Biodegradable poly(ethylene glycol) hydrogels based on a self-elimination degradation mechanism

A multicrosslinked network composite hydrogel scaffold based on DLP photocuring printing for nasal cartilage repair

Natural hydrogels are widely employed in tissue engineering and have excellent biodegradability and biocompatibility. Unfortunately, the utilization of such hydrogels in the field of three-dimensional (3D) printing nasal cartilage is constrained by their subpar mechanical characteristics. In this study, we provide a multicrosslinked network hybrid ink made of photocurable gelatin, hyaluronic acid, and acrylamide (AM). The ink may be processed into intricate 3D hydrogel structures with good biocompatibility and high stiffness properties using 3D printing technology based on digital light processing (DLP), including intricate shapes resembling noses. By varying the AM content, the mechanical behavior and biocompatibility of the hydrogels can be adjusted. In comparison to the gelatin methacryloyl (GelMA)/hyaluronic acid methacryloyl (HAMA) hydrogel, adding AM considerably enhances the hydrogel's mechanical properties while also enhancing printing quality. Meanwhile, the biocompatibility of the multicrosslinked network hydrogels and the development of cartilage were assessed using neonatal Sprague-Dawley (SD) rat chondrocytes (CChons). Cells sown on the hydrogels considerably multiplied after 7 days of culture and kept up the expression of particular proteins. Together, our findings point to GelMA/HAMA/polyacrylamide (PAM) hydrogel as a potential material for nasal cartilage restoration. The photocuring multicrosslinked network ink composed of appropriate proportions of GelMA/HAMA/PAM is very suitable for DLP 3D printing and will play an important role in the construction of nasal cartilage, ear cartilage, articular cartilage, and other tissues and organs in the future. Notably, previous studies have not explored the application of 3D-printed GelMA/HAMA/PAM hydrogels for nasal cartilage regeneration.

Advancements in Regenerative Hydrogels in Skin Wound Treatment: A Comprehensive Review

This state-of-the-art review explores the emerging field of regenerative hydrogels and their profound impact on the treatment of skin wounds. Regenerative hydrogels, composed mainly of water-absorbing polymers, have garnered attention in wound healing, particularly for skin wounds. Their unique properties make them well suited for tissue regeneration. Notable benefits include excellent water retention, creating a crucially moist wound environment for optimal healing, and facilitating cell migration, and proliferation. Biocompatibility is a key feature, minimizing adverse reactions and promoting the natural healing process. Acting as a supportive scaffold for cell growth, hydrogels mimic the extracellular matrix, aiding the attachment and proliferation of cells like fibroblasts and keratinocytes. Engineered for controlled drug release, hydrogels enhance wound healing by promoting angiogenesis, reducing inflammation, and preventing infection. The demonstrated acceleration of the wound healing process, particularly beneficial for chronic or impaired healing wounds, adds to their appeal. Easy application and conformity to various wound shapes make hydrogels practical, including in irregular or challenging areas. Scar minimization through tissue regeneration is crucial, especially in cosmetic and functional regions. Hydrogels contribute to pain management by creating a protective barrier, reducing friction, and fostering a soothing environment. Some hydrogels, with inherent antimicrobial properties, aid in infection prevention, which is a crucial aspect of successful wound healing. Their flexibility and ability to conform to wound contours ensure optimal tissue contact, enhancing overall treatment effectiveness. In summary, regenerative hydrogels present a promising approach for improving skin wound healing outcomes across diverse clinical scenarios. This review provides a comprehensive analysis of the benefits, mechanisms, and challenges associated with the use of regenerative hydrogels in the treatment of skin wounds. In this review, the authors likely delve into the application of rational design principles to enhance the efficacy and performance of hydrogels in promoting wound healing. Through an exploration of various methodologies and approaches, this paper is poised to highlight how these principles have been instrumental in refining the design of hydrogels, potentially revolutionizing their therapeutic potential in addressing skin wounds. By synthesizing current knowledge and highlighting potential avenues for future research, this review aims to contribute to the advancement of regenerative medicine and ultimately improve clinical outcomes for patients with skin wounds.

Injectable Hydrogels Prepared Using Novel Synthetic Short Peptides with Defined Structure and Gelatin as Scaffolds to Support Cell and Tissue Growth

Animal-derived basement-membrane matrices such as Geltrex are used to grow cells and tissues. Particularly, these are commonly applied to support tumor growth in animals for cancer research. However, a material derived from an animal source has an undefined composition, and may thus have unavoidable batch-to-batch variation in properties. To overcome these issues, a series of synthetic short peptides to form hydrogels is designed in combination with gelatin to promote cell adhesion and growth. The peptides have sequences of (X1Y1X2Y2)2 , where X1 and X2 are hydrophobic residues, while Y1 and Y2 are hydrophilic residues. The peptides spontaneously fold and self-assemble into a β-sheet secondary structure upon contact with salts, and then aggregate to form hydrophilic networks of hydrogels. Hybrid hydrogels formed by mixing the peptide IEVEIRVK (IVK8) with gelatin are injectable and enzymatically degradable. The hybrid hydrogels at optimal compositions support SW480 and HepG2 tumor spheroid growth in vitro as effectively as Geltrex. More importantly, the peptide/gelatin hydrogels support tumor growth in a SW480 human colorectal adenocarcinoma xenograft mouse model. Altogether, the results illustrate that the synthetic peptide/gelatin hybrid hydrogel is a promising scaffold that can be used to support cell and tissue growth both in vitro and in vivo.

An injectable photopolymerizable chitosan hydrogel doped anti-inflammatory peptide for long-lasting periodontal pocket delivery and periodontitis therapy

Periodontitis is a common chronic inflammatory disease caused by plaque that leads to alveolar bone resorption and tooth loss. Inflammation control and achieving better tissue repair are the key to periodontitis treatment. In this study, human β-Defensin 1 short motif Pep-B with inflammation inhibition and differentiation regulation properties, is firstly used in the treatment of periodontitis, and an injectable photopolymerizable Pep-B/chitosan methacryloyl composite hydrogel (CMSA/Pep-B) is constructed. We confirm that Pep-B improves inflammation, and restores osteogenic behavior and function of injured stem cells. CMSA/Pep-B has good injectability, fluidity and photopolymerizability, and can sustainably release Pep-B to maintain drug concentration in periodontal pockets. Furthermore, animal experiments showed that CMSA/Pep-B significantly ameliorated the inflammation of the periodontium and reduced the alveolar bone loss by decreasing inflammatory infiltration, osteoclast formation and collagen destruction. In conclusion, CMSA/Pep-B is envisaged to be a novel bioactive material or therapeutic drug for treating periodontitis.

