CROSS-LINKABLE CELLULOSE AS 3D PRINTING MATERIAL

Abstract

A method for 3D printing is provided, using crosslinkable microfibrillated cellulose (MFC). The 3D printed structure is treated to provide crosslinking of the MFC.

Claims

1. A method for 3D printing, comprising the steps of: a. providing a composition comprising crosslinkable microfibrillated cellulose (MFC), wherein the crosslinkable MFC is phosphorylated microfibrillated cellulose (P-MFC) or dialdehyde microfibrillated cellulose (DA-MFC); b. 3D printing said composition into a 3D structure; and, c. treating said 3D structure to provide crosslinking of the MFC.

2. The method according to claim 1, wherein the crosslinkable MFC is phosphorylated microfibrillated cellulose (P-MFC).

3. The method according to claim 1, wherein the composition comprising crosslinkable MFC is a suspension, a paste or powder comprising crosslinkable MFC.

4. The method according to claim 1, wherein said composition comprising crosslinkable MFC comprises more than 25%, by weight, crosslinkable MFC.

5. The method according to claim 1, wherein said composition comprising crosslinkable MFC further comprises at least one additional components.

6. The method according to claim 1, wherein the composition comprising crosslinkable MFC does not comprise additional crosslinking agents.

7. The method according to claim 1, wherein said crosslinkable MFC is phosphorylated microfibrillated cellulose (P-MFC), and wherein said treatment in step c is heat treatment at a temperature of between 60 and 200° C., preferably between 70 and 120° C.

8. The method according to claim 1, wherein said crosslinkable MFC is dialdehyde microfibrillated cellulose (DA-MFC), and wherein said treatment in step c is reducing a pH to a pH of 7 or below.

9. The method according to claim 1, wherein said treatment in step c takes place for a time of between 10 and 180 minutes.

10. The method according to claim 1, further comprising the step of drying said 3D structure, before the treatment in step c.

11. A 3D printed structure comprising crosslinked MFC.

12. The 3D printed structure according to claim 11, further comprising one or more biological cells.

13. The 3D printed structure according to claim 11, wherein the 3D printed structure comprises a scaffold for growth of biological cells and further comprises biological cells grown on the 3D printed structure.

14. The method according to claim 5, wherein the at least one additional components comprises a synthetic polymer, a polyvinyl alcohol (PVOH), or an inorganic filler.

15. The method according to claim 1, wherein the composition comprising crosslinkable MFC is an aqueous suspension.

16. The method according to claim 1 further comprising: d. growing one or more biological cells on the 3D structure.

Description

SCHEMATIC DESCRIPTION OF THE FIGURES

[0046] FIG. 1: Shows a 2D top view of the human nose model printed with the different samples.

[0047] FIG. 2: Shows a 3D side view of the human nose model printed with the different samples (the lines represent the xx, yy, zz axes).

EXAMPLE

[0048] 3D printing of P-MFC and re-swelling capacity and properties of the 3D printed materials.

Samples:

[0049] Aqueous dispersions of: [0050] Enzymatically pre-treated native MFC (N-MFC; .sup.˜4% solids content) [0051] Phosphorylated MFC (P-MFC; degree of functionalization=0.86 mmol/g; .sup.˜2% solids content; food grade green colorant) [0052] Commercial bioink Cellink Xplore (according to manufacturer contains cellulose nanocrystals, alginate and coloring agent; .sup.˜16% solids content)

Method:

[0053] Human nose shapes (size: 15.05×19.23×8.50 mm; FIGS. 1 and 2) were 3D printed at RT with all the samples by using an Inkredible+ 3D bioprinter operating at a pressure in the range 50-70 kPa. Prior to printing, the samples were carefully loaded into 3 mL cartridges connected to conical nozzles (22G; made of polypropylene) to avoid air bubbles. The wet weight of the printed shapes was recorded after printing. They were then allowed to dry at the temperature and times listed in Table 1. In the case of the Cellink Xplore 3D printed shapes, a crosslinker solution consisting of 100 mM aqueous calcium chloride was added dropwise to some of the shapes immediately after printing. Three replicates were 3D printed and tested for each sample and drying conditions.

Testing:

[0054] The samples were re-wetted after drying by soaking in deionized water for 20 minutes. The weight was recorded for the re-wet sample and the re-swelling capacity (or swelling recovery) was calculated as (w.sub.rw/w.sub.iw)*100, where w.sub.re stands for the weight of the re-wet sample and w.sub.iw for the weight of the initial wet sample (prior to drying). Some properties of the 3D printed structures, namely compressibility, flexibility, elasticity and shape recovery, were then qualitatively and manually/visually assessed using a rating scale of 0-5, in which 0 means inexistent and 5 means very high. Compressibility was assessed by compressing the 3D printed shapes between the fingers; flexibility was assessed by manually bending the 3D printed shapes; elasticity was assessed by gently manually stretching the 3D printed shapes; shape recovery was visually assessed by comparing the shape of the re-wetted 3D printed shape after drying with the original wet shape.

Results:

[0055] P-MFC dispersion, which comprised lower solids content than the benchmark materials (N-MFC and Cellink Xplore), proved to be a good bioink for 3D printing, and human nose 3D shapes were successfully printed. Crosslinked P-MFC-based 3D shapes (both dried at 70° C. and 105° C.) presented higher swelling recovery than the crosslinked Cellink Xplore bioink-based counterpart, as shown by the re-swelling capacity values. N-MFC-based 3D shapes presented the lowest re-swelling capacity, irrespectively of the drying conditions, likely due to an extensive degree of hornification upon drying, which is typical for unmodified MFC samples. Moreover, the re-wetted 3D shapes based on N-MFC didn't present any compressibility, flexibility or elasticity, and the shape recovery was extremely low. On the other hand, P-MFC-based 3D shapes were the ones demonstrating the highest compressibility, flexibility and elasticity, especially the one dried at 105° C. (highest crosslinking degree). Even though none of the 3D printed materials fully recovered the shape upon drying, the P-MFC-based 3D shape dried at 105° C. presented high shape recovery, similarly to the Cellink Xplore-based counterparts, indicating that the crosslinking of P-MFC without the addition of external crosslinkers is a viable route for the preparation of 3D printed materials with good performance.

TABLE-US-00001 TABLE 1 Drying conditions, re-swelling capacity and qualitative assessment of the compressibility, flexibility, elasticity and shape recovery of the printed 3D shapes upon drying and subsequent re-swelling in water. Drying Drying Re-swelling Manual/Visual assessment (Rating scale: 0-5) temperature time capacity Shape Sample (° C.) (h) (%) Compressibility Flexibility Elasticity recovery P-MFC RT 48 36 ± 8 3 3 2 3 70 2 55 ± 8 2 2 1 3 105 0.83 (=50 44 ± 5 3 4 4 4 min) N-MFC RT 48 14 ± 3 0 0 0 1 70 2 15 ± 4 0 0 0 1 Cellink RT 48 54 ± 4 0 1 0 4 Xplore