oxygen levels in common transplantation sites. Additionally, replacing implanted devices at the end of the graft lifetime is often infeasible and, if possible, generally requires invasive surgical procedures. This report presents the design and testing of a modular transcutaneous biphasic cell delivery device which provides enhanced and unlimited oxygen supply by direct contact with the atmosphere. Critically, the cell delivery unit was demountable from the fixed components of the device, allowing for surgery-free refilling of the therapeutic cells. Mass transfer studies showed significantly improved performance of the biphasic device in comparison to subcutaneous controls. The device was also tested for islet encapsulation in an immunocompetent diabetes rodent model. Robust cell survival and diabetes correction was observed following a rat-to-mouse xenograft. Lastly, non-surgical cell refilling was demonstrated in dogs. These studies show the feasibility of this novel device for cell replacement therapies

The confluence of protein engineering techniques and delivery protocols are providing new opportunities in cell biology. In particular, techniques that render the membrane of cells transiently permeable make the introduction of nongenetically encodable macromolecular probes into cells possible. This, in turn, can enable the monitoring of intracellular processes in ways that can be both precise and quantitative, ushering an area that one may envision as cellular biochemistry. Herein, the author reviews pioneering examples of such new cell-based assays, provides evidence that challenges the paradigm that cell penetration is a necessarily damaging and stressful event for cells, and highlights some of the challenges that should be addressed to fully unlock the potential of this nascent field.

Complex 3D artificial tissue constructs are extensively investigated for tissue regeneration. Frequently, materials and cells are delivered separately without benefitting from the synergistic effect of combined administration. Cell delivery inside a material construct provides the cells with a supportive environment by presenting biochemical, mechanical, and structural signals to direct cell behavior. Conversely, the cell/material interaction is poorly understood at the micron scale and new systems are required to investigate the effect of micron-scale features on cell functionality. Consequently, cells are encapsulated in microgels to avoid diffusion limitations of nutrients and waste and facilitate analysis techniques of single or collective cells. However, up to now, the production of soft cell-loaded microgels by microfluidics is limited to spherical microgels. Here, a novel method is presented to produce monodisperse, anisometric poly(ethylene) glycol microgels to study cells inside an anisometric architecture. These microgels can potentially direct cell growth and can be injected as rod-shaped mini-tissues that further assemble into organized macroscopic and macroporous structures post-injection. Their aspect ratios are adjusted with flow parameters, while mechanical and biochemical properties are altered by modifying the precursors. Encapsulated primary fibroblasts are viable and spread and migrate across the 3D microgel structure.

Multifunctional nanomaterials with simultaneous therapeutic and imaging functions explore new strategies for the treatment of various diseases. Conjugated polymers (CPs) are considered as novel candidates to serve as multifunctional delivery systems due to their high fluorescence quantum yield, good photostability, and low cytotoxicity. Highly sensitive sensing and imaging properties of CPs are well reviewed, while the applications of CPs as delivery systems are rarely covered. This feature article mainly focuses on CP-based multifunctional non-viral delivery systems for drug, protein, gene, and cell delivery. Promising directions for the further development of CP-based delivery systems are also discussed.

The broad aim underlying the present research was to investigate the distribution and homing of bone marrow-derived macrophages in a rodent model of transient middle cerebral artery occlusion using MRI and ultrasmall superparamagnetic iron oxide (USPIO) to magnetically label bone marrow-derived macrophages. The specific aim was to assess the intra-carotid infusion route for bone marrow-derived macrophage delivery at reperfusion. Fifteen Sprague–Dawley rats sustained 1 h of middle cerebral artery occlusion. USPIO-labeled bone marrow-derived macrophages were slowly injected for 5 min immediately after reperfusion in ischemic animals (n = 7), 1 h after the end of surgery in sham animals (n = 5) and very shortly after anesthesia in healthy animals (n = 3). Multiparametric MRI was performed at day 0, just after cell administration, and repeated at day 1. Immunohistological analysis included Prussian blue for iron detection and rat endothelial cell antigen-1 for endothelium visualization. Intra-carotid cell delivery brought a large number of cells to the ipsilateral hemisphere of the brain, as seen on both MRI and immunohistology. However, it was associated with high mortality (50%). The study of sham animals demonstrated that intra-carotid cell delivery could induce ischemic lesions and may thus favor additional brain damage. The present study highlights severe drawbacks to the intra-carotid delivery of macrophages at the time of reperfusion in this rodent model of transient cerebral ischemia. Multiparametric MRI appears to be a method of choice to monitor longitudinally the effects of cell infusion, allowing the assessment of both cell fate with the help of magnetic labeling and of potential tissue damage. Copyright © 2012 John Wiley & Sons, Ltd.

