Semitransparent bandages based on chitosan and extracellular matrix for photochemical tissue bonding

Use of photosensitive molecules in the crosslinking of biopolymers: applications and considerations in biomaterials development

The development of diverse types of biomaterials has significantly contributed to bringing new biomedical strategies to treat clinical conditions. Applications of these biomaterials can range from mechanical support and protection of injured tissues to joint replacement, tissue implants, and drug delivery systems. Among the strategies commonly used to prepare biomaterials, the use of electromagnetic radiation to initiate crosslinking stands out. The predominance of photo-induced polymerization methods relies on a fast, efficient, and straightforward process that can be easily adjusted to clinical needs. This strategy consists of irradiating the components that form the material with photons in the near ultraviolet-visible wavelength range (i.e., ∼310 to 750 nm) in the presence of a photoactive molecule. Upon photon absorption, photosensitive molecules can generate excited species that initiate photopolymerization through different reaction mechanisms. However, this process could promote undesired side reactions depending on the target zone or treatment type (e.g., oxidative stress and modification of biomolecules such as proteins and lipids). This review explores the basic concepts behind the photopolymerization process of ex situ and in situ biomaterials. Particular emphasis was put on the photosensitization initiated by the most employed photosensitizers and the photoreactions that they mediate in aqueous media. Finally, the undesired oxidation reactions at the bio-interface and potential solutions are presented.

Preparation and Use of Decellularized Extracellular Matrix for Tissue Engineering

The multidisciplinary fields of tissue engineering and regenerative medicine have the potential to revolutionize the practise of medicine through the abilities to repair, regenerate, or replace tissues and organs with functional engineered constructs. To this end, tissue engineering combines scaffolding materials with cells and biologically active molecules into constructs with the appropriate structures and properties for tissue/organ regeneration, where scaffolding materials and biomolecules are the keys to mimic the native extracellular matrix (ECM). For this, one emerging way is to decellularize the native ECM into the materials suitable for, directly or in combination with other materials, creating functional constructs. Over the past decade, decellularized ECM (or dECM) has greatly facilitated the advance of tissue engineering and regenerative medicine, while being challenged in many ways. This article reviews the recent development of dECM for tissue engineering and regenerative medicine, with a focus on the preparation of dECM along with its influence on cell culture, the modification of dECM for use as a scaffolding material, and the novel techniques and emerging trends in processing dECM into functional constructs. We highlight the success of dECM and constructs in the in vitro, in vivo, and clinical applications and further identify the key issues and challenges involved, along with a discussion of future research directions.

Synergistic Antimicrobial Activity of a Nanopillar Surface on a Chitosan Hydrogel

Despite ongoing efforts and technology development, the contamination of medical device surfaces by disease-causing microbes remains problematic. Two approaches to producing antimicrobial surfaces are using antimicrobial materials and applying physical topography such as nanopatterns. In this work, we describe the use of physical topography on a soft hydrogel to control microbial growth. We demonstrate this approach by using chitosan hydrogel films with nanopillars having periodicities ranging from 300 to 500 nm. The flat hydrophilic chitosan films exhibit antimicrobial activity against the pathogenic bacteria Pseudomonas aeruginosa and filamentous fungi Fusarium oxysporum. The addition of nanopillars to the hydrogel surface further reduces the growth of P. aeruginosa and F. oxysporum up to ∼52 and ∼99%, respectively. Multiple modes of antimicrobial action appear to act synergistically to inhibit microbial growth on the nanopillar hydrogels. We verified that the strongly bactericidal and fungicidal nanopillared material retains biocompatibility to human epithelial cells with the MTT assay. The nanopillared material is a promising candidate for applications that require a biocompatible and antimicrobial film. The study demonstrates that taking advantage of multiple modes of antimicrobial action can effectively inhibit pathogenic microbial growth.

Porous chitosan adhesives with L-DOPA for enhanced photochemical tissue bonding

L-3,4-dihydroxyphenylalanine (L-DOPA) is a naturally occurring catechol that is known to increase the adhesive strength of various materials used for tissue repair. With the aim of fortifying a porous and erodible chitosan-based adhesive film, L-DOPA was incorporated in its fabrication for stronger photochemical tissue bonding (PTB), a repair technique that uses light and a photosensitiser to promote tissue adhesion. The results showed that L-DOPA did indeed increase the tissue bonding strength of the films when photoactivated by a green LED, with a maximum strength recorded of approximately 30 kPa, 1.4 times higher than in its absence. The addition of L-DOPA also did not appreciably change the swelling, mechanical and erodible properties of the film. This study showed that strong, porous and erodible adhesive films for PTB made from biocompatible materials can be obtained through a simple inclusion of a natural additive such as L-DOPA, which was simply mixed with chitosan without any chemical modifications. In vitro studies using human fibroblasts showed no negative effect on cell proliferation indicating that these films are biocompatible. The films are convenient for various surgical applications as they can provide strong tissue support and a microporous environment for cellular infusion without the use of sutures. STATEMENT OF SIGNIFICANCE: Tissue adhesives are not as strong as sutures on wounds under stress. Our group has previously demonstrated that strong sutureless tissue repair can be realised with chitosan-based adhesive films that photochemically bond to tissue when irradiated with green light. The advantage of this technique is that films are easier to handle than glues and sutures, and their crosslinking reactions can be controlled with light. However, these films are not optimal for high-tension tissue regenerative applications because of their non-porous structure, which cannot facilitate cell and nutrient exchange at the wound site. The present study resolves this issue, as we obtained a strong and porous photoactivated chitosan-based adhesive film, by simply using freeze drying and adding L-DOPA.