Temperature-Responsive Polymer Brush Coatings for Advanced Biomedical Applications

Biomedical applications of stimuli-responsive nanomaterials

Nanomaterials have aroused great interests in drug delivery due to their nanoscale structure, facile modifiability, and multifunctional physicochemical properties. Currently, stimuli-responsive nanomaterials that can respond to endogenous or exogenous stimulus display strong potentials in biomedical applications. In comparison with conventional nanomaterials, stimuli-responsive nanomaterials can improve therapeutic efficiency and reduce the toxicity of drugs toward normal tissues through specific targeting and on-demand drug release at pathological sites. In this review, we summarize the responsive mechanism of a variety of stimulus, including pH, redox, and enzymes within pathological microenvironment, as well as exogenous stimulus such as thermal effect, magnetic field, light, and ultrasound. After that, biomedical applications (e.g., drug delivery, imaging, and theranostics) of stimuli-responsive nanomaterials in a diverse array of common diseases, including cardiovascular diseases, cancer, neurological disorders, inflammation, and bacterial infection, are presented and discussed. Finally, the remaining challenges and outlooks of future research directions for the biomedical applications of stimuli-responsive nanomaterials are also discussed. We hope that this review can provide valuable guidance for developing stimuli-responsive nanomaterials and accelerate their biomedical applications in diseases diagnosis and treatment.

Synthesis of Raspberry-like Nanoparticles via Surface Grafting of Positively Charged Polyelectrolyte Brushes: Colloidal Stability and Surface Properties

A method to synthesize stable, raspberry-like nanoparticles (NPs), using surface grafting of poly(glycidyl methacrylate) (PGMA) brushes on a polystyrene (PS) core with varying grafting densities, is reported. A two-step functionalization reaction of PGMA epoxide groups comprising an amination step first using ethylene diamine and then followed by a quaternization using glycidyltrimethylammonium chloride generates permanently and positively charged polyelectrolyte brushes, which result in both steric and electrostatic stabilization. The dispersion stability of the brush-bearing NPs is dramatically improved compared to that of the pristine PS core in salt solutions at ambient (25 °C) and elevated temperatures (60 °C). Additionally, the grafted polyelectrolyte chains undergo a reversible swelling in the presence of different ionic strength (IS) salts, which modulate the surface properties, including roughness, stiffness, and adhesion. An atomic force microscope under both dry and wet conditions was used to image conformational changes of the polyelectrolyte chains during the swelling and deswelling transitions as well as to probe the nanomechanical properties by analyzing the corresponding force-sample separation curves. The quaternized polyelectrolyte brushes undergo a conformational transition from a collapsed state to a swelled state in the osmotic brush (OB) regime triggered by the osmotic gradient of mobile ions to the interior of the polymer chain. At IS ∼ 1 M, the brushes contract and the globules reform (salted brush state) as evidenced by an increase in the surface roughness and a reduction in the adhesion of the brushes. Beyond IS ∼ 1 M, quartz crystal microbalance with dissipation monitoring measurements show that salt uptake continues to take place predominantly on the exterior surface of the brush since salt adsorption is not accompanied by a size increase as measured by dynamic light scattering. The study adds new insights into our understanding of the behavior of NPs bearing salt-responsive polyelectrolyte brushes with adaptive swelling thresholds that can ultimately modulate surface properties.

Mild Quantitative One Step Removal of Macrophages from Cocultures with Human Umbilical Vein Endothelial Cells Using Thermoresponsive Poly(Di(Ethylene Glycol)Methyl Ether Methacrylate) Brushes

The authors report on a mild, label-free, and fast method for the separation of human umbilical vein endothelial cells (HUVEC), which are relevant cells, whose use is not limited to studies of endothelial dysfunction, from cocultures with macrophages to afford HUVEC in ≈100% purity. Poly(di(ethylene glycol)methyl ether methacrylate) (PDEGMA) brushes with a dry thickness of (5 ± 1) nm afford the highly effective one-step separation by selective HUVEC detachment, which is based on the brushes' thermoresponsive behavior. Below the thermal transition at 32 °C the brushes swells and desorbs attached proteins, resulting in markedly decreased cell adhesion. Specifically, HUVEC and macrophages, which are differentiated from THP-1 monocytes, are seeded and attached to PDEGMA brushes at 37°C. After decreasing the temperature to 22°C, HUVEC shows a decrease in their cell area, while the macrophages are not markedly affected by the temperature change. After mild flushing with a cell culture medium, the HUVEC can be released from the surface and reseeded again with ≈100% purity on a new surface. With this selective cell separation and removal method, it is possible to separate and thereby purify HUVEC from macrophages without the use of any releasing reagent or expensive labels, such as antibodies.

