Замените элемент <button>
директивой <md-button>
:
<div flex layout="row" layout-align="center center">
<div flex-sm="100" flex-gt-sm="90" flex-gt-md="70" flex-gt-lg="50" class="md-whiteframe-z2">
<md-content class="md-padding">
<div flex-sm="100" flex-gt-sm="80" layout-sm="column">
<form name="contactForm" data-ng-submit="sendMail()">
<md-input-container>
<label>Name:</label>
<input ng-model="contactName" required>
</md-input-container>
<md-input-container flex>
<label>Email:</label>
<input type="email" ng-model="contactEmail" required>
</md-input-container>
<md-input-container>
<label>Message:</label>
<textarea ng-model="contactMsg" columns="1" md-maxlength="150" required></textarea>
</md-input-container>
̶<̶b̶u̶t̶t̶o̶n̶ ̶t̶y̶p̶e̶=̶"̶s̶u̶b̶m̶i̶t̶"̶>̶S̶e̶n̶d̶<̶/̶b̶u̶t̶t̶o̶n̶>̶
<md-button type="submit" class="md-primary"
ng-class="{'md-raised md-hue-1': (contactForm.$dirty && contactForm.$valid) }"
aria-label="Send">Send</md-button>
</form>
</div>
</md-content>
</div>
</div>
Для получения дополнительной информации см. Материал AngularJS <md-button>
Справочник по API .