Because your tape was longer than the book itself, you should have some excess tape on the top and bottom of the book. Go to source Any leftover tape should be trimmed. Avoid folding leftover tape over, as this may make your book harder to open. Method 2. Ensure your pages have at least 1 inch 2. If you printed your pages using a conventional Word document, you should automatically have 1 inch 2.
If you wrote your pages by hand, make sure the writing has a margin. Use a hand-held hole-puncher for a clean look. Repeat the process on the bottom of the page. Ensure your holes line up properly. Use a ruler to draw a faint line connecting the two holes. Use a pencil so you can erase the line later on. You can also choose to draw a thick line with pen or permanent marker if you want the line to remain on the cover.
Make sure your holes are on the line. Choose a simple black tape for a classic look or go for a colorful design if you want something more personalized. Thread the ribbon in and out of each hole. Loop the ribbon back through the top and bottom holes and tie.
Looping the ribbon a second time reinforces the binding. Depending on how many pages you have, loop it a third time for an even stronger binding. Tie it off with a simple knot or a fancy bow, and cut off excess. Method 3.
Use a bone folder or the top of your nail to get a crisp fold. You can fold individually or in groups, depending on how many pages you have. Use a ruler to measure how long the book is. Divide your measurement by 6. This bookbinding method requires 5 holes at the crease. They should be equally spread apart, but the spacing between the dots will depend on how large your paper is.
Do this on the inside of the crease, and use a ruler to make sure your measurements are precise. Then, each progressive dot will be 1. Your fifth dot should be 1. Pierce each station with an awl. An awl is used to pierce small holes in anything from paper to leather to wood. Put your needle through the third station and pull about 2 inches 5.
Put your needle through the fourth station. Your needle and thread should now be on the inside of the crease. Let go of the rest of the thread and pull it through as needed. Thread your needle through the fifth station and back through the fourth station. Go through the second station.
Your needle should now be on the outside by station two. Put your needle through the first station and back through the second station. Your needle should go inside the first station and then go back outside the second station. Your thread should now be facing away from the crease. Finish by pulling your thread through the third station. Every station should be threaded, and your book should now have thread both inside and outside of the crease. Tie the thread to itself and pull firmly.
Method 4. Tape the edge of your paper with clear tape to reinforce it. On the contrary, vat photopolymerization VP is capable of fabricating 3D hydrogels with higher geometrical complexity and finer accuracy, with no substantial spatial resolution effect on the printing time 26 , 29 , In VP, the projection of light triggers a localized solidification of a liquid formulation, layer-by-layer, leading to the fabrication of precise self-standing 3D structures with fine spatiotemporal control 31 , 32 , DLP is a sequential layer-by-layer maskless photolithography technique, in which an entire slice of the object with controlled thickness is selectively solidified in a single exposure by a UV or visible light projection of a 2D pattern on a liquid photocurable resin.
The build platform is then moved to fill the printing area with the uncured resin before fabricating the next layer, repeating the process until complete fabrication. In DLP it is possible to obtain flat vertical surfaces with negligible distortion and great shape fidelity because the conversion of the liquid into a solid is very fast, since it is based on a photopolymerization reaction.
In vat polymerization, unlike the extrusion-based process, there is no need for support material, and therefore lattices with overhanging features and through-holes show clean and sharp edges This is particularly significant for 3D printing of hydrogels, for which complex architectures are difficult to obtain via extrusion-based technologies 26 , 30 , Moreover, there are fewer limitations on the viscosity range suitable for the fabrication process, but the material choices are limited to liquid or soluble photopolymers, which might be a disadvantage 18 , Unfortunately, the material requirements for SH hydrogels do not seem to match light-activated 3D printing 36 , Vat photopolymerization relies on reactions that yield a densely chemically cross-linked network to enable the accurate tuning of the macrostructure and mesostructure simultaneously 30 , At the same time, the SH mechanism depends on long-range chain mobility and reversible interactions.
Its efficiency decreases proportionally with the increase of the cross-linking density because it hinders the migration of macromolecules through the surfaces 39 , Both characteristics are typically not present together in a hydrogel, which makes challenging to construct self-standing complex and high-resolution structures combined with intrinsic SH 36 , Finally, a major challenge is the essential presence of water, which allows for a facilitated interdiffusion of the macromolecules.
