Nature eloquently utilizes hierarchical structures to form the world around us. Applying the hierarchical architecture paradigm to smart materials can provide a basis for a new genre of actuators which produce complex actuation motions. One promising example of cellular architecture-active knits-provides complex three-dimensional distributed actuation motions with expanded operational performance through a hierarchically organized structure. The hierarchical structure arranges a single fiber of active material, such as shape memory alloys (SMAs), into a cellular network of interlacing adjacent loops according to a knitting grid. This paper defines a four-level hierarchical classification of knit structures: the basic knit loop, knit patterns, grid patterns, and restructured grids. Each level of the hierarchy provides increased architectural complexity, resulting in expanded kinematic actuation motions of active knits. The range of kinematic actuation motions are displayed through experimental examples of different SMA active knits. The results from this paper illustrate and classify the ways in which each level of the hierarchical knit architecture leverages the performance of the base smart material to generate unique actuation motions, providing necessary insight to best exploit this new actuation paradigm.

Background-Recent work indicates that mechanical force induces small-bowel growth, although methods reported do not have direct clinical application. We report a clinically feasible technique of enterogenesis and describe intestinal function in this model.

Distributed manipulation systems induce motions on objects through the application of many external forces. An actuator array performs distributed manipulation using a planar array of many small stationary elements (which are called cells) that cooperate to manipulate larger objects. Typically, highly dense actuator arrays are modeled as spatially continuous, programmable force fields, although in many implementations a relatively small number of actuators supports an object and continuous assumptions break down. This paper serves two purposes: to present a methodology for modeling and analyzing the dynamics of manipulation on a highly discrete actuator array and to present a methodology for designing manipulation strategies on discrete actuator arrays. This is done in the context of a particular macro-scale actuator array comprising a fixed planar array of motorized wheels. Modeling of the dynamics takes into account several models of the interaction between the actuators and the object, the distribution of the weight of the object among the supports, and the discrete nature of the system. Under certain modeling assumptions, the manipulation dynamics of an object are extremely simple for a given set of supporting cells. An inversion of these piecewisecontinuous dynamics generates a fully continuous open-loop manipulation strategy, effectively smoothing out the discontinuities. The authors show that although the resulting manipulation field may stably position and orient any object in the continuous field case, discreteness causes many objects to experience unstable rotational equilibria. Thus, poor orientation precision is a limitation of openloop manipulation using discrete actuator arrays and motivates the use of feedback. The authors also derive closed-loop manipulation strategies through an inversion of the discrete dynamics that reduce the many-input, three-output distributed control problem to a standard three-input, three-output control problem that operates under

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Active knits are a unique architectural approach to meeting emerging smart structure needs for distributed high strain actuation with simultaneous force generation. This paper presents an analytical state-based model for predicting the actuation response of a shape memory alloy (SMA) garter knit textile. Garter knits generate significant contraction against moderate to large loads when heated, due to the continuous interlocked network of loops of SMA wire. For this knit architecture, the states of operation are defined on the basis of the thermal and mechanical loading of the textile, the resulting phase change of the SMA, and the load path