Hydrogel/bioactive glass composites for bone regeneration applications: Synthesis and characterisation

Advanced supramolecular hydrogels and their applications in the formulation of next-generation bioinks for tissue engineering: A review

Supramolecular hydrogels are three-dimensional structures composed of cross-linked macromolecules interconnected by dynamic physical bonds, which allow them to absorb and retain significant volumes of water. Their intrinsic properties, such as viscoelasticity, self-healing capabilities, and high water content, render them promising materials for cell-laden scaffolds utilized in bioinks. This review systematically summarizes the current state-of-the-art advancements in hydrogels for tissue engineering, categorizing them based on the nature of their supramolecular interactions. Particular emphasis is placed on the classification of supramolecular hydrogels and their associated properties, including kinetics, mechanical characteristics, responsiveness, and swelling behavior. The review specifically addresses the criteria that hydrogels must fulfill prior to their application in bioinks. Achieving biocompatibility and bioactivity necessitates the careful selection of hydrogel compositions with suitable properties, as well as the incorporation of external organic or inorganic bioactive molecules. Methods for measuring and enhancing biophysical and biochemical properties are discussed in detail, alongside an exploration of the unique requirements of bioinks tailored for each additive manufacturing method. This review paper serves as an instructive resource for the construction and characterization of supramolecular hydrogels, facilitating their application in bioinks for tissue engineering.

Functional Hydrogel Interfaces for Cartilage and Bone Regeneration

Effective treatment of bone diseases is quite tricky due to the unique nature of bone tissue and the complexity of the bone repair process. In combination with biological materials, cells and biological factors can provide a highly effective and safe treatment strategy for bone repair and regeneration, especially based on these multifunctional hydrogel interface materials. However, itis still a challenge to formulate hydrogel materials with fascinating properties (e.g., biological activity, controllable biodegradability, mechanical strength, excellent cell/tissue adhesion, and controllable release properties) for their clinical applications in complex bone repair processes. In this review, we will highlight recent advances in developing functional interface hydrogels. We then discuss the barriers to  producing of functional hydrogel materials without sacrificing their inherent properties, and potential applications in cartilage and bone repair are discussed. Multifunctional hydrogel interface materials can serve as a fundamental building block for bone tissue engineering.

Investigating the Promising P28 Peptide-Loaded Chitosan/Ceramic Bone Scaffolds for Bone Regeneration

Bone has the ability to heal itself; however, bone defects fail to heal once the damage exceeds a critical size. Bone regeneration remains a significant clinical challenge, with autograft considered the ideal bone graft material due to its sufficient porosity, osteogenic cells, and biological growth factors. However, limitations to bone grafting, such as limited bone stock and high resorption rates, have led to a great deal of research into developing bone graft substitutes. The P28 peptide is a small molecule bioactive biomimetic alternative to mimic the bone morphogenetic protein 2 (BMP-2). In this study, we investigated the potential of P28-loaded hybrid scaffolds to mimic the natural bone structure for enhancing the bone regeneration process. We hypothesized that the peptide-loaded scaffolds and nude scaffolds both have the potential to promote bone healing, and the bone healing process is accelerated by the release of the peptide. To verify our hypothesis, C2C12 cells were evaluated for the presence of calcium deposits by histological stain at 7 and 14 days in cultures with hybrid scaffolds. Total RNA was isolated from C2C12 cells cultured with hybrid scaffolds for 7 and 14 days to assess osteoblast differentiation. The project findings demonstrated that the hybrid scaffold could enhance osteoblast differentiation and significantly improve the therapeutic effects of the scaffold in bone regeneration.

Evaluation of drug release efficiency and antibacterial property of a pH-responsive dextran-based silver nanocomposite hydrogel

The bioavailability of curcumin (CUR), a highly lipophilic and commonly used anticancer drug, is mainly affected by its poor solubility in aqueous environment and quick metabolism. These challenges can be met by employing delivery systems. Nanocomposite materials have been used as delivery systems to enhance the solubility and dissolution rate of the drug. This study aims to develop dextran-graft-poly(4-acryloylmorpholine) silver nanocomposite using a microwave-assisted method to evaluate its drug-release efficiency and antimicrobial activity. The materials were characterized by FT-IR, FE-SEM, EDS, XRD, HR-TEM, TGA, and BET techniques. Drug loading and release efficiency were evaluated using CUR as the model drug. The swelling and drug release studies were conducted in buffer solutions of pH 1.2 and 7.4. Staphylococcus aureus and Escherichia coli were employed to evaluate the antibacterial activity. The cytotoxicity was assessed by MTT assay against the breast MCF-10. Higher swelling and drug release were observed at pH 1.2 than 7.4. Nanocomposite hydrogel exhibited antibacterial activity against the tested bacterial strains. Cytotoxicity study proved the safety of the developed matrix. The results suggest the developed nanocomposite hydrogel to be a promising polymer matrix for the sustained release of CUR for cancer treatment that requires infectious control.

Modulation of 3D Bioprintability in Polysaccharide Bioink by Bioglass Nanoparticles and Multiple Metal Ions for Tissue Engineering

BACKGROUND

Bioglasses are used in applications related to bone rehabilitation and repair. The mechanical and bioactive properties of polysaccharides like alginate and agarose can be modulated or improved using bioglass nanoparticles. Further essential metal ions used as crosslinker have the potential to supplement cultured cells for better growth and proliferation.

METHOD

In this study, the alginate bioink is modulated for fabrication of tissue engineering scaffolds by extrusion-based 3D bioprinting using agarose, bioglass nanoparticles and combination of essential trace elements such as iron, zinc, and copper. Homogeneous bioink was obtained by in situ mixing and bioprinting of its components with twin screw extruder (TSE) based 3D bioprinting, and then distribution of metal ions was induced through post-printing diffusion of metal ions in the printed scaffolds. The mechanical and 3d bioprinting properties, microscopic structure, biocompatibility of the crosslinked alginate/agarose hydrogels were analyzed for different concentrations of bioglass. The adipose derived mesenchymal stem cells (ADMSC) and osteoblast cells (MC3T3) were used to evaluate this hydrogel's biological performances.

