Microgels produced using microfluidic on-chip polymer blending for controlled released of VEGF encoding lentivectors

Functionalized hydrogels as smart gene delivery systems to treat musculoskeletal disorders

Despite critical advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy based on the delivery of therapeutic genetic sequences has strong value to offer effective, durable options to decisively manage such disorders. Furthermore, scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy, allowing for the spatiotemporal delivery of candidate genes to sites of injury. Among the many scaffolds for musculoskeletal research, hydrogels raised increasing attention in addition to other potent systems (solid, hybrid scaffolds) due to their versatility and competence as drug and cell carriers in tissue engineering and wound dressing. Attractive functionalities of hydrogels for musculoskeletal therapy include their injectability, stimuli-responsiveness, self-healing, and nanocomposition that may further allow to upgrade of them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. Such functionalized hydrogels may also be tuned to successfully transfer therapeutic genes in a minimally invasive manner in order to protect their cargos and allow for their long-term effects. In light of such features, this review focuses on functionalized hydrogels and demonstrates their competence for the treatment of musculoskeletal disorders using gene therapy procedures, from gene therapy principles to hydrogel functionalization methods and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are being discussed in the perspective of translation in patients. STATEMENT OF SIGNIFICANCE: Despite advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy has strong value in offering effective, durable options to decisively manage such disorders. Scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy. Among many scaffolds for musculoskeletal research, hydrogels raised increasing attention. Functionalities including injectability, stimuli-responsiveness, and self-healing, tune them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. This review introduces functionalized hydrogels for musculoskeletal disorder treatment using gene therapy procedures, from gene therapy principles to functionalized hydrogels and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are discussed from the perspective of translation in patients.

Hydrogels in Gene Delivery Techniques for Regenerative Medicine and Tissue Engineering

Hydrogels are 3D networks swollen with water. They are biocompatible, strong, and moldable and are emerging as a promising biomedical material for regenerative medicine and tissue engineering to deliver therapeutic genes. The excellent natural extracellular matrix simulation properties of hydrogels enable them to be co-cultured with cells or enhance the expression of viral or non-viral vectors. Its biocompatibility, high strength, and degradation performance also make the action process of carriers in tissues more ideal, making it an ideal biomedical material. It has been shown that hydrogel-based gene delivery technologies have the potential to play therapy-relevant roles in organs such as bone, cartilage, nerve, skin, reproductive organs, and liver in animal experiments and preclinical trials. This paper reviews recent articles on hydrogels in gene delivery and explains the manufacture, applications, developmental timeline, limitations, and future directions of hydrogel-based gene delivery techniques.

3D printing microporous scaffolds from modular bioinks containing sacrificial, cell-encapsulating microgels

Microgel-based biomaterials have inherent porosity and are often extrudable, making them well-suited for 3D bioprinting applications. Cells are commonly introduced into these granular inks post-printing using cell infiltration. However, due to slow cell migration speeds, this strategy struggles to achieve depth-independent cell distributions within thick 3D printed geometries. To address this, we leverage granular ink modularity by combining two microgels with distinct functions: (1) structural, UV-crosslinkable microgels made from gelatin methacryloyl (GelMA) and (2) sacrificial, cell-laden microgels made from oxidized alginate (AlgOx). We hypothesize that encapsulating cells within sacrificial AlgOx microgels would enable the simultaneous introduction of void space and release of cells at depths unachievable through cell infiltration alone. Blending the microgels in different ratios produces a family of highly printable GelMA : AlgOx microgel inks with void fractions ranging from 0.03 to 0.35. As expected, void fraction influences the morphology of human umbilical vein endothelial cells (HUVEC) within GelMA : AlgOx inks. Crucially, void fraction does not alter the ideal HUVEC distribution seen throughout the depth of 3D printed samples. This work presents a strategy for fabricating constructs with tunable porosity and depth-independent cell distribution, highlighting the promise of microgel-based inks for 3D bioprinting.

