Yahya Elsayed

Fabrication and characterisation of biomimetic, electrospun gelatin fibre scaffolds for tunica media-equivalent, tissue engineered vascular grafts

It is increasingly recognised that biomimetic, natural polymers mimicking the extracellular matrix (ECM) have low thrombogenicity and functional motifs that regulate cell-matrix interactions, with these factors being critical for tissue engineered vascular grafts especially grafts of small diameter. Gelatin constitutes a low cost substitute of soluble collagen but gelatin scaffolds so far have shown generally low strength and suture retention strength. In this study, we have devised the fabrication of novel, electrospun, multilayer, gelatin fibre scaffolds, with controlled fibre layer orientation, and optimised gelatin crosslinking to achieve not only compliance equivalent to that of coronary artery but also for the first time strength of the wet tubular acellular scaffold (swollen with absorbed water) same as that of the tunica media of coronary artery in both circumferential and axial directions. Most importantly, for the first time for natural scaffolds and in particular gelatin, high suture retention strength was achieved in the range of 1.8-1.94 N for wet acellular scaffolds, same or better than that for fresh saphenous vein. The study presents the investigations to relate the electrospinning process parameters to the microstructural parameters of the scaffold, which are further related to the mechanical performance data of wet, crosslinked, electrospun scaffolds in both circumferential and axial tubular directions. The scaffolds exhibited excellent performance in human smooth muscle cell (SMC) proliferation, with SMCs seeded on the top surface adhering, elongating and aligning along the local fibres, migrating through the scaffold thickness and populating a transverse distance of 186 μm and 240 μm 9 days post-seeding for scaffolds of initial dry porosity of 74 and 83%, respectively.

Smooth muscle tissue engineering in crosslinked electrospun gelatin scaffolds.

Crosslinked, multi-layer electrospun gelatin fiber scaffolds with generally ±45 degree fiber orientation have been used to grow human umbilical vein smooth muscle cells (HUVSMCs) to create a vascular tunica media graft. Scaffolds of different fiber diameter (2-5 μm in wet state), pore size, and porosity (16-21% in wet state) were assessed in terms of cell adherence and viability, cell proliferation, and migration in both in-plane and transverse directions through the scaffold as a function of time under static cell culture conditions. HUVSMC cell viability reached between 80 and 92% for all scaffolds after 9 days in culture. HUVSMCs adhered, elongated, and orientated in the fiber direction, and migrated through a scaffold thickness of 200-235 μm 9 days post-seeding under static conditions. The best scaffold was then used to assess the tissue engineering of HUVSMCs under dynamic conditions for a rotating, cell seeded, tubular scaffold in the bioreactor containing the culture medium. Dynamic conditions almost doubled the rate of cell proliferation through the scaffold, forming full tissue throughout a scaffold of 250-300 μm thickness 6 days post-seeding.

A unified system identification approach for a class of pneumatically-driven soft actuators

The class of Pneumatically-driven Low-pressure Soft Actuators (PLSA) is a popular choice potentially used in the surgical robotic applications. One fundamental problem lying in the PLSA research is the lack of a generally validated model for the complex nonlinear dynamic behaviours. In this paper, a unified identification approach for the general PLSAs is proposed. It is a parameter-independent way directly used to identify the dynamical relation between the actuating pressures and the principal degrees of freedom of a PLSA, the bending and the steering. The approach is based on a modified auxiliary kinematic setting and a newly developed identification model structure, named DIO-PWL-OBF. Following the concluded identification procedure, the implementations for the single chamber bending and the double chamber bending and steering are demonstrated separately. The results show that the proposed approach can accurately capture the nonlinear pressure-shape dynamical relation. The approach is also efficient in real-time applications. It can be further used to improve the current control design for the PLSAs in robotic applications. A unified system identification approach is proposed.The approach is used to identify the nonlinear pressure-shape dynamic relation.The used auxiliary kinematic setting can be implemented by gyroscopic sensors.

Crimped braided sleeves for soft, actuating arm in robotic abdominal surgery.

Abstract Background: This paper investigates different types of crimped, braided sleeve used for a soft arm for robotic abdominal surgery, with the sleeve required to contain balloon expansion in the pneumatically actuating arm while it follows the required bending, elongation and diameter reduction of the arm. Material and methods: Three types of crimped, braided sleeves from PET (BraidPET) or nylon (BraidGreyNylon and BraidNylon, with different monofilament diameters) were fabricated and tested including geometrical and microstructural characterisation of the crimp and braid, mechanical tests and medical scratching tests for organ damage of domestic pigs. Results: BraidPET caused some organ damage, sliding under normal force of 2-5 N; this was attributed to the high roughness of the braid pattern, the higher friction coefficient of polyethylene terephthalate (PET) compared to nylon, and the high frequency of the crimp peaks for this sleeve. No organ damage was observed for the BraidNylon, attributed to both the lower roughness of the braid pattern and the low friction coefficient of nylon. BraidNylon also required the lowest tensile force during its elongation to similar maximum strain as that of BraidPET, translating to low power requirements. Conclusion: BraidNylon is recommended for the crimped sleeve of the arm designed for robotic abdominal surgery.