Additive Manufacturing of Biomaterials-Design Principles and Their Implementation

Additive manufacturing (AM, also known as 3D printing) is an advanced manufacturing technique that has enabled progress in the design and fabrication of customised or patient-specific (meta-)biomaterials and biomedical devices (e.g., implants, prosthetics, and orthotics) with complex internal microstructures and tuneable properties. In the past few decades, several design guidelines have been proposed for creating porous lattice structures, particularly for biomedical applications. Meanwhile, the capabilities of AM to fabricate a wide range of biomaterials, including metals and their alloys, polymers, and ceramics, have been exploited, offering unprecedented benefits to medical professionals and patients alike. In this review article, we provide an overview of the design principles that have been developed and used for the AM of biomaterials as well as those dealing with three major categories of biomaterials, i.e., metals (and their alloys), polymers, and ceramics. The design strategies can be categorised as: library-based design, topology optimisation, bio-inspired design, and meta-biomaterials. Recent developments related to the biomedical applications and fabrication methods of AM aimed at enhancing the quality of final 3D-printed biomaterials and improving their physical, mechanical, and biological characteristics are also highlighted. Finally, examples of 3D-printed biomaterials with tuned properties and functionalities are presented.

Emerging zero-dimensional to four-dimensional biomaterials for bone regeneration

Bone is one of the most sophisticated and dynamic tissues in the human body, and is characterized by its remarkable potential for regeneration. In most cases, bone has the capacity to be restored to its original form with homeostatic functionality after injury without any remaining scarring. Throughout the fascinating processes of bone regeneration, a plethora of cell lineages and signaling molecules, together with the extracellular matrix, are precisely regulated at multiple length and time scales. However, conditions, such as delayed unions (or nonunion) and critical-sized bone defects, represent thorny challenges for orthopedic surgeons. During recent decades, a variety of novel biomaterials have been designed to mimic the organic and inorganic structure of the bone microenvironment, which have tremendously promoted and accelerated bone healing throughout different stages of bone regeneration. Advances in tissue engineering endowed bone scaffolds with phenomenal osteoconductivity, osteoinductivity, vascularization and neurotization effects as well as alluring properties, such as antibacterial effects. According to the dimensional structure and functional mechanism, these biomaterials are categorized as zero-dimensional, one-dimensional, two-dimensional, three-dimensional, and four-dimensional biomaterials. In this review, we comprehensively summarized the astounding advances in emerging biomaterials for bone regeneration by categorizing them as zero-dimensional to four-dimensional biomaterials, which were further elucidated by typical examples. Hopefully, this review will provide some inspiration for the future design of biomaterials for bone tissue engineering.

In situ Forming Hyperbranched PEG-Thiolated Hyaluronic Acid Hydrogels With Honey-Mimetic Antibacterial Properties

The rapidly increasing resistance of bacteria to currently approved antibiotic drugs makes surgical interventions and the treatment of bacterial infections increasingly difficult. In recent years, complementary strategies to classical antibiotic therapy have, therefore, gained importance. One of these strategies is the use of medicinal honey in the treatment of bacterially colonized wounds. One of the several bactericidal effects of honey is based on the in situ generation of hydrogen peroxide through the activity of the enzyme glucose oxidase. The strategy underlying this work is to mimic this antibacterial redox effect of honey in an injectable, biocompatible, and rapidly forming hydrogel. The hydrogel was obtained by thiol–ene click reaction between hyperbranched polyethylene glycol diacrylate (HB PEGDA), synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization, and thiolated hyaluronic acid (HA-SH). After mixing 500 µL HB PEGDA (10%, w/w) and 500 µL HA-SH (1%, w/w) solutions, hydrogels formed in ∼60 s (HB PEGDA/HA-SH 10.0–1.0), as assessed by the tube inverting test. The HB PEGDA/HA-SH 10.0–1.0 hydrogel (200 µL) was resistant to in vitro dissolution in water for at least 64 days, absorbing up to 130 wt% of water. Varying glucose oxidase (GO) amounts (0–500 U/L) and constant glucose content (2.5 wt%) were loaded into HB PEGDA and HA-SH solutions, respectively, before hydrogel formation. Then, the release of H₂O₂ was evaluated through a colorimetric pertitanic acid assay. The GO content of 250 U/L was selected, allowing the formation of 10.8 ± 1.4 mmol H₂O₂/L hydrogel in 24 h, under static conditions. The cytocompatibility of HB PEGDA/HA-SH 10.0–1.0 hydrogels loaded with different GO activities (≤ 500 U/L) at a constant glucose amount (2.5 wt%) was investigated by in vitro assays at 24 h with L929 and HaCaT cell lines, according to DIN EN ISO 10993-5. The tests showed cytocompatibility for GO enzyme activity up to 250 U/L for both cell lines. The antibacterial activity of HB PEGDA/HA-SH 10.0–1.0 hydrogels loaded with increasing amounts of GO was demonstrated against various gram-positive bacteria (S. aureus and S. epidermidis), antibiotic-resistant gram-positive bacteria (MRSA and MRSE), gram-negative bacteria (P. aeruginosa, E. coli, and A. baumanii), and antibiotic-resistant gram-negative strains (P. aeruginosa and E. coli) using agar diffusion tests. For all gram-positive bacterial strains, increasing efficacy was measured with increasing GO activity. For the two P. aeruginosa strains, efficacy was shown only from an enzyme activity of 125 U/L and for E. coli and A. baumanii, efficacy was shown only from 250 U/L enzyme activity. HB PEGDA/HA-SH 10.0–1.0 hydrogels loaded with ≤250 U/L GO and 2.5 wt% glucose are promising formulations due to their fast-forming properties, cytocompatibility, and ability to produce antibacterial H₂O₂, warranting future investigations for bacterial infection treatment, such as wound care.