Architecting oxidized alginate methacrylate hydrogels with tunable characteristics by altering the sequence of the cross-linking steps, methacrylation reaction time, and polymer concentration

In this study, biodegradable oxidized methacrylated alginate (OMA) hydrogels with controllable mechanical properties were engineered. An ionic and photo cross-linking combination was employed to fabricate dual cross-linked hydrogels. By altering the degree of methacrylation and polymer concentration, hydrogels with an elastic modulus of 4.85 ± 0.13 to 21.02 ± 0.91 kPa, controllable swelling, and degradation kinetics, and cross-link density in the range of 1.0 × 10^-5 to 6.5 × 10^-5 mol/cm³ were obtained. Moreover, evaluating the effect of cross-linking sequence on the hydrogels' mechanical properties demonstrated that in comparison to the hydrogels fabricated by ionic cross-linking followed by photo-polymerization, hydrogels produced by photo-polymerization followed by ionic cross-linking retain a stiffer gel network with more compact structure. Cytocompatibility examination was performed via MTT assay against L929 fibroblasts, and all the hydrogel samples demonstrated high cell viability (>80%). The findings demonstrate the significant effect of the sequence of cross-linking as a novel tool to tune the OMA hydrogel's final properties which can serve as a useful platform for tissue engineering applications.

Scalable Production of Biomedical Microparticles via High-Throughput Microfluidic Step Emulsification

Drug microcarriers are widely used in disease treatment, and microfluidics is well established in the preparation of microcarrier particles. A proper design of the microfluidic platform toward scalable production of drug microcarriers can extend its application values in wound healing, where large numbers of microcarriers are required. Here, a microfluidic step emulsification method for the preparation of monodisperse droplets is presented. The droplet size depends primarily on the microchannel depth rather than flow rate, making the system robust for high-throughput production of droplets and hydrogel microparticles. Based on this platform, basic fibroblast growth factor (bFGF) is uniformly encapsulated in the microparticles, and black phosphorus (BP) is incorporated for controllable release via near-infrared (NIR) stimulation. The microparticles serve as drug carriers to be applied to the wound site, inducing angiogenesis and collagen deposition, thereby accelerating wound repair. These results indicate that the step emulsification technique provides a promising solution to scalable production of drug microcarriers for wound healing as well as tissue regeneration.

Construction of vascularized tissue-engineered breast with dual angiogenic and adipogenic micro-tissues

Hydrogel-based micro-tissue engineering technique, a bottom-up approach, is promising in constructing soft tissue of large size with homogeneous spatial distribution and superior regeneration capacity compared to the top-down approach. However, most of the studies employed micro-tissues with simple mesenchymal stem cells, which could hardly meet the growth of matrix and vessels. Therefore, we recommend a dual micro-tissues assembly strategy to construct vascularized tissue-engineered breast grafts (TEBGs). Adipose micro-tissues (AMs) and vessel micro-tissues (VMs) were fabricated by seeding adipose-derived stem cells (ADSCs) and human umbilical vein endothelial cells (HUVECs) on collagen microgels (COLs) with a uniform diameter of ∼250 ​μm, respectively. TEBGs were constructed by injecting the dual micro-tissues into 3D printed breast-like Thermoplastic Urethane (TPU) scaffolds, then implanted into the subcutaneous pockets on the back of nude mice. After 3 months of implantation, TEBGs based on dual micro-tissues performed larger volume of adipose tissue regeneration and neo-vessel formation compared to TEBGs based on single AMs. This study extends the application of micro-tissue engineering technique for the construction of soft grafts, and is expected to be useful for creating heterogeneous tissue constructs in the future.

Advanced Microfluidic Technologies for Lipid Nano-Microsystems from Synthesis to Biological Application

Microfluidics is an emerging technology that can be employed as a powerful tool for designing lipid nano-microsized structures for biological applications. Those lipid structures can be used as carrying vehicles for a wide range of drugs and genetic materials. Microfluidic technology also allows the design of sustainable processes with less financial demand, while it can be scaled up using parallelization to increase production. From this perspective, this article reviews the recent advances in the synthesis of lipid-based nanostructures through microfluidics (liposomes, lipoplexes, lipid nanoparticles, core-shell nanoparticles, and biomimetic nanovesicles). Besides that, this review describes the recent microfluidic approaches to produce lipid micro-sized structures as giant unilamellar vesicles. New strategies are also described for the controlled release of the lipid payloads using microgels and droplet-based microfluidics. To address the importance of microfluidics for lipid-nanoparticle screening, an overview of how microfluidic systems can be used to mimic the cellular environment is also presented. Future trends and perspectives in designing novel nano and micro scales are also discussed herein.