RESULTS

The porosity of hydrogels significantly improves with the incorporation of the bioglass. More bioglass concentration results in improved mechanical (compressive, dynamic, and cyclic) and 3D bioprinting properties. Cell growth and extracellular matrix are also enhanced with bioglass concentration.

CONCLUSION

For bioprinting of the bioinks, the advanced TSE head was attached to 3D bioprinter and in situ fabrication of cell encapsulated scaffold was obtained with optimized composition considering minimal effects on cell damage. Fabricated bioinks demonstrate a biocompatible and noncytotoxic scaffold for culturing MC3T3 and ADMSC, while bioglass controls the cellular behaviors such as cell growth and extracellular matrix formation.

Preparation, properties and in vitro osteogensis of self-reinforcing injectable hydrogel

As an attractive biomaterial for bone reconstruction, injectable biomaterials have many prominent characteristics such as good biocompatibility and bone-filling ability. However, there are weak as load-bearing scaffolds. In this study, polyvinyl alcohol (PVA) and bioactive glass (BAG) were interpenetrated into sodium alginate (SA) network to obtain self-enhanced injectable hydrogel. The optimum ratio of PVA/SA/BAG hydrogel was determined based on injectability, gelation time and chemical characterization. Results showed that the selected ratio had the shortest gelation time of 3.5min, and the hydrogel had a rough surface and good coagulation property. The hydrogel was capable of carrying 1kg of weight by mineralization for 14 d The compressive strength, compressive modulus, and fracture energy of the hydrogel reached 0.12MPa, 0.376MPa and 17.750kJ m-2, respectively. Meanwhile, the hydrogel had high moisture content and dissolution rate, and it was sensitive to temperature and ionic strength. Hydroxyapatite was generated on the hydrogel surface, and the hydrogel pores increased, and the pore size enlarged. The biocompatibility of PVA/SA/BAG hydrogel was analyzed using hemolysis and cytotoxicity assays. Results revealed its good biocompatibility with low hemolysis rate and no cytotoxicity to MC3T3-E1 cells. The hydrogel was also found to promote the differentiation of MC3T3-E1 cells with significantly increased in ALP activity and expression of relevant differentiation factors. In vitro mineralization assay showed an increase in calcium nodules and calcification area, indicating the ability of hydrogel to promote mineralization MC3T3-E1 cells. These findings indicated that PVA/SA/BAG hydrogel had potential uses in the field of irregular bone-defect repair due to its injectability, cytocompatibility, and tailorable functionality.

Wound healing strategies based on nanoparticles incorporated in hydrogel wound patches

The intricate, tightly controlled mechanism of wound healing that is a vital physiological mechanism is essential to maintaining the skin's natural barrier function. Numerous studies have focused on wound healing as it is a massive burden on the healthcare system. Wound repair is a complicated process with various cell types and microenvironment conditions. In wound healing studies, novel therapeutic approaches have been proposed to deliver an effective treatment. Nanoparticle-based materials are preferred due to their antibacterial activity, biocompatibility, and increased mechanical strength in wound healing. They can be divided into six main groups: metal NPs, ceramic NPs, polymer NPs, self-assembled NPs, composite NPs, and nanoparticle-loaded hydrogels. Each group shows several advantages and disadvantages, and which material will be used depends on the type, depth, and area of the wound. Better wound care/healing techniques are now possible, thanks to the development of wound healing strategies based on these materials, which mimic the extracellular matrix (ECM) microenvironment of the wound. Bearing this in mind, here we reviewed current studies on which NPs have been used in wound healing and how this strategy has become a key biotechnological procedure to treat skin infections and wounds.

Synthesis and Characterisation of Hydrogels Based on Poly (N-Vinylcaprolactam) with Diethylene Glycol Diacrylate

Poly (N-vinylcaprolactam) is a polymer that is biocompatible, water-soluble, thermally sensitive, non-toxic, and nonionic. In this study, the preparation of hydrogels based on Poly (N-vinylcaprolactam) with diethylene glycol diacrylate is presented. The N-Vinylcaprolactam-based hydrogels are synthesised by using a photopolymerisation technique using diethylene glycol diacrylate as a crosslinking agent, and Diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator. The structure of the polymers is investigated via Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy. The polymers are further characterised using differential scanning calorimetry and swelling analysis. This study is conducted to determine the characteristics of P (N-vinylcaprolactam) with diethylene glycol diacrylate, including the addition of Vinylacetate or N-Vinylpyrrolidone, and to examine the effects on the phase transition. Although various methods of free-radical polymerisation have synthesised the homopolymer, this is the first study to report the synthesis of Poly (N-vinylcaprolactam) with diethylene glycol diacrylate by using free-radical photopolymerisation, using Diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide to initiate the reaction. FTIR analysis shows that the NVCL-based copolymers are successfully polymerised through UV photopolymerisation. DSC analysis indicates that increasing the concentration of crosslinker results in a decrease in the glass transition temperature. Swelling analysis displays that the lower the concentration of crosslinker present in the hydrogel, the quicker the hydrogels reach their maximum swelling ratio.

Synthesis and Characterizations of Bioactive Glass Nanoparticle-Incorporated Triblock Copolymeric Injectable Hydrogel for Bone Tissue Engineering

Recently, injectable hydrogels have attracted much interest in tissue engineering (TE) applications because of their controlled flowability, adaptability, and easy handling properties. This work emphasizes the synthesis and characterizations of bioactive glass (BAG) nanoparticle-reinforced poly(ethylene glycol) (PEG)- and poly(N-vinylcarbazole) (pNVC)-based minimally invasive composite injectable hydrogel suitable for bone regeneration. First, the copolymer was synthesized from a combination of PEG and pNVC through reversible addition-fragmentation chain-transfer (RAFT) polymerization and nanocomposite hydrogel constructs were subsequently prepared by conjugating BAG particles at varying loading concentrations. Gel permeation chromatography (GPC) analysis confirmed the controlled nature of the polymer. Various physicochemical characterization results confirmed the successful synthesis of copolymer and nanocomposite hydrogels that showed good gelling and injectability properties. Our optimal nanocomposite hydrogel formulation showed excellent swelling properties in comparison to the copolymeric hydrogel due to the presence of hydrophilic BAG particles. The bone cell proliferation rate was found to be evidently higher in the nanocomposite hydrogel than in the copolymeric hydrogel. Moreover, the enhanced level of ALP activity and apatite mineralization for the nanocomposite in comparison to that for the copolymeric hydrogel indicates accelerated in vitro osteogenesis. Overall, our study findings indicate BAG particle-conjugated nanocomposite hydrogels can be used as promising grafting materials in orthopedic reconstructive surgeries complementary to conventional bone graft substitutes in cancellous bone defects due to their 3D porous framework, minimal invasiveness, and ability to form any desired shape to match irregular bone defects.

