Add an custom properties to manipulate and indicate states of the objects in the hands, such as position of a plunger.

[Acvarium]

Till this moment animation actions include only bones including special bones for locations and rotations of objects in hands. State of the objects and information of which object in which moment of animation must be in specific hand was done by hardcoded. It is not a flexible way. I did some reserch and testing in friday and found out that FBX and Unity support a custom propertys. This propertis can include and extracted when needed all date of object states. And it can be also used to work more efficiently with in blender and can be animated

[Acvarium]

Usage of properties

leftObjID - integer object identifier in the left hand rightObjID - integer object identifier in the right hand

0: no object;
1: Sharps Disposal;
2: Syringe;
3: Alcohol Bottle;
4: Needle;
5: Medicine;
6: ClothInHand;

_leftModifer01 - integer object modifier (syringe) in hand

0: only syringe barrel 
1: added syringe plunger
2: added needle

_rightModifer01 - not used

__leftModifer02 - modifier of an object in the hand with values from 0.0 to 1.0. At the moment it only used to determine the position of the plunger of a syringe, where 0.0 - piston fully pushed, 1.0 - pulled up to a reasonable limit

__rightModifer02 - not used

[Acvarium]

As Alex found out, Unity currently cannot work with animated properties. That is why I added work around. I added two bones to armature: prop.L and prop.R. All properties that needed now packaged in to x,y,z of that bones