National Science Foundation     |     Directorate for Engineering  (ENG)
Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)
 
CBET Award Achievements (Nuggets)
Notable Accomplishments from CBET Awards
 
 
Optimization of Bioreactor Based Tissue Engineering of Bone
 
Cato T. Laurencin    University of Virginia

Background:  The replacement or restoration of function of traumatized, damaged or lost bone is an increasingly significant clinical problem in the US and around the world.  It has been estimated that about 900,000 bone grafting procedures are done annually in the United State alone.  Traditional materials for treating bone defects are bone grafts such as autografts and allografts.  Even though autografts are considered the gold standard for bone repair due to their optimal reparative properties, they suffer from serious drawbacks such as additional expense and trauma to the patient and limited availability, which seriously limit their applications.  Allografts, bone grafts harvested from cadavers, are more easily available in sufficient quantities but have serious disadvantages such as high costs, risk of disease transfer including viral infection and immunogenicity.  Due to the aforementioned limitations of biologically derived bone grafts, tissue engineering of bone has emerged as an alternative approach in the design and development of bone substitutes.
 
Tissue engineering can be defined as the application of biological, chemical, and engineering principles towards the repair, restoration or regeneration of tissues using cells, factors, and biomaterials alone or in combination.  The classic paradigm for in vitro tissue engineering of bone involves the isolation and culture of donor osteoblasts or osteoprogenitor cells within 3-dimensional biomaterials as scaffolds under conditions which support tissue growth of new bone.  By combining appropriately engineered biomaterials, cells, and cell culture conditions, strategies may ultimately be found to produce synthetic bone grafts capable of providing bony repair.
 
One major constraint in the use of 3-D biomaterials as scaffolding for new bone growth has been the limitation of cell migration and tissue ingrowth within these structures.  As cells located in the interior scaffold receive nutrients only through diffusion from the surrounding media in static culture, many investigators have speculated that high cell density on the exterior of the scaffold may deplete nutrient supply before these nutrients can diffuse to the scaffold interior to support tissue growth.  In addition, diffusive limitations may also inhibit the removal of cytotoxic degradation and metabolic waste products produced in the scaffold interior.  Though several attempts have been made to alter scaffold geometry to provide adequate diffusion within 3-D constructs, ingrowth limitations within 3-D scaffolds remain a pervasive problem in tissue engineering.
 
The goal of this research is to utilize high aspect-ratio vessel bioreactors (HARVs) to enhance the formation of bony tissue in biocompatible, biodegradable polymeric scaffolds previously designed for bone repair.  As mentioned above, overcoming diffusion limitations in static cell culture environments is critical, and thus is central to the work in this research.

Results:  Over the past year the efforts of the Laurencin team have been focused on the development of a scaffold that contains both biocompatible, resorbable polymer and nanocrystalline hydroxyapatite, the latter of which is similar to the natural component of bone and therefore may enhance overall bone formation.  Additionally bone marrow cells, known to possess a sub-population of stem cells capable of forming several types of connective tissue (bone, ligament, cartilage, muscle, etc) were placed on scaffolds and cultured in rotating bioreactors.  Cells were evaluated periodically (after 3, 7, 14, and 21 days in the bioreactor) to evaluate their phenotypic expression.  Results were encouraging, as the multipotential cells were directed to form bone on the scaffolds while in the bioreactor.  Additionally, robust cell growth and bone formation was evident on the interior portion of the scaffolds, the region most challenging to infiltrate, and the region that was the motivation behind the use of the rotating bioreactor (see Figures A and B).

Cato Laurencin
 
Figure A:  Polymer/ceramic composite scaffold prior to culture, free of mineralized tissue.
 
Figure B:  Polymer/ceramic composite scaffold after dynamic culture.  The image shows the cross-section of the scaffold after 21 days of bioreactor cell culture.  Alizarin Red stain (purple) shows mineralized tissue, abundant at the center of the scaffold.
 
Credit:  Cato T. Laurencin M.D., Ph.D., University of Virginia
 
Work from this grant has been published in peer reviewed journals:
 
    (1)  Lv, Q., Laurencin C.T., "Human mesenchymal stem cell proliferation, differentiation, and mineralization on 3-dimensional nano hydroxyapatite-polymeric composite scaffolds for tissue regeneration."  Proceedings of the Society for Biomaterials 33, 168, 2007.
 
    (2)  Wafa I. Abdel-Fattah, Tao Jiang, Gehan El-Tabie El-Bassyouni and Cato T. Laurencin, "Synthesis, characterization of chitosans and fabrication of sintered chitosan microsphere matrices for bone tissue engineering." Acta Biomaterialia, Volume 3, Issue 4, July 2007, Pages 503-514.
 
    (3)  Tao Jiang, Wafa I. Abdel-Fattah and Cato T. Laurencin, "In vitro evaluation of chitosan/poly(lactic acid-glycolic acid) sintered microsphere scaffolds for bone tissue engineering." Biomaterials, Volume 27, Issue 28, October 2006, Pages 4894-4903.
 
    (4)  Justin Lee Brown, Lakshmi S. Nair, Jared Bender, Harry R. Allcock and Cato T. Laurencin, "The formation of an apatite coating on carboxylated polyphosphazenes via a biomimetic process." Materials Letters, Volume 61, Issue 17, July 2007, Pages 3692-3695.

