What is chitin? Why is it useful to arthropods?

Chitin

Chitin is a polysaccharide abundant in nature, which constitutes the exoskeleton of arthropods, such as insects and crustaceans.

From: Medical Biochemistry , 2017

Coagulopathy and Hemorrhage

Anton N. Sidawy Doc, MPH , in Rutherford's Vascular Surgery and Endovascular Therapy , 2019

Chitins

The modified Rapid Deployment Hemostat (mRDH, Marine Polymer Technologies, Inc., Danvers, MA) bandage is a lyophilized matrix of acetylated, poly-Northward-acetyl glucosamine-containing nanofibers. The bandage apace binds and absorbs plasma proteins from blood. The nanofibers interact with receptors on platelets to stimulate activation and coagulation also as agglutinating and activating RBCs. These interactions with platelets and RBCs result in the generation of thrombin and the degradation of a fibrin mesh. In addition to the formation of this hemostatic plug, thromboxane (from the activated platelets) and endothelin-1 (from endothelial contact with the bandage) upshot vasoconstriction. ¹²¹ Case series from military machine utilise support the efficacy of this agent for at to the lowest degree temporary control of hemorrhage. ^117,122

Chitin

Nidal H. Daraghmeh , ... Adnan A. Badwan , in Profiles of Drug Substances, Excipients and Related Methodology, 2011

5.ii.1 Product of chitin sheets

Chitin sheets are excellent for employ in biomedical devices due to their biodegradability and lack of toxicity. These sheets can be prepared by simple procedures. A solution of α-chitin, in saturated calcium chloride dihydrate–methanol solvent system, is dropped into excess of distilled h2o with gentle mixing to desolubilize the α-chitin; the obtained chitin hydrogel is decanted several times with distilled water and filtered. α-Chitin sheets are obtained after the evaporation of water.

Due to the loose crystalline structure of β-chitin, it tin can exist highly bloated in water by vigorous mixing using a suitable blender and forms a hydrogel. A intermission volition be formed by the addition of backlog h2o to the β-chitin hydrogel which is so filtered to form the β-chitin sheets.

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Developmental Signaling in Plants

Thou. He , Y. Wu , in The Enzymes, 2016

ii.three CERK1

Chitin is a major cell wall component constitute in fungi but not in plants. Chitin and its fragments, chitin oligosaccharides ( N-acetylchitooligosaccharides), act as a group of cardinal pathogen elicitors that are perceived by plant cells to trigger PTI [68]. Through a genetic screen for Arabidopsis mutants that showed altered responses to chitin, a T-DNA insertional line and a Ds-transposon line were institute to be completely insensitive to chitin treatment. The knockout mutants are incapable of responding to chitin elicitor to induce ROS burst and MAPK activation, and display impaired resistance to incompatible fugal pathogen. The corresponding cistron, CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1), encodes a RLK containing three lysine motifs (LysMs) in the ectodomain and a Ser/Thr kinase domain in the cytosol, continued by a transmembrane domain. LysM motif was originally plant every bit a characteristic feature in the enzymes degrading cell wall in leaner and chitinases in yeast and lower plants, suggesting the LysM motif-containing ECD of CERK1 was potentially responsible for direct chitin bounden [69,seventy]. The association of CERK1 and chitin was confirmed by different approaches. In a fluorescence microscopic observation, CERK1-EGFP was detected to demark to chitin beads in yeast cells [71]. An analogousness purification assay was employed to show the binding of chitin to CERK1 in Arabidopsis cells. Importantly, chitin ligand induces rapid phosphorylation of CERK1, indicating kinase activation serves as cardinal mechanism to transduce apoplastic signals into cellular responses in chitin signaling [72]. At final, the crystal structural results provide the states detailed insights into the molecular mechanism of the perception of chitin by CERK1. But LysM2 of CERK1 binds to a chitin pentamer, and the bounden of chitin to CERK1-ECD does not cause conformational change, while chitin octamer induces dimerization of CERK1-ECD [73], serving as a key step for initiating downstream signaling events such equally intracellular kinase domain phosphorylation of CERK1 [72].