Compartmental and COMSOL Multiphysics 3D Modeling of Drug Diffusion to the Vitreous Following the Administration of a Sustained-Release Drug Delivery System

The purpose of this study was to examine antibiotic drug transport from a hydrogel drug delivery system (DDS) using a computational model and a 3D model of the eye. Hydrogel DDSs loaded with vancomycin (VAN) were synthesized and release behavior was characterized in vitro. Four different compartmental and four COMSOL models of the eye were developed to describe transport into the vitreous originating from a DDS placed topically, in the subconjunctiva, subretinally, and intravitreally. The concentration of the simulated DDS was assumed to be the initial concentration of the hydrogel DDS. The simulation was executed over 1500 and 100 h for the compartmental and COMSOL models, respectively. Based on the MATLAB model, topical, subconjunctival, subretinal and vitreous administration took most (~500 h to least (0 h) amount of time to reach peak concentrations in the vitreous, respectively. All routes successfully achieved therapeutic levels of drug (0.007 mg/mL) in the vitreous. These models predict the relative build-up of drug in the vitreous following DDS administration in four different points of origin in the eye. Our model may eventually be used to explore the minimum loading dose of drug required in our DDS leading to reduced drug use and waste.

Effect of mesenchymal stromal cells encapsulated within polyethylene glycol-collagen hydrogels formed in situ on alkali-burned corneas in an ex vivo organ culture model

BACKGROUND AIMS

Corneal inflammation after alkali burns often results in vision loss due to corneal opacification and neovascularization. Mesenchymal stem cells (MSCs) and their secreted factors (secretome) have been studied for their anti-inflammatory and anti-angiogenic properties with encouraging results. However, topical instillation of MSCs or their secretome is often accompanied by issues related to delivery or rapid washout. Polyethylene glycol (PEG) and collagen are well-known biomaterials used extensively in scaffolds for tissue engineering. To effectively suppress alkaline burn-induced corneal injury, the authors proposed encapsulating MSCs within collagen gels cross-linked with multi-functional PEG-succinimidyl esters as a means to deliver the secretome of immobilized MSCs.

METHODS

Human MSCs were added to a neutralized collagen solution and mixed with a solution of four-arm PEG-N-hydroxysuccinimide. An ex vivo organ culture was conducted using rabbit corneas injured by alkali burn. MSCs were encapsulated within PEG-collagen hydrogels and injected onto the wounded cornea immediately following alkali burn and washing. Photographs of the ocular surface were taken over a period of 7 days after the alkali burn and processed for immunohistochemical evaluation. Samples were split into three groups: injury without treatment, MSCs alone, and MSCs encapsulated within PEG-collagen hydrogels.

RESULTS

All corneas in ex vivo organ culture lost their transparency immediately after alkali burn, and only the groups treated with MSCs and MSCs encapsulated within PEG-collagen hydrogels recovered some transparency after 7 days. Immunohistochemical analysis revealed increased expression of vimentin in the anterior corneal stroma of the group without treatment indicative of fibrotic healing, whereas less stromal vimentin was detected in the group containing MSCs encapsulated within the PEG-collagen hydrogels.

CONCLUSIONS

PEG-collagen hydrogels enable the encapsulation of viable MSCs capable of releasing secreted factors onto the ocular surface. Encapsulating MSCs within PEG-collagen hydrogels may be a promising method for delivering their therapeutic benefits in cases of ocular inflammatory diseases, such as alkali burn injuries.

Design and Development of Hybrid Hydrogels for Biomedical Applications: Recent Trends in Anticancer Drug Delivery and Tissue Engineering

The applications of hydrogels in biomedical field has been since multiple decades. Discoveries in biology and chemistry render this platform endowed with much engineering potentials and growing continuously. Novel approaches in constructing these materials have led to the production of complex hybrid hydrogels systems that can incorporate both natural and synthetic polymers and other functional moieties for mediated cell response, tunable release kinetic profiles, thus they are used and research for diverse biomedical applications. Recent advancement in this field has established promising techniques for the development of biorelevant materials for construction of hybrid hydrogels with potential applications in the delivery of cancer therapeutics, drug discovery, and re-generative medicines. In this review, recent trends in advanced hybrid hydrogels systems incorporating nano/microstructures, their synthesis, and their potential applications in tissue engineering and anticancer drug delivery has been discussed. Examples of some new approaches including click reactions implementation, 3D printing, and photopatterning for the development of these materials has been briefly discussed. In addition, the application of biomolecules and motifs for desired outcomes, and tailoring of their transport and kinetic behavior for achieving desired outcomes in hybrid nanogels has also been reviewed.

In vivo performance of a bilayer wrap to prevent abdominal adhesions

There is a high prevalence of intra-abdominal adhesions following bowel resection, which can result in chronic pain, bowel obstruction, and morbidity. Although commercial adhesion barriers have been widely utilized for colonic resections, these barriers do not prevent anastomotic leakage resulting from reduced healing of the anastomosis, which can result in long-term health problems. To address this limitation, we have developed an adhesive bilayer wrap with selective bioactivity to simultaneously prevent intra-abdominal adhesion formation and promote anastomotic healing. Reactive electrospinning was used to generate a crosslinked gelatin mesh to serve as a cell-instructive substrate to improve anastomotic healing. A coating of poly(ethylene glycol) (PEG) foam was applied to the bioactive mesh to generate an antifouling layer and prevent intra-abdominal adhesions. After in vitro confirmation of selective bioactivity, the composite wrap was compared after 2 weeks to a commercial product (Interceed^Ⓡ) in an in vivo rat colonic abrasion model for prevention of intra-abdominal adhesions. The composite bilayer wrap was able to prevent intra-abdominal adhesions when clinical placement was maintained. The composite bilayer wrap was further modified to include tissue adhesive properties for improved efficacy. Preliminary studies indicated that the adhesive composite bilayer wrap maintained a maximum shear strength comparable to Interceed^Ⓡ and greater than fibrin glue. Overall, this work resulted in an initial proof-of-concept device that was shown to effectively prevent intra-abdominal adhesion formation in vivo. The composite bilayer wrap studied here could lead to an improved technology for improved healing of intestinal anastomoses.