Microvascular Experimentation in the Chick Chorioallantoic Membrane as a Model for Screening Angiogenic Agents including from Gene-Modified Cells

The chick chorioallantoic membrane (CAM) assay model of angiogenesis has been highlighted as a relatively quick, low cost and effective model for the study of pro-angiogenic and anti-angiogenic factors. The chick CAM is a highly vascularised extraembryonic membrane which functions for gas exchange, nutrient exchange and waste removal for the growing chick embryo. It is beneficial as it can function as a treatment screening tool, which bridges the gap between cell based in vitro studies and in vivo animal experimentation. In this review, we explore the benefits and drawbacks of the CAM assay to study microcirculation, by the investigation of each distinct stage of the CAM assay procedure, including cultivation techniques, treatment applications and methods of determining an angiogenic response using this assay. We detail the angiogenic effect of treatments, including drugs, metabolites, genes and cells used in conjunction with the CAM assay, while also highlighting the testing of genetically modified cells. We also present a detailed exploration of the advantages and limitations of different CAM analysis techniques, including visual assessment, histological and molecular analysis along with vascular casting methods and live blood flow observations.

Effect of TEOA on the Process of Photopolymerization at 532 nm and Properties of Nanogels

Nanogel is an important kind of biomaterials applied for wound dressings, drug delivery, medical diagnostics and biosensors. The properties of nanogels closely depend on the density of the crosslinking network. In this study, the role of triethanolamine (TEOA) in the effect on the crosslinking degree of nanogels based on poly(ethylene glycol) diacrylate (PEGDA) was investigated and illustrated. The effect of TEOA on the process of photopolymerization at 532 nm and properties of the nanogels was systematically investigated by using UV-vis spectroscopy, FT-IR spectroscopy, ¹ H NMR, DLS, SEM, AFM and DSC. In brief, the double bond conversion of photopolymerization and the crosslinking degree of nanogels can be effectively regulated by TEOA.

Chips for Biomaterials and Biomaterials for Chips: Recent Advances at the Interface between Microfabrication and Biomaterials Research

In recent years, the use of microfabrication techniques has allowed biomaterials studies which were originally carried out at larger length scales to be miniaturized as so-called "on-chip" experiments. These miniaturized experiments have a range of advantages which have led to an increase in their popularity. A range of biomaterial shapes and compositions are synthesized or manufactured on chip. Moreover, chips are developed to investigate specific aspects of interactions between biomaterials and biological systems. Finally, biomaterials are used in microfabricated devices to replicate the physiological microenvironment in studies using so-called "organ-on-chip," "tissue-on-chip" or "disease-on-chip" models, which can reduce the use of animal models with their inherent high cost and ethical issues, and due to the possible use of human cells can increase the translation of research from lab to clinic. This review gives an overview of recent developments at the interface between microfabrication and biomaterials science, and indicates potential future directions that the field may take. In particular, a trend toward increased scale and automation is apparent, allowing both industrial production of micron-scale biomaterials and high-throughput screening of the interaction of diverse materials libraries with cells and bioengineered tissues and organs.

Droplet Microfluidics for Tumor Drug-Related Studies and Programmable Artificial Cells

Anticancer drug development is a crucial step toward cancer treatment, that requires realistic predictions of malignant tissue development and sophisticated drug delivery. Tumors often acquire drug resistance and drug efficacy, hence cannot be accurately predicted in 2D tumor cell cultures. On the other hand, 3D cultures, including multicellular tumor spheroids (MCTSs), mimic the in vivo cellular arrangement and provide robust platforms for drug testing when grown in hydrogels with characteristics similar to the living body. Microparticles and liposomes are considered smart drug delivery vehicles, are able to target cancerous tissue, and can release entrapped drugs on demand. Microfluidics serve as a high-throughput tool for reproducible, flexible, and automated production of droplet-based microscale constructs, tailored to the desired final application. In this review, it is described how natural hydrogels in combination with droplet microfluidics can generate MCTSs, and the use of microfluidics to produce tumor targeting microparticles and liposomes. One of the highlights of the review documents the use of the bottom-up construction methodologies of synthetic biology for the formation of artificial cellular assemblies, which may additionally incorporate both target cancer cells and prospective drug candidates, as an integrated "droplet incubator" drug assay platform.