A Development of New Material for 4D Printing and the Material Properties Comparison between the Conventional and Stereolithography Polymerised NVCL Hydrogels

The term 4D printing refers to the idea that the shape or properties of a printed object can be changed when an external stimulus is applied. In this contribution, a temperature-responsive polymer Poly (N-vinyl caprolactam) (PNVCL), which is normally prepared via radical free polymerization, was used to justify the 4D printing concept. As a result, by using a Stereolithography (SLA) 3D printer, 4D prints were successfully prepared. These prints were able to demonstrate intelligent and reversible expansion/shrinkage behaviour as the temperature increases and decreases. Additionally, in order to examine the differences in chemical structure, thermal properties, mechanical properties, and swelling behaviours of the photopolymerised and printed parts, a series of characterisation tests, including Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), goniometry, tensile test, gel fraction measurement and pulsatile swelling study were performed on this study. In conclusion, the differences between polymerisation methods are significant; despite their chemical structures and thermal properties being similar, there were significant differences with regard to tensile properties, swellability and wettability of samples. The implications of conducting this study are remarkable, not only in providing a new way of preparing NVCL, but also in demonstrating the possibility of using 4D printed NVCL for practical applications.

Adjusting Some Properties of Poly(methacrylic acid) (Nano)Composite Hydrogels by Means of Silicon-Containing Inorganic Fillers

The present work aims to show how the main properties of poly(methacrylic acid) (PMAA) hydrogels can be engineered by means of several silicon-based fillers (Laponite XLS/XLG, montmorillonite (Mt), pyrogenic silica (PS)) employed at 10 wt% concentration based on MAA. Various techniques (FT-IR, XRD, TGA, SEM, TEM, DLS, rheological measurements, UV-VIS) were used to comparatively study the effect of these fillers, in correlation with their characteristics, upon the structure and swelling, viscoelastic, and water decontamination properties of (nano)composite hydrogels. The experiments demonstrated that the nanocomposite hydrogel morphology was dictated by the way the filler particles dispersed in water. The equilibrium swelling degree (SDe) depended on both the pH of the environment and the filler nature. At pH 1.2, a slight crosslinking effect of the fillers was evidenced, increasing in the order Mt < Laponite < PS. At pH > pKaMAA (pH 5.4; 7.4; 9.5), the Laponite/Mt-containing hydrogels displayed a higher SDe as compared to the neat one, while at pH 7.4/9.5 the PS-filled hydrogels surprisingly displayed the highest SDe. Rheological measurements on as-prepared hydrogels showed that the filler addition improved the mechanical properties. After equilibrium swelling at pH 5.4, G’ and G” depended on the filler, the Laponite-reinforced hydrogels proving to be the strongest. The (nano)composite hydrogels synthesized displayed filler-dependent absorption properties of two cationic dyes used as model water pollutants, Laponite XLS-reinforced hydrogel demonstrating both the highest absorption rate and absorption capacity. Besides wastewater purification, the (nano)composite hydrogels described here may also find applications in the pharmaceutical field as devices for the controlled release of drugs.

WPI Hydrogels with a Prolonged Drug-Release Profile for Antimicrobial Therapy

Infectious sequelae caused by surgery are a significant problem in modern medicine due to their reduction of therapeutic effectiveness and the patients’ quality of life.Recently, new methods of local antimicrobial prophylaxis of postoperative sequelae have been actively developed. They allow high local concentrations of drugs to be achieved, increasing the antibiotic therapy’s effectiveness while reducing its side effects. We have developed and characterized antimicrobial hydrogels based on an inexpensive and biocompatible natural substance from the dairy industry—whey protein isolate—as matrices for drug delivery. The release of cefazolin from the pores of hydrogel structures directly depends on the amount of the loaded drug and occurs in a prolonged manner for three days. Simultaneously with the antibiotic release, hydrogel swelling and partial degradation occurs. The WPI hydrogels absorb solvent, doubling in size in three days and retaining cefazolin throughout the duration of the experiment. The antimicrobial activity of cefazolin-loaded WPI hydrogels against Staphylococcus aureus growth is prolonged in comparison to that of the free cefazolin. The overall cytotoxic effect of cefazolin-containing WPI hydrogels is lower than that of free antibiotics. Thus, our work shows that antimicrobial WPI hydrogels are suitable candidates for local antibiotic therapy of infectious surgical sequelae.

Multifunctional GelMA platforms with nanomaterials for advanced tissue therapeutics

Polymeric hydrogels are fascinating platforms as 3D scaffolds for tissue repair and delivery systems of therapeutic molecules and cells. Among others, methacrylated gelatin (GelMA) has become a representative hydrogel formulation, finding various biomedical applications. Recent efforts on GelMA-based hydrogels have been devoted to combining them with bioactive and functional nanomaterials, aiming to provide enhanced physicochemical and biological properties to GelMA. The benefits of this approach are multiple: i) reinforcing mechanical properties, ii) modulating viscoelastic property to allow 3D printability of bio-inks, iii) rendering electrical/magnetic property to produce electro-/magneto-active hydrogels for the repair of specific tissues (e.g., muscle, nerve), iv) providing stimuli-responsiveness to actively deliver therapeutic molecules, and v) endowing therapeutic capacity in tissue repair process (e.g., antioxidant effects). The nanomaterial-combined GelMA systems have shown significantly enhanced and extraordinary behaviors in various tissues (bone, skin, cardiac, and nerve) that are rarely observable with GelMA. Here we systematically review these recent efforts in nanomaterials-combined GelMA hydrogels that are considered as next-generation multifunctional platforms for tissue therapeutics. The approaches used in GelMA can also apply to other existing polymeric hydrogel systems.

