Patent Publication Number: US-9420783-B2

Title: Making imprinted particle structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned co-pending U.S. patent application Ser. No. 14/526,595, filed Oct. 29, 2014, entitled Imprinted Multi-layer Structure, by Cok et al, to commonly-assigned U.S. patent application Ser. No. 14/526,603 (U.S. Pat. No. 9,186,698), filed Oct. 29, 2014, entitled Making Imprinted Multi-layer Structure, by Cok et al, to commonly-assigned co-pending U.S. patent application Ser. No. 14/526,611, filed Oct. 29, 2014, entitled Imprinted Multi-layer Biocidal Particle Structure, by Cok et al, to commonly-assigned co-pending U.S. patent application Ser. No. 14/526,619, filed Oct. 29, 2014, entitled Making Imprinted Multi-layer Biocidal Particle Structure, by Cok et al, to commonly-assigned co-pending U.S. patent application Ser. No. 14/526,640, filed Oct. 29, 2014, entitled Using Imprinted Multi-layer Biocidal Particle Structure, by Cok et al, to commonly-assigned co-pending U.S. patent application Ser. No. 14/526,646, filed Oct. 29, 2014, entitled Imprinted Particle Structure, by Cok et al, to commonly-assigned co-pending U.S. patent application Ser. No. 14/526,691, filed Oct. 29, 2014, entitled Using Imprinted Particle Structure, by Cok et al, and to commonly-assigned co pending U.S. patent application Ser. No. 14/519,451, filed Oct. 21, 2014, entitled Making Colored Biocidal Multi-Layer Structure, by Scheible et al, the disclosures of which are incorporated herein. 
     FIELD OF THE INVENTION 
     The present invention relates to biocidal layers having antimicrobial efficacy on a surface. 
     BACKGROUND OF THE INVENTION 
     Widespread attention has been focused in recent years on the consequences of bacterial and fungal contamination contracted by contact with common surfaces and objects. Some noteworthy examples include the sometimes fatal outcome from food poisoning due to the presence of particular strains of  Escherichia coli  in undercooked beef;  Salmonella  contamination in undercooked and unwashed poultry food products; as well as illnesses and skin irritations due to  Staphylococcus aureus  and other micro-organisms. Anthrax is an acute infectious disease caused by the spore-forming bacterium  bacillus anthracis . Allergic reactions to molds and yeasts are a major concern to many consumers and insurance companies alike. In addition, significant fear has arisen in regard to the development of antibiotic-resistant strains of bacteria, such as methicillin-resistant  Staphylococcus aureus  (MRSA) and vancomycin-resistant  Enterococcus  (VRE). The U.S. Centers for Disease Control and Prevention estimates that 10% of patients contract additional diseases during their hospital stay and that the total deaths resulting from these nosocomially-contracted illnesses exceeds those suffered from vehicular traffic accidents and homicides. In response to these concerns, manufacturers have begun incorporating antimicrobial agents into materials used to produce objects for commercial, institutional, residential, and personal use. 
     Noble metal ions such as silver and gold ions are known for their antimicrobial properties and have been used in medical care for many years to prevent and treat infection. In recent years, this technology has been applied to consumer products to prevent the transmission of infectious disease and to kill harmful bacteria such as  Staphylococcus aureus  and  Salmonella . In common practice, noble metals, metal ions, metal salts, or compounds containing metal ions having antimicrobial properties can be applied to surfaces to impart an antimicrobial property to the surface. If, or when, the surface is inoculated with harmful microbes, the antimicrobial metal ions or metal complexes, if present in effective concentrations, will slow or even prevent altogether the growth of those microbes. Recently, silver sulfate, Ag 2 SO 4 , described in U.S. Pat. No. 7,579,396, U.S. Patent Application Publication 2008/0242794, U.S. Patent Application Publication 2009/0291147, U.S. Patent Application Publication 2010/0093851, and U.S. Patent Application Publication 2010/0160486 has been shown to provide efficacious antimicrobial protection in polymer composites. The United States Environmental Protection Agency (EPA) evaluated silver sulfate as a biocide and registered its use as part of EPA Reg. No, 59441-8 EPA EST. NO. 59441-NY-001. In granting that registration, the EPA determined that silver sulfate was safe and effective in providing antibacterial and antifungal protection. 
     Antimicrobial activity is not limited to noble metals but is also observed in other metals such as copper and organic materials such as triclosan, and some polymeric materials. 
     It is important that the antimicrobial active element, molecule, or compound be present on the surface of the article at a concentration sufficient to inhibit microbial growth. This concentration, for a particular antimicrobial agent and bacterium, is often referred to as the minimum inhibitory concentration (MIC). It is also important that the antimicrobial agent be present on the surface of the article at a concentration significantly below that which can be harmful to the user of the article. This prevents harmful side effects of the article and decreases the risk to the user, while providing the benefit of reducing microbial contamination. There is a problem in that the rate of release of antimicrobial ions from antimicrobial films can be too facile, such that the antimicrobial article can quickly be depleted of antimicrobial active materials and become inert or non-functional. Depletion results from rapid diffusion of the active materials into the biological environment with which they are in contact, for example, water soluble biocides exposed to aqueous or humid environments. It is desirable that the rate of release of the antimicrobial ions or molecules be controlled such that the concentration of antimicrobials remains above the MIC. The concentration should remain there over the duration of use of the antimicrobial article. The desired rate of exchange of the antimicrobial can depend upon a number of factors including the identity of the antimicrobial metal ion, the specific microbe to be targeted, and the intended use and duration of use of the antimicrobial article. 
