Hydrogels for tissue engineering and delivery of tissue-inducing substances

Enhanced osteochondral repair by leukocyte-depleted platelet-rich plasma in combination with adipose-derived mesenchymal stromal cells encapsulated in a three-dimensional photocrosslinked injectable hydrogel in a rabbit model

INTRODUCTION

Intra-articular injection of adipose-derived mesenchymal stromal cells (ASCs) and/or platelet-rich plasma (PRP) have been reported to independently and synergistically improve healing of osteochondral lesions in animal models. However, their independent and combined effects when localized to an osteochondral lesion by encapsulation within a photocrosslinkable methacrylated gelatin hydrogel (GelMA) have not been explored. Herein we investigated a unique combination of allogeneic ASCs and PRP embedded in GelMA as a single-stage treatment for osteochondral regeneration in a rabbit model.

METHODS

Thirty mature rabbits were divided into six experimental groups: (1) Sham; (2) Defect; (3) GelMA; (4) GelMA + ASCs; (5) GelMA + PRP; and (6) GelMA + ASCs + PRP.At 12 weeks following surgical repair, osteochondral regeneration was assessed on the basis of gross appearance, biomechanical properties, histological and immunohistochemical characteristics, and subchondral bone volume.

RESULTS

In terms of mechanical property reflecting the ability of neotissue to bear stress, PRP only group were significantly lower than the Sham group (p = 0.0098). On the other hand, ASCs only and ASCs combined with PRP groups did not exhibit significantly difference, which suggesting that incorporation of ASCs assists in restoring the ability of the neotissue to bear stresses similarly to native tissue (p = 0.346, p = 0.40, respectively). Safranin O in ASCs combined with PRP group was significantly higher than the Defect and GelMA only groups (p = 0.0009, p = 0.0017, respectively). Additionally, ASCs only and ASCs combined with PRP groups presented especially strong staining for collagen type II. Surprisingly, PRP only and PRP + ASCs groups tended to exhibit higher collagen type I and collagen type X staining compared to ASCs only group, suggesting a potential PRP-mediated hypertrophic effect.

CONCLUSION

Regeneration of a focal osteochondral defect in a rabbit model was improved by a single-stage treatment of a photocrosslinked hydrogel containing allogenic ASCs and autologous PRP, with the combination of ASCs and PRP producing superior benefit than either alone. No experimental construct fully restored all properties of the native, healthy osteochondral unit, which may require longer follow-up or further modification of PRP and/or ASCs characteristics.

Microstructure of the silk fibroin-based hydrogel scaffolds derived from the orb-web spider Trichonephila clavata

Due to the unique properties of the silk fibroin (SF) made from silkworm, SF-based hydrogels have recently received significant attention for various biomedical applications. However, research on the SF-based hydrogels isolated from spider silks has been rtricted due to the limited collection and preparation of naïve silk materials. Therefore, this study focused on the microstructural characteristics of hydrogel scaffolds derived from two types of woven silk glands: the major ampullate gland (MAG) and the tubuliform gland (TG), in the orb-web spider Trichonephila clavate. We compared these spider glands with those of the silk fibroin (SF) hydrogel scaffold extracted from the cocoon of the insect silkworm Bombyx mori. Our FESEM analysis revealed that the SF hydrogel has high porosity, translucency, and a loose upper structure, with attached SF fibers providing stability. The MAG hydrogel displayed even higher porosity, as well as elongated fibrous structures, and improved mechanical properties: while the TG hydrogel showed increased porosity, ridge-like or wall-like structures, and stable biocapacity formed by physical crosslinking. Due to their powerful and versatile microstructural characteristics, the MAG and TG hydrogels can become tailored substrates, very effective for tissue engineering and regenerative medicine applications.

Interplay between Diffusion and Bond Cleavage Reaction for Determining Release in Polymer-Drug Conjugates

In conjugated polymeric drug delivery systems, both the covalent bond degradation rate and the diffusion of the freely moving drug particles affect the release profile of the formulation. Using Monte Carlo simulations in spherical matrices, the release kinetics resulting from the competition between the reaction and diffusion processes is discussed. For different values of the relative bond cleavage rate, varied over four orders of magnitude, the evolution of (i) the number of bonded drug molecules, (ii) the fraction of the freely moved detached drug within the polymer matrix, and (iii) the resulting fractional release of the drug is presented. The characteristic release time scale is found to increase by several orders of magnitude as the cleavage reaction rate constant decreases. The two extreme rate-limiting cases where either the diffusion or the reaction dominates the release are clearly distinguishable. The crossover between the diffusion-controlled and reaction-controlled regimes is also examined and a simple analytical formula is presented that can describe the full dependence of the release time on the bond cleavage rate constant. This simple relation is provided simply by the sum of the characteristic time for purely diffusional release and the bond cleavage decay time, which equals the inverse of the reaction rate constant.

