Visible light-curable polymers for biomedical applications

A photocrosslinking antibacterial decellularized matrix hydrogel with nanofiber for cutaneous wound healing

ddECMMA is the methacrylating product of decellularized dermal extracellular matrix with biological signals and capable of photocrosslinking. Thiolated chitosan (TCS) is an effective antibacterial component. PCLPBA is a kind of plasma-treated polycaprolactone nanofiber dispersions (PCLP) that regulates macrophage polarization and promotes angiogenesis. In this study, we obtained ddECMMA via methacrylation reaction. TCS was prepared by reaction between chitosan and thioglycolic acid. PCLPBA was fabricated via reaction between PCLP and 3-buten-1-amine. TCS and PCLPBA were mixed in ddECMMA solution and photocrosslinked to form DTP4 hydrogel. The hydrogel showed rapid gelation, good mechanical strength, antibacterial and antioxidant properties. When it was cocultured with NIH 3T3 cells, the cells showed good morphology and proliferation rate. After applying it to the full-thickness cutaneous wound, wounds almost healed in 2 weeks via re-epithelialization and neovascularization with negligible scar tissue. The results indicate that DTP4 hydrogel is a promising candidate for clinic skin wound healing.

Facile engineering of ECM-mimetic injectable dual crosslinking hydrogels with excellent mechanical resilience, tissue adhesion, and biocompatibility

Injectable hydrogels have aroused ever-increasing interest for their cell/biomaterial delivery ability through minimally invasive procedures. Nevertheless, it is still a challenge to simply fabricate natural biopolymer-based injectable hydrogels possessing satisfactory mechanical properties, bioadhesion, and cell delivery ability. Herein, we describe a facile dual crosslinking (DC) strategy for preparing extracellular matrix (ECM) mimetic hydrogels with desirable comprehensive performance. The chondroitin sulfate (CS)- and gelatin (Gel)-based single crosslinked (SC) hydrogels were first developed via reversible borate ester bonds, and further strengthened through the Michael-addition crosslinking reaction or visible-light initiated photopolymerization with thiol-containing polyethylene glycol (PEG) crosslinkers. The dynamic SC hydrogels showed good injectability, pH-sensitive gel-sol transformation, and self-adhesion ability to various biological tissues such as skin, liver, and intervertebral disc. The mechanically tough DC hydrogels displayed tunable stiffness, and resilience to compression load (up to 90% strain) owing to the effective energy dissipation mechanism. The formed DC hydrogels after subcutaneous injection well integrated with surrounding tissues and exhibited fast self-recovery properties. Moreover, the photoencapsulation of human mesenchymal stem cells (hMSCs) within the developed DC hydrogels was achieved and has been proved to be biocompatible, highlighting the great potential of the photopolymerized DC hydrogels in cell delivery and three-dimensional (3D) cell culture. This biomimetic, mechanically resilient, adhesive, and cytocompatible injectable DC hydrogel could serve as a promising candidate for tissue engineering.

Rapid Activation of Diazirine Biomaterials with the Blue Light Photocatalyst

Carbene-based macromolecules are an emerging new stimuli-sensitive class of biomaterials that avoid the impediments of free radical polymerization but maintain a rapid liquid-to-biorubber transition. Activation of diazirine-grafted polycaprolactone polyol (CaproGlu) is limited to UVA wavelengths that have tissue exposure constraints and limited light intensities. For the first time, UVA is circumvented with visible light-emitting diodes at 445 nm (blue) to rapidly activate diazirine-to-carbene covalent cross-linking. Iridium photocatalysts serve to initiate diazirine, despite having little to no absorption at 445 nm. CaproGlu's liquid organic matrix dissolves the photocatalyst with no solvents required, creating a light transparent matrix. Considerable differences in cross-linking chemistry are observed in UVA vs visible/photocatalyst formulations. Empirical analysis and theoretical calculations reveal a more efficient conversion of diazirine directly to carbene with no diazoalkane intermediate detected. Photorheometry results demonstrate a correlation between shear moduli, joules light dose, and the lower limits of photocatalyst concentration required for the liquid-to-biorubber transition. Adhesion strength on ex vivo hydrated tissues exceeds that of cyanoacrylates, with a fixation strength of up to 20 kg·f·cm². Preliminary toxicity assessment on leachates and materials directly in contact with mammalian fibroblast cells displays no signs of fibroblast cytotoxicity.