     Antimicrobial coatings are known in the prior art, for example as described in U.S. Patent Application Publication No. 2010/0034900. This disclosure teaches a method of coating a substrate with biocide particles dispersed into a coating so that the particles are in contact with the environment. Non-planar coatings are also known to provide surface topographies for non-toxic bio-adhesion control, for example as disclosed in U.S. Pat. No. 7,143,709. 
     Imprinting methods useful for forming surface topographies are taught in CN102063951. As discussed in CN102063951, a pattern of micro-channels are formed in a substrate using an embossing technique. Embossing methods are generally known in the prior art and typically include coating a curable liquid, such as a polymer, onto a rigid substrate. A pattern of micro-channels is embossed (impressed or imprinted) onto the polymer layer by a master having an inverted pattern of structures formed on its surface. The polymer is then cured. 
     Fabrics or materials incorporating biocidal elements are known in the art and commercially available. U.S. Pat. No. 5,662,991 describes a biocidal fabric with a pattern of biocidal beads. U.S. Pat. No. 5,980,620 discloses a means of inhibiting bacterial growth on a coated substrate comprising a substantially dry powder coating containing a biocide. U.S. Pat. No. 6,437,021 teaches a water-insoluble polymeric support containing a biocide. Methods for depositing thin silver-comprising films on non-conducting substrates are taught in U.S. Patent Application Publication No. 2014/0170298. 
     SUMMARY OF THE INVENTION 
     The efficacy of antimicrobial coatings and materials depend at least in part on their structure and surface area. The cost of the coatings also depends upon the quantity of materials in the coatings. There is a need, therefore, for antimicrobial coatings with improved efficacy and reduced costs. 
     In accordance with the present invention, a method of making an multi-layer biocidal structure includes: 
     providing a support; 
     locating a first curable layer on the support; 
     locating a second layer on or over the first curable layer, the second layer having multiple biocidal particles located within the second layer; 
     imprinting the first curable layer and the second layer in a single step with an imprinting stamp having a structure with a depth greater than the thickness of the second layer; 
     curing the first curable layer to form a first cured layer with a second layer; and 
     removing the imprinting stamp. 
     The present invention provides a biocidal multi-layer structure that provides improved antimicrobial properties with thinner layers having increased surface area made in a cost-efficient process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used to designate identical features that are common to the figures, and wherein: 
         FIG. 1  is a cross section of a multi-layer structure illustrating an embodiment of the present invention; 
         FIGS. 2A and 2B  are cross sections of multi-layer structures in other embodiments of the present invention; 
         FIG. 3  is a cross section of a multi-layer structure including particles in an embodiment of the present invention; 
         FIGS. 4A-4F  are cross sections of sequential construction steps useful in a method of the present invention; 
         FIGS. 5A-5F  are cross sections of sequential construction steps useful in another method of the present invention; 
         FIGS. 6A-6D  are cross sections of sequential construction steps useful in yet another method of the present invention; 
         FIG. 7  is a flow diagram illustrating a method of the present invention; 
         FIGS. 8A and 8B  are flow diagrams illustrating alternative methods of the present invention; and 
         FIG. 9  is a flow diagram illustrating another method of the present invention. 
     
    
    
     The Figures are not drawn to scale since the variation in size of various elements in the Figures is too great to permit depiction to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a multi-layer structure useful in forming an antimicrobial article on a support. Multi-layer structures of the present invention provide improved antimicrobial properties with thinner layers having increased surface area made in a cost-efficient process. In useful methods of the present invention, multiple uncured coatings are formed on a support, imprinted together, and then cured together. A thin top layer can include reduced quantities of antimicrobial materials or antimicrobial particles. The imprinted layers provide a greater surface area for the antimicrobial materials and a topographical structure that inhibits the growth and reproduction of microbes. Coating and imprinting processes provide a cost-efficient manufacturing method. 
     Referring to  FIG. 1 , in an embodiment of the present invention, an imprinted multi-layer structure  5  includes a support  30  having a support thickness  36 . A bi-layer  7  having a topographical structure is located on or over the support  30 . The structured bi-layer  7  includes a first cured layer  10  including a first cross-linked material on or over the support  30  and a second cured layer  20  including a second material different from the first material on or over the first cured layer  10  on a side of the first cured layer  10  opposite the support  30 . The first cured layer  10  has a first cured layer thickness  16  and the second cured layer  20  has a second-layer thickness  26 . Indentations  80  are located in the first and second cured layers  10 ,  20  to form a topographical structure with a depth  46 . The first material of the first cured layer  10  is cross-linked to the second material of the second cured layer  20  and the depth  46  of the bi-layer  7  structure is greater than the second-layer thickness  26  of the second cured layer  20 . Coating or other deposition methods for forming multiple layers on a substrate are known in the art, as are imprinting methods useful for forming the indentations  80  in the first and second cured layers  10 ,  20 . 
     In an embodiment, the second cured layer  20  is thinner than the first cured layer  10 . As shown in  FIG. 1 , the first cured layer  10  has portions with the first-layer thickness  16  that are thicker than the second-layer thickness  26 . 
