Patent Description:
Commercially available 3D printing resins are polymers suitable in stereolithographic printing (SLA) and Digital Light Processing (DLP), in particular acrylic resins (homo or co-polymers polyacrylates or mixtures thereof) and silicone resins (or rubbers).

The plant material derives from suitable treatment and grinding of agricultural waste, until particles of average size between <NUM> and <NUM> microns (mm) are obtained.

The invention also relates to the preparation of models (mock-ups) of organs or tissues using the composition of the invention, as well as to the models thus prepared.

It is known that printing technologies 3D have become an instrument widely used in many sectors, including the production of organ models, for example for teaching and/or simulating surgeries in preparation for particularly complex operations. This need has created an increasing demand for materials that allow to realize models with improved mechanical properties compared to those obtainable using the 3D printing resins existing on the market, in particular in terms of elasticity and flexibility.

The addition of plant fibres to the polymers can contribute to the improvement of the mechanical properties, even if it poses problems, such as the need for adequate drying of the natural, hydrophilic fibres, before the addition and the need to use polymers with low melting temperatures to avoid thermal degradation of the natural fibres themselves. The increasing attention to the environment, together with the need for new materials for rapid prototyping, have encouraged the search for compounds consisting of polymers and plant fillers.

In fact, additive polymers obtained by mixing synthetic resins with vegetable material are known.

<NPL>) evaluate different polymers for 3D printing with fused deposition modelling (FDM) added with natural fillers (such as wood flour, rice or coconut husks, hemp fibres or flax) which, being mainly agricultural waste products often locally sourced, have the advantage of reducing costs and decreasing the environmental impact of the compound. The polymers studied are those typically used in FDM, such as polyethylene (PE), polypropylene (PP), acrylonitrile-butadiene-stirene (ABS), polycarbonate (PC), polysulfone (PSU), polyetherimide (PEI) and poly-(lactic acid) (PLA), of which it has been evaluated whether the addition of natural fibres can exert a reinforcing function, also by printing the composites with FDM technique instead of with traditional techniques (e.g. extrusion). The results show that ABS and PLA do not benefit from the addition of natural fillers, while other polymers such as polyolefins are more performing. No data, however, is reported on more elastic polymers, such as silicone rubbers or polynitrile rubbers for 3D printing and with devices different from those for FDM.

<NPL>) illustrate the main research results on composite polymers with biodegradable fillers and from renewable sources. In particular, the production and characterization of polymeric composites based on recyclable polymers such as polyolefins, filled with fibres and particles extracted from plants (generally relatively abundant) or from plant wastes, is reported. The most known and used natural-organic fillers are flour and wood fibres. Other natural-organic fillers, including cellulose, cotton, flax, sisal, kenaf, jute, hemp, starch, began to find application.

Patent document <CIT> describes a biocomposite, in which the reinforcing material consists of vegetable fibers from scraps (pseudo-banana stem), which constitute a renewable source which is abundantly available. The polymer matrix is instead a propylene homo or copolymer in virgin or waste form. Properties such as tensile strength, elongation at break, impact strength and hardness of the resulting composite material show that the vegetable fillers used are durable with respect to the thermoplastic material as such. However, in this document no materials obtained from matrices other than PP are considered, nor vegetable wastes other than fibers derived from banana plants, which are not available in all geographical areas of the planet.

Patent document <CIT> claims a biodegradable composite comprising one or more biodegradable polymers, selected from poly (butylene adipate-co-terephthalate) (PBAT), poly (lactic acid) (PLA), poly (butylene succinate) (PBS), poly (butylene succinate-co-adipate) (PBSA), polycaprolactone (PCL) and polyhydrosalcanoates (PHA), among others, including a filler present in an amount which can reach <NUM>% by weight. The filler may include tea or coffee by-products, perennial grass, agricultural residue and the agricultural residue includes flakes, stems and leaves. An in situ method for producing the biodegradable composite is also claimed. However, such a document does not consider the process of preparing the natural material to be used as a filler, which is of importance for the final characteristics exhibited by the biocomposite.