GSK3 inhibitor-loaded osteotropic Pluronic hydrogel effectively mitigates periodontal tissue damage associated with experimental periodontitis

Periodontitis is a chronic inflammatory disease caused by complex interactions between the host immune system and pathogens that affect the integrity of periodontium. To prevent disease progression and thus preserve alveolar bone structure, simultaneous anti-inflammatory and osteogenic intervention are essential. Hence, a glycogen synthase kinase 3 beta inhibitor (BIO) was selected as a potent inflammation modulator and osteogenic agent to achieve this treatment objective. BIO's lack of osteotropicity, poor water solubility, and potential long-term systemic side effects, however, have hampered its clinical applications. To address these limitations, pyrophosphorylated Pluronic F127 (F127-PPi) was synthesized and mixed with regular F127 to prepare an injectable and thermoresponsive hydrogel formulation (PF127) of BIO, which could adhere to hard tissue and gradually release BIO to exert its therapeutic effects locally. Comparing to F127 hydrogel, PF127 hydrogels exhibited stronger binding to hydroxyapatite (HA). Additionally, BIO's solubility in PF127 solution was dramatically improved over F127 solution and the improvement was proportional to the polymer concentration. When evaluated on a rat model of periodontitis, PF127-BIO hydrogel treatment was found to be very effective in preserving alveolar bone and ligament, and preventing periodontal inflammation, as shown by the micro-CT and histological data, respectively. Altogether, these findings suggested that the thermoresponsive PF127 hydrogel is an effective local drug delivery system for better clinical management of periodontitis and associated pathologies.

Injectable Poly(ethylene glycol) Hydrogels Cross-Linked by Metal-Phenolic Complex and Albumin for Controlled Drug Release

Injectable hydrogel is advantageous as a drug reservoir for controlled drug release since its injectability provides minimally invasive access to internal tissues and irregular-shaped target sites. Herein, we fabricated pH-responsive injectable hydrogels constructed of a supramolecular cross-link network, which contained tannic acid (TA), Fe(III), poly(ethylene glycol) (PEG), and bovine serum albumin (BSA) for controlled drug release. The hydrogel precursors rapidly turned into a gel when co-injected with NaOH in a time scale of seconds. The hydrogel properties and drug release profiles are all tunable by adjusting the concentrations of BSA, NaOH, and doxorubicin (DOX). The Young's moduli range from 3.19 ± 0.93 to 43.24 ± 1.37 kPa that match internal soft tissues. The hydrogel lasts more than 3 weeks and gradually releases doxorubicin up to 123.6 ± 1.7 μg at pH 6.4. The results of the physical properties and drug release suggest supramolecular interactions that correspond to Fourier transform infrared (FTIR) results. In vitro cytotoxicity was also assessed using L929 cells, and the results demonstrated the material biocompatibility. The tunable properties, controlled release profiles, and biocompatibility of injectable poly(ethylene glycol) hydrogels support that they have great potential as a drug-releasing material for localized treatments.

New Developments in Medical Applications of Hybrid Hydrogels Containing Natural Polymers

New trends in biomedical applications of the hybrid polymeric hydrogels, obtained by combining natural polymers with synthetic ones, have been reviewed. Homopolysaccharides, heteropolysaccharides, as well as polypeptides, proteins and nucleic acids, are presented from the point of view of their ability to form hydrogels with synthetic polymers, the preparation procedures for polymeric organic hybrid hydrogels, general physico-chemical properties and main biomedical applications (i.e., tissue engineering, wound dressing, drug delivery, etc.).

Calcium Phosphate Incorporated Bacterial Cellulose-Polyvinylpyrrolidone Based Hydrogel Scaffold: Structural Property and Cell Viability Study for Bone Regeneration Application

This work focuses on the analysis of structural and functional properties of calcium phosphate (CaP) incorporated bacterial cellulose (BC)-polyvinylpyrrolidone (PVP) based hydrogel scaffolds referred to as “CaP/BC-PVP”. CaP is incorporated in the scaffolds in the form of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) in different concentrations (β-TCP: HA (w/w) = 20:80, 40:60, and 50:50). The scaffolds were characterized on the basis of porosity, thermal, biodegradation, mechanical, and cell viability/cytocompatibility properties. The structural properties of all the hydrogel scaffolds show significant porosity. The biodegradation of “CaP/BC-PVP” scaffold was evaluated following hydrolytic degradation. Weight loss profile, pH change, scanning electron microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) study confirm the significant degradability of the scaffolds. It is observed that a 50:50_CaP/BC-PVP scaffold has the highest degree of degradation. On the other hand, the compressive strengths of CaP/BC-PVP hydrogel scaffolds are found between 0.21 to 0.31 MPa, which is comparable with the human trabecular bone. The cell viability study is performed with a human osteosarcoma Saos-2 cell line, where significant cell viability is observed in all the hydrogel scaffolds. This indicated their ability to facilitate cell growth and cell proliferation. Considering all these substantial properties, CaP/BC-PVP hydrogel scaffolds can be suggested for detailed investigation in the context of bone regeneration application.

Hydrogels: soft matters in photomedicine

Photodynamic therapy (PDT), a shining beacon in the realm of photomedicine, is a non-invasive technique that utilizes dye-based photosensitizers (PSs) in conjunction with light and oxygen to produce reactive oxygen species to combat malignant tissues and infectious microorganisms. Yet, for PDT to become a common, routine therapy, it is still necessary to overcome limitations such as photosensitizer solubility, long-term side effects (e.g., photosensitivity) and to develop safe, biocompatible and target-specific formulations. Polymer based drug delivery platforms are an effective strategy for the delivery of PSs for PDT applications. Among them, hydrogels and 3D polymer scaffolds with the ability to swell in aqueous media have been deeply investigated. Particularly, hydrogel-based formulations present real potential to fulfill all requirements of an ideal PDT platform by overcoming the solubility issues, while improving the selectivity and targeting drawbacks of the PSs alone. In this perspective, we summarize the use of hydrogels as carrier systems of PSs to enhance the effectiveness of PDT against infections and cancer. Their potential in environmental and biomedical applications, such as tissue engineering photoremediation and photochemistry, is also discussed.