CERK1 is regulated at dissimilar aspects. A mutant allele cerk1-4, bearing a L124F mutation at the LYM2 motif in the ectodomain of CERK1, exhibits overaccumulation of SA and enhanced cell expiry upon pathogen infection. N-terminus of CERK1-iv is sufficient to cause cerk1-4 phenotype and kinase activity is not needed, suggesting ectodomain shedding is likely involved in CERK1 regulation. Ectodomain shedding of CERK1 occurring in wild-type plants is abolished in cerk1-4, demonstrating a common mechanism of proteolysis of transmembrane poly peptide in animals and plants [74]. In a yeast two-hybrid screen using CERK1 kinase domain as bait, a LRR-RLK LIK1 was identified. CERK1 interacts with and phosphorylates LIK1. lik1 mutant plants showroom enhanced responses to chitin elicitor, suggesting LIK1 functions as a negative regulator in chitin-triggered amnesty [75]. CERK1 is regulated by two splicing factors, SUA and RSN2, at posttranscriptional level. The pre-mRNA of CERK1 is not properly spliced in sua or rsn2 mutant that shows impaired chitin responses and enhanced susceptibility to bacterial infection [76].

CERK1 carries out boosted biological functions besides chitin signaling. CERK1 also functions in bacterial disease resistance by limiting bacterial growth. To promote pathogenesis, bacterial Type III virulent effector AvrPtoB, an E3-liagse, is delivered into host cell and interacts with CERK1, leading to polyubiquitination of CERK1, which results in CERK1 degradation and subsequent disruption of CERK1-mediated elicitor signaling [77]. Peptidoglycans (PGNs), major components in bacterial cell wall, human action as elicitors to trigger immune responses in animals and plants. CERK1 forms circuitous with two RLPs, LYM1 and LYM3, to recognize PGN signals to induce cellular responses. Mutation in CERK1, LYM1, or LYM3 causes dampened sensitivity to PGN stimuli and enhanced susceptibility to bacterial infection [78]. In addition to amnesty triggered past fungal pathogens, rice CERK1, NFR1/LYK3/OsCERK1, is required to actuate symbiosis signaling pathway to plant mycorrhizal interaction between fungi and rice [79]. CERK1 and CEBiP, a RLP functioning as chitin receptor, are both required in rice to trigger PTI induced by chitin. Both of the homologs of CERK1 and CEBiP in wheat are essential for activating chitin responses, suggesting a common receptor complex in cereal plants [eighty]. Iii homologs of rice CEBiP are present in Arabidopsis genome. Biochemical assay indicated one of the AtCEBiPs, AtLYM2, is able to bind chitin with a high affinity. Notwithstanding, knockout of one or all three AtCEBiPs, or overexpression of either AtCEBiP, fails to display contradistinct chitin responses compared to wild-type plants. It suggests that despite possessing chitin-binding analogousness, AtCEBiPs are not engaged in chitin signaling in Arabidopsis, indicating distinct chitin receptor complexes in institute species [81]. Nonetheless, AtLYM2, but not AtCERK1, was reported to part in reducing molecular flux via plasmadesmata in response to chitin presence [82]. LysM receptor kinase Bti9, SlLyk11, SlLyk12, and SlLyk13 were identified as homologs of AtCERK1 in tomato plant [83]. RNAi lines with reduced expression of Bti9 and SlLyk13 show enhanced susceptibility to P. syringae. Effector AvrPtoB interacts with Bti9 and inhibits its kinase action [83]. Chitin-binding effector Slp1 was found to act as a CEBiP competitor to ward off chitin-induced immunity in rice [84].

Of note, a recent study has challenged CERK1 as the major chitin receptor. In contrast to the depression chitin-binding affinity of CERK1, LYK5, a homolog of CERK1 in Arabidopsis, exhibits much higher chitin-binding affinity. Mutations in both LYK5 and LYK4, homolog of LYK5, in a unmarried found atomic number 82 to complete eliminated sensitivity to chitin elicitor in term of ROS consecration. LYK5, therefore, has been proposed to be the chief chitin receptor [85,86].

