Patent Publication Number: US-2020289809-A1

Title: Functional member and method of fabricating the same

Description:
BAKGROUND 
     The present disclosure relates to a functional member and a method of fabricating the functional member. 
     Studies have been made on functional members including a plurality of microneedles that are tiny needle-like protrusions formed on a surface of the functional members for use in various applications making use of, for example, the water repellent properties on the surface and for use in medical nanopatches. A method of fabricating microneedles is disclosed (Japanese Laid-open Patent Publication No. 2008-246492), in which ablation processing is performed on a glass substrate by irradiating the glass substrate with, for example, a femtosecond laser beam to form a master mold having a plurality of needle-like depressions, and the patterns of the needle-like depressions are transferred to a resin to form a secondary mold having needle-like protrusions, and then a tertiary mold is formed to finally fabricate needles made of resin. 
     SUMMARY 
     There is a need for providing a functional member including a plurality of microneedles on a surface with more freedom of size, and a method of fabricating the functional member in an easier way. 
     According to an embodiment, a functional member includes: a plurality of microneedles on a surface. Further, the microneedles adjacent to each other are spaced apart by a pitch ranging from 1 to 500 μm, and the microneedles have a diameter ranging from 0.25 to 250 μm and have a height ranging from 5 to 200 μm. 
     According to an embodiment, a method of fabricating a functional member made of metal and including a plurality of microneedles on a surface includes: emitting a laser beam on a surface of a raw member and performing scanning with the laser beam in a first direction at a pitch d. 
     Further, the microneedles are spaced apart by a pitch ranging from 1 to 500 μm, and the microneedles have a diameter ranging from 0.25 to 250 μm and have a height ranging from 5 to 200 μm, and a spot size radius of the laser beam is indicated as ω, and a parameter Δ relative to ω is set to satisfy 0&lt;Δ&lt;2ω, and the pitch d is set to satisfy d&lt;2ω+Δ. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a functional member according to an embodiment; 
         FIG. 2  is a diagram illustrating a microphotograph of a surface of the functional member illustrated in  FIG. 1 ; 
         FIG. 3  is an enlarged view of tips of microneedles illustrated in  FIG. 2 ; 
         FIG. 4  is a schematic sectional view of a surface and the vicinity of the surface of the functional member illustrated in  FIG. 1 ; 
         FIG. 5  is a diagram illustrating an example method of fabricating the functional member illustrated in  FIG. 1 ; 
         FIG. 6  is a diagram illustrating how to form microneedles; 
         FIG. 7  is a diagram illustrating an example scanning pattern of sub-laser beams; 
         FIG. 8  is a diagram illustrating another example scanning pattern of the sub-laser beams; and 
         FIG. 9  is a diagram illustrating an example method of fabricating a functional member made of resin. 
     
    
    
     DETAILED DESCRIPTION 
     The method disclosed in Japanese Laid-open Patent Publication No. 2008-246492 implements femtosecond laser ablation, and thus, the size of the needle-like depressions and the resulting needles is restricted to the spot size of the femtosecond laser beam. In addition, molds are formed in a plurality of processes before a final product is produced, thereby complicating the manufacturing process. 
     The following describes an embodiment of the present disclosure with reference to the accompanying drawings. The embodiment is not intended to limit the scope of the present disclosure. Same reference signs are given to the same or corresponding elements in the drawings. The drawings are illustrated schematically and thus it should be noted that, for example, the relation between dimensions of the elements and the ratio of the elements may differ from the actual ones. Dimensional relation or ratio of elements may differ between the drawings. 
     Embodiment 
       FIG. 1  is a schematic diagram of a functional member according to an embodiment. This functional member  1  is made of metal. In the present embodiment, the functional member  1  is made of stainless steel, but the functional member  1  may be made of other types of metal such as aluminum metal. The shape of the functional member  1  is, but not limited to, a plate shape in the present embodiment. 
     A plurality of microneedles are formed on a surface la of the functional member  1 .  FIG. 2  is a diagram illustrating a microphotograph of the surface  1   a  of the functional member  1 .  FIG. 2  includes a scale for indicating the size, and the value of one division of the scale is 2.0 μm. As illustrated in  FIG. 2 , the surface  1   a  has a plurality of microneedles  1   b . The microneedles  1   b  are arranged in a plurality of rows in the direction indicated by an arrow Ar 1 . 