Advanced applications of strontium-containing biomaterials in bone tissue engineering

Strontium (Sr) and strontium ranelate (SR) are commonly used therapeutic drugs for patients suffering from osteoporosis. Researches have showed that Sr can significantly improve the biological activity and physicochemical properties of materials in vitro and in vivo. Therefore, a large number of strontium containing biomaterials have been developed for repairing bone defects and promoting osseointegration. In this review, we provide a comprehensive overview of Sr-containing biomaterials along with the current state of their clinical use. For this purpose, the different types of biomaterials including calcium phosphate, bioactive glass, and polymers are discussed and provided future outlook on the fabrication of the next-generation multifunctional and smart biomaterials.

Viscoelastic properties of pNIPAM-hydrogels: A mode-coupling theory study

We investigate the viscoelastic properties of poly(N-isopropylacrylamide) (pNIPAM) hydrogels cross-linked with glutaraldehyde by means of small amplitude oscillatory and steady shear experiments in dependence on the frequency and shear rate. These properties are strongly influenced by the ratio of monomer and glutaraldehyde as a cross-linker. Due to the thermosensitivity of pNIPAM, the rheological properties of these hydrogels can be tuned by the temperature as an external stimulus. The experimentally obtained viscosities and linear viscoelastic moduli are analyzed by a schematic mode-coupling ansatz employing a rescaled F₁₂-model.

Methacrylic acid based microgels and hybrid microgels

Methacrylic acid based microgels have got much consideration in the last two decades because of their potential uses in different fields owing to their responsive behaviour towards external stimuli. Synthesis, properties and uses of methacrylic acid based microgels and their hybrids have been critically reviewed in this article. With minute change in external stimuli such as pH and ionic strength of medium, these microgels show quick swelling/deswelling reversibly. The methacrylic acid based microgels have been widely reported for applications in the area of nanotechnology, drug delivery, sensing and catalysis due to their responsive behaviour. A critical review of current research development in this field along with upcoming perception is presented here. This discussion is concluded with proposed probable future studies for additional growth in this field of research.

Drug Delivery Strategies and Biomedical Significance of Hydrogels: Translational Considerations

Hydrogels are a promising and attractive option as polymeric gel networks, which have immensely fascinated researchers across the globe because of their outstanding characteristics such as elevated swellability, the permeability of oxygen at a high rate, good biocompatibility, easy loading, and drug release. Hydrogels have been extensively used for several purposes in the biomedical sector using versatile polymers of synthetic and natural origin. This review focuses on functional polymeric materials for the fabrication of hydrogels, evaluation of different parameters of biocompatibility and stability, and their application as carriers for drugs delivery, tissue engineering and other therapeutic purposes. The outcome of various studies on the use of hydrogels in different segments and how they have been appropriately altered in numerous ways to attain the desired targeted delivery of therapeutic agents is summarized. Patents and clinical trials conducted on hydrogel-based products, along with scale-up translation, are also mentioned in detail. Finally, the potential of the hydrogel in the biomedical sector is discussed, along with its further possibilities for improvement for the development of sophisticated smart hydrogels with pivotal biomedical functions.

Dual-responsive nisin loaded chondroitin sulfate nanogel for treatment of bacterial infection in soft tissues

Chondroitin sulfate-Nisin nanogels (CS-N NGs) were prepared by electrostatic interaction for nisin delivery as an antibacterial agent in the treatment of bacterial infections caused by some clinical strains of methicillin-resistant and methicillin-sensitive Staphylococcus aureus (S. aureus). The physical properties of CS-N NGs were evaluated using Fourier-transform infrared spectroscopy, dynamic light scattering, and field emission scanning electron microscopy. The average diameter of obtained CS-N NGs was about 65 nm and the stability of nanogels was assessed by zeta potential measurement. Enzyme and pH-responsibility of CS-N NGs due to the presence of susceptible bonds in chondroitin sulfate resulted in effective and controlled release of nisin in the simulated infectious medium. Also, the ability of prepared CS-N NGs for eradicating clinical methicillin resistance S. aureus strain was confirmed by Broth Microdilution Method (BMD) and the cytotoxicity analysis was carried out on Human Dermal Fibroblast (HDF) cells by MTT assay method. Based on the results, this versatile drug carrier could efficiently deliver the cationic antimicrobial peptides as a natural antibiotic for growth inhibition of methicillin-resistant S. aureus strains and further destroying the bacteria in the treatment of subcutaneous infections caused by methicillin-resistant S. aureus strains.