Coaxial bioprinting of cell-laden vascular constructs using a gelatin–tyramine bioink

The study revealed that linear distribution of multiple vascular cells could be achieved using synthetic bioink with short gelling time and a coaxial printing system.

3D Printing Applied to Tissue Engineered Vascular Grafts

The broad clinical use of synthetic vascular grafts for vascular diseases is limited by their thrombogenicity and low patency rate, especially for vessels with a diameter inferior to 6 mm. Alternatives such as tissue-engineered vascular grafts (TEVGs), have gained increasing interest. Among the different manufacturing approaches, 3D bioprinting presents numerous advantages and enables the fabrication of multi-scale, multi-material, and multicellular tissues with heterogeneous and functional intrinsic structures. Extrusion-, inkjet- and light-based 3D printing techniques have been used for the fabrication of TEVG out of hydrogels, cells, and/or solid polymers. This review discusses the state-of-the-art research on the use of 3D printing for TEVG with a focus on the biomaterials and deposition methods.

Local Toxicity of Topically Administrated Thermoresponsive Systems: In Vitro Studies with In Vivo Correlation

Thermoresponsive materials have the ability to respond to a small change in temperature-a property that makes them useful in a wide range of applications and medical devices. Although very promising, there is only little conclusive data about the cytotoxicity and tissue toxicity of these materials. This work studied the biocompatibility of three Food and Drug Administration approved thermoresponsive polymers: poly( N-isopropyl acrylamide), poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) tri-block copolymer, and poly(lactic acid-co-glycolic acid) and poly(ethylene glycol) tri-block copolymer. Fibroblast NIH 3T3 and HaCaT keratinocyte cells were used for the cytotoxicity testing and a mouse model for the in vivo evaluation. In vivo results generally showed similar trends as the results seen in vitro, with all tested materials presenting a satisfactory biocompatibility in vivo. pNIPAM, however, showed the highest toxicity both in vitro and in vivo, which was explained by the release of harmful monomers and impurities. More data focusing on the biocompatibility of novel thermoresponsive biomaterials will facilitate the use of existing and future medical devices.

Alginate/poly(amidoamine) injectable hybrid hydrogel for cell delivery

A covalently cross-linked injectable hybrid hydrogel, namely, alginate/poly(amidoamine) (PAMAM), with the objective of cell delivery was innovatively designed and synthesized using tetra-amino-functional PAMAM dendrimer as the cross-linker. With the increase in percentage of PAMAM cross-linker, the pore size and swelling ratio of hydrogels were in the range of 57 ± 18 μm to 88 ± 25 μm and 110 ± 16 to 157 ± 20, respectively. The study of attachment and proliferation of MC3T3-E1 pre-osteoblasts using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay through indirect and direct contact methods indicated a continuous increase in metabolically active live cells with time, implying non-cytotoxicity of the synthesized hydrogel. The live–dead assay showed >95% of live cells for alginate/PAMAM hydrogels, suggesting viability of the encapsulated cells. When the percentage of PAMAM cross-linker in alginate/PAMAM hydrogel was increased from 5 to 25, the percentage degradation rate decreased from 1.1 to 0.29%/day. Given that the poly(ethylene glycol) is commonly used cross-linker for hydrogel syntheses, we compared the behavior with poly(ethylene glycol). The incorporation of poly(ethylene glycol) in alginate/PAMAM hydrogel reduced the activity of MC3T3-E1 cells and their viability compared to the alginate/PAMAM hydrogels. The protonation of amino groups in alginate/PAMAM injectables under physiological conditions led to the formation of cationic hydrogels. These cationic hydrogels showed enhanced cell encapsulation and attachment ability because of electrostatic interaction with negatively charged cell surface as determined by cell adhesion and extensions from scanning electron microscope and vinculin assay and ability of in situ calcium phosphate mineralization. These observations point toward the potential use as an injectable scaffold for cell delivery and tissue engineering applications.

Broad-Spectrum Antibacterial Activity of Proteolytically Stable Self-Assembled αγ-Hybrid Peptide Gels

Bacterial infections pose a serious threat to mankind, and there is immense interest in the design and development of self-assembled peptide gels using ultrashort peptides for antibacterial applications. The peptide gels containing natural amino acids suffer from poor stability against proteolytic enzymes. Therefore, there is a need to design and develop peptide gels with improved stability against proteolytic enzymes. In the present work, we report the synthesis and characterization of α/γ hybrid peptides Boc-D-Phe-γ⁴-L-Phe-PEA (NH007) and Boc-L-Phe-γ⁴-L-Phe-PEA (NH009) to improve the proteolytic stability. Both of the dipeptides were found to self-assemble into gels in aqueous DMSO (3-5% w/v), and the self-assembly process was studied using FTIR and CD, which indicated antiparallel β-sheet formation with random coils in NH007 gels and random or unordered conformation in NH009. The rheological studies indicated viscoelastic characteristics for both gels; the storage modulus ( G') for NH007 and NH009 gels (3% w/v) was estimated as 0.2 and 0.5 MPa, higher than the loss modulus ( G''). Also, both gels demonstrated self-healing characteristics for six consecutive cycles when subjected to varying strains of 0.1 and 30% (200 s each). The peptide gels were incubated with a mocktail of proteolytic enzymes, proteinase K, pepsin, and chymotrypsin, and stability was monitored using RP HPLC. Up to 23 and 40% degradation was observed for NH007 (3%, w/v) in 24 and 36 h, and 77 and 94% degradation was observed for NH009 (3%, w/v), within the same period. Thus α/γ hybrid peptide gels containing D-Phe exhibited higher stability than gels fabricated using L-Phe. The use of D-residue in α/γ hybrid peptide significantly enhanced the stability of peptides against proteolytic enzymes, as the stability data reported in this work are possibly the best in class. Both peptide gels exhibited broad-spectrum antibacterial activity against Gram-negative and Gram-positive bacteria, such as Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus. The Pseudomonas aeruginosa and Staphylococcus aureus, in particular, are known to develop resistance. The NH007 (3%, w/v) demonstrated 65% inhibition, whereas NH009 (3%, w/v) showed 78% inhibition, with potent activity against Pseudomonas aeruginosa. Mechanistic studies, using SEM, HR-TEM, and bacterial live-dead assay, indicated entrapment of bacteria in gel networks, followed by interaction with cell membrane components and lysis. Cell viability (MTT assay) and toxicity (LDH assay) studies showed that both gels are not toxic to NIH 3T3 mouse embryonic fibroblast cells (mammalian). MTT assay showed >85% cell viability, and LDH assay exhibited not more than 15% cytotoxicity, even at higher concentrations (5%, w/v) and prolonged exposures (48 h). Overall, studies indicate the potential application of gels developed from the α/γ hybrid peptides in preventing biomaterial-related infections.