       FIG. 3  is an enlarged view of tips of the microneedles  1   b .  FIG. 3  includes a scale for indicating the size, and the value of one division of the scale is 0.5 μm. As illustrated in  FIG. 3 , the tips of the microneedles  1   b  have minute indentations and protrusions having a diameter equal to or smaller than 500 nm. 
       FIG. 4  is a schematic sectional view of the surface  1   a  and the vicinity of the surface  1   a  of the functional member  1 . The microneedles  1   b  extend in a height direction from the surface  1   a . Adjacent microneedles  1   b  are spaced apart by a pitch ranging from 1 to 500 μm. The pitch between the adjacent microneedles  1   b  is a pitch between the tips of the adjacent microneedles  1   b . The microneedles  1   b  each have a diameter ranging from 0.25 to 250 μm. The diameter of the microneedles  1   b  is a mean value of the diameters from a diameter close to the surface  1   a  to a diameter at the tip of the microneedles  1   b . When the microneedles  1   b  have a cross-section other than a circle, the diameter of a circle having the same area of this cross-section is used as the diameter of the cross-section. The microneedles  1   b  have a height ranging from 5 to 200 μm from the surface  1   a.    
     The microneedles  1   b  have a bent shape. For example, the microneedles  1   b  extend from the surface  1   a  such that the microneedles  1   b  cross an imaginary straight-line  1  perpendicular to the surface  1   a  and extend without crossing the straight-line  1  and then cross the straight-line  1  again. The outer shape of the microneedles  1   b  is, for example, a substantial upright cone with a base on the surface  1   a  and having a dent on a part of the outer circumferential surface. Examples of the cone include a right circular cone and an oblique circular cone. 
     A microhole  1   c  is formed on the surface  1   a  between the microneedles  1   b  (see  FIG. 2 ). The microhole  1   c  has an inner diameter corresponding to, for example, the diameter of the microneedles  1   b . For example, the microhole  1   c  is formed at substantially the middle between two adjacent microneedles  1   b . The inner diameter of the microhole  1   c  is an inner diameter of the microhole  1   c  at the edge of the surface  1   a.    
     The functional member  1  includes a plurality of microneedles  1   b  with much freedom of size, and the microneedles  1   b  having various sizes are formed on the surface  1   a . This structure provides a higher water repellency. When the functional member  1  is used as a junction member having a function of contacting and joining, for example, resin, the microneedles  1   b  provide increased anchoring properties and increased adhesiveness, thereby increasing bonding properties. When the functional member  1  is used as a catalyst retention member, the microneedles  1   b  provide increased catalyst absorption properties, thereby increasing catalyst retainability. In particular, since the functional member  1  has bent microneedles  1   b , such microneedles  1   b  further increase water repellency, bonding properties, and catalyst retainability. 
     Fabrication Method 
     Described next is an example method of fabricating the functional member  1  with reference to  FIGS. 5 and 6 . A fabrication apparatus  100  for implementing this fabrication method includes a laser device  101 , a galvanometer scanner  102 , a diffractive optical element  103 , and an fθ lens  104 . A raw member  2  is a member to be processed to fabricate the functional member  1 , and is a plate member made of stainless steel. 
     The laser device  101  includes a laser light source such as an optical fiber laser and emits, for example, a laser beam L that is a subnanosecond to nanosecond pulsed laser beam having a pulse width ranging from 0.1 to 999 nanoseconds. Using the subnanosecond to nanosecond pulsed laser beam can increase the scanning speed (processing speed) compared to using a femtosecond pulsed laser beam. This configuration can increase manufacturability of the functional member  1 . 
     The galvanometer scanner  102  includes galvanometer mirrors  102   a,    102   b  each rotated by an electric motor. The laser beam L emitted by the laser device  101  is reflected from the rotating galvanometer mirrors  102   a,    102   b  to use the laser beam L for scanning. 
     The diffractive optical element  103  splits the laser beam L into N sub-laser beams, where N is an integer equal to or larger than two. In this fabrication method, the diffractive optical element  103  splits the laser beam L into three sub-laser beams L 1 , L 2 , L 3 . 