[Methods of improving the mechanical properties of hydrogels and their research progress in bone tissue engineering]

OBJECTIVE

To review the methods of improving the mechanical properties of hydrogels and the research progress in bone tissue engineering.

METHODS

The recent domestic and foreign literature on hydrogels in bone tissue engineering was reviewed, and the methods of improving the mechanical properties of hydrogels and the effect of bone repair in vivo and in vitro were summarized.

RESULTS

Hydrogels are widely used in bone tissue engineering, but their mechanical properties are poor. Improving the mechanical properties of hydrogels can enhance bone repair. The methods of improving the mechanical properties of hydrogels include the construction of dual network structures, inorganic nanoparticle composites, introduction of conductive materials, and fiber network reinforcement. These methods can improve the mechanical properties of hydrogels to various degrees while also demonstrating a significant bone repair impact.

CONCLUSION

The mechanical properties of hydrogels can be effectively improved by modifying the system, components, and fiber structure, and bone repair can be effectively promoted.

A biopolymer hydrogel electrostatically reinforced by amino-functionalized bioactive glass for accelerated bone regeneration

Composite hydrogels incorporating natural polymers and bioactive glass (BG) are promising materials for bone regeneration. However, their applications are compromised by the poor interfacial compatibility between organic and inorganic phases. In this study, we developed an electrostatically reinforced hydrogel (CAG) with improved interfacial compatibility by introducing amino-functionalized 45S5 BG to the alginate/gellan gum (AG) matrix. BAG composed of AG and unmodified BG (10 to 100 μm in size) was prepared as a control. Compared with BAG, CAG had a more uniform porous structure with a pore size of 200 μm and optimal compressive strength of 66 kPa. Furthermore, CAG promoted the M2 phenotype transition of macrophages and up-regulated the osteogenic gene expression of stem cells. The new bone formation in vivo was also accelerated due to the enhanced biomineralization of CAG. Overall, this work suggests CAG with improved interfacial compatibility is an ideal material for bone regeneration application.

Injectable nanocomposite hydrogels as an emerging platform for biomedical applications: A review

Hydrogels have attracted much attention for biomedical and pharmaceutical applications due to the similarity of their biomimetic structure to the extracellular matrix of natural living tissues, tunable soft porous microarchitecture, superb biomechanical properties, proper biocompatibility, etc. Injectable hydrogels are an exciting type of hydrogels that can be easily injected into the target sites using needles or catheters in a minimally invasive manner. The more comfortable use, less pain, faster recovery period, lower costs, and fewer side effects make injectable hydrogels more attractive to both patients and clinicians in comparison to non-injectable hydrogels. However, it is difficult to achieve an ideal injectable hydrogel using just a single material (i.e., polymer). This challenge can be overcome by incorporating nanofillers into the polymeric matrix to engineer injectable nanocomposite hydrogels with combined or synergistic properties gained from the constituents. This work aims to critically review injectable nanocomposite hydrogels, their preparation methods, properties, functionalities, and versatile biomedical and pharmaceutical applications such as tissue engineering, drug delivery, and cancer labeling and therapy. The most common natural and synthetic polymers as matrices together with the most popular nanomaterials as reinforcements, including nanoceramics, carbon-based nanostructures, metallic nanomaterials, and various nanosized polymeric materials, are highlighted in this review.

Biomaterial design strategies to address obstacles in craniomaxillofacial bone repair

Biomaterial design to repair craniomaxillofacial defects has largely focused on promoting bone regeneration, while there are many additional factors that influence this process. The bone microenvironment is complex, with various mechanical property differences between cortical and cancellous bone, a unique porous architecture, and multiple cell types that must maintain homeostasis. This complex environment includes a vascular architecture to deliver cells and nutrients, osteoblasts which form new bone, osteoclasts which resorb excess bone, and upon injury, inflammatory cells and bacteria which can lead to failure to repair. To create biomaterials able to regenerate these large missing portions of bone on par with autograft materials, design of these materials must include methods to overcome multiple obstacles to effective, efficient bone regeneration. These obstacles include infection and biofilm formation on the biomaterial surface, fibrous tissue formation resulting from ill-fitting implants or persistent inflammation, non-bone tissue formation such as cartilage from improper biomaterial signals to cells, and voids in bone infill or lengthy implant degradation times. Novel biomaterial designs may provide approaches to effectively induce osteogenesis and new bone formation, include design motifs that facilitate surgical handling, intraoperative modification and promote conformal fitting within complex defect geometries, induce a pro-healing immune response, and prevent bacterial infection. In this review, we discuss the bone injury microenvironment and methods of biomaterial design to overcome these obstacles, which if unaddressed, may result in failure of the implant to regenerate host bone.

Novel Hydrogels of Chitosan and Poly(vinyl alcohol) Reinforced with Inorganic Particles of Bioactive Glass

Chitosan (CS) and poly(vinyl alcohol) (PVA) hydrogels, a polymeric system that shows a broad potential in biomedical applications, were developed. Despite the advantages they present, their mechanical properties are insufficient to support the loads that appear on the body. Thus, it was proposed to reinforce these gels with inorganic glass particles (BG) in order to improve mechanical properties and bioactivity and to see how this reinforcement affects levofloxacin drug release kinetics. Scanning electron microscopy (SEM), X-ray diffraction (XRD), swelling tests, rheology and drug release studies characterized the resulting hydrogels. The experimental results verified the bioactivity of these gels, showed an improvement of the mechanical properties and proved that the added bioactive glass does affect the release kinetics.

