Roy K Aaron

Alpert Medical School - Brown University, Providence, Rhode Island, United States

Are you Roy K Aaron?

Claim your profile

Publications (67)167.03 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Achieving stable device integration is challenging in orthopedic applications, particularly for prosthetic attachment, because of the many different hard tissue interfaces. Such osseointegrated devices undergo poor hard tissue integration caused by wear, lack of proper bone formation, and infection. The challenge with nanotextured titanium is to find a surface that prevents bacterial growth, while supporting bone cell proliferation to improve hard tissue integration. This study examined the influence of nanotextured titanium, with and without patterns, created through electron beam evaporation on bone formation and integration. In vitro and in vivo data provided data that these nanotextured surfaces improved bone growth compared to their conventional, non-nanotextured titanium surfaces.
    Bioengineering Conference, 2009 IEEE 35th Annual Northeast; 01/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: Growth factors have become an important component for tissue engineering and regenerative medicine. Insulin-like growth factor-I (IGF-I) and transforming growth factor-beta1 (TGF-beta 1) in particular have great significance in cartilage tissue engineering. Here, we describe sequential release of IGF-I and TGF-beta 1 from modular designed poly(l,d-lactic-co-glycolic acid) (PLGA) scaffolds. Growth factors were encapsulated in PLGA microspheres using spontaneous emulsion, and in vitro release kinetics was characterized by ELISA. Incorporating BSA in the IGF-I formulations decreased the initial burst from 80% to 20%, while using uncapped PLGA rather than capped decreased the initial burst of TGF-beta 1 from 60% to 0% upon hydration. The bioactivity of released IGF-I and TGF-beta 1 was determined using MCF-7 proliferation assay and HT-2 inhibition assay, respectively. Both growth factors were released for up to 70 days in bioactive form. Scaffolds were fabricated by fusing bioactive IGF-I and TGF-beta 1 microspheres with dichloromethane vapor. Three scaffolds with tailored release kinetics were fabricated: IGF-I and TGF-beta 1 released continuously, TGF-beta 1 with IGF-I released sequentially after 10 days, and IGF-I with TGF-beta 1 released sequentially after 7 days. Scaffold swelling and degradation were characterized, indicating a peak swelling ratio of 4 after 7 days of incubation and showing 50% mass loss after 28 days, both consistent with scaffold release kinetics. The ability of these scaffolds to release IGF-I and TGF-beta 1 sequentially makes them very useful for cartilage tissue engineering applications.
    Biomaterials 05/2008; 29(10):1518-25. · 8.31 Impact Factor
  • Deborah McK. Ciombor, Roy K. Aaron
    [Show abstract] [Hide abstract]
    ABSTRACT: Biophysical techniques have been applied for the enhancement of bone repair in general and avascular necrosis (AVN) of the femoral head in particular. For AVN of the femoral head, electric and electromagnetic fields and acoustic waves have been used to promote bone formation and preserve the femoral head. The presence of a repair process within the femoral head and the potential to prevent resorption of subchondral trabeculae has provided the conceptual basis for using pharmacologic and biophysical techniques in the hopes of altering the balance of bone production and resorption in favor of maintaining bone mass and structure, preventing subchondral fracture, and preserving the hip. Electric stimulation has been used both invasively with core decompression and noninvasively with a capacitively coupled technique. Although some results were encouraging, minimal improvements in hip survival were demonstrated. Electromagnetic fields have also been used with and without core decompression. Some encouraging results in terms of pain relief, hip stability, and hip survival were demonstrated. Recently, acoustic shock wave therapy has been used with promising early results. Large scale, multicenter, prospective randomized studies are now needed to firmly establish one or another biophysical technique as effective therapies for AVN of the femoral head.
    Techniques in Orthopaedics 02/2008; 23(1):11-17.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Musculoskeletal war wounds often involve massive injury to bone and soft tissue that differ markedly in character and extent compared with most injuries seen in civilian practice. These complex injuries have challenged orthopaedic surgeons to the limits of their treatment abilities on the battlefield, during medical evacuation, and in subsequent definitive or reconstructive treatment. Newer methodologies are being used in the treatment of these wounds to prevent so-called second hit complications, decrease complications associated with prolonged medical evacuation, reduce the incidence of infection, and restore optimal function. Basic science advances hold the promise of providing foundations for future treatment options that may improve both bone and soft-tissue healing. Research on the treatment of these often devastating wounds also will have broad applicability to trauma resulting from acts of terrorism or from natural disasters.