Recent Progress on Polysaccharide-Based Hydrogels for Controlled Delivery of Therapeutic Biomolecules

A plethora of applications using polysaccharides have been developed in recent years due to their availability as well as their frequent nontoxicity and biodegradability. These polymers are usually obtained from renewable sources or are byproducts of industrial processes, thus, their use is collaborative in waste management and shows promise for an enhanced sustainable circular economy. Regarding the development of novel delivery systems for biotherapeutics, the potential of polysaccharides is attractive for the previously mentioned properties and also for the possibility of chemical modification of their structures, their ability to form matrixes of diverse architectures and mechanical properties, as well as for their ability to maintain bioactivity following incorporation of the biomolecules into the matrix. Biotherapeutics, such as proteins, growth factors, gene vectors, enzymes, hormones, DNA/RNA, and antibodies are currently in use as major therapeutics in a wide range of pathologies. In the present review, we summarize recent progress in the development of polysaccharide-based hydrogels of diverse nature, alone or in combination with other polymers or drug delivery systems, which have been implemented in the delivery of biotherapeutics in the pharmaceutical and biomedical fields.

Polysaccharide-Based Materials Created by Physical Processes: From Preparation to Biomedical Applications

Polysaccharide-based materials created by physical processes have received considerable attention for biomedical applications. These structures are often made by associating charged polyelectrolytes in aqueous solutions, avoiding toxic chemistries (crosslinking agents). We review the principal polysaccharides (glycosaminoglycans, marine polysaccharides, and derivatives) containing ionizable groups in their structures and cellulose (neutral polysaccharide). Physical materials with high stability in aqueous media can be developed depending on the selected strategy. We review strategies, including coacervation, ionotropic gelation, electrospinning, layer-by-layer coating, gelation of polymer blends, solvent evaporation, and freezing-thawing methods, that create polysaccharide-based assemblies via in situ (one-step) methods for biomedical applications. We focus on materials used for growth factor (GFs) delivery, scaffolds, antimicrobial coatings, and wound dressings.

Microfluidic on-chip production of microgels using combined geometries

Microfluidic on-chip production of microgels using external gelation can serve numerous applications that involve encapsulation of sensitive cargos. Nevertheless, on-chip production of microgels in microfluidic devices can be challenging due to problems induced by the rapid increase in precursor solution viscosity like clogging. Here, a novel design incorporating a step, which includes a sudden increase in cross-sectional area, before a flow-focusing nozzle was proposed for microfluidic droplet generators. Besides, a shielding oil phase was utilized to avoid the occurrence of emulsification and gelation stages simultaneously. The step which was located before the flow-focusing nozzle facilitated the full shielding of the dispersed phase due to 3-dimensional fluid flow in this geometry. The results showed that the microfluidic device was capable of generating highly monodispersed spherical droplets (CV < 2% for step and CV < 5% for flow-focusing nozzle) with an average diameter in the range of 90-190 μm, both in step and flow-focusing nozzle. Moreover, it was proved that the device could adequately create a shelter for the dispersed phase regardless of the droplet formation locus. The ability of this microfluidic device in the production of microgels was validated by creating alginate microgels (with an average diameter of ~ 100 μm) through an external gelation process with on-chip calcium chloride emulsion in mineral oil.

Materials promoting viral gene delivery

Therapeutic viral gene delivery is an emerging technology which aims to correct genetic mutations by introducing new genetic information to cells either to correct a faulty gene or to initiate cell death in oncolytic treatments. In recent years, significant scientific progress has led to several clinical trials resulting in the approval of gene therapies for human treatment. However, successful therapies remain limited due to a number of challenges such as inefficient cell uptake, low transduction efficiency (TE), limited tropism, liver toxicity and immune response. To adress these issues and increase the number of available therapies, additives from a broad range of materials like polymers, peptides, lipids, nanoparticles, and small molecules have been applied so far. The scope of this review is to highlight these selected delivery systems from a materials perspective.