On the other side, water enlarges the interchain distances, which lowers secondary forces and limits self-repair 36 , Therefore, it is crucial to find the right balance between cross-linking density and water content to enable an effective SH process. There are few reports of VP-3D-printed objects fabricated with intrinsically SH polymeric materials, related mainly to elastomers. These systems are based on the diffusion of a mending agent, such as Poly caprolactone upon heating and cooling 41 , electrostatic interactions, such as hydrogen bonds 42 and ionic bonds 43 , or dynamic covalent chemistry, such as disulfide bonds However, to the best of our knowledge, there are no reports on 3D-printed hydrogels produced via VP with self-repairing properties due to the chemical, physical, and technological limitations described above.
We successfully merged the intriguing characteristics of the VP printing process with SH properties to fabricate 3D-printed hydrogels with complex structures and SH ability at room temperature without any stimuli. These results were achieved by using only commercially available compounds which are able to effectively interact via dispersive forces such as Poly vinyl alcohol PVA and photocurable species, like acrylic acid AAc , and Poly ethylene glycol diacrylate PEGDA 45 , 46 , 47 , 48 , while the printing is performed using a commercial DLP printer.
This work offers a general and easily adaptable approach to develop self-repairing hydrogels with complex 3D architecture via VP for applications in diverse fields, ranging from biomedicine and wearable sensors to robotics and energy harvesting. The system was designed as a sequential semi-IPN by adding the precursors of the chemical covalent network to a solution containing a linear polymer.
After polymerization, the linear polymer is entrapped in the cross-linked matrix The photocurable ink was prepared by mixing an aqueous solution of unmodified non-crosslinked Poly vinyl alcohol PVA with acrylic acid AAc , the cross-linker Poly ethylene glycol diacrylate PEGDA , and a water-compatible photoinitiator based on diphenyl 2,4,6-trimethylbenzoyl phosphine oxide TPO 49 Fig.
PVA was selected because of its inherent properties, such as chain interdiffusion and the presence of hydrogen bond-forming hydroxyl groups, which make PVA an attractive material for applications in efficiently SH and biocompatible hydrogels 45 , 46 , 47 , 48 , 50 , Likewise, higher MW did not show acceptable results because of the high viscosity even at low concentrations. The selected water-soluble acrylates, AAc and PEGDA, have been widely exploited for VP to fabricate high-resolution objects because of their ability to undergo rapid photoinduced radical photopolymerization in large amounts of water 52 , In addition, the carboxylic groups of the acrylic acid can form multiple hydrogen bonds with the PVA chains and, hence, contribute to the SH ability Furthermore, a considerable amount of water prevents the use of many commercial photoinitiators because most of those which match the wavelength used in VP printing show low solubility in water Therefore, the application of our developed water-compatible photoinitiator nanoparticles was crucial to achieve rapid printing using a commercial printer 49 , Figure 1b depicts the formation of the semi-IPN: the physical network is mixed with the precursors of the chemical network which is formed during light irradiation 17 , The result is a hydrogel composed of PVA chains that are homogeneously distributed and incorporated within a cross-linked acrylic matrix.
The homogeneity is confirmed both by the transparency of the formulations and printed objects, and by ATR-IR spectra collected in different points of dried samples, in which typical peaks of both PVA and AAc are present simultaneously Supplementary Fig. This semi-IPN should allow the system to recover from damages: once the covalent bonds are broken, the damage can be overcome by restoring the reversible physical cross-linking amid the cut interfaces Furthermore, as it will be shown, the self-repair occurs without external stimuli or adhesives and is only due to internal forces.
This is because the printed material itself is already rich in functional groups, which are able to form hydrogen bonding. Furthermore, the hydrogel contains a large proportion of water, providing PVA mobility to migrate across the ruptured interface 7 , At last, these secondary forces should be strong enough to be effective despite the significant amount of water in the gel 45 , To assess the suitability of the proposed system as ink for DLP printing, we evaluated the effect of the relative concentrations of PVA and AAc, to control the extent of secondary forces and to define the printability window.
The compositions of the tested formulations are presented in Supplementary Table 3. We found that the viscosity of the resulting solutions drastically increased with increasing concentration of PVA Supplementary Fig. We also conducted preliminary experiments to determine the effects of the PVA concentration on the photopolymerization kinetics through photo-rheology experiments Fig. This indicates that the presence of PVA does not decrease the reactivity of the acrylate species.
Furthermore, we found that the effect of the photoinitiator concentration on the kinetics of the reaction was negligible Fig. Since the SH performance is expected to increase with increasing PVA content, we will present here mostly the results related to the 3D printable ink containing the highest PVA concentration, i.
In the printing compositions, we used only one concentration of the chemical cross-linker, PEGDA, at a molar ratio of to acrylic acid.
