Patent Publication Number: US-2022211522-A1

Title: 3d printed prosthetic liners and sockets

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to prosthetic devices, and more particularly relates to prosthetic liners and sockets, and related methods for making prosthetic liners and sockets. 
     BACKGROUND 
     It is highly desirable that prosthetic liners conform closely to the residual limb, and accommodate all surface contours and sub-surface bone elements of the residual limb. They should also provide a comfortable cushion between the residual limb and the hard socket of the prosthesis that is to be fitted over the residual limb. 
     Generally, liners are made from silicone, polyurethane or other elastomeric materials that have been formulated as suitable substances for suspension type liners. Such elastomer materials are configured to have the appropriate hardness, elongation, tensile, and other properties, to provide a comfortable, as well as a functional liner. 
     Much like prosthetic liners, orthotic or prosthetic sleeves provide support and reinforcement for muscles, joints, and extremities of those in need of assistance, such sleeves are not limited to use for amputees but may be applied to existing limbs to provide support in a manner associated with conventional orthotic devices. Orthotic and prosthetic sleeves of this type are described in, for example, U.S. Pat. No. 6,592,539. 
     While effective solutions have been proposed and implemented, it is still highly desirable to improve comfort of such liners or sleeves to ever so increase their ability to conform to irregularities on a residual limb, to accommodate a wider variety of limbs with fewer sizes of liners, and provide an amputee with enhanced comfort at a residual limb interface with a prosthesis while maintaining sufficient strength and durability. Moreover, it is particularly desirable to provide a liner or sleeve wherein means is made available which distributes pressure of the liner against a prosthesis while providing superior stretchability. 
     Prosthetic limbs are attached to a human residual limb by various suspension means. A sleeve is a common method of suspension. A sleeve is a tubular structure with an opening at each end and is typically constructed of the same or similar materials used in liners. A sleeve overlaps the socket, the proximal portion of the liner which extends above the socket, and a portion of the amputee&#39;s leg. A sleeve increases the amount of skin contact between a prosthetic leg and the residual limb and also creates a hermetic seal between the limb and the socket. Additional types or methods of suspension may be used in addition to or in place of a sleeve, such as a pin on the distal end of the liner which is retained by a mechanism located at the distal end of a socket. Suction suspension utilizes a one way valve where the valve is located in the socket wall or pneumatically connected to the socket by a fitting or tubing. When the liner residual limb is inserted into the socket, air is expelled and in combination with a sleeve, a low vacuum condition is created between the liner and the socket. The resulting vacuum condition creates suspension forces which retain the prosthetic leg onto the limb. Active vacuum suspension employs a pump which creates a high vacuum condition between the liner and the limb and essentially eliminates all motion, or pistoning, between the liner and socket. All suspension methods rely on friction between the liner, sleeve (if utilized) and the residual limb to retain the prosthetic leg on the residual limb. 
     Because the polymeric material of the liner grips the skin of the residual limb, the socket and associated prosthesis is retained on the residual limb. However, the inherent nature of the liner material not only grips tightly on the residual limb, it also insulates the limb, trapping moisture and heat. If a sufficient amount of perspiration is trapped between the residual limb and the liner interior, then the interface between the skin and the liner and sleeve becomes lubricated by sweat and the grip of the liner on the residual limb is reduced and suspension of the prostheses may be compromised. Virtually all amputees experience significant discomfort due to the lack of ventilation and the insulatory nature of prosthetic socket environment. This environment creates several undesirable conditions, i.e.: (1) elevated skin temperature in combination with moisture results in decreased tissue strength and increased susceptibility to tissue damage, which makes the skin more susceptible to rashes, ulcers, and discomfort; (2) the moist, warm skin environment creates conditions conducive for bacterial growth that makes the skin susceptible to bacterial infection and other skin disorders; and (3) the trapped sweat results in a foul odor emanating from the limb. 
     One primary purpose of a prosthetic liner is to improve the pressure distribution between the limb and the socket. Prosthetic sockets are custom made devices, however; existing construction processes are not perfect and internal socket shapes don&#39;t match limb shapes perfectly. In addition, residual limbs are highly variable with regards to how much tissue is covering bony structures. Some regions of a residual limb are all soft tissue with no underlying bone structure and some areas have only skin covering the bone structure. Therefore a great deal of variation exists in the amount of cushion between the bone and a socket, and hence bony areas with little tissue between the bone and socket experience high pressures while areas with significant amounts of soft tissue between the bone and socket experience low pressures. High interfacial pressures between the residual limb and the socket result in tissue damage and discomfort. 
     Current prosthetic sockets are typically made of rigid carbon fiber composite materials. Temporary sockets, frequently referred to as check sockets, are constructed of thick thermoplastic materials and are also rigid. Sockets are typically formed as rigid structures to facilitate the transfer forces from the residual human limb to a prosthetic device, such as a prosthetic foot located proximal of the socket. The purpose of the socket and liner, which are frequently used in combination with a sleeve, is to secure and attach a prosthetic limb to a user&#39;s residual limb. Sufficient socket rigidity is required so the proximal prosthetic device is reliably located in space, for example, to facilitate ambulation. Due to various limitations of current socket manufacturing processes, a socket is largely monolithic. Minor variations in the thickness and the layering of fiber reinforcement layers are possible and utilized. However, the end result is that a prosthetic socket is rigid and it is not practical to use a socket without a liner due to discomfort between the residual limb and the socket. Furthermore, existing prosthetic sockets, liners, and sleeves provide insufficient cooling the residual human limb. 
     Liners for orthotic devices function in a similar manner to prosthetic liners, with a soft surface against the skin and a harder backing layer against the soft layer. Because a orthotic device transfers less force to the human body, softer and less expensive materials may be used. An orthotic liner typically includes fabric layered secured to a foam material, where the fabric is arranged to contact the skin of the user. The foam material of an orthotic liner is typically layered against a thermoplastic material and/or a strap. When combined, the layers of fabric, foam, and a thermoplastic and/or strap constitute an orthotic support. Fabric and foam materials absorb moisture and sweat in addition to providing limited friction against the skin. Providing optimal friction against skin is a useful way of transferring forces and maintaining an optimal location of an orthotic or prosthetic device on the human body. 
     For the foregoing reasons, there is a need to provide improved liners, sleeves and sockets that provide improved fit, conformability, and pressure distribution. There also is a need to provide these components with improved air circulation and increased heat conduction characteristics 
     SUMMARY 
     One aspect of the present disclosure relates to a prosthetic device that includes a polymer lattice structure. The lattice structure includes a first surface arranged to face toward a residual limb, a second surface arranged to face away from the residual limb, a thickness between the first and second surfaces, and a variable lattice density across the thickness. 