     The fθ lens  104  focuses the laser beam, which is used for equiangular scanning by the galvanometer scanner  102 , on a certain plane and scans the plane at an equal speed. The certain plane is set to be coincident with a surface  2   a  of the raw member  2  placed on a stage (not illustrated). Thus, the sub-laser beams L 1 , L 2 , L 3  are emitted for scanning while being focused on the surface  2   a  of the raw member  2  by the fθ lens  104 . Emitting the sub-laser beams L 1 , L 2 , L 3  to the surface  2   a  of the raw member  2  can form the microneedles  1   b  and the inner diameter of the microholes  1   c.    
     In forming the microneedles  1   b  and the microholes  1   c , it is preferred that the raw member  2 , which is a processing target, is irradiated with the laser beam L and processed in an inert gas atmosphere such as nitrogen or argon. This configuration prevents acceleration of process due to oxygen and can stably form the microneedles  1   b  and the microholes  1   c.    
       FIG. 6  is a diagram illustrating how to form the microneedles  1   b . As illustrated in  FIG. 6 , the sub-laser beams L 1 , L 2  are emitted to the surface  2   a  of the raw member  2 , and the galvanometer scanner  102  performs scanning with the sub-laser beams L 1 , L 2  in a first direction (indicated by an arrow Ar 2 ) with a pitch d therebetween. The sub-laser beam L 3  is used for scanning in the first direction with the pitch d from the sub-laser beam L 2 , but for ease of description, the sub-laser beam L 3  is omitted from the illustration and from the description as appropriate. 
     Let the spot size radius of respective beam spots BS 1 , BS 2  of the sub-laser beams L 1 , L 2  on the surface  2   a  be ω. In this case, a parameter Δ relative to ω is set to satisfy 0&lt;Δ&lt;2ω, and the pitch d is set to satisfy d&lt;2ω+Δ. Scanning the raw member  2  with the sub-laser beams L 1 , L 2  melts and removes the material of the raw member  2  in certain ranges from the respective centers of the beam spots BS 1 , BS 2  of the sub-laser beams L 1 , L 2 , but the material of the raw member  2  in a region between the sub-laser beams L 1 , L 2  remains and becomes a row of microneedles  1   b . In the same manner, another row of microneedles  1   b  is formed in a region between the sub-laser beams L 2 , L 3 . The row of microneedles  1   b  formed by the sub-laser beams L 1 , L 2  and the row of microneedles  1   b  formed by the sub-laser beams L 2 , L 3  are spaced apart at about the pitch d. 
     The diameter of the microneedles  1   b  can be adjusted by adjusting at least one of the pitch d, the spot size radius ω, Δ, the fluence of the laser beam L or the sub-laser beams L 1 , L 2 , L 3 , the scanning speed, and the processing atmospheric gas. It is desirable that Δ is set appropriately in forming the rows of microneedles  1   b . It is preferred that the scanning speed has a certain low value such as 20 m/s or lower. The pitch d is, for example, 10 μm, and the spot size radius ω is, for example, 10 μm. In particular, it is preferred that the diameter of the microneedles  1   b  is adjusted by adjusting the pitch d and the spot size radius ω. 
     In the first scan, the sub-laser beams L 1 , L 2 , L 3  are used for scanning in the first direction from a first end of a range to be formed with the microneedles  1   b  to a second end opposite to the first end, at which the first scan ends and then the process proceeds to the second scan. In the second scan, the sub-laser beams L 1 , L 2 , L 3  are used for scanning from an irradiation start position at the first end. This irradiation start position is shifted from the irradiation position of the first scan in a direction orthogonal to the first direction, and the sub-laser beams L 1 , L 2 , L 3  are used for scanning in the first direction. In the third scan and after, the sub-laser beams L 1 , L 2 , L 3  are used for scanning only in the first direction in the same manner as described above, and many microneedles  1   b  are formed in a desirable range. The functional member  1  can be fabricated in this manner. 
     The process of splitting the laser beam L into the sub-laser beams L 1 , L 2 , L 3  and performing scanning with the sub-laser beams to form the microneedles  1   b  can reduce the takt time to about one-third compared to the takt time of a case using the laser beam L to form the microneedles lb. 
       FIG. 7  is a diagram illustrating an example scanning pattern of the sub-laser beams L 1 , L 2 , L 3 .  FIG. 7  illustrates a scanning pattern seen in a direction perpendicular to the surface  2   a  of the raw member  2 . When the number of sub-laser beams is N and the respective N sub-laser beams are spaced apart at a pitch D, and when a certain sub-laser beam of the N sub-laser beams is used for scanning at a scan pitch I, the scanning pattern satisfies I=N*D. 