     As used herein, a structured layer is a layer that is not smooth or not planar on a microscopic scale corresponding to the magnitude of the indentations  80 . For example if the support  30  is planar, a structured layer formed on the support  30  according to the present invention is flat but non-planar and is not smooth. If the support  30  is not planar but is smooth, for example having a surface that is curved in one or more dimensions (such as a spherical section), a structured layer formed on the support  30  according to the present invention is also non-planar but is not smooth. Whether or not the support  30  is planar, the structured layer can include indentations  80 , channels, pits, holes, extended portions, mesas or other physical elements or structures. In one embodiment, the surface is rough. The structure depth  46  of the structured bi-layer  7  is the distance from the portion of the structured bi-layer  7  furthest from the support  30  to the portion of the structured bi-layer  7  that is closest to the support  30  in a direction that is orthogonal to a surface of the support  30 . 
     In an embodiment, the first cured layer  10  is located on or over the support  30 . The support  30  is any layer that is capable of supporting the first and second cured layers  10 ,  20  and in different embodiments is rigid, flexible, or transparent and, for example is a substrate made of glass, plastic, paper, or vinyl or combinations of such materials or other materials. In an embodiment, the first cured layer  10  is cross linked to the second cured layer  20  to provide rigidity and improved strength for the layers. 
     In a useful arrangement, the support  30  is adhered, for example with an adhesive layer  50  such as a pressure-sensitive adhesive or glue such as wall-paper glue, to a surface  8  of a structure  40 . The surface  8  is any surface  8 , planar or non-planar that is desired to resist the growth of biologically undesirable organisms, including microbes, bacteria, or fungi. In various applications, the structure  40  is a structure such as a wall, floor, table top, door, handle, cover, device, or any structure  40  having the surface  8  likely to come into contact with a human. The imprinted multi-layer structure  5  can form a wall paper or plastic wrap for structures  40 . 
     In an embodiment of the present invention, the second cured layer  20  includes a second material that is different from the first cross-linked material in the first cured layer  10 . In another embodiment of the present invention, the second material includes a second cross-linked material that is the same as the first cross-linked material. In this embodiment, either the first cross-linked material includes a third material that is not in the second cross-linked material or the second cross-linked material includes a third material that is not in the first cross-linked material. Therefore, the first cross-linked material and second material are different or include different materials. 
     In one embodiment, the second cured layer  20  is electrically conductive and the first cured layer  10  is electrically insulating. Electrically conductive materials, for example polyethyldioxythiophene (PEDOT) are known in the art, as are insulating polymers or resins. In an embodiment, the second cured layer  20  is electrically conductive. 
     Referring to  FIG. 2A , in another embodiment the second cured layer  20  ( FIG. 1 ) is chemically patterned to form a patterned second cured layer  21  that has conductive portions  21   a  and non-conductive portions  21   b . Materials and methods for pattern-wise inhibiting the electrical conductivity of PEDOT are known. By patterning such inhibiting chemicals over the extent of the second cured layer  20  ( FIG. 1 ), the electrical conductivity of the second cured layer  20  is likewise patterned to form the patterned second cured layer  21  with conductive portions  21   a  and non-conductive portions  21   b.    
     As shown in  FIG. 2A  in a further embodiment, a binder primer  52  is located between the first cured layer  10  and the support  30 . The binder primer  52  can be an adhesive layer  50  that adheres the first cured layer  10  to the support  30 . Alternatively, or in addition, the binder primer  52  can form a support surface on which the first cured layer  10  is readily coated, for example by controlling the surface energy of the support surface or the first cured layer  10 . In another embodiment not shown in  FIG. 1 or 2 , the binder primer  52  or the adhesive  50  is located between the first cured layer  10  and the second cured layer  20  or the patterned second cured layer  21  to adhere the first cured layer  10  and the second cured layers  20  or the patterned second cured layer  21  together and enable the second cured layer  20  or the patterned second cured layer  21  to be coated over the first cured layer  10  before the first cured layer  10  and the second cured layer  20  or the patterned second cured layer  21  are imprinted to form the indentations  80  of the bi-layer  7  and the imprinted multi-layer structure  5 . 
     In a useful arrangement illustrated in  FIG. 2B , the indentations  80  of the bi-layer  7  contain a third cured material  42 , for example electrically conductive material that forms an electrical conductor. In an embodiment, such an electrically conductive third cured material  42  is formed by coating a liquid conductive ink, for example containing metallic nano-particles, over the surface of the structured bi-layer  7 , removing the conductive ink from surface portions of the structured bi-layer  7  leaving remaining conductive ink in the indentations  80 , and curing the liquid conductive ink to form electrical conductors. Suitable liquid conductive inks are known in the art and are electrically conductive after curing. In another embodiment, the conductivity of the third cured material  42  is greater than the conductivity of the second cured layer  20  or the patterned second cured layer  21 . 
     A combination of the electrically conductive third cured material  42  and the patterned second cured layer  21  with conductive portions  21   a  and non-conductive portions  21   b  can form an electrical circuit or patterned conductor. The electrical circuit can electrically connect separated electrical conductors in the indentations  80  or can include separate circuits in the indentations  80  and the patterned second cured layer  21 . The electrical circuit can connect electronic computing devices such as integrated circuits (not shown). 