A review on preparations, properties, and applications of cis-ortho-hydroxyl polysaccharides hydrogels crosslinked with borax

Polysaccharides-based hydrogel has many advantages such as biocompatibility, self-repair property, and biodegradability. It has been widely applied in various fields and has attracted great attention of researchers. The natural polysaccharides involved in this review include fenugreek gum, guar gum, locust bean gum, gellan gum, sodium alginate, agarose, and konjac glucomannan etc. Borax is a highly effective crosslinking agent for cis-ortho-hydroxyl polysaccharides. This paper focused on the synthesis mechanism, functional additives, characteristics, and applications of borax crosslinked cis-ortho-hydroxyl polysaccharides hydrogels (BHs). Moreover, the factors affecting BHs performance such as temperature, pH, and media were analyzed. Its mechanical and self-repair properties are enhanced by the dynamic and reversible borate/di-diol, which play a significant role in sensors, biomedicine, and tissue engineering. This review summarizes the research progress of BHs for the first time. Additionally, hoping to contribute to the development of this field, the review analyzes the correlation of performance through the SPSS 26 software.

Multifunctional temperature-responsive polymers as advanced biomaterials and beyond

The versatility and applicability of thermoresponsive polymeric systems have led to great interest and a multitude of publications. Of particular significance, multifunctional poly(N-isopropylacrylamide) (PNIPAAm) systems based on PNIPAAm copolymerized with various functional comonomers or based on PNIPAAm combined with nanomaterials exhibiting unique properties. These multifunctional PNIPAAm systems have revolutionized several biomedical fields such as controlled drug delivery, tissue engineering, self-healing materials, and beyond (e.g., environmental treatment applications). Here, we review these multifunctional PNIPAAm-based systems with various cofunctionalities, as well as highlight their unique applications. For instance, addition of hydrophilic or hydrophobic comonomers can allow for polymer lower critical solution temperature modification, which is especially helpful for physiological applications. Natural comonomers with desirable functionalities have also drawn significant attention as pressure surmounts to develop greener, more sustainable materials. Typically, these systems also tend to be more biocompatible and biodegradable and can be advantageous for use in biopharmaceutical and environmental applications. PNIPAAm-based polymeric nanocomposites are reviewed as well, where incorporation of inorganic or carbon nanomaterials creates synergistic systems that tend to be more robust and widely applicable than the individual components.

Unravelling the formation of BAB block copolymer assemblies during PISA in water

BAB triblock copolymers prepared by PISA in water self-assemble into a transient network of bridged micelles. The slowdown of the exchange of B blocks between micelles during PISA is highlighted as well as the parameters affecting the polymerization.

Chitosan Microbeads Produced by One-Step Scalable Stirred Emulsification: A Promising Process for Cell Therapy Applications

Cell microencapsulation is a promising approach to improve cell therapy outcomes by protecting injected cells from rapid dispersion and allowing bidirectional diffusion of nutrients, oxygen, and waste that promote cell survival in the target tissues. Here, we describe a simple and scalable emulsification method to encapsulate animal cells in chitosan microbeads using thermosensitive gel formulations without any chemical modification and cross-linker. The process consists of a water-in-oil emulsion where the aqueous phase droplets contain cells (L929 fibroblasts or human mesenchymal stromal cells), chitosan acidic solution and gelling agents (sodium hydrogen carbonate and phosphate buffer or beta-glycerophosphate). The oil temperature is maintained at 37 °C, allowing rapid physical gelation of the microbeads. Alginate beads prepared with the same method were used as a control. Microbeads with a diameter of 300-450 μm were successfully produced. Chitosan and alginate (2% w/v) microbeads presented similar rigidity in compression, but chitosan microbeads endured >80% strain without rupture, while alginate microbeads presented fragile breakage at <50% strain. High cell viability and metabolic activity were observed after up to 7 days in culture for encapsulated cells. Mesenchymal stromal cells encapsulated in chitosan microbeads released higher amounts of the vascular endothelial growth factor after 24 h compared to the cells encapsulated in manually cast macrogels. Moreover, microbeads were injectable through 23G needles without significant deformation or rupture. The emulsion-generated chitosan microbeads are a promising delivery vehicle for therapeutic cells because of their cytocompatibility, biodegradation, mechanical strength, and injectability. Clinical-scale encapsulation of therapeutic cells such as mesenchymal stromal cells in chitosan microbeads can readily be achieved using this simple and scalable emulsion-based process.

