Multi-Material SLA 3D-Printer

I want to design a multi-material 3D printer which could print at least 3 different materials. so that complex designs like toothbrush which is made up of hard plastic (in the handle) and soft brussels.

The first part is to decide which type of 3D printer (out of FDM, Polyjet, SLS, SLA) would be the best viable solution for this problem.
Which type of approach to go with (bottom-up or top-down). So after some research, I went with SLA type printer with the bottom-up approach. I have also sketched a model.

BRAIN - STORMING

SKETCHING AND MODELING

PROBLEMS AND SOLUTION

PROBLEMS AND SOLUTION

Problem -

The liquid resin may accumulate around the perimeter of the object and the bottom of the cured layer causing adhesion problems due to contamination with another uncured resin

Solution -

Process
1. Cleaning - using ultrasound to clean the build layer after it is submerged in an isopropyl bath. The shockwaves of the ultrasound help in agitating the residual resin.
2. Drying build layer - Fan system is adopted to dry the build surface and make it ready to print another layer.

FINAL RENDER

Due to technical difficulty, the render is a little bit glitchy.