     The prosthetic device may include a flexible liner, and the lattice density increases from the first toward the second surfaces. The lattice structure may have a continuous, single-piece construction. The lattice structure may have a void content of at least 5%. The lattice structure may have a porosity that permits airflow through the thickness from the first surface to the second surface. The lattice structure may include an elastomeric material. The lattice structure may include an antimicrobial material. The prosthetic device may also include a fabric material positioned on the first surface, the lattice structure being formed directly on the fabric material. 
     Another aspect of the present disclosure relates to a prosthetic liner or sleeve that includes a polymer lattice structure having a first surface arranged to face toward a residual limb, a second surface arranged to face away from the residual limb, a porosity that permits airflow through the lattice structure from the first surface to the second surface, a closed distal end, and an open proximal end. 
     The lattice structure may include a thickness between the first and second surfaces, and a variable lattice density across the thickness. The lattice density may be lowest at the first surface and highest at the second surface. The lattice structure may include an elastomeric material. The prosthetic liner may include a receiver formed in the closed distal end, wherein the receiver is configured to connect the liner to a prosthetic device. 
     Another aspect of the present disclosure relates to a prosthetic sleeve. Prosthetic sleeves are commonly used to create a seal between a socket, a liner, and a residual limb such that a negative pressure environment can exist within the socket. Prosthetic sleeves may also be used as a frictional suspension system by providing friction between the skin of the residual limb and the sleeve, and friction between the sleeve and the liner and/or socket, thus keeping a prosthetic limb attached to the residual limb. 
     A further aspect of the present disclosure relates to a prosthetic socket that includes a first surface arranged to face toward a residual limb, the first surface having a first rigidity, a second surface arranged to face away from the residual limb, the second surface having a second rigidity that is greater than the first rigidity, and a continuous, single-piece construction. 
     The first surface may include a first structural density and the second surface includes a second structural density. The prosthetic socket may also include a plurality of apertures formed therein and extending through at least the second surface. The prosthetic socket may also include a closed distal end, an open proximal end, a hollow interior sized to receive the residual limb, and connection feature formed in the closed distal end. 
     The present disclosure also is directed to a method of manufacturing a prosthetic device. The method may include forming a first portion of the prosthetic device with a first lattice structure, and forming a second portion of the prosthetic device with a second lattice structure having at least one of a different property than that of the first lattice structure. The first and second lattice structures are formed as a continuous, integral structure using an additive manufacturing process. 
     The at least one different property may include at least one of lattice density, material composition, lattice structure, compressibility, porosity and rigidity. The first portion may be a liner and the second portion may be a socket. The prosthetic device may be a flexible liner, the first portion may be an inner layer of the liner, and the second portion may be a second layer of the liner. The prosthetic device may be a socket, the first portion may be a first layer of the socket, and the second portion may be a second layer of the socket. 
     The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the spirit and scope of the appended claims. Features which are believed to be characteristic of the concepts disclosed herein, both as to their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purpose of illustration and description only, and not as a definition of the limits of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the nature and advantages of the embodiments may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. 
         FIG. 1  is a cross-sectional side view of an example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 2  is a cross-sectional side view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 3  is a cross-sectional side view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 4  is a cross-sectional side view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 5  is a cross-sectional side view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 6A  is a side view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 6B  is a close up view of a cross-section of the 3D printed prosthetic device shown in  FIG. 6A . 
         FIG. 7  is a close up view of a cross-section of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 8  is a close up view of a cross-section of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 9  is a cross-sectional side view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 10  is a perspective view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 11  is a perspective view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 12  is a cross-sectional side view of another example 3D printed prosthetic device in accordance with the present disclosure. 
         FIG. 13 . is a cross-sectional side view of a distal end portion of another example 3D printed prosthetic device with a locking pin in accordance with the present disclosure. 
         FIG. 14  is a cross-sectional side view of a distal end portion of another example 3D printed prosthetic device with a locking pin in accordance with the present disclosure. 
         FIG. 15  is a chart showing atomic lattice structures for use with the 3D printed prosthetic devices of the present disclosure. 
         FIGS. 16A-16F  are perspective views of example lattice structures for use with the 3D printed prosthetic devices disclosed herein. 
         FIG. 17  is a flow diagram illustrating an example method in accordance with the present disclosure. 
     
    
    
     While the embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, the exemplary embodiments described herein are not intended to be limited to the particular forms disclosed. Rather, the instant disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims. 
     DETAILED DESCRIPTION 
     The present disclosure is generally directed to prosthetic devices, and more particularly relates to prosthetic liners and sockets, and related methods for making prosthetic liners and sockets. The prosthetic liners and sockets disclosed herein may be formed concurrently and together as a unitary, integral structure. In some embodiments, the prosthetic liner, socket, or combination thereof may be formed using an additive manufacturing process, such as a 3D printing process. Various materials may be used to form the prosthetic liner and socket devices disclosed herein. In some embodiments, the same material may be used to form both the liner and socket, and a lattice structure of the liner and socket may be different to provide different amounts of stiffness, airflow, and other properties. 
     Additive manufacturing, also known as 3D printing, utilizes a variety of technologies to create a structure. One technology uses focused laser energy to create chemical reactions which cure liquid polymer in a bath layer by layer. Another method extrudes melted material layer by layer. These methods all add material to a part or structure in thin layers, typically about 0.003 inches to about 0.030 inches of thickness per layer. Each layer of new material being applied bonds to the existing layer by means of the melted entanglement of polymer chains or by chemical reactions or some combination of the two. 
     Additive manufacturing methods have the ability to create sparse structures. These structures may be similar to a 3Dimensional truss structure where rods or beams of material are connected produce efficient, light-weight structures. By altering the angles, thickness, and/or frequency of the individual rods or beams it is possible to control the mechanical response of the resulting structure. 
     The additive nature of the technology may provide the ability to create complex geometry and other desirable properties in a cost effective manner. Many of these geometric shapes cannot be created using other known manufacturing method. For example, liners with lattice type structures can be optimized for performance by varying the density or the geometry of the lattice. The liner can be customized in a variety of ways by merely changing the digital 3D model used to create the liner. Each liner can be customized to meet the user&#39;s specific needs with little impact on manufacturing costs. 
     The most common 3D printing materials used today are polymers, which are an acceptable material for liner and socket constructions. Liners and sockets created using 3D printing can have wide temperature compatibility, variable strength and/or stiffness, and be biocompatible. Since components are constructed one thin layer at a time, normal design restrictions such as angles and contour, lattice density, surface characteristics, smoothness, and undercuts do not necessarily apply to 3D printed articles. Not only does 3D printing allow more design freedom, it also allows complete customization of designs. Current additive manufacturing technologies may be perfectly suited in many instances for producing custom liners, custom sockets, and liner/socket combinations. 