Fabrication of Hydrogel Materials for Biomedical Applications

Hydrogels are three-dimensional hydrophilic polymeric networks that can be made from a wide range of natural and synthetic polymers. This review discusses recent advanced engineering methods to fabricate hydrogels for biomedical applications with emphasis in cardiac constructs and wound healing. Layer-by-Layer (LbL) assembly offers a tissue-engineered construct with robust and highly ordered structures for cell proliferation and differentiation. Three-dimensional printings, including inkjet printing, fused deposition modeling, and stereolithographic apparatus, have been widely employed to fabricate complex structures (e.g., heart valves). Moreover, the state-of-the-art design of intelligent/stimulus-responsive hydrogels can be used for a wide range of biomedical applications, including drug delivery, glucose delivery, shape memory, wound dressings, and so on. In the future, an increasing number of hydrogels with tunable mechanical properties and versatile functions will be developed for biomedical applications by employing advanced engineering techniques with novel material design.

Heterogeneity is key to hydrogel-based cartilage tissue regeneration

Degradable hydrogels have been developed to provide initial mechanical support to encapsulated cells while facilitating the growth of neo-tissues. When cells are encapsulated within degradable hydrogels, the process of neo-tissue growth is complicated by the coupled phenomena of transport of large extracellular matrix macromolecules and the rate of hydrogel degradation. If hydrogel degradation is too slow, neo-tissue growth is hindered, whereas if it is too fast, complete loss of mechanical integrity can occur. Therefore, there is a need for effective modelling techniques to predict hydrogel designs based on the growth parameters of the neo-tissue. In this article, hydrolytically degradable hydrogels are investigated due to their promise in tissue engineering. A key output of the model focuses on the ability of the construct to maintain overall structural integrity as the construct transitions from a pure hydrogel to engineered neo-tissue. We show that heterogeneity in cross-link density and cell distribution is the key to this successful transition and ultimately to achieve tissue growth. Specifically, we find that optimally large regions of weak cross-linking around cells in the hydrogel and well-connected and dense cell clusters create the optimum conditions needed for neo-tissue growth while maintaining structural integrity. Experimental observations using cartilage cells encapsulated in a hydrolytically degradable hydrogel are compared with model predictions to show the potential of the proposed model.

Biohybrid methacrylated gelatin/polyacrylamide hydrogels for cartilage repair

We prepared a biohybrid hydrogel based on acrylamide and GelMA, having good mechanical properties, thermal stability, and bioactivity for cartilage regeneration.

Electrospun Poly(lactide-co-glycolide-co-3(S)-methyl-morpholine-2,5-dione) Nanofibrous Scaffolds for Tissue Engineering

Biomimetic scaffolds have been investigated in vascular tissue engineering for many years. Excellent biodegradable materials are desired as temporary scaffolds to support cell growth and disappear gradually with the progress of guided tissue regeneration. In the present paper, a series of biodegradable copolymers were synthesized and used to prepared micro/nanofibrous scaffolds for vascular tissue engineering. Poly(lactide-co-glycolide-co-3(S)-methyl-morpholine-2,5-dione) [P(LA-co-GA-co-MMD)] copolymers with different l-lactide (LA), glycolide (GA), and 3(S)-methyl-2,5-morpholinedione (MMD) contents were synthesized using stannous octoate as a catalyst. Moreover, the P(LA-co-GA-co-MMD) nanofibrous scaffolds were prepared by electrospinning technology. The morphology of scaffolds was analyzed by scanning electron microscopy (SEM), and the results showed that the fibers are smooth, regular, and randomly oriented with diameters of 700 ± 100 nm. The weight loss of scaffolds increased significantly with the increasing content of MMD, indicating good biodegradable property of the scaffolds. In addition, the cytocompatibility of electrospun nanofibrous scaffolds was tested by human umbilical vein endothelial cells. It is demonstrated that the cells could attach and proliferate well on P(LA-co-GA-co-MMD) scaffolds and, consequently, form a cell monolayer fully covering on the scaffold surface. Furthermore, the P(LA-co-GA-co-MMD) scaffolds benefit to excellent cell infiltration after subcutaneous implantation. These results indicated that the P(LA-co-GA-co-MMD) nanofibrous scaffolds could be potential candidates for vascular tissue engineering.

