stringr: extract words containing a specific word

Consider this simple example

dataframe <- data_frame(text = c('WAFF;WOFF;WIFF200;WIFF12',
                                 'WUFF;WEFF;WIFF2;BIGWIFF'))

> dataframe
# A tibble: 2 x 1
                      text
                     <chr>
1 WAFF;WOFF;WIFF200;WIFF12
2  WUFF;WEFF;WIFF2;BIGWIFF

Here I want to extract the words containing WIFF, that is I want to end up with a dataframe like this

> output
# A tibble: 2 x 1
            text
           <chr>
1 WIFF200;WIFF12
2  WIFF2;BIGWIFF

I tried to use

dataframe %>% 
  mutate( mystring = str_extract(text, regex('\bwiff\b', ignore_case=TRUE)))

but this only retuns NAs. Any ideas?

Thanks!