     An example of such customization relates to a custom liner that is specifically designed for the residual limb of the individual recipient. A 3D printed liner created using a scanned data file of the limb would improve the ability to provide a correct fit of the limb for maximum comfort. In addition to providing an accurate fit, a 3D printed liner can be designed such that the structural compression stiffness, bending stiffness, and heat conduction properties can vary continuously along any dimension. Localized areas can be made softer or harder, and/or be made more rigid or more flexible. Current liner and socket designs are generally based upon a monolithic structure and properties. 
     The majority of residual limbs are generally cylindrical. Some, particularly short residual limbs are conical, but for the sake of simplicity and descriptive purposes, a cylindrical coordinate system will be used. The axial or longitudinal direction runs in the direction of the long arm or leg bones (femur, humerus, tibia or radius) and runs in the distal to proximal direction (or visa-versa). The radial direction is the distance from the longitudinal axis, and as applied to sockets and liners may also be referred to as the through-the-thickness direction because it extends through the thickness of a liner and socket (except at the closed end of the cylinder, where it runs in the axial or longitudinal direction). The circumferential direction is the angular position about the longitudinal axis. 
     While the thickness of the material may taper somewhat from the distal to the proximal ends, circumferentially, the thickness, and hence compression and bending stiffness, is typically constant in the circumferential direction, although it is possible to produce a liner with regions of increased thickness to provide additional cushion over bony areas. 
     Creating a lightweight, porous, and/or variable stiffness structure by additive manufacturing techniques typically utilizes a repeating cell structure. Cell structures can mimic naturally occurring atomic structures such as cubic, tetragonal, orthorhombic, rhombohedral, monoclinic, triclinic, including body centered, face centered, and base centered variations of these atomic cells shown in  FIG. 15 . The atom positions in such cell structures may represent connection points between multiple individual truss members which may consists of rods or beams of material. Another naturally occurring cell structure is honeycomb. However, cell structures do not need to mimic naturally occurring structures. For example, additive manufacturing can be used to create a series of interconnected coil springs. By altering the angles, thickness, and/or frequency of the individual rods or beams used to create an additive manufactured cell structure it is possible to control the mechanical response of the resulting structure. 
     Various additive manufacturing technologies are available and those applicable to polymer materials include Powder Bed Fusion (PBF), Vat Photopolymerization, Material Extrusion, and Material Jetting. Powder bed fusion includes Selective Laser Melting (SLM), selective laser sintering (SLS) and selective heat sintering (SHS). PBF involves spreading a thin layer of powdered material on a surface and then melting the powder to fuse the particles. Thermal energy in the form of a laser or a heated print head provide the required melt energy. 
     Vat photopolymerization utilizes liquid photopolymer resin bath and a laser to create localized chemical reaction resulting in a polymer structure. Stereolithography (SLA) is the most common method with variations including Direct Light Processing (DLP) which uses microscopic mirrors to project the laser at multiple locations to eliminate the necessity of tracing each layer with the laser, and Continuous Direct Light Processing (CDLP) adds a continuously moving build platform. DLP and CDLP result in faster part build times. Vat Photopolymerization may be a preferred method to create parts made with elastomeric materials. 
     Material Extrusion consists of Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF). In this process, a small thermoplastic filament is extruded through a heated nozzle and melt bonded to the previous layer of deposited material. 
     Material Jetting utilizes tiny print head nozzles to dispense tiny droplets of photopolymer layer by layer. UV light is used to cure the droplets. This technique is similar to the process used in ink jet printing. 
     Sockets are typically constructed of fiber reinforced plastic (FRP) because of the high strength, durability and low density properties of these materials. The cylindrical shape of the socket may be well-suited for the use of hard and stiff materials that do not bend or deflect significantly during use. Amputees who have been fortunate enough to retain limb joints, such as knee or elbow joints can find the relatively simple design of commonly available liners and sockets to be inadequate. For example, amputees that use below-the-knee prosthetics generally require a liner that conforms to a range of joint positions possible by an intact, functioning knee joint. As the joint moves, related tendon and muscle structures also move, and a socket must accommodate these movement, which makes creating a well-fitting socket a difficult task. Adding flexibility to a localized area of the socket can alleviate some of these difficulties. 
     Typical off-the-shelf liners often do not provide a comfortable fit over the entire range of motion of the joint. Even at small bending angles, the fit of the liner behind the knee can be lost due to bunching or gathering behind the knee. When flexing the knee joint, one or more folds may form in the portion of the liner overlying the region behind the knee. The folds generally occur in a lateral direction, i.e., roughly perpendicular to the length of the leg. However, more complex, crinkle-type folds can also occur. The pinching and pulling of underlying skin which can occur with such folds can result in patient discomfort. As the knee joint undergoes flexion, the relatively relaxed liner surface disposed over the kneecap (the “anterior surface’) must stretch and bend in order to accommodate the change in conformation of the knee joint, as well as the increase in anterior skin surface area which accompanies the change. A 3D printed liner could be formed in such a way to accommodate for stretch and bending by simply altering the geometry of the lattice of the polymer material. 
     Additionally, 3D printed structures may offer the unique ability to separate and disconnect properties which have historically been considered inherent material properties. For example, as a material is stretched in one direction/dimension the material contracts in the other two dimensions (i.e., the Poisson&#39;s effect). A 3D printed structure having a lattice structure has a response dependent on the geometry of the lattice, not necessarily on the direction a force is applied. This is different than the response of the material used to create the lattice structure. Additive manufacturing can be used to create auxetic material structures with a negative Poisson&#39;s ratio, which results in material expansion in one or more directions perpendicular to an applied tensile force and contraction in one or more directions perpendicular to an applied compressive force. 
     Auxetic material structures present a method to address unique problems experienced by amputees. As an amputee uses a lower limb prosthetic device over the course of a day, the pressures experienced by the residual limb result in fluid being forces out of the limb. This loss of fluid reduces limb volume and results in a poor socket fit. The most common method to deal with this volume loss is to place fabric socks over the liner during the course of the day to fill the volume in the socket. Auxetic materials have a negative Poisson&#39;s ratio. Because Auxetic materials expand in a direction perpendicular to an applied force, these structures will experience volumetric contraction when compressed, which may reduce the hydrostatic pressures in a socket and hence reduce fluid loss in the limb. Auxetic materials also experience volumetric expansion under tensile forces, which may improve the frictional forces between a liner and the skin and improve limb retention on the limb. Auxetic materials or structures may be used in combination with positive Poisson&#39;s ratio materials to create beneficial effect to an amputee. 
     Additive manufactured structures can be made using a variety of materials, which include thermoset polymers, thermoplastic polymers, metals, and fiber reinforced composites. Elastomers are commonly defined as rubber-like materials. Elastomers can be defined by hardness, maximum elongation, modulus, Possion&#39;s ratio, or glass transition temperature and by combinations of these properties. Elastomeric materials are available in a wide range of hardnesses or stiffnesses ranging from hard elastomers with a Young&#39;s modulus of 500,000 psi to very soft elastomers with a secant modulus of 50 psi at 100% elongation. As elastomeric materials become harder their properties become more linear elastic and follow Hooke&#39;s Law. Hence it can be difficult to differentiate an elastomer material from a non-elastomer material. 