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Analysis of Glycans; Polysaccharide Functional Properties

S. Tokura , H. Tamura , in Comprehensive Glycoscience, 2007

2.fourteen.5.ane Original Functions of Chitin

Chitin has been prepared commercially by the alternative treatments of crustacean shells in dilute muriatic acid to remove calcium carbonate and boiling in dilute alkaline metal solution to remove proteins as reported by Hackman. ¹⁴¹ Though in that location are several methods to set up higher-purity chitin from crustaceans than that by the method of Hackman, ^142–146 the latter method has more often than not and commercially been applied to set up chitin due to its simplicity. But the grooming of chitin seems to depend on the source of chitin, because Lovell, Lafleur, and Hoskins reported on the training of chitin from crayfish waste by applying hydrogen peroxide ¹⁴⁷ and Kishi prepared chitin from silkworm in a like way. ¹⁴⁸ The molecular weight of chitin was estimated by viscosity measurement of chitosan in acerb acid aqueous solution following the deacetylation of chitin nether concentrated sodium hydroxide aqueous solution at boiling temperature due to the insolubility of chitin. ¹⁴⁹ The conventional viscosity equation to estimate the molecular weight of chitin was proposed by applying N-reacetylated chitosan (chitins) with various molecular weights, since a mild solvent organization, calcium chloride dehydrate saturated methanol, was found to deliquesce chitin even at room temperature past applying mechanical stirring: ¹⁵⁰

$\eta =\mathrm{Thousand}{M}^{\alpha }\left\{\text{where}\mathrm{Yard}=2.54\times {10}^{-2}\text{and}\alpha =0.54\right\}$

As the solubility of chitin in the solvent was limited, chitin molecules precipitate even in the presence of small amounts of other solvents, including water, alcohol, and then on. The chitin hydrogel was produced by the add-on of water and followed by extensive dialysis to remove solvents and salts. The regeneration of chitin into nonwoven fabrics has been reported without whatever binder. ¹⁵¹

Although chitin is known to exist sparingly soluble in general solvents, α- and β-chitin powders have been practical to wound healing because of stimulation of epidermal cell recovery in animal bodies. ¹⁵¹ The hydrogel of β-chitin prepared by vigorous mechanical agitation of β-chitin powder in h2o was also constitute to have a similar effect. ¹⁵¹ This was also the case with the α-chitin hydrogel, which was prepared by the addition of a large excess of h2o to chitin solution, since chitin was constitute to dissolve in calcium chloride dehydrate saturated methanol. ¹⁵² Both hydrogels were applied successfully to prepare nonwoven chitin fabrics which shows a strong cationic belongings to adsorb anionic compounds without reduction of biodegradability of chitin. ¹⁵² The chemic modification of chitin has been shown to become much easier under milder conditions than that of solid chitin pulverisation due to solvolysis of chitin molecules. ¹⁵³

Chitin fine pulverisation was get-go practical as a wound-healing accelerator by Balassa in 1970. A fungal mat including Penicillium was also practical for wound healing following chemical treatments, defatted by chloroform and sterilization. ^154–158

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Biologically derived scaffolds