     Referring to  FIG. 3  in another useful embodiment of the imprinted multi-layer structure  5  having the bi-layer  7 , the second cured layer  20  ( FIG. 1 ) includes particles  60  that can be biocidal particles  60 , for example that have a silver component, have a sulfur component, have a copper component, are a salt, are a silver sulfate salt or other biocidal particles, or include phosphors to form a biocidal second cured layer  20   a . In an embodiment, the biocidal second cured layer  20   a  has a surface  22  on a side of the biocidal second cured layer  20   a  opposite the first cured layer  10  and support  30  and portions of the particles  60  extend beyond the surface  22  forming exposed particles  62 . The particles  60  can also have a distribution of sizes so that some of the particles  60  are large particles  64  that can, but do not necessarily, extend beyond the surface  22  and are therefore also exposed particles  62 . The particles  60  are located within and between the indentations  80  of the structure bi-layer  7  and include both the large particles  64  and the exposed particles  62 . 
     In this embodiment, the second cured layer  20  ( FIG. 1 ) is a biocidal second cured layer  20   a . By biocidal layer is meant herein any layer that resists the growth of undesirable biological organisms, including microbes, bacteria, or fungi or more generally, eukaryotes, prokaryotes, or viruses. In particular, the biocidal second cured layer  20   a  inhibits the growth, reproduction, or life of infectious micro-organisms that cause illness or death in humans or animals and especially antibiotic-resistant strains of bacteria. The biocidal second cured layer  20   a  is rendered biocidal by including particles  60  such as ionic metals or metal salts in the biocidal second cured layer  20   a . The particles  60  reside in the biocidal second cured layer  20   a . In an embodiment, some of the particles  60  in the biocidal second cured layer  20   a  are exposed particles  62  that extend from the second-layer first side  22  into the environment and can interact with any environmental contaminants or biological organisms in the environment. Exposed particles  62  are thus more likely to be efficacious in destroying microbes. In various embodiments, the particles  60  are silver or copper, are a metal sulfate, have a silver component, are a salt, have a sulfur component, have a copper component, are a silver sulfate salt, or include phosphors. In an embodiment, the biocidal second cured layer  20   a  is thinner than the first cured layer  10  so that the second-layer thickness  26  is less than the first-layer thickness  16 , thus reducing the quantity of particles  60  that are required in the biocidal second cured layer  20   a . In an alternative embodiment, the second-layer thickness  26  is greater than the first-layer thickness  16 . 
     In an embodiment, the particles  60  are coated, for example with the material in the second cured layer  20  ( FIG. 1 ). 
     In other embodiments, the biocidal second cured layer  20   a  has a thickness that is less than at least one diameter of one or more of the particles  60 , has a thickness that is less than a mean diameter of the particles  60 , or has a thickness that is less than the median diameter of the particles  60 . Alternatively, the particles  60  have at least one diameter between 0.05 and 25 microns. In such embodiments, one or more of the particles  60  will be exposed particles  62 . If such exposed particles  62  are biocidal, the exposed particles  62  can inhibit the growth or reproduction of microbes or destroy any microbes on the surface of the biocidal second cured layer  20   a . In yet another arrangement, the biocidal second cured layer  20   a  is greater than or equal to 0.5 microns thick and less than or equal to 20 microns thick or the first cured layer  10  on the support  30  includes particles  60  (not shown in  FIG. 3 ). 
     The indentations  80  form a topographical non-planar layer in the second cured layer  20 , the patterned second cured layer  21 , or the biocidal second cured layer  20   a  that is not smooth and is inhospitable to the growth and reproduction of microbes. In yet another embodiment, the first or second cured layers  10 ,  20 , the patterned second cured layer  21 , or the biocidal second cured layer  20   a  have a hydrophobic surface, for example by providing a roughened surface either by imprinting or by a treatment such as sandblasting or exposure to energetic gases or plasmas. 
     Referring to  FIGS. 4A to 4F  and  FIG. 7 , a method of the present invention includes making the imprinted multi-layer structure  5  having the support  30  ( FIG. 4A ) in step  100  ( FIG. 7 ). A first curable layer  13  including a first material is located on or over the support  30  ( FIG. 4B ) in step  105 . A second curable layer  23  including a second material different from the first material is located on or over the first curable layer  13  in step  110  ( FIG. 4C ) before the first curable layer  13  is cured. The first curable layer  13  and the second curable layer  23  are formed in various ways, including extrusion or coating, for example spin coating, curtain coating, or hopper coating, or other methods known in the art. In other embodiments of the present invention, locating the first curable layer  13  includes laminating a first curable material on or over the support  30  or locating the second curable layer  23  includes laminating a second curable material on or over the first curable layer  13 . 
     The first curable layer  13  and the second curable layer  23  are imprinted in a single step  125  with an imprinting stamp  90  having a structure with a structure depth  46  greater than the second layer thickness  26  of the second curable layer  23  ( FIG. 4D ) and then cured in a single step  130 , for example with heat or radiation  92  to form the first cured layer  10  and the second cured layer  20  ( FIG. 4E ). The imprinting stamp  90  is removed in step  135  to form an imprinted structured bi-layer  7  with a structure depth  46  greater than the second-layer thickness  26  of the second cured layer  20  ( FIG. 4F ) to form the structured bi-layer  7  of the imprinted multi-layer structure  5  of the present invention. 
