Accomplishments

National Science Foundation's Graduate Research Fellowship

8/2009-8/2012

National Science Foundation's GK-12 Fellowship

5/2012-5/2013

Tissue Engineering Young Investigator Council

1/2014-12/2014

Wake Forest Institute of Regenerative Medicine Young Investigator Award, TERMIS

12/2014

Whitaker International Program Fellowship

1/2015-1/2017

UK Regenerative Medicine Platform Special Merit Award

9/2017

Education

Imperial College London

Postdoctoral
Materials and Bioengineering
2014 - 2017

Cornell University

Ph.D.
Biomedical Engineering
2014

Cornell University

M.S.
Biomedical Engineering

2012

North Carolina State University

B.S.
Biomedical Engineering
2009

Selected Articles

Enhanced Boundary Lubrication properties of Engineered Menisci by Lubricin Localization with Insulin-like Growth Factor I Treatment
Journal of Biomechanics
2014-06-26

In this study we analyzed the effects of IGF-I on the boundary lubricating ability of engineered meniscal tissue using a high density collagen gel seeded with meniscal fibrochondrocytes. Biochemical, histological, immunohistochemical, and tribological analyses were carried out to determine a construct's ability to functionally localize lubricin. Our study revealed that supplementation with IGF-I enhanced both the proliferation of cells within the construct as well as enhanced the anabolic activity of the seeded cells. Growth factor supplementation also facilitated the localization of ECM constituents (i.e. fibronectin and type II collagen) near the tissue surface that are important for the localization of lubricin, a boundary lubricant. Consequently, we found localized lubricin in the constructs supplemented with IGF-I. Tribologically, we demonstrated that lubricin serves as a boundary lubricant adsorbed to native meniscal surfaces. Lubricin removal from the native meniscus surface increased boundary friction coefficient by 40%. For the engineered constructs, the lubricin localization facilitated by growth factor supplementation also reduced friction coefficient by a similar margin, but similar results were not evident in control constructs. This study demonstrates that the use of growth factors in meniscal tissue engineering can enhance tribological properties by facilitating the localization of boundary lubricants at the surface of engineered tissue.

Characterization of Mesenchymal Stem Cells and Fibrochondrocytes in 3D co-culture: analysis of cell shape, matrix production, and mechanical performance
Stem Cell Research & Therapy
2016-03-02

Bone marrow mesenchymal stem cells (MSCs) have shown positive therapeutic effects for meniscus regeneration and repair. Preliminary in vitro work has indicated positive results for MSC applications for meniscus tissue engineering; however, more information is needed on how to direct MSC behavior. The objective of this study was to examine the effect of MSC co-culture with primary meniscal fibrochondrocytes (FCCs) in a three-dimensional collagen scaffold in fibrochondrogenic media. Co-culture of MSCs and FCCs was hypothesized to facilitate the transition of MSCs to a FCC cell phenotype as measured by matrix secretion and morphology. MSCs and FCCs were isolated from bovine bone marrow and meniscus, respectively. Cells were seeded in a 20 mg/mL high-density type I collagen gel at MSC:FCC ratios of 0:100, 25:75, 50:50, 75:25, and 100:0. Constructs were cultured for up to 2 weeks and then analyzed for cell morphology, glycosaminoglycan content, collagen content, and production of collagen type I, II, and X. Cells were homogeneously mixed throughout the scaffold and cells had limited direct cell–cell contact. After 2 weeks in culture, MSCs transitioned from a spindle-like morphology toward a rounded phenotype, while FCCs remained rounded throughout culture. Although MSC shape changed with culture, the overall size was significantly larger than FCCs throughout culture. While 75:25 and 100:0 (MSC mono-culture) culture groups produced significantly more glycosaminoglycan (GAG)/DNA than FCCs in mono-culture, GAG retention was highest in 50:50 co-cultures. Similarly, the aggregate modulus was highest in 100:0 and 50:50 co-cultures. All samples contained both collagen types I and II after 2 weeks, and collagen type X expression was evident only in MSC mono-culture gels. MSCs shift to a FCC morphology in both mono- and co-culture. Co-culture reduced hypertrophy by MSCs, indicated by collagen type X. This study shows that MSC phenotype can be influenced by indirect homogeneous cell culture in a three-dimensional gel, demonstrating the applicability of MSCs in meniscus tissue engineering applications.