M. Numata , D.Fifty. Kaplan , in Advanced Wound Repair Therapies, 2011

20.8.two Chitin

Chitin, a biopolymer of North-acetylglucosamine with some glucosamine, is the main component of the jail cell walls of fungi, the exoskeletons of arthropods such as crustaceans and insects, the radulas of mollusks and the beaks of cephalopods. Relatively high biocompatibility of chitin scaffolds with MSCs has been shown in vitro with immunohistochemistry and fluorescence con-focal microscopy (Li et al., 2004). Bioresorbable β-chitin sponges as scaffolds for 3D civilization of chondrocytes have been developed. Cell layers at the surface of the β-chitin sponge were filled with chondrocytes and abundant extracellular matrix. β-chitin sponges tin therefore exist considered biocompatible and useful scaffolds for 3D chondrocyte civilisation (Abe et al., 2004). Chitin has been combined with several polymers and bioactive molecules to improve mechanical properties and cellular adhesion. Composites of β-chitin with octacalcium phosphate (OCP) or hydroxylapatite prepared past precipitation of the mineral into chitin scaffolds have been investigated and oriented precipitation of OCP crystals was formed within the chitin layers. Mechanical factors are a principal cause for the orientation of OCP crystals with the a-centrality almost normal to the chitin fibers, perchance considering the compartmentalized space in the chitin governs the orientation of the crystals (Falini et al., 2001; 2002). Porous hydroxyapatite-chitin materials with 25%, l% and 75% (w/w) hydroxyapatite prepared by freeze-drying have shown not-cytotoxicity, in vivo degradability and supported the proliferation of MSCs-induced osteoblasts, demonstrating the potential of hydroxyapatite-chitin matrices as suitable substrates for tissue engineered os substitutes (Ge et al., 2004). Hydroxyapatite/collagen/poly(l-lactide) (PLLA) scaffolds reinforced past chitin fibers for bone-tissue engineering had lower cytotoxicity confronting MSCs as well as approximately 4-fold higher compressive strength than scaffolds without chitin fibers (Li et al., 2006). Porous 3D PLLA scaffolds reinforced by the chitin fibers (thirty%) demonstrated higher attachment, proliferation, differentiation, and mineralization with osteoblasts than PLLA solitary (Li X et al., 2009).

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Polymers in Biology and Medicine

E.-H. Song , ... D.1000. Ratner , in Polymer Science: A Comprehensive Reference, 2012

ix.08.3.2.1 Chemical structure and properties

Chitin, the second most abundant natural polysaccharide, after cellulose, is a linear polymer equanimous of repeating β(ane,four)- North-acetylglucosamine units ( Effigy xviii ). Chitin exists in the shells of arthropods such equally crabs, shrimps, and insects and is also produced by fungi and bacteria. Chitosan, the partially N-deacetylated analog of chitin, is a heteropolysaccharide consisting of d-glucosamine and N-acetyl-d-glucosamine. The presence of complimentary amino groups makes chitosan a natural cationic polymer and presents chemical functionality for facile derivatization of the chitosan polymer. Both chitin and chitosan are rigid and crystalline polymers, contributing to their force and insolubility in water at neutral pH. In acidic conditions, chitosan tin be dissolved due to the protonation of free amino groups, while chitin is insoluble. The molecular weight of chitin and chitosan tin can be as high as x^{half dozen}  Da. ¹²⁶

Figure 18. Chemic structures of chitin and chitosan (R   =   H or Ac (Ac <   50%)).

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Assay of Glycans; Polysaccharide Functional Backdrop

N. Ohno , in Comprehensive Glycoscience, 2007

2.17.6 Chitin

Chitin, a β1-4-linked homopolymer of N-acetylglucosamine residues, is an essential component of the cell wall of fungi, comprising approximately ten% of the prison cell wall components. ^156–158 Chitin is as well present in many organisms other than fungi, and has been studied from various perspectives including industrial applications. Chitin is generally a pocket-sized component in the yeast cell wall, bookkeeping for just 1–2% of the jail cell wall dry mass, whereas filamentous fungi contain higher levels of chitin, up to ten–30% of the cell wall dry weight. In both yeasts and filamentous fungi, chitin contributes to the mechanical force of the jail cell wall. Without chitin synthesis, growing hyphae tend to lyse and form pronounced bulges unless the osmolarity of the medium is increased. Genes encoding chitin synthases have been isolated from many yeasts and filamentous fungi and have been classified into half dozen classes according to their sequence similarity. Nigh yeasts and filamentous fungi contain multiple chitin synthase-encoding genes. Chitin synthesis has besides been shown to be essential in the compensatory response to jail cell wall stress. Jail cell wall damage caused by mutations in cell wall-related genes results in hyperaccumulation of chitin. Inability of the cells to respond to cell wall harm induced lysis, indicating the importance of the chitin response to forestall cell death.