Polymer Brushes and Surface Nanostructures: Molecular Design, Precise Synthesis, and Self-Assembly

For over two decades, polymer brushes have found wide applications in industry and scientific research. Now, polymer brush research has been a significant research focus in the community of polymer science. In this review paper, we give an introduction to the synthesis, self-assembly, and applications of one-dimensional (1D) polymer brushes on polymer backbones, two-dimensional (2D) polymer brushes on flat surfaces, and three-dimensional (3D) polymer brushes on spherical particles. Examples of the synthesis of polymer brushes on different substrates are provided. Studies on the formation of the surface nanostructures on solid surfaces are also reviewed in this article. Multicomponent polymer brushes on solid surfaces are able to self-assemble into surface micelles (s-micelles). If the s-micelles are linked to the substrates through cleavable linkages, the s-micelles can be cleaved from the substrates, and the cleaved s-micelles are able to self-assemble into hierarchical structures. The formation of the surface nanostructures by coassembly of polymer brushes and "free" polymer chains (coassembly approach) or polymerization-induced surface self-assembly approach, is discussed. The applications of the polymer brushes in colloid and biomedical science are summarized. Finally, perspectives on the development of polymer brushes are offered in this article.

Guard Cell-Inspired Ion Channels: Harnessing the Photomechanical Effect via Supramolecular Assembly of Cross-Linked Azobenzene/Polymers

Stimuli-responsive ion nanochannels have attracted considerable attention in various fields because of their remote controllability of ionic transportation. For photoresponsive ion nanochannels, however, achieving precise regulation of ion conductivity is still challenging, primarily due to the difficulty of programmable structural changes in confined environments. Moreover, the relationship between noncontact photo-stimulation in nanoscale and light-induced ion conductivity has not been well understood. In this work, a versatile design for fabricating guard cell-inspired photoswitchable ion channels is presented by infiltrating azobenzene-cross-linked polymer (AAZO-PDAC) into nanoporous anodic aluminum oxide (AAO) membranes. The azobenzene-cross-linked polymer is formed by azobenzene chromophore (AAZO)-cross-linked poly(diallyldimethylammonium chloride) (PDAC) with electrostatic interactions. Under UV irradiation, the trans-AAZO isomerizes to the cis-AAZO, causing the volume compression of the polymer network, whereas, in darkness, the cis-AAZO reverts to the trans-AAZO, leading to the recovery of the structure. Consequently, the resultant nanopore sizes can be manipulated by the photomechanical effect of the AAZO-PDAC polymers. By adding ionic liquids, the ion conductivity of the light-driven ion nanochannels can be controlled with good repeatability and fast responses (within seconds) in multiple cycles. The ion channels have promising potential in the applications of biomimetic materials, sensors, and biomedical sciences.

Thermoresponsive Smart Copolymer Coatings Based on P(NIPAM-co-HEMA) and P(OEGMA-co-HEMA) Brushes for Regenerative Medicine

The fabrication of multifunctional, thermoresponsive platforms for regenerative medicine based on polymers that can be easily functionalized is one of the most important challenges in modern biomaterials science. In this study, we utilized atom transfer radical polymerization (ATRP) to produce two series of novel smart copolymer brush coatings. These coatings were based on copolymerizing 2-hydroxyethyl methacrylate (HEMA) with either oligo(ethylene glycol) methyl ether methacrylate (OEGMA) or N-isopropylacrylamide (NIPAM). The chemical compositions of the resulting brush coatings, namely, poly(oligo(ethylene glycol) methyl ether methacrylate-co-2-hydroxyethyl methacrylate) (P(OEGMA-co-HEMA)) and poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (P(NIPAM-co-HEMA)), were predicted using reactive ratios of the monomers. These predictions were then verified using time-of-flight-secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The thermoresponsiveness of the coatings was examined through water contact angle (CA) measurements at different temperatures, revealing a transition driven by lower critical solution temperature (LCST) or upper critical solution temperature (UCST) or a vanishing transition. The type of transition observed depended on the chemical composition of the coatings. Furthermore, it was demonstrated that the transition temperature of the coatings could be easily adjusted by modifying their composition. The topography of the coatings was characterized using atomic force microscopy (AFM). To assess the biocompatibility of the coatings, dermal fibroblast cultures were employed, and the results indicated that none of the coatings exhibited cytotoxicity. However, the shape and arrangement of the cells were significantly influenced by the chemical structure of the coating. Additionally, the viability of the cells was correlated with the wettability and roughness of the coatings, which determined the initial adhesion of the cells. Lastly, the temperature-induced changes in the properties of the fabricated copolymer coatings effectively controlled cell morphology, adhesion, and spontaneous detachment in a noninvasive, enzyme-free manner that was confirmed using optical microscopy.

Biocompatible Polymer for Self-Humidification

Lung supportive devices (LSDs) have been extensively utilized in treating patients diagnosed with various respiratory disorders. However, these devices can cause moisture depletion in the upper airway by interfering with the natural lubrication and air conditioning process. To remedy this, current technologies implement heated humidification processes, which are bulky, costly, and nonfriendly. However, it has been demonstrated that in a breath cycle, the amount of water vapor in the exhaled air is of a similar quantity to the amount needed to humidify the inhaled air. This research proposes to trap the moisture from exhaled air and reuse it during inhalation by developing a state-of-the-art hydrophilic/hydrophobic polymer tuned to deliver this purpose. Using the atom transfer radical polymerization (ATRP) method, a substrate was successfully created by incorporating poly (N-isopropyl acrylamide) (PNIPAM) onto cotton. The fabricated material exhibited a water vapor release rate of 24.2 ± 1.054%/min at 32 °C, indicating its ability to humidify the inhaled air effectively. These findings highlight the potential of the developed material as a promising solution for applications requiring rapid moisture recovery.