    Instructional course lectures 02/2008; 57:65-86.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bone marrow edema is seen in osteoarthritis, avascular necrosis, and other clinical conditions including the bone marrow edema syndrome. Bone marrow edema is associated with bone pain and may be related to the pathophysiology of osteoarthritis. Our hypothesis is that bone marrow edema is associated with a reduction in perfusion in subchondral bone, which contributes to focal and segmental bone necrosis and cartilage breakdown. We further hypothesize that altered fluid dynamics in subchondral bone comprise part of the physicochemical environment to which osteocytes are highly sensitive and alter their cytokine expression profile in response to changes in fluid flow, pressure, and oxygen gradients. We have used contrast-enhanced magnetic resonance imaging with Gd-DTPA to characterize changes in subchondral bone perfusion in two relevant and related models-the Dunkin-Hartley guinea pig model of osteoarthritis and human bone marrow edema associated with osteoarthritis and avascular necrosis. Pharmacokinetic modeling was used to extract dynamic parameters of perfusion. Representative time-intensity curves are derived, which characterize normal bone and bone with marrow edema. Dynamic contrast-enhanced magnetic resonance imaging may be a useful tool for the early diagnosis of bone perfusion abnormalities and may be used to characterize marrow edema associated with a number of clinical conditions. This technique may also shed light on the pathophysiology of subchondral perfusion in osteoarthritis and avascular necrosis.
    Annals of the New York Academy of Sciences 12/2007; 1117:124-37. · 4.31 Impact Factor
  • Osteoarthritis and Cartilage 12/2007; 15. · 4.26 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: PURPOSE Bone marrow edema (BME)can be associated with osteoarthritis (OA), avascular necrosis (AVN), and other causes. Its pathophysiology remains largely unknown. In this study, we compare perfusion kinetics of normal marrow and BME using dynamic, contrast-enhanced (DCE)-MRI. METHOD AND MATERIALS DCE-MR imaging of the knee (n=15), hip (n=8), or ankle (n=2) was performed on 25 adults using a 1.5T magnet. VIBE sequence was performed before and during IV administration of 0.1mmol/kg of gadodiamide at 2cc/sec. Uniform ROIs were placed on BME and normal marrow to generate time-intensity curves. DCE-MRI images were analyzed with customized IDL 6.1 software. Pharmacokinetic modeling was performed using the Brix model to generate values for initial slope, amplitude parameter (A), and rate constants of gadodiamide transfer from interstitial space to plasma (kep), and elimination from plasma (kel). Student’s t- and nonparametric tests were used to compare kinetic parameters. RESULTS There were 17 women and 8 men; mean age, 55.2 yrs (range, 22-92); OA was present in 13; AVN, 9; nonspecific BME, 3. Compared to normal marrow, kinetic parameters of enhancement in areas of BME included higher initial slope [(BME, 95.2±50.1 (mean±st dev); normal marrow, 50.7±38.1; p<.001], higher A (0.99±0.42; 0.44±0.35; p<.001), lower kep (3.58±2.98; 5.40±4.44; p=.004), and lower kel (-0.037±0.036; 0.091±0.021; p<.001). In areas of BME around AVN, there was significantly lower A (AVN, 0.64±0.41; OA, 1.14±0.33; p=.009) and lower kel (-0.058±0.042; -0.023±0.034; p=.04) compared to BME adjacent to OA, but no significant difference in either initial slope (70.35±65.80; 111.79±46.87; p=.06) or kep (4.90±3.99; 3.20±2.63; p=.26). CONCLUSION DCE-MRI can be used to investigate enhancement kinetics in bone marrow and demonstrates relative increased perfusion and permeability but slow transfer of gadodiamide from the vascular space to areas of BME. Kinetic analysis of contrast-enhancement shows differences in BME associated AVN compared to osteoarthritis. CLINICAL RELEVANCE/APPLICATION DCE-MRI shows differences in enhancement kinetics between normal and edematous bone marrow.
    Radiological Society of North America 2007 Scientific Assembly and Annual Meeting; 11/2007
  • [Show abstract] [Hide abstract]
    ABSTRACT: In vitro cartilage tissue engineering culture systems benefit from a fine balance of biochemical and mechanical components to maintain the chondrocyte phenotype. This balance, however, can be disrupted by using typical methods for cultivating chondrogenic cells in medium supplemented with fetal bovine serum (FBS) and growth factors. Our goal was to determine the effects of fluid-dynamic stimuli, fetal bovine serum and dexamethasone on the chondrogenesis of 14-day synoviocyte pellet cultures in the presence of TGF-beta1. We employed a pellet culture system that provides a highly cellular three-dimensional structure that permits differentiation and extracellular matrix synthesis. Our results indicated that FBS inhibited glycosaminoglycan (GAG) and type II collagen production. Interestingly, the effect of dynamic stimuli was modulated by the presence of FBS; mixed serum-free cultures had increased GAG production, whereas mixed cultures with 10% FBS exhibited less GAG production compared with their static counterparts, possibly due to pronounced suppressive effects of FBS via increased transport. Dexamethasone addition during the first week of culture resulted in enhanced extracellular matrix production and increased cellularity. Moreover, the presence of 10% FBS in addition to ITS(+) and TGF-beta1 did not significantly increase cell proliferation compared with serum-free medium. These results indicate the importance of a comprehensive analysis of growth conditions for each cell culture system.