Mechanically robust photodegradable gelatin hydrogels for 3D cell culture and in situ mechanical modification

Highly conjugated, hydrophobically modified gelatin hydrogels were synthesized, polymerized and degraded with orthogonal wavelengths of light.

Improving the Mechanical Rigidity of Hyaluronic Acid by Integration of a Supramolecular Peptide Matrix

Hyaluronic acid (HA), a major component of the extracellular matrix, is an attractive material for various medical applications. Yet, its low mechanical rigidity and fast in vivo degradation hinder its utilization. Here, we demonstrate the reinforcement of HA by its integration with a low-molecular-weight peptide hydrogelator to produce a composite hydrogel. The formulation of HA with the fluorenylmethoxycarbonyl diphenylalanine (FmocFF) peptide, one of the most studied self-assembling hydrogel-forming building blocks, showing notable mechanical properties, resulted in the formation of stable, homogeneous hydrogels. Electron microscopy analysis demonstrated a uniform distribution of the two matrices in the composite forms. The composite hydrogels showed improved mechanical properties and stability to enzymatic degradation while maintaining their biocompatibility. Moreover, the storage modulus of the FmocFF/HA composite hydrogels reached up to 25 kPa. The composite hydrogels allowed sustained release of curcumin, a hydrophobic polyphenol showing antioxidant, anti-inflammatory, and antitumor activities. Importantly, the rate of curcumin release was modulated as a function of the concentration of the FmocFF peptide within the hydrogel matrix. This work provides a new approach for conferring mechanical rigidity and stability to HA without the need of cross-linking, thus potentially facilitating its utilization in different clinical applications, such as sustained drug release.

A novel hydrogel scaffold for periodontal ligament stem cells

Periodontal ligament stem cells (PDLSCs) possess extensive regeneration potential. However, their therapeutic application demands a scaffold with appropriate properties. HydroMatrix (HydM) is a novel injectable peptide nanofiber hydrogel developed recently for cell culture. Our aim was to test whether HydM would be a suitable scaffold for proliferation and osteogenic differentiation of PDLSCs. PDLSCs were seeded on non-coated or HydM-coated surfaces. Both real-time impedance analysis and cell viability assay documented cell growth on HydM. PDLSCs showed healthy, fibroblast-like morphology on the hydrogel. After a 3-week-long culture in osteogenic medium, mineralization was much more intense in HydM cultures compared to control. Alkaline phosphatase activity of the cells grown on the gels reached the non-coated control levels. Our data provided evidence that PDLSCs can adhere, survive, migrate, and proliferate on HydM and this gel also supports their osteogenic differentiation. We first applied impedimetry for dental stem cells cultured on a scaffold. HydM is ideal for in vitro studies of PDLSCs. It may also serve not only as a reference material but also in the future as a promising biocompatible scaffold for preclinical studies.

Preparation and Characterization of Silver Sulfadiazine-Loaded Polyvinyl Alcohol Hydrogels as an Antibacterial Wound Dressing

In this study, we prepared a series of silver sulfadiazine (AgSD)-loaded polyvinyl alcohol (PVA) hydrogels via electron beam (e-beam) irradiation. Our objective was to explore the influence of e-beam irradiation on the chemical structure and crystallinity of AgSD and the antibacterial properties of AgSD/PVA hydrogels. Prior to irradiation, we mixed AgSD in PVA solution in 2 forms, either suspended in water (WS) or dissolved in ammonia solution (AS). We noted that nano silver was released from AgSD/PVA-AS hydrogels immersed in deionized water, while it would not happen in AgSD/PVA-WS hydrogels. Both kinds of AgSD/PVA hydrogels exhibited good antibacterial activities against gram-negative Escherichia coli and gram-positive Staphylococcus aureus. And their antibacterial activity was not obviously affected by different dosages of e-beam irradiation. Moreover, the antibacterial activity of the AgSD/PVA-WS hydrogels was stronger than that of AgSD/PVA-AS. Accordingly, the cell cytotoxicity of the AgSD/PVA-WS hydrogels was higher than that of AgSD/PVA-AS. Our study results reveal that e-beam irradiation of PVA solution with dispersed AgSD is a simple and efficient way to prepare AgSD/PVA hydrogels, which might be an ideal antibacterial wound dressing.