Patent document <CIT> claims a compound, comprising a coated reinforcing biofiber and a plastic resin, which once molded has a flexural modulus (ASTM D790) of at least <NUM>% more than a compound in which the biofiber is not coated. In this compound the coated biofiber is composed of plastisol and <NUM>-<NUM>% of biofiber. The plastic resin present in the compound is selected from the group consisting of acrylonitrile-butadiene-stirene (ABS), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polybutylene terephthalate (PBT), polymethylmethacrylate (PMMA), stirene-acrylonitrile (San), polyphenylene ether (PPE), polycarbonate (PC), stirene-butadiene-stirene (SBS), acrylic polymers, polyolefins, polymethylmethacrylate (PMMA), polyethyleneterephthalate glycol comonomer (PETG), elastomeric thermoplastic copolyester (COPE) and combinations thereof, and the biofiber comprises vegetable material selected from the group consisting of wood fiber, wood flour, flax, grass fibrils, plant shell fragments, peels fragments, plant pulp, plant peel, seeds of plants, vegetable fibres and combinations thereof. In the claimed compound plastisol, when melted as resin, has a Shore D hardness (ASTM D2240-<NUM> after <NUM> seconds) greater than <NUM>, a tensile strength (ASTM D638) of more than about <NUM> MPa, a percent elongation (ASTM D638) of less than <NUM>%. The document shows how rigid materials can be obtained by adding plastic polymeric resins with suitably treated natural vegetable fillers.

<CIT> discloses compositions for 3D printing comprising a silicone resin and potato starch ether.

The prior art highlights the criticality of the choice of the polymeric component and of the choice and treatment of the natural vegetable filler, in order to obtain a biocomposite with particular characteristics of flexibility and elasticity.

In any case, no printing resin 3D currently available on the market allows to print (with any of the printing techniques 3D available) objects which have the mechanical characteristics required by the models of organs, for example the heart, such as to realistically represent the functions proper to that organ.

The object of the present invention is to overcome the limitations of the prior art by providing a composite product based on polymers suitable for 3D SLA and/or DLP printing, with characteristics of elasticity and flexibility sufficient for the realization of organ models, in particular hearts, realistic for teaching and training of medical personnel or simulation of surgical operations and resisting multiple use cycles, in which the additional component derives from vegetable wastes.

The main object of the present invention is therefore the use of a composition comprising one or more commercially available 3D printing resins, selected from acrylic resins (homo- or co-polymers polyacrylates or mixtures thereof) and silicone resins (or rubbers), mixed with plant material selected from the families of Solenaceae (potatoes, Aubergines, tomatoes, peppers) and the genus Fragaria (strawberries) in a process for the preparation of organ or tissue models. The parts of the plants used are mainly leaves, roots and stems.

Another object of the present invention is the preparation of mock-ups of organs or tissues, for example humans, using the composition of the invention.

This preparation process comprises the following main steps:.

A further object of the present invention are the products thus prepared. Such products can be models of organs or tissues.

The printing techniques 3D used in the first step preferably are.

Other printing techniques, such as FDM, fused deposition modeling (which normally uses filament-shaped polymers), are not used with the resins of the invention, since the characteristics of the material are not suitable and clog the nozzle, thus irreparably damaging it.

Thermoplastic polyurethanes and PLA are not used as 3D printing resins, since:.

The process of the present invention allows to obtain a final product having physical characteristics similar to a product (even of medium size) Completely made of material having Shore A equal to or less than <NUM> and which maintains over time the flexibility and elasticity typical of materials with this Shore. At the same time, however, the final product undertakes a high degree of energy elongation and return and characteristics of impact or stress resistance, typical of materials with Shore A equal to or greater than <NUM> (wiper rubbers).

The molded parts of this material have the appearance and behave like the silicone molded parts, and are strong enough to be used for multiple cycles, even in critical dynamic stress situations, such as prolonged compressive stress, while maintaining their characteristics of elasticity, resolution and compactness over time, without cracks.

In the case of a mock-up (model) of a heart thus produced, it is therefore possible for example to attempt to simulate, with a discrete approximation (with suitable instrumentation and techniques) the phases of the cardiac cycle:.

It is briefly noted here that the Shore scale is designed to test the hardness of elastomers or plastomers, for example rubber or plastic, characterized by reversible deformations. The elastic deformation of the material is measured in terms of the depth of penetration of a movable truncated cone point (Shore type A) which initially protrudes <NUM> from the hole of a plate and is subject to a constant force produced by a spring. By pressing the plate onto the surface of the material to be examined, the penetrator returns toward the inside of the hole of the plate itself in relation to the hardness. The Shore hardness is measured in a scale of from <NUM> to <NUM>, proportional to the linear displacement of the tip, produced during the testing step on the elastic material, with respect to its initial rest position.

The ASTM D2240-<NUM> method contemplates twelve different Shore measurement scales: Type A, B, C, D, DO, E, M, O, <NUM>, <NUM>, OOO-S, AND R. The difference between the scales is in the form/size of the penetrator and in the force applied thereto. In each of the scales the hardness may take values from <NUM> to <NUM>. It is therefore always necessary to specify the hardness value together with the scale to which it refers, for example: hardness <NUM> Shore A, often referred to as 80A more briefly. The most used scales are in fact the A and D, respectively for materials of lower or higher hardness. Although the two scales have some overlap margin, there is no common conversion formula in their ranges, since the two hardnesses obtained with the type A and type D durometers exhibit a correlation strongly dependant on the type of material examined.