     Elastomers are difficult to characterize because they have viscoelastic properties. The mechanical response of an elastomer is partially elastic and partially viscoelastic. A viscoelastic response is characterized by a linear spring in parallel with a dashpot. A dashpot is a damping device such as a hydraulic cylinder. The spring provides resistance to compression and extension, while the dashpot slows both the compression and extension, and the recovery from compression and extension. Hence the mechanical response is time dependent. 
     For the purposes of this application, an elastomer is defined as a material which can be stretched to 10% elongation at room temperature and recover 70% of the deformation within 10 seconds when the stretching load is removed. 
     Indentation hardness testing is a method of characterizing the stiffness of a material. This type of test may also be known as a durometer, indentation or durometer hardness test. Hardness testing can be performed on a wide range of materials, from the hardest steels to soft elastomers. ASTM D 2240, DIN 53505, and ISO R/868 are comparable methods used for testing both soft elastomers and hard plastic materials and the results are stated on the Shore scale. The commonly used Shore harness scales, in increasing order of hardness, are 000-S, 000, 00, 0, and A-D. The Shore D, A and 00 scales are most commonly used because these 3 scales result in a functional continuum for hardnesses in most situations. Shore-OO 63 is approximately equivalent to Shore-A 20 and Shore-A 73 is approximately equivalent to Shore-D 20. Typical commonly known material hardness are Shore-OO 20 for chewing gum, Shore-A 25 for a rubber band, Shore-A 70 for tire tread, and Shore-D 70-90 for rigid plastics like nylon and polyethylene. Some structural plastics and composite materials have hardnesses which exceed the Shore scales. Shore-000-S and Shore-000 scales are typically used for soft foams or sponges. 
     Most currently available prosthetic liners and sleeves have a hardness of approximately Shore-00 50, although values from around Shore-00 30 to Shore-00 70 may be in use. One of the advantages of additive manufacturing is the ability to utilize a lattice structure, sometimes known as a sparse structure. As the void content of a material increases, for example in foams, the material becomes softer. Hence, attaining the desired stiffness when utilizing a lattice structure in a prosthetic liner there may be a need to utilize a stiffer raw material, as compared to monolithic liner. The Shore hardness of the material used in an additive manufactured liner utilizing a lattice structure may extend into the Shore A or D scales for the material loaded adjacent to the skin. 
     When combining a liner with a socket into a single, unitary structure the stiffness of the material used may increase as the distance from the limb increases (the radial or through-the thickness direction) to provide the required stiffness and strength to resist reaction forces and yet allow a soft interface next to the residual limb. This may be achieved by changing the stiffness of the material, by changing the density of the lattice structure, by changing the geometry of the lattice, or all of the above. Therefore the stiffness of the raw material on the outside of the structure (at the maximum radial distance) may extend into the Shore-D scale and beyond. 
     3D printed liners and sockets provide the option of changing the lattice structure to make sections harder or softer and control the mechanical response of the structure in different directions. The cell structure can be altered such that the stiffness changes in one direction, for example, the radial or through-the-thickness direction, while leaving the stiffness in the axial and/or circumferential directions the same, or even increasing the stiffness in the axial and/or circumferential directions in different directions. With the option of changing material lattice modulus or stiffness, enhanced stability, security, fit comfort, and performance may be achieved. 
     In one embodiment, the material used to create a lattice structure varies in hardness through the thickness. Elastomers materials are typically available in different hardnesses and these different hardness formulations have similar atomic or chemical structures. As a result, materials from the same family product tend to bond to each other well. It is also possible to find materials from different manufacturers which bond well to each other. For example, the material used to form the liner or socket may be changed to a material of a different hardness during the additive manufacturing process. If the two materials are compatible, a strong connection will typically occur at the interface between the two materials. In one example, this approach may provide a soft inner layer against the skin and a stiffer, stronger structure on the outer layers (or visa-versa) as part of a laminated lattice structure. 
     In another variation, a lattice liner construction includes a trellis or web structure of polymeric material. This construction provides a porous structure, wherein air can flow freely through the liner. With the natural movements of the body, air can circulate through the socket and/or liner. This ability for air to flow through the lattice structure of the liner may provide a climatizing characteristic for improved comfort as well as enhanced skin integrity and a reduction of odor. A measure of air permeability is rate of airflow passing perpendicularly through a known area under a prescribed air pressure differential between the two surfaces of a material. A common test for fabric materials is ASTM D737-96. This test method can be adapted to thicker materials. A socket or liner, or combination of the two, with an air permeability greater than 2 ft 3 /min/ft 2  may be particularly advantageous in hot climates. 
     In another embodiment, the liner and socket could be made as a single piece using a 3D printing process. An inner surface of the liner (adjacent the skin of the wearer) may be relatively pliable and soft (e.g., like a cloth or even be formed directly on a sheet of cloth), and an outer surface of the liner could be made rigid so as to be supportive of the prosthesis. Both the inner and outer surfaces of the combined liner/socket structure could be made with a plurality of ventilation pathways to enhance air circulation. 
     Using lattice style construction for the liner and/or socket may provide passageways that improve breathability for the residual limb, thus eliminating many of the limitations of conventional liners and sockets. Further, suppleness for wearer comfort available using existing polymeric/elastomeric gel liner materials can be maintained or duplicated with a 3D printed liner structure. 
     Some advantages related to the 3D printed liners and sockets disclosed herein include improved breathability of the liner, socket or combination liner/socket via an open lattice structure. Such improved breathability may provide climate control, reduction of bacteria and germs, and the ability to wash the device and have near instant drying of the device. Another advantage relates to the ability to customize properties of the device. For example, the device may have a customized hardness or softness in a particular areas when using a single material. The device may have different hardness or softness in particular areas by using materials with different hardness properties. The device may have sections with different rigidity and flexibility properties. The device may have variable compressible/expandable properties that allow for physical changes in a person&#39;s residual limb. Further, as mentioned above, the socket and liner may be formed as a single-piece, unitary device. In addition, a complete prosthetic limb may be 3D printed, including a foot or hand. 
     Referring now to  FIG. 1 , an example 3D printed device  10  is shown and described. The 3D printed device  10  includes a liner portion  12 , a socket portion  14 , and a receiver  16 . The 3D printed device  10  is shown mounted to a limb  18 , such as a residual limb remaining after an amputation. An example of a residual limb may be a residual limb associated with a below-the-knee amputation. 
