Study On The Adhesive Effect Of Adhesive Disc Of Parthenocissus Tricuspidata

Liana Parthenocissus tricuspidata is a versatile climbing plant, which has attracted greatinterest for many years. However, rare attention was paid on the adhesive disc of P.tricuspidata. The self-clinging P. tricuspidata can climb on stone mountains, roadside stonebanks and house outside walls with tendrils to obtain vertical growth. At the end of thetendrils, it develops adhesive discs that attach themselves quite firmly to the substrate.According to our study, a single mature adhesive disc of P. tricuspidata has an average massof only about0.0005g, an average attached area of about1.22mm2and an adhesive force ofabout13.7N but can, on average, support a combined weight of stem, leaf, branchlet, andtendril which is260times greater than its own weight during the growth, and can sustain amaximum pulling force which is2800000times higher than that produced by its own weight.In order to fully realize the super adhesive effect of adhesive disc, we systematically studiedits microstructure, chemical composition and adhesion mechanism, and on this basis, wemimicked the surface morphology of adhesive disc.In our experiment of scanning electron microscopy (SEM), we found that epidermal cellsurfaces of the adhesive disc firstly appeared very folded, but developed into a densely packedpattern of hemispheres. When stimulated, a heavy sticky fluid was secreted; the adhesive fluidpassed through the wall of epidermal cells, accumulating under the cuticle and causing it to ableb, and was finally secreted from the ruptured holes. Meanwhile, epidermal cells nearest thepoint of contact elongated extensively and divided periclinically, whereas the left epidermalcells swelled and underwent anticlinal divisions. During the subsequent senescence andlignifications, the epidermal cells would present a honeycomb-like surface appearance in fullymature adhesive disc.We first used high-performance liquid chromatography/mass spectrometry (HPLC/MS)to preliminarily analyze the chemical composition of adhesive disc. The data analysissuggested that there are at least21components in the adhesive disc of P. tricuspidata. Theformulas demonstrated that most of the21compounds contain nitrogen, sulfur and oxygen.These compounds are widely known for their ability to generate polarity, hydrogen bondingwould be a weak adhesion for P. tricuspidata climbing. In addition,6metal elements (K, Na,Ca, Mg, Fe and Mn) were identified in the adhesive disc of P. tricuspidata. Between them, theCa content is the most and calcium ions may be involved in the process of adhesion.Although the sticking ability of P. tricuspidata has been known for hundreds of years,the component-structure-property relations of adhesive disc are sparsely studied. Based on our experimental studies on the microstructural examinations and adhesive properties of adhesivedisc, we proposed new hypotheses of interface reaction leading to adhesive disc "anchor" andnegative pressure resulting in a closed space to elucidate the mechanism of adhesion, in thisway the adhesive disc has a perfect form closure with the substrate.In order to appraise the adhesive contribution of two nature contact structures of P.tricuspidata, biomimetic polystyrene (PS) pillar-like and honeycomb-like microstructuresinspired by the adhesive disc were prepared via a regular alumina template and hierarchicalalumina template, respectively. Through analogy analysis of the adhesive force on thesebiomimetic surface structures, we believed that the finger-like cells of young adhesive dischave a positioning function for pre-adhesion; and the microchannels inside the matureadhesive disc took charge of the accumulation and transportation of mucilage, thesesponge-like structures of cells and cell clusters enhanced the adhesive strength between theadhesive disc and substrate.The beauty and miracle can be created by a natural power, so understanding thesuper-adhesion mechanism of biological systems is of great scientific significance and aprerequisite for bio-inspired design of adhesive systems. Evidently, more experimental andtheoretical works are imperative to fully understand the super adhesive effect of adhesive discof P. tricuspidata and this work is quite useful for future studies.