Design optimisation of soft silicone pneumatic actuators using finite element analysis

The current trend in soft robotic solutions is to pneumatically actuate chambers within manipulators that feature elastomeric material. This work describes the development of a repeating module actuator with each module capable of producing 3 degrees of freedom, as well as longitudinal expansion, intended for use as a laparoscopic tool in minimal invasive surgery. The design of the manipulator geometry as well as the choice of suitable material is dependent on the application, range of motion, and the suitable actuation pressure. This work describes the use of finite element analysis to simulate the range of motion of the hyperelastic response of two different soft silicones. Different geometry ratios and channel designs of the actuator are then optimized in terms of bending angle, maximum stress generated, radial expansion due to air pressure, and the amount of free area that the design allows in the actuator for other tools necessary in laparoscopic surgery. The optimum geometries are then selected as candidates for the development of the repeating module design, and the addition of skins to the module is investigated for the optimized module design.

Designing and modeling pore size distribution in tissue scaffolds

Abstract This chapter investigates the influence that pore morphology and the composition of tissue engineering scaffolds have on cellular behavior and mechanical performance. The chapter will also discuss typical scaffold fabrication techniques in terms of the pore morphology they are capable of producing. The effects that pore size, geometry, type of pore, and pore size distribution have on fluid flow through the tissue engineering construct is established using equations that simulate the behavior in terms of the pore morphology. A case study involving gelatin electrospun scaffolds that mimic the tunica media of a small diameter blood vessel provides an example of the correlation between experimental findings and predictions in terms of the mechanical integrity of a range of scaffolds as well as establishing a link between cell proliferation and the characteristics of the pores within scaffolds.

A new coefficient-adaptive orthonormal basis function model structure for identifying a class of pneumatic soft actuators

The class of Pneumatically-driven Lower-pressure Soft Actuators (PLSA) is a popular research topic as it can be potentially used in the surgical robotic applications. One fundamental problem lying in the PLSA research is the lack of a generally validated model for the complex nonlinear dynamic behaviours. In this paper, a new coefficient-adaptive orthonormal basis function model structure is specifically developed for the identification of the general PLSAs. It is a parameter-independent way directly used to identify the dynamic relation between the actuating pressures and the principal degrees of freedom of a PLSA, the bending and the steering. The approach is based on a modified auxiliary kinematic setting. Following the discussion of the identification procedure, the implementations for the double chamber bending and steering are demonstrated. The results show that the proposed approach can accurately capture the nonlinear pressure-shape dynamics. The approach is also efficient in the real-time applications. It can be further used to improve the current control design for the PLSAs in robotic applications.

Tuneable Stiffness Design of Soft Continuum Manipulator

Soft continuum robots are highly deformable and manoeuvrable manipulators, capable of navigating through confined space and interacting safely with their surrounding environment, making them ideal for minimally invasive surgical applications. A crucial requirement of a soft robot is to control its overall stiffness efficiently, in order to execute the necessary surgical task in an unstructured environment. This paper presents a comparative study detailing the stiffness characterization of two soft manipulator designs and the formulation of a dynamic stiffness matrix for the purpose of disturbance rejection and stiffness control for precise tip positioning. An empirical approach is used to accurately describe the stiffness characteristics along the length of the manipulator and the derived stiffness matrix is applied in real-time control to reject disturbances. Further, the capability of the two types of soft robots to reject disturbances using the dynamic control technique is tested and compared. The results presented in this paper provide new insights into controlling the stiffness of soft continuum robots for minimally invasive surgical applications.

A Material-based Model for the Simulation and Control of Soft Robot Actuator

An innovative material-based model is described for a three-pneumatic channel, soft robot actuator and implemented in simulations and control. Two types of material models are investigated: a soft, hyperelastic material model and a novel visco-hyperelastic material model are presented and evaluated in simulations of one-channel operation. The advanced visco-hyperelastic model is further demonstrated in control under multi-channel actuation. Finally, a soft linear elastic material model was used in finite element analysis of the soft three-pneumatic channel actuator within SOFA, moving inside a pipe and interacting with its rigid wall or with a soft hemispherical object attached to that wall. A collision model was used for these interactions and the simulations yielded “virtual haptic” 3d-force profiles at monitored nodes at the free- and fixed-end of the actuator.