Chitosan, the deacetylated derivative of chitin, is likewise an important constituent of the jail cell wall at various stages of the life wheel of some fungal species. ¹⁵⁸ Notwithstanding, it is also not clear how prevalent chitosan is among fungi. Chitosan is not direct synthesized. Instead, secreted enzymes, the chitin deacetylases (EC 3.v.i.41), change the chitin to chitosan during biosynthesis. Chitosan is a polycation, which is much more soluble than neutrally charged chitin. Of the few fungal species able to synthesize chitosan, those belonging to the Mucorales have been shown to generate chitosan during vegetative growth, whereas Sa. cerevisiae but produces chitosan during sporulation.

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Electrospun biomaterials for dermal regeneration

E.A. Growney Kalaf , ... S.A. Sell , in Electrospun Materials for Tissue Engineering science and Biomedical Applications, 2017

nine.2.1.iv Chitin/chitosan

Chitin is the main structural amino polysaccharide establish in the exoskeleton of invertebrates, crustaceans, and insects [ ninety,91]. Chitosan, a natural poly-N-acetyl-glucosamine, is derived from chitin via alkaline deacetylation [91]. Both of these polymers are appropriate for skin tissue engineering due to their inherent biocompatibility, biodegradability, bioactivity, antibacterial, and wound healing properties [87,90,91]. Additionally, chitin/chitosan can also exhibit local hemostatic effects [91]. 1 study compared electrospun chitin nanofibers (Chi-N) with commercially available chitin microfibers (Chi-M). The Chi-N matrices, which were spun out of HFIP, demonstrated fiber diameters of 50–460 nm, while the Chi-M matrices had a cobweb diameter of viii.77   μm. To continue, the nanofibers began to enzymatically degrade subsequently approximately 14 days both in vitro and in vivo, a suitable time frame for dermal regeneration. After culture with NHOK, NHEK, and NHGF, it was observed that the Chi-Due north matrices allowed for more than cellular attachment and spreading than the Chi-K matrices; nonetheless, the degree of each for both scaffolds was much less than the polystyrene (PS) command. Following a coating of type I collagen, the chitin nanofibers exhibited more cellular attachment than the microfibers and the PS control (cell spreading was like between Chi-N and Chi-Yard matrices) [xc].

Chitosan nanofibers composite with PEO accept been previously electrospun from acetic acid for a third-degree burn wound dressing application (type IIIa and IIIb degree burns). Mail implantation, these scaffolds demonstrated high antibacterial properties due to the presence of chitosan and excellent exudate absorption. Resultantly, the electrospun sheets were able to promote wound ventilation and stimulate skin tissue regeneration. Biodegradation of these scaffolds allowed for less mechanical damage to the wound and less pain upon dressing replacements. Finally, the chitosan nanofiber dressing supported a highly desirable healing fourth dimension of approximately xiv days (Table nine.4) [92,93].

Table nine.iv. Summary of natural biopolymers for bioengineered, electrospun skin

Cloth	Composition characteristics	Inherent backdrop	Advantages	References
Collagen type I	– Two α1 and ane α2 chains – 50–500   nm in bore – Triple helical structure	– Naturally occurring – RGD binding sites – Can be obtained from a variety of sources	– Biocompatible – Biodegradable – No immunogenic or cytotoxic response	[5,63,64,74]
Silk fibroin (B. mori)	– Hydrophilic and hydrophobic coblock polymer – Light and heavy chain	– Naturally occurring – RGD bounden sites – Wearisome degradation rate	– Biocompatible – High force – No toxic degradation products	[78–81]
Gelatin	– Derivative of collagen – Denatured class of collagen triple helix	– Naturally occurring – Local hemostatic effect – Activates macrophages	– Biocompatible – Nonantigenic – Low price	[64,85–87]
Chitin/chitosan	– Chitin: amino polysaccharide – Chitosan: poly-Due north-acetyl-glycosaminoglycan	– Naturally occurring – Local hemostatic effect – Chitosan is obtain via element of group i deacetylation of chitin	– Biocompatible – Biodegradable – Bioactive – Antibacterial – Wound healing backdrop	[87,ninety,91]

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Biomaterials and Clinical Use

