Here is a list of online books about Bioengineering in various formats available for free :

Applied Tissue Engineering

edited by Minoru Ueda, 2011, 76 pages, 8.9MB, PDF

Bioethanol: Science and technology of fuel alcohol

by Graeme M. Walker, 2010, 114 pages, 4MB, PDF

Biomass Properties and Fire Prediction Tools

by Miltiadis Boboulos, 2010, 61 pages, 3.5MB, PDF

Biomechanics

Wikibooks, 2010

Biomedical Engineering: Technical Applications in Medicine

edited by R. Hudak, M. Penhaker, J. Majernik, 2012, 420 pp, 24MB, PDF

Biomimetic Based Applications

by Anne George, 2011, 572 pages, 35MB, PDF

Biomimetics: Learning from Nature

edited by Amitava Mukherjee, 2010, 534 pages, 75MB, PDF

Biotechnology of Biopolymers

edited by Magdy Elnashar, 2011, 364 pp, 26MB, PDF

Bone Regeneration

edited by Haim Tal, 2012, 340 pp, 44MB, PDF

Enzyme Technology (Book Unavailable)

by Martin F. Chaplin, Christopher Bucke, 1990, 280 pages

Fluid Bed Particle Processing

by Peter Dybdahl Hede, 2006, 80 pages, 6.2MB, PDF

Genes, Technology and Policy

by Jose Maria A. Ochave, 2003, 52 pages, 500KB, PDF

Intelligent and Biosensors

edited by Vernon S. Somerset, 2010

Medical Robotics

edited by Vanja Bozovic, 2008, 526 pages, 11MB, PDF

Methods in Industrial Biotechnology for Chemical Engineers

by W. B. V. Kandasamy, F. Smarandache, 2008, 126 pages, 2.5MB, PDF

Micro- and Nano-Transport of Biomolecules

by David Bakewell, 2009, 96 pages, 4.8MB, PDF

Polymer science and engineering: the shifting research frontiers National Academies, 1994, 199 pages, 7.5MB, PDF

The Practical Streambank Bioengineering Guide

by Gary Bentrup, 1998, 150 pages, 3.4MB, PDF

Protein Engineering: Technology and Application

by Tomohisa Ogawa, 2013, 187 pp, 11MB, PDF

Regenerative Medicine and Tissue Engineering

by Jose A. Andrades (ed.),  2013, 853 pp, 77MB, PDF

Rehabilitation Robotics

edited by Sashi S Kommu, 2007, 648 pages, 9.4MB, PDF

Robot Surgery

edited by Seung Hyuk Baik, 2010, 172 pages, 22MB, PDF

Tissue Engineering

edited by Daniel Eberli, 2010, 534 pages, 48MB, PDF