QbD Design, Formulation, Optimization and Evaluation of Trans-Tympanic Reverse Gelatination Gel of Norfloxacin: Investigating Gene-Gene Interactions to Enhance Therapeutic Efficacy

Traditional otic drug delivery methods lack controlled release capabilities, making reverse gelatination gels a promising alternative. Reverse gelatination gels are colloidal systems that transition from a sol to a gel phase at the target site, providing controlled drug release over an extended period. Thermosensitive norfloxacin reverse gelatination gels were developed using a Quality by Design (QbD)-based optimization approach. The formulations were evaluated for their in vitro release profile, rheological behavior, visual appearance, pH, gelling time, and sol-gel transition temperature. The results show that the gelation temperatures of the formulations ranged from 33 to 37 °C, with gelling durations between 35 and 90 s. The drug content in the formulations was uniform, with entrapment efficiency ranging from 55% to 95%. Among the formulations, F10 exhibited the most favorable properties and was selected for a stability study lasting 60 days. Ex-vivo release data demonstrate that the F10 formulation achieved 95.6percentage of drug release at 360 min. This study successfully developed thermosensitive norfloxacin reverse gelatination gels using a QbD-based optimization approach. The selected formulation, F10, exhibited desirable properties in terms of gelling temperature, drug content, and release profile. These gels hold potential for the controlled delivery of norfloxacin in the treatment of ear infections.

Overview of Electrospinning for Tissue Engineering Applications

Tissue engineering (TE) is an emerging field of study that incorporates the principles of biology, medicine, and engineering for designing biological substitutes to maintain, restore, or improve tissue functions with the goal of avoiding organ transplantation. Amongst the various scaffolding techniques, electrospinning is one of the most widely used techniques to synthesise a nanofibrous scaffold. Electrospinning as a potential tissue engineering scaffolding technique has attracted a great deal of interest and has been widely discussed in many studies. The high surface-to-volume ratio of nanofibres, coupled with their ability to fabricate scaffolds that may mimic extracellular matrices, facilitates cell migration, proliferation, adhesion, and differentiation. These are all very desirable properties for TE applications. However, despite its widespread use and distinct advantages, electrospun scaffolds suffer from two major practical limitations: poor cell penetration and poor load-bearing applications. Furthermore, electrospun scaffolds have low mechanical strength. Several solutions have been offered by various research groups to overcome these limitations. This review provides an overview of the electrospinning techniques used to synthesise nanofibres for TE applications. In addition, we describe current research on nanofibre fabrication and characterisation, including the main limitations of electrospinning and some possible solutions to overcome these limitations.

Strategies for Developing Shape-Shifting Behaviours and Potential Applications of Poly (N-vinyl Caprolactam) Hydrogels

Stimuli-responsive hydrogels are one type of smart hydrogel, which can expand/contract in water according to changes in the surrounding environment. However, it is difficult to develop flexible shapeshifting behaviours by using a single hydrogel material. This study exploited a new method to utilise single and bilayer structures to allow hydrogel-based materials to exhibit controllable shape-shifting behaviours. Although other studies have demonstrated similar transformation behaviours, this is the first report of such smart materials developed using photopolymerised N-vinyl caprolactam (NVCL)-based polymers. Our contribution provides a straightforward method in the fabrication of deformable structures. In the presence of water, the bending behaviours (vertex-to-vertex and edge-to-edge) were achieved in monolayer squares. By controlling the content and combination of the NVCL solutions with elastic resin, the bilayer strips were prepared. The expected reversible self-bending and self-helixing behaviours were achieved in specific types of samples. In addition, by limiting the expansion time of the bilayer, the layered flower samples exhibited predictable self-curving shape transformation behaviour in at least three cycles of testing. These structures displayed the capacity of self-transformation, and the value and functionality of the produced components are reflected in this paper.

Thermosensitive Polymer-Modified Mesoporous Silica for pH and Temperature-Responsive Drug Delivery

A mesoporous silica-based drug delivery system (MS@PNIPAm-PAAm NPs) was synthesized by conjugating the PNIPAm-PAAm copolymer onto the mesoporous silica (MS) surface as a gatekeeper that responds to temperature and pH changes. The drug delivery studies are carried out in vitro at different pH (7.4, 6.5, and 5.0) and temperatures (such as 25 °C and 42 °C, respectively). The surface conjugated copolymer (PNIPAm-PAAm) acts as a gatekeeper below the lower critical solution temperature (LCST) (<32 °C) and as a collapsed globule structure above LCST (>32 °C), resulting in controlled drug delivery from the MS@PNIPAm-PAAm system. Furthermore, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cellular internalization results support the prepared MS@PNIPAm-PAAm NPs being biocompatible and readily taken up by MDA-MB-231 cells. The prepared MS@PNIPAm-PAAm NPs, with their pH-responsive drug release behavior and good biocompatibility, could be used as a drug delivery vehicle where sustained drug release at higher temperatures is required.