Background: Recent studies have indicated that bone marrow stromal cells (BMSC) may improve neurological function when transplanted into animal model of central nervous system (CNS) disorders including cerebral infarct. However, there are few studies that evaluate the therapeutic benefits of direct and intravenous BMSC transplantation for cerebral infarct. Objective: This study was aimed to clarify the favorable route of cell delivery for cerebral infarct in rats. Methods: The rats were subjected to permanent middle cerebral artery occlusion. The BMSC were labeled with near infrared (NIR)-emitting quantum dots, and were transplanted directly (1×10^7 cells) or intravenously (3×10^7 cells) at 7 days after the insult. Using in vivo NIR fluorescence imaging technique, the behaviors of BMSC were serially visualized during 4 weeks after transplantation. Motor function was also assessed. Immunohistochemistry was performed to evaluate the fate of the engrafted BMSC. Results: Direct, but not intravenous, transplantation of BMSC significantly enhanced functional recovery. In vivo NIR fluorescence imaging could clearly visualize their migration towards cerebral infarct during 4 weeks after transplantation in direct group, but not in intravenous, group. The BMSC were widely distributed in the ischemic brain and some of them expressed neural cell markers in the direct group, but not in the intravenous group. Conclusion: These findings strongly suggest that intravenous administration of BMSC has limited effectiveness at clinically relevant timing and direct administration should be chosen for patients with ischemic stroke, although further studies would be warranted to establish the treatment protocol.

Knowledge of immunity enables us to predict that the reactions set in response to infection with helminth would prevent concomitant disease driven by an opposing spectrum of immune events. In another way, the immune response generated to combat the helminth infection could counteract the immunopathological reactions that drive autoimmune diseases. Rodent model systems recapitulate many aspects of human autoimmune diseases and have been enormously useful in defining mechanisms of immunopathology after infection. From this theoretical perspective, many researchers have proved that infection with a variety of helminth can ameliorate disease in murine model systems. Thus, helminth-evoked Th2 events were shown to improve disorders in which Th1 events predominated. This raised the question, 'Can this information be translated into therapies for autoimmune diseases in humans via actual infection, cell delivery or drug intervention?' In this review, we will present some experimental trails to treat autoimmune disorders through establishment of some parasitic infections.

We developed a method to produce discrete fibrin microthreads, which can be seeded with human mesenchymal stem cells (hMSCs) and used as a suture to enhance the efficiency and localization of cell delivery. To assess the efficacy of fibrin microthreads to support hMSC attachment, proliferation, and survival, microthreads (100 μm diameter per microthread) were bundled together, seeded with 50,000 hMSCs for 2 h, and cultured for 5 days. Cell density on microthread bundles increased over time in culture to a maximum average density of 731 ± 101 cells/mm2 after 5 days. A LIVE/DEAD assay confirmed that the cells were viable, and Ki-67 staining verified hMSC proliferation. In addition, functional differentiation assays demonstrated that hMSCs cultured on microthreads retained their ability to differentiate into adipocytes and osteocytes. The results of this study demonstrate that fibrin microthreads support hMSC viability and proliferation, while maintaining their multipotency. We anticipate that these cell-seeded fibrin microthreads will serve as a platform technology to improve localized delivery and engraftment of viable cells to damaged tissue. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2011.

Conventional wound therapy utilizes wound coverage to prevent infection, trauma, and fluid and thermal loss. However, this approach is often inadequate for large and/or chronic wounds, which require active intervention via therapeutic cells to promote healing. To address this need, a patch which delivers multipotent adult progenitor cells (MAPCs) is developed. Medical-grade polyurethane (PU) films are modified using plasma immersion ion implantation (PIII), which creates a radical-rich layer capable of rapidly and covalently attaching biomolecules. It is demonstrated that a short treatment duration of 400 s maximizes surface activation and wettability, minimizes reduction in gas permeability, and preserves the hydrolytic resistance of the PU film. The reactivity of PIII-treated PU is utilized to immobilize the extracellular matrix protein tropoelastin in a functional conformation that stably withstands medical-grade ethylene oxide sterilization. The PIII-treated tropoelastin-functionalized patch significantly promotes MAPC adhesion and proliferation over standard PU, while fully maintaining cell phenotype. Topical application of the MAPC-seeded patch transfers cells to a human skin model, while undelivered MAPCs repopulate the patch surface for subsequent cell transfer. The potential of this new wound patch as a reservoir for the sustained delivery of therapeutic MAPCs and cell-secreted factors for large and/or non-healing wounds is indicated in the findings. Refereed/Peer-reviewed

A capsule-type microrobot exhibits "pick-and-drop" (P&D) motion to hold a particle within a confined volume and transports it via a corkscrewing motion. The P&D motion is possible because the capsule-type microrobot has two parts: a plunger and a cap. The fabricated microrobots are wirelessly controlled by a magnetic manipulator. Drugs or cells can be encapsulated in the container of the capsule-type microrobot by the P&D motion or attached to the surface of the cap, which can be used as a supporting structure. Therefore, the capsule-type microrobot can deliver suspended or adherent cells. The drug or cells are minimally exposed or not completely exposed to the surrounding fluid and do not experience shear force when encapsulated in the container. As a proof-of-concept, secure transportation of microparticles in the confined volume of the capsule via P&D motion is demonstrated. In addition, the cap is used as a scaffold for neuronal cell culture on a rat brain slice to demonstrate its biocompatibility and feasibility for targeted cell delivery. The proposed capsule-type microrobot is suitable for diverse applications, as it protects the encapsulated materials.

Objective: The purpose of this study was to quantify the mass transport capabilities of implanted scaffolds for in vivo diagnostics, therapeutics, and cell delivery. We utilized matrix morphology t...

The objective of this study was to test the hypothesis that bovine dermal fibroblasts can survive aerosol delivery via an airbrush with mean cell survival rates greater than 50%. This technology has great implications for burn and other wound therapies, for delivery of genetically altered cells in gene therapies, and for tissue engineering with tissue scaffolds. Bovine dermal fibroblasts were suspended at a concentration of 200,000 cells/mL in Hank's Balanced Salt Solution, and delivered into six-well tissue culture plates using a Badger 100G airbrush. Cells were delivered through three nozzle diameters (312, 484, and 746 microm) at five different air pressures (41, 55, 69, 96, and 124 kPa). Nine repetitions were performed for each treatment group, and cell viability was measured using trypan blue exclusion assay. Mean cell viability ranged from 37 to 94%, and depended on the combination of nozzle diameter and delivery pressure (p < 0.0001). Linear regression analysis was used to develop a stochastic model of cell delivery viability as a function of nozzle diameter and delivery air pressure. This study demonstrates the feasibility of using an airbrush to deliver viable cells in an aerosol to a substrate.

Biomaterials are key factors in regenerative medicine. Matrices used for cell delivery are especially important, as they provide support to transplanted cells that is essential for promoting cell survival, retention, and desirable phenotypes. Injectable matrices have become promising and attractive due to their minimum invasiveness and ease of use. Conventional injectable matrices mostly use hydrogel precursor solutions that form solid, cell-laden hydrogel scaffolds in situ. However, these materials are associated with challenges in biocompatibility, shear-induced cell death, lack of control over cellular phenotype, lack of macroporosity and remodeling, and relatively weak mechanical strength. This Progress Report provides a brief overview of recent progress in developing injectable matrices to overcome the limitations of conventional in situ hydrogels. Biocompatible chemistry and shear-thinning hydrogels have been introduced to promote cell survival and retention. Emerging investigations of the effects of matrix properties on cellular function in 3D provide important guidelines for promoting desirable cellular phenotypes. Moreover, several novel approaches are combining injectability with macroporosity to achieve macroporous, injectable matrices for cell delivery.

Biomimetic materials have drawn more and more attention in recent years. Regeneration of large bone defects is still a major clinical challenge. In addition, vascularization plays an important role in the process of large bone regeneration and microchannel structure can induce endothelial cells to form rudimentary vasculature. In recent years, 3D printing scaffolds are major materials for large bone defect repair. However, these traditional 3D scaffolds have low porosity and nonchannel structure, which impede angiogenesis and osteogenesis. In this study, inspired by the microstructure of natural plant lotus root, biomimetic materials with lotus root‐like structures are successfully prepared via a modified 3D printing strategy. Compared with traditional 3D materials, these biomimetic materials can significantly improve in vitro cell attachment and proliferation as well as promote in vivo osteogenesis, indicating potential application for cell delivery and bone regeneration.

Purpose: To maximize mass transport into biomaterial scaffolds for regenerative medicine, in vivo diagnostics, therapeutics, and cell delivery. We utilized matrix morphology to encourage long-term ...

A new thermogelling chitosan-glycerophosphate system has been recently proposed for biomedical applications such as drug and cell delivery. The objectives of this work were to characterize the effect of steam sterilization on the in vitro and in vivo end performances of the gel and to develop a filtration-based method to assess its sterility. Autoclaving 2% (w/v) chitosan solutions for as short as 10 min resulted in a 30% decrease in molecular weight, 3-5-fold decrease in dynamic viscosity, and substantial loss of mechanical properties of the resulting gel. However, sterilization did not impair the ability of the system to form a gel at 37 degrees C. The antimicrobial activity of chitosan against several microorganisms was evaluated after inoculation of chitosan solutions and removal of the cells by filtration. It was found that, although chitosan was bacteriostatic against the heat sterilization bioindicator Bacillus stearothermophilus, the bacteria could rapidly grow after separation from the chitosan solution by filtration. This indicated that B. stearothermophilus is an adequate strain to validate a heat sterilization method on chitosan preparations, and accordingly this strain was used to assess the sterility of chitosan solution following a 10 min autoclaving time.