from keras.models import Sequential
from keras.layers import LSTM
from keras.layers import TimeDistributed
from keras.layers import Bidirectional
...
model = Sequential()
model.add(Embedding(max_features, 128, input_length=maxlen))
model.add(Bidirectional(LSTM(64)))
model.add(Dropout(0.5))
model.add(Dense(1, activation='sigmoid'))