    Journal of Tissue Engineering and Regenerative Medicine 11/2007; 1(6):436-42. · 4.43 Impact Factor
  • Medicine and health, Rhode Island 02/2007; 90(1):6-9.
  • Roy K Aaron, Jeffrey R Morgan
    Medicine and health, Rhode Island 02/2007; 90(1):4-6.
  • [Show abstract] [Hide abstract]
    ABSTRACT: PURPOSE Bone Marrow Edema (BME) has been associated with many diseases including osteoathritis and osteonecrosis; however, the pathophysiology of BME is not known. In this study, we investigate perfusion kinetics of BME with dynamic contrast enhanced MRI (DCE-MRI). METHOD AND MATERIALS MR imaging was performed on 16 adults with BME using a 1.5T magnet (Symphony; Siemens, Erlangen, Germany) and a standard knee coil. Prior to DCE-MRI, short tau inversion recovery MR imaging (STIR) [3500/17/150 (TR/TE/TI)] and multi-echo conventional spin-echo intermediate- and T2-weighted (2320/20,30 [TR/TE]) MR imaging was performed to localize the largest focus of BME. DCE-MRI using the volumetric interpolated breath-hold examination sequence [5.50/2.89 (TR/TE); 10° (flip-angle), 350 Hz/pixel (bandwidth); 16cm (FOV); 5mm, slice thickness; one excitation; and 256 x 151, matrix] was performed before and during intravenous administration of 0.1mmol/kg of gadodiamide at 2cc/sec. DCE-MRI images were analyzed with customized IDL 6.1 software. Separate regions of interest (ROIs) were placed on areas of BME and normal bone marrow, and signal intensity-time curves were generated. Pharmacokinetic modeling was performed using the two-compartment Brix model to generate rate constants [A], [kep], and [kel]. A paired Student’s t-test was used to compare kinetic parameters between normal and edematous marrow. RESULTS Signal intensity-time curves demonstrate higher wash-in rate and lower wash-out in bone marrow edema when compared with normal tissue. Brix model parameters show higher mean [A] (p=9.1 E-6), lower [kep] (p=0.036) and lower [kel] (p=0.017) in bone marrow edema compared to normal bone marrow. CONCLUSION DCE-MRI demonstrates significantly increased perfusion and reduced contrast elimination in BME compared to normal bone marrow. Lower wash-out rate may be explained by increased intraosseus pressure in BME, which may lead to outflow obstruction and therefore decreased [kel]. These results are consistent with previous studies performed on Dunkin-Hartley guinea pig animal models. CLINICAL RELEVANCE/APPLICATION Pharmacokinetic modeling of bone marrow perfusion using DCE-MRI can provide insight into the pathophysiology of bone marrow edema.
    Radiological Society of North America 2006 Scientific Assembly and Annual Meeting; 11/2006
  • Roy K Aaron, Deborah McK Ciombor
    [Show abstract] [Hide abstract]
    ABSTRACT: Organ transplantation has undeniably increased the longevity and quality of life of patients with end-stage organ failure. Its has, however, introduced the skeletal complications of (1) fragility fractures and decreased bone density due to pretransplant bone loss and immunosuppressive therapy, and (2) avascular necrosis leading to subchondral fracture and secondary osteoarthritis. This article reviews these two skeletal complications of solid-organ transplantation that lead to structural failure of bone and result in significant morbidity and reduced quality of life.
    Surgical Clinics of North America 11/2006; 86(5):1237-55, viii. · 1.93 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The focus of our research program is the restoration of limb function through a biohybrid approach. We consider the limb conceptually as a biohybrid organ consisting of biological tissue, endoprostheses (including neural devices and joint replacements), and exoprostheses. The biohybrid limb maximizes biological function and functional articulations with optimized human-prosthesis interfaces. Our long-term goals are to create biomimetic prostheses, optimized control systems for prostheses, and optimized human-prosthesis interfaces using both limb lengthening and osseointegration techniques.
