In vivo evaluation of medical device-associated inflammation using a macrophage-specific positron emission tomography (PET) imaging probe.

To image implant-surrounding activated macrophages, a macrophage-specific PET probe was prepared by conjugating folic acid (FA) and 2,2',2″,2‴-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetracetic acid (DOTA) to polyethylene glycol (PEG) and then labeling the conjugate with Ga-68. In vivo PET imaging evaluations demonstrate that the probe is able to detect foreign body reactions, and more importantly, quantify the degree of inflammatory responses to an implanted medical device. These results were further validated by histological analysis.

Fibroblast/fibrocyte: surface interaction dictates tissue reactions to micropillar implants.

Micropillar technology has shown great promise for medical implants or sensors in recent years. To study the influence of surface topography on cellular responses, polydimethylsiloxane (PDMS) micropillar arrays with pillar spacing (20-70 µm) and height (14-25 µm) have been fabricated. The influence of micropillar arrays on cellular behavior was tested both in vitro and in vivo. Interestingly, in vitro, we observe a distinct response for 3T3 fibroblasts and RAW 264.7 macrophages to the topographical cues tested. Attachment and proliferation of fibroblasts was substantially enhanced by increasing pillar height, whereas macrophage adherence is significantly diminished by reduced pillar spacing. When implanted in the subcutaneous cavity of BALB/c mice for 14 days, we find a prevailing trend with capsule cell density and capsule thickness increasing, as both pillar height and spacing rise. Collagen deposition and neoangiogenesis, two pivotal factors in granulation tissue maturation, are also observed to have a stronger response to the increase in both pillar height and spacing. In contradiction to our original hypothesis, we observed that fibroblasts rather than macrophages are a key contributor to the in vivo outcome of micropillar arrays. Investigation into fibroblast activation, however, revealed that recruited fibrocytes, rather than resident fibroblasts, correspond to the in vivo outcome. The results from this work support the critical and often overlooked role of fibrocytes in tissue response to biomaterial implants with varying topography.

Hiring and screening practices of agencies supplying paid caregivers to older adults.

OBJECTIVES: To assess what screening practices agencies use in hiring caregivers and how caregiver competency is measured before assigning responsibilities in caring for older adults. DESIGN: One-to-one phone interviews in which interviewers posed as prospective clients seeking a caregiver for an older adult relative. SETTING: Cross-sectional cohort of agencies supplying paid caregivers to older adults in Illinois, California, Florida, Colorado, Arizona, Wisconsin, and Indiana. PARTICIPANTS: Four hundred sixty-two home care agencies were contacted, of which 84 were no longer in service, 165 offered only nursing care, and 33 were excluded; 180 agencies completed interviews. MEASUREMENTS: Agencies were surveyed about their hiring methods, screening measures, training practices, skill competencies assessments, and supervision. Two coders qualitatively analyzed open-ended responses. RESULTS: To recruit caregivers, agencies primarily used print and Internet (e.g., Craigslist.com) advertising (n = 69, 39.2%) and word-of-mouth referrals (n = 49, 27.8%). In hiring, agencies required prior "life experiences" (n = 121, 68.8%) few of which (n = 33, 27.2%) were specific to caregiving. Screening measures included federal criminal background checks (n = 96, 55.8%) and drug testing (n = 56, 31.8%). Agencies stated that the paid caregiver could perform skills, such as medication reminding (n = 169, 96.0%). Skill competency was assessed according to caregiver self-report (n = 103, 58.5%), testing (n = 62, 35.2%), and client feedback (n = 62, 35.2%). General caregiver training length ranged from 0 to 7 days. Supervision ranged from none to weekly and included home visits, telephone calls, and caregivers visiting the central office. CONCLUSION: Using an agency to hire paid caregivers may give older adults and their families a false sense of security regarding the background and skill set of the caregiver.

The pivotal role of fibrocytes and mast cells in mediating fibrotic reactions to biomaterials.

Almost all biomaterial implants are surrounded by a fibrotic capsule, although the mechanism of biomaterial-mediated fibrotic reactions is mostly unclear. To search for the types of cells responsible for triggering the tissue responses, we used poly-L glycolic acid polymers capable of releasing various reagents. We first identified that CD45(+)/Collagen 1(+) fibrocytes are recruited and resided within the fibrotic capsule at the implant interface. Interestingly, we found that the recruitment of fibrocytes and the extent of fibrotic tissue formation (collagen type I production) were substantially enhanced and reduced by the localized release of compound 48/80 and cromolyn, respectively. Since it is well established that compound 48/80 and cromolyn alter mast cell reactions, we hypothesized that mast cells are responsible for triggering fibrocyte recruitment and subsequent fibrotic capsule formation surrounding biomaterial implants. To directly test this hypothesis, similar studies were carried out using mast cell deficient mice, WBB6F1/J-Kit(W)/Kit(W-v)/, and their congenic controls. Indeed, mast cell deficient mice prompted substantially less fibrocyte and myofibroblast responses in comparison to C57 wild type mice controls. Most interestingly, subcutaneous mast cell reconstitution of WBB6F1/J-Kit(W)/Kit(W-v)/J mice almost completely restored the fibrocyte response in comparison to the C57 wild type response. These results indicate that the initial biomaterial interaction resulting in the stimulation of mast cells and degranulation byproducts not only stimulates the inflammatory cascade but significantly alters the downstream fibrocyte response and degree of fibrosis.

Real time monitoring of biomaterial-mediated inflammatory responses via macrophage-targeting NIR nanoprobes.

Medical implant-mediated inflammatory responses, often involving high levels of macrophages, are typically determined by histological analyses. These methods however are time consuming and require many animals to monitor the kinetics of inflammatory reactions and to generate reproducible outcomes. Recent studies have shown that activated macrophages in inflamed tissue express high levels of folate receptor (FR). In this study, FR-targeting NIR nanoprobes were fabricated and then tested for their ability to detect and quantify the extent of biomaterial-mediated inflammatory responses in vivo. Indeed, FR-targeting nanoprobes preferentially accumulate on activated macrophage surfaces. When administered intravenously, we found that the FR-targeting nanoprobes distinctively gathered in the inflamed tissues and that a different extent of FR-targeting nanoprobe gathering could be found in tissues implanted with different types of biomaterials. Most importantly, we found that there was a good relationship between the extent of inflammatory reactions and the intensity of nanoprobe-associated NIR signal in tissue. Our results support that FR-targeting NIR nanoprobes can be used to monitor and quantify the extent of macrophage recruitment and the degree of an implants' biocompatibility in real time.