1Graduate School of Engineering, Tottori University, 4-101 Koyama-Cho Minami, Tottori 680-8552, Japan; pj. ca. u-irottot. ude@B1003T41D (Y. F. A. ); pj. ca. u-irottot. mehc@awazi-h (H. I. ); pj. ca. u-irottot. mehc@otomirom (M. M. ); pj. ca. u-irottot. mehc@otomias (H. S. )Find articles by.
2Faculty of Agriculture, Tottori University, 4-101 Koyama-Cho Minami, Tottori 680-8553, Japan; moc.liamtoh@729atnog (M.E.); pj.ca.u-irottot.sesum@akanimak (H.K.)Find articles by
2Faculty of Agriculture, Tottori University, 4-101 Koyama-Cho Minami, Tottori 680-8553, Japan; moc.liamtoh@729atnog (M.E.); pj.ca.u-irottot.sesum@akanimak (H.K.)Find articles by
1Graduate School of Engineering, Tottori University, 4-101 Koyama-Cho Minami, Tottori 680-8552, Japan; pj. ca. u-irottot. ude@B1003T41D (Y. F. A. ); pj. ca. u-irottot. mehc@awazi-h (H. I. ); pj. ca. u-irottot. mehc@otomirom (M. M. ); pj. ca. u-irottot. mehc@otomias (H. S. )Find articles by.
1Graduate School of Engineering, Tottori University, 4-101 Koyama-Cho Minami, Tottori 680-8552, Japan; pj. ca. u-irottot. ude@B1003T41D (Y. F. A. ); pj. ca. u-irottot. mehc@awazi-h (H. I. ); pj. ca. u-irottot. mehc@otomirom (M. M. ); pj. ca. u-irottot. mehc@otomias (H. S. )Find articles by.
1Graduate School of Engineering, Tottori University, 4-101 Koyama-Cho Minami, Tottori 680-8552, Japan; pj. ca. u-irottot. ude@B1003T41D (Y. F. A. ); pj. ca. u-irottot. mehc@awazi-h (H. I. ); pj. ca. u-irottot. mehc@otomirom (M. M. ); pj. ca. u-irottot. mehc@otomias (H. S. )Find articles by.
1Graduate School of Engineering, Tottori University, 4-101 Koyama-Cho Minami, Tottori 680-8552, Japan; pj. ca. u-irottot. ude@B1003T41D (Y. F. A. ); pj. ca. u-irottot. mehc@awazi-h (H. I. ); pj. ca. u-irottot. mehc@otomirom (M. M. ); pj. ca. u-irottot. mehc@otomias (H. S. )Find articles by.
From crab shells, a protein/CaCO3/chitin nanofiber complex was made by using a high-pressure water-jet (HPWJ) system to do some simple mechanical work. Chemical treatments, like using sodium hydroxide and hydrochloric acid to get rid of protein and calcium carbonate, were not used in the preparation process. Thus, it was economically and environmentally friendly. The nanofibers obtained had uniform width and dispersed homogeneously in water. Nanofibers were characterized in morphology, transparency, and viscosity. Results indicated that the shell was mostly disintegrated into nanofibers at above five cycles of the HPWJ system. The chemical structure of the nanofiber was maintained even after extensive mechanical treatments. After that, it was discovered that the nanofiber complex helped tomatoes grow better in a hydroponics system. This suggests that the mechanical treatments worked well to add minerals to the system. The nanofiber complex was spread out evenly, which made it easier to use as fertilizer than the crab shell flakes.
Chitin is a highly abundant carbohydrate polymer occurring primarily in crab shells. Crab shells have a hierarchically-ordered organization [1]. The stiff chitin molecules are lined up against each other to make α-chitin nanofibers that have a long, crystalline structure. These nanofibers are covered by a protein layer. The next layer is made up of groups of protein/chitin nanofibers that twist together to form a plywood-like structure that is slowly turned around its own axis. Calcium carbonate, consisting of calcite crystal, is embedded in the small cavity of the helicoidally-shaped structure. In a previous study, we took chitin nanofibers from crab shells and made them ready by giving them a simple mechanical treatment [2]. Chitin nanofibers have a specific shape [3], a high surface-to-volume ratio [4], good biological properties [7–10], and high mechanical strength [5–6].