    The Journal of the American Academy of Orthopaedic Surgeons 11/2006; 14(10 Spec No.):S198-204. · 2.40 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study explores the suitability of using encapsulated genetically modified fibroblasts for orthopedic tissue engineering by examining cell survival and persistence of human transforming growth factor-beta (hTGF-beta) overexpression in xenogeneic and allogeneic implant models. Human wild-type fibroblasts, modified to produce a latent form of hTGF-beta, and murine mutant-type fibroblasts, engineered to release a constitutively active form of hTGF-beta, were encapsulated separately in Ca2+ -alginate microcapsules. Following a percentage viability assessment by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) test, microcapsules were implanted into either the subcutaneous or intraperitoneal cavities of mice. Explanted encapsulated cells were characterized for percentage viability and subjected to a release study and a viability test 1 week and 3 weeks following implantation, a time frame consistent with the requirement for orthopedic tissue engineering application of this growth factor. On average, percentage viabilities of encapsulated cells were 64%at implantation, 52% at explantation, and 56%after 1 week following either 1- or 3-week explantation. hTGF-beta release declined following in vivo implantation, more so for xenogeneic than allogeneic models, but remained in the clinically attractive range of 2 to 30 ng/(10(6) implanted cells 24 h). This technical platform for hTGF-beta is very encouraging for cartilage regeneration using orthopedic tissue engineering, and further evaluation is warranted.
    Tissue Engineering 08/2006; 12(7):1733-9. · 4.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The role of arthroscopic débridement in the treatment of osteoarthritis of the knee remains to be defined, and few clinical and radiographic characteristics have been quantitatively associated with the outcome. The hypothesis of this study was that the outcome of arthroscopic débridement for osteoarthritis of the knee is associated with preoperative clinical and radiographic features and intraoperative characteristics and that there are subsets of patients who are more and less likely to respond favorably to the treatment. We performed a cross-sectional study of a consecutive cohort of 122 patients who underwent arthroscopic débridement for the treatment of osteoarthritis of the knee that had been unresponsive to anti-inflammatory therapy. One hundred and ten patients were followed for a mean of thirty-four months. Pain was assessed with the pain domain of the Knee Society scoring system. Radiographs were scored with the Kellgren-Lawrence method, and limb alignment and the widths of the medial and lateral joint spaces were measured. The severity of cartilage lesions was scored intraoperatively with a modified Noyes grading system. Specific methods of data collection and analysis were incorporated to minimize bias. Fifty-two (90%) of fifty-eight knees with mild arthritis, normal alignment, and a joint space width of > or = 3 mm were improved after arthroscopic débridement. Conversely, only five (25%) of twenty knees with severe arthritis, limb malalignment, and a joint space width of < 2 mm had substantial relief of symptoms. Of seventy-two patients who had improvement, forty-four (61%) had it within six months after the arthroscopy. The severity of the lesion was highly predictive of the clinical outcome both in patients with mild arthritis and in those with severe arthritis. The severity of the arthritis, as assessed preoperatively with radiography and intraoperatively by rating the severity of cartilage lesions, influences the clinical outcome of arthroscopic débridement of an osteoarthritic knee. Knees with severe arthritis fare poorly, whereas those with mild arthritis fare well. We could not predict the outcome for knees with moderate arthritis. We believe that these observations are relevant for establishing indications for arthroscopy in patients with osteoarthritis of the knee and may be useful for designing studies with a more rigorous experimental design.
    The Journal of Bone and Joint Surgery 06/2006; 88(5):936-43. · 4.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Skeletal tissues respond to the physical demands of their environment by altering the synthesis and organization of the extracellular matrix. These observations have major implications for how physical environmental demands result in the clinical observations of atrophy and hypertrophy, and how manipulation of the physical environment can be used therapeutically to stimulate repair. Electrical stimulation will be considered as a paradigm of how musculoskeletal tissues respond to physical stimuli. A model of demineralized bone matrix-induced endochondral ossification has been used because it epitomizes the cell biology of endochondral bone formation in a temporally consistent way. We have studied cartilage and bone matrix production, the temporal locus of cell responsiveness, signal dosimetry, and the synthesis of signaling cytokines (TGF-beta) using biochemical, immunohistochemical, and molecular techniques. Exposure to certain electrical environments enhances chondrocyte differentiation reflected as a temporal acceleration and quantitative increase of cartilage extracellular matrix, earlier onset of osteogenesis, and more mature trabecular bone. The cell pool competent to respond resides in the mesenchymal stage. The enhancement in chondrogenesis is associated with an increase in TGF-beta synthesis mediated at least in part by binding of the transcription factor AP-1 and may be modulated specifically by phosphorylation of JNK. The clinical practice of orthopedics has empirically created a variety of biophysical environments in attempts to optimize skeletal repair. We are beginning to understand the biological effects of biophysical stimulation and are now poised to replace empiricism with treatment paradigms based upon physiologic understandings of dose and biologic response.