3D Bioprinting of Spatially Heterogeneous Collagen Constructs for Cartilage Tissue Engineering
ACS Biomaterials Science & Engineering
2016-08-03

3D printing of biological tissues has been of increasing interest to the biomaterials community in part because of its potential to produce spatially heterogeneous constructs. Such technology is particularly promising for orthopedic applications, which require the generation of complex geometries to match patient anatomy and complex microstructures to produce spatial heterogeneity and anisotropy. Prior research has demonstrated the capacity to create precisely shaped 3D printed constructs using biocompatible alginate hydrogels. However, alginate is extremely compliant and brittle, and high-density collagen hydrogels could be a preferable option for load-bearing applications. This research focused on developing and evaluating a method of printing soft tissue implants with high-density collagen hydrogels using a commercially available 3D printer, modified for tissue-engineering purposes. The tissue constructs, seeded with primary meniscal fibrochondrocytes, were evaluated using measures of geometric fidelity, cell viability, mechanical properties, and fiber microstructure. The constructs were found to be mechanically stable and were able to support and maintain cell growth. Furthermore, heterogeneous 3D-printed constructs were generated, consisting of discrete domains with distinct mechanical properties.

The Effect of the Duration of Mechanical Stimulation and Post-Stimulation Culture on the Structure and Properties of Dynamically Compressed Tissue-Engineered Menisci
Tissue Engineering
2012-09-23

This study investigates the effects of cyclic hydrostatic pressure (CHP) on chondrogenic differentiation of human adipose-derived stem cells (hASCs) in three-dimensional (3-D) agarose constructs maintained in a complete growth medium without soluble chondrogenic inducing factors. hASCs were seeded in 2% agarose hydrogels and exposed to 7.5 MPa CHP for 4 h per day at a frequency of 1 Hz for up to 21 days. On days 0, 7, 14, and 21, the expression levels of collagen II, Sox9, aggrecan, and cartilage oligomeric matrix protein (COMP) were examined by real-time reverse transcriptase–polymerase chain reaction analysis. Gene expression analysis found collagen II mRNA expression in only the CHP-loaded construct at day 14 and at no other time during the study. CHP-loaded hASCs exhibited upregulated mRNA expression of Sox9, aggrecan, and COMP at day 7 relative to unloaded controls, suggesting that CHP initiated chondrogenic differentiation of hASCs in a manner similar to human bone marrow-derived mesenchymal stem cells (hMSC). By day 14, however, loaded hASC constructs exhibited significantly lower mRNA expression of the chondrogenic markers than unloaded controls. Additionally, by day 21, the samples exhibited little measurable mRNA expression at all, suggesting a decreased viability. Histological analysis validated the lack of mRNA expression at day 21 for both the loaded and unloaded control samples with a visible decrease in the cell number and change in morphology. A comparative study with hASCs and hMSCs further examined long-term cell viability in 3-D agarose constructs of both cell types. Decreased cell metabolic activity was observed throughout the 21-day experimental period in both the CHP-loaded and control constructs of both hMSCs and hASCs, suggesting a decrease in cell metabolic activity, alluding to a decrease in cell viability. This suggests that a 2% agarose hydrogel may not optimally support hASC or hMSC viability in a complete growth medium in the absence of soluble chondrogenic inducing factors over long culture durations. The findings of this study suggest that CHP initiates hASC chondrogenic differentiation, even in the absence of soluble chondrogenic inductive factors, confirming the importance of considering both mechanical stimuli and appropriate 3-D culture for cartilage tissue engineering using hASCs.