As an intermediate between chitosan and glucosamine, the fishing industry keeps some of the chitin in crab shells, but throws away the rest of the shell as industrial waste. Chitin is made from crab shells that have been treated with water-based NaOH and HCl solutions to get rid of proteins and calcium carbonate [11]. Then, a big process is needed to get rid of the large amounts of calcium carbonate and protein that are left over. The price of commercial chitin, which is currently around 5,000 Japanese Yen/kg, covers the cost of this process. In a previous study [12], we looked into ways to cut costs by skipping the process of removing proteins. The protein/chitin nanofiber complex, thus obtained, could reinforce acrylic resin film and increase its mechanical properties. Moreover, the protein layer on the chitin nanofiber behaved as a substrate for the biomineralization of calcium carbonate. Because of that study, we thought it might be possible to turn the chitin in crab shells into nanofibers without taking out the protein and calcium carbonate. Simplification of the preparation process would significantly reduce the production cost of nanofiber. Furthermore, eliminating the use of chemicals for purification would render the process more environmentally friendly. In this study, we report on the direct disintegration of crab shells using our proposed method. Then, we describe in detail the protein/CaCO3/chitin nanofiber complex that we got and talk about how it could be used as a plant fertilizer, since it is well known that crab shells help plants grow.
The Surprising Makeup of Crab Shells A Closer Look at This Protective Armor
Crab shells – also known as exoskeletons – are complex, fascinating structures that play a crucial role in a crab’s survival. But what exactly are these hardy outer coverings made of? The primary building block of crab shells is chitin, a natural polymer that provides strength and flexibility. Let’s take a closer dive into the composition, properties and functions of crab shell exoskeletons.
What is Chitin and Why is it Important?
Chitin is a long-chain polysaccharide that contains nitrogen and is structurally similar to cellulose It forms crystalline nanofibers that assemble into tightly-woven sheets This gives crab shells their trademark durability and hardness. Chitin accounts for 20-50% of the total crab shell composition. It acts as the scaffolding that lends structural integrity to the shell. Without chitin, crab shells would completely lack shape and strength.
In addition to defense, chitin also assists with growth. As juvenile crabs increase in size, they periodically shed their rigid shells in a process called molting. The new shell hardens and allows for a larger body volume until the crab outgrows it and molts again. Chitin’s dynamic nature enables both protection and expansion.
Other Shell Components and Their Roles
While chitin represents the core foundation, crab shells contain other substances that enable their functioning:
-
Minerals – Minerals like calcium carbonate make up 20-50% of crab shells. Calcium lends additional solidity to fortify the structure.
-
Proteins – Shell proteins constitute 20-40% of the composition. They interconnect and interface with chitin to enhance shell engineering.
-
Lipids and pigments – Small amounts of waterproofing lipids and carotenoid pigments provide coloration.
This mixture of components generates a formidable suit of armor with just the right blend of strength, resiliency and flexibility. The shell’s multi-faceted physical properties equip crabs for the harsh demands of their environments.
Crab Shell Strength and Durability
The robust nature of crab shell exoskeletons is striking. Their toughness originates from the orderly, layered assembly of chitin nanofibers. Individual fibers arranged in parallel and stacked in sheets resist external stresses. This stiff but flexible configuration distributes applied forces efficiently throughout the structure.
Crab shells demonstrate tremendous fracture resistance. Their chitin scaffolds can withstand heavy blows from predators. Shells also grant protection against punctures from sharp objects. And they confer resistance to the crushing pressures of ocean depths. Their durability helps crabs conquer the challenges of their habitats.
Variations Between Crab Species
Over 6,700 crab species populate diverse aquatic and terrestrial settings. Accordingly, shell composition and architecture can differ somewhat between crab types. Specific adaptations help crabs thrive in their particular surroundings. For example:
-
Spider crabs have long, slender legs and a round, temnocyst-covered shell for camouflaging on the seafloor.
-
Fiddler crabs evolved a single giant claw for mating displays, digging burrows and defending territory.
-
Yeti crabs sport a furry exterior of bacteria that harnesses geothermal vent chemicals.
Despite these specialized modifications, all crab shells contain chitin as an essential element. The exact levels and structural patterns result in tailored exoskeletons.