     An imprinted multi-layer structure  5  having the structured bi-layer  7  of the present invention has been constructed in a method of the present invention using cross-linkable materials such as curable resins (for example using SU8 at suitable viscosities and PEDOT) coated on a glass surface and imprinted using a PDMS stamp to form micro-structures in the bi-layer  7 . Electrically conductive PEDOT layers have been patterned to form circuit or wiring patterns and conductive inks have been located and cured in the micro-channels to form cured conductive wires. 
     Referring further to  FIG. 7  in an embodiment of the present invention, the surface  8  of the structure  40  is identified in step  150 . The surface  8  is a surface which it is desired to keep free of microbes, for example a wall, floor, table top, door, handle, knob, cover, or device surface, especially any surface  8  found in any type of medical institution. In an embodiment, the surface  8  is planar; in another embodiment, the surface  8  is non-planar. In step  155 , an adhesive is located, for example on the surface  8  or on the side of the support  30  opposite the first cured layer  10 , to form the adhesive layer  50 . The support  30  is adhered to the surface  8  in step  160 . In a further embodiment, the support  30 , first cured layer  10 , and second cured layer  20  are heated to shrink the imprinted multi-layer structure  5  on the surface  8  if the surface  8  is non-planar. In an embodiment, the heating step (not shown separately) is also the adhesion step  160  and a separate adhesive layer  50  is not necessary or used. In an embodiment, the second cured layer  20  is thinner than the first cured layer  10 . 
     In another embodiment, referring to  FIG. 2 , the third cured material  42 , for example a liquid conductive ink, is located in the indentations  80  of the bi-layer  7 , for example by coating the surface and indentations  80  of the second cured layer  20  with a liquid conductive ink, wiping the surface of the second cured layer  20  to remove excess liquid conductive ink from the surface but not the indentations  80 , and curing the liquid conductive ink in the indentations  80  to form an electrical conductors in each of the indentations  80 . Such coating, wiping, and curing methods and materials are known in the art. 
     Referring next to  FIGS. 5A to 5F  and to  FIG. 7  again, a dispersion of particles  60  is formed in step  120  in the second cross-linkable material for example before locating a biocidal second curable layer  23   a  on or over the first curable layer  13  ( FIG. 5A ). In an embodiment, a dispersion of particles  60  is formed in a carrier such as a liquid, for example a curable resin, in a container  66 . Making and coating liquids with dispersed particles is known in the art. A dispersion having antimicrobial particles  60  has been made. The dispersion included three-micron silver sulfate particles milled in an SU8 liquid to an average particle size of one micron, and successfully coated on glass and tested with  E. coli  bacteria. In an alternative, the biocidal second curable layer  23   a  is made separately and laminated on or over the first curable layer  13 . 
     After steps  100  and  105  of  FIG. 7  and as shown in  FIGS. 4A and 4B , the dispersion is coated or a layer laminated on the first curable layer  13  to form the biocidal second curable layer  23   a  ( FIG. 5B ). The silver sulfate particle dispersion noted above was spin-coated on the glass support  30 , cured, and tested for anti-microbial efficacy. As shown in  FIG. 5C , the first curable layer  13  and biocidal second curable layer  23   a  (the biocidal second curable layer  23   a  including the particles  60 ) on the support  30  are imprinted in step  125  with the stamp  90  and cured with radiation  92  in step  130  to form the first cured layer  10  and biocidal second cured layer  20   a . In an embodiment, the curing step  130  includes cross-linking the first curable layer  13  to the biocidal second curable layer  23   a . The stamp is removed in step  135  to form the imprinted multi-layer structure  5  having the structured bi-layer  7  shown in  FIG. 5D . Imprinting methods using stamps are known in the art. 
     As shown in  FIG. 5E , in a further embodiment of the present invention, a portion of the biocidal second cured layer  20   a  is removed in step  140 , for example by etching or using energetic particles  94  such as with plasma etching, reactive plasma etching, ion etching, or sandblasting the first cured layer  10  or the biocidal second cured layer  20   a . Such a removal treatment can remove any coating over the exposed particles  62  and further expose the exposed particles  62  to the environment. Alternatively, particles  60  are exposed by washing the first or second cured layer  10 ,  20 . In an embodiment, the second-layer thickness  26 B after the removal step  140  is less than the second-layer thickness  26 A ( FIG. 5D ) before the removal step  140 . 
     As shown in  FIG. 5F , the result of the process is an imprinted multi-layer structure  5  with a structured bi-layer  7  including first cured layer  10  and biocidal second cured layers  20   a  on the support  30 . The biocidal second cured layer  20   a  includes particles  60 , including large particles  64  and exposed particles  62  in a second material, for example a second cured material. A coating of silver sulfate particles dispersed in SU8 has been exposed to plasma to reduce the coating thickness and further expose the particles  60  to the environment. 
     In an embodiment, the first cured layer  10  includes a first cross-linkable material, the biocidal second cured layer  20   a  includes a second cross-linkable material and the curing step  130  cross-links the first cross-linkable material to the second cross-linkable material. In another embodiment, the first material includes a first cross-linkable material and the second material includes a second cross-linkable material that is different from the first cross-linkable material and the curing step  130  cross-links the first cross-linkable material to the second cross-linkable material. Alternatively, the first material includes a first cross-linkable material, the second material includes a second cross-linkable material that is the same as the first cross-linkable material, and a third material is included in either the first material or the second material but not both the first and second materials and the curing step  130  cross-links the first cross-linkable material to the second cross-linkable material. 