Biodegradable PEI modified complex micelles as gene carriers with tunable gene transfection efficiency for ECs

In recent years, gene therapy has evoked an increasing interest in clinical treatments of coronary diseases because it is a potential strategy to realize rapid endothelialization of artificial vascular grafts. The balance of high transfection efficiency and low cytotoxicity of nonviral gene carriers is an important issue to be solved. In this study, we aim to establish a gene delivery system offering an elegant way to tune the transfection activity and cytotoxicity. Biodegradable complex micelles were prepared from polyethylenimine-b-poly(lactide-co-3(S)-methyl-morpholine-2,5-dione)-b-polyethylenimine (PEI-b-PLMD-b-PEI) and methoxy-poly(ethylene glycol)-b-poly(lactide-co-3(S)-methyl-morpholine-2,5-dione) (mPEG-b-PLMD) copolymers by a co-assembly method. Then the ZNF580 gene plasmid (pDNA) was encapsulated into the complex micelles. The hydrodynamic size and zeta potential of these complex micelles and micelles/pDNA complexes indicated that they were feasible for use in cellular uptake and gene transfection. As expected, the transfection efficiency and cytotoxicity of these micelles/pDNA complexes could be conveniently tuned by changing the mass ratio of mPEG-b-PLMD to PEI-b-PLMD-b-PEI (3/1, 2/2, 1/3 and 0/4) in the mixed mPEG/PEI shell. The transfection efficiency increased as the mass ratio of mPEG-b-PLMD/PEI-b-PLMD-b-PEI decreased from 3/1 to 0/4, while the cytotoxicity showed an opposite tendency. Moreover, ZNF580 protein expression determined by Western blot analysis and the migration of transfected endothelial cells (ECs) by wound healing assay were consistent with the result of transfection efficiency. All these results indicated that the co-assembled complex micelles could act as suitable gene carriers with tunable gene transfection efficiency and cytotoxicity, which should have great potential for the transfection of vascular ECs.

Injectable hydrogels based on poly(ethylene glycol) and derivatives as functional biomaterials

The design criteria for injectable, in situ-gelling hydrogels are reviewed in conjunction with highlights on recent progress in the preparation of injectable PEG and PEG-analogue poly(oligoethylene glycol methacrylate) (POEGMA) hydrogels.

An optical sensing strategy leading to in situ monitoring of the degradation of mesoporous magnetic supraparticles in cells

Mesoporous magnetic supraparticles (meso-MSPs) as multifunctional targeted drug carriers have attracted much attention, because of their easy magnetic-field manipulation and in situ sensing functionality. In this paper, a Fe(3+)-selective chemodosimeter fluorescent probe (FP-1) was synthesized and loaded inside of the meso-MSPs (meso-MSPs/probe); the meso-MSPs/probe nanocomposites were then used to monitor the degradation of meso-MSPs in cells. In our experiments, strong fluorescence intensity was observed in HeLa cells, because of their acidic intracellular environment, which can quickly degrade the meso-MSPs and then release Fe(3+) ions in cells that, in turn, activate the fluorescence of FP-1. Meanwhile, a very weak fluorescence signal was detected in HEK 293T cells due to the relative neutral intracellular environment of HEK 293T cells, which prevented the Fe(3+) ion from leaching out of meso-MSPs. Moreover, this degradation-luminescence relationship of the meso-MSPs/probe nanocomposites not only assisted us to understand the degradation status of meso-MSPs in cells, but also allowed us to recognize the peculiarity of different cells with various intracellular environments.

Pharmaceutical and toxicological properties of engineered nanomaterials for drug delivery

Novel engineered nanomaterials (ENMs) are being developed to enhance therapy. The physicochemical properties of ENMs can be manipulated to control/direct biodistribution and target delivery, but these alterations also have implications for toxicity. It is well known that size plays a significant role in determining ENM effects since simply nanosizing a safe bulk material can render it toxic. However, charge, shape, rigidity, and surface modifications also have a significant influence on the biodistribution and toxicity of nanoscale drug delivery systems (NDDSs). In this review, NDDSs are considered in terms of platform technologies, materials, and physical properties that impart their pharmaceutical and toxicological effects. Moving forward, the development of safe and effective nanomedicines requires standardized protocols for determining the physical characteristics of ENMs as well as assessing their potential long-term toxicity. When such protocols are established, the remarkable promise of nanomedicine to improve the diagnosis and treatment of human disease can be fulfilled.

Mathematical model of the role of degradation on matrix development in hydrogel scaffold

Despite tremendous advances in the field of tissue engineering, a number of obstacles are still hindering its successful translation to the clinic. One of these challenges has been to design cell-laden scaffolds that can provide an appropriate environment for cells to successfully synthesize new tissue while providing a mechanical support that can resist physiological loads at the early stage of in situ implementation. A solution to this problem has been to balance tissue growth and scaffold degradation by creating new hydrogel systems that possess both hydrolytic and enzymatic degradation behaviors. Very little is known, however, about the complex behavior of these systems, emphasizing the need for a rigorous mathematical approach that can eventually assist and guide experimental advances. This paper introduces a mathematical and numerical formulation based on mixture theory, to describe the degradation, swelling, and transport of extracellular matrix (ECM) molecules released by cartilage cells (chondrocytes) within a hydrogel scaffold. The model particularly investigates the relative roles of hydrolytic and enzymatic degradations on ECM diffusion and their impacts on two important outcomes: the extent of ECM transport (and deposition) and the evolution of the scaffold's mechanical integrity. Numerical results based on finite element show that if properly tuned, enzymatic degradation differs from hydrolytic degradation in that it can create a degradation front that is key to maintaining scaffold stiffness while allowing ECM deposition. These results therefore suggest a hydrogel design that could enable successful in situ cartilage tissue engineering.

Extracellular delivery of modified oligonucleotide and superparamagnetic iron oxide nanoparticles from a degradable hydrogel triggered by tumor acidosis

Chemically modified antisense RNA oligonucleotides (antagomir) offer promise for cancer therapies but suffer from poor therapeutic effect after systemic administration. Chemical modification or loading in degradable hydrogels can offer improvements in the accuracy and efficacy for sustained delivery at specific sites. In our approach, antagomir were entrapped with degradable poly(ethylene glycol) (PEG)-based hydrogels, with and without incorporation of imidazole. Superparamagnetic iron oxide nanoparticles (SPION) were simultaneously loaded with intent for magnetic resonance imaging (MRI). The incorporation of imidazole into the PEG hydrogels led to a tunable-pH-response that dictated hydrogel swelling ratio and release rate of antagomir and SPION. As a result, the PEG-imidazole hydrogel swelling ratio and degradation over a 5 week period changed up to 734% and 149% as the pH dropped from 7.4 to 6.7, respectively. The swelling ratio of PEG-imidazole hydrogels was completely reversible over repeatable cycles of pH change. The stimuli-responsive behavior of PEG-imidazole hydrogels was used for the release of antagomir and SPION under conditions consistent with tumor acidosis. This manuscript demonstrates feasibility in designing tunable-pH-responsive hydrogels for loading multimodality therapeutic and contrast agents to enhance the bioactivity of chemically modified antisense RNA oligonucleotide and SPION for acidosis-related tumor therapy and MRI imaging applications.