Crab Shell Shedding and Growth
In order for crabs to expand in size, they must periodically shed their confining shells. This molting process entails:
-
Separation of the old shell from the body.
-
Absorption of water to expand the body.
-
Hardening of a larger new shell.
Molting leaves crabs vulnerable until their replacement shell fully calcifies. Fortunately, this sequence enables indeterminate growth. By repeatedly shedding shells, crabs can continue increasing in dimension throughout their lifespan.
Industrial and Medical Applications
Beyond their biological purpose, crab shells provide a valuable raw material for generating derivative bioproducts. Their chitin content offers a range of industrial, agricultural and medical applications:
-
Wound dressings – Chitosan from shell chitin accelerates healing.
-
Water purification – Chitin acts as an absorbent adsorbent.
-
Food preservation – Antimicrobial chitosan coatings prevent spoilage.
-
Cosmetics – Moisturizing, antioxidant properties.
-
Biodegradable packaging – Chitin films are eco-friendly alternatives.
The list continues well beyond this brief sampling. As an annually renewable, high-performance material, crab shells are a promising resource.
An Essential Protective Barrier
The sturdy exoskeleton of the crab shell fulfills a pivotal evolutionary purpose: safeguarding the delicate interior against harm. Its specialized composition and architecture equip crabs for the extreme demands of their environments. Chitin lends exceptional structural properties as the predominant constituent. Additional components fine-tune the shell’s performance and features. Though thick and hard, shells permit flexibility for growth through molting. Their simultaneous strength and expandability provide an ingenious survival advantage. Beyond defense, discarded shells offer a multitude of applications that can benefit industry and medicine. Crab shell exoskeletons are a wonder of natural engineering whose merits we are only beginning to fully grasp. Their secrets have much yet to teach us.
Materials and Methods
The raw shells of Chionoecetes opilio (red snow crab) and α-chitin powder with a 6. 4% deacetylation degree were obtained from Koyo Chemicals. Other chemicals were purchased from Aldrich or Kanto Chemicals and were used as received. Tomato seeds were purchased from the Marutane Seed Co. , Ltd. , Kyoto, Japan.
Plant Growth Effect of the Protein/CaCO3/Chitin Nanofiber Complex
Tomato plants grown in a hydroponic system were treated with nanofibers once a week. After the fifth nanofiber treatment, the tomato plants that had been given protein/CaCO3/chitin nanofibers had much older leaves, wider stems, and taller plants than the control plants (,). That the crab shell powder had on tomato plant growth was about the same as that of mineralized chitin-protein composite nanofibers. It was written in that the effects of crab shell powder were not very different after the fifth and ninth treatments (p. 05) from those of protein/CaCO3/chitin nanofibers in terms of the plants’ leaf count and stem diameter However, after five treatments, the two supplements had very different effects on the tomato plants’ height (p 05); with the protein/CaCO3/chitin nanofibers exhibiting the better effect on tomato growth. The difference was because of how mechanical treatment caused minerals to quickly be released from the nanofiber network into the hydroponics system. It was also easy to use the mechanically-disintegrated protein/CaCO3/chitin nanofibers because they were liquid, unlike the insoluble, roughly-crushed crab shell powder.