This was the lowest concentration of cross-linker that enabled successful printing. Increasing concentration of PEGDA results in a higher cross-linking density, which still enabled printing 3D objects but affected negatively the SH properties.
The apparent values for cross-linking, including physical and chemical bonds, were estimated from the elastic shear modulus at the plateau of the formulations, using Eq. We determined the crosslinking density for formulations without PVA to be 4. Supplementary Table 3 shows the calculated values for the various PVA ratios. The printed objects are characterized by flat surfaces, straight elements, and clean and sharp edges Fig.
Objects which are difficult to print, for example, objects having overhanging features and through-holes, could be printed with this composition without any support. As an example of a complex structure, we printed objects with rotational symmetry and independent self-standing segments, with smooth rounded surfaces and a central pillar, which are shown in Fig. It should be also noted that this high structural quality could be accomplished only after overcoming several printing-related obstacles of this formulation.
The main crucial challenge was to avoid the evaporation of water during the exothermic polymerization reaction. At last, the high photoreactivity of the monomer led to the thickening of the ink and eventually uncontrolled polymerization, with loss of printing precision. We overcame this challenge by carefully flushing a water aerosol over the printing area during printing Fig. The optimized parameters are reported in the method section.
Furthermore, the motion of the building platform should be very slow to avoid the incorporation of air bubbles in the ink, which can lead to detachment of the printed object and interlayer delamination, and to give enough time to the resin to flow and fill the gap for printing the following layer. In addition, to avoid polymerization over the exposed areas and to achieve a better resolution, a water-soluble dye was added. This lead to better confinement of the polymerization at the x-y plane, lower light penetration depth, and better control over the photoinitiation kinetics 34 , 57 , The sample printed with no dye shows extensive polymerization and its shape is undefined, while the addition of a dye results in good shape fidelity with sharp edges and flat surfaces.
As depicted in Supplementary Fig. At the same time, the resolution along the Z -axis is not only related to the dye concentration but is also strongly affected by the ink viscosity and, therefore, by the PVA concentration that results in a tendency to delaminate the layers immersed in a thick formulation because of an increase in the adhesion forces Supplementary Fig. Although the dimensional accuracy of these printed samples is in good agreement with previous SH hydrogels 3D printed via deposition-based printing, the presented system enables better precision, CAD fidelity, shape fixity, and edge sharpness 15 , 20 , Several 3D-printed objects having different shapes were cut into two pieces, and then the two parts were rapidly placed in contact to demonstrate qualitatively the SH properties.
For better visualization of the SH, two samples printed with different colors, red and green, were cut and rejoined Fig. As shown, the structures were indeed macroscopically repaired.
The adhesion happened instantly upon rejoining, and the mended hydrogel could immediately hold its weight and bear bending deformation without breaking apart Fig. The SH can be attributed to the efficient adhesion at the rejoined surface, which is facilitated by hydrogen bond formation between carboxylic and hydroxyl groups across the interface 45 , Furthermore, additional experiments showed that the SH on freshly cut surfaces is indeed more efficient than simple adhesion forces Supplementary Movie 2.
This behavior can be explained by a considerable amount of hydrogen bond-forming groups which are available on the freshly cut surface and strengthen the interactions at the interface. It can be argued that the SH mechanism is similar to the behavior of pressure-sensitive adhesives PSA between two separate surfaces. Our material shows rheological properties below the Dahlquist criterion, therefore the mechanism of SH can also be influenced by surface self-adhesiveness at the interface.
However, this aspect does not exclude that the material is SH, since macroscopic self-repairing can be defined as the recovery of the initial mechanical properties 36 , Indeed, the restoration of complex architectures with overhanging features was successfully achieved Fig. The samples could withstand a bending deformation immediately upon rejoining.
Tensile tests were performed at different SH times to give a quantitative temporal evaluation of the SH process Fig. As seen, the system considerably recovers already within the first two hours. The increase with time may be a result of the PVA interdiffusion The possibility of diffusion beyond the interface plan was also evaluated qualitatively using two water-soluble dyes in different sides. After rejoining, purple color is observed at the interface. Note that the two dyes have different diffusivity in the hydrogel, and therefore the purple color appears to be only at one side of the interface Supplementary Fig.
The variability in the stress—strain curves shown in Fig. Pristine samples abruptly separated after reaching the ultimate tensile strength. In contrast, the healed samples did not split at once but gradually detached along the cut region. Quick links Open research. Data policies. Publishing policies. Author satisfaction. The Transfer Desk service. Quick links Books Publishing. Code of Conduct. SEO Guide. Learn more From award-winning research to major reference works, Palgrave publishes books across the humanities, social sciences and business.
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