Biomaterial Based Strategies for Engineering New Lymphatic Vasculature

The lymphatic system is essential for tissue regeneration and repair due to its pivotal role in resolving inflammation, immune cell surveillance, lipid transport, and maintaining tissue homeostasis. Loss of functional lymphatic vasculature is directly implicated in a variety of diseases, including lymphedema, obesity, and the progression of cardiovascular diseases. Strategies that stimulate the formation of new lymphatic vessels (lymphangiogenesis) could provide an appealing new approach to reverse the progression of these diseases. However, lymphangiogenesis is relatively understudied and stimulating therapeutic lymphangiogenesis faces challenges in precise control of lymphatic vessel formation. Biomaterial delivery systems could be used to unleash the therapeutic potential of lymphangiogenesis for a variety of tissue regenerative applications due to their ability to achieve precise spatial and temporal control of multiple therapeutics, direct tissue regeneration, and improve the survival of delivered cells. In this review, the authors begin by introducing therapeutic lymphangiogenesis as a target for tissue regeneration, then an overview of lymphatic vasculature will be presented followed by a description of the mechanisms responsible for promoting new lymphatic vessels. Importantly, this work will review and discuss current biomaterial applications for stimulating lymphangiogenesis. Finally, challenges and future directions for utilizing biomaterials for lymphangiogenic based treatments are considered.

HEMA based pH-sensitive semi IPN microgels for oral delivery; a rationale approach for ketoprofen

Objectives: The study aimed to develop safe, effective, and targeted drug delivery system for administration of nonsteroidal anti-inflammatory drugs (NSAIDs) in the form of microgels. We developed pH responsive microgels to overcome the mucosal damage caused by traditional immediate release dosage forms. Colon targeting and controlled release formulations have the potential to improve efficacy and reduce undesirable effects associated with NSAIDs.Methods: The pH sensitive oral hydrogel demonstrates the potential to target the colon. Cellulose acetate phthalate (CAP) and hydroxyethyl methacrylate (HEMA) based microgel particles were produced using a free radical polymerization technique using ammonium persulfate (APS) initiator and methylenebisacrylamide (MBA) as the crosslinking agent. Swelling and in-vitro drug release studies were performed at a range of pH conditions. The produced formulations were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy (SEM), and X-ray diffraction. Biocompatibility of the microgels was analyzed in cytotoxicity studies.Key findings: The swelling and release rate were negligible at pH 1.2, which confirmed the pH-responsiveness of CAP-co-poly(HEMA). The co-polymeric system prevents the release of ketoprofen sodium in the stomach owing to limited swelling at gastric pH, whilst promoting release at the basic pH observed in the colon. SEM images confirmed porous nature of the microgels that facilitate effective drug diffusion through the polymeric matrix. Cytotoxicity studies revealed biocompatibility of hydrogels.Conclusion: These investigations showed that that the controlled drug release and gastro-protective drug delivery of NSAIDS was achieved using CAP-co-poly(HEMA) microgel particles.

Computational-Based Design of Hydrogels with Predictable Mesh Properties

Hydrogel systems are an appealing class of therapeutic delivery vehicles, though it can be challenging to design hydrogels that maintain desired spatiotemporal presentation of therapeutic cargo. In this work, we propose a different approach in which computational tools are developed that creates a theoretical representation of the hydrogel polymer network to design hydrogels with predefined mesh properties critical for controlling therapeutic delivery. We postulated and confirmed that the computational model could incorporate properties of alginate polymers, including polymer content, monomer composition and polymer chain radius, to accurately predict cross-link density and mesh size for a wide range of alginate hydrogels. Additionally, the simulations provided a robust strategy to determine the mesh size distribution and identified properties to control the mesh size of alginate hydrogels. Furthermore, the model was validated for additional hydrogel systems and provided a high degree of correlation (R² > 0.95) to the mesh sizes determined for both fibrin and polyethylene glycol (PEG) hydrogels. Finally, a full factorial and Box-Behnken design of experiments (DOE) approach utilized in combination with the computational model predicted that the mesh size of hydrogels could be varied from approximately 5 nm to 5 μm through controlling properties of the polymer network. Overall, this computational model of the hydrogel polymer network provides a rapid and accessible strategy to predict hydrogel mesh properties and ultimately design hydrogel systems with desired mesh properties for potential therapeutic applications.