Conductive and Thermo-Responsive Composite Hydrogels with Poly(N-isopropylacrylamide) and Carbon Nanotubes Fabricated by Two-Step Photopolymerization

Biocompatible and conductive polymer hydrogels are the subject of intensive research in the bioengineering field because of their use in bioelectronic devices and for the fabrication of electro-responsive tissues and drug delivery systems. In this study, we report the synthesis of conductive composite hydrogels consisting of a poly(N-isopropylacrylamide) (PNIPAM) matrix embedding carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) using a two-step photopolymerization method. Thermo-responsive hydrogels with controlled hydrophilicity and conductivity were prepared by varying the carbon nanotube concentration in the range 0.5-3 wt%. The thermal response of the PNIPAM-based composite hydrogels was measured by differential scanning calorimetry with both ultrapure water and PBS solution as swelling liquid. Results show that the endothermic peak associated with the temperature-induced volume phase transition (VPT) shifts to higher temperatures upon increasing the concentration of the nanotubes, indicating that more energy is required to dissociate the hydrogen bonds of the polymer/filler network. In PBS solution, the swelling ratios and the VPT temperatures of the composite hydrogels are reduced because of salt-induced screening of the oppositely charged polymer/filler assembly, and the electrical resistivity decreases by a factor of 10 with respect to the water-swollen hydrogels.

Evaluation of the Antibacterial Properties of Polyvinyl Alcohol-Pullulan Scaffolds Loaded with Nepeta racemosa Lam. Essential Oil and Perspectives for Possible Applications

Essential oil of Nepeta racemosa Lam. was extracted and characterized to determine its antimicrobial activity and potential use in applications. The essential oil was loaded on polyvinyl alcohol-pullulan films and gels and characterized by optical microscopy, scanning electron microscopy, and UV-Vis spectroscopy before having its antimicrobial capacities assessed. The essential oil extracted from Nepeta racemosa Lam. was characterized using gas chromatography coupled with mass spectroscopy, which indicated that the most abundant component was nepetalic acid (55.5%), followed by eucalyptol (10.7%) and other compounds with concentrations of about 5% or less. The essential oil, as well as the loaded films and gels, exhibited good antibacterial activity on both gram-positive and gram-negative strains, with growth inhibition zones larger in some cases than for gentamicin, indicating excellent premises for using these essential-oil-loaded materials for applications in the food industry or biomedicine.

Increasing Bioavailability of Trans-Ferulic Acid by Encapsulation in Functionalized Mesoporous Silica

Two types of mesoporous materials, MCM-41 and MCM-48, were functionalized by the soft-template method using (3-aminopropyl)triethoxysilane (APTES) as a modifying agent. The obtained mesoporous silica materials were loaded with trans-ferulic acid (FA). In order to establish the morphology and structure of mesoporous materials, a series of specific techniques were used such as: X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer-Emmet-Teller (BET), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). We monitored the in vitro release of the loaded FA at two different pH values, by using simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). Additionally, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Candida albicans ATCC 10231 were used to evaluate the antimicrobial activity of FA loaded mesoporous silica materials. In conclusion such functionalized mesoporous materials can be employed as controlled release systems for polyphenols extracted from natural sources.

Temperature- and pH-Responsive Schizophrenic Copolymer Brush Coatings with Enhanced Temperature Response in Pure Water

Novel brush coatings were fabricated with glass surface-grafted chains copolymerized using surface-initiated atom transfer radical polymerization (SI-ATRP) from 2-(2-methoxyethoxy)ethyl methacrylate (OEGMA188) and acrylamide (AAm), taken in different proportions. P(OEGMA188-co-AAm) brushes with AAm mole fraction >44% (determined with XPS and TOF-SIMS spectroscopy) and nearly constant with the depth copolymer composition (TOF-SIMS profiling) exhibit unusual temperature-induced transformations: The contact angle of water droplets on P(OEGMA188-co-AAm) coatings increases by ∼45° with temperature, compared to 17-18° for POEGMA188 and PAAm. The thickness of coatings immersed in water and the morphology of coatings imaged in air show a temperature response for POEGMA188 (using reflectance spectroscopy and AFM, respectively), but this response is weak for P(OEGMA188-co-AAm) and absent for PAAm. This suggests mechanisms more complex than a simple transition between hydrated loose coils and hydrophobic collapsed chains. For POEGMA188, the hydrogen bonds between the ether oxygens of poly(ethylene glycol) and water hydrogens are formed below the transition temperature T_c and disrupted above T_c when polymer-polymer interactions are favored. Different hydrogen bond structures of PAAm include free amide groups, cis-trans-multimers, and trans-multimers of amide groups. Here, hydrogen bonds between free amide groups and water dominate at T < T_c but structures favored at T > T_c, such as cis-trans-multimers and trans-multimers of amide groups, can still be hydrated. The enhanced temperature-dependent response of wettability for P(OEGMA188-co-AAm) with a high mole fraction of AAm suggests the formation at T_c of more hydrophobic structures, realized by hydrogen bonding between the ether oxygens of OEGMA188 and the amide fragments of AAm, where water molecules are caged. Furthermore, P(OEGMA188-co-AAm) coatings immersed in pH buffer solutions exhibit a 'schizophrenic' behavior in wettability, with transitions that mimic LCST and UCST for pH = 3, LCST for pH = 5 and 7, and any transition blocked for pH = 9.