Bioactivity reinforced surface patch bound collagen-pectin hydrogel

In this report, we discuss the design of a novel collagen/pectin (CP) hybrid composite hydrogel (CPBG) containing in-situ mineralized bioactive glass (BG) particles to simulate an integrative 3D cell environment. Systematic analysis of the CP sol revealed collagen and pectin molecules interacted regardless of both possessing similar net negative charge through the mechanism of surface patch binding interaction. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) confirmed this associative interaction which resulted in the formation of a hybrid crosslinked network with the BG nanoparticles acting as pseudo crosslink junctions. Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX) and Transmission Electron Microscopy (TEM) results confirmed uniform mineralization of BG particles, and their synergetic interaction with the network. The in-vitro bioactivity tests on CPBG indicated the formation of bone-like hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) microcrystals on its surface after interaction with simulated body fluid. This hydrogel was loaded with a model antifungal drug amphotericin-B (AmB) and tested against Candida albicans. The AmB release kinetics from the hydrogel followed the Fickian mechanism and showed direct proportionality to gel swelling behavior. Rheological analysis revealed the viscoelastic compatibility of CPBG for the mechanical load bearing applications. Cell viability tests indicated appreciable compatibility of the hydrogel against U2OS and HaCaT cell lines. FDA/PI on the hydrogel portrayed preferential U2OS cell adhesion on hydrophobic hydroxyapatite layer compared to hydrophilic surfaces, thereby promising the regeneration of both soft and hard tissues.

Gold nanorods enable noninvasive longitudinal monitoring of hydrogels in vivo with photoacoustic tomography

Longitudinal in vivo monitoring is essential for the design and evaluation of biomaterials. An ideal method would provide three-dimensional quantitative information, high spatial resolution, deep tissue penetration, and contrast between tissue and material structures. Photoacoustic (PA) or optoacoustic imaging is a hybrid technique that allows three-dimensional imaging with high spatial resolution. In addition, photoacoustic imaging allows for imaging of vascularization based on the intrinsic contrast of hemoglobin. In this study, we investigated photoacoustic computed tomography (PACT) as a tool for longitudinal monitoring of an implanted hydrogel in a small animal model. Hydrogels were loaded with gold nanorods to enhance contrast and imaged weekly for 8 weeks. PACT allowed non-invasive three-dimensional, quantitative imaging of the hydrogels over the entire 8 weeks. Quantitative volume analysis was used to evaluate the in vivo degradation kinetics of the implants which deviated slightly from in vitro predictions. Multispectral imaging allowed for the simultaneous analysis of hydrogel degradation and local vascularization. These results provide support for the substantial potential of PACT as a tool for insight into biomaterial performance in vivo.

Effect of Stereolithography 3D Printing on the Properties of PEGDMA Hydrogels

Stereolithography (SLA)-based 3D printing has proven to have several advantages over traditional fabrication techniques as it allows for the control of hydrogel synthesis at a very high resolution, making possible the creation of tissue-engineered devices with microarchitecture similar to the tissues they are replacing. Much of the previous work in hydrogels for tissue engineering applications have utilised the ultraviolet (UV) chamber bulk photopolymerisation method for preparing test specimens. Therefore, it is essential to directly compare SLA 3D printing to this more traditional approach to elucidate the differences in hydrogels prepared by each fabrication method. Polyethyleneglycol dimethacrylate (PEGDMA) is an ideally suited material for a comparative study of the impact that SLA fabrication has on performance, as the properties of traditional UV chamber-cured hydrogels have been extensively characterised. The present study was conducted to compare the material properties of PEGDMA hydrogels prepared using UV chamber photopolymerisation and SLA 3D printing. From the subsequent testing, SLA-fabricated hydrogels were shown to maintain similar thermal and chemical performance to UV chamber-cured hydrogels but had a higher compressive strength and tensile stiffness, as well as increased hydrophilicity. These differences are attributed to the increased exposure to UV light SLA samples received compared to traditionally UV chamber-cured samples.

Photochemical Activity of Black Phosphorus for Near-Infrared Light Controlled In Situ Biomineralization

The photochemical activity of black phosphorus (BP) in near-infrared (NIR) light controlled in situ biomineralization is investigated. Owing to the excellent NIR absorption, irradiation with NIR light not only promotes degradation of BP into PO4 3-, but also enhances the chemical activity to accelerate the reaction between PO4 3- and Ca2+ and promote in situ biomineralization. Mineralization of hydrogels is demonstrated by the preparation of BP incorporated hydrogel (BP@Hydrogel) which delivers greatly improved biomineralization performance under NIR illumination. The biomineralization process which can be controlled by modulating the light irradiation time and location has a high potential in controlling the mechanical properties and osteoinductive ability in tissue engineering. This study also provides insights into the degradation, photochemical activity, and new biological/biomedical applications of BP.

Synthesis and characterization of osteoinductive visible light-activated adhesive composites with antimicrobial properties

Orthopedic surgical procedures based on the use of conventional biological graft tissues are often associated with serious post-operative complications such as immune rejection, bacterial infection, and poor osseointegration. Bioresorbable bone graft substitutes have emerged as attractive alternatives to conventional strategies because they can mimic the composition and mechanical properties of the native bone. Among these, bioactive glasses (BGs) hold great potential to be used as biomaterials for bone tissue engineering owing to their biomimetic composition and high biocompatibility and osteoinductivity. Here, we report the development of a novel composite biomaterial for bone tissue engineering based on the incorporation of a modified strontium- and lithium-doped 58S BG (i.e., BG-5/5) into gelatin methacryloyl (GelMA) hydrogels. We characterized the physicochemical properties of the BG formulation via different analytical techniques. Composite hydrogels were then prepared by directly adding BG-5/5 to the GelMA hydrogel precursor, followed by photocrosslinking of the polymeric network via visible light. We characterized the physical, mechanical, and adhesive properties of GelMA/BG-5/5 composites, as well as their in vitro cytocompatibility and osteoinductivity. In addition, we evaluated the antimicrobial properties of these composites in vitro, using a strain of methicillin-resistant Staphylococcus Aureus. GelMA/BG-5/5 composites combined the functional characteristics of the inorganic BG component, with the biocompatibility, biodegradability, and biomimetic composition of the hydrogel network. This novel biomaterial could be used for developing osteoinductive scaffolds or implant surface coatings with intrinsic antimicrobial properties and higher therapeutic efficacy.