Photoresponsive Hydrogels with Photoswitchable Mechanical Properties Allow Time-Resolved Analysis of Cellular Responses to Matrix Stiffening

As cell function and phenotype can be directed by the mechanical characteristics of the surrounding matrix, hydrogels have become important platforms for cell culture systems, with properties that can be tuned by external stimuli, such as divalent cations, enzymatic treatment, and pH. However, many of these stimuli can directly affect cell behavior, making it difficult to distinguish purely mechanical signaling events. This study reports on the development of a hydrogel that incorporates photoswitchable cross-linkers, which can reversibly alter their stiffness upon irradiation with the appropriate wavelength of light. Furthermore, this study reports the response of bone-marrow-derived mesenchymal stem cells (MSCs) on these hydrogels that were stiffened systematically by irradiation with blue light. The substrates were shown to be noncytotoxic, and crucially MSCs were not affected by blue-light exposure. Time-resolved analysis of cell morphology showed characteristic cell spreading and increased aspect ratios in response to greater substrate stiffness. This hydrogel provides a platform to study mechanosignaling in cells responding to dynamic changes in stiffness, offering a new way to study mechanotransduction signaling pathways and biological processes, with implicit changes to tissue mechanics, such as development, ageing, and fibrosis.

Natural and Synthetic Biodegradable Polymers: Different Scaffolds for Cell Expansion and Tissue Formation

The formation of tissue produced by implanted cells is influenced greatly by the scaffold onto which they are seeded. In the long term it is often preferable to use a biodegradable material scaffold so that all the implanted materials will disappear, leaving behind only the generated tissue. Research in this area has identified several natural biodegradable materials. Among them, hydrogels are receiving increasing attention due to their ability to retain a great quantity of water, their good biocompatibility, their low interfacial tension, and the minimal mechanical and frictional irritation that they cause. Biocompatibility is not an intrinsic property of materials; rather it depends on the biological environment and the tolerability that exists with respect to specific polymer-tissue interactions. The most often utilized biodegradable synthetic polymers for 3D scaffolds in tissue engineering are saturated poly-a-hydroxy esters, including poly(lactic acid) (PLA) and poly(glycolic acid) (PGA), as well as poly(lactic-co-lycolide) (PLGA) copolymers. Hard materials provide compressive and torsional strength; hydrogels and other soft composites more effectively promote cell expansion and tissue formation. This review focuses on the future potential for understanding the characteristics of the biomaterials considered evaluated for clinical use in order to repair or to replace a sizable defect by only harvesting a small tissue sample.

Hydrogels for Biomedical Applications: Their Characteristics and the Mechanisms behind Them

Hydrogels are hydrophilic, three-dimensional networks that are able to absorb large quantities of water or biological fluids, and thus have the potential to be used as prime candidates for biosensors, drug delivery vectors, and carriers or matrices for cells in tissue engineering. In this critical review article, advantages of the hydrogels that overcome the limitations from other types of biomaterials will be discussed. Hydrogels, depending on their chemical composition, are responsive to various stimuli including heating, pH, light, and chemicals. Two swelling mechanisms will be discussed to give a detailed understanding of how the structure parameters affect swelling properties, followed by the gelation mechanism and mesh size calculation. Hydrogels prepared from natural materials such as polysaccharides and polypeptides, along with different types of synthetic hydrogels from the recent reported literature, will be discussed in detail. Finally, attention will be given to biomedical applications of different kinds of hydrogels including cell culture, self-healing, and drug delivery.

Temporal Control of Osteoblast Cell Growth and Behavior Dictated by Nanotopography and Shear Stress

Biomaterial design involves assessment of cellular response to nanotopography parameters such as shape, dimension of nanotopography features. Here, the effect of nanotopography alongside the in vivo factor, shear stress, on osteoblast cell behavior, is reported. Tantalum oxide nanodots of 50 or 100 nm diameter were engineered using anodized aluminum oxide as a template. Bare tantalum nitride coated silicon substrates were taken as control (flat). MG63 (osteoblast) cells were seeded for 72 hours on flat, 50 or 100 nm nanodots and modulation in cell morphology, cell viability and expression of integrins was studied. Cells displayed a well-extended morphology on 50 nm nanodots in contrast to an elongated morphology on 100 nm nanodots, as observed by scanning electron microscopy and immunofluorescence staining, thereby confirming the cellular response to different nanotopographies. Based on quantitative real-time polymerase chain reaction data, a greater fold change in the expression of α1 , α2 , α3 , α8 , α9 , [Formula: see text], β1 , β4 , β5 , β7 and β8 integrins was observed in cells cultured on 100 nm than on 50 nm nanodots. Moreover, in the presence of a shear stress of 2 dyne/cm², a 52% increase in the cell viability after culturing the cells for 72 hours was observed on 100 nm nanodots as compared to 50 nm nanodots, thereby validating the effect of shear stress on cell behavior. Duration-of-culture experiments revealed 100 nm nanodots to be an ideal nanotopography choice to engineer optimized implant geometries for an ideal cell response. This study highlights the in vivo factors which need to be considered while designing nanotopographies for in vivo applications, for an ideal response as the cell-nanomaterial interface. Applications in the field of Biomedical, tissue engineering and cancer research are expected.