Synthesis and Characterization of a pH- and Temperature-Sensitive Fe3O4-SiO2-Poly(NVCL-co-MAA) Nanocomposite for Controlled Delivery of Doxorubicin Anticancer Drug

This work reports the synthesis, characterization, and in vitro release studies of pH- and temperature-sensitive Fe₃O₄-SiO₂-poly(NVCL-co-MAA) nanocomposite. Fe₃O₄ nanoparticles were prepared by chemical coprecipitation, coated with SiO₂ by the Stöber method, and functionalized with vinyl groups. The copolymer poly(N-vinylcaprolactam-co-methacrylic acid) (poly(NVCL-co-MAA)) was grafted onto the functionalized Fe₃O₄-SiO₂ nanoparticles by free radical polymerization. XRD, FTIR, TGA, VSM, and TEM techniques were performed to characterize the nanocomposite. The release behavior of Doxorubicin (DOX) loaded in the nanocomposite at pH 5.8 and 7.4, and two temperatures, 25 and 37 °C, was studied. According to the release studies, approximately 55% of DOX is released in 72 h at pH 7.4, regardless of temperature. At pH 5.8, 78% of DOX was released in 48 h at 25 °C, and when increasing the temperature to 37 °C, more than 95 % of DOX was released in 24 h. The DOX release data treated with Zero-order, first-order, Higuchi, and Korsmeyer-Peppas models showed that Higuchi's model best fits the data, indicating that the DOX is released by diffusion. The findings suggest that the synthesized nanocomposite may be useful as a DOX carrier in biomedical applications.

Hybrid Microcapsules for Encapsulation and Controlled Release of Rosemary Essential Oil

The foremost objective of this work is to assess the microcapsules composition (polymer-based and polymer/clay-based) effect, on the release of rosemary essential oil into w/o medium and evaluate their antioxidant activity. Calcium alginate (CA) and calcium alginate/montmorillonite hybrid (CA-MTN) microcapsules were developed following an ionotropic crosslinking gelation and were used as host materials for the encapsulation of rosemary essential oil. The unloaded/loaded CA and hybrid CA-MTN microcapsules were characterized by Fourier transform infra-red (FT-ATR) spectroscopy, thermal analysis (TGA), scanning electron microscopy (SEM) and DPPH assay. The evaluation of the microcapsule's physicochemical properties has shown that the clay filling with montmorillonite improved the microcapsule's properties. The encapsulation efficiency improved significantly in hybrid CA-MTN microcapsules and exhibited higher values ranging from 81 for CA to 83% for hybrid CA-MTN and a loading capacity of 71 for CA and 73% for hybrid CA-MTN, owing to the large adsorption capacity of the sodic clay. Moreover, the hybrid CA-MTN microcapsules showed a time-extended release of rosemary essential oil compared to CA microcapsules. Finally, the DPPH assay displayed a higher reduction of free radicals in hybrid CA-MNT-REO (12.8%) than CA-REO (10%) loaded microcapsules. These results proved that the clay-alginate combination provides microcapsules with enhanced properties compared to the polymer-based microcapsules.

Recent Advances in Cell Sheet Engineering: From Fabrication to Clinical Translation

Cell sheet engineering, a scaffold-free tissue fabrication technique, has proven to be an important breakthrough technology in regenerative medicine. Over the past two decades, the field has developed rapidly in terms of investigating fabrication techniques and multipurpose applications in regenerative medicine and biological research. This review highlights the most important achievements in cell sheet engineering to date. We first discuss cell sheet harvesting systems, which have been introduced in temperature-responsive surfaces and other systems to overcome the limitations of conventional cell harvesting methods. In addition, we describe several techniques of cell sheet transfer for preclinical (in vitro and in vivo) and clinical trials. This review also covers cell sheet cryopreservation, which allows short- and long-term storage of cells. Subsequently, we discuss the cell sheet properties of angiogenic cytokines and vasculogenesis. Finally, we discuss updates to various applications, from biological research to clinical translation. We believe that the present review, which shows and compares fundamental technologies and recent advances in cell engineering, can potentially be helpful for new and experienced researchers to promote the further development of tissue engineering in different applications.

Polymeric Materials, Advances and Applications in Tissue Engineering: A Review

Tissue Engineering (TE) is an interdisciplinary field that encompasses materials science in combination with biological and engineering sciences. In recent years, an increase in the demand for therapeutic strategies for improving quality of life has necessitated innovative approaches to designing intelligent biomaterials aimed at the regeneration of tissues and organs. Polymeric porous scaffolds play a critical role in TE strategies for providing a favorable environment for tissue restoration and establishing the interaction of the biomaterial with cells and inducing substances. This article reviewed the various polymeric scaffold materials and their production techniques, as well as the basic elements and principles of TE. Several interesting strategies in eight main TE application areas of epithelial, bone, uterine, vascular, nerve, cartilaginous, cardiac, and urinary tissue were included with the aim of learning about current approaches in TE. Different polymer-based medical devices approved for use in clinical trials and a wide variety of polymeric biomaterials are currently available as commercial products. However, there still are obstacles that limit the clinical translation of TE implants for use wide in humans, and much research work is still needed in the field of regenerative medicine.