Additive Manufacturing of Personalized Pharmaceutical Dosage Forms via Stereolithography

The introduction of three-dimensional printing (3DP) has created exciting possibilities for the fabrication of dosage forms, paving the way for personalized medicine. In this study, oral dosage forms of two drug concentrations, namely 2.50% and 5.00%, were fabricated via stereolithography (SLA) using a novel photopolymerizable resin formulation based on a monomer mixture that, to date, has not been reported in the literature, with paracetamol and aspirin selected as model drugs. In order to produce the dosage forms, the ratio of poly(ethylene glycol) diacrylate (PEGDA) to poly(caprolactone) triol was varied with diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure TPO) utilized as the photoinitiator. The fabrication of 28 dosages in one print process was possible and the printed dosage forms were characterized for their drug release properties. It was established that both drugs displayed a sustained release over a 24-h period. The physical properties were also investigated, illustrating that SLA affords accurate printing of dosages with some statistically significant differences observed from the targeted dimensional range, indicating an area for future process improvement. The work presented in this paper demonstrates that SLA has the ability to produce small, individualized batches which may be tailored to meet patients’ specific needs or provide for the localized production of pharmaceutical dosage forms.

Preparation of Biodegradable Polyethylene Glycol Dimethacrylate Hydrogels via Thiol-ene Chemistry

Through the control of the molecular weight, water content and monomer concentration, polyethylene glycol dimethacrylate (PEGDMA) based hydrogels have been adapted for numerous applications, including as structural scaffolds, drug delivery vehicles and cell carriers. However, due to the low biodegradability rates, the use of PEGDMA in tissue engineering has been limited. Thiol-based monomers have been shown to improve the degradation rates of several PEG-based hydrogels, though their impact on several material properties has not been as well defined. In this work, several mercaptopropianoates, as well as mercaptoacetates, were mixed with PEGDMA and copolymerized. Following an initial polymerization check, it was determined that mercaptoacetate-based thiol monomers did not polymerize in the presence of PEGDMA, whereas mercaptopropionates were more successful. The wettability, and the compressive and tensile strength, in addition to the thermal properties, were determined for successfully copolymerized samples via a combination of differential scanning calorimetry, dynamic mechanical analysis, unconfined compression, and goniometry. Further study determined that dipentaerythritol hexa(3-mercaptopropionate) (DiPETMP) successfully enhanced the biodegradability of PEGDMA.

A tough and novel dual-response PAA/P(NiPAAM-co-PEGDMA) IPN hydrogels with ceramics by photopolymerization for consolidation of bone fragments following fracture

In this work, a novel dual-response hydrogel for enhanced bone repair following multiple fractures was investigated. The conventional treatment of multiple bone fracture consists on removing smaller bone fragments from the body in a surgery, followed by the fixation of the bone using screws and plates. This work proposes an alternative for this treatment via in situ UV-initiated radical polymerization of a novel IPN hydrogel composed of PAA/P(NiPAAM-co-PEGDMA) incorporated with ceramic additives. The influence of different additives on mechanical properties and sensitivity of the polymer, as well as the prepolymer mixture, were investigated in order to analyse the suitability of the composites for bone healing applications. This material exhibited an interpenetrating network, confirmed by FTIR, with ceramics particles dispersed in between the polymer network. These structures presented high strength by tensile tests, sensitivity to pH and temperature and a decrease on Tg values of NiPAAm depending on the amount of PEGDMA and ceramics added; although, the addition of ceramics to these composites did not decrease their stability drastically. Finally, cytotoxicity tests revealed variations on the toxicity, whereas the addition of TCP presented to be non-toxic and that the cell viability increased when ceramics additives were incorporated into the polymeric matrix with an increased reporter activity of NF-κB, associated with aiding fibroblast adhesion. Hence, it was possible to optimise feedstock ratios to increase the applicability of the prepolymer mixture as a potential treatment of multiple fractures.

Evaluation of the materials properties, stability and cell response of a range of PEGDMA hydrogels for tissue engineering applications

The main aim of this study was to examine the stability of a range of polyethyleneglycol dimethacrylate (PEGDMA) hydrogels over a 28-day period in simulated physiological solution. Upon optimisation of the ultraviolet (UV) curing conditions, the PEGDMA hydrogels were prepared using four different monomer concentrations (25, 50, 75 and 100 wt% PEGDMA) in water and cross-linked by photopolymerisation. Initial results revealed a correlation between monomer concentration and swelling behaviour, where a decrease in swelling was observed with increase in monomer content. On storage in physiological solutions at 37 °C, a decrease in the weight remaining of the hydrogels and the pH of the solutions was observed over a 28-day period. Using scanning electron microscopy, the surface topography of the hydrogels appeared to get smoother and in parallel changes in hydrophilicty were observed, with the biggest changes observed for the higher monomer concentrations where water contact angle values were seen to increase toward 90°. However, the mechanical properties remained relatively unaffected and there was no adverse effect on cell metabolic activity observed for cells grown in the presence of PEGDMA samples or using elution methods. Looking at the combination of mechanical chemical and thermal properties shown these results are an important finding for scaffolds intended for tissue engineering applications, where provision of mechanical support without the elicitation of an inflammatory response due to polymer degradation products is crucial for successful integration and neotissue formation during the first 28 days post implantation.

Regeneration and Repair of Skin Wounds: Various Strategies for Treatment

Skin as a mechanical barrier between the inner and outer environment of our body protects us against infection and electrolyte loss. This organ consists of 3 layers: the epidermis, dermis, and hypodermis. Any disruption in the integrity of skin leads to the formation of wounds, which are divided into 2 main categories: acute wounds and chronic wounds. Generally, acute wounds heal relatively faster. In contrast to acute wounds, closure of chronic wounds is delayed by 3 months after the initial insult. Treatment of chronic wounds has been one of the most challenging issues in the field of regenerative medicine, promoting scientists to develop various therapeutic strategies for a fast, qualified, and most cost-effective treatment modality. Here, we reviewed more recent approaches, including the development of stem cell therapy, tissue-engineered skin substitutes, and skin equivalents, for the healing of complex wounds.