Role of Mechanical Factors in Applications of Stimuli-Responsive Polymer Gels - Status and Prospects

Due to their unique characteristics such as multifold change of volume in response to minute change in the environment, resemblance of soft biological tissues, ability to operate in wet environments, and chemical tailorability, stimuli responsive gels represent a versatile and very promising class of materials for sensors, muscle-type actuators, biomedical applications, and autonomous intelligent structures. Success of these materials in practical applications largely depends on their ability to fulfill application-specific mechanical requirements. This article provides an overview of recent application-driven development of covalent polymer gels with special emphasis on the relevant mechanical factors and properties. A short account of mechanisms of gel swelling and mechanical characteristics of importance to stimuli-responsive gels is presented. The review highlights major barriers for wider application of these materials and discusses latest advances and potential future directions toward overcoming these barriers, including interpenetrating networks, homogeneous networks, nanocomposites, and nanofilamentary gels.

Nanostructured ultra-thin patches for ultrasound-modulated delivery of anti-restenotic drug

This work aims to demonstrate the possibility to fabricate ultra-thin polymeric films loaded with an anti-restenotic drug and capable of tunable drug release kinetics for the local treatment of restenosis. Vascular nanopatches are composed of a poly(lactic acid) supporting membrane (thickness: ~250 nm) on which 20 polyelectrolyte bilayers (overall thickness: ~70 nm) are alternatively deposited. The anti-restenotic drug is embedded in the middle of the polyelectrolyte structure, and released by diffusion mechanisms. Nanofilm fabrication procedure and detailed morphological characterization are reported here. Barium titanate nanoparticles (showing piezoelectric properties) are included in the polymeric support and their role is investigated in terms of influence on nanofilm morphology, drug release kinetics, and cell response. Results show an efficient drug release from the polyelectrolyte structure in phosphate-buffered saline, and a clear antiproliferative effect on human smooth muscle cells, which are responsible for restenosis. In addition, preliminary evidences of ultrasound-mediated modulation of drug release kinetics are reported, thus evaluating the influence of barium titanate nanoparticles on the release mechanism. Such data were integrated with quantitative piezoelectric and thermal measurements. These results open new avenues for a fine control of local therapies based on smart responsive materials.

In Vivo Assessment of Bone Regeneration in Alginate/Bone ECM Hydrogels with Incorporated Skeletal Stem Cells and Single Growth Factors

The current study has investigated the use of decellularised, demineralised bone extracellular matrix (ECM) hydrogel constructs for in vivo tissue mineralisation and bone formation. Stro-1-enriched human bone marrow stromal cells were incorporated together with select growth factors including VEGF, TGF-β3, BMP-2, PTHrP and VitD3, to augment bone formation, and mixed with alginate for structural support. Growth factors were delivered through fast (non-osteogenic factors) and slow (osteogenic factors) release PLGA microparticles. Constructs of 5 mm length were implanted in vivo for 28 days within mice. Dense tissue assessed by micro-CT correlated with histologically assessed mineralised bone formation in all constructs. Exogenous growth factor addition did not enhance bone formation further compared to alginate/bone ECM (ALG/ECM) hydrogels alone. UV irradiation reduced bone formation through degradation of intrinsic growth factors within the bone ECM component and possibly also ECM cross-linking. BMP-2 and VitD3 rescued osteogenic induction. ALG/ECM hydrogels appeared highly osteoinductive and delivery of angiogenic or chondrogenic growth factors led to altered bone formation. All constructs demonstrated extensive host tissue invasion and vascularisation aiding integration and implant longevity. The proposed hydrogel system functioned without the need for growth factor incorporation or an exogenous inducible cell source. Optimal growth factor concentrations and spatiotemporal release profiles require further assessment, as the bone ECM component may suffer batch variability between donor materials. In summary, ALG/ECM hydrogels provide a versatile biomaterial scaffold for utilisation within regenerative medicine which may be tailored, ultimately, to form the tissue of choice through incorporation of select growth factors.

