Path prediction of flexible needles based on Fokker-Planck equation and disjunctive Kriging model

Path prediction of flexible needles based on the Fokker-Planck equation and disjunctive Kriging model is proposed to improve accuracy and consider the nonlinearity and anisotropy of soft tissues.The stochastic differential equation is developed into the Fokker-Planck equation with Gaussian noise,and the position and orientation probability density function of flexible needles are then optimized by the stochastic differential equation.The probability density function obtains the mean and covariance of flexible needle movement and helps plan puncture paths by combining with the probabilistic path algorithm.The weight coefficients of the ordinary Kriging are extended to nonlinear functions to optimize the planned puncture path,and the Hermite expansion is used to calculate nonlinear parameter values of the disjunctive Kriging optimization model.Finally,simulation experiments are performed.Detailed comparison results under different path planning maps show that the kinematics model can plan optimal puncture paths under clinical requirements with an error far less than 2 mm.It can effectively optimize the path prediction model and help improve the target rate of soft tissue puncture with flexible needles through data analysis and processing of the mean value and covariance parameters derived by the probability density and disjunctive Kriging algorithms.

SILICON NEEDLE ARRAY ON FLEXIBLE SUBSTRATE FOR FLUID TRANSFER

Transdermal delivery is an attractive alternative, but it is limited by the extremely low permeability of skin. To solve this problem, a novel means--micro needle array based on micro electro-mechanical system （MEMS） technology, is provided to increase permeability of human skin with efficiency, safety and painless delivery. The fabrication method consists of a sequence of deep-reactive ion etching （DRIE）, anisotropic wet etching and conformal thin film deposition. The novel technology can enable the realization of micro fabricated micro needle array on a flexible silicon substrate. The micro needle array can be mounted on non-planar surface or even on flexible objects such as a human fingers and arms. The fabricated hollow wall straight micro needles are 200 μm in length, 30 μm inner diameter, and 50 μm outer diameter with 250 μm center-to-center spacing. Flow rate test proves that the polymeric base construction is important to function of micro needles array in package. Glucose solvent tests show that surface tension is the dominant force to affect the characters of flow in micro needles channel.

Dynamical modeling and controllability analysis of a flexible needle in soft tissue

This paper is concerned with deriving a dynamic model of a moderately flexible needle inserted into soft tissue,where the model’s output is the needle deflection.The main advantages of the proposed dynamic modeling approach are that the presented model structure involves parameters that are all measurable or identifiable by simple exper-iments and that it considers the same inputs that are currently used in the clinical practice of manual needle insertion.Conventional manual needle insertion suffers from the fact that flexible needles bend during insertion and their trajectories often vary from those planned,resulting in positioning errors.Enhancement of needle insertion accuracy via robot-assisted needle steering has received significant attention in the past decade.A common assumption in previous research has been that the needle behavior during insertion can be adequately described by static models relating the needle’s forces and torques to its deflection.For closed-loop control purposes,however,a dynamic model of the flexible needle in soft tissue is desired.In this paper,we propose a Lagrangian-based dynamic model for the coupled needle/tissue system,and analyze the response of the dynamic system.Steerability(controllability)analysis is also performed,which is only possible with a dynamic model.The proposed dynamic model can serve as a cornerstone of future research into designing dynamics-based control strategies for closed-loop needle steering in soft tissue aimed at minimizing position error.