3D bioprinting for biomedical devices and tissue engineering: A review of recent trends and advances

3D printing,an additive manufacturing based technology for precise 3D construction,is currently widely employed to enhance applicability and function of cell laden scaffolds.Research on novel compatible biomaterials for bioprinting exhibiting fast crosslinking properties is an essential prerequisite toward advancing 3D printing applications in tissue engineering.Printability to improve fabrication process and cell encapsulation are two of the main factors to be considered in development of 3D bioprinting.Other important factors include but are not limited to printing fidelity,stability,crosslinking time,biocompatibility,cell encapsulation and proliferation,shear-thinning properties,and mechanical properties such as mechanical strength and elasticity.In this review,we recite recent promising advances in bioink development as well as bioprinting methods.Also,an effort has been made to include studies with diverse types of crosslinking methods such as photo,chemical and ultraviolet(UV).We also propose the challenges and future outlook of 3D bioprinting application in medical sciences and discuss the high performance bioinks.

Viscosity and degradation controlled injectable hydrogel for esophageal endoscopic submucosal dissection

Endoscopic submucosal dissection(ESD)is a common procedure to treat early and precancerous gastrointestinal lesions.Via submucosal injection,a liquid cushion is created to lift and separate the lesion and malignant part from the muscular layer where the formed indispensable space is convenient for endoscopic incision.Saline is a most common submucosal injection liquid,but the formed liquid pad lasts only a short time,and thus repeated injections increase the potential risk of adverse events.Hydrogels with high osmotic pressure and high viscosity are used as an alternate;however,with some drawbacks such as tissue damage,excessive injection resistance,and high cost.Here,we reported a nature derived hydrogel of gelatin-oxidized alginate(G-OALG).Based on the rheological analysis and compare to commercial endoscopic mucosal resection(EMR)solution(0.25%hyaluronic acid,HA),a designed G-OALG hydrogel of desired concentration and composition showed higher performances in controllable gelation and injectability,higher viscosity and more stable structures.The G-OALG gel also showed lower propulsion resistance than 0.25%HA in the injection force assessment under standard endoscopic instruments,which eased the surgical operation.In addition,the G-OALG hydrogel showed good in vivo degradability biocompatibility.By comparing the results acquired via ESD to normal saline,the G-OALG shows great histocompatibility and excellent endoscopic injectability,and enables create a longer-lasting submucosal cushion.All the features have been confirmed in the living both pig and rat models.The G-OALG could be a promising submucosal injection agent for esophageal ESD.

Bridging wounds:tissue adhesives’essential mechanisms,synthesis and characterization,bioinspired adhesives and future perspectives

Bioadhesives act as a bridge in wound closure by forming an effective interface to protect against liquid and gas leakage and aid the stoppage of bleeding.To their credit,tissue adhesives have made an indelible impact on almost all wound-related surgeries.Their unique properties include minimal damage to tissues,low chance of infection,ease of use and short wound-closure time.In contrast,classic closures,like suturing and stapling,exhibit potential additional complications with long operation times and undesirable inflammatory responses.Although tremendous progress has been made in the development of tissue adhesives,they are not yet ideal.Therefore,highlighting and summarizing existing adhesive designs and synthesis,and comparing the different products will contribute to future development.This review first provides a summary of current commercial traditional tissue adhesives.Then,based on adhesion interaction mechanisms,the tissue adhesives are categorized into three main types:adhesive patches that bind molecularly with tissue,tissuestitching adhesives based on pre-polymer or precursor solutions,and bioinspired or biomimetic tissue adhesives.Their specific adhesion mechanisms,properties and related applications are discussed.The adhesion mechanisms of commercial traditional adhesives as well as their limitations and shortcomings are also reviewed.Finally,we also discuss the future perspectives of tissue adhesives.