Design, Characterization and Pharmacokinetic-Pharmacodynamic Evaluation of Poloxamer and Kappa-Carrageenan-Based Dual-Responsive In Situ Gel of Nebivolol for Treatment of Open-Angle Glaucoma

This study developed a dual-responsive in situ gel of nebivolol (NEB), a selective β-adrenergic antagonist. The gel could achieve sustained concentrations in the aqueous humor to effectively treat glaucoma. The gel was prepared using a combination of poloxamers (Poloxamer-407 (P407) and Poloxamer-188 (P188)) and kappa-carrageenan (κCRG) as thermo-responsive and ion-sensitive polymers, respectively. Box-Behnken design (BBD) was used to optimize the effect of three critical formulation factors (concentration of P407, P188 and κCRG) on two critical response variables (sol-to-gel transition temperature of 33-35 °C and minimum solution state viscosity) of the in situ gel. A desirability function was employed to find the optimal concentrations of P407, P188 and κCRG that yielded a gel with the desired sol-to-gel transition temperature and solution state viscosity. An NEB-loaded gel was prepared using the optimized conditions and evaluated for in vitro drug release properties and ex vivo ocular irritation studies. Furthermore, ocular pharmacokinetic and pharmacodynamics studies were conducted in rabbits for the optimized formulation. The optimized NEB-loaded gel containing P407, P188 and κCRG had a sol-to-gel transition temperature of 34 °C and exhibited minimum viscosity (212 ± 2 cP at 25 °C). The optimized NEB-loaded gel sustained drug release with 86% drug release at the end of 24 h. The optimized formulation was well tolerated in the eye. Ocular pharmacokinetic studies revealed that the optimized in situ gel resulted in higher concentrations of NEB in aqueous humor compared to the NEB suspension. The aqueous humor C_max of the optimized in situ gel (35.14 ± 2.25 ng/mL) was 1.2 fold higher than that of the NEB suspension (28.2 ± 3.1 ng/mL), while the AUC_0-∞ of the optimized in situ gel (381.8 ± 18.32 ng/mL*h) was 2 fold higher than that of the NEB suspension (194.9 ± 12.17 ng/mL*h). The systemic exposure of NEB was significantly reduced for the optimized in situ gel, with a 2.7-fold reduction in the plasma C_max and a 4.1-fold reduction in the plasma AUC_0-∞ compared with the NEB suspension. The optimized gel produced a higher and sustained reduction in the intra-ocular pressure compared with the NEB suspension. The optimized gel was more effective in treating glaucoma than the NEB suspension due to its mucoadhesive properties, sustained drug release and reduced drug loss. Lower systemic exposure of the optimized gel indicates that the systemic side effects can be significantly reduced compared to the NEB suspension, particularly in the long-term management of glaucoma.

Manuka Honey/2-Hydroxyethyl Methacrylate/Gelatin Hybrid Hydrogel Scaffolds for Potential Tissue Regeneration

Scaffolding biomaterials are gaining great importance due to their beneficial properties for medical purposes. Targeted biomaterial engineering strategies through the synergy of different material types can be applied to design hybrid scaffolding biomaterials with advantageous properties for biomedical applications. In our research, a novel combination of the bioactive agent Manuka honey (MHo) with 2-hydroxyethyl methacrylate/gelatin (HG) hydrogel scaffolds was created as an efficient bioactive platform for biomedical applications. The effects of Manuka honey content on structural characteristics, porosity, swelling performance, in vitro degradation, and in vitro biocompatibility (fibroblast and keratinocyte cell lines) of hybrid hydrogel scaffolds were studied using Fourier transform infrared spectroscopy, the gravimetric method, and in vitro MTT biocompatibility assays. The engineered hybrid hydrogel scaffolds show advantageous properties, including porosity in the range of 71.25% to 90.09%, specific pH- and temperature-dependent swelling performance, and convenient absorption capacity. In vitro degradation studies showed scaffold degradability ranging from 6.27% to 27.18% for four weeks. In vitro biocompatibility assays on healthy human fibroblast (MRC5 cells) and keratinocyte (HaCaT cells) cell lines by MTT tests showed that cell viability depends on the Manuka honey content loaded in the HG hydrogel scaffolds. A sample containing the highest Manuka honey content (30%) exhibited the best biocompatible properties. The obtained results reveal that the synergy of the bioactive agent, Manuka honey, with 2-hydroxyethyl methacrylate/gelatin as hybrid hydrogel scaffolds has potential for biomedical purposes. By tuning the Manuka honey content in HG hydrogel scaffolds advantageous properties of hybrid scaffolds can be achieved for biomedical applications.