     The liner portion  12  defines an inner surface  30 . The socket portion  14  defines an outer surface  34 . The inner and outer surfaces  30 ,  34  converge at an interface  32 . The 3D printed device  10  includes a proximal end  20  (also referred to as an open end or an open proximal end), and a distal end  22  (also referred to as a closed end or a closed distal end). The 3D printed device  10  includes or defines a cavity into which the limb  18  is positioned. The receiver  16  is formed in or positioned at the distal end  22 . The receiver  16  may be sized and configured for attachment of the 3D printed device  10  to a prosthetic device such as a lower leg prosthesis (e.g., a prosthetic pilon, prosthetic knee, prosthetic foot, pump mechanism, or the like). The receiver  16  is shown having a recess formed in a protruding portion at the distal end  22 . Other receiver structures may be used in other embodiments, wherein the receiver may have different sizes, shapes, or orientations on the 3D printed device  10  and still provide a similar function for connection to a prosthetic device or component. 
     The 3D printed device  10  comprises a lattice structure. The lattice structure of the liner portion  12  is configured to have a softer, less rigid structure as compared to the lattice structure of the socket portion  14 . The lattice structure of the liner and socket portions  12 ,  14  may have different lattice shapes, lattice sizes, and/or be comprised of different materials. In some embodiments, a solid layer may be formed along either the inner surface  30  or outer surface  34 . 
     The solid surface may include a relatively thin layer that is formed along the lattice structure of the liner and/or socket portion  12 ,  14 . The solid surface may provide certain advantages or properties for the 3D printed device  10 . For example, a solid surface along the outer surface  34  may inhibit passage of fluid such as air, vapor and/or liquids, and/or prevents solids such as dirt and debris from passing into the lattice structure of the 3D printed device  10 . A solid surface along inner surface  30  may prevent passage of fluids such as air, vapor, or liquid from passing into the lattice structure from the interior cavity of the 3D printed device  10 . A solid surface along the inner surface  30  may also provide improved comfort at the interface with limb  18 . In other embodiments, such as those described below, portions of the inner or outer surface  30 ,  34  may comprise openings to facilitate passage of air, vapor, and/or liquids into or through the wall of the 3D printed device  10  to facilitate heat transfer, humidity transfer, air circulation, cooling, heating, and the like toward or away from a limb  18  positioned within the 3D printed device  10 . 
       FIG. 2  illustrates another example of 3D printed device  100  having a liner portion of  112  and a socket portion  114 . The socket portion  114  may be configured as a conventional rigid socket having a receiver  16  formed in a closed distal end thereof. The liner portion  112  may be formed as a relatively soft lattice structure that functions similar to a conventional liner that is used with a conventional socket. A portion of the receiver  16  may be formed in the liner portion  112 . 
     In some embodiments, the liner portion  112  is formed separately from the socket portion  114 . This separate construction may permit mounting of the liner portion  112  to the limb  18  followed by, in a later step, insertion of the limb  18  with liner portion  112  into the socket portion  114 . In other arrangements, the liner portion  112  and socket portions  114  are formed as a single, unitary piece such that the liner portion  112  is inseparable from the socket portion  114 . The liner portion  112  and socket portion  114  may be formed as a single continuous piece using a 3D printing manufacturing process such as those described herein. 
     The liner portion  112  may be formed with a lattice structure. The lattice structure may be continuous through the thickness of the sidewall of the liner portion  112 . The socket portion  114  may have a lattice structure with a greater density than the density of the liner portion  112 . Alternatively, the socket portion  114  may have a solid construction through its thickness. 
       FIG. 3  illustrates another example of 3D printed device  200  mounted to a support bracket  238 . The 3D printed device  200  may have a semi-rigid construction. The 3D printed device  200  may be mounted directly to the support bracket  238  to provide additional support and strength to adequately support the limb  18 . The support brackets  238  may be secured to the 3D printed device  200  using a plurality of straps  240 A,  240 B. The straps  240 A and  240 B may wrap circumferentially around the exterior surface of the 3D printed device  200  and be secured directly to the support bracket  238 . The straps  240 A and  240 B may comprise a fabric material, or may comprise a flexible polymeric material. The  240 A and  240 B may include brackets, clasps, fasteners or the like releasably secure or permanently connect the 3D printed device  200  to the support bracket  238 . Interlocking features may be provided between the support bracket  238  and the outer shell  236  to reduce relative movement between the two parts. Straps  240 A and  240 B may be 3D printed and may be integrated into the support bracket  238  or the outer shell  236 . Support bracket  238  may also be 3D printed. 
     The support bracket  238  may include a receiver  216  positioned at a distal end thereof. The receiver  216  may be aligned with a closed distal end  222  of the 3D printed device  200 . In some arrangements, the 3D printed device  200  may include a recess or other receiver feature formed in the distal end  222 . The receiver feature in the 3D printed device  200  may be aligned with the receiver  216  of the support bracket  238  to provide improved connection between a distal mounted prosthetic device and the 3D printed device  200  and support bracket  238 . 
     The 3D printed device  200  may include a liner portion  212  and an outer shell  236 . The outer shell  236  may have a different lattice structure than that of the liner portion  212 . The liner portion  212  may have a lattice structure that provides a relatively soft interface with the limb  18 . The outer shell  236  may have a semi-rigid lattice structure that provides increased rigidity as compared to that of the liner portion  212 , but that typically is less than the rigidity of the socket portion  14  described above with reference to  FIG. 1 . 
     In other embodiments, the entire 3D printed device  200  may comprise a single lattice structure such as the soft lattice structure of the liner portion  212  or the semi-rigid lattice structure of the outer shell  236 . In still further embodiments, the liner portion  212  and outer shell  236  may be provided along only a portion of the length of the 3D printed device  200  between a proximal open end  220  and the closed distal end  222 . Various embodiments are described with reference with to the figures that follow showing different types of lattice structures at different locations along the length of the 3D printed device. 
       FIG. 4  illustrates a 3D printed device  300  that includes a liner portion  312 , a socket portion  314 , and a receiver  16 . The 3D printed device  300  further includes a relatively soft area  342  and a relatively hard area  344 . The soft area  342  includes a softer lattice structure  343  as compared to the lattice structure of the liner portion  312 . The hard area  344  may include a semi-rigid lattice or harder lattice as compared to the lattice structure of the liner portion  312 , but softer and less rigid than the lattice structure of the socket portion  314 . 
     The soft area  342  may be positioned along a side wall of the 3D printed device  10  at a location spaced between the open proximal end  320  and the closed distal end  322 . The hard area  344  may be positioned along the closed distal end  322 . The soft and hard areas  342 ,  344  may be positioned at any desired location on the 3D printed device  300  to provide desirable properties related to the function of the 3D printed device  300 , including comfort for the wearer at the interface with limb  18 . For example, the soft area  342  may be positioned to interface with a portion of the limb  18  that is sensitive to pressure. The hard area  344  area may be arranged to provide additional support for the limb  18  and/or the receiver  16 . 