High Density type I Collagen Gels for Tissue Engineering of Whole Menisci
Acta Biomaterialia
2013-08-30

This study investigates the potential of high density type I collagen gels as an injectable scaffold for tissue engineering of whole menisci, and compares these results with previous strategies using alginate as an injectable scaffold. Bovine meniscal fibrochondrocytes were mixed with collagen and injected into micro-computed tomography-based molds to create 10 and 20 mg ml−1 menisci that were cultured for up to 4 weeks and compared with cultured alginate menisci. Contraction, histological, confocal microscopy, biochemical and mechanical analysis were performed to determine tissue development. After 4 weeks culture, collagen menisci had preserved their shape and significantly improved their biochemical and mechanical properties. Both 10 and 20 mg ml−1 menisci maintained their DNA content while significantly improving the glycosaminoglycan and collagen content, at values significantly higher than the alginate controls. Collagen menisci matched the alginate control in terms of the equilibrium modulus, and developed a 3- to 6-fold higher tensile modulus than alginate by 4 weeks. Further fibrochondrocytes were able to reorganize the collagen gels into a more fibrous appearance similar to native menisci.

Induction of Fiber Alignment and Mechanical Anisotropy in Tissue Engineered Menisci with Mechanical Anchoring
Journal of Biomechanics
2015-05-31

This study investigated the effect of mechanical anchoring on the development of fiber organization and anisotropy in anatomically shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were mixed with collagen and injected into molds designed to produce meniscus implants with 12 mm extensions at each horn. After a day of static culture, 10 and 20 mg/ml collagen menisci were either clamped or unclamped and cultured for up to 8 weeks. Clamped menisci were anchored in culture trays throughout culture to mimic the native meniscus horn attachment sites, restrict contraction circumferentially, and encourage circumferential alignment. Clamped menisci retained their size and shape, and by 8 weeks developed circumferential and radial fiber organization that resembled native meniscus. Clamping also increased collagen accumulation and improved mechanical properties compared to unclamped menisci. Enhanced organization in clamped menisci was further reflected in the development of anisotropic tensile properties, with 2–3 fold higher circumferential moduli compared to radial moduli, a similar ratio to native meniscus. Ten and 20 mg/ml clamped menisci had similar levels of organization, with 20 mg/ml menisci producing larger diameter fibers and significantly better mechanical properties. Collectively, these data demonstrate the benefit of using bio-inspired mechanical boundary conditions to drive the formation of a highly organized collagen fiber network.

Physiologically Distributed Loading Patterns Drive the Formation of Zonally Organized Collagen Structures in Tissue Engineered Meniscus
Tissue Engineering
2016-06-26

The meniscus is a dense fibrocartilage tissue that withstands the complex loads of the knee via a unique organization of collagen fibers. Attempts to condition engineered menisci with compression or tensile loading alone have failed to reproduce complex structure on the microscale or anatomic scale. Here we show that axial loading of anatomically shaped tissue-engineered meniscus constructs produced spatial distributions of local strain similar to those seen in the meniscus when the knee is loaded at full extension. Such loading drove formation of tissue with large organized collagen fibers, levels of mechanical anisotropy, and compressive moduli that match native tissue. Loading accelerated the development of native-sized and aligned circumferential and radial collagen fibers. These loading patterns contained both tensile and compressive components that enhanced the major biochemical and functional properties of the meniscus, with loading significantly improved glycosaminoglycan (GAG) accumulation 200–250%, collagen accumulation 40–55%, equilibrium modulus 1000–1800%, and tensile moduli 500–1200% (radial and circumferential). Furthermore, this study demonstrates local changes in mechanical environment drive heterogeneous tissue development and organization within individual constructs, highlighting the importance of recapitulating native loading environments. Loaded menisci developed cartilage-like tissue with rounded cells, a dense collagen matrix, and increased GAG accumulation in the more compressively loaded horns, and fibrous collagen-rich tissue in the more tensile loaded outer 2/3, similar to native menisci. Loaded constructs reached a level of organization not seen in any previous engineered menisci and demonstrate great promise as meniscal replacements.