Building biocompatible hydrogels for tissue engineering of the brain and spinal cord

Tissue engineering strategies employing biomaterials have made great progress in the last few decades. However, the tissues of the brain and spinal cord pose unique challenges due to a separate immune system and their nature as soft tissue. Because of this, neural tissue engineering for the brain and spinal cord may require re-establishing biocompatibility and functionality of biomaterials that have previously been successful for tissue engineering in the body. The goal of this review is to briefly describe the distinctive properties of the central nervous system, specifically the neuroimmune response, and to describe the factors which contribute to building polymer hydrogels compatible with this tissue. These factors include polymer chemistry, polymerization and degradation, and the physical and mechanical properties of the hydrogel. By understanding the necessities in making hydrogels biocompatible with tissue of the brain and spinal cord, tissue engineers can then functionalize these materials for repairing and replacing tissue in the central nervous system.

Controlled delivery of recombinant adeno-associated virus serotype 2 using pH-sensitive poly(ethylene glycol)-poly-L-histidine hydrogels

Loading of viral vectors in synthetic polymers is a promising strategy for overcoming hurdles associated with viral gene delivery. For enhanced gene expression at a specific site, gene transfer by using hydrogels represents a versatile approach. In this study, adeno-associated virus serotype 2 containing the green fluorescent protein gene (rAAV2-GFP) were loaded into poly(ethylene glycol) (PEG) hydrogels, with and without incorporation of poly-L-hisditine (polyHis). Inclusion of polyHis created pH responsive hydrogels in a physiological range of tissues, containing the damaged vasculature and activated phagocytosis. The fraction of polyHis used controlled the degree of swelling, water uptake and subsequent degradation of the hydrogels and release rate of rAAV2-GFP. The swelling ratio of the PEG-polyHis hydrogels increased inversely with environment pH. As pH declined from 7.4 to 6.0, PEG-polyHis hydrogel swelling ratio and degradation rate increased 875% and 135%, respectively. As a result, release and transduction efficiency of the rAAV2-GFP from PEG-polyHis hydrogel in human HT-1080 fibrosarcoma cells increased significantly compared to a PEG hydrogel. Transduction rate can be controlled by the hydrogels' polyHis concentration and is sensitive to localized decreases in pH consistent with inflammation. This is relevant to optimizing parameters for wound care and regenerative medicine applications.

Nanostructured PEG-based hydrogels with tunable physical properties for gene delivery to human mesenchymal stem cells

Effective delivery of DNA to direct cell behavior in a well defined three dimensional scaffold offers a superior approach in tissue engineering. In this study, we synthesized biodegradable nanostructured hydrogels with tunable physical properties for cell and gene delivery. The hydrogels were formed via Michael addition chemistry by reacting a four-arm acrylate-terminated PEG with a four-arm thiol-functionalized PEG. Nanosized micelles self-assembled from the amphiphilic PEG-b-polycarbonate diblock copolymer, having reactive end-groups, were chemically incorporated into the hydrogel networks at various contents. The use of Michael addition chemistry allows for in situ hydrogel formation under the physiological conditions. Mechanical property analysis of the hydrogels revealed a correlation between the content of micelles and the storage modulus of the hydrogels. Internal morphology of hydrogels was observed using a field emission scanning electron microscope, which showed that the number and/or size of the pores in the hydrogel increased with increasing micelle content due to reduced crosslinking degree. There exists an optimal micelle content for cell proliferation and gene transfection. MTT assays demonstrated the highest cell viability in the hydrogel with 20% micelles. The gene expression level in hMSCs in the hydrogel with 20% micelles was also significantly higher than that in the hydrogel without micelles. The enhanced cell viability and gene expression in the hydrogel with the optimized micelle content are likely attributed to the physical properties that provide a better environment for cell-matrix interactions. Therefore, incorporating micelles into the hydrogel is a good strategy to control cellular behavior in 3-D through changes in physical properties of the microenvironment.

Influence of molecular size on the retention of polymeric nanocarrier diagnostic agents in breast ducts

PURPOSE

To investigate the influence of nanocarrier molecular size and shape on breast duct retention in normal rats using a non-invasive optical imaging method.

METHODS

Fluorescein-labeled PEG nanocarriers of different molecular weights and shapes (linear, two-arm, four-arm, and eight-arm) were intraductally administered (50 nmol) to female Sprague-Dawley rats. Whole body images were obtained non-invasively. Fluorescence intensities (i.e., amount remaining in duct) were plotted against time to estimate the nanocarrier ductal retention half-lives (t(1/2)). Plasma samples were taken and the pharmacokinetics (Tmax, Cmax) of absorbed nanocarriers was also assessed.

RESULTS

The t(1/2) of linear 12, 20, 30, 40, and two-arm 60 kDa nanocarriers were 6.7 ± 0.9, 16.1 ± 4.1, 16.6 ± 3.4, 21.5 ± 2.7, and 19.5 ± 6.1 h, whereas the four-arm 20, 40, and eight-arm 20 kDa had t(1/2) of 9.0 ± 0.5, 11.5 ± 1.9, and 12.6 ± 3.0 h. The t(1/2) of unconjugated fluorescein was significantly lower (14.5 ± 1.4 min). The Tmax for 12, 40, 60 kDa nanocarriers were 1, 24, and 32 h, respectively, and only 30 min for fluorescein.

CONCLUSIONS

Since normal breast ducts are highly permeable, the use of nanocarriers may be helpful in prolonging ductal retention of diagnostic and/or therapeutic agents.