     The soft and hard areas  342 ,  344  may extend through an entire thickness of the 3D printed device  300  from an inner surface to an outer surface thereof. Alternatively, as shown in  FIG. 4 , the lattice structures  343 ,  345  of the soft and hard areas  342 ,  344  may extend through only a portion of the thickness between the inner and outer surfaces, such as through the thickness of the liner portion  312  but not the socket portion  314 . The 3D printed device  300  may include multiple soft and hard areas  342 ,  344  at any desired location. Further, the soft and hard areas may be combined or arranged side-by-side. In one embodiment, a soft area  342  is positioned within or between two hard areas  344 . 
     Referring now to  FIG. 5 , a 3D printed device  400  is shown including a liner portion  412 , a second portion  414 , and a receiver  16 . The 3D printed device  400  also includes one or more flexible sections  446  that comprise a softer lattice  442  as compared to the lattice structures of the liner and socket portions  412 ,  414 . The flexible sections  446  may be positioned at any desired location on the 3D printed device  400 , such as along a side wall at a location spaced between an open proximal end  420  and a closed distal end  442 . The soft lattice structure  442  may extend through an entire thickness of the 3D printed device between inner and outer surfaces thereof. 
     The flexible sections  446  may provide bending, compression, extension/expansion, and/or deformation of a 3D printed device  400  to accommodate, for example, movement of the limb  18 . In one example, the limb  18  includes a joint  19 , such as a knee joint, and the flexible sections  446  are aligned circumferentially with the joint  19 . The flexible sections may permit, for example, compression of the 3D printed device along a back side of the joint during bending, and expansion or deformation of the 3D printed device along a front side of the joint  19  during bending. In the embodiment shown in  FIG. 5 , the limb  18  may include a knee joint  19  with a rear of the knee joint positioned along the left side and a front of the joint  19  positioned along the right side. The amount of flexible section  446  along the length of the 3D printed device between the proximal and distal ends  420 ,  422  may be greater along the front or anterior side of the joint  19  as compared to the length along the rear or posterior side of the joint  19 . The flexible sections  446  may extend around only portions of a circumference of the 3D printed device  400 . Alternatively, the flexible sections  446  may extend around an entire circumference of the 3D printed device  400 . The flexible sections  446  may be used with any of the 3D printed device embodiments disclosed herein. Likewise, any of the features disclosed in any of the embodiments described with reference to the figures may be interchangeable with other embodiments disclosed herein. 
     Referring now to  FIGS. 6A and 6B , a 3D printed device  500  is shown including a liner portion  512 , a socket portion  514 , and a receiver  16 . The socket portion  514  includes a plurality of ventilation ports  548  extending therethrough from the outer surface of the 3D printed device  500  to the liner portion  512  as shown in at least  FIG. 6B . The liner and socket portions  512 ,  514  may comprise different lattice structures that provide different levels of rigidity, flexibility, airflow, compressibility, heat transfer, and other properties. The lattice structure of the liner portion  512  may permit fluid flow therethrough, such as the flow of air. The ventilation ports  548  may permit the fluid flow  550  to pass from an outer surface  534  to an inner surface  530  of the 3D printed device  500 , and to permit fluid flow  550  (air, vapor and/or liquid) to pass from the inner surface  30  and the limb  18  through the thickness of the 3D printed device  500  and out through the ventilation ports  548 . A fluid flow  550  may also comprise the transfer of heat to or from the limb  18 . The ventilation ports  548  may also act as heat transfer ports to better facilitate transfer of heat from a limb  18  through the 3D printed device  500  to atmosphere. 
     The ventilation ports  548  may be positioned at any desired location along the outer surface  534  of the 3D printed device  500 . In some examples, the ventilation ports  548  have a circular or oval shape, whereas in other embodiments different shapes may be used such as triangular, polygonal, elongate strips or the like. The ventilation ports  548  may be arranged in a pattern, such as rows and/or columns. In other embodiments, the ventilation ports  548  are arranged randomly along the outer surface  534 . In some embodiments, one or more ventilation ports  548  may be positioned along the closed distal end  522  and act as one or more drainage ports to permit flow of liquid (e.g., perspiration) from the limb  18  out of the 3D printed device  500 . The ventilation portion  548  may have different sizes at various locations on the outer surface  534 . The liner portion  512  may have different lattice structures at different locations on the 3D printed device  500  to provide different amounts or types of fluid flow  550  that are intended or advantageous for that portion of the device. 
     The 3D printed device  500  may include a single lattice structure, the dual lattice structure shown in  FIGS. 6A and 6B , or three or more lattice structures at various locations through the thickness, along a length, or around a circumference of the 3D printed device  500 . 
       FIG. 7  shows a close up view of another example 3D printed device  600  that includes a liner portion  612  that includes a relative soft lattice structure, a socket portion  614  that includes a relatively rigid lattice structure, and an intermediate portion  636  that includes a semi-rigid lattice structure. The 3D printed device  600  may also include an inner surface layer  652  along inner surface  630  that includes a cloth-like material or a lattice structure that provides a cloth-like feel for the user. The inner surface layer  652  may comprise a lattice structure that is different from the other liner portions  612 ,  614 ,  636 . In at least some embodiments, the inner surface layer  652  may comprise a different material than the materials used for the other portions  612 ,  614 ,  636 . In some embodiments, the inner surface layer  652  may comprise a fabric material or fabric fibers or polymer materials typically used in fabric fibers. The inner surface layer  652  may be formed concurrently with one or more of the other portions  612 ,  614 ,  636  using a 3D printing process. 
     The 3D printed device  600  may be referred to as an integral socket and liner device. The 3D printed device  600  may be referred to as an integral liner with an internal fabric surface or internal surface with a fabric-like feel. 
       FIG. 8  illustrates a 3D printed device  700  that includes at least a liner portion  712  and an inner surface layer  752  positioned along an inner surface  730 . The inner surface layer  752  may comprise the same or similar properties, attributes, lattice structure and/or material composition as described above for inner surface layer  652 . The 3D printed device  700  may be referred to as a 3D printed liner having a first lattice structure associated with the liner portion  712  and a second lattice structure associated with the inner surface layer  752 . The 3D printed device  700  may be used with a traditional prosthetic socket, or may be used with other devices such as the support bracket  238  described with reference to  FIG. 3  or any of the other 3D printed devices disclosed herein. 
       FIG. 9  illustrates another example 3D printed device  800 . The 3D printed device  800  includes a liner portion,  812 , a socket portion  814 , and a receiver  16 . The 3D printed device  800  may have a different thickness T 1  at one location (a standard thickness), a second thickness T 2  (a greater thickness) at another location, and a third thickness T 3  (a reduced thickness) at other locations along the 3D printed device  800 . The different thicknesses, T 1 , T 2 , T 3  may be provided by varying a thickness of the liner portion  812 . In other embodiments, the thicknesses T 1 , T 2 , T 3  may be varied by changing the thickness of the socket portion  814 , or by changing the thickness of both of the liner and socket portions  812 ,  814 . In other embodiments, an additional lattice structure or layer may be added in the area for the increased thickness T 2 , which may be referred to as an increased thickness area  892 . A reduced thickness portion  894  may have the thickness T 3 . The remaining portions may be referred to as standard thickness areas  890 , having a thickness T 1 . 
