Going below and beyond the surface: Microneedle structure, materials, drugs, fabrication, and applications for wound healing and tissue regeneration

Microneedle, as a novel drug delivery system, has attracted widespread attention due to its non-invasiveness, painless and simple administration, controllable drug delivery, and diverse cargo loading capacity. Although microneedles are initially designed to penetrate stratum corneum of skin for transdermal drug delivery, they, recently, have been used to promote wound healing and regeneration of diverse tissues and organs and the results are promising. Despite there are reviews about microneedles, few of them focus on wound healing and tissue regeneration. Here, we review the recent advances of microneedles in this field. We first give an overview of microneedle system in terms of its potential cargos (e.g., small molecules, macromolecules, nucleic acids, nanoparticles, extracellular vesicle, cells), structural designs (e.g., multidrug structures, adhesive structures), material selection, and drug release mechanisms. Then we briefly summarize different microneedle fabrication methods, including their advantages and limitations. We finally summarize the recent progress of microneedle-assisted wound healing and tissue regeneration (e.g., skin, cardiac, bone, tendon, ocular, vascular, oral, hair, spinal cord, and uterine tissues). We expect that our article would serve as a guideline for readers to design their microneedle systems according to different applications, including material selection, drug selection, and structure design, for achieving better healing and regeneration efficacy.

Application of TPMS structure in bone regeneration

Bone defect repair,due to its complex process in nature,has become a costly issue in modern day medicine.This causes a growing demand for a bone substitute that is effective and easy to construct.Recently,triply periodic minimal surface(TPMS)scaffolds,which embody trabecular bone-mimicking hyperboloidal topography,have become a promising candidate for this exact role due to their unique structure to promote many cellular processes.In response to the growing popularity of TPMS scaffolds amongst researchers,this review discusses the effect of different parameters(including pore size,porosity,and pore shape,as well as their influences on mechanical property,permeability,and curvature),along with the controlling and designing of such parameters,on bone regeneration to serve as a guide for future researchers in designing and utilizing TPMS scaffolds for bone regeneration purposes.