Preparation,Mechanical and Biological Properties of Inkjet Printed Alginate/Gelatin Hydrogel

3D printing has made remarkable progress in soft tissue reconstruction enabling the custom design of complex material implants with patient specific geometry.The aim of this study was to inkjet print mechanically reinforced biocompatible hydrogels.Here,we developed a double crosslinked ink by optimizing the rheological properties of solutions of sodium alginate(NaAlg),NaAlg/transglutaminase(TG),CaCl_(2)and gelatin/CaCl_(2).The results showed that a two-component ink system comprising NaAlg(4%w/v)/TG(0.8%w/v)and gelatin(4%w/v)/CaCl_(2)(3%w/v)gave optimum printability.The mechanical and biological properties of printed alginate/gelatin hydrogels prepared from inks with different gelatin contents,and incorporated fibroblasts,were characterized by Scanning Electron Microscope(SEM),mechanical testing and laser confocal microscopy.The compressive moduli of alginate/gelatin hydrogels could be adjusted from 19.2 kPa±1.2 kPa to 65.9 kPa±3.3 kPa by increasing the content of gelatin.After incubation for 7 d,fibroblasts had permeated all printed hydrogels and the rate of proliferation increased with increasing gelatin content.The highest cell proliferation rate(497%)was obtained in a hydrogel containing 4.5%(w/v)gelatin.This study offers a new strategy for the fabrication of 3D structures used to mimic the function of native tissues.

3D Bioprinted Skin Substitutes for Accelerated Wound Healing and Reduced Scar

The shortage of skin for grafting continues to be a major problem in the treatment of serious skin injuries.3D bioprinting provides a new way to solve this problem.However,current 3D printed skin is less effective in treatment of large wounds because of severe shrinkage and scarring.In this study,bionically designed bilayer skin was fabricated using an extrusion-based bioprinter and a gelatin/sodium alginate/gelatin methacrylate hydrogel with excellent physical and biological properties.Full-thickness skin wounds were created in the back of nude mice and treated with bioprinted skin or hydrogel.Bioprinted skin accelerated wound healing,reduced wound contraction and scarring,and facilitated wound skin epithelialization compared with the bioprinted hydrogel or untreated wound.The skin from the wound was collected 28 days after grafting for histology and immunofluorescence analysis.The thickness of the dermis and epidermis of the bioprinted skin was similar to that of nude mice.Microvascular formation in the dermis and dense keratinocytes in the epidermis of the bioprinted skin were observed.This study provides a potential treatment strategy for reducing skin contraction and scar in large skin wounds.

Direct-writing Process and in vivo Evaluation of Prevascularized Composite Constructs for Muscle Tissue Engineering Application

Tissue engineered skeletal muscle is expected to treat muscle defects caused by trauma and disease.However,designing and manufacturing thick and complex tissue engineered skeletal muscle requires vascularization to ensure its internal cell viability and nutrient supply in vitro.In this article,we developed a set of Direct-Writing(DW)bio-printing procedure to manufacture a prevascularized composite construct with Human Umbilical Vein Endothelial Cell(HUVEC)and C2C12 cells for muscle tissue engineering application.We put the cells into the construct during the DW process to obtain the prevascularization and intend to promote its vascularization in vivo later.The constructs with cells or without cells were implanted respectively into nude mice back for 3 weeks,after which the mice healthily live for all the time and all the implants are tightly bonded to the host.From immunohistochemical analysis,CD31-positive blood vessels existed in the implanted samples with cells are more substantial than those without cells,but the implanted samples with HUVEC and C2C12 cells have much more number of small blood vessels distributing evenly.Moreover,the implants with cells,especially that with HUVEC and C2C12 cells,are able to get better fusion with the host skin and subcutaneous tissues.Histological analysis demonstrates that our DW-based constructs have the potential to be getting to vascularize the tissue engineered muscle.