The effect of albumin and cholesterol on the biotribological behavior of hydrogels for contact lenses

The irritation/discomfort associated with the use of contact lenses (CLs) is often related to the eyelid-lens friction. Although the use of such devices is widespread, the information about the influence of the lacrimal fluid biomolecules on the tribological behavior of the CLs hydrogels is scarce. In this work, we investigated the effect of the presence of albumin and cholesterol in the lubricant medium, on the frictional response of two model hydrogels for CLs: a hydroxyethylmethacrylate based hydrogel, HEMA/PVP, and a silicone based one, TRIS/NVP/HEMA. Tribological experiments were done in a nanotribometer, in water and in the presence of solutions of those biomolecules. It was observed a significant increase of the friction coefficient (μ) for HEMA/PVP when the lubricant contains cholesterol, and for TRIS/NVP/HEMA when it contains albumin. Solid-state NMR and DSC analysis revealed that HEMA/PVP hydrated in cholesterol solution has a lower amount of free and loosely bound water than the hydrogel hydrated in water. Therefore, a smaller amount of water shall be released into the contact region during the friction tests with cholesterol solution, leading to a thinner film in the contact zone, and consequently to a higher μ. Concerning TRIS/NVP/HEMA, QCM-D studies showed that this hydrogel adsorbs less albumin than HEMA/PVP and that the formed film is more rigid, which can explain the increase of μ. The obtained results contribute to understand the influence of lacrimal fluid composition on the tribological behavior of CLs materials, being relevant for the selection and optimization of these devices.

STATEMENT OF SIGNIFICANCE

Understanding the tribological behavior of contact lenses (CLs) materials in contact with the lacrimal fluid and the role of its components is of major importance to optimize the comfort and overall success of these devices. Nevertheless, the available information on this subject in the literature is scarce. In this work, the effect of albumin and cholesterol (two of the main components of the lacrimal fluid) on the frictional response of distinct types of hydrogels suitable for CLs, is compared, for the first time. Significant differences were observed with the two molecules, depending on the material, stressing the need to further study this issue to understand, predict and optimize the in vivo performance of CLs.

Novel nanocomposite biomaterials with controlled copper/calcium release capability for bone tissue engineering multifunctional scaffolds

This work aimed to develop novel composite biomaterials for bone tissue engineering (BTE) made of bioactive glass nanoparticles (Nbg) and alginate cross-linked with Cu(2+) or Ca(2+) (AlgNbgCu, AlgNbgCa, respectively). Two-dimensional scaffolds were prepared and the nanocomposite biomaterials were characterized in terms of morphology, mechanical strength, bioactivity, biodegradability, swelling capacity, release profile of the cross-linking cations and angiogenic properties. It was found that both Cu(2+) and Ca(2+) are released in a controlled and sustained manner with no burst release observed. Finally, in vitro results indicated that the bioactive ions released from both nanocomposite biomaterials were able to stimulate the differentiation of rat bone marrow-derived mesenchymal stem cells towards the osteogenic lineage. In addition, the typical endothelial cell property of forming tubes in Matrigel was observed for human umbilical vein endothelial cells when in contact with the novel biomaterials, particularly AlgNbgCu, which indicates their angiogenic properties. Hence, novel nanocomposite biomaterials made of Nbg and alginate cross-linked with Cu(2+) or Ca(2+) were developed with potential applications for preparation of multifunctional scaffolds for BTE.

B(12)-mediated, long wavelength photopolymerization of hydrogels

Medical hydrogel applications have expanded rapidly over the past decade. Implantation in patients by noninvasive injection is preferred, but this requires hydrogel solidification from a low viscosity solution to occur in vivo via an applied stimuli. Transdermal photo-cross-linking of acrylated biopolymers with photoinitiators and lights offers a mild, spatiotemporally controlled solidification trigger. However, the current short wavelength initiators limit curing depth and efficacy because they do not absorb within the optical window of tissue (600-900 nm). As a solution to the current wavelength limitations, we report the development of a red light responsive initiator capable of polymerizing a range of acrylated monomers. Photoactivation occurs within a range of skin type models containing high biochromophore concentrations.

Complex dynamic substrate control: dual-tone hydrogel photoresists allow double-dissociation of topography and modulus

Complex substrate control is demonstrated with a dual-tone hydrogel photoresist. By exposing a photodegradable hydrogel to UV light through a photomask, both swollen and eroded micropatterns with a decreased modulus can be created on the surface under different exposure conditions. This provides an important tool for investigating the synergistic effects of spatially heterogeneous mechanical and topological cues on cell behavior.