Scientific Uniqueness:  This work is unique in that it utilizes novel culture systems to overcome limitations found in conventional cell culture approaches in combination with scaffolds uniquely designed to not only encourage bone repair but also integrate with dynamic culture to enhance bone formation.

This project addresses the NSF Strategic Outcome Goals, as described in the NSF Strategic Plan 2006-2011, as follows:
 
Primary Strategic Outcome Goal:      (1) Discovery:  This project provides fundamental information regarding the efficacy of dynamic culture bioreactors as a tool to overcome limitations of conventional strategies for scaffold-based bone regeneration.
                                                                   (1) Discovery Category:
                                                                          - Biological Sciences
                                                                          - Engineering Research

 
Secondary Strategic Outcome Goal:  (2) Learning:  This project includes participation of undergraduate students, graduate students, and post doctoral students from engineering and life sciences both domestically and internationally.
 
                                                                   (2) Learning Categories:
                                                                          - Undergraduate Education and Undergraduate Student Research
                                                                          - Graduate Education and Graduate Student Research
                                                                          - Postdoctoral Education
                                                                          - International Research Experiences for Undergrad & Graduate Students

In terms of Intellectual Merit, this work is notable.  A multidisciplinary approach is taken towards the development of novel polymer based matrices in rotating bioreactors for bone tissue engineering. The development of a matrix of this sort combined with novel tissue culture technology provides opportunities for studying polymer-cell interactions, polymer matrix effects on cellular response, and effects of transport on cellular response in matrix based systems.

In terms of Broader Impacts, this work is notable.  Three-dimensional bone/bioerodible polymer matrices have been found to have tremendously important clinical uses.  For example, many fractures are complicated by nonunion, where the wound site consists of fibrous tissue and debris.  Many individuals suffering from fracture non-unions live painful disabled lives.  The use of polymeric matrices for bone regeneration presents an exciting treatment modality for healing atrophic non-unions.  Craniofacial implants, used in the treatment of congenital defects, in cases of trauma, or as post-surgical implants for cancer treatment, currently rely on inert materials, which do not incorporate tissue.  These bone/polymer matrices could find real use in these areas as implants, which, over time, would regenerate into normal bone tissue.

This research is Transformative.  The regeneration of hard tissue in vitro has been hindered by incomplete tissue ingrowth throughout synthetic scaffolds due to inherent limitations of static culture techniques.  The development of dynamic culture methods, together with the simultaneous development of scaffolds uniquely suited to these dynamic environments, expands the potential for this technology well beyond those previously observed.

This research represents Broadening Participation.  This research has a special impact on the training of underrepresented minority students at the undergraduate and graduate levels, and hence greatly enriches the level of scientific resources available to our nation.  In the years in which the laboratory of Dr. Laurencin has been in operation at M.I.T., MCP-Hahnemann School of Medicine, and the University of Virginia, over 92 underrepresented minority students at the undergraduate, graduate, and post-graduate levels have undertaken research projects in the lab, with 28 students completing graduate or post graduate degrees, award presentations and honors research theses.  The principal investigator has been responsible for training minority post-doctoral associates who work in science and engineering fields both in industry and in academia.
 
Minority students undertaking projects in Dr. Laurencin's laboratory have been among the best students at their schools.  For example, Tommy Thomas, an African-American, won M.I.T.'s prize for the best undergraduate material science thesis.  James Cooper, an African-American, won the school's prestigious Westinghouse award as a first year graduate student.  Chris Taylor and Natalee Campbell, both former Medical College of Pennsylvania/Hahnemann University medical students, each received the Bristol Myers Squibb Research Award.  Alton Williams, an African-American, has won the TRW Undergraduate Award for Excellence in Research.  Edward Botchwey, an African-American, won a GEM fellowship (from the National Consortium for Graduate Degrees for Minorities in Engineering and Science, Inc.) as a Ph.D. student at the University of Pennsylvania performing graduate research study in Engineering in Dr. Laurencin's laboratory, and is now an Assistant Professor in the Department of Biomedical Engineering at the University of Virginia.

Existing or potential Societal Benefits of this research:  The replacement or restoration of function of traumatized, damaged or lost bone is an increasingly significant clinical problem in the US and around the world.  It has been estimated that about 900,000 bone grafting procedures are done annually in the United State alone.  Traditional materials for treating bone defects are bone grafts such as autografts and allografts, but both approaches possess considerable limitations.  Tissue engineering of bone has emerged as an alternative approach in the design and development of bone substitutes, and stands to be a vital part of the armamentarium available to clinicians to combat orthopaedic injuries in an ever-aging population.


 
Program Director:
 
 
 
Ted A. Conway
CBET Program Director - Research to Aid Persons with Disabilities
     
NSF Award Number:   0503207
     
Award Title:
 
  Optimization of Bioreactor Based Tissue Engineering of Bone
     
PI Name:   Cato Laurencin
     
Institution Name:   University of Virginia Main Campus
     
Program Element Code:   5342
     
NSF Investments:
 
  - Understanding Complex Biological Systems (including the
      interfaces of life, physical, and computational sciences)
     
CBET Nugget:

  FY 2009


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This Nugget was Updated on 24 September 2009.