The material of vegetable origin, before being mixed with the printing resins 3D, is suitably treated. Preferably, the treatment of the vegetable material comprises the following steps:.

Grinding takes place inside equipments such as grinding wheels (or mills), generally consisting of a grinding chamber inside which mobile grinding elements operate. These grinding elements exert a force on each particle to be ground; as a consequence, the particles can undergo an elastic (or reversible) deformation if, after the application of the force has ceased, they return to the original shape, or a plastic deformation, if they undergo an irreversible deformation. In addition to a certain applied force, for typical load values for each material, the particles are broken. Usually, the individual particles are crushed by following any irregularities or imperfections inside the individual particles.

The blade crusher is essentially formed by a grinding chamber, in which a horizontal shaft, to which blades are fixed, rotates. Below the chamber there is an interchangeable perforated grid. As the shaft rotates, the blades force the material against the grid by crushing it. All smaller pieces of the grid holes pass to an underlying collector (single pass).

The hammer mill consists of a cylindrical chamber and a central axis with <NUM>-<NUM> stainless steel articulated hammers. In the lower part of the mill there is an interchangeable grid which makes the ground material come out. When the axle rotates the hammers, due to the centrifugal force, they are arranged radially and grind the material introduced from above. This type of grinding exploits the impact forces and is suitable for grinding dry materials or fibrous materials, but also for wet grinding. In the case of hard and friable products, the particle size can reach up to <NUM>. In the case of the present invention, a single passage is realized, to reach particle diameters of about <NUM>.

The vertical elliptical chamber micronizing mill consists of a vertical elliptical chamber inside which the air or generally the gas enters under pressure (<NUM>-<NUM>/cm<NUM>) through a series of nozzles located in the lower part. The material to be micronized enters by means of a feeder, is brought to high speed by the fluid and is ground; finally, the material in fine powder is made to leave the mill. With this process it is possible to reach about <NUM>-<NUM> microns.

The opposite jet mill operates in a similar manner to the previous one, with the fundamental difference that <NUM> opposing air jets enter the grinding chamber through two nozzles located on the same axis. Two jets collide in the micronization zone, causing the solid particles to collide, which thus break. The feeding takes place from a vibrating hopper, from which the already fine particles are entrained by the air jet. The micronization takes place by self-operation and friction. The particles are then transported into the classifying chamber; the smaller ones are dragged toward the outlet, the others fall into the zone and are re-launched into the micronization zone.

Some (non-limiting) examples of the present invention are given below.

The first experimental tests were carried out in order to understand whether the component of vegetable origin could be added to commercial resins used for printing 3D to give the final molded product the characteristics of greater elasticity, flexibility and resistance to prolonged use.

The material of vegetable origin tested consists of fibers of vegetable origin deriving from the leaves, roots and stems of the following plants: lettuce, rocket, radicchio, beans, pumpkin, courgette, Solenacaee (tomato, aubergine, potato, peppers) and Fragraria (strawberries were selected). These were derived from scraps from aquaponic cultures.

The tests were carried out initially by preparing mixtures of plant components deriving from different plants.

The first tests were carried out using random mixtures of vegetable wastes, which had not been selected and divided. Subsequently it was decided to select (in Example <NUM>) the individual plant varieties.

It was observed that this approach did not lead to significant improvements with respect to the characteristics of the starting 3D printing resins. First of all, in fact, the main problem was a different density coming from the original resins, combined with a higher density of the material of vegetable origin. The <NUM>%-<NUM>% tested mixtures had always different densities. Probably due to the heterogeneous and always different mix of the vegetable sources used.

The experiment however was important, because it determined that a random mix of plant material does not serve to determine the change in elasticity condition, but it was necessary to select (as then best shown in Example <NUM>) the individual plant varieties.

In a second experiment it was then decided to use the individual varieties of plants in the different parts (leaves, roots, drums) by varying the percentages of these individual parts inside the material of vegetable origin. Mixtures with a particle size of <NUM> microns were obtained.

Commercial 3D printing resins having a low hardness (lowest possible Shore A) have been selected for testing. In fact, the density of the resins is increased with lower Shore A, allowing to improve the general densitometry of the final compound.