Arginine-Coated Nanoglobules for the Nasal Delivery of Insulin

Multiple daily injections via subcutaneous route are the primary modes of insulin delivery for patients with Diabetes Mellitus. While this process is invasive, painful and may cause patients to develop lipohypertrophy at injection site, the perception of fear surrounding this process causes patients to delay in initiation and remain persistent with insulin therapy over time. Moreover, poor glycemic control may often lead to acute complications, such as severe hypoglycemia and nocturnal hypoglycemia, especially in older patients with diabetes. To address the imperative need for a patient-convenient non-invasive insulin therapy, an insulin-loaded arginine-coated self-emulsifying nanoglobule system (INS-LANano) was developed for nasal delivery of insulin with a biodegradable cationic surfactant-Lauroyl Ethyl Arginate (LAE). Incorporation of LAE resulted in formation of positively charged nanoglobules with L-arginine oriented on the surface. LANano enabled binding of insulin molecules on the surface of nanoglobules via an electrostatic interaction between negatively charged α-helix and LAE molecules at physiological pH. INS-LANano showed a hydrodynamic diameter of 23.38 nm with a surface charge of +0.118 mV. The binding efficiency of insulin on LANano globules was confirmed by zeta potential, circular dichroism (CD) spectroscopy and centrifugal ultrafiltration studies. The attachment of insulin with permeation-enhancing nanoglobules demonstrated significantly higher in vitro permeability of insulin of 15.2% compared to insulin solution across human airway epithelial cell (Calu-3) monolayer. Upon intranasal administration of INS-LANano to diabetic rats at 2 IU/kg insulin dose, a rapid absorption of insulin with significantly higher Cmax of 14.3 mU/L and relative bioavailability (BA) of 23.3% was observed. Therefore, the INS-LANano formulation significant translational potential for intranasal delivery of insulin.

Application of Multi-Layered Temperature-Responsive Polymer Brushes Coating on Titanium Surface to Inhibit Biofilm Associated Infection in Orthopedic Surgery

Infection associated with biomedical implants remains the main cause of failure, leading to reoperation after orthopedic surgery. Orthopedic infections are characterized by microbial biofilm formation on the implant surface, which makes it challenging to diagnose and treat. One potential method to prevent and treat such complications is to deliver a sufficient dose of antibiotics at the onset of infection. This strategy can be realized by coating the implant with thermoregulatory polymers and triggering the release of antibiotics during the acute phase of infection. We developed a multi-layered temperature-responsive polymer brush (MLTRPB) coating that can release antibiotics once the temperature reaches a lower critical solution temperature (LCST). The coating system was developed using copolymers composed of diethylene glycol methyl ether methacrylate and 2-hydroxyethyl methacrylate by alternatively fabricating monomers layer by layer on the titanium surface. LCST was set to the temperature of 38-40 °C, a local temperature that can be reached during infection. The antibiotic elution characteristics were investigated, and the antimicrobial efficacy was tested against S. aureus species (Xen29 ATCC 29 213) using one to four layers of MLTRPB. Both in vitro and in vivo assessments demonstrated preventive effects when more than four layers of the coating were applied, ensuring promising antibacterial effects of the MLTRPB coating.

Growth Factor Binding Peptides in Poly (Ethylene Glycol) Diacrylate (PEGDA)-Based Hydrogels for an Improved Healing Response of Human Dermal Fibroblasts

Growth factors (GF) are critical cytokines in wound healing. However, the direct delivery of these biochemical cues into a wound site significantly increases the cost of wound dressings and can lead to a strong immunological response due to the introduction of a foreign source of GFs. To overcome this challenge, we designed a poly(ethylene glycol) diacrylate (PEGDA) hydrogel with the potential capacity to sequester autologous GFs directly from the wound site. We demonstrated that synthetic peptide sequences covalently tethered to PEGDA hydrogels physically retained human transforming growth factor beta 1 (hTGFβ1) and human vascular endothelial growth factor (hVEGF) at 3.2 and 0.6 ng/mm², respectively. In addition, we demonstrated that retained hTGFβ1 and hVEGF enhanced human dermal fibroblasts (HDFa) average cell surface area and proliferation, respectively, and that exposure to both GFs resulted in up to 1.9-fold higher fraction of area covered relative to the control. After five days in culture, relative to the control surface, non-covalently bound hTGFβ1 significantly increased the expression of collagen type I and hTGFβ1 and downregulated vimentin and matrix metalloproteinase 1 expression. Cumulatively, the response of HDFa to hTGFβ1 aligns well with the expected response of fibroblasts during the early stages of wound healing.

Improved Hemocompatibility on Superhemophobic Micro-Nano-Structured Titanium Surfaces

Blood-contacting titanium-based implants such as endovascular stents and heart valve casings are prone to blood clotting due to improper interactions at the surface level. In complement, the current clinical demand for cardiovascular implants is at a new apex. Hence, there is a crucial necessity to fabricate an implant with optimal mechanical properties and improved blood compatibility, while simultaneously interacting differentially with cells and other microbial agents. The present study intends to develop a superhydrophobic implant surface with the novel micro-nano topography, developed using a facile thermochemical process. The surface topography, apparent contact angle, and crystal structure are characterized on different surfaces. The hemo/blood compatibility on different surfaces is assessed by evaluating hemolysis, fibrinogen adsorption, cell adhesion and identification, thrombin generation, complement activation, and whole blood clotting kinetics. The results indicate that the super-hemo/hydrophobic micro-nano titanium surface improved hemocompatibility by significantly reducing fibrinogen adsorption, platelet adhesion, and leukocyte adhesion. Thus, the developed surface has high potential to be used as an implant. Further studies are directed towards analyzing the mechanisms causing the improved hemocompatibility of micro/nano surface features under dynamic in vitro and in vivo conditions.