Scaffolding Strategies for Tissue Engineering and Regenerative Medicine Applications

During the past two decades, tissue engineering and the regenerative medicine field have invested in the regeneration and reconstruction of pathologically altered tissues, such as cartilage, bone, skin, heart valves, nerves and tendons, and many others. The 3D structured scaffolds and hydrogels alone or combined with bioactive molecules or genes and cells are able to guide the development of functional engineered tissues, and provide mechanical support during in vivo implantation. Naturally derived and synthetic polymers, bioresorbable inorganic materials, and respective hybrids, and decellularized tissue have been considered as scaffolding biomaterials, owing to their boosted structural, mechanical, and biological properties. A diversity of biomaterials, current treatment strategies, and emergent technologies used for 3D scaffolds and hydrogel processing, and the tissue-specific considerations for scaffolding for Tissue engineering (TE) purposes are herein highlighted and discussed in depth. The newest procedures focusing on the 3D behavior and multi-cellular interactions of native tissues for further use for in vitro model processing are also outlined. Completed and ongoing preclinical research trials for TE applications using scaffolds and hydrogels, challenges, and future prospects of research in the regenerative medicine field are also presented.

Physicochemical and biological investigation of oxygen plasma modified electrospun polyurethane scaffolds for connective tissue engineering application

In this study, electrospinning was selected to fabricate randomly oriented polyurethane (PU) nanofibers for tissue engineering application, and the surface of scaffolds was exposed to oxygen plasma flow. The morphology structure of the PU scaffolds before and after oxygen plasma treatment was observed using scanning electron microscopy (SEM) micrographs, and the fiber diameter distribution was measured using Image J software. The results demonstrated that oxygen plasma modification reduces the fiber diameter without any other special effects on fiber microstructure. Water drop contact angle and swelling ratio of PU constructs were performed to estimate the water-scaffolds interactions. The results revealed improvement of hydrophilicity by oxygen plasma treatment. Atomic force microscopy test was done to analyze a topological characteristic of the scaffolds, and it was found out that oxygen plasma treatment decreases the roughness of the scaffolds. The biological behavior of the scaffolds was investigated by SEM observation and MTT assay after L-929 fibroblast cells culture. In vitro assays demonstrated biocompatibility, cellular attachments, and filopodia formation on plasma modified samples. These results suggest that oxygen plasma treatment improves the physicochemical and biological properties of PU scaffolds to create a more hydrophilic surface which facilitates cell attachments and proliferation.

in situ Fabrication of Biological Chitosan and Gelatin-Based Hydrogels Loading Biphasic Calcium Phosphate Nanoparticles for Bone Tissue Regeneration

Adjustably biodegradable materials have gained much attention in biomedical applications. Among of them, various hydrogel-based scaffolds have applied for regenerating soft and hard tissues. In this study, according to differently biological properties of gelatin or chitosan as well as biphasic calcium phosphate nanoparticles (BCPNPs), several injectable nanocomposite hydrogels (INgel) were enzymatically fabricated from a phenolic chitosan derivative (PCD), phenolic gelatin derivative (PGD) and BCPNPs. According the change of H2O2 concentration with follow-up the time, the in situ formation of INgel was varied from 35 to 80 s. The degradation rate of the nanocomposite materials significantly related to in presence of collagenase that expended from 3 days to over one month depending on amount of the formulated PCD. The BCPNPs-encapsulated PCD-PGD INgel enhanced mineralization in the simulated biofluid. Fluorescent cytotoxicity assay indicated that the INgel was fabricated from a higher amount of the PGD resulting in a significant proliferation of bone marrow mesenchymal stem cells. These preliminary results exhibited a great potential of the INgel for bone regeneration.

Controlled release of antibiotics from photopolymerized hydrogels: Kinetics and microbiological studies

The development of convenient synthetic methods and improved materials for the production of high load-capacity and biocompatible drug delivery systems is a challenging task with important implications in health sciences. In this work, acrylamide/2-hydroxyethylmethacrylate and N-isopropylacrylamide/2-hydroxyethylmethacrylate hydrogels were synthesized by photopolymerization using energy-efficient green-LEDs. A functionalized silsesquioxane was used as both crosslinker and co-initiator for the photopolymerization. The hybrid organic-inorganic nature of the silsesquioxane improved the resulting hydrogels' properties increasing their swelling capacity and biocompatibility. Additionally, the mild conditions used during the photopolymerization allowed the synthesis of hydrogels in the presence of antibiotics yielding high load-capacity materials in which the drug preserves its molecular structure and antimicrobial activity (as confirmed by HPLC and microbiological assays). The materials were characterized by FTIR, DSC and SEM. Additionally, the kinetics of gels´ swelling and drug release were studied under physiological conditions (pH 7.4 and 37 °C). The results demonstrate how hydrogel composition affects the antibiotics-release kinetics. The final drug release percentage increased with increasing molar fraction of acrylamide or N-isopropylacrylamide and in most cases exceeded 85%. Finally, the antibacterial effect of loaded gels was characterized using a number of assays against Gram negative and Gram positive bacteria. The observed antibacterial effect correlated well with swelling and drug release results. Furthermore, gels are not toxic for isolated erythrocytes as demonstrated by haemolytic tests. Overall, our results indicate that the produced hydrogels are promising materials to develop controlled drug-delivery devices such as capsules, dermatological patches and others.