Visible light-induced cross-linking of porcine pericardium for the improvement of endothelialization, anti-tearing, and anticalcification properties

Population aging and the development of transcatheter aortic valve replacement boost the implantation of bioprosthetic heart valves (BHVs) in patients worldwide. However, the traditional glutaraldehyde cross-linked BHVs fail within 12-15 years mainly due to leaflet tear and calcification defects. In this study, a novel visible light-induced cross-linking of the porcine pericardium (PP) was realized by the photo-oxidation of the furfuryl-modified PP in the presence of Rose Bengal. The resulting material showed comparable collagen stability with the glutaraldehyde cross-linked PP and appropriate biomechanical properties such as tensile strength, modulus, and elongation, suggesting that this material could meet the general requirement for BHVs. Besides, this cross-linked PP showed significantly improved cytocompatibility compared with the Glut-cross-linked PP, with no cytotoxicity to L929 cells and the ability to support HUVECgrowth. Meanwhile, this material showed superior anti-tearing performance and much less calcification than the Glut-cross-linked PP in hope of reducing the risk of BHV failure. Considering these results, the visible light-induced cross-linking method proposed in this study could provide a promising way to construct a biocompatible and robust biomaterial for the fabrication of the BHV.

The Effect of Heat Treatment toward Glycerol-Based, Photocurable Polymeric Scaffold: Mechanical, Degradation and Biocompatibility

Photocurable polymers have become increasingly important for their quick prototyping and high accuracy when used in three dimensional (3D) printing. However, some of the common photocurable polymers are known to be brittle, cytotoxic and present low impact resistance, all of which limit their applications in medicine. In this study, thermal treatment was studied for its effect and potential applications on the mechanical properties, degradability and biocompatibility of glycerol-based photocurable polymers, poly(glycerol sebacate) acrylate (PGSA). In addition to the slight increase in elongation at break, a two-fold increase in both Young's modulus and ultimate tensile strength were also observed after thermal treatment for the production of thermally treated PGSA (tPGSA). Moreover, the degradation rate of tPGSA significantly decreased due to the increase in crosslinking density in thermal treatment. The significant increase in cell viability and metabolic activity on both flat films and 3D-printed scaffolds via digital light processing-additive manufacturing (DLP-AM) demonstrated high in vitro biocompatibility of tPGSA. The histological studies and immune staining indicated that tPGSA elicited minimum immune responses. In addition, while many scaffolds suffer from instability through sterilization processes, it was proven that once glycerol-based polymers have been treated thermally, the influence of autoclaving the scaffolds were minimized. Therefore, thermal treatment is considered an effective method for the overall enhancement and stabilization of photocurable glycerol-based polymeric scaffolds in medicine-related applications.

Visible light-curable water-soluble chitosan derivative, chitosan hydrogel, and preparation method: a patent evaluation of US2019202998A1

Introduction: Water soluble polysaccharides are versatile structural materials that can be used for the design of biocompatible hydrogels and wet dressings in wound healing applications. Glycol chitosan (GC) is an example of a multifunctional water-soluble chitosan derivative that has inherent wound healing properties and reactive sites for chemical modification.Areas covered: United States (US) patent US2019202998A1 describes the preparation of a novel wound healing technology based on a three-dimensional (3D) crosslinked GC hydrogel (GCH) wet dressing, prepared via the synthesis of PEG1K-biscarboxylic acid-g-Glycol Chitosan-g-methacrylate using visible light induced photocrosslinking. The selected polymeric network enables the encapsulation of additional growth factors or bioactives on reactive sites. Wet dressings in US2019202998A1 were evaluated against a commercially available control for in vitro release, cytotoxicity, and in vivo wound healing ability in a preliminary mouse model, with the overall wound healing performance consistent with related GC-based hydrogels.Expert opinion: Comprehensive biocompatibility and antimicrobial testing of the hydrogel is not reported in US2019202998A1, and is recommended as further work to enable clinical applicability. The invention disclosed in US2019202998A1 can potentially be integrated with 3D bioprinting and sensor technology for the preparation of 'smart' hydrogel wound dressings, and is a potential area for future research.