Light-assisted direct-write of 3D functional biomaterials

Light-assisted 3D direct-printing of biomaterials and cellular-scaffolds has the potential to develop novel lab-on-a-chip devices (LOCs) for a variety of biomedical applications, from drug discovery and diagnostic testing to in vitro tissue engineering and regeneration. Direct-writing describes a broad family of fabrication methods that typically employ computer-controlled translational stages to manufacture structures at multi-length scales. This review focuses on light-assisted direct-write fabrication for generating 3D functional scaffolds with precise micro- and nano-architecture, using both synthetic as well as naturally derived biomaterials. Two bioprinting approaches are discussed in detail - projection printing and laser-based systems - where each method is capable of modulating multiple scaffold parameters, such as 3D architecture, mechanical properties (e.g. stiffness), Poisson's ratio, chemical gradients, biological cell distributions, and porosity. The light-assisted direct-writing techniques described in this review provide the reader with alternative approaches to fabricate 3D biomaterials for utility in LOCs.

3D-Printed Biopolymers for Tissue Engineering Application

3D printing technology has recently gained substantial interest for potential applications in tissue engineering due to the ability of making a three-dimensional object of virtually any shape from a digital model. 3D-printed biopolymers, which combine the 3D printing technology and biopolymers, have shown great potential in tissue engineering applications and are receiving significant attention, which has resulted in the development of numerous research programs regarding the material systems which are available for 3D printing. This review focuses on recent advances in the development of biopolymer materials, including natural biopolymer-based materials and synthetic biopolymer-based materials prepared using 3D printing technology, and some future challenges and applications of this technology are discussed.

Chitosan-g-hematin: enzyme-mimicking polymeric catalyst for adhesive hydrogels

Phenol derivative-containing adhesive hydrogels has been widely recognized as having potential for biomedical applications, but their conventional production methods, utilizing a moderate/strong base, alkaline buffers, the addition of oxidizing agents or the use of enzymes, require alternative approaches to improve their biocompatibility. In this study, we report a polymeric, enzyme-mimetic biocatalyst, hematin-grafted chitosan (chitosan-g-hem), which results in effective gelation without the use of alkaline buffers or enzymes. Furthermore, gelation occurs under mild physiological conditions. Chitosan-g-hem biocatalyst (0.01%, w/v) has excellent catalytic properties, forming chitosan-catechol hydrogels rapidly (within 5 min). In vivo adhesive force measurement demonstrated that the hydrogel formed by the chitosan-g-hem activity showed an increase in adhesion force (33.6 ± 5.9 kPa) compared with the same hydrogel formed by pH-induced catechol oxidation (20.6 ± 5.5 kPa) in mouse subcutaneous tissue. Using the chitosan-g-hem biocatalyst, other catechol-functionalized polymers (hyaluronic acid-catechol and poly(vinyl alcohol)-catechol) also formed hydrogels, indicating that chitosan-g-hem can be used as a general polymeric catalyst for preparing catechol-containing hydrogels.

A biodegradable thermosensitive hydrogel with tuneable properties for mimicking three-dimensional microenvironments of stem cells

Chitosan-g-poly(N-isopropylacrylamide) was synthesized as a stem cell mimicking microenvironment. Solubility and gel mechanical strength were optimised through manipulating the grafting parameters.

Switchable antimicrobial and antifouling hydrogels with enhanced mechanical properties

New switchable hydrogels are developed. Under acidic conditions, hydrogels undergo self-cyclization and can catch and kill bacteria. Under neutral/basic conditions, hydrogels undergo ring-opening and can release killed bacterial cells and resist protein adsorption and bacterial attachment. Smart hydrogels also show a dramatically improved mechanical property, which is highly desired for biomedical applications.

The effects of 5-fluorouracil on flexor tendon healing by using a biodegradable gelatin, slow releasing system: experimental study in a hen model

This study investigated the effects of 5-fluorouracil in a slow-release biodegradable gelatin system on tendon healing. Gelatin blocks prepared in a size of 10 × 20 × 1 mm were loaded with 10, 20, and 30 mg of 5-fluorouracil, and 30 adult white Leghorn chickens were used. The tendons to the third and fourth toes were severed and repaired. The extremities were casted for three weeks. After sacrifice, the tendons were examined histologically and biomechanically for adhesion formation. The 10 mg-loaded gelatin group showed a decrease in adhesion formation when compared with the operative control group; the 20 and 30 mg groups showed signs of severe inflammation. Low doses of 5-fluorouracil applied via a slow-release gelatin system reduced adhesion formation in flexor tendon healing.