| Day after Treatment | Treatment | Number of Passes | Number of Leaves | Stem Diameter (mm) | Plant Height (cm) |
|---|---|---|---|---|---|
| 5 weeks | Distilled water | – | 3.2 ± 0.1 a | 1.4 ± 0.0 a | 0.9 ± 0.1 a |
| HYPONeX | – | 8.3 ± 0.2 b | 3.0 ± 0.2 b | 11.6 ± 0.8 b | |
| Crab shell | – | 6.0 ± 0.3 c | 2.0 ± 0.1 c | 4.3 ± 0.2 c,d,e | |
| Protein/CaCO3/chitin nanofiber | 0 | 6.3 ± 0.2 c | 2.2 ± 0.1 c | 6.8 ± 1.9 c | |
| 5 | 5.8 ± 0.3 c | 2.0 ± 0.1 c | 4.4 ± 0.4 c,d | ||
| 50 | 6.7 ± 0.2 c | 2.2 ± 0.1 c | 5.0 ± 0.1 c | ||
| Protein/chitin nanofiber | 0 | 3.1 ± 0.2 a | 1.4 ± 0.0 a | 1.0 ± 0.1 a | |
| 5 | 3.5 ± 0.2 a | 1.5 ± 0.0 a | 1.4 ± 0.1 a,d,e | ||
| 50 | 3.6 ± 0.2 a | 1.5 ± 0.0 a | 1.2 ± 0.1 a,e | ||
| Chitin nanofiber | 0 | 3.2 ± 0.1 a | 1.4 ± 0.0 a | 1.0 ± 0.1 a | |
| 5 | 3.0 ± 0.3 a | 1.4 ± 0.0 a | 1.0 ± 0.1 a | ||
| 50 | 3.0 ± 0.1 a | 1.4 ± 0.0 a | 0.9 ± 0.0 a | ||
| 9 weeks | Distilled water | – | ND | ||
| HYPONeX | – | 9.7 ± 0.4 a | 3.3 ± 0.1 a | 16.6 ± 0.5 a | |
| Crab shell | – | 8.4 ± 0.5 a | 2.1 ± 0.1 b | 7.0 ± 0.9 b | |
| Protein/CaCO3/chitin nanofiber | 0 | 9.1 ± 0.3 a | 2.2 ± 0.1 b | 9.1 ± 0.6 b | |
| 5 | 8.6 ± 0.3 a | 2.2 ± 0.1 b | 7.8 ± 0.6 b | ||
| 50 | 9.2 ± 0.3 a | 2.3 ± 0.1 b | 9.3 ± 0.5 b | ||
| Protein/chitin nanofiber | 0 | ND | |||
| 5 | ND | ||||
| 50 | ND | ||||
| Chitin nanofiber | 0 | ND | |||
| 5 | ND | ||||
| 50 | ND | ||||
On the other hand, neither protein/chitin nanofibers nor chitin nanofibers had any effect on tomato growth. At the ninth nanofibers treatment, tomato plants that were given protein/chitin nanofiber, chitin nanofiber, or distilled water (DW) died. On the other hand, tomato plants that were given protein/CaCO3/chitin nanofibers or crab shells grew well. These results indicated that the protein/CaCO3/chitin nanofibers might act as a fertilizer. For growth, plants need more than just essential minerals like nitrogen, phosphorus, and potassium. They also need calcium, sulfur, magnesium, and trace minerals. Chitin nanofibers and protein/chitin nanofibers both have nitrogen, which plants need to grow, but they may not have enough minerals to help plants grow. Even though protein/CaCO3/chitin nanofibers didn’t have as big of an impact as the commercial nutrient HYPONeX, they might work well as a fertilizer after they are improved even more. It was also found that there were no big differences in tomato growth between the nanofibers that had been treated with different numbers of passes of the HPWJ system. As a result, the 0 pass sample of protein/CaCO3/chitin nanofibers that was roughly crushed by a grinder with two passes could be a cheap material that can be used as plant food.
What’s Inside a Hermit Crab Shell?
Could a chemical found in crab shells make batteries more sustainable?
Crustaceans such as crabs, shrimps and lobsters have exoskeletons made of cells that contain chitin, a polysaccharide that makes their shells hard and resistant. Photograph: Eric Risberg/AP Scientists want to use a chemical found in crab and lobster shells to make batteries more sustainable, according to research.
What are seashells made of?
Seashells are the exoskeletons of mollusks such as snails, clams, oysters and many others. Such shells have three distinct layers and are composed mostly of calcium carbonate with only a small quantity of protein–no more than 2 percent. These shells, unlike typical animal structures, are not made up of cells.
Can crab shells make batteries?
Materials scientists want to use the nanostructures found in crab shells as templates for new battery materials. Crab shells usually are just a nuisance that you have to crack and dig through to get the delicious meat inside. But one team of materials scientists thinks the shells could help them fabricate materials for long lasting batteries.
How do you make carbon from crab shells?
To make their “crab carbon,” the researchers heated crab shells to temperatures exceeding 1000 F. They then added the carbon to a solution of either tin sulfide (SnS 2) or iron sulfide (FeS 2 ), then dried them to form anodes.