S.S. Shetye , ... Fifty.J. Soslowsky , in Comprehensive Biomaterials II, 2017

7.xviii.5.1.two Polysaccharides: Chitin, chitosan, alginate, and hyaluronan

Chitin is a 1 of the near abundant natural polysaccharides. It is a linear polymer with loftier crystallinity and chemically inert. ¹³⁴ It is plentiful, inexpensive, and biodegradable. Additionally, chitin has depression immunogenicity and does non induce toxic reactions. Chitin enhances cellular proliferation and migration as well as accelerates wound healing. ¹³⁵ Chitin scaffolds have also been shown to enhance collagen production at the repair site. ¹³⁵ The pore size and thickness of the chitin fabric can exist altered to control the mechanical strength of the construct. The diameter of fibers and density of chitin fabric can also be manipulated to control the degradation rate of the construct. Chitin is degraded by macrophages and decomposes more speedily in vivo than other available scaffold materials. Since chitin fibers are partially absorbed early on and already possess low initial force, chitin scaffolds must be supplemented with mechanically stronger materials in order to grade an effective scaffold. For example, a braided combination of chitin and poly-e-caprolactone (PCL) provides adequate initial forcefulness to a rabbit Achilles tendon repair. ¹³⁶

Chitosan, alginate and hyaluronan are resorbable polysaccharides with very similar properties to chitin. Chitosan is derived from chitin. Alginate is a non-toxic, non-inflammatory polysaccharide derived from brown seaweed and can exist candy in water. Hyaluronan (HA) is a repetitive linear GAG composed of N-acetyl-glucosamine and disaccharides of glucuronic acid. HA is a vital component of ECM, and its roles include interaction with proteoglycans and link proteins, facilitation of cell migration, differentiation, and adhesion, as well as eliciting electrostatic interactions with GAGs. ⁶⁰ Similar chitin, these materials produce a minimal foreign body reaction and controllable mechanical and biodegradable backdrop. Chitosan, alginate and hyaluronan lonely possess low mechanical force and tin acquit inconsistently with seeded cells. This trouble may be ameliorated by combining them with other materials, or occasionally each other, to potentially increase strength and cell adhesion capabilities forming a more viable scaffold. For example, chitosan and alginate are ordinarily paired with agarose or hyaluronan to improve scaffold operation. Hyaluronan–chitosan scaffolds take also been shown to enhance fiber mechanical properties improve adhesion to patellar tendon fibroblasts in vitro compared to chitosan scaffolds solitary or a control group consisting of polyglactin 910. ¹³⁷

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Biologically Inspired and Biomolecular Materials

S.S. Silva , ... R.L. Reis , in Comprehensive Biomaterials II, 2017

2.11.2.1.2.1 Chitin and chitosan

Chitin and chitosan are polysaccharides with not bad structural possibilities for the creation of the derivatives and matrices for dissimilar biomedical applications, including TERM. ¹⁷ Chitin (β-(1-4)-poly-Due north-acetyl-d-glucosamine) can be establish in shells of crustaceous such every bit crabs and shrimps. ^17a Furthermore, chitin tin likewise exist extracted from endoskeletons of cephalopods. Depending on its source, chitin can be characterized by α- and β-class, distinguished by stiff and weak inter- and intramolecular bonds, respectively. ^eighteen This polymer has appealing properties namely biocompatibility, tumor cell growth suppression, acceleration of wound healing and antimicrobial action. ^2a,17a These properties have encouraged the production of chitin-containing products such equally artificial blood vessels, tumor inhibitors, vascular implants and dressing for burns. Despite the promising biomedical use of chitin, its application has been limited due to its potent inter- and intra-molecular bonding between the polymer chain, which results in a lack of solubility in water and mutual organic solvents. ^2a Nevertheless, contempo studies proposed that ionic liquids (ILs), divers as organic salts like 1-butyl-3-methylimidazolium acetate, ^xix can exist used not only as a solvent but besides as reaction media of some polysaccharides, including chitin, ²⁰ chitosan, ²¹ cellulose ²² and silk fibroin. ²³ In particular, chitin/IL solutions can exist used in the preparation of second and 3D-based matrices namely gels, films, sponges and micro/NPs. Given the operation of the resulting chitin-based matrices, they may be practical in drug delivery, bone regeneration, gene commitment, and skin repair. ^20a,c,24

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