     In some embodiments, the 3D printed device  800  may include only the standard thickness area  890  with thickness T 1  and increased thickness area  892  with thickness T 2 . In other embodiments, the 3D printed device  800  may include standard thickness areas  890  having thickness T 1  and one or more reduced thickness portions  894  having thickness T 3 . In further embodiments, the 3D printed device  800  may include multiple reduced thickness sections  894  and/or multiple increased thickness sections  892  and/or no standard thickness areas  890 . 
       FIG. 9  illustrates the increased thickness area  892  having a gradually increasing thickness that varies from the standard thickness T 1  to the increased thickness T 2 . The reduced thickness portion  894  is shown having a thickness that varies from the standard thickness T 1  gradually to the reduced thickness T 3 . These gradual changes in the thickness may be customized to match the contours, shapes, sizes and surface features of the limb  18 . 
     Generally, the 3D printed device  800  may have a relatively constant outer perimeter size defined by the socket portion  814  and the outer surface  834 , and a variable sized or shaped inner surface  830  defined by the minor portion  812 . In other embodiments, such as mentioned above, additional layers may be added, for example in the increased thickness area  892 . In the reduced thickness areas  894 , the thickness of both the liner portion  812  and socket portion  814  may be reduced, or only the thickness of the liner portion  812  may be reduced. As with the other embodiments disclosed herein, more than two different lattice structures may be used through the thickness of the 3D printed device, or only one of the lattice structures (e.g., the relatively hard or rigid lattice structure of the socket portion  814 ) may be used at certain locations such as adjacent to the receiver  16  at the closed distal end  822  or only the relatively soft lattice structure of the liner portion  812  in the area of the open proximal end  820 . 
       FIGS. 10 and 11  illustrate example lattice structures that may be used with the various 3D printed devices disclosed herein.  FIG. 10  illustrates a 3D printed device  900  that includes an outer layer  956  that is substantially solid and/or continuous, and a first lattice structure  954  that is relatively open and comprised of substantially linear crossing members or struts.  FIG. 11  shows a second lattice structure  1054  and an outer layer  1056 . The outer layer  1056  may be substantially solid and/or continuous rather than including an open lattice structure. The second lattice structure  1054  may have different shaped and sized struts, such as struts that have a contoured shape, and the resulting lattice structure may include circular, spherical or other shapes. 
     The first and second lattice structures  954 ,  1054  shown in  FIGS. 10 and 11  are exemplary only. Many other lattice structures may be used for any of the features disclosed with reference to the figures for use as liners, socket features, or the like.  FIGS. 15 and 16  shows a few additional lattice structures that are contemplated. Varying the shape and size of the individual members of the lattice structure may influence the softness, rigidity and other properties of the lattice structure. Similarly, changing the materials, using different processes for curing and/or forming the materials, and other considerations may also influence the relative softness, rigidity and other properties of the resulting lattice structure. Further, the use of a solid layer, such as the outer layers  956 ,  1056  may influence properties of the 3D printed devices  900 ,  1000 . Removing the solid surface may increase softness, whereas increasing the thickness of the outer layer or using both an inner and outer solid surface layer may increase the rigidity of the overall 3D printed device. 
       FIG. 12  illustrates another example 3D printed device  1100  that includes a liner portion  1112  and a socket portion  1114 . The liner portion  1112  includes one or more liner nubs  1160  positioned around a circumference of the liner portion  1112 . The nubs  1160  may extend radially outward from an outer surface of the liner portion  1112 . The nubs  1160  may be formed as a continuous structure with the remainder of the liner portion  1112 . The nubs  1160  may extend continuously around a perimeter of the liner portion  1112 . Alternatively, a plurality of individual nubs may be positioned at spaced apart locations around a circumference and/or along a length of the liner portion  1112 . 
     The socket portion  1114  may include one or more openings  1162  sized to receive one or more of the nubs  1160 . The opening  1162  may include separate openings sized to receive each of the individual nubs  1160 . In some embodiments, the opening  1162  may be sized and arranged to accommodate multiple nubs  1160 . The nubs, when secured within openings  1162  may provide a positive connection between the liner portion  1112  and the socket  1114 . The positive connection may limit longitudinal movement of the liner  1112  relative to the socket  1114 . One or more openings may not extend completely through the socket portion  1114  and may be recesses on the interior surface of the socket portion. In at least some arrangements, the interface between the nubs  1160  and openings  1162  may limit relative rotational movement between the liner portion  1112  and socket portion  1114 . The nubs  1160  may be removed from their position within the openings  1162 . For example, a radially inward directed force may be applied to the nubs  1160  to remove them from the openings  1162  such that the liner portion  1112  can be moved relative to the socket portion  1114  (e.g., rotated or translated longitudinally relative to each other). 
     The liner portion  1112  and socket portion  1114  may comprise lattice structures such as those lattice structures described above with reference to  FIGS. 1-11 . The lattice structure of the liner portion  1112  may have a relatively soft or compressible construction and may permit fluid flow there through. The socket portion  1114  may comprise a different, more rigid lattice structure that provides additional support for the limb  18 . 
     The liner portion  1112  may be formed separate from the socket portion  1114 . The liner portion  1112  and socket portion  1114  may be assembled as shown in  FIG. 12  prior to insertion of the limb  18 . In other embodiments, the liner  1112  is mounted to the limb  18  followed by the limb  18  with liner  1112  being inserted into the socket portion  1114 . The liner portion  1112  and socket portion  1114  may also be formed using various 3D printed methods. The liner portion  1112  and socket portion  1114  may be formed using a 3D model of the limb  18  so as to provide a customized size and shape for an improved interface between the limb  18  and one or both of the liner portion  1112  and socket portion  1114 . A 3D model of a limb  18  may be used as part of the manufacturing process for any of the 3D printed devices disclosed herein. 
     The nub  1160  is shown with a tapered surface along a leading edge that promotes insertion of the nubs  1160  into the internal cavity and openings  1162  of the socket portion  1114  when the liner  1112  is inserted distally into the socket portion  1114 . A rear surface of the nubs  1160  have a step surface (e.g., a surface arranged generally perpendicular relative to the outer surface of the liner portion  1112 ). This step surface may provide an interface with a rear surface of the opening  1162  to limit removal of the liner portion  1112  relative to the socket portion  1114 . Other shapes and sizes are possible for the nub  1160  and the openings  1162 . 
