The group of private-equity firms that last week sweetened its offer to buy Biomet Inc. today began a tender offer to buy the Warsaw medical device maker's shares for about $11.4 billion. The offer of $46 a share, which expires July 11, is contingent upon at least 75 percent of all shares being tendered. A tender offer avoids a shareholder vote, allowing a buyer to more quickly acquire a company. Biomet's prospective buyers are LVB Acquisition LLC, Goldman Sachs & Co., Kohlberg Kravis Roberts and Texas Pacific Group. The consortium raised its offer last week after a Maryland shareholder-advisory firm urged shareholders to reject the previous offer of $10.9 billion.