Some results obtained using different plant components added to some of the most common 3D printing resins of the DLP and SLA type are reported below. In the former, UV sources are used to carry out the polymerization. Instead, laser sources are used in SLAs to obtain polymerization. These results are reported in Tables <NUM>, <NUM> and <NUM>.

This experiment was useful not only to better understand which plant products were the best to use (Solenaceae and Fragraria), but it showed that the best plant material is that composed of: <NUM>% leaves, <NUM>% stems and <NUM>% roots.

In a third experiment only those deriving from Solenaceae and Fragraria were used as components of plant origin, in particular with derivatives of tomato, pepper and strawberry plants.

Moreover, the process of obtaining the material of vegetable origin and its micronization was improved, reaching a product with particle size below <NUM> microns. This result has led to a marked improvement in the component of plant origin, which has led to better results in terms of strength and elasticity.

A process was then carried out comprising the following steps:.

Once micronized, the material is added to the printing resin 3D, at predetermined concentrations, as reported in Tables <NUM> and <NUM>.

The results obtained with mixtures containing components of vegetable origin at <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% and <NUM>% (by weight) are reported below.

It is recalled that the plant material was composed of: <NUM>% Solenaceae (<NUM>% leaves, <NUM>% stems, <NUM>% roots) and <NUM>% Fragraria (<NUM>% leaves, <NUM>% stems), <NUM>% roots).

Although under the best conditions (SLA resin with SHORE A <NUM>) and material of vegetable origin at <NUM>% it was found that the resistance and elasticity properties conferred to the realized mockups, they retained their characteristics for no more than <NUM> days and then gradually lost their elasticity, reaching values similar to the standard resin as such, after about <NUM> days of exposure to light and air.

In the course of this third test set, it has been recognized, in a random manner, that by percolating the composition of the invention over a structure (racks) made of the standard resin as such, the elasticity properties were stored for more than <NUM> days.

In this experiment, shelves made with a honeycomb shape of about <NUM> microns in diameter with the 3D standard SHORE A <NUM> printing resin were used, on which a composition, composed of silicone rubber (distributed by Resin Srl of La Spezia) is percolated with a Shore A <NUM> or Shore A <NUM>. These silicone rubbers must be activated with a suitable catalyst containing dimethylbis((<NUM>-oxoneodecyl)oxy)stannane, ethyl silicate, ethyl polysilicate.

The scaffold thus produced was then left in the laminar chamber sucked, under UV lamp, for about <NUM> minutes.

In this case, mixtures were carried out with different percentages of silicone rubber, catalyst and material of vegetable origin.

The main characteristic of this compound is to polymerize directly, without the need for UV or laser sources, given the presence of a catalyzing agent acting at room temperature. The results obtained with such compositions are reported in Table <NUM>.

In the best conditions (3D molded shelves with SLA SHORE <NUM> resin and percolated with <NUM>% SHORE A <NUM> silicone rubber, <NUM>% vegetable material and <NUM>% catalyst) the elasticity and strength capacities are improved by <NUM>% compared to a normal mock-ups molded with SLA SHORE a <NUM> resin. In practice, it is as if the mock-up had a elasticity with SHORE a <NUM>, while maintaining a better resistance and wear over time than the standard one.

Moreover, these characteristics are maintained for <NUM> weeks, after which a loss of elasticity equal to <NUM>% occurs.

In this experiment an SLA resin of the acrylic type was used with SHORE A equal to <NUM> (elastic resin SHORE <NUM> of Formlabs), which has the following characteristics: SHORE A hardness: <NUM>; elongation at break % <NUM>; tensile strength (MPa) <NUM>; tear strength (kn/m) <NUM>.

The experiments were carried out in order to be able to realize the honeycomb shelving with different types of printers (Formlabs, Wanhao, Anycubic), reducing the honeycomb structure to <NUM> microns.

Tests were then carried out using various mixtures having the following compositions:.

The results obtained are further improved and are reported in the following Table <NUM>.

It is noted that, under the best conditions obtainable, the obtained mock-up maintains a <NUM>% elasticity higher than the printing 3D as such, i.e. as if it had an elasticity and flexibility of a molded article with a hypothetical SHORE a <NUM> resin, but with a capacity not to break once subjected to several cycles of insertion and circulation of fluids equal to a mock-up made with resins at SHORE A <NUM>.

Claim 1:
Use of a composition comprising one or more commercially available resins for 3D printing, selected from the acrylic resins, optionally homo- or co-polymers polyacrylates or their mixtures thereof, and silicone resins, mixed with material of plant origin selected in the families of the Solenaceae, optionally potatoes, eggplant, tomatoes, peppers and in the genus of Fragaria, optionally strawberries, in a process for the preparation of organ or tissue models.