In vivo systemic toxicity assessment of an oxidized dextrin-based hydrogel and its effectiveness as a carrier and stabilizer of granular synthetic bone substitutes

The worldwide incidence of bone disorders is raising, mainly due to aging population. The lack of effective treatments is pushing the development of synthetic bone substitutes (SBSs). Most ceramic-based SBSs commercially available display limited handling properties. Attempting to solve these issues and achieve wider acceptance by the clinicians, granular ceramics have been associated with hydrogels (HGs) to produce injectable/moldable SBSs. Dextrin, a low-molecular-weight carbohydrate, was used to develop a fully resorbable and injectable HG. It was first oxidized with sodium periodate and then cross-linked with adipic acid dihydrazide. The in vivo biocompatibility and safety of the dextrin-based HG was assessed by subacute systemic toxicity and skin sensitization tests, using rodent models. The results showed that the HG did not induce any systemic toxic effect, skin reaction, or genotoxicity, neither impaired the bone repair/regeneration process. Then, the HG was successfully combined with granular bone substitute, registered as Bonelike (250-500 μm) to obtain a moldable/injectable SBS, which was implanted in tibial fractures in goats for 3 and 6 weeks. The obtained results showed that HG allowed the stabilization of the granules into the defect, ensuring effective handling, and molding properties of the formulation, as well as an efficient cohesion of the granules. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1678-1689, 2019.

Sustained Release from Injectable Composite Gels Loaded with Silver Nanowires Designed to Combat Bacterial Resistance in Bone Regeneration Applications

One-dimensional nanostructures, such as silver nanowires (AgNWs), have attracted considerable attention owing to their outstanding electrical, thermal and antimicrobial properties. However, their application in the prevention of infections linked to bone tissue regeneration intervention has not yet been explored. Here we report on the development of an innovative scaffold prepared from chitosan, composite hydroxyapatite and AgNWs (CS-HACS-AgNWs) having both bioactive and antibacterial properties. In vitro results highlighted the antibacterial potential of AgNWs against both gram-positive and gram-negative bacteria. The CS-HACS-AgNWs composite scaffold demonstrated suitable Ca/P deposition, improved gel strength, reduced gelation time, and sustained Ag⁺ release within therapeutic concentrations. Antibacterial studies showed that the composite formulation was capable of inhibiting bacterial growth in suspension, and able to completely prevent biofilm formation on the scaffold in the presence of resistant strains. The hydrogels were also shown to be biocompatible, allowing cell proliferation. In summary, the developed CS-HACS-AgNWs composite hydrogels demonstrated significant potential as a scaffold material to be employed in bone regenerative medicine, as they present enhanced mechanical strength combined with the ability to allow calcium salts deposition, while efficiently decreasing the risk of infections. The results presented justify further investigations into the potential clinical applications of these materials.

Bioactive glass ions induce efficient osteogenic differentiation of human adipose stem cells encapsulated in gellan gum and collagen type I hydrogels

BACKGROUND

Due to unmet need for bone augmentation, our aim was to promote osteogenic differentiation of human adipose stem cells (hASCs) encapsulated in gellan gum (GG) or collagen type I (COL) hydrogels with bioactive glass (experimental glass 2-06 of composition [wt-%]: Na₂O 12.1, K₂O 14.0, CaO 19.8, P₂O5 2.5, B₂O₃ 1.6, SiO₂ 50.0) extract based osteogenic medium (BaG OM) for bone construct development. GG hydrogels were crosslinked with spermidine (GG-SPD) or BaG extract (GG-BaG).

METHODS

Mechanical properties of cell-free GG-SPD, GG-BaG, and COL hydrogels were tested in osteogenic medium (OM) or BaG OM at 0, 14, and 21 d. Hydrogel embedded hASCs were cultured in OM or BaG OM for 3, 14, and 21 d, and analyzed for viability, cell number, osteogenic gene expression, osteocalcin production, and mineralization. Hydroxyapatite-stained GG-SPD samples were imaged with Optical Projection Tomography (OPT) and Selective Plane Illumination Microscopy (SPIM) in OM and BaG OM at 21 d. Furthermore, Raman spectroscopy was used to study the calcium phosphate (CaP) content of hASC-secreted ECM in GG-SPD, GG-BaG, and COL at 21 d in BaG OM.

RESULTS

The results showed viable rounded cells in GG whereas hASCs were elongated in COL. Importantly, BaG OM induced significantly higher cell number and higher osteogenic gene expression in COL. In both hydrogels, BaG OM induced strong mineralization confirmed as CaP by Raman spectroscopy and significantly improved mechanical properties. GG-BaG hydrogels rescued hASC mineralization in OM. OPT and SPIM showed homogeneous 3D cell distribution with strong mineralization in BaG OM. Also, strong osteocalcin production was visible in COL.

CONCLUSIONS

Overall, we showed efficacious osteogenesis of hASCs in 3D hydrogels with BaG OM with potential for bone-like grafts.

Chitosan/hydroxyapatite (HA)/hydroxypropylmethyl cellulose (HPMC) spongy scaffolds-synthesis and evaluation as potential alveolar bone substitutes

Alveolar bone loss is associated with infections and its augmentation is a pre-requisite for the success of dental implants. In present study, we aim to develop and evaluate novel freeze dried doxycycline loaded chitosan (CS)/hydroxyapatite (HA) spongy scaffolds where hydroxypropylmethyl cellulose (HPMC) was added as a crosslinker. Scaffolds displayed compressive strength of 14MPa/cm³ and 0.34 as elastic response. The interconnected pore diameter was 41-273μm, favorably provided the template supporting cells and transport. An overall 10% degradation was seen after 14day's studies at pH 7.4 in PBS. Doxycycline hyclate, a frequently used drug to counter oral infections, demonstrated an initial burst release (6-8h), followed by a sustain release profile for the remaining 64h. CS/HA/HPMC scaffolds were nontoxic and promoted pre-osteoblast cell viability as seen with live/dead calcein staining after 24h where scaffolds with 10% and 25% HPMC by weight of scaffold had more viable cells. Scaffolds with 10%, 20% and 25% HPMC by weight of scaffold showed efficient cellular adhesion as seen in scanning electron microscopy images (day 8) indicating that pre-osteoblast cells were able to adhere well on the surface and into the porous structure via cytoplasmic extensions. Hoechst 33258 nuclear staining at day 2 and 8 indicated cell proliferation which was further supported byMTT assay at day 2, 4 and 8. Although all scaffolds supported pre-osteoblast cell viability, alkaline phosphatase (ALP) staining demonstrated that upon induction, differentiation was pronounced in case of scaffolds with 10% HMPC scaffolds. Conclusively, these materials having all the required mechanical and biological properties are potential candidates for alveolar bone regeneration.