Adjustable Thermo-Responsive, Cell-Adhesive Tissue Engineering Scaffolds for Cell Stimulation through Periodic Changes in Culture Temperature

A three-dimensional (3D) scaffold ideally provides hierarchical complexity and imitates the chemistry and mechanical properties of the natural cell environment. Here, we report on a stimuli-responsive photo-cross-linkable resin formulation for the fabrication of scaffolds by continuous digital light processing (cDLP), which allows for the mechano-stimulation of adherent cells. The resin comprises a network-forming trifunctional acrylate ester monomer (trimethylolpropane triacrylate, or TMPTA), N-isopropyl acrylamide (NiPAAm), cationic dimethylaminoethyl acrylate (DMAEA) for enhanced cell interaction, and 4-acryloyl morpholine (AMO) to adjust the phase transition temperature (T_trans) of the equilibrium swollen cross-polymerized scaffold. With glycofurol as a biocompatible solvent, controlled three-dimensional structures were fabricated and the transition temperatures were adjusted by resin composition. The effects of the thermally induced mechano-stimulation were investigated with mouse fibroblasts (L929) and myoblasts (C2C12) on printed constructs. Periodic changes in the culture temperature stimulated the myoblast proliferation.

Recent Advances in the Biomedical Applications of Functionalized Nanogels

Nanomaterials have been extensively used in several applications in the past few decades related to biomedicine and healthcare. Among them, nanogels (NGs) have emerged as an important nanoplatform with the properties of both hydrogels and nanoparticles for the controlled/sustained delivery of chemo drugs, nucleic acids, or other bioactive molecules for therapeutic or diagnostic purposes. In the recent past, significant research efforts have been invested in synthesizing NGs through various synthetic methodologies such as free radical polymerization, reversible addition-fragmentation chain-transfer method (RAFT) and atom transfer radical polymerization (ATRP), as well as emulsion techniques. With further polymeric functionalizations using activated esters, thiol-ene/yne processes, imines/oximes formation, cycloadditions, nucleophilic addition reactions of isocyanates, ring-opening, and multicomponent reactions were used to obtain functionalized NGs for targeted delivery of drug and other compounds. NGs are particularly intriguing for use in the areas of diagnosis, analytics, and biomedicine due to their nanodimensionality, material characteristics, physiological stability, tunable multi-functionality, and biocompatibility. Numerous NGs with a wide range of functionalities and various external/internal stimuli-responsive modalities have been possible with novel synthetic reliable methodologies. Such continuous development of innovative, intelligent materials with novel characteristics is crucial for nanomedicine for next-generation biomedical applications. This paper reviews the synthesis and various functionalization strategies of NGs with a focus on the recent advances in different biomedical applications of these surface modified/functionalized single-/dual-/multi-responsive NGs, with various active targeting moieties, in the fields of cancer theranostics, immunotherapy, antimicrobial/antiviral, antigen presentation for the vaccine, sensing, wound healing, thrombolysis, tissue engineering, and regenerative medicine.

Antibacterial Activity and Biocompatibility with the Concentration of Ginger Fraction in Biodegradable Gelatin Methacryloyl (GelMA) Hydrogel Coating for Medical Implants

The gingerols and shogaols derived from ginger have excellent antibacterial properties against oral bacteria. However, some researchers have noted their dose-dependent potential toxicity. The aim of this study was to enhance the biofunctionality and biocompatibility of the application of ginger to dental titanium screws. To increase the amount of coating of the n-hexane-fractionated ginger on the titanium surface and to control its release, ginger was loaded in different concentrations in a photo-crosslinkable GelMA hydrogel. To improve coating stability of the ginger hydrogel (GH), the wettability of the surface was modified by pre-calcification (TNC), then GH was applied on the surface. As a result, the ginger fraction, with a high content of phenolic compounds, was effective in the inhibition of the growth of S. mutans and P. gingivalis. The GH slowly released the main compounds of ginger and showed excellent antibacterial effects with the concentration. Although bone regeneration was slightly reduced with the ginger-loading concentration due to the increased contents of polyphenolic compounds, it was strongly supplemented through the promotion of osteosis formation by the hydrogel and TNC coating. Finally, we proved the biosafety and superior biofunctionalities the GH-TNC coating on a Ti implant. However, it is recommended to use an appropriate concentration, because an excessive concentration of ginger may affect the improved biocompatibility in clinical applications.

Preparation of Temperature-Responsive Antibody–Nanoparticles by RAFT-Mediated Grafting from Polymerization

Herein, we report the preparation of temperature-responsive antibody–nanoparticles by the direct polymerization of N-isopropylacrylamide (NIPAAm) from immunoglobulin G (IgG). To this end, a chain transfer agent (CTA) was introduced into IgG, followed by the precipitation polymerization of NIPAAm in an aqueous medium via reversible addition–fragmentation chain transfer polymerization above the lower critical solution temperature (LCST). Consequently, antibody–polymer particles with diameters of approximately 100–200 nm were formed. Owing to the entanglement of the grafted polymers via partial chemical crosslinking, the antibody–nanoparticles maintained their stability even at temperatures below the LCST. Further, the dispersed nanoparticles could be collected by thermal precipitation above the LCST. Additionally, the antibody–nanoparticles formulation could maintain its binding constant and exhibited a good resistance against enzymatic treatment. Thus, the proposed antibody–nanoparticles can be useful for maximizing the therapeutic potential of antibody–drug conjugates or efficacies of immunoassays and antibody recovery and recycling.