Scale-up of nature's tissue weaving algorithms to engineer advanced functional materials

Abstract

We are literally the stuff from which our tissue fabrics and their fibers are woven and spun. The arrangement of collagen, elastin and other structural proteins in space and time embodies our tissues and organs with amazing resilience and multifunctional smart properties. For example, the periosteum, a soft tissue sleeve that envelops all nonarticular bony surfaces of the body, comprises an inherently "smart" material that gives hard bones added strength under high impact loads. Yet a paucity of scalable bottom-up approaches stymies the harnessing of smart tissues' biological, mechanical and organizational detail to create advanced functional materials. Here, a novel approach is established to scale up the multidimensional fiber patterns of natural soft tissue weaves for rapid prototyping of advanced functional materials. First second harmonic generation and two-photon excitation microscopy is used to map the microscopic three-dimensional (3D) alignment, composition and distribution of the collagen and elastin fibers of periosteum, the soft tissue sheath bounding all nonarticular bone surfaces in our bodies. Then, using engineering rendering software to scale up this natural tissue fabric, as well as multidimensional weaving algorithms, macroscopic tissue prototypes are created using a computer-controlled jacquard loom. The capacity to prototype scaled up architectures of natural fabrics provides a new avenue to create advanced functional materials.

Figure 1. Periosteum as a woven interface between bone and muscle.

(a) Transverse section of ovine femur diaphysis (B: bone, P: periosteum, M: muscle, dashed white squares indicate regions of interest, ROI, along the major (1, 2) and minor (3, 4) centroidal axes of bone, which are marked as dashed lines2829). Periosteum and bone are ‘velcroed’ together by Sharpey’s fibers (b): outlined image of collagen arrangement making up two Sharpey’s fibers) that anchor the soft tissue sleeve to the hard surface of bone through a multitude of connections that distribute force without concentrating stresses. In turn, periosteum and muscle are physically connected by higher order architectures including springs (c - white square depicted in higher resolution in d, with springs highlighted by solid white arrows, cf. Supplementary Animation 1, Supplementary Figure 2, respectively, for additional dimension and higher resolution) and struts interwoven between the two (f & Supplementary Animation 2). (c) A 6 × 4 tiled image of the periosteum (P) bounded by bone (B) and skeletal muscle (M, muscle fascicles in cross section). Second harmonic signal from collagen fibers (dotted white arrows), shown in green; elastin signal shown in orange; Procion Red (PR) tracer delineating vascularization. ROI (white square) enlarged (d) to better visualize elastin fibers (indicated by arrows) and projected in 3D (e) from z-stack with 0.5 μm spacing in the z-direction. (f) Direct attachment of muscle, via struts, to the periosteum, and (g) blood vessel (BV) transecting the periosteum (P) (Supplementary Animation 3). (b–g) Numbered, dashed white boxes on upper right of each image correspond to ROIs along the major and minor axes depicted in (a).

Figure 2. Schematic diagram illustrating the process for bottom-up weaving of multidimensional, natural tissue-inspired fabrics.

(a–d) A transverse section of an ovine femur mid-diaphysis, with periosteum and surrounding muscle intact, stained with procion red solution. (e,f) Acquisition of high-resolution z-stacks using paired SHIM and TPEM imaging protocols to visualize structural proteins including collagen and elastin. (g–i) 3D rendering of z-stacks to convert image sequence into STL files for 3D computational modeling. (j) Conversion of virtual model into a physical model using multidimensional weaving technology; periosteum-inspired fabric shown above, right. (k) Optimization of novel functional textile via mechanical testing. J.L.N. created all schematic drawings depicted in this figure.

Figure 3

(a–c) 3D rendering of z-stacks (depth circa 40 μm) of SHG/collagen channel to STL files. 3D modeling of SHIM (c) together with TPEM and procion red channels comprising (d) weak collagen, (e) strong collagen, (f) vascularization, (g) weak elastin, (h) strong elastin signals, combined in (i), where xyz voxel size is 0.48 μm × 0.48 μm × 0.5 μm. (j–m) Ratio of collagen: elastin fibers across (j) different ovine specimens (n = 5) and (k) axially along same specimen (n = 3). Periosteal width across (l) different ovine specimens (n = 5) and (m) axially along the same specimen (n = 3).

Figure 4

(a) Stereographs of woven swatches consisting of various warp and (weft) combinations (x12.5). (b,c) Individual value plot comparing elastic moduli of prototypes comprising different combinations, i.e. warp (weft), of nylon, elastane and silk (*p < 0.05). (d) Strain maps of prototypes at t₀, t_f/2, t_f, where t = time, and f = final.

Figure 5. Recursive weaving and spinning concept.

(a–e) Example of a tensile testing of anisotropic sheep femur periosteum samples, analogous to testing of swatches in Fig. 4. (b,c) DIC imaging of displacements under load at time zero and 562 seconds. (d,e) Strain mapping overlay on (b,c). Used with permission after. (f) Testing of the highly complex, multidimensional fabric of periosteum in situ and ex vivo, under stance shift load. Heterogenous strain map at one point in time is depicted in color using digital image correlation and high resolution imaging (using high definition television lens). The dashed line in this view is orthogonal to the middiaphyseal imaging carried out using second harmonic imaging of collagen and elastin per Fig. 1(a), on the anterior aspect (corresponds to side of bone with ROI indicated by dashed square 3. Used with permission after. (g) Schematic representation of fabric complexity showing weave of spatially and temporally varying threads, where the color scale depicts either local strains analogous to the endogenous tissue or, from an inverse perspective, local fiber stiffness. (h) Schematic depiction of recursive step where program algorithm is used to spin anisotropic, viscoelastic threads and to weave fabric. Adapted with permission.