A Way to Predict Gold Nanoparticles/Polymer Hybrid Microgel Agglomeration Based on Rheological Studies

In this work, a detailed rheological study of hybrid poly(acrylamide-co-acrylic acid) P(AAm-co-AAc) aqueous microgel dispersions is performed. Our intention is to understand how the presence of gold nanoparticles, AuNP, embedded within the microgel matrix, affects the viscoelastic properties, the colloidal gel structure formation, and the structure recovery after cessation of the deformation of the aqueous microgel dispersions. Frequency sweep experiments confirmed that hybrid microgel dispersions present a gel-like behavior and that the presence of AuNP content within microgel matrix contributes to the elasticity of the microgel dispersions. Strain sweep test confirmed that hybrid microgels aqueous dispersion also form colloidal gel structures that break upon deformation but that can be recovered when the deformation decreases. The fractal analysis performed to hybrid microgels, by applying Shih et al. and Wu and Morbidelli's scaling theories, evidenced that AuNP significantly affects the colloidal gel structure configuration ending up with the formation of agglomerates or microgel clusters with closer structures in comparison to the reference P(AAm-co-AAc) aqueous microgel dispersions.

Recent Advances in Droplet-based Microfluidic Technologies for Biochemistry and Molecular Biology

Recently, droplet-based microfluidic systems have been widely used in various biochemical and molecular biological assays. Since this platform technique allows manipulation of large amounts of data and also provides absolute accuracy in comparison to conventional bioanalytical approaches, over the last decade a range of basic biochemical and molecular biological operations have been transferred to drop-based microfluidic formats. In this review, we introduce recent advances and examples of droplet-based microfluidic techniques that have been applied in biochemistry and molecular biology research including genomics, proteomics and cellomics. Their advantages and weaknesses in various applications are also comprehensively discussed here. The purpose of this review is to provide a new point of view and current status in droplet-based microfluidics to biochemists and molecular biologists. We hope that this review will accelerate communications between researchers who are working in droplet-based microfluidics, biochemistry and molecular biology.

Characterizing the encapsulation and release of lentivectors and adeno-associated vectors from degradable alginate hydrogels

Gene therapy using viral vectors has been licensed for clinical use both in the European Union and the United States. Lentivectors (LV) and adeno-associated vectors (AAV) are two promising and FDA approved gene-therapy viral vectors. Many future applications of these vectors will benefit from targeting specific regions of interest within the body. Therefore, building on the early success of these vectors may depend on finding effective delivery systems to localize therapeutic administration. Degradable alginate hydrogels have been tested as appealing delivery vehicles for the controlled delivery of vector payloads. In this study, we compare the ability of two different degradable alginate hydrogel formulations to efficiently deliver LV and AAV. We propose that release rates of viral vectors are dependent on the physical properties of both the hydrogels and vectors. Here, we demonstrate that the initial strength and degradation rate of alginate hydrogels provides levers of control for tuning LV release but do not provide control in the release of AAV. While both alginate formulations used showed sustained release of both LV and AAV, LV release was shown to be dependent on alginate hydrogel degradation, while AAV release was largely governed by diffusive mechanisms. Altogether, this study demonstrates alginate's use as a possible delivery platform for LV and, for the first time, AAV - highlighting the potential of injectable degradable alginate hydrogels to be used as a versatile delivery tool in gene therapy applications.

Thermoresponsive Poly(N-Isopropylacrylamide-co-Dimethylaminoethyl Methacrylate) Microgel Aqueous Dispersions with Potential Antimicrobial Properties

The work herein describes the preparation of thermoresponsive microgels with potential antimicrobial properties. Most of the work performed so far regarding microgels with antimicrobial activity, deals with the ability of microgels to carry and release antibiotics or antimicrobial agents (antimicrobial peptides). The originality of this work lies in the possibility of developing intrinsic antimicrobial microgels by copolymerization of the well-known thermoresponsive monomer, N-isopropylacrylamide (NIPAM) with dimethylaminoethyl methacrylate (DMAEMA), a water-soluble monomer, to form microgels via precipitation polymerization (radical polymerization). Due to the presence of a tertiary amine in the DMAEMA comonomer, microgels can be modified by N-alkylation reaction with methyl and butyl iodide. This quaternization confers positive charges to the microgel surfaces and thus the potential antimicrobial activity. The effect of DMAEMA content and its quaternization with both, methyl and butyl iodide is evaluated in terms of thermal and surface charge properties, as well as in the microgel size and viscoelastic behavior. Finally, a preliminary study of the antimicrobial activity against different microorganisms is also performed in terms of minimum inhibitory concentration (MIC). From this study we determined that in contrast with butylated microgels, methylated ones show potential antimicrobial activity and good physical properties besides of maintaining microgel thermo-responsiveness.