    Annals of the New York Academy of Sciences 05/2006; 1068:513-31. · 4.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A systematic investigation of protein encapsulation in polylactic-co-glycolic-acid (PLGA) was carried out using the formation of a w/o/o emulsion followed by solvent removal. Various factors were studied, including composition of the suspension medium and the relative amounts of aqueous phase containing protein to polymer solution. High yields of microsphere fabrication were achieved by using silicon oil containing methylene chloride as a suspension medium instead of pure silicon oil, with minimal loss of polymer and protein drug (<2%). The amount of aqueous phase influenced the process and successful encapsulation was obtained if the volume ratios of aqueous phase to polymer solution were less than 5% (v/v) at a wide range of polymer concentration (2-15% g ml-1). Protein encapsulation by this w/o/o emulsion and solvent removal method has a high yield of microsphere fabrication and protein encapsulation (98%). In addition, it provides an easy way to control the release rate of protein encapsulated in microspheres by modulating their porosity in fabrication process.
    Journal of Microencapsulation 03/2006; 23(2):183-94. · 1.88 Impact Factor
  • Deborah McK Ciombor, Roy K Aaron
    [Show abstract] [Hide abstract]
    ABSTRACT: Electric and electromagnetic fields regulate extra-cellular matrix synthesis and stimulate repair of fractures and nonunions. Studies of electric and electromagnetic fields suggest they (1) regulate proteoglycan and collagen synthesis and increase bone formation in models of endochondral ossification, (2) accelerate bone formation and repair, (3) increase union rates in fractures previously refractory to healing, and (4) produce results equivalent to bone grafts. Electric and electromagnetic fields regulate the expression of genes in connective tissue cells for extra-cellular matrix proteins, which results in an increase in cartilage and bone. They also increase gene expression for and synthesis of growth factors, which may be an intermediary mechanism of activity and may amplify field effects through autocrine and paracrine signaling.
    Foot and Ankle Clinics of North America 01/2006; 10(4):579-93, vii. · 0.84 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study was undertaken to develop an in situ source of transforming growth factor-beta1 (TGF-beta1), one of several molecules potentially useful for a tissue-engineered bioartificial cartilage. Primary human fibroblasts and murine NIH 3T3 cells were genetically modified via viral transfection to express human TGF-beta1. Two viral constructs were used, one expressing a gene encoding for the latent and the other for the constitutively active form of the growth factor. Unmodified cells served as controls. Four genetically modified cohorts and two controls were separately encapsulated in a 1.8% alginate solution using a vibrating nozzle and 0.15M calcium chloride crosslinking bath. Diameter of the spherical capsules was 410 +/- 87 microm. In vitro release rate measured over 168 hours varied with cell types and ranged from 2-17 pg/(milligram of capsules x 24 h) or 2-17 ng/(10(6) cells x 24 h). None of the formulations exhibited a large initial bolus release. Even when serum-supplemented medium was not replenished, cell viabilities remained over 55% after 1 week for all cell types. Microencapsulated genetically modified cells were capable of a constitutive synthesis and delivery of biologically significant quantity of TGF-beta1 for at least 168 hours and thus are of potential utility for artificial cartilage and other orthopedic tissue engineering applications.
    ASAIO Journal 06/2005; 51(4):379-84. · 1.39 Impact Factor
  • ASAIO Journal 01/2005; 51(2). · 1.39 Impact Factor

Publication Stats

1k Citations
167.03 Total Impact Points

Institutions

  • 2004–2014
    • Alpert Medical School - Brown University
      • Department of Orthopaedics
      Providence, Rhode Island, United States
  • 1984–2011
    • Brown University
      • • Department of Orthopaedics
      • • Center for Biomedical Engineering
      • • Department of Medicine
      Providence, Rhode Island, United States
  • 2009
    • Columbia University
      • College of Physicians and Surgeons
      New York City, NY, United States
  • 1988–2002
    • Rhode Island Hospital
      Providence, Rhode Island, United States
  • 1993
    • Roger Williams University
      Bristol, Rhode Island, United States
  • 1989–1990
    • University of Rhode Island
      Kingston, Rhode Island, United States