Moving Towards a Finer Way of Light-Cured Resin-Based Restorative Dental Materials: Recent Advances in Photoinitiating Systems Based on Iodonium Salts

The photoinduced polymerization of monomers is currently an essential tool in various industries. The photopolymerization process plays an increasingly important role in biomedical applications. It is especially used in the production of dental composites. It also exhibits unique properties, such as a short time of polymerization of composites (up to a few seconds), low energy consumption, and spatial resolution (polymerization only in irradiated areas). This paper describes a short overview of the history and classification of different typical monomers and photoinitiating systems such as bimolecular photoinitiator system containing camphorquinone and aromatic amine, 1-phenyl-1,2-propanedione, phosphine derivatives, germanium derivatives, hexaarylbiimidazole derivatives, silane-based derivatives and thioxanthone derivatives used in the production of dental composites with their limitations and disadvantages. Moreover, this article represents the challenges faced when using the latest inventions in the field of dental materials, with a particular focus on photoinitiating systems based on iodonium salts. The beneficial properties of dental composites cured using initiation systems based on iodonium salts have been demonstrated.

Water-Soluble Photoinitiators in Biomedical Applications

Light-initiated polymerization processes are currently an important tool in various industrial fields. The advancement of technology has resulted in the use of photopolymerization in various biomedical applications, such as the production of 3D hydrogel structures, the encapsulation of cells, and in drug delivery systems. The use of photopolymerization processes requires an appropriate initiating system that, in biomedical applications, must meet additional criteria such as high water solubility, non-toxicity to cells, and compatibility with visible low-power light sources. This article is a literature review on those compounds that act as photoinitiators of photopolymerization processes in biomedical applications. The division of initiators according to the method of photoinitiation was described and the related mechanisms were discussed. Examples from each group of photoinitiators are presented, and their benefits, limitations, and applications are outlined.

1-Aryl-2-(triisopropylsilyl)ethane-1,2-diones: Toward a New Class of Visible Type I Photoinitiators for Free Radical Polymerization of Methacrylates

1-Aryl-2-(triisopropylsilyl)ethane-1,2-diones (SEDs) are proposed here as a new class of visible Type I photoinitiators (PIs) for free radical polymerization under air upon exposure to blue (@455 nm) and green (@520 nm) LEDs. Remarkably, these new systems present good polymerization performances and excellent bleaching properties compared to camphorquinone-based systems, and transparent polymers are obtained upon visible light irradiation. Real-time Fourier transform infrared spectroscopy is used to monitor the polymerization profiles. Molecular orbital calculations are also carried out for a better understanding of the structure/reactivity relationship of the photoinitiators.

Photo-Cured Glycol Chitosan Hydrogel for Ovarian Cancer Drug Delivery

In this study, we prepared an injectable drug delivery depot system based on a visible light-cured glycol chitosan (GC) hydrogel containing paclitaxel (PTX)-complexed beta-cyclodextrin (β-CD) (GC/CD/PTX) for ovarian cancer (OC) therapy using a tumor-bearing mouse model. The hydrogel depot system had a 23.8 Pa of storage modulus at 100 rad/s after visible light irradiation for 10 s. In addition, GC was swollen as a function of time. However, GC had no degradation with the time change. Eventually, the swollen GC matrix affected the releases of PTX and CD/PTX. GC/PTX and GC/CD/PTX exhibited a controlled release of PTX for 7 days. In addition, GC/CD/PTX had a rapid PTX release for 7 days due to improved water solubility of PTX through CD/PTX complex. In vitro cell viability tests showed that GC/CD/PTX had a lower cell viability percentage than the free PTX solution and GC/PTX. Additionally, GC/CD/PTX resulted in a superior antitumor effect against OC. Consequently, we suggest that the GC/CD system might have clinical potential for OC therapy by improving the water solubility of PTX, as PTX is included into the cavity of β-CD.