     Specifically, N is three in  FIG. 7 . In a first scan S 1 , the sub-laser beams L 1 , L 2 , L 3  are used for scanning while being spaced apart at a pitch D=d. In a subsequent second scan S 2 , the sub-laser beam L 1  in the second scan is used for scanning at a scan pitch I=3d from the sub-laser beam L 1  in the first scan. In the same manner, in a third scan S 3 , the sub-laser beam L 1  in the third scan is used for scanning at the scan pitch I=3d from the sub-laser beam L 1  in the second scan. The sub-laser beams L 2 , L 3  are also used for scanning at the scan pitch I=3d. In this regard, the sub-laser beams L 1 , L 2 , L 3  are used for scanning at the equal pitch d. 
       FIG. 8  is a diagram illustrating another example scanning pattern of the sub-laser beams L 1 , L 2 , L 3 .  FIG. 8  illustrates a scanning pattern seen in a direction perpendicular to the surface  2   a  of the raw member  2 . When the number of sub-laser beams is N and the respective N sub-laser beams are spaced apart at a pitch D, and when a certain sub-laser beam of the N sub-laser beams is used for scanning at a scan pitch I, the scanning pattern satisfies I=1/N*D. 
     Specifically, N is three in  FIG. 8 . In the first scan S 1 , the sub-laser beams L 1 , L 2 , L 3  are used for scanning while being spaced apart at a pitch D=d. In the subsequent second scan S 2 , the sub-laser beam L 1  in the second scan is used for scanning at a scan pitch I=⅓*d from the sub-laser beam L 1  in the first scan. In the same manner, in the third scan S 3 , the sub-laser beam L 1  in the third scan is used for scanning at the scan pitch I=⅓*d from the sub-laser beam L 1  in the second scan. The sub-laser beams L 2 , L 3  are also used for scanning at the scan pitch I=⅓*d. In this regard, the sub-laser beams L 1 , L 2 , L 3  are used for scanning at the equal pitch of I=⅓*d. The pitch I in this case corresponds to the pitch d. 
     N is three in  FIGS. 7 and 8 . When N is an integer equal to or larger than two and I=N*D or I=1/N*D is satisfied, N sub-laser beams can be used for scanning at an equal pitch. When the laser beam L is not split into sub-laser beams, N is set to one and both I=N*D and I=1/N*D are satisfied. In this case, the laser beam L is used for scanning at a pitch D or I. When N is equal to or larger than two, the takt time can be reduced to, for example, about one-Nth. 
     Using the functional member  1  fabricated by the fabrication method described above as a mold and transferring the microneedles  1   b  onto resin can fabricate a resin functional member including a plurality of microneedles on a surface. 
       FIG. 9  is a diagram illustrating an example method of fabricating a functional member made of resin. First, the functional member  1  including a plurality of microneedles  1   b  on the surface  1   a  is prepared as a mold and a resin  3  such as thermosetting resin is applied to the surface  1   a , and the resin  3  is cured and then removed from the functional member  1 . In this process, a functional member  4  made of resin having a plurality of microholes  4   b  on a surface  4   a  is fabricated. The microholes  4   b  have a shape transferred from the shape of the microneedles  1   b.    
     Subsequently, the functional member  4  is used as a mold and a resin  5  such as thermosetting resin is applied to the surface  4   a,  and the resin  5  is cured and then removed from the functional member  4 . In this process, a functional member  6  made of resin including a plurality of microneedles  6   b  on a surface  6 a is fabricated. The microholes  6   b  have a shape transferred from the shape of the microneedles  1   b  of the functional member  1 . 
     The embodiment above is not intended to limit the scope of the present disclosure. Combinations, as appropriate, of the constituent elements described above are also included in the scope of the present disclosure. Further effects and modifications can be easily derived by those skilled in the art. Accordingly, broader embodiments of the present disclosure are not limited to the embodiment above and various modifications may be made. 
     INDUSTRIAL APPLICABILITY 
     As described above, the functional member and the method of fabricating the functional member according to the present disclosure are suitable for use in various applications using, for example, water repellent properties of the functional member and for use in medical nanopatches. 
     REFERENCE SIGNS LIST 
     According to the present disclosure, a functional member including a plurality of microneedles on a surface with more freedom of size can be achieved more easily. 
     Although the disclosure has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.