Biomedical subjects

Hod Lipson

Publications and source records attributed to Hod Lipson.

6 recordsLinked to original sources

PubMed2006

Resilient machines through continuous self-modeling.

Animals sustain the ability to operate after injury by creating qualitatively different compensatory behaviors. Although such robustness would be desirable in engineered systems, most machines fail in the face of unexpected damage. We describe a robot that can recover from such change autonomously, through continuous self-modeling. A four-legged machine uses actuation-sensation relationships to indirectly infer its own structure, and it then uses this self-model to generate forward locomotion. When a leg part is removed, it adapts the self-models, leading to the generation of alternative gaits. This concept may help develop more robust machines and shed light on self-modeling in animals.

Algorithms↗

PubMed2006

Spontaneous emergence of periodic patterns in a biologically inspired simulation of photonic structures.

We simulate an evolutionary process in the lab for designing a novel high confinement photonic structure, starting with a set of completely random patterns, with no insight on the initial geometrical pattern. We show a spontaneous emergence of periodical patterns as well as previously unseen high confinement subwavelength bowtie regions. The evolved structure has a Q of 300 and an ultrasmall modal volume of 0.112 (lambda/2n)3. The emergence of the periodic patterns in the structure indicates that periodicity is a principal condition for effective control of the distribution of light.

Journal Article↗

PubMed2006

Direct freeform fabrication of seeded hydrogels in arbitrary geometries.

A major challenge in tissue engineering is the generation of cell-seeded implants with structures that mimic native tissue, both in anatomic geometries and intratissue cell distributions. By combining the strengths of injection molding tissue engineering with those of solid freeform fabrication (SFF), three-dimensional (3-D) pre-seeded implants were fabricated without custom-tooling, enabling efficient production of patient-specific implants. The incorporation of SFF technology also enabled the fabrication of geometrically complex, multiple-material implants with spatially heterogeneous properties that would otherwise be challenging to produce. Utilizing a custom-built robotic SFF platform and gel deposition tools, alginate hydrogel was used with calcium sulfate as a crosslinking agent to produce pre-seeded living implants of arbitrary geometries. The process was determined to be sterile and viable at 94 +/- 5%. The GAG and hydroxyproline production was found to be similar to that of other implants fabricated using the same materials with different shaping methods. The geometric fidelity of the process was quantified by using the printing platform as a computerized measurement machine (CMM); the RMS surface roughness of printed samples in the z-dimension was found to be 0.16 +/- 0.02 mm.

Alginates↗

PubMed2005

Robotics: self-reproducing machines.

Self-reproduction is central to biological life for long-term sustainability and evolutionary adaptation. Although these traits would also be desirable in many engineered systems, the principles of self-reproduction have not been exploited in machine design. Here we create simple machines that act as autonomous modular robots and are capable of physical self-reproduction using a set of cubes.

Animals↗

PubMed2004

Networks, dynamics, and modularity.

The identification of general principles relating structure to dynamics has been a major goal in the study of complex networks. We propose that the special case of linear network dynamics provides a natural framework within which a number of interesting yet tractable problems can be defined. We report the emergence of modularity and hierarchical organization in evolved networks supporting asymptotically stable linear dynamics. Numerical experiments demonstrate that linear stability benefits from the presence of a hierarchy of modules and that this architecture improves the robustness of network stability to random perturbations in network structure. This work illustrates an approach to network science which is simultaneously structural and dynamical in nature.

Linear Models↗

PubMed2002

On the origin of modular variation.

We study the dynamics of modularization in a minimal substrate. A module is a functional unit relatively separable from its surrounding structure. Although it is known that modularity is useful both for robustness and for evolvability (Wagner 1996), there is no quantitative model describing how such modularity might originally emerge. Here we suggest, using simple computer simulations, that modularity arises spontaneously in evolutionary systems in response to variation, and that the amount of modular separation is logarithmically proportional to the rate of variation. Consequently, we predict that modular architectures would appear in correlation with high environmental change rates. Because this quantitative model does not require any special substrate to occur, it may also shed light on the origin of modular variation in nature. This observed relationship also indicates that modular design is a generic phenomenon that might be applicable to other fields, such as engineering: Engineering design methods based on evolutionary simulation would benefit from evolving to variable, rather than stationary, fitness criteria, as a weak and problem-independent method for inducing modularity.

Adaptation, Physiological↗