Biomedical subjects

Robert Eberhart

Publications and source records attributed to Robert Eberhart.

6 recordsLinked to original sources

PubMed2006

Selective tessellation algorithm for modeling interactions between surgical instruments and tissues.

We present a selective spatial tessellation algorithm that is specifically optimized for instrument-to-tissue and instrument-to-instrument collision detection cases, which are the essential part of interaction modeling in surgery simulation with haptic feedback. Virtual surgeries demand haptic rate collision solutions only when instruments are involved in collisions. Other collision cases can be processed at slower rates. The proposed selective tessellation algorithm is capable of differentiating among various collision cases and assigning different priorities to their processing. Without making assumptions about any object movement, the algorithm derives clipping volume as collision detection regions which tightly enclose the objects of interest. Results of implementation of the algorithm in a surgical simulation are provided.

Algorithms↗

PubMed2005

Permeable guidance channels containing microfilament scaffolds enhance axon growth and maturation.

Successful peripheral nerve regeneration is still limited in artificial conduits, especially for long lesion gaps. In this study, porous poly(L-lactide-co-DL-lactide, 75:25) (PLA) conduits were manufactured with 16 poly(L-lactide) (PLLA) microfilaments aligned inside the lumen. Fourteen and 18 mm lesion gaps were created in a rat sciatic nerve lesion model. To evaluate the combined effect of permeable PLA conduits and microfilament bundles on axon growth, four types of implants were tested for each lesion gap: PLA conduits with 16 filaments; PLA conduits without filaments; silicone conduits with 16 filaments; and silicone conduits without filaments. Ten weeks following implantation, regeneration within the distal nerve was compared between corresponding groups. Antibodies against the markers S100, calcitonin gene related peptide (CGRP), RMDO95, and P0 were used to identify Schwann cells, unmyelinated axons, myelinated axons, and myelin, respectively. Results demonstrated that the filament scaffold enhanced tissue cable formation and Schwann cell migration in all groups. The filament scaffold enhanced axonal regeneration toward the distal stump, especially across long lesion gaps, but significance was only achieved with PLA conduits. When compared to corresponding silicone conduits, permeable PLA conduits enhanced myelinated axon regeneration across both lesion gaps and achieved significance only in combination with filament scaffolds. Myelin staining indicated PLA conduits supported axon myelination with better myelin quantity and quality when compared to silicone conduits.

Absorbable Implants↗

PubMed2005

Haptic herniorrhaphy simulation with robust and fast collision detection algorithm.

Collision detection and soft tissue deformation are two major research challenges in real time VR based simulation, especially when haptic feedback is required. We have developed a real time collision detection algorithm for a prototype laparoscopic surgery trainer. However, this algorithm makes no assumptions about its applications and thus can be a generic solution to complicated collision detection problems. For soft tissue modeling, we use the mass-spring model enhanced with volume constraint and, stability control methods. We use both the new collision detection and tissue modeling algorithms in a bimanual hernia repair simulator which performs a mesh prosthesis stapling operation in real time.

Algorithms↗

PubMed2004

Synergistic improvements in cell and axonal migration across sciatic nerve lesion gaps using bioresorbable filaments and heregulin-beta1.

The success of entubulation for peripheral nerve regeneration is still limited, especially with long lesion gaps. In this study, we examined if regeneration could be enhanced by constructing implants to both align axonal growth and promote Schwann cell proliferation and migration. Silicone implants were used to bridge a 1.4-cm gap in the rat sciatic nerve. Adult female Sprague-Dawley rats were divided into four groups of tubes containing either 1) Matrigel; 2) Matrigel and heregulin; 3) Matrigel and poly(L-lactic acid) (PLLA) microfilaments; or 4) Matrigel, PLLA microfilaments, and heregulin. Ten weeks postimplantation, the number of axons and Schwann cells were measured at the distal end of implants. Implants with microfilaments displayed better tissue cable formation, increased Schwann cell migration, and regeneration of anti-calcitonin gene-related peptide-positive axons, but not RMDO95-positive axons compared with nonfilament-containing groups. Heregulin treatment caused an increase in Schwann cell number, but it demonstrated no significant improvement in either tissue cable formation or axon number. Extensive regeneration was observed through implants containing Matrigel, microfilaments, and heregulin, which induced significant improvements in the number and longitudinal organization of both Schwann cells and axons. These results indicate that physical guidance of microfilaments and the Schwann cell growth factor, heregulin, act synergistically to improve nerve regeneration across long lesion gaps.

Animals↗

PubMed2002

Simulation of bleeding during laparoscopic herniorrhaphy.

Simulation of intragastric bleeding due to an accidental cut by the surgeon is an important component of a virtual laparoscopic herniorrhaphy trainer. We present a method for simulating bleeding during laparoscopic hemiorrhaphy here. The various approaches used in previous research work are reviewed and our present approach is justified. Physically based fluid models used in computer graphics are used to simulate bleeding.

Algorithms↗

PubMed2002

Adaptive hybrid interpolation techniques for direct Haptic rendering of isosurfaces.

Direct Haptic rendering of voxels from an anatomical dataset provides patient specific haptic feedback vital for diagnosis and surgical planning. Our algorithm uses zero sets of scalar trivariate function for polynomial interpolation with sixty-four neighborhood points to generate isosurfaces on the fly for haptic rendering. This approach gives continuity in surfaces as well as better capture of isosurface features of the medical dataset. The detailed algorithm is presented along with the description of results from haptically rendering medical datasets.

Algorithms↗