       FIGS. 13 and 14  illustrate cross sectional views of distal end portions of additional 3D printed devices having a pin extending distally therefrom.  FIG. 13  illustrates a 3D printed device having a relatively soft, first lattice portion  1212 , a relatively hard, second lattice portion  1214 , and a semi-rigid lattice portion  1236 . The semi-rigid portion may be arranged between the soft and hard portions  1212 ,  1214 , or arranged at other locations adjacent one or both of the soft and hard portions  1212 ,  1214 . The 3D printed device  120  may include more than three lattice structures. A receiver  16  may be formed in the hard portion  1214  and configured to releasably connect a pin  1264  to the 3D printed device  1200 . The pin  1264  may include a plurality of threads  1263  at a proximal end thereof that are configured to threadibly engage receiver  16 . The pin  1264  may also include an engagement portion  1265 . The engagement portion  1265  may be configured to releasably secure the 3D printed device  1200  to a prosthetic component such as a prosthetic socket. 
     The lattice structure of the 3D printed device  1200  may have a variable lattice density through its thickness at the distal end  1222  of the device. The variable density of the lattice may change from a softer or less dense lattice structure  1212  to the semi-rigid lattice structure  1236  to the hard lattice structure  1214 , wherein the hard lattice structure is the most dense and/or rigid. The lattice structure of the 3D printed device  1200  may include not only a variation in the density of the lattice structure but also a variation in the structure itself including, for example, the shape and size of individual struts of the lattice structure, the shape and size of the resultant lattice structure (e.g., hexagonal, circular, spherical, etc.), or the relative orientation of the lattice structure members. Furthermore, the 3D printed device  1200  may have different material compositions for the various portions. For example, a harder more rigid material may be used in the area of the hard portion  1214  to provide additional support for the pin  1264 . 
     Generally, the 3D printed device  1200  may be formed as a separate piece from the pin  1264 , and the pin  1264  may be mounted and/or assembled to the 3D printed device  1200  in a separate assembly step. In another embodiment, a 3D printed device  1300  shown in  FIG. 14  includes a pin  1364  that is integrally formed as a single piece with the remaining soft portion  1312 , hard portion  1214  and semi-rigid portion  1236 . The pin  1364  may comprise a similar material as other portions of the 3D printed device  1300 . For example, the pin  1364  may comprise a polymeric material, which when formed is a solid structure has significant rigidity and strength, and when formed as a lattice structure, such as the soft portion  1212 , has a relatively soft, compressible and resilient structure. 
     In other embodiments, the pin  1364  may be formed as an integral piece with the hard portion  1314  and/or other portions of the 3D printed device  1300 . Remaining portions of the 3D printed device  1300  are formed directly onto or into integral connection with the preformed pin  1364  and/or hard portion  1314  such that the entire 3D printed device  1300  is considered an integral single piece. Other manufacturing methods and techniques may be used to form the 3D printed devices  1200 ,  1300  described with reference to  FIGS. 13 and 14 . 
       FIG. 15  illustrates atomic cell structures used as fundamental building blocks for many of the lattice structures that could be used with the 3D printed devices disclosed herein. The cell structures show in  FIG. 15  can mimic naturally occurring atomic structures such as cubic, tetragonal, orthorhombic, rhombohedral, monoclinic, triclinic, including body centered, face centered, and base centered variations of these atomic cells 
       FIGS. 16A-16F  illustrate various lattice structures that may be possible for use with the 3D printed devices disclosed herein. Each of the lattice structures  1570  ( FIG. 16A ),  1572  ( FIG. 16B ),  1574  ( FIG. 16C ),  1576  ( FIG. 16D ),  1578  ( FIG. 16E ), and  1580  ( FIG. 16F ) have unique shapes, sizes, and orientations for the individual strut members of the lattice structure as well as the resulting shapes and other features of the lattice structure as a whole. The various lattice structures shown in  FIGS. 16A-16F  may each provide different properties such as strength, compressibility, flexibility, elasticity, resistance to torque, etc.  FIG. 16F  shows an example of a lattice unit cell utilizing both semi-circular and straight beams between unit cell connection points. Because the curved beams are not as stiff as the straight beams, the cell is stiffer in compression in Direction  3  than and in Directions  1  and  2 . When the straight beams are compressed in Direction  1 , the straight beams will demonstrate a high stiffness until buckling occurs, at which point the stiffness will decrease dramatically. The behavior of the curved beams, when compressed in either Direction  1  or  2 , do not exhibit buckling behavior. The curved beams are pre-buckled by their semi-circular shape. 
     The examples shown in  FIG. 16A-16F  are exemplary only of the infinite number of lattice structure designs that are possible. The lattice designs that are used for various portions of any of the 3D printed devices disclosed herein may be optimized for use as liner, socket, connector pin, internal liner surfaces, exterior protective surfaces, and other features of a 3D printed device that is used and/or capable of being used with a limb such as a residual limb of an amputee. 
     The various lattice structures disclosed herein may provide certain advantages as compared to other types of materials such as the ability to integrally form a liner structure with a relatively soft liner structure and a relatively rigid or hard socket structure. The various lattice structures may also provide breathability, heat transfer, and the like that are not available with existing liners and/or sockets for use with residual limbs. Further, the example lattice structures disclosed herein may be easily adjusted in size, shape, orientation, and position along the device in order to customize the interface with a residual limb, provide support, cushioning, and/or flexibility to address certain specific features of the residual limbs such as a joint, termination point of a bone, scar tissue on the limb, or the like. 
       FIG. 17  is a flow diagram illustrating an example method of forming a 3D printed device, particularly a 3D printed device that is configured for use with a person&#39;s limb, such as a prosthetic device. A first step of a method  1600  includes forming a first portion of the prosthetic device with a first lattice structure. A second step  1610  may include forming a second portion of the prosthetic device with a second lattice structure having at least one different property than that of the first lattice structure. A step  1615  includes forming the first and second lattice structures as a continuous, integral structure using an additive manufacturing process. 
     The at least one different property may include at least one of lattice density, material composition, lattice structure, compressibility, porosity, and rigidity. The first portion may be a liner and the second portion may be a socket. The prosthetic device may be a flexible liner, and the first portion is an inner layer of the liner, and the second portion is a second layer of the liner. When the prosthetic device is a socket, the first portion may be a first layer of the socket and the second portion may be a second layer of the socket. 
     The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the present systems and methods and their practical applications, to thereby enable others skilled in the art to best utilize the present systems and methods and various embodiments with various modifications as may be suited to the particular use contemplated. 
     Unless otherwise noted, the terms “a” or “an,” as used in the specification and claims, are to be construed as meaning “at least one of.” In addition, for ease of use, the words “including” and “having,” as used in the specification and claims, are interchangeable with and have the same meaning as the word “comprising.” In addition, the term “based on” as used in the specification and the claims is to be construed as meaning “based at least upon.”