     In another embodiment of the present invention, referring back to  FIG. 1 , the first cured layer  10  and the second cured layer  20  are not necessarily cross-linked. In such an embodiment, the biocidal imprinted multi-layer structure  5  includes the support  30  and the bi-layer  7  having a topographical structure on or over the support  30 . The structured bi-layer  7  includes the first cured layer  10  on or over the support  30  and the second cured layer  20  on or over the first cured layer  10  on a side of the first cured layer  10  opposite the support  30 . The structure of the structured bi-layer  7  has at least one structure depth  46  that is greater than the second-layer thickness  26  of the second cured layer  20 . In an embodiment, multiple biocidal particles  60  are located only in the second cured layer  20 . 
     Similarly, according to a method of the present invention and referring again to  FIG. 7  and  FIGS. 5A-5F , a method of making a biocidal imprinted multi-layer structure  5  includes providing the support  30  in step  100 , locating the first curable layer  13  on the support  30  in step  105 , forming a dispersion of multiple biocidal particles  60  in step  120 , locating the biocidal second curable layer  23   a  on the first curable layer  13  in step  110  using the dispersion, the biocidal second curable layer  23   a  having multiple biocidal particles  60  dispersed within the biocidal second curable layer  23   a , imprinting the first curable layer  13  and the biocidal second curable layer  23   a  in a single step with an imprinting stamp  90  having a structure with a depth greater than the thickness of the biocidal second curable layer  23   a  in step  125 , curing the first curable layer  13  and the biocidal second curable layer  23   a  in a single step to form the first cured layer  10  and the biocidal second cured layer  20   a  in step  130 , and removing the imprinting stamp  90  in step  135 . 
     In yet another embodiment of the present invention, not separately illustrated, the layer on a side of the first cured layer  10  opposite the support  30  (e.g. corresponding to the second cured layer  20 ) is a second layer that is not necessarily a cured layer and is not cross-linked. In various embodiments, this second layer is non-conductive, conductive, pattern-wise conductive, or include biocidal particles  60 . The second layer is in a spatial relationship to the first cured layer  10  on a side of the first cured layer  10  opposite the support  30 . The structure of the structured bi-layer  7  has at least one structure depth  46  that is greater than the second-layer thickness  26  of the second layer. Multiple biocidal particles  60  are located only in the second layer. In an embodiment the particles  60  are fixed in, fixed on, or adhered to the cross-linked material in the first cured layer  10 . 
     Referring to the sequential structures illustrated in  FIGS. 6A-6D  and the flow charts of  FIGS. 8A and 8B , an alternative method of making a biocidal bi-layer  7  includes providing the support  30  in step  100  and locating the first curable layer  13  on the support  30  in step  105  (as shown in  FIG. 7 ). Referring to  FIG. 8A  and  FIG. 6A , a biocidal second layer  25   a  is located on or over the first curable layer  13 . The biocidal second layer  25   a  includes multiple biocidal particles  60  located within the second cured layer  20 . 
     Referring specifically to  FIG. 8A  in an embodiment, the biocidal particles  60  are provided in step  300  and then mechanically distributed over the first curable layer  13  in step  305 . For example, the particles are agitated within a container or on a surface to form a uniform distribution of particles  60  and then released above the first curable layer  13  so that the particles  60  fall under the influence of gravity onto the first curable layer  13 . Ways to distribute particles  60  over a layer are known in the art. The distribution of particles  60  on the first curable layer  13  forms the biocidal second layer  25   a  on the first curable layer  13  (equivalent to step  110  in  FIG. 7 ) as shown in  FIG. 6A . 
     Referring specifically to  FIG. 8B , in an alternative embodiment, particles  60  are provided in step  300  and dispersed into an evaporable liquid in step  310  (and as shown in step  120  in  FIG. 7 ) to form a dispersion. This dispersion is distinguished from that of  FIG. 5A  in that is evaporable rather than curable. The dispersion is coated on or over the first curable layer  13  in step  320 , for example by spin coating, hopper coating, curtain coating or other methods known in the art. The dispersion is then dried in step  330  (and as shown in step  110  of  FIG. 7 ), for example by heating or drying without curing the first curable layer  13  or at least without completely curing the first curable layer  13 , to form the biocidal second layer  25   a . The biocidal second layer  25   a  is formed as a layer of particles  60  on the surface of the first curable layer  13  as shown in  FIG. 6A . 
     The first curable layer  13  and the biocidal second layer  25   a  are then imprinted with an imprinting stamp having a structure with a depth greater than the thickness of the second curable layer in a single step in step  125 , referring now to  FIG. 7  and as shown in  FIG. 6B . As shown in  FIG. 6C , the particles  60  of the biocidal second layer  25   a  are impressed by the imprinting stamp into the first curable layer  13 . In one embodiment of the present invention, the particles  60  of the biocidal second layer  25   a  are impressed completely into the first curable layer  13  so that the biocidal second layer  25   a  is a part of the first curable layer  13  (as shown in  FIG. 6C ) and is transformed into the biocidal second curable layer  23   a . In this case, the biocidal second curable layer  23   a  overlaps with the first curable layer  13  so that the entire biocidal second curable layer  23   a  is in common with a portion of the first curable layer  13 . In an alternative embodiment of the present invention shown in  FIG. 6D , at least some of the particles  60  of the biocidal second layer  25   a  ( FIG. 6B ) are impressed only part way into the first curable layer  13  so that the biocidal second curable layer  23   a  overlaps a part of the first curable layer  13 . The exposed particles  62  extending beyond the surface of the first curable layer  13  (as shown in  FIG. 6D ) form the biocidal second layer  25   a  and does not overlap with the first curable layer  13 . 