Visible Light-Cured Glycol Chitosan Hydrogel Containing a Beta-Cyclodextrin-Curcumin Inclusion Complex Improves Wound Healing In Vivo

Scarless wound healing is ideal for patients suffering from soft tissue defects. In this study, we prepared a novel wet dressing (β-CD-ic-CUR/GC) based on the visible light-cured glycol chitosan (GC) hydrogel and inclusion complex between beta-cyclodextrin (β-CD) and curcumin (CUR). We also evaluated its efficacy in the acceleration of wound healing as compared to that of CUR-loaded GC (CUR/GC). The conjugation of glycidyl methacrylate (GM) to GC for photo-curing was confirmed by ¹H-NMR measurement, and the photo-cured GC hydrogel was characterized by the analyses of rheology, swelling ratio, SEM and degradation rate. After visible light irradiation, the surface/cross-sectional morphologies and storage (G′)/loss (G′′) moduli revealed the formation of hydrogel with interconnected porosity. The dressing β-CD-ic-CUR/GC exhibited a controlled release of 90% CUR in a sustained manner for 30 days. On the other hand, CUR/GC showed CUR release of 16%. β-CD acted as an excipient in improving the water-solubility of CUR and affected the release behavior of CUR. The in vivo animal tests including measurement of the remaining unhealed wound area and histological analyses showed that β-CD-ic-CUR/GC may have potential as a wet dressing agent to enhance soft tissue recovery in open fractures.

Injectable hydrogel-based scaffolds for tissue engineering applications

Hydrogels are highly hydrated materials that may absorb from 10% to 20% up to hundreds of times their dry weight in water and are composed of three-dimensional hydrophilic polymeric networks that are similar to those in natural tissue. The structural integrity of hydrogels depends on cross-links formed between the polymer chains. Hydrogels have been extensively explored as injectable cell delivery systems, owing to their high tissue-like water content, ability to mimic extracellular matrix, homogeneously encapsulated cells, efficient mass transfer, amenability to chemical and physical modifications, and minimally invasive delivery. A variety of naturally and synthetically derived materials have been used to form injectable hydrogels for tissue engineering applications. The current review article focuses on these biomaterials, on the design parameters of injectable scaffolds, and on the

3D Culture of Chondrocytes in Gelatin Hydrogels with Different Stiffness

Gelatin hydrogels can mimic the microenvironments of natural tissues and encapsulate cells homogeneously, which makes them attractive for cartilage tissue engineering. Both the mechanical and biochemical properties of hydrogels can affect the phenotype of chondrocytes. However, the influence of each property on chondrocyte phenotype is unclear due to the difficulty in separating the roles of these properties. In this study, we aimed to study the influence of hydrogel stiffness on chondrocyte phenotype while excluding the role of biochemical factors, such as adhesion site density in the hydrogels. By altering the degree of methacryloyl functionalization, gelatin hydrogels with different stiffnesses of 3.8, 17.1, and 29.9 kPa Young's modulus were prepared from the same concentration of gelatin methacryloyl (GelMA) macromers. Bovine articular chondrocytes were encapsulated in the hydrogels and cultured for 14 days. The influence of hydrogel stiffness on the cell behaviors including cell viability, cell morphology, and maintenance of chondrogenic phenotype was evaluated. GelMA hydrogels with high stiffness (29.9 kPa) showed the best results on maintaining chondrogenic phenotype. These results will be useful for the design and preparation of scaffolds for cartilage tissue engineering.