Matrix Mediated Viral Gene Delivery: A Review

Polymeric matrices inherently protect viral vectors from pre-existing immune conditions, limit dissemination to off-target sites, and can sustain vector release. Advancing methodologies in development of particulate based vehicles have led to improved encapsulation of viral vectors. Polymeric delivery systems have contributed to increasing cellular transduction, responsive release mechanisms, cellular infiltration, and cellular signaling. Synthetic polymers are easily customizable, and are capable of balancing matrix retention with cellular infiltration. Natural polymers contain inherent biorecognizable motifs adding therapeutic efficacy to the incorporated viral vector. Recombinant polymers use highly conserved motifs to carefully engineer matrices, allowing for precise design including elements of vector retention and responsive release mechanisms. Composite polymer systems provide opportunities to create matrices with unique properties. Carefully designed matrices can control spatiotemporal release patterns that synergize with approaches in regenerative medicine and antitumor therapies.

Local Structure of Ca2+ Alginate Hydrogels Gelled via Competitive Ligand Exchange and Measured by Small Angle X-Ray Scattering

Alginates, being linear anionic co-polymers of 1,4-linked residues β-d-ManA (M) and α-l-GulA (G), are widely applied as hydrogel biomaterials due to their favourable in vivo biocompatibility and convenient ionic crosslinking. The "egg-box" model is the prevailing description of the local structure of junction zones that form between the alginate chains and divalent cations, such as Ca2+, when ionic gelation occurs. In the present study we address to what extent signatures of lateral dimerization and further lateral association of junction zones also represent a valid model for the gelation of alginate using the recently reported method of competitive ligand exchange of chelated Ca2+ ions as a method for introducing gelling ions at constant pH. Small angle X-ray scattering with a q range from 0.1 to 3.3 nm-1 was employed to determine local structure in the hydrogel, using a custom-made fluid sample cell inserted in the X-ray beam. The scattering volume was intended to be localized to the contact zone between the two injected aqueous alginate solutions, and data was captured to resolve the kinetics of the structure formation at three different conditions of pH. The data show evolution of the local structure for the Ca2+ induced formation of junction zones in an alginate with 68% G residues, characterized by cross-sectional radii that could be accounted for by a two-component, broken rod like model. The evolution of the two component weight fractions apparently underpinned the connectivity, as reflected in the rheological data.

Application of drug delivery systems for the controlled delivery of growth factors to treat nervous system injury

Nervous system injury represent the most common injury and was unique clinical challenge. Using of growth factors (GFs) for the treatment of nervous system injury showed effectiveness in halting its process. However, simple application of GFs could not achieve high efficacy because of its rapid diffusion into body fluids and lost from the lesion site. The drug delivery systems (DDSs) construction used to deliver GFs were investigated so that they could surmount its rapid diffusion and retain at the injury site. This study summarizes commonly used DDSs for sustained release of GFs that provide neuroprotection or restoration effects for nervous system injury.

Erythrocyte fouling on micro-engineered membranes

Crossflow microfiltration of plasma from blood through microsieves in a microchannel is potentially useful in many biomedical applications, including clinically as a wearable water removal device under development by the authors. We report experiments that correlate filtration rates, transmembrane pressures (TMP) and shear rates during filtration through a microscopically high channel bounded by a low intrinsic resistance photolithographically-produced porous semiconductor membrane. These experiments allowed observation of erythrocyte behavior at the filtering surface and showed how their unique deformability properties dominated filtration resistance. At low filtration rates (corresponding to low TMP), they rolled along the filter surface, but at higher filtration rates (corresponding to higher TMP), they anchored themselves to the filter membrane, forming a self-assembled, incomplete monolayer. The incompleteness of the layer was an essential feature of the monolayer's ability to support sustainable filtration. Maximum steady-state filtration flux was a function of wall shear rate, as predicted by conventional crossflow filtration theory, but, contrary to theories based on convective diffusion, showed weak dependence of filtration on erythrocyte concentration. Post-filtration scanning electron micrographs revealed significant capture and deformation of erythrocytes in all filter pores in the range 0.25 to 2 μm diameter. We report filtration rates through these filters and describe a largely unrecognized mechanism that allows stable filtration in the presence of substantial cell layers.