     In step  130 , the first curable layer  13  and the second curable layer  23  (or biocidal second curable layer  23   a ) is cured in a single step to form the first cured layer  10  and second cured layer  20  or biocidal second cured layer  20   a  and fix the particles  60  in the bi-layer  7 . If the first curable layer  13  includes a cross-linkable material, the step  130  of curing the first curable layer  13  and the second curable layer  23  or biocidal second curable layer  23   a  fixes the particles  60  within the cross-linkable material. In step  135 , the imprinting stamp is removed. Optionally, a portion of the second layer is removed in step  140  and the bi-layer  7  adhered to the surface  8 . 
     In the embodiments of  FIGS. 8A and 8B , the biocidal second curable layer  23   a  with the particles  60  is considered to overlap with the first curable layer  13  and the first cured layer  10  so that a portion of the first curable layer  13  is in common with the second curable layer  23  or biocidal second curable layer  23   a . In an alternative understanding, a portion of the first curable layer  13  is converted into the second curable layer  23  or biocidal second curable layer  23   a  when the particles  60  are impressed into the first curable layer  13  so that the first curable layer  13  is reduced in thickness and at least a portion of the second curable layer  23  or biocidal second curable layer  23   a  is cured. These understandings of the first curable layer  13  and second layer (second curable layer  23 , biocidal second curable layer  23   a , or biocidal second layer  25   a ) and understanding of the first cured layer  10  and second layer (second cured layer  20 , biocidal second cured layer  20   a , biocidal second layer  25   a ) are equivalent in practice, since they result in a layer of particles at least partially embedded in the first cured layer  10 . Essentially, the second curable layer  23 , biocidal second curable layer  23   a , and biocidal second layer  25   a  are all embodiments of a second layer formed on first curable layer  13  before the first curable layer  13  is cured to form the first cured layer  10 . Likewise, the second cured layer  20 , biocidal second cured layer  20   a , and biocidal second layer  25   a  are all embodiments of a second layer formed on first cured layer  10  after the first curable layer  13  is cured to form the first cured layer  10 . To illustrate these different understandings of the first cured layer  10  and the biocidal second cured layer  20   a  or biocidal second layer  25   a , a dashed line demarcates the two layers in  FIGS. 6C and 6D . Whether the layers are considered to be separate layers or to overlap is a matter of perspective having little practical consequence. 
     Thus, in various embodiments, a portion of a second layer is in common with a portion of the first cured layer  10  or an entire second layer is in common with a portion of the first cured layer  10 . In various embodiments, the second layer is a curable or cured layer, is non-conductive, is conductive, or includes biocidal particles. In yet another embodiment, cured portions of the second layer are removed (step  140 ) so that only the particles  60  remain adhered to the first cured layer  10  so that none of the second layer is in common with a portion of the first cured layer  10  (not shown). 
     In yet another embodiment, the first cured layer  10  or the second cured layer  20 , biocidal second cured layer  20   a , or biocidal second layer  25   a  have a hydrophobic surface, for example by providing a roughened surface either by imprinting or by a treatment such as sandblasting or exposure to energetic gases or plasmas or from the presence of the biocidal particles  60 . 
     In a further embodiment of the present invention, the first cured layer  10 , the second cured layer  20 , the biocidal second cured layer  20   a , or the support  30  is or includes a heat-shrink film, for example polyolefin, polyvinylchloride, polyethylene, or polypropylene. Any of the first cured layer  10 , the second cured layer  20 , the biocidal second cured layer  20   a , or the support  30  can include cross linking materials that are cross linked for example by radiation or heat to provide strength. 
     Referring to  FIG. 9 , in various embodiment of the present invention, any of the biocidal bi-layers  7  or the biocidal imprinted multi-layer structures  5  described above, including those of  FIG. 3, 5D, 5F , or  6 D is located on a surface  8  in step  200  and observed over time in step  205 . Periodically or as needed, the imprinted multi-layer structure  5  is cleaned in step  210 , for example by washing with water or with a cleaning fluid, or wiping the multi-layer structure  5 . The imprinted multi-layer structure  5  is repeatedly observed (step  205 ) and cleaned (step  210 ) until it is no longer efficacious for its intended purpose. The biocidal imprinted multi-layer structure  5  is replaced, removed, or covered over in step  220 . 
     In an embodiment, the cleaning step removes dead micro-organisms or dirt from the surface  22  of the biocidal second cured layer  20   a  so that the biocidal efficacy of the particles  60  is improved in the absence of the dead micro-organisms or dirt. Useful cleaners include hydrogen peroxide, for example 2% hydrogen peroxide, water, soap in water, or a citrus-based cleaner. In an embodiment, the 2% hydrogen peroxide solution is reactive to make oxygen radicals that improve the efficacy of particles  60 . In various embodiments, cleaning is accomplished by spraying the surface  22  of the biocidal second cured layer  20   a  with a cleaner and then wiping or rubbing the surface  22 . The cleaner can dissolve the biocidal second cured layer  20   a  material (e.g. cross linking material) and the wiping or rubbing can remove dissolved material or abrade the surface  22  of the biocidal second cured layer  20   a  to expose other particles  60  or increase the exposed surface area of exposed particles  62 . 
     Alternatively, the cleaning or washing step  210  refreshes the particles  60 , for example by a chemical process, to improve their biocidal efficacy. This can be done, for example, by ionizing the particles  60 , by removing oxidation layers on the particles  60 , or by removing extraneous materials such as dust from the particles  60 . 
     Replacement of the biocidal second cured layer  20   a  or biocidal second layer  25   a  can proceed in a variety of ways. In one embodiment, another biocidal imprinted multi-layer structure  5  is simply located over the biocidal imprinted multi-layer structure  5 . Thus, the biocidal multi-layer structure  5  becomes the structure  40  and another biocidal imprinted multi-layer structure  5  is applied to the structure  40 , for example with an adhesive layer  50  ( FIG. 1 ). In another embodiment, the biocidal imprinted multi-layer structure  5  is removed and another biocidal imprinted multi-layer structure  5  put in its place. As shown in  FIG. 1 , the support  30  is adhered to the structure  40  with an adhesive layer  50 . Chemical or heat treatments are applied to the biocidal multi-layer structure  5  to loosen, dissolve, or remove the adhesive layer  50  so the biocidal imprinted multi-layer structure  5  can be removed and another adhesive layer  50  applied to the structure  40  to adhere the biocidal imprinted multi-layer structure  5  to the structure  40 . In an embodiment, the biocidal imprinted multi-layer structure  5  is peeled from the structure  40  and another biocidal imprinted multi-layer structure  5  having an adhesive layer  50  is adhered to the structure  40 . 
     Alternatively, portions of the biocidal imprinted multi-layer structure  5  are removed, for example at least a portion of the biocidal second cured layer  20   a  is mechanically separated from the first cured layer  10 . In an embodiment, the biocidal second cured layer  20   a  is peeled from the first cured layer  10 . Alternatively, the biocidal second cured layer  20   a  is abraded and removed by abrasion from the first cured layer  10 . In another embodiment, the biocidal second cured layer  20   a  is chemically separable from the first cured layer  10  or chemically dissolvable in a substance that does not dissolve the first cured layer  10 . In a useful embodiment, a substance that chemically separates the biocidal second cured layer  20   a  from the first cured layer  10  or that chemically dissolves the biocidal second cured layer  20   a  is a cleaning agent. In an embodiment, the biocidal second cured layer  20   a  is repeatedly cleaned, for example by spraying the biocidal second cured layer  20   a  with a cleaning agent and then rubbing or wiping the biocidal second cured layer  20   a , and at each cleaning a portion of the biocidal second cured layer  20   a  is removed to gradually expose the first cured layer  10 . 
     In another embodiment of the present invention, fluorescent or phosphorescent materials are included in the second cured layer  20  or biocidal second cured layer  20   a  and are illuminated. The fluorescent or phosphorescent materials respond to ultra-violet, visible, or infrared illumination and emit light that can be seen or detected and compared to a threshold emission value. Thus, the continuing presence of the second cured layer  20  or biocidal second cured layer  20   a  is observed. When light emission in response to illumination is no longer present at a desired level, the second cured layer  20  or biocidal second cured layer  20   a  is replaced. 
     The present invention is useful in a wide variety of environments and on a wide variety of surfaces  8 , particularly surfaces  8  that are frequently handled by humans. The present invention can reduce the microbial load in an environment and is especially useful in medical facilities. 
     The invention has been described in detail with particular reference to certain embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           5  multi-layer structure 
           7  bi-layer 
           8  surface 
           10  first cured layer 
           13  first curable layer 
           16  first-layer thickness 
           20  second cured layer 
           20   a  biocidal second cured layer 
           21  patterned second cured layer 
           21   a  conductive portion 
           21   b  non-conductive portion 
           22  surface 
           23  second curable layer 
           23   a  biocidal second curable layer 
           25   a  biocidal second layer 
           26 ,  26 A,  26 B second-layer thickness 
           30  support 
           36  support thickness 
           40  structure 
           42  third cured material 
           46  structure depth 
           50  adhesive layer 
           52  binder primer 
           60  particle 
           62  exposed particle 
           64  large particle 
           66  container 
           80  indentations 
           90  stamp 
           92  radiation 
           94  energetic particles 
           100  provide support step 
           105  locate first layer step 
           110  locate second layer step 
           120  form dispersion step 
           125  imprint first and second layers step 
           130  cure first and second layers step 
           135  remove stamp step 
           140  remove second layer portion step 
           150  identify surface step 
           155  locate adhesive step 
           160  adhere support to surface step 
           200  locate structure step 
           205  observe structure step 
           210  clean structure step 
           220  replace biocidal layer step 
           300  provide particles step 
           305  mechanically distribute particles on first layer step 
           310  disperse particles in evaporable liquid step 
           320  coat dispersion on first layer step 
           330  evaporate liquid to form second layer step