results=a(1,1)+','+a(1,2);

Undefined function or method 'plus' for input arguments of type 'cell'

results = [a{1,1} a{1,2}];

strjoin(a(1,1:2).')

>> c = {'banana';'orange'}
>> strjoin(c(:)',',')
ans =

banana,orange

mystr